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Applications Engineering Manual - EarthWise Intelligent Variable Air

1. sensor and the unit controller on each y j water source heat pump as well as the DE wires between each unit controller and the centralized system level controller SE see Using wireless technology p 90 system level Benefits include faster project completion controller and easier relocation when space layout or use changes in the future as well as making it easier to upgrade an older system to reap the benefits of networked unit controls water source i _ d A d heat pump with a DDC unit controller zone temperature sensor o A we This configuration provides an opportunity to optimize system operation with capabilities such as L Centralized system scheduling and shutdown based on occupancy 2 Override to allow the system to operate when a zone is occupied after scheduled hours indicated through the use of a timed override button on the zone sensor 3 Enabling morning warm up and cool down sequences including optimal start 4 Centralized alarms to indicate problems required service or needed maintenance 5 Trend logging to help anticipate potential system problems 6 Integration with the dedicated outdoorair system or other systems serving the building such as lighting security and fire safety Unit Level Control Unit level control for a piece of HVAC equipment typically involves the use of several control loops to employ specific functions plus var
2. heat pumps water circulating pumps pond For a building site that already contains a pond or if local building codes require water retention ponds for short term storage of surface run off a SWHP system can be very cost effective Surface water systems typically use a series of closed loops of piping similar to the spiral loop pattern used with some ground coupled heat pump systems The pipes are submerged in a pond or lake and secured to concrete anchors so they float 9 to 18 in 23 to 46 cm above the bottom of the pond allowing for sufficient flow around the heat exchanger The pipes should be submerged at least 6 to 8 ft 2 to 2 5 m below the surface of the pond preferably deeper maintaining adequate thermal mass even during low water levels 152 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Variations Typical installations require 300 to 500 ft of pipe per block cooling ton 26 to 43 m kW and approximately 3000 ft of surface water per cooling ton 79 m2 kW The recommended minimum total surface water area is about 20 000 ft 1900 m2 This type of system will likely experience greater loop temperature variations than a ground coupled system which result in lower heat pump efficiencies However the lower installed cost may compensate for the reduction in efficiency Note Rivers or other bodies of water that have appreciable currents should be avoided The
3. mia T lt supply strainer with blow down valve and hose connector System balancing can be an arduous task because adjusting any ball valve changes the system pressures so the other valves may need to be re adjusted to ensure the proper flow rate e Manual flow control device circuit setter Manual balancing using an in line flow measurement device such as a circuit setter offers a simplified approach compared to the conventional technique of measuring the water temperature change across the unit and calculating the corresponding flow rate The circuit setter flow controller installed in the leaving water pipe for each WSHP Figure 30 combines the readout and the adjustment feature in one device Figure 30 Manual flow control device circuit setter for water balancing circuit setter isolation valve gt return manual ball valve with 3 pressure temperature port ier lt supply A strainer with blow down valve and hose connector Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components While this simplifies the task of water balancing at each WSHP the other valves may still need to be re adjusted since adjusting any circuit setter changes the system pressures e Automatic flow control device In larger syste
4. vertical vertical stack WSHPs WSHPs water to water heat pump serving an air handling unit AHRI ISO rating standards The Air Conditioning Heating and Refrigeration Institute AHRI establishes rating standards for many types of HVAC equipment The International Organization for Standardization ISO facilitates the international coordination and unification of standards The objective of ANSI AHRI ASHRAE ISO Standards 13256 1 1998 Water to Air and Brine to Air Heat Pumps Testing and Rating for Performance and 13256 2 1998 Water to Water and Brine to Water Heat Pumps Testing and Rating for Performance is to promote the consistent rating of various types and sizes of water source heat pumps They cover equipment that is designed for use in either water source ground coupled or ground water heat pump systems Table 3 and Table 4 include a summary of these standard rating conditions 30 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Table 3 AHRI ISO 13256 1 Standard Rating Conditions for Waterto Air Heat Pumps Water source heat pumps Ground source heat pumps Ground water heat pumps Cooling mode Airflow rate specified by the manufacturer Entering air dry bulb temperature 80 6 F 27 C 80 6 F 27 C 80 6 F 27 C Entering air wet bulb temperature 66 2 F 19 C 66 2 F 19 C 66 2 F 19 C External stat
5. S TRANE Applications Engineering Manual Water Source and Ground Source Heat Pump Systems November 2013 SYS APMO10 EN WaterSource and Ground Source Heat Pump Systems by J ohn Murphy applications engineer with Beth Bakkum information designer SYS APM010 EN 2013 Trane All rights reserved TRANE As a leading HVAC manufacturer we deem it our responsibility to serve the building industry by regularly disseminating information that promotes the effective application of building comfort systems For that reason we regularly publish educational materials such as this one to share information gathered from laboratory research testing programs and practical experience This publication focuses on water source heat pump WSHP and ground source heat pump GSHP systems including boiler tower ground coupled ground water and surface water systems These systems are used to provide comfortin a wide range of building types and climates To encourage proper design and application of a WSHP system this guide discusses the advantages and drawbacks of the system reviews the various components that make up the system proposes solutions to common design challenges explores several system variations and discusses system level control We encourage engineering professionals who design building comfort systems to become familiar with the contents of this manual and to use it as a reference Architects building owners equi
6. 1 cee eee n een ennes 175 Occupied standby mode 0c e cence eee eens 176 Unoccupied mode 000 cece tees 176 Morning warm up or cool down mode 00000 178 Scheduling asrasa ia a aaa aaa aaia d BRAA RA aE A RAA Beadle se 179 Water loop temperature control 1 0 0 0 cece eee eens 180 Bypassing the ground heat exchanger 0000 eas 181 Preheat for morning warm up 0 0c 183 Precool loop for morning cool down 000 005 183 Safetles ia tea a E one whee eee eek aha a p ens 184 Building pressure control 0 0 0 cece eee eens 185 System optimization 0 0 6 eee 187 Optimal Start sc eet oe ete Ea EE ea en ead akan 187 Demand controlled ventilation 0 000 cc eee eee ees 188 Reset dedicated OA leaving air temperature 191 Loop temperature optimization 0 00 cece eee 193 Coordination with other building systems 0 0005 194 Glossary eis seh bes swe ee eee E Yedda a ARE REE eS a wha 28S 195 Referen sS oo54 tic oina sak ee kee bee ee Sei esd pN eiaa pE dees 207 INGEN john ce nde iwadaae sein a E a ener cond E adaa a O a a 211 vi Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE Overview of a Water Source Heat Pump System In atypical watersource heat pump WSHP system each zone has a dedicated WSHP that cools or heats air to maintain the desired temperature in that zone A WS
7. Ethylene Glycol Propylene Glycol Concentration volume Concentration volume Temperature Freeze protection Burst protection Freeze protection Burst protection 20 F 7 C 16 11 18 12 10 F 12 C 25 17 29 20 O F 18 C 33 22 36 24 10 F 23 C 39 26 42 28 20 F 29 C 44 30 46 30 30 F 34 C 48 30 50 33 40 F 40 C 52 30 54 35 50 F 46 C 56 30 57 35 60 F 51 C 60 30 60 35 Source Dow Chemical Company 2008 HVAC Application Guide Heat Transfer Fluids for HVAC and Refrigeration Systems www dow com heattrans If the closed circuit cooling tower is bypassed during sub freezing weather meaning that fluid does not flow out through the tower see Figure 113 p 170 a concentration that provides burst protection is usually sufficient A concentration that provides freeze protection is only needed in those cases where no ice crystals can be permitted to form which would be the case if the tower was not bypassed during sub freezing weather or where there is inadequate expansion volume available The advantage of this approach is that it is predictable and relatively easy to maintain However adding antifreeze to the loop degrades the capacity and efficiency of the heat pumps possibly increasing the size and cost of these components In addition it increases the fluid pressure drop through the system which increases pump energy use Therefore ensure that the selection of individual h
8. S TRANE Primary System Components Conditioning the outdoor air with a dedicated system allows the local heat pumps to handle only the zone loads and not the ventilation load This can result in more stable comfort control lower indoor humidity levels see Methods for improving dehumidification performance p 103 and possibly smaller heat pumps In facilities that require special filtering of the outdoor air or humidification during the winter a dedicated OA system allows these processes to be handled in a centralized unit Dedicated OA system configurations Following are four example dedicated OA system configurations that are commonly used to deliver the conditioned outdoor air in a WSHP system Table 10 summarizes the advantages and drawbacks of each configuration Conditioned OA delivered directly to each zone The example configuration shown in Figure 40 delivers the conditioned outdoor air CA directly to each zone through a separate duct system and diffusers The WSHP conditions only recirculated air RA Figure 40 Conditioned OA delivered directly to each zone dedicated SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 59 Se TRANE Primary System Components Figure 41 depicts another example of delivering conditioned OA directly to the zone In this case a vertical WSHP installed in an adjacent closet conditions recirculated air Figure 41 Conditioned OA ducted directly to a classroom
9. hallway Limit the use of flexible ductwork Flexible ductwork is sometimes used to connect the sheet metal ductto the inlet of each supply air diffuser allowing for some flexibility when the ductwork and ceiling are not installed at the same time However it is best to limit the use of flexible duct to no longer than 6 ft 2 m sections to minimize the turbulence and high pressure drop associated with flexible duct If the overall length of duct between the WSHP and diffuser is greater than this sheet metal should be used for the initial sections of ductwork while limiting the use of flexible duct to no more than the last 6 ft 2 m needed to connect to the supply air diffusers Add a balancing damper in the runout duct for each supply air diffuser This allows adjustment to deliver the desired airflow to different spaces or portions of a space served by the WSHP Many types of diffusers are available with an integral balancing damper to simplify installation Supply air diffusers Proper selection and placement of supply air diffusers generates air movement throughout the occupied zone eliminating areas of stagnant and stratified air increasing air circulation and preventing cold air dumping Other publications contain more complete details related to sizing and locating supply air diffusers but the following are a few general recommendations Select and lay out supply air diffusers to achieve at least an 80 percent A
10. p 135 Heat Addition A heat adder is used to maintain the temperature of the water in the distribution loop above a pre determined lower limit such as 60 F 162C fora boiler tower WSHP system Hot water boiler In a boiler ftower WSHP system the heat adder is typically a hot water boiler operated either by electricity or a fossil fuel such as natural gas or heating oil Alternatively buildings that contain separate hot water or steam heating systems may use a heat exchanger to add heat to the water distribution loop This isolates the water in the distribution loop from the water in the other system A hot water boiler is a pressure vessel that typically consists of a water tank or tubes with water flowing through them a heat exchanger fuel burners exhaust vents and controls It transfers the heat generated by burning fuel to either water or steam The majority of boilers used in WSHP systems are low pressure lt 160 psig 1100 kPa and lt 250 F 120 C hot water boilers Water Source and Ground Source Heat Pump Systems 49 eS TRANE Primary System Components For more information on the various types of boilers refer to Chapter 31 Boilers of the 2008 ASHRAE Handbook HVAC Systems and Equipment www ashrae org The Boiler Book from Cleaver Brooks www boilerspec com or the Gas Boilers design guide from the New Buildings Institute www newbuildings org 50 Water Source and Ground Source Heat Pump Syst
11. Figure 21 Typical water source heat pump configurations small vertical large vertical vertical stack console rooftop WSHP configurations Water source heat pumps are available in several configurations to suit various building types Figure 21 A horizontal WSHP is designed for installation in a ceiling plenum with supply air ducted to the zone They are typically used in buildings where floor space is at a premium such as office buildings schools and retail strip malls A vertical WSHP is designed for installation in a closet or maintenance room with supply air ducted to the zone Common applications for smaller vertical units include schools apartments condominiums dormitories and extended care facilities Larger vertical units are generally used for very large zones such as cafeterias and large meeting rooms A console WSHP is designed for installation within the occupied space often under windows in perimeter zones hallways or entryways They may also be used when ducted units are not feasible Typical applications include office buildings apartment buildings dormitories hotels and extended care facilities A vertical stack WSHP is designed for installation in the corner of a room in a multi story building with supply air typically delivered directly into the zone They are designed to be stacked above each other to minimize the cost of installing piping and electrical service Common application
12. Loop temperature optimization p 193 In climates that experience cold outdoor temperatures climate zones 3 through 8 Section 6 5 2 2 3 requires the system be designed and controlled to minimize heat loss through the heat rejecter during cold weather Ifa closed circuit cooling tower is used the cooling tower must be equipped with low leakage dampers to prevent airflow when heat rejection is not needed Alternatively a valve can be installed to bypass water around the tower when heat rejection is not needed e Ifan open cooling tower is used in conjunction with an intermediate heat exchanger the pump in the separate cooling tower loop must be turned off when heat rejection is not needed e Ifan open cooling tower is used without an intermediate heat exchanger that is the loop water passes directly through the open tower a valve must be installed to bypass water around the tower when heat rejection is not needed Section 6 5 4 4 1 requires that each WSHP be equipped with two position valve that automatically closes to shut off water flow whenever the compressor turns off see Isolation valves and flow control devices p 39 This means that the pump s must be capable of handling variable flow Heat pumps that are equipped with a waterside economizer coil are exempt from this requirement If total pump system power exceeds 5 hp 3 7 kW Section 6 5 4 4 2 requires the pump be equipped with a variable speed drive
13. Low temperature storage The most common approach for adding hot water storage to a WSHP system is to simply store heat at temperatures that correspond to the typical limits of loop operation between 60 F 16 C to 90 F 32 C for example A low temperature storage tank is typically installed upstream of the boiler and downstream of the heat pumps to allow the boiler to quickly add heat to the loop during normal operation Figure 37 Figure 37 Low temperature storage tank added to the loop SSS low temperature water storage tank SYS APM010 EN Water Source and Ground Source Heat Pump Systems 53 eS TRANE Primary System Components With this low temperature storage approach no additional heating equipment is needed and the tank can also be used for other purposes e If the electric utility has a time of day rate structure during cold weather the boiler could be operated during off peak hours when the cost of electricity is lower to increase the temperature of the water inside the loop and storage tank This would allow the heat pump compressors those operating in the heating mode to operate more efficiently during on peak hours when the cost of electricity is higher and use less electricity This is especially valuable if the system uses an electric boiler because it shifts operation of the boiler to the off peak period e Ifthe electric utility has a time of day rate structure during the co
14. boiler less system see Electric resistance heat in the WSHP boiler less system p 57 a cooling only unit containing a separate gas fired burner or electric heater would likely be preferred to prevent overcooling the loop during cool weather and increasing the need to use the electric resistance heat in the individual heat pumps The primary advantage of using a water cooled DX unit that is connected to the loop is improved efficiency Water cooled condensing is typically more efficient than air cooled condensing equipment and for cooling dominated buildings the excess heat rejected to the loop by the heat pumps can be extracted by the dedicated OA unit for use in heating the entering outdoor air during cool weather In addition the dedicated OA unit and individual heat pumps share the same cooling tower for heat rejection avoiding the space needed outside to install two separate pieces of heat rejection equipment However selection of a loop connected unit is more complicated as its performance is inter related to the performance and selection of the water source heat pumps and other components of the water distribution loop Both the cooling tower and boiler will typically need to be larger than if the dedicated OA unitis standalone Similar to an air cooled unit a packaged water cooled unit typically offers less flexibility in selection and fewer options while a split DX system increases flexibility since the
15. e Atthe shallower depth ground temperatures are subject to seasonal temperature variations rainfall and snow melting Obtaining the same loop temperatures as a vertical loop requires a more complicated design with longer pipe lengths e The longer pipe lengths also require more antifreeze solution when necessary than vertical loops e The pipe is at greater risk of damage during backfilling of the trenches Design of the ground heat exchanger The ground heat exchanger must be sized to maintain the loop temperature within the minimum and maximum limits for which the heat pumps have been selected And it must be sized to maintain those temperatures over the expected life of the system If the heat exchanger is too small the ground temperature may increase over time degrading the performance of the system Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Variations Figure 92 Components of a vertical ground heat exchanger supply and return headers R Ca ALON wee PR peo reverse OLE SS KN return U tube SYS APM010 EN Water Source and Ground Source Heat Pump Systems This section focuses primarily on vertical closed loop ground heat exchangers Due to limited land availability this is the most common type of ground heat exchanger used in commercial or institutional buildings The primary components of the vertical ground heat exchanger
16. indicator to minimize ongoing maintenance Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Issues and Challenges Ventilation Ventilation refers to the introduction of an adequate amount of fresh outdoor air to dilute contaminants that are generated inside the building by people equipment processes or furnishings This requires the removal of an equal quantity of air from the building The Ventilation Rate Procedure Section 6 2 in ASHRAE Standard 62 1 Ventilation for Acceptable Indoor Air Quality prescribes the quantity of outdoor air that must be delivered to each zone based on the expected use of that zone and then prescribes how to calculate the outdoor airflow needed at the system level intake In addition Section 5 of this standard includes several requirements related to the design of the ventilation equipment and distribution system The requirements related to ventilation system controls particulate filtration and humidity control are each discussed in other sections of this manual Note Because ASHRAE 62 1 is under continuous maintenance it can change frequently This manual is based on the 2010 published version of the standard Refer to the most current version for specific requirements Zone level ventilation requirements ASHRAE 62 1 requires the following three step procedure to determine the outdoor airflow required for each ventilation zone L Calculate t
17. 1830 cfm 0 86 m3 s 450 cfm at 52 F 0 21 m3 s at 11 C 4 Cold Air System 1380 cfm 0 65 m3 s Since both dedicated OA systems dehumidify the same quantity of outdoor air to the same leaving air dew point the required capacity and airflow of the dedicated OA unit are the same whether the outdoor air is delivered neutral or cold The impact on the local WSHPs however is significant see Table 11 Compared to a neutral air system a dedicated OA system that delivers cold air directly to each zone or to the supply side of each WSHP e Requires less overall cooling capacity The required capacity of the dedicated OA unit is the same for both configurations but the required cooling capacity of each heat pump is less in a cold air system than in a neutral air system e Requires less overall cooling energy for much of the year By taking advantage of the sensible cooling already done by the dedicated OA unit the cold air system requires less cooling energy at each heat pump The neutral air system throws away this sensible cooling benefit by reheating the air to approximately zone temperature See Figure 45 p 64 e Requires less overall fan airflow and therefore less fan energy The airflow delivered by the dedicated OA unit is the same for both configurations but for those zones that require seasonal cooling and heating the supply airflow delivered by the heat pump is less in a cold air system than in a neutral air sy
18. 1a 1b economizer not required a ae 3b 3c 4a 4b 4c 5a 5b 5c 6a gt 54 000 Btu hr 16 kW Excerpt from Table 6 5 1A of ASHRAE Standard 90 1 2010 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org For all climate zones except climate zone 1a and 1b this section requires an economizer if the rated cooling capacity of the WSHP is 54 000 Btu hr 16 kW which equates to 4 5 tons or larger Most horizontal vertical vertical stack and console heat pumps are smaller than this limit in which case an economizer would not be required This interpretation is confirmed by example 6 II in the Standard 90 1 User s Manual Like other requirements in the standard there are several exceptions provided For instance an economizer can be avoided per exception i if the heat pump cooling efficiency meets or exceeds the requirements in Table 6 3 2 of the standard For example in Climate Zone 2A if the cooling efficiency of the WSHP is at least 17 percent higher than the minimum efficiency listed in Table 6 8 1B of the standard the economizer can be eliminated When required either an airside or waterside economizer can be used provided that it meets the requirements stated in Section 6 5 1 of the standard The design team might consider one of the following potential solutions Ifthe WSHP has an outdoorair intake as might be the case with a rooftop style WSHP an airside e
19. At the traditional design condition peak outdoor dry bulb temperature this example system mixes 450 cfm 0 2 m3 s of outdoor air required for ventilation with 1050 cfm 0 5 m3 s of air recirculated from the zone and then delivers the 1 500 cfm 0 7 m3 s of supply air at 58 F 14 4 C to offset the sensible cooling load in the zone and maintain the zone temperature at setpoint Plotting this system on a psychrometric chart the resulting relative humidity in the zone is 55 percent at this design condition Figure 71 Figure 7L Full versus part load dehumidification performance of a basic constant volume mixed air system conventional WSHP Part Load Peak dry bulb Peak dew point Mild rainy day 96 F DB 76 WB 76 F DP 84 F DB 70 F DB 69 F WB 74 F DB 55 RH 74 F DB 67 RH 74 F DB 72 RH SA 81 F DB 77 F DB 72 F DB 58 F DB 63 F DB 66 F DB 1500 cfm 1500 cfm 1500 cfm f peak dry bulb mild rainy f full load part load J a oA e e a Se T MA S etma A 5 a S At part load conditions when the zone sensible cooling load decreases this conventional WSHP continues to supply a constant volume of air to the zone Meanwhile the compressor cycles on and off which results in a warmer average temperature delivered to the zone Although this control action successfully maintains the zone dry bulb temperature at setpoint the cycling compressor reduces the amount of moisture removed and zone humidity ri
20. Direct versus indirect evaporative cooling 65 F DB 58 F WB ow 53 F DP rs ak Q Do a S 5 On ling 93 F DB WATE o s 58 F WB 22 F DP OA Ans indirect evaporative cooling The leaving air temperature depends on how much the dry bulb temperature of the entering air exceeds its wet bulb temperature For example if the condition of the entering outdoor air OA is 93 F dry bulb and 58 F wet bulb 34 C DB 14 C WB and the direct evaporative process is 80 percent effective the condition of the leaving air OA will be 65 F DB and 58 F WB 18 C DB 14 C WB DBTieaving DBTentering effectiveness x DBTentering WBTentering DBTleaving 93 F 0 80 x 93 F 58 F 65 F DBTleaving 34 C 0 80 x 34 C 14 C 18 C SYS APM010 EN S TRANE Primary System Components For a dedicated OA system direct evaporative cooling is most applicable in dry climates where the outdoor dew point is well below the desired dew point indoors A conventional cooling coil may be required to supplement the evaporative cooling process during times of the year when the outdoor dew point is higher Indirect evaporative cooling typically uses an evaporative cooling tower to cool water and then pumps this water through a conventional cooling coil to cool the air This approach does not involve the evaporation of water into the air stream so it does not increase the dew point of the air Figure 59 In some applic
21. Finally water source heat pumps can easily be applied in a ground coupled system Ground coupled systems use the earth as the heat rejecter and heat adder to reduce or eliminate the need to operate a cooling tower or boiler Water Source and Ground Source Heat Pump Systems SY S APM 010 EN All heat recovery is not equal It is important to understand that while several types of systems can incorporate heat recovery the energy saving benefits are not the same for all systems To illustrate this point let s compare a WSHP system to a variable refrigerant flow VRF system In a typical WSHP system all the heat pumps in the building are connected to a common water loop Therefore heat can be recovered from any zone operating in cooling mode and provided to any zone operating in heating mode regardless of its location in the building In a VRF system multiple indoor terminals are connected to an outdoor air cooled condensing unit via refrigerant piping However in most buildings all of the VRF terminals are not connected to a single refrigeration circuit Presently when a VRF system is designed for heat recovery the maximum system refrigerant circuit size is 20 tons 70 kW For a building that requires more cooling than this multiple systems must be used To demonstrate consider the example office building shown in Figure 8 The East Open Office Area requires 20 tons 70 kW of cooling both the Nort
22. S TRANE System Design Variations Figure 9L Spiral heat exchanger 140 Spiral loops A variation of the multiple layer horizontal loop is the spiral loop Figure 91 The spiral loop includes a roll of pipe that is unraveled into circular loops tied together and then placed either vertically in a trench or horizontally in an open pit The spiral loop generally requires more total piping typically between 500 and 1000 ft per block cooling ton 43 to 86 m kW but less trenching than multiple layer horizontal loops Both horizontal and spiral loop systems are generally associated with small commercial or residential buildings where land requirements are less of a factor Advantages of spiral loops include e Less land area and less trenching is typically required for spiral loops than for traditional horizontal loops e Installation costs are typically lower than for traditional horizontal loops because less trenching is required e Trenching costs are typically lower than the drilling costs associated with vertical loop installation Spiral loops may not build up as much heat over time as vertical loops because the pipes are closer to the surface where heat can be dissipated to the atmosphere Drawbacks include e Spiral loops require a larger area of land than vertical loops e Spiral loops require more total length of piping than either vertical or horizontal loops which increases pump energy use
23. Vbz p 91 Table 30 Example of occupied standby mode Occupied mode Occupied standby mode Lights on off Zone cooling setpoint 75 F 24 C 77 F 25 C Outdoor airflow required2 310 cfm 153 L s 60 cfm 28 L s 1 Based on a 1000 ft 93 m2 conference room with a design zone population Pz of 50 people 2 According to Table 6 1 of ANSI ASHRAE Standard 62 1 2010 the required outdoor airflow rates for a conference room are Rp 5 cfm p 2 5 L s p Ra 0 06 cfm ft2 0 3 L s m2 During occupied mode Vbz Rp x Pz Ra x Az 5 cfm p x 50 people 0 06 cfm ft2 x 1000 ft2 310 cfm 2 5 L s p x 50 people 0 3 L s m2 x 93 m2 153 L s During occupied standby mode Vbz 5 cfm p x O people 0 06 cfm ft2 x 1000 ft 60 cfm 2 5 L s p x 0 people 0 3 L s m2 x 93 m2 28 L s When the occupancy sensor indicates that the zone is again occupied the zone is switched back to occupied mode Unoccupied mode When the building is unoccupied the BAS can allow the temperature in the zones to drift away cooler or warmer from the occupied setpoints see Zone is unoccupied p 4 But the system must still prevent the zones from getting too cold perhaps 60 F 16 C or too hot perhaps 90 F 32 C In addition when unoccupied the building does not typically require outdoor air for ventilation or to replace exhaust air so the dedicated outdoor air system can be turne
24. WSHP compressor energy use boiler energy use 65 900 Btu hr 19 3 kW 66 200 Btu hr 19 4 kW 1 This analysis assumes the waterside economizer coil is capable of offsetting the 5 000 Btu hr 1 5 kW cooling load in Zone 2 with either entering water temperature 45 F 7 2 C or 55 F 12 8 C The waterside economizer coil may need to be larger to offset the entire cooling load with warmer water 2 This example analysis assumes a gas fired boiler with 80 percent efficiency If however an electric boiler with 100 percent efficiency is used the overall building energy use would be equal at these two loop temperatures The colder loop water temperature decreases compressor efficiency COP for those heat pumps operating in heating mode However the heat of compression increases a less efficient compressor requires more power and generates more heat so that less heat must be extracted from the loop to offset the same zone heating load which means less heat must be added to the loop by the boiler In addition those heat pumps operating in cooling mode using a waterside economizer coil are rejecting heat to the loop which further reduces the amount of heat that must be added by the boiler In this example allowing the loop water temperature to drop from 55 F 12 8 C to 45 F 72 C has the following results e WSHP heating efficiency decreases from 4 04 COP to 3 70 COP e WSHP compressor power increases from 4 43 kW
25. dedicated outdoor air unit horizontal WSHPs CA Again this might be a packaged unit or a split system A packaged water cooled DX unit can be installed indoors or outdoors since it does not require outdoor air for condensing A split DX system is comprised of a water cooled condensing unit which is typically installed inside the building and an air handling unit which can be installed indoors or outdoors The water cooled DX refrigeration circuit may be used for cooling only or it might be reversible so that it can switch to operate as a heat pump Most applications use a reversible refrigeration circuit allowing the unit to operate in either the cooling or heating mode This allows for improved heating efficiency due to the higher COP of the heat pump Note however that the dedicated OA unit will likely be operating in the heating mode whenever the SYS APM010 EN Water Source and Ground Source Heat Pump Systems 75 eS TRANE Primary System Components outdoor temperature is below 50 F to 60 F 10 C to 16 C which will cause the loop temperature to decrease and may require the boiler to operate more often than in a system where the dedicated OA unitis not connected to the loop However even though the boiler will likely need to operate more often the overall heating COP will still likely be higher than using a gas fired burner or electric heater in the dedicated OA unit In a
26. heat exchanger f reversing valve Note A variation of the water source heat pump called a water to water heat pump see Figure 22 p 29 contains two refrigerant to water heat exchangers and no refrigerant to air heat exchanger Components of the DX refrigeration circuit Each WSHP includes at least one compressor Some models may use multiple compressors Depending on its size and manufacturer this compressor may be rotary rolling piston reciprocating or scroll type Figure 11 The selection of the type of compressor generally depends on the capacity and electrical requirements of the WSHP Figure 1L Types of compressors typically used in a WSHP rotary rolling piston reciprocating scroll Water Source and Ground Source Heat Pump Systems 13 eS TRANE Primary System Components Methods of compressor capacity modulation Traditionally smaller capacity heat pumps have contained a single compressor that cycles on and off Larger capacity heat pumps often have multiple compressors allowing for multiple stages of capacity control Recently some heat pumps have been equipped with either a two stage variable capacity Digital or variable speed compressor Compared to the on off compressor historically used in this type of equipment these other methods of compressor capacity modulation are better able to match cooling or heating capacity with the changing load in the zone This typically improves comfort and in s
27. lt 1 0 during heating mode Conditioned outdoor air may not be able to be delivered at a cold temperature due to concerns over condensation within the ceiling plenum rather it must typically be reheated closer to a neutral temperature Fans inside the heat pumps must operate continuously to provide ventilation during scheduled occupancy rather than cycling off with the compressor If the dedicated OA system operates during unoccupied periods e g for after hours humidity control or preoccupancy purge the fans inside the heat pumps typically must operate also SYS APM010 EN Water Source and Ground Source Heat Pump Systems 63 eS TRANE Primary System Components 64 Water Source and Ground Source Heat Pump Systems Neutral versus cold air delivery Regardless of where the conditioned outdoor air is delivered the dedicated OA unit should dehumidify the outdoor air so that it is drier than the zone This offsets the latent load associated with ventilation and if the dew point temperature of the conditioned outdoor air is lower than the dew point in the zone Figure 45 also offsets some or all of the zone latent loads This approach can adequately limit indoor humidity levels at both full and part load conditions without the need for additional dehumidification enhancements in the local heat pumps see Methods for improving dehumidification performance p 103 Many dedicated OA systems are designed to
28. quantity of outdoor air is delivered to each zone Voz Which procedure to use depends on the configuration of the ventilation system Many WSHP systems use a dedicated outdoor air system to deliver only outdoor air to the individual zones defined by ASHRAE 62 1 as a 100 percent outdoorair system In some WSHP configurations such as rooftop or some vertical models outdoor air may be brought in through the WSHP itself defined by ASHRAE 62 1 as a single zone system assuming that the WSHP serves only a single ventilation zone Note If outdoor air is delivered through a WSHP that serves more than one ventilation zone it might be classified by ASHRAE 62 1 as a multiple zone recirculating system In that case the outdoor airflow delivered to the system level outdoorair intake at the WSHP would need to be determined using Section 6 2 5 of ASHRAE 62 1 SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 93 S TRANE System Design Issues and Challenges Figure 65 Example office building with a WSHP system E2 warehouse north offices north north conference room interior offices west offices south east offices interior offices south conference room south offices z Calculating system intake airflow Vot for a dedicated outdoor air system Most WSHP systems use a dedicated 100 percent outdoor air system to condition all the outdoor air for the system As descr
29. space Heat is carried by convective flows created by heat sources into the upper part of the zone where is extracted thermal expansion valve A type of expansion device that uses a thermally actuated valve to sense and control the flow rate of liquid refrigerant to the evaporator throw Horizontal or vertical axial distance an air stream travels after leaving an air outlet before the maximum stream velocity is reduced to a specified terminal velocity defined by ASHRAE Standard 70 total energy recovery The transfer of sensible and latent moisture heat between two or more air streams or between two locations within the same air stream total energy wheel A rotating heat recovery device that recovers sensible temperature and latent humidity heat from one air stream and releases it to another adjacent air stream Also known as a rotary heat exchanger passive desiccant wheel heat wheel or enthalpy wheel transmission loss A term used to measure the effect of a barrier on reducing the amount of transmitted sound It is the ratio of sound power on the receiver side of a barrier to the sound power on the source side Traq damper Trane s flow measuring outdoor air damper TXV See thermal expansion valve Water Source and Ground Source Heat Pump Systems 205 206 u tube The component of a ground heat exchanger that is inserted into the borehole It is typically constructed of two continuous sections of high density p
30. this type of system typically has the lowest installed cost of any ground source system because it requires fewer wells and less length of piping There are however three notable considerations that must be addressed when investigating this use of this type of system The first consideration is water quality If the ground water is allowed to flow through the heat pump refrigerant to water heat exchangers they will be subject to fouling minerals in the water scaling on the internal surfaces of the heat exchanger tubes which reduces heat transfer and degrades efficiency Scaling can be reduced by periodically cleaning the heat exchangers but the acidic solutions used to de scale the heat exchanger can also cause corrosion To help ensure that the water flowing through the heat pumps is clean an intermediate plate and frame heat exchanger is recommended This eliminates the problem of scaling in the individual heat pumps requiring that only the centrally located plate and frame heat exchanger be cleaned However the inefficiency of this additional heat exchanger results in a slightly warmer during the cooling season or slightly colder during the heating season fluid temperature in the loop which decreases heat pump efficiency compared to an open ground water system In some applications two heat exchangers are installed so one can be cleaned while the other is in operation The second consideration is the need for an adequate s
31. 19 kW and lt 135 000 Btu hr 40 kW 86 F 30 C 12 0 EER 3 51 COP water source heat pump heating mode lt 135 000 Btu hr 40 kw in terms of cooling capacity 68 F 20 C 4 2 COP ground source heat pump cooling mode lt 135 000 Btu hr 40 kW 77 F 25 C 13 4 EER 3 93 COP ground source heat pump heating mode lt 135 000 Btu hr 40 kw in terms of cooling capacity 32 F 0 C 3 1 COP ground water heat pump cooling mode lt 135 000 Btu hr 40 kW 59 F 15 C 16 2 EER 4 75 COP ground water heat pump heating mode lt 135 000 Btu hr 40 kw in terms of cooling capacity 50 F 10 C 3 6 COP Source Table 6 8 1B from ASHRAE Standard 90 1 2010 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org 12 Water Source and Ground Source Heat Pump Systems SYS APM010 EN ASHRAE 90 1 defines the fan system design conditions as the operating conditions that can be expected to occur during normal system operation that result in the highest supply airflow rate to conditioned spaces served by the system S TRANE System Design Issues and Challenges Maximum allowable fan system power Because fan energy use depends heavily on the design of the air distribution system itis difficult to prescribe a minimum efficiency requirement for a fan Therefore Section 6 5 3 1 of ASHRAE 90 1 prescri
32. 30 2 Stanke D and Bradley B 2001 Design Tips for Effective Efficient Dedicated Ventilation Systems Trane Engineers Newsletter 30 3 Stanke D and Bradley B 2002 Managing the Ins and Outs of Building Pressurization Trane Engineers Newsletter 31 2 Stanke D and Bradley B 2006 Keeping Cool with Outdoor Air Airside Economizers Trane Engineers Newsletter 35 2 Trane 2005 ASHRAE Standard 62 1 2004 Ventilation Requirements Engineers Newsletter Live satellite broadcast APP CM C023 EN September 21 DVD La Crosse WI AVS Group 2005 CO2 Based Demand Controlled Ventilation Engineers Newsletter Live satellite broadcast APP CMC024 EN November 16 DVD La Crosse WI AVS Group 2002 Commercial Building Pressurization Engineers Newsletter Live satellite broadcast APP APVO13 EN April 17 DVD La Crosse WI AVS Group 2001 Geothermal Heat Pump Systems Engineers Newsletter Live broadcast APP CMC007 EN May 23 DVD La Crosse WI AVS Group 2006 HVAC Systems and Airside Economizers Engineers Newsletter Live broadcast APP CMC026 EN May 3 DVD La Crosse WI AVS Group ee 2012 Energy Saving Strategies for Water Source and Ground Source Heat Pump Systems Engineers Newsletter Live broadcast APP CM C045 EN June 6 DVD La Crosse WI AVS Group U S Green Building Council USGBC 2009 Leadership in Energy and Environ
33. 52 F 11 1 C in this example S TRANE System Design Issues and Challenges Figure 78 Dehumidification performance of a dedicated OA system at peak dry bulb condition peak dry bulb full load dedicated OA unit 96 F DB 76 F WB WSHP A a O RA S 0 oO 74 F DB z F z SA CA 50 RH 56 6 F DB ZF De o 52 F DP o At the part load peak dew point condition Figure 79 the dedicated OA unit continues to deliver the outdoor air at the same conditions 71 F DB 217 C DB and 52 F DP 111 C DP Because the sensible cooling load in the zone is lower the compressor in the WSHP cycles to maintain zone temperature at setpoint This example assumes the WSHP includes a single on off compressor and a constant speed fan The resulting zone humidity is 56 percent RH Figure 79 Dehumidification performance of a dedicated OA system at peak dew point condition peak dew point part load OA 76 F DP 84 F DB dedicated OA unit 63 9 F DB amp SA WSHP S On RA 8 gt FDB z is CA 56 RH 71 F DB a 52 De 3 Even though the cycling compressor results in less dehumidification provided by the WSHP the 450 cfm 0 21 m s of outdoor air delivered by the dedicated OA unitis dry enough to offset the zone latent load and prevent the indoor humidity level from rising too high SYS APM010 EN Water Source and Ground Source Heat Pump Systems 107 S TRANE System Design Issues
34. 7 Once each path has been identified individual elements can be analyzed for oner a e their contribution For example the supply airborne path includes various analysis software visit www tranecds com duct elements elbows straight duct junctions diffusers and so on and a room correction factor Algorithms available from ASHRAE can be used to calculate the acoustical effect of each duct element The effect of changing an element such as removing the lining from a section of ductwork can also be calculated Software tools make these algorithms easier to use SYS APM010 EN Water Source and Ground Source Heat Pump Systems 127 E TRANE System Design Issues and Challenges For more acoustic and vibration related recommendations for water source heat pump systems refer to the ASHRAE manual A Practical Guide to Noise and Vibration Control Step 4 Sum the results to determine the acoustical performance of the installation Once the contributions of the individual paths for a particular receiver location are calculated they must be added together to determine the total sound at the receiver A unique sum is required for each critical receiver location Step 5 Compare the summations with the acoustical goals in the context of the project budget The sum of the sound paths for a particular receiver location is a prediction of the sound level at that location If the sum is lower than the sound target for that location the
35. 73 F DB RA 74 F DB 62 RH cc 61 F DB SA 66 F DB Table 19 compares performance at the example mild rainy condition The constant speed WSHP with hot gas reheat provides 2 8 tons 9 9 kW of cooling and the fan moves 1 500 cfm 0 7 m3 s while the variable speed WSHP provides 2 1 tons 7 4 kW of cooling and the fan moves only 850 cfm 0 4 m3 s This results in less compressor energy and less fan energy Table 19 Example part load performance mild rainy day Constant speed Variable speed Constant speed WSHP WSHP WSHP with HGRH Zone relative 72 62 62 humidity Cooling load 1 8 tons 2 1 tons 2 8 tons 6 3 kW 7 4 kW 9 9 kW Fan airflow 1500 cfm 850 cfm 1500 cfm 0 7 m3 s 0 4 m3 s 0 7 m3 s Water Source and Ground Source Heat Pump Systems 105 E TRANE System Design Issues and Challenges For more information on using a dedicated outdoor air system to improve dehumidification performance including how to determine the leaving air dew point required to offset the zone latent loads refer to the Trane application manual Dehumidification in HVAC Systems SYS APM004 EN Figure 77 Example dedicated outdoorair system with a console style WSHP dedicated OA unit CA SA 71 F DB A 52 F DP WSHP Q A 1 500 cfm E Ra In many applications the variable speed WSHP may do a good enough job of limiting indoor humidity levels avoiding the need to equip the
36. 87 But check the dimensions carefully this door may be wider than the cabinet and require different clearances Water Source and Ground Source Heat Pump Systems 133 S TRANE System Design Issues and Challenges 134 Figure 87 Recommendations for vertical stack models exploded view consider acoustical trade off of ducting supply air locate WSHP away from sound sensitive areas af install flush mounted return air door accessory Ducting the supply air rather than discharging it directly into the occupied space provides an opportunity to provide some attenuation refer to the discussion of the supply airborne sound path for vertical heat pumps p 132 The use of ductwork however requires the fan to operate at a higher speed to overcome the added pressure loss and this results in more noise generated by the fan To minimize sound use ductwork for either all or none of the supply air outlets Sound data is provided by either AHRI Standard 350 Sound Rating of Non Ducted Indoor Air Conditioning Equipment or AHRI Standard 260 Sound Rating of Ducted Air Moving and Conditioning Equipment depending on whether the vertical stack heat pump discharges directly into the occupied space or if the supply air is ducted Cooling towers and other ancillary equipment Sound is an important consideration when selecting and locating outdoor equipment such as cooling towers or dedicated outdoorair units Comm
37. AHU typically has more options for fans air cleaning devices air to air energy recovery devices and sound attenuation In addition a split system allows all water loop piping to be located inside the building thereby reducing the risk of freezing Airhandling unit connected to a water chiller or water to water heat pump standalone or connected to the water loop Probably the most flexible type of dedicated OA equipment is an airhandling unit connected to a water chiller or water to water heat pump The water chiller may be a standalone air cooled chiller or a water cooled chiller that is connected to the water distribution loop One advantage of using a standalone chiller is that the selection and performance of the chiller is independent of the water source heat pumps and other components of the water distribution loop Also the dedicated OA system can be operated to control indoor humidity after hours for example without requiring the water distribution loop pumps and possibly the boiler or cooling tower to operate 76 Water Source and Ground Source Heat Pump Systems SYS APMO10 EN S TRANE Primary System Components i Alternatively a water cooled chiller or water to water heat pump can be eee e E a connected to the water distribution loop The water cooled chiller may be either cooling or heating refer to the used for cooling only or it might be piped into the water distribution loop to Trane application manual Centra
38. As the heating load decreases the compressor operates for a shorter period of time between cycles Traditionally smaller capacity heat pumps have contained a single constant speed compressor that cycles on and off Larger capacity heat pumps often have multiple compressors allowing for multiple stages of capacity control Recently some heat pumps have been equipped with either a two stage variable capacity or variable speed compressor see Methods of compressor capacity modulation p 14 Compared to the on off compressor historically used in this type of equipment these newer methods of compressor capacity modulation are better able to match cooling or heating capacity with the changing load in the zone Typically the fan inside the WSHP operates continuously during the occupied mode However if a dedicated outdoor air system delivers conditioned OA directly to each zone the fan inside the WSHP could be configured to cycle off whenever the compressor cycles off reducing fan energy use In addition if the heat pump is equipped with either a two stage variable capacity or variable speed compressor or if it includes more than one compressor the fan may be controlled to operate at a reduced speed and airflow when the compressor operates at reduced capacity see Multiple speed fan operation p 21 If an electric resistance heater is installed inside the WSHP or in the downstream ductwork see Electric resistance h
39. Ez Voz cfm South conf room 5 30 0 06 3000 330 0 8 413 413 System total Vot Voz SYS APM010 EN Water Source and Ground Source Heat Pump Systems 97 eS TRANE System Design Issues and Challenges For more information on the dehumidification performance of a constant volume system with cycling compressors refer to the Trane application manual Dehumidification in HVAC Systems SYS APM004 EN and the Trane Engineers Newsletter Better Part Load Dehumidification ADM APNO11 EN Dynamic reset of intake airflow Section 6 2 7 of ASHRAE 62 1 explicitly permits dynamic reset of intake outdoor airflow as operating conditions change as long as the system provides at least the required breathing zone outdoor airflow whenever a zone is occupied The standard specifically mentions resetting intake airflow in response to variations in zone population As the number of people occupying a zone varies the quantity of outdoor air required to properly ventilate that zone varies This strategy commonly referred to as demand controlled ventilation attempts to dynamically reset the outdoor airflow delivered to a zone based on the changing population in that zone Some of the commonly used methods of assessing zone population include time of day occupancy schedules in the building automation system BAS occupancy sensors and carbon dioxide CO2 sensors For more information see Demand controlled
40. Heat pipes may usea tilt controller bypass dampers or aseries of solenoid valves to shut off refrigerant flow for individual heat pipes Wheels use a modulating damper to bypass air around the exhaust side of the wheel or vary the rotational speed of the wheel Provide a method for frost prevention in cold climates Any air to air energy recovery device that preconditions outdoor air is subject to frost buildup during very cold weather If the surface temperature of the device falls below the dew point of the exhaust air water vapor will condense on the exhaust side of the device If the exhaust side surface temperature falls below 32 F 0 C this water freezes eventually blocking airflow The method used for frost prevention depends on the device Typically one of the following two approaches is used 1 reduce the heat transfer capacity of the energy recovery device which results in a warmer 72 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components exhaust side surface temperature or 2 preheat either the outdoor or exhaust air before it enters the device which also raises the surface temperature of the device to prevent frosting For most applications and most climates reducing heat transfer capacity by modulating an OA bypass damper for example is sufficient for frost prevention However for applications with extremely cold OA and or higher indoor humidity levels during cold we
41. Qloop V Xp XCp XAT where V volume of fluid inside the loop gal L p density of the fluid Ib gal kg L Cp specific heat of the fluid Btu lb F kJ kg K AT initial loop temperature minus lower limit F K Using the same example consider that the WSHP system serving the building has a water loop volume of 600 gal 2300 L which is preheated to SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 55 eS TRANE Primary System Components 90 F 32 C prior to the start of the morning warm up period The density of water is 8 33 Ib gal 1 0 Kg L and the specific heat of water is LO Btu lb F 4 18 kJ kg K The loop lower limit at which the boiler will be activated is 60 F 16 C Qloop 600 gal x 8 33 Ib gal x 1 0 Btu lb F x 90 F 60 F 150 000 Btu Qloop 2300 L x LO kg L x 4 18 kj kg K x 32 C 16 C 155 000 kj In this example the loop by itself can provide a total of 150 000 Btu 155 000 kj of heat to the heat pumps 3 Calculate the size of the storage tank The difference between the total amount of heat that must be extracted from the loop during morning warm up mode and the heat stored by the water loop by itself determines the amount of heat that must be added to the loop by the hot water boiler and or the storage tank If the intent is to avoid the need to operate the boiler during the morning warm up period as might be the case when an electric boiler is bei
42. Sensible cooling provided by dedicated OA system Qca 1 085 x Voz X Tzone Tca Neutral air delivery Tea 71 F 22 C 1 470 Btu hr 0 43 kW 1 470 Btu hr 0 43 kW 1 560 Btu hr 0 46 kW 1 430 Btu hr 0 42 kW Cold air delivery Toa 52 F 11 C 10 740 Btu hr 3 1 kW 10 740 Btu hr 3 1 kW 11 500 Btu hr 3 4 kW 10 500 Btu hr 3 1 kW Sensible cooling required by local WSHP Qwshp Qzone sensible Qca Neutral air delivery tea SAE 22 C 28 330 Btu hr 8 3 kW 25 330 Btu hr 7 4 kW 25 340 Btu hr 7 4 kW 26 870 Btu hr 7 9 kW Cold air delivery Tea 52 F 11 C 19 100 Btu hr 5 6 kW 16 100 Btu hr 4 7 kW 15 400 Btu hr 4 5 kW 17 800 Btu hr 5 2 kW Airflow required by local WSHP assuming Tsa 55 F 13 C Qwshp 1 085 x Vsa x Tzone Tsa Neutral air delivery 3 Tea 71 F 22 C 1380 cfm 0 65 m s 1230 cfm 0 58 m3 s 1230 cfm 0 58 m3 s 1300 cfm 0 61 m3 s Cold air delivery 780 cfm 0 37 m3 s 750 cfm 0 35 m3 s 860 cfm 0 41 m3 s 930 cfm 0 44 m3 s Tea 52 F 11 C Consider however if the same dedicated OA unit dehumidifies the outdoor air to the same 52 F 11 C dew point but delivers it cold not reheated to neutral The conditioned outdoor air is still dry enough to offset the latent load in the classrooms but because it is delivered at a dry bulb temperature that is much cooler than the zone tem
43. TRANE System Design Variations Complicating the matter further in a commercial or institutional application per ton per kW could refer to peak cooling load block cooling load connected load or installed capacity or some type of net operational cooling load Depending on which load is being used as the basis for the rule of thumb the result may lead to significant oversizing or undersizing of the ground heat exchanger Water Source and Ground Source Heat Pump Systems dictated by ambient weather conditions meaning that heat gain or loss through the building envelope is typically the largest component of the load the unit is operating in either heating or cooling mode for a season rather than cycling between heating and cooling modes often Because of these characteristics and the fact that residences typically have similar occupancy patterns the use of rules of thumb for sizing the ground heat exchanger has been somewhat successful for residential applications in similar geographical areas with similar weather conditions and soil types In a commercial or institutional application however multiple heat pumps are typically connected to the same loop And since the building cooling and heating loads are heavily influenced by internal heat gains people lights heat generating equipment and less influenced by heat gain or loss through the building envelope it is common for some units to operate in the coo
44. air OA and then condenses on the cold coil surface The series desiccant wheel allows the AHU to deliver drier air at 45 F 7 C dew point in this example without requiring a lower leaving coil temperature Figure 58 Example performance of a series desiccant wheel in a dedicated 15 40 OA unit wet bulb temperature F 20 ecs 50 CA 180 45 160 40 140 z 3 35 120 lt Pon 5 100 Q O S OA 80 a t S EA 60 9 Qa lt 40 o 20 0 70 80 90 100 110 dry bulb temperature F When a series desiccant wheel is used in a dedicated OA unit it may be necessary to preheat the entering outdoor air OA when the relative humidity is high on a mild rainy day for example Using a preheat coil to raise the dry bulb temperature slightly 5 F to 20 F 3 C to 11 C for example lowers the relative humidity of the air Lowering the relative humidity of the air entering the regeneration upstream side of the wheel allows the desiccant to reject water vapor to the regeneration air thus enabling it to adsorb water vapor from the process air downstream of the cooling coil Typically the amount of heat added by the preheat coil is small and it may be required for only a small number of hours throughout the year Therefore it Water Source and Ground Source Heat Pump Systems 81 eS TRANE Primary System Components For more information on evaporative cooling refer to Chapter 40 Evaporat
45. and typically results in more compressor energy savings In hot and dry climates however bringing in 100 percent outdoor air can actually increase mechanical cooling energy even if the outdoor air enthalpy is low Because of this Table 6 5 11 3A of ASHRAE 90 1 prohibits the use of a fixed enthalpy high limit shutoff strategy in many of the dry and marine climate zones Differential or comparative enthalpy control uses sensors to measure both the dry bulb temperature and humidity of both the outdoor air and return air The controller calculates the enthalpy of both air streams and uses the lower enthalpy air to satisfy the cooling load The economizer is disabled whenever the outdoor air enthalpy is higher than the return air enthalpy Theinstalled cost of differential enthalpy control is higher than for the other control methods because it requires humidity sensing for both outdoor and return air But it may result in the most compressor energy saved compared to the other control types Climate building use and utility costs impact the operating cost differences of these different methods of airside economizer control When the outdoor air is cool enough that the airside economizer provides all the needed cooling capacity the compressor is shut off and the WSHP is not rejecting heat to the water loop Without heat being rejected from those heat pumps that are operating in cooling mode the heat pumps that are operating in heat
46. at which moisture leaves the air and condenses on surfaces diffuser A device connected to the end of the supply duct system used to distribute the supply air into the conditioned space direct digital control DDC A method of terminal unit control using an electric motor to operate the airmodulation damper actuator It uses a microprocessor that enables digital communication between the unit controller and a central building automation system direct drive plenum fan A type of plenum fan in which the motor is mounted directly to the end of the fan wheel shaft eliminating the need for sheaves or belts direct expansion DX system A system that uses the refrigerant directly as the cooling media The refrigerant inside the finned tube evaporator absorbs heat directly from the air used for space conditioning direct fired burner A fuel burning device in which the heat from combustion and the products of combustion are transferred directly to the air stream being heated direct return piping A type of piping arrangement that minimizes the amount of piping by returning the water along the same path as it was supplied displacement ventilation See thermal displacement ventilation diversity See building diversity draft Undesired local cooling of a body caused by low temperature and air movement drain pan A device positioned under a cooling coil to collect condensate and direct it to a drainage system draw thru A confi
47. based on current operating conditions For example if most of the heat pumps are operating in the cooling mode the system level controller could allow the loop temperature to drift colder to 50 F 10 C for example increasing the benefit of the waterside economizers However if most of the heat pumps are operating in the heating mode the controller could maintain a warmer loop temperature 60 F 16 C for example to increase the efficiency of the compressors operating in the heating mode An airside economizer is probably the most well known type of economizer It uses cool outdoor air as a source of free cooling whenever possible For WSHP systems its use is typically limited to rooftop style WSHPs since they are equipped with an outdoorair damper Figure 108 Figure 108 Airside economizer in a rooftop WSHP When itis cold outside and the zone requires heating the outdoorair damper is closed to aminimum position to bring in the minimum quantity of outdoor air required for ventilation Figure 109 SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 163 E TRANE System Controls 164 Figure 109 Typical airside economizer control for a constant volume WSHP modulated integrated mechanical heating economizer economizer cooling 100 E3 O OA damper position OA damper position mechanical cooling capacity Ayede Buljooo jedjueYydaw 0 cold OA temperature j ho
48. boiler off OJ 32 C heat pumps in cooling mode Water Source and Ground Source Heat Pump Systems 5 TRANE Overview of a Water Source Heat Pump System During cold weather when most or all of the heat pumps are operating in heating mode heat is extracted from the water loop and transferred to the air This causes the temperature of the water in the loop to decrease making it necessary to add heat to the water Figure 6 A heat adder such as a hot water boiler is used to add heat to the loop maintaining a leaving water temperature of approximately 60 F 16 C Figure 6 System operation during cold weather winter SSS cooling tower off water circulating pumps on 60 F boiler on 16 C heat pumps in heating mode During mild weather such as spring or fall the heat pumps serving the sunny perimeter and interior of the building may operate in cooling mode and reject heat to the water loop At the same time the heat pumps serving the shady perimeter of the building may operate in heating mode and extract heat from the water loop Heat rejected by units operating in cooling mode raises the loop temperature while heat extracted by units operating in heating mode lowers the loop temperature If the water temperature stays between about 60 F 16 C and 90 F 32 C for example neither the boiler nor the cooling t
49. changing over time While eliminating both the cooling tower and boiler likely results in the greatest overall energy savings for many applications it requires a larger and more expensive ground heat exchanger Adding a small cooling tower to the loop for a cooling dominated application or adding a small boiler for a heating dominated application can reduce the size of the ground heat exchanger making a GCHP system more economically feasible see Hybrid ground coupled heat pump systems p 149 Ground heat exchanger configurations The pipes that make up the ground heat exchanger are typically oriented in either a vertical horizontal or spiral pattern Any of these patterns can be designed to provide the same fluid temperatures under a given set of conditions The choice depends on available land soil conditions and excavation costs Vertical loops Vertical loops are the most common in commercial applications due to the limited land that is generally available to bury the heat exchanger Figure 89 Vertical boreholes with a diameter of 4 to 6 in 10 to 15 cm each are drilled to depths of 200 to 500 ft 60 to 150 m typically about 10 to 20 ft 3 to 6 m apart A closed piping loop is inserted into each borehole after which the hole is grouted and backfilled The HVAC design engineer should be familiar with federal state and local codes for drilling of water wells or boreholes for ground coupled systems since the
50. cold water is produced by the heat pumps that are serving the perimeter zones which would be operating in the heating mode regardless S TRANE System Controls For example if the zone requires cooling and the entering water temperature is below the economizer enable setpoint the three way valve diverts the cool loop water through the waterside economizer coil If the economizer cannot sufficiently cool the zone by itself then the unit level controller will cycle on the compressor to provide more cooling capacity In this manner both the waterside economizer and compressor are used simultaneously In a boiler tower WSHP system the boiler is controlled to prevent the water loop temperature from dropping below a pre defined lower setpoint 60 F 16 C for example However to allow a waterside economizer to provide a significant benefit this temperature setpoint may need to be set lower than normal colder than 60 F 16 C for example and it must be lower than the economizer enable setpoint Allowing a colder loop temperature will increase the benefit of waterside economizing in those zones that require cooling but it will reduce the efficiency of any WSHP compressors that are operating in the heating mode Therefore these two setpoints need to be carefully selected to minimize overall system energy use Alternatively the system level controller could be programmed to automatically change the lower loop temperature setpoint
51. conventional boiler tower WSHP system or with a ground coupled system 156 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE System Design Variations Figure 103 Hybrid WSHP system with water cooled chiller and air handling units cooling tower O ii Ga H a boiler Oj water cooled chiller air handling unit Water Source and Ground Source Heat Pump Systems 157 TRANE System Controls This chapter discusses the control of a water source heat pump system Unit level control refers to the functions required to control and protect each individual piece of equipment System level control refers to the intelligent coordination of the individual pieces of equipment so they operate together as a reliable efficient system Historically some WSHP systems have been installed with very simplistic controls some people might argue they were too simplistic Like other systems however WSHP system controls have advanced to make use of communicating digital controls e Non communicating thermostat control The lowest level of control typically uses a non communicating mechanical thermostat for each WSHP and a standalone control panel in the mechanical room Figure 104 Installed cost is low because no communication wire needs to be pulled to connect the individual heat pumps with the centralized loop control panel However functio
52. dehumidify the outdoor air and then reheat it to approximately zone temperature neutral Delivering the dehumidified outdoor air at a neutral dry bulb temperature can simplify control because it has no impact on the zone sensible cooling or heating loads However when a chilled water or DX cooling coil is used for dehumidification a by product of that process is that the dry bulb temperature of the air leaving the coil is colder than the zone Figure 45 If the dehumidified outdoor air DH is reheated to neutral CA most of the sensible cooling performed by the dedicated OA unit is wasted Figure 45 Sensible cooling is a by product of cold coil dehumidification Q If the dedicated OA system delivers air directly to each zone see Figure 40 p 59 or to the supply side of each WSHP see Figure 43 p 61 the dehumidified outdoor air DH can be delivered cold rather than reheated to neutral The low dry bulb temperature of the conditioned OA offsets part of the sensible cooling load in the zone reducing the energy used by the local SYS APM010 EN S TRANE Primary System Components heat pump At design conditions this means that the heat pump can be sized for less airflow and less cooling capacity than in a neutral air system As an example consider a four classroom wing of an elementary school served by a dedicated OA system Table 11 The dedicated OA unit dehumidifies the outdo
53. each water circulating pump to protect the pumps from debris flowing inside the water distribution loop supply air Air that is delivered to the zone by mechanical means for ventilation heating cooling humidification or dehumidification Water Source and Ground Source Heat Pump Systems SYS APM 010 EN SYS APMO10 EN supply air diffuser See diffuser supply duct system A system that is typically constructed of ductwork fittings and diffusers This system transports the supply air from the air conditioning equipment to the conditioned space surface water system A type of ground source heat pump system that uses a series of closed loops of piping submerged in a pond or lake surge A condition of unstable fan operation where the air alternately flows backward and forward through the fan wheel generating noise and vibration TAB Test adjust and balance thermal conductivity Time rate of heat flow through a homogeneous material expressed in units of Btu hrfte F W mK This property characterizes the rate at which heat transfers from the ground heat exchanger to the surrounding soil thermal diffusivity Calculated by dividing the measured thermal conductivity of the ground and by the estimated heat capacity of the ground often expressed in units of ft day m2 day thermal displacement ventilation A method of air distribution in which cool air is supplied at low velocity directly to the lower part of the occupied
54. for heating making it attractive for a building where each tenant is billed for the electricity used to cool and heat their space only With an electric resistance heater installed the zone can still be supplied with heat if the compressor fails or if the water pump fails and cannot circulate water through the heat pump Potential improvement in perceived comfort due to warmer supply air temperatures that are possible from electric heat during heating mode May increase the size of electrical wiring to the individual heat pumps which impacts installed cost Unable to use a hot water storage tank to limit electrical demand during morning warm up or to shift energy use to an off peak period this drawback may be minimal in locations where the electric utility does not use a time of day rate structure or does not include a demand charge Not able to use a fossil fuel such as natural gas propane or fuel oil as the heat source which depending on local utility rates may result in higher utility bills Uses more energy since the COP of an electric resistance heater is 1 0 while the heating COP of a WSHP might be between 3 0 and 6 0 depending on model and operating conditions 58 For a boilerless WSHP system in a cold climate where most of the heat pumps may need to operate in the heating mode simultaneously very little heat will be added to the loop During such a situation heat loss through the tower and any exposed or underg
55. from 72 percent with the constant speed fan SEU to 62 percent with the multiple speed fan and variable speed compressor SYS APM010 EN Water Source and Ground Source Heat Pump Systems 103 S TRANE System Design Issues and Challenges Figure 74 Dehumidification performance of a multiple speed supply fan at mild rainy condition 70 F DB mild rainy OA 69 F WB part load o MA POIN DB Dre 0 SA RA 60 F DB 74 F DB 62 RH epuoj4 a iAUosyoer Hot gas reheat in the WSHP unit Another option for controlling humidity is to reheat temper the dehumidified supply air with heat recovered from the refrigeration circuit in the WSHP This is sometimes referred to as hot gas reheat In this configuration the air is first cooled and dehumidified by the refrigerant to air heat exchanger then reheated by the reheat coil to control not only the dry bulb temperature but also the humidity level in the zone Figure 75 Figure 75 Hot gas reheat for humidity control water loop refrigerant to air heat exchanger expansion device reheat coil reversing valve refrigerant to water heat exchanger reheat valve 104 Water Source and Ground Source Heat Pump Systems SYS APM 010 EN SYS APMO010 EN S TRANE System Design Issues and Challenges Doesn t ASHRAE Standard 90 1 prohibit the use of reheat for humidity control While Section 6 5 2 3 of ASHRAE 90 1 limits the use of reheat for the purp
56. ground heat exchanger to estimate the average loop temperature for each month To demonstrate the impact of the building operation on the size of the ground heat exchanger consider if this same building is operated for 24 hours a day seven days a week The design block cooling load remains unchanged since it occurs during the daytime but the total monthly heating and cooling loads will be significantly higher With this extended operation there are more months where both cooling and heating are needed and there is a much larger demand for cooling in each month Using the same 8 by 8 rectangular borefield each borehole must now be 600 ft 180 m deep The primary cause of this drastic increase in length is the increased heat rejected to the ground due to cooling operation To reduce the required depth a larger borefield with more boreholes and or greater spacing between boreholes could be used Or a small fluid cooler Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN For more information on the design and layout of ground heat exchangers refer to Chapter 34 Geothermal Energy in the 2011 ASHRAE Handbook HVAC Applications www ashrae org the ASHRAE manual Ground Source Heat Pumps Design of Geothermal Systems for Commercial and Institutional Buildings and the International Ground Source Heat Pump Association IGSHPA manual Closed Loop Ground Source Heat Pump Systems Installation Gui
57. heat pump with hot gas reheat In this example the WSHP with hot gas reheat could be controlled to maintain a lower zone humidity level but that would result in even more compressor energy use While the heat used for reheat is recovered energy it is not free it comes at the price of increased compressor energy If a project requires lower space humidity levels 50 or 55 percent RH for example a more efficient approach would be to use a dedicated outdoor air system to dehumidify the outdoor air centrally This would result in lower indoor humidity levels and is more efficient that equipping the heat pumps with hot gas reheat Condition the outdoor air with a separate dedicated unit The most common way to improve the dehumidification performance of a WSHP system is to use a dedicated outdoorair system to separately dehumidify all of the outdoor air to a dew point that is drier than the zone This conditioned outdoor air CA is then either l Ducted directly to each zone 2 Ducted to thesupply side of each WSHP where it mixes with supply air from the heat pump before being delivered to the zone 3 Ducted to the intake of each WSHP where it mixes with recirculated air from the zone 4 Ducted to the ceiling plenum near the intake of each WSHP where it mixes with recirculated air from the zone before entering the WSHP For more discussion see Dedicated OA system configurations p 59 In any of these configurations the
58. include Figure 92 e Supply and return headers Pipes used to convey the total system flow from the loop inside the building to the individual parallel U tubes Headers are typically constructed of larger diameter pipe to minimize pressure drop and are typically installed in a reverse return configuration to better equalize pressure drops and balance flows through the individual U tubes e U tubes Pipes that convey fluid from the supply header down into a borehole or trench and then returned back up the same borehole or trench to the return header The pipe includes a 180 degree fitting or U bend at the bottom of a borehole or at the end of a trench The heat exchanger typically consists of multiple U tubes connected to the supply and return headers The U tubes are typically installed in a parallel configuration so that only a portion of the total system flow rate travels through a single U tube minimizing overall pressure drop The piping used for the ground heat exchanger is typically high density polyethylene HDPE with thermally fused joints Pipe diameter for the U tubes ranges from 0 75 in 20 mm to 125 in 60 mm depending on the diameter of the borehole A borefield is typically laid out to ensure proper separation of the individual U tubes Common configurations include arranging the boreholes in a straight line L shaped pattern or rectangle Figure 93 Figure 93 Examples of vertical heat exchanger configura
59. limited Stage 3 Start the cooling tower fan This forces more air to flow across the tubes increasing the amount of heat rejected A two speed fan multiple fans or a fan equipped with a VFD provide additional stages of heat rejection capacity and avoid excessive cycling Varying airflow allows for closer temperature control reduces tower fan energy use and helps prevent freezing during cold weather Figure 113 Control of a closed circuit cooling tower discharge dampers closed circuit cooling tower roof spray pump tower isolation valve water circulating pumps Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE System Controls If a closed circuit cooling tower is expected to be exposed to ambient temperatures colder than 32 F 0 C consider operating the tower as a dry cooler when the ambient temperature drops below about 45 F 7 C In this mode the spray pump is shut off and the fan continues to operate Heat rejection occurs as the cold outdoor air passes over the dry tubes of the heat exchanger If a constant speed fan is used the reduced airside pressure drop of the dry heat exchanger will result in a higher airflow rate In this case contact the tower manufacturer to ensure that the fan motor will not overload due to the reduced pressure drop and higher airflow An alternative approach is to equip the cooling tower with a VFD and possibly even modu
60. of outdoor air being brought into the building is reduced for many hours during the year The energy recovery device provides less benefit because there is less outdoor air to precondition and with less air entering the building less air is exhausted Air exhausted by local exhaust fans and exfiltration due to building pressurization are relatively constant so when DCV reduces intake airflow less centralized exhaust air is available for energy recovery Provide a means to properly control the device at part load During mild weather the energy recovery device should be shutoff to avoid transferring unwanted heat from the exhaust air to the outdoor air For example when the enthalpy of the outdoor air is less than the enthalpy of the exhaust air a total energy wheel should be turned off to prevent increasing the cooling energy use In addition when itis cool outside and the dedicated OA system needs to add heat to the entering air many dedicated OA systems will require a means to modulate the capacity of the energy recovery to avoid overheating the air Unnecessarily operating the device at full capacity may require recooling and wastes energy The method used for capacity control depends on the device Coil loops either vary the speed of the circulation pump or use a three way mixing valve to bypass some of the fluid around the exhaust side coil Fixed plate heat exchangers often use a modulating damper to bypass some of the exhaustair
61. operate in the cooling mode a waterside economizer can be used to completely eliminate the need to operate the compressor s at such conditions see Economizer control p 162 This also avoids the need to install a water regulating valve Water flow rate The water flow rate through the refrigerant to water heat exchanger impacts the capacity and energy use of the heat pump compressor cooling tower and water circulating pumps Therefore it is important to assess the impact of water flow rate on overall system performance The water flow rate through a WSHP is typically between 2 2 and 3 4 gpm ton 0 039 to 0 061 L s kW with 3 0 gpm ton 0 054 L s kW being a good rule of thumb that often achieves a good balance between compressor efficiency and pump energy use Increasing the water flow rate improves the efficiency of the heat pump compressor but it increases pump energy use Decreasing the water flow rate reduces pump energy use but it decreases both the capacity and efficiency of the WSHP In climates that experience more hours of high outdoor wet bulb temperatures higher flow rates may be beneficial because SYS APMO10 EN S TRANE Primary System Components of the warmer water temperatures leaving the cooling tower In climates that experience fewer hours of high outdoor wet bulb temperatures lower flow rates may be beneficial because of the cooler water temperatures leaving the cooling tower Do not use less than
62. orient WSHP so air turns at duct elbow in same direction as fan rotation install on pad to minimize vibration transmission For an application where return air is ducted into the closet either directly to the inlet or just into the closet space install a door with sufficient transmission loss to reduce casing radiated sound entering the occupied space Itis also critical to use a gasketed tight fitting door to avoid the flanking paths associated with gaps under and around the door 2 Supply airbome Sound leaving the discharge of the WSHP travels down the supply ductwork through the supply air diffusers and into the occupied space Supply airborne sound can be reduced by adding an acoustical liner to the supply ductwork Acoustical analysis can be used to determine the required lining thickness and length of ductwork that needs to be lined Another convenient way to add absorptive duct liner is to use lined flex duct as the final section that connects to the diffuser Careful attention should be paid to the attachment of the flex to the diffuser avoid sharp turns and pinched ducts at and near the diffuser Sizing ductwork for low velocity and low static pressure loss will reduce the sound produced by the fan As a general rule maintain the velocity in main duct sections below 750 fpm 3 8 m s and below 600 fpm 3 1 m s in runout duct sections When an elbow is located near the discharge of the WSHP orient the elbow so that the
63. outdoor airflow Vpz whenever a zone is occupied As the number of people occupying a zone varies the quantity of outdoor air required to properly ventilate that zone also varies This energy saving control approach is discussed further in Demand controlled ventilation p 188 System Level Control System level control refers to the intelligent coordination of the individual pieces of equipment so they operate together as a reliable efficient system Typically each watersource heat pump is equipped with a dedicated unit level controller that responds to the cooling and heating demands of the zone A system level controller can be used to monitor system operation and to coordinate all these pieces for optimized system control Figure 116 Ata minimum a system level controller should be used to operate the water circulating pumps coordinate cooling tower and boiler operation to maintain the proper temperature in the water loop and provide centralized monitoring of system operation Figure 116 System level control of a WSHP system exhaust fan water source heat pumps system level controller With this configuration each unit level controller is capable of performing its functions even if communication with the system level controller is lost Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Controls Coordination during different operating modes One of the most imp
64. reduces installed cost and lowers airside pressure drop which results in less fan energy used 86 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components However open plenum returns should not be used when prohibited by local codes Controls The control of a water source heat pump system is often grouped into unit level and system level control functions Unit level control refers to the functions required to control and protect each individual piece of equipment System level control refers to the intelligent coordination of the individual pieces of equipment so they operate together as an efficient system A common analogy is to view the individual unit level controllers as members of an orchestra and the system level controller as the conductor In a typical system each WSHP is equipped with a unit level controller and the water circulating pumps cooling tower and boiler are each equipped with separate unit level controllers In some applications these unit level controllers operate with no system level coordination In other applications the unit level controllers are connected to a centralized system level controller Figure 62 With this configuration each unit level controller is capable of performing its functions even if communication with the system level controller is lost Note Common unit level and system level control functions for a WSHP system are discussed in de
65. sensor is installed far enough downstream of the boiler that the hot water leaving the boiler adequately mixes with any bypassed water To avoid large temperature swings as individual steps of boiler capacity energize or de energize be sure to provide an adequate number of stages For an electric boiler time delays between stages of heating capacity prevent all stages from energizing simultaneously thereby limiting in rush current Dedicated outdoorair system The most common approach to controlling the dedicated outdoorair system is to turn iton when the building is expected to be occupied The same time of day schedule that is used to start and stop the WSHP system is used to start and stop the dedicated OA system The fan in the dedicated OA equipment is activated to bring in the required amount of outdoor air for ventilation and cooling dehumidification or heating is modulated to maintain the discharge air at the desired conditions Water Source and Ground Source Heat Pump Systems 173 E TRANE System Controls 174 The simplest approach operates the dedicated OA system to deliver a constant quantity of outdoor air to each zone during the occupied mode regardless of the level of occupancy As mentioned in Dynamic reset of intake airflow p 98 however ASHRAE Standard 62 1 permits dynamic reset of intake outdoor airflow as operating conditions change as long as the system provides at least the required breathing zone
66. shows the zone level ventilation calculations for an example 12 room wing of a hotel While the required breathing zone outdoor airflow Vbz is only 25 cfm 0 012 m3 s for each guest room the zone air distribution effectiveness E2 of 0 5 increases the required zone outdoor airflow Voz to 50 cfm 0 024 m3ys For this example the required system outdoor air intake flow Vot is 624 cfm 0 29 m3 s Note Although Table 6 4 of ASHRAE 62 1 only requires a minimum exhaust rate of 25 cfm 0 012 m s for a private restroom assuming continuous exhaust fan operation for this example the restroom exhaust airflow would need to be increased to 50 cfm 0 024 m3 s to draw 50 cfm 0 024 m3 s of air into the zone from the corridor Table 16 100 OA system ventilation calculations for example hotel building with OA delivered to a central conidor Rp cfm p Pz qty Ra cfm ft2 Az ft2 Vbz cfm Ez Voz cfm Guest room 101 5 2 0 06 250 25 0 5 50 Guest room 102 5 2 0 06 250 25 0 5 50 Guest room 103 5 2 0 06 250 25 0 5 50 Guest room 104 5 2 0 06 250 25 0 5 50 Guest room 105 5 2 0 06 250 25 0 5 50 Guest room 106 5 2 0 06 250 25 0 5 50 Guest room 107 5 2 0 06 250 25 0 5 50 Guest room 108 5 2 0 06 250 25 0 5 50 Guest room 109 5 2 0 06 250 25 0 5 50 Guest room 110 5 2 0 06 250 25 0 5 50 Guest room 111 5 2 0 06 250 25 0 5 50 Guest room 112 5 2 0 06 250 25 0 5 50 Corridor 0 06 400 24 1 0 24 Syste
67. sum of the nameplate motor powers for all fans that operate at peak design cooling conditions must be no greater than the value listed in Table 21 For example if the design supply airflow for a rooftop style WSHP is 7600 cfm 3 6 m3 s or 3600 L s the total allowable nameplate motor power for the fan system is 8 4 hp 6 1 kW Allowable Nameplate Motor Power 7600 cfm x 0 0011 8 4 hp Allowable Nameplate Motor Power 3600 L s x 0 0017 6 1 kW This limit applies to the sum of all fans that operate at peak design cooling conditions for this particular system Option 2 is based on input power to the fan shaft brake horsepower To comply using Option 2 the sum of the fan input powers for all fans that operate at peak design conditions must be no greater than the value listed in Table 21 This fan power limitation contains an adjustment to account for special filters and other devices A gt PD x CFM device 4131 A PD xL Sdevice 650 000 where PD pressure drop adjustment for each applicable device Table 21 in H20 Pa CFM device L Sdevice design airflow through each applicable device Table 21 cfm L s 114 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE System Design Issues and Challenges Table 22 Fan power limitation pressure drop adjustments Pressure drop credit Adjustment PD Fully ducted return and or exhaust air systems 0 5 in
68. sump heater 48 supplemental heat 150 151 supply duct system 84 supply air diffusers 85 86 surface water heat pump system 152 153 System Analyzer 123 system controls 158 160 system intake airflow 94 system level control 174 194 T TAP 127 thermal conductivity 144 thermal diffusivity 144 thermal expansion valve 15 18 77 thermal zoning 88 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APM010 EN thermostat communicating thermostat control 159 non programmable 176 time of day schedule 98 158 167 173 175 176 180 187 189 191 194 time of day utility rate 54 58 total energy wheel 70 80 TRACE 700 123 145 two stage compressor 21 U undisturbed ground temperature 144 unit level control 160 174 unoccupied mode 177 U tube 141 vV valves balancing 37 40 isolation 18 manual ball type 40 shut off 41 water regulating 18 39 variable flow pumping 34 variable frequency drive VFD 34 168 variable speed compressor 14 21 103 161 vault 142 ventilation 91 98 demand controlled 119 system level requirement 93 vertical loops 138 vertical stack WSHP 28 w water distribution loop 32 120 water heater See boiler water loop temperature control 180 water circulating pump 32 167 water cooled chiller 156 water cooled DX unit 75 water regulating valve 18 39 waterside economizer 162 water source heat pump 12 30 control of 161 167 water source heat pump system basic operation 2
69. temperature sensor is typically located slightly downstream of the water circulating pumps Figure 120 Additionally a loop return water temperature sensor is often located downstream of the heat pumps but upstream of the cooling tower Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE System Controls Figure 120 Water loop temperature control closed circuit cooling tower roof spray pump EM tower isolation valve loop return water AWWWi temperature hot water 4 boiler boiler mixing valve water circulating pumps loop supply water temperature 82 WSHPs When the loop supply water temperature reaches the upper setpoint 90 F 32 C for example the system level controller activates the cooling tower to reject heat from the water loop see Cooling tower p 169 for discussion of the various methods of cooling tower control When the loop supply water temperature reaches the lower setpoint 60 F 16 C for example the system level controller activates the boiler to add heat to the water loop see Hot water boiler p 172 for discussion of the various methods of boiler control Between these two setpoints both the cooling tower and boiler remain off Contact the equipment manufacturer to ensure that the loop temperature remains within the acceptable operating limits of the specific equipment Bypas
70. that are routed in different directions or switching to rigid metal round duct 4 Retum airbome The inlet of a horizontal style WSHP can be either ducted or un ducted In an un ducted system the return air enters the ceiling plenum through the return air grille and travels through an open ceiling plenum to the inlet of the WSHP A fully ducted return system uses ductwork to connect the return air grille directly to the WSHP inlet In a partially ducted system a section of return ductwork is connected to the WSHP inlet but it does not connect to the return air grille Avoid placing the return air grille near the WSHP inlet Figure 85 Moving the grille at least 6 ft 18 m away from the inlet will reduce the return airborne sound that enters the space All ducted returns will benefit from acoustical lining Size all return duct components for low velocity Partially ducted returns will benefit if the open end of the duct has no obstruction such as a grille and includes at least four equivalent duct diameters of straight duct prior to the WSHP inlet An un ducted return may benefit by connecting an acoustically lined elbow to the return air grille with the opening facing away from the WSHP inlet WSHP vertical units Vertical water source heat pumps are typically installed in a closet adjacent to the occupied space with supply air ducted to diffusers Air returns from the space through a return air grille or louver in the closet door un
71. the perimeter zones These self contained air conditioners include all the components of the refrigeration circuit including a water cooled condenser that is connected to the same water distribution loop that serves the heat pumps Figure 102 Hybrid WSHP system with self contained VAV air conditioners ASS cooling tower boiler OJ By oo 7 to VAV terminals serving water cooled self interior contained VAV air zones conditioner Since the interior zones in this example have variable loads but will nearly always require cooling the VAV terminal units vary the airflow supplied to those interior zones At reduced cooling loads the VFD on the supply fan SYS APM010 EN Water Source and Ground Source Heat Pump Systems 155 S TRANE System Design Variations For more information on using a centralized chiller heater in a ground coupled system refer to the Trane application manual Central Geothermal Systems SYS APM009 EN results in part load fan energy savings Heat is rejected from the self contained units into the common water loop where it can be extracted by the heat pumps that are providing heat to the perimeter zones Water to water heat pump or water cooled chiller serving AHU Another example of a hybrid WSHP system shown in Figure 52 p 77 includes a water to water heat pump which is connected to the water distribution loop serving an air handling unit AHU that
72. the efficiency of the refrigeration cycle TXVs used in heat pumps may be bi directional meaning that the refrigerant flows in one direction during the cooling mode and in the opposite direction during the heating mode The alternative would be to design the refrigerant piping inside the heat pump to ensure that refrigerant flow through the valve is in the same direction in either mode The reversing valve sometimes called a four way valve reverses the direction of the refrigerant flow through the cycle as described in the next section This allows the WSHP to change operation of the refrigeration circuit to provide either cooling or heating Figure 13 Water Source and Ground Source Heat Pump Systems 15 Se TRANE Primary System Components WSHP operation during cooling mode Figure 14 Hot high pressure refrigerant vapor is pumped from the compressor to the refrigerant to water heat exchanger that in the cooling mode functions as the condenser Inside this heat exchanger heat is transferred from the hot refrigerant vapor to the lower temperature water warming the water and cooling the refrigerant causing it to condense into a liquid Figure 14 Operation of a WSHP in the cooling mode expansion device refrigerant to air heat exchanger compressor cooled air reversing valve refrigerant to water heat exchanger This liquid refrigerant then flows through an expansion device that reduces the press
73. the ground during the heating season In this case the temperature of the ground can decrease over time In either case future operation and efficiency of the heat pumps is compromised by this change in ground temperature In many areas of the country this imbalance requires the ground heat exchanger to be larger to prevent the ground temperature from changing over time The cost to install such a large heat exchanger often dissuades people from considering a GCHP system In a hybrid GCHP system however either a small cooling tower for a cooling dominated application or a small boiler for a heating dominated application is installed on the loop to supplement the heat rejection or heat addition capacity of the ground heat exchanger This approach reduces the required size and cost of the heat exchanger by avoiding the imbalance described previously While the overall energy use may not be as low as in a system with a larger heat exchanger this approach often results in a more acceptable return on investment In a hybrid system neither of the separate pieces needs to be sized for design capacity since they complement each another In a cooling dominated application a small cooling tower or possibly even a dry cooler is connected to the loop Figure 98 SYS APM010 EN Water Source and Ground Source Heat Pump Systems 149 S TRANE System Design Variations Figure 98 Hybrid GCHP system with supplemental heat rejection for
74. the manufacturer s minimum recommended flow rate as this may increase the risk of the compressor tripping off on a safety limit high pressure cutout during the cooling mode or low temperature cutout during the heating mode Fan Each water source heat pump contains a fan to draw return air from the zone and through the components of the heat pump before discharging it into the zone This fan must create a high enough pressure at its outlet A to overcome the pressure losses associated with pushing the air through the supply ductwork and supply air diffusers A to B or through the supply air grille in the case of a console type or vertical stack WSHP Figure 16 In addition the fan must create a low enough pressure at its inlet D to overcome the pressure losses associated with drawing the air through the return air grille and possibly the open ceiling plenum and or return ductwork B to C and then through the filter and refrigerant to air heat exchanger inside the WSHP C to D Figure 16 WSHP with supply ductwork zone return air grille WSHP supply ductwork diffusers zone ceiling plenum unit return ductwork A oug supply supply fan pressure increase static pressure relative to outdoors relief damper or louver Due to the pressure drop through the return air path the pressure in this path C might be lower than the ambient pressure A central relief fan can be used to raise the pressure of the ai
75. the week with pump 2 serving as standby then the following week pump 2 would be operated with pump 1 serving as standby Cooling tower When the loop supply water temperature reaches the upper setpoint 90 F 32 C for example the system level controller activates the cooling tower to reject heat from the water loop As mentioned previously most boiler tower WSHP systems use either a closed circuit cooling tower sometimes called a fluid cooler or an open cooling tower with an intermediate heat exchanger SYS APMO010 EN Water Source and Ground Source Heat Pump Systems 169 S TRANE System Controls 170 Closed circuit cooling tower A typical sequence for controlling a closed circuit cooling tower Figure 113 s Stage 1 Open the discharge dampers and isolation valve If the temperature of the outdoor air is cooler than the water inside the tubes this allows air to move through the tower via natural convection and a small amount of heat will be rejected from the water loop No tower fan or circulation pump energy is used but the amount of heat rejected is limited Stage 2 Start the spray pump This circulates water from the sump to wet the outer surfaces of the tubes The evaporative cooling effect increases the amount of heat transferred from the water inside the tubes to the air that is flowing across the tubes still via natural convection No tower fan energy is used but the amount of heat rejected is still
76. to 4 83 kW to offset the heating load in Zone 1 Heat of compression increases from 15 100 Btu hr 4 4 kW to 16 500 Btu hr 4 8 kW due to the compressor operating less efficiently e Amount of heat that must be extracted from the loop zone heating load heat of compression decreases from 45 900 Btu hr 13 4 kW to 44 500 Btu hr 13 0 kW Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Issues and Challenges In addition the heat pump serving Zone 2 is operating in the cooling mode using a waterside economizer coil The 5 000 Btu hr 1 5 kW cooling load is rejected to the loop which further reduces the amount of heat that must be added to the loop by the boiler Operating the loop at a colder water temperature does increase the energy used by those WSHP compressors operating in the heating mode but it decreases the energy used by the boiler In this example the overall building heating energy use is less when the system operates at 45 F 7 2 C with a waterside economizer than when it operates at 55 F 12 8 C Therefore a pre cooling waterside economizer coil may be used to meet the requirements stated in Section 6 5 1 of Standard 90 1 without violating Section 6 5 14 Demand controlled ventilation Section 6 4 3 9 of ASHRAE 90 1 requires some method of demand controlled ventilation for any zone larger than 500 ft 50 m2 that has a design occupancy of more than 40 people 100
77. to measure the dry bulb temperature of the outdoor air The controller compares this temperature to a predetermined high limit shutoff setting and disables the economizer whenever the outdoor dry bulb temperature is above this limit This method is simple reliable and relatively inexpensive However in non arid climates if the high limit shutoff setting is too high this control Water Source and Ground Source Heat Pump Systems SYS APM 010 EN For more information on the various methods of controlling airside economizers and their impact on system performance refer to the Trane Engineers Newsletter Live broadcast DVD titled HVAC Systems and Airside Economizers APP CMC026 EN and the Trane Engineers Newsletter Airside Economizers ADM APNO20 EN S TRANE System Controls strategy can bring in cool but humid outdoor air which may raise indoor humidity levels and increase compressor energy use e Fixed enthalpy control uses sensors to measure both the dry bulb temperature and humidity of the outdoor air The controller then calculates the enthalpy of the outdoor air and compares it to a predetermined high limit shutoff setting The economizer is disabled whenever the outdoorair enthalpy is above this limit This method requires an added outdoor humidity sensor so it costs more than fixed dry bulb control But in most climates fixed enthalpy control helps prevent bringing in cool humid outdoor air for economizing
78. tte 58 Dedicated Outdoor Air System 00 c cette eee 58 Dedicated OA system configurations 0 0 c eee eee 59 Neutral versus cold air delivery 00 000 cece eee eee 64 Exhaust air energy recovery 2 tees 70 Dedicated OA equipment typ S 0 ee 73 Air Distri DUON os asiia ness meen aces ee ee dead E E en manatee 83 Supply duct system 0 0 ete 84 Supply air diffusers 0 0 ec tees 85 Return air path aca amram aiaa aa aaa a AA I a aE o a EEE A AEA A E EA a 86 CONTOS arenen EA oa dod E EEE pallens pasha E ENE 87 System Design Issues and Challenges nananana anaana 88 Thermal Zoning 06 0 aranne 88 Perimeter versus interior ZONES assusa saaana 88 Optimizing the number of Zones 00000 eee 89 Locating the zone Sensor 0 0 cece ee 90 Using wireless technology 0 0c cece eee eee 90 Ventilation o addii kei ve se ia Wh aie Ri Eh Gs Rh AN w Ree ie eee 91 Zone level ventilation requirements 006 0 cee eee eee 91 System level ventilation requirement 0 00 ccc eee 93 Dynamic reset of intake airflow 0 00 0 cee eee 98 iv Water Source and Ground Source Heat Pump Systems SYS APMO10 EN S TRANE Table of Contents Humidity Control 0 0c a ka ma aa aa iani a aa a a Sa aiaa e a 98 Dehumidification 0 ccc eee nent a a 98 Dehumidification impact of compressor cycling 98 Full load versus p
79. turn of the elbow is in the same direction as the rotation of the fan Figure 86 Avoid close coupled fittings in the ductwork as these create high pressure loss and turbulence that generates sound When possible separate turns or fittings with straight duct sections that are at least four to five duct Water Source and Ground Source Heat Pump Systems SY S APM 010 EN SYS APMO010 EN S TRANE System Design Issues and Challenges diameters in length Check the static pressure drop against the static capability of the fan Finally remember that supply air diffusers generate sound that will be added to the sound coming from the WSHP Select diffusers at least 10 NC points below the desired NC level for the space Avoid turbulence at the diffuser by placing the balancing damper near the duct take off rather than near the diffuser 3 Supply breakout Sound traveling down the ductwork can also travel though the duct walls into the ceiling plenum and then through the ceiling into the occupied space This is generally only a problem on the main supply duct near the WSHP When breakout sound is a problem it can be reduced by routing the main duct over a non sound sensitive area a corridor for example splitting the main duct into multiple smaller ducts that are routed in different directions or switching to rigid metal round duct 4 Retum airbome As described previously the inlet of a vertical style WSHP can be either ducted or un du
80. which could impact the size of the cooling tower and or boiler and may impact the electrical demand charge from the utility Demand controlled ventilation As mentioned in Dynamic reset of intake airflow p 98 ASHRAE Standard 62 1 permits dynamic reset of intake outdoor airflow as operating conditions change as long as the system provides at least the required breathing zone outdoor airflow Voz whenever a zone is occupied As the number of people occupying a zone varies the quantity of outdoor air required to properly ventilate that zone also varies Demand controlled ventilation DCV is a strategy that attempts to dynamically reset the outdoor airflow delivered to a zone based on changing population within that zone By installing a VAV terminal unit for each zone and equipping the fan in the dedicated OA unit with a VFD to vary airflow a dedicated OA system can implement DCV Figure 126 A time of day TOD schedule occupancy OCC sensor or carbon dioxide CO2 sensor is used with the VAV terminal unit to reset the outdoor airflow delivered to a given zone The VFD in the dedicated OA unit varies airflow to ensure each zone receives the airflow desired Figure 126 Demand controlled ventilation with a dedicated OA system dedicated OA unit 188 Water Source and Ground Source Heat Pump Systems SYS APM010 EN For more information on CO2 based demand con
81. with a reversible refrigeration cycle Return air from the zone is drawn into the WSHP through the intake Figure 9 This air passes through a filter the refrigerant to air heat exchanger and fan before it is discharged directly into the zone or through supply ductwork and supply air diffusers Figure 9 Typical horizontal style water source heat pump water loop expansion device connections condensate drain line R ee Oo Bi em ll f _ compressor E 1 2 2 N A X A D g z A 7 ob a sah s 20 Gra SS 8 3S ze D v o co DY OY Ep pa O g a control box 0o00 filter a reversing valve Reversible direct expansion DX refrigeration circuit The direct expansion DX vaporcompression refrigeration circuit of a WSHP is comprised of one or more compressors a refrigerant to air heat exchanger a refrigerant to water heat exchanger an expansion device and a reversing valve Figure 9 and Figure 10 This refrigeration circuit is pre engineered and assembled in a factory so no field installed refrigerant piping is required Water Source and Ground Source Heat Pump Systems SYS APMO10 EN SYS APMO010 EN S TRANE Primary System Components Figure 10 Components of the DX refrigeration circuit in a WSHP exploded view refrigerant to air heat exchanger expansion device compressor refrigerant to water
82. 0 ft2 of floor area 40 people 100 m2 provided that the system serving that zone is equipped with an airside economizer or a modulating outdoor air damper or if the design system level outdoor airflow is greater than 3000 cfm 14 m3j s If outdoor air is brought directly into a WSHP as might be the case with a rooftop style unit the heat pump may already be equipped with an airside economizer or modulating outdoor air damper In this case it would be required to employ some method of demand controlled ventilation if it serves a zone that meets the minimum size and occupant density criteria mentioned above In most WSHP systems however the outdoor air required for ventilation is typically conditioned and delivered by a dedicated OA system The dedicated OA unit is probably not equipped with an airside economizer or modulating outdoor air damper Therefore the system level intake airflow Vot would need to be greater than 3000 cfm 1 4 m3 s for DCV to be required And then DCV would only need to be implemented in those zones that meet the minimum size and occupant density criteria mentioned above However like other requirements in the standard there are several exceptions provided The following exceptions are the most likely to apply to a typical WSHP system e Exception a If the dedicated OA unit includes an exhaust air energy recovery device which complies with Section 6 5 6 1 of the standard then it is exempt from t
83. 0 or 100 heat pumps Table 4 AHRI ISO 13256 2 Standard Rating Conditions for Water to Water Heat Pumps Water source heat pumps Ground source heat pumps Ground water heat pumps Cooling mode Load side liquid flow rate specified by the manufacturer Load side entering liquid temperature 53 6 F 12 C 53 6 F 12 C 53 6 F 12 C Source side liquid flow rate specified by the manufacturer Source side entering liquid temperature 86 F 30 C 77 F 25 C 59 F 15 C Heating mode Load side liquid flow rate specified by the manufacturer Load side entering liquid temperature 104 F 40 C 104 F 40 C 104 F 40 C Source side liquid flow rate specified by the manufacturer Source side entering liquid temperature 68 F 20 C 32 F 0 C 50 F 10 C SYS APMO010 EN Water Source and Ground Source Heat Pump Systems 31 Se TRANE Primary System Components 32 Water Source and Ground Source Heat Pump Systems Water Distribution Loop The individual water source heat pumps are connected to a common water distribution loop This loop consists of piping pumps valves an air separator and expansion tank and other accessories It also connects to the heat rejecter and heat adder In the example shown in Figure 24 a closed circuit cooling tower is used as the heat rejecter and
84. 01 4 HEPA and ULPA Filters Source 2008 ASHRAE Handbook HVAC Systems and Equipment Chapter 28 Table 3 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org SYS APM010 EN Water Source and Ground Source Heat Pump Systems 23 Se TRANE Primary System Components Key factors to consider when selecting particulate filter types for a specific application include e Target particle size and degree of cleanliness required collection efficiency The collection efficiency of a particulate filter is a function of how well it removes particles of various sizes Filters with higher efficiencies remove a higher percentage of particles and smaller particles than filters with lower efficiencies Since particulate contaminants vary in size it is important to define the contaminants of concern for a given facility when selecting the type of filter to be used see Table 2 e Allowable airside pressure drop A direct correlation usually exists between collection efficiency and airside pressure drop Generally a filter with a higher efficiency will cause a higher pressure drop in the passing air stream increasing fan energy use The number of pleats in a media filter determines the surface area of the media In general the more surface area the lower the airside pressure drop Pressure drop is also related to air velocity higher air velocity through a media filter results in a highe
85. 0c cece cece eee eens 135 Ground coupled heat pump systems 00 cee eee eee 136 Surface water heat pump systems 0c cece eee eee 152 Ground water heat pump systems 00 0 eee eee eee 153 Hybrid WSHP System Configurations 0 00 cece cece ees 155 Water cooled self contained VAV systems serving interior zones 155 Water to water heat pump or water cooled chiller serving AHU 156 System COntrols 240 dc dwkdun sabia ddcin dhe kodimd howe daa ome emae mde 158 Unit Level Control isa ce ie wu poker e PRRs eee Moe kudin aiya epia eae 160 Water source heat PUMP 2 161 Zone temperature Control 2 ee eee eee 161 Economizer control 000 eee 162 Hot gas reheat for humidity control 0005 165 Evaporator freeze protection 00 c cece eee ees 166 SAMCUES vtec anias Sees hae EA E Rat arn Sane aoe raed are eee 167 Water circulating puMp S anaana aea 167 Cooling tower 0 cette nen nent e nena 169 Closed circuit cooling tower 2 2 2 00 cee eee ee 170 Open cooling tower 0 00 171 SYS APMO10 EN Water Source and Ground Source Heat Pump Systems v eS TRANE Table of Contents Hot water boiler 1 0 ccc eee ene e tent en eens 172 Dedicated outdoor air system 00002 eee 173 System Level Control 0 ccc tne e teen neaes 174 Coordination during different operating modes 175 Occupied mode
86. 15 percent of design capacity Stage 2 Start the cooling tower fan This draws more air through the tower fill increasing the amount of heat rejected A two speed fan multiple fans or a fan equipped with a VFD provide additional stages of heat rejection capacity and avoid excessive cycling Varying airflow allows for closer temperature control and results in reduced tower fan energy use Water Source and Ground Source Heat Pump Systems 171 E TRANE System Controls Figure 114 Control of an open cooling tower with intermediate heat exchanger open cooling tower roof A tower circulating pump Q intermediate heat exchanger water circulating pumps Hot water boiler When the loop supply water temperature reaches the lower setpoint 60 F 16 C for example the system level controller activates the boiler to add heat to the water loop The hot water boiler is typically equipped with a dedicated unit level controller that varies the heating capacity of the boiler The controller also monitors boiler operation and protects it from damage by preventing it from operating outside acceptable limits Specific details about the boiler controller should be obtained from the manufacturer In many WSHP systems the hot water boiler is decoupled from the main water loop Figure 115 using a three way mixing valve to add heat to the water loop by blending in hot water from the boiler When activated the boiler controll
87. 169 freeze protection 46 49 171 evaporator 166 167 frost prevention 71 72 G GLHEPRO 145 glycol 47 ground heat exchanger bypassing 181 182 configurations 138 140 design of 140 148 sizing 145 ground coupled heat pump system 49 124 136 151 ground water heat pump system 153 154 grout 147 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APM010 EN H harmonic currents 20 HDPE 141 header pipes 142 heat addition 49 58 heat exchanger 15 19 27 29 49 air to air 69 73 122 intermediate 42 44 49 heat of vaporization 50 heat pipe 71 72 heat recovery 6 8 9 111 heat rejection 42 49 150 171 device 151 heat tape 48 HEPA filter 23 high limit shutoff setting 164 high temperature storage 54 horizontal loops 139 horizontal WSHP 28 hose kit 41 hot gas reheat 104 165 hot water boiler 49 57 control of 172 173 hot water storage 53 57 humidification 72 110 111 humidifier 110 humidity control 63 98 111 hybrid system 149 configurations 155 156 hydronic accessories 41 I IAQ See indoor air quality indirect evaporative cooling 83 indoor air quality 91 98 infiltration 185 inhibitor concentrations 48 insulation 38 48 integrated economizer mode 164 interior zones 89 intermediate heat exchanger 42 44 49 isolation valve 18 39 L LEED 26 loop temperature optimization 193 low temperature storage 53 54 M manual ball valves 40 MERV 22 26 115 mixing valve 72 172 1
88. 2 will operate with Pump 1 acting as the standby pump In a WSHP system that employs distributed pumping each heat pump contains a small single or dual pump module sized to meet the flow requirement of just that heat pump Figure 25 When the heat pump compressor turns off the pump serving that heat pump also turns off Figure 25 Distributed pumping system non ducted return air Distributed pumping is most commonly used in single pipe systems see Figure 27 p 37 and in ground coupled systems where each heat pump is connected to a dedicated ground heat exchanger Figure 95 p 143 SYS APM010 EN Water Source and Ground Source Heat Pump Systems 33 Se TRANE Primary System Components For many WSHP systems variable flow pumping is a prescriptive requirement of ASHRAE Standard 90 1 see WSHP distribution loop design and control pe L200 Advantages of centralized pumping include e Fewer pumps to install fewer connections reduce risk of leaks e Centralized pump maintenance and fewer strainers to clean e Pumps can typically be selected to better match the application which can result in higher pump efficiency Advantages of distributed pumping include e Eliminates the need to install a motorized isolation valve at each heat pump although a check valve may be required instead e Often eliminates the need for pump capacity control to achieve variable flow since each small pump turns off when the heat pu
89. 35 5 C 97 6 F 36 4 C 42 4 F 5 8 C 40 gpm 2 5 L s 60 gpm 90 0 F 3 8 L s 32 2 C 52 0 F 11 1 C PS source side heat load side heat exchanger exchanger If desired the warm water leaving the source side heat exchanger at 97 6 F 36 4 C in this example can be diverted through a reheat coil in the AHU to reheat the dehumidified air After leaving the reheat coil the water is returned to the main loop When it is cold outside the reversing valve changes the operation of the refrigeration circuit of the water to water heat pump to the heating mode Hot water leaving the load side heat exchanger is pumped through the coil in the AHU to heat the entering outdoor air Figure 54 and Table 12 The heat pump extracts heat from the loop water thereby cooling the water flowing through the source side heat exchanger Figure 54 Operation of water to water heat pump in heating mode L 2000 cfm 0 94 m3 s 20 F DB 7 C DB 93 8 F 40 gpm 60 gpm 60 F 3 8 L s 15 6 C 80 F 26 7 C PSs source side heat load side heat exchanger exchanger Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Table 12 Water to water heat pump operating modes Heat pump Source side Load side pump Reheat valve operation pump Ps PL Vr Operating mode modulate to coolin co
90. 7 benefits of 7 10 challenges of 11 configurations 28 30 design issues and challenges 88 134 overview 1 11 primary system components 12 87 system controls 158 160 system design variations 135 156 water to water heat pump 28 156 winterized cooling tower 48 WSHP See water source heat pump system Z zone air distribution effectiveness 92 zone outdoor airflow 65 91 93 96 98 zone sensors 159 Water Source and Ground Source Heat Pump Systems 215 S TRANE Trane optimizes the performance of homes and buildings around the world A business of Ingersoll Rand the leader in creating and sustaining safe comfortable and energy efficient environments Trane offers a broad portfolio of advanced controls and HVAC systems comprehensive building services and parts For more information visit www Trane com Trane has a policy of continuous product and product data improvement and reserves the right to change design and specifications without notice 2013 Trane All rights reserved We are committed to using environmentally SYS APM010 EN 1 Nov 2013 conscious print practices that reduce waste de Supersedes SYS APM010 EN Nov 2011 Ingersoll Rand
91. 81 morning cool down 178 179 187 precool loop for 183 184 morning warm up 178 179 187 preheat for 183 multiple speed fan 22 103 N nameplate motor power 114 neutral versus cold air delivery 64 night setback 51 176 Non communicating thermostat 158 non condensing boiler 50 173 non programmable thermostat 176 Water Source and Ground Source Heat Pump Systems 213 214 Oo occupancy sensor 176 189 occupied mode 175 occupied standby mode 176 open cooling tower 43 44 49 120 control 171 optimal start 124 160 187 188 P perimeter zones 88 pipe insulation 38 pipe sizing 38 plate and frame heat exchanger 43 polyethylene pipes 135 136 141 propylene glycol 48 pumping centralized vs distributed 32 constant vs variable flow 34 purge 141 PVC pipe 51 R refrigerant to air heat exchanger 15 101 104 113 166 refrigerant to water heat exchanger 15 28 32 37 39 43 77 154 162 167 refrigeration circuit 155 components of 1 direct expansion 12 return air grilles 93 return air path 86 reverse return piping arrangement 36 138 141 reversing valve 15 rooftop WSHP 28 30 33 114 163 S scaling 43 136 154 scheduling 179 seasonal operation 5 7 sensible energy recovery devices 71 series desiccant wheel 80 setback temperatures 4 shut off valves 41 single pipe system 37 spiral loops 140 spray pump 170 standby pump 33 169 storage tank 51 53 58 storage See hot water storage strainer 40 41
92. A sensor is used to monitor the concentration of CO2 in the zone which is being continuously produced by the occupants The difference between the CO2 concentration in the zone and the outdoor CO2 concentration can be used as an indicator of the per person ventilation rate cfm person m3 s person SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 189 S TRANE System Controls 190 Note In most locations the concentration of CO2 outdoors remains relatively constant Because of this and in lieu of installing an outdoor CO2 sensor most designers use either a one time reading of the outdoor CO2 concentration at the building site or a conservative value from historical readings This simplifies control lowers the installed cost and often increases accuracy because it avoids the potential inaccuracy of an outdoor sensor The measured concentration of CO2 in the zone is then communicated to the unit level controller on a VAV terminal unit and used to reset the outdoor airflow currently delivered to that zone Figure 127 If the CO2 concentration in the zone is less than or equal to the minimum CO2 limit the damper modulates to deliver aless than design base outdoor airflow On the other hand if the CO2 concentration is greater than or equal to the maximum COz limit the damper modulates to deliver the design outdoor airflow If the CO2 concentration is between the minimum and maximum CO limits the outdoor airflow is adj
93. DPI at cooling design airflow Air Diffusion Performance Index ADPI is a measure of diffuser performance when delivering cool air to the zone Water Source and Ground Source Heat Pump Systems 85 eS TRANE Primary System Components e When ceiling mounted diffusers will deliver warm air to the zone try to limit the difference between the supply air temperature and the zone temperature to 15 F 8 C Limiting the supply air temperature during heating avoids excessive temperature stratification when supplying warm air from overhead This may also increase the zone air distribution effectiveness used to determine outdoor airflow required for ventilation see Impact of zone air distribution effectiveness p 92 e In perimeter zones with high heat loss through the building envelope position diffusers to blanket the perimeter wall or window area This helps prevent downdraft problems that can occur when large volumes of heated air are distributed through ceiling mounted diffusers Retum air path When a WSHP is installed outside of the occupied zone return air typically leaves the zone through a ceiling or wall mounted return air grille and travels through the open ceiling plenum back to the intake of the WSHP This minimizes installed cost and lowers the pressure loss through the return air path Alternatively some applications use sheet metal ductwork for all or part of the return air path This increases installe
94. ERV rating of at least 6 be installed upstream of the coil In some applications high efficiency filtration of the outdoor air may be desired or required see Table 2 p 23 For example if the building is located in an area of the country that exceeds the U S EPA limit for airborne particles with a diameter of 10 microns or less PM 10 ASHRAE 62 1 Section 6 2 1 requires a M ERV 6 filter be used to clean the outdoor air before it is introduced to any occupied space If the building is located in an area that exceeds the EPA limit for airborne particles with a diameter of 2 5 microns or less PM2 5 the standard requires a MERV 11 filter be used to clean the outdoor air Some high efficiency filtration systems incorporate a lower efficiency pre filter upstream to capture larger particles and thus extend the useful life of the higher efficiency filter downstream The benefit of this longer life however must be carefully weighed against the additional cost and pressure drop of the upstream pre filters as well as the labor required to periodically replace them 26 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Condensate management F Preventing moisture problems in buildings is a shared responsibility among Or more information on water f i r 4 EEEREN in bullae E all parties involved in the design construction maintenance and use of the proper condensate trap design
95. H20 125 Pa Airflow control devices in the return and or exhaust air path Exhaust filters scrubbers or other exhaust air treatment 0 5 in H20 125 Pa Pressure drop through device at fan system design condition MERV 9 through 12 particulate filtration 0 5 in H20 125 Pa MERV 13 through 15 particulate filtration 0 9 in H20 225 Pa MERV 16 and higher particulate filtration or electronically enhanced filters 2 x clean filter pressure drop at fan system design condition Carbon and other gas phase air cleaners Biosafety cabinet Clean filter pressure drop at fan system design condition Pressure drop through device at fan system design condition Exhaust air energy recovery device e g wheel heat pipe fixed plate heat exchanger other than coil loop 2 2 x Effectiveness 0 5 in H20 550 x Effectiveness 125 Pa for each air stream Coil loop Evaporative humidifier cooler in series with another cooling coil 0 6 in H20 150 Pa for each air stream Pressure drop through device at fan system design condition Sound attenuation section 0 15 in H20 38 Pa Exhaust system serving fume hoods 0 35 in H20 85 Pa Laboratory and vivarium exhaust systems in high rise buildings 0 25 in H20 60 Pa for each 100 ft 30 m of vertical duct exceeding 75 ft 25 m Excerpt from Table 6 5 3 1 1B of ASHRAE Standard 90 1 2010 American Society of He
96. HP 28 106 128 constant flow pumping 34 controls 87 system 158 160 system level 174 194 unit level 160 174 cool down mode 178 179 183 184 187 cooling tower 42 49 closed circuit 42 43 control 121 169 open 43 44 COP 8 corridor 95 Water Source and Ground Source Heat Pump Systems TRANE 211 212 D deadband 4 dedicated outdoor air system 58 83 93 calculating system intake airflow 95 control of 173 dehumidification 98 demand controlled ventilation 119 188 desiccant dehumidification wheel 80 differential pressure sensor 168 185 direct evaporative cooling 82 direct expansion refrigeration circuit 12 direct return piping arrangement 36 dirt holding capacity 24 distributed pumping 32 diversity 35 drain pan 27 99 100 167 dry cooler 47 149 171 dynamic reset of intake airflow 98 E economizer 116 control 162 165 electric boiler 54 55 173 electric heat 8 57 58 76 82 122 161 electronically commutated motor ECM 20 Energy Cost Budget ECB 112 energy efficiency 111 124 enthalpy wheel 71 Environmental Protection Agency 26 122 evaporative cooling 82 83 170 evaporator freeze protection 166 167 exhaust air energy recovery 70 73 110 121 122 expansion device 15 expansion tank 42 F fan 19 161 170 171 175 177 179 185 fan power limit 114 filters 22 26 114 HEPA cartridge 23 flexible duct 85 flow control 40 41 flow control device 36 39 41 automatic 41 manual 40 fluid cooler 42 146
97. HP contains all the components of a refrigeration circuit including one or more compressors a refrigerant to air heat exchanger a refrigerant to water heat exchanger and an expansion device Figure 1 In addition a reversing valve allows the WSHP to reverse the direction of refrigerant flow and change the operation of the refrigeration circuit to provide either cooling or heating Figure L Components of a WSHP water loop expansion device connections condensate drain line drain ae pan Ee wo 4 i compressor i I S N 4 Po 2i EA JN ga a BAd R TE p Ee GG ve 0 E Bo v o Xx De v o Eo Dp oY Eo Lc Oo 2 control box ooo ae filter a reversing valve Depending on the style of equipment used a WSHP may be installed along the wall within the occupied space in the ceiling plenum above the space ina closet or mechanical room near the space or on the roof of the building Return air from the zone is drawn into the WSHP through the intake Figure 1 This air passes through a filter refrigerant to air heat exchanger and fan before itis discharged either directly into the zone or through supply ductwork and supply air diffusers All the heat pumps are connected to a common water loop Figure 2 Also connected to this loop are a heat rejecter such as a cooling tower fluid cooler or ground heat exchanger a heat adder
98. RAE 2008 ASHRAE Handbook HVAC Systems and Equipment Atlanta GA ASHRAE 1995 Commercial Institutional Ground Source Heat Pump Engineering Manual Atlanta GA ASHRAE 1997 Ground Source Heat Pumps Design of Geothermal Systems for Commercial and Institutional Buildings Atlanta GA ASHRAE 2002 Designer s Guide to Ceiling Based Air Diffusion Atlanta GA ASHRAE 1992 Gravimetric and Dust Spot Procedures for Testing Air Cleaning Devices Used in General Ventilation for Removing Particulate Matter ASHRAE Standard 52 1 1992 Atlanta GA ASHRAE 200L Humidity Control Design Guide for Commercial and Institutional Buildings Atlanta GA ASHRAE 2007 Method of Testing General Ventilation AirCleaning Devices for Removal Efficiency by Particle Size ASHRAE Standard 52 2 2007 Atlanta GA ASHRAE 2011 Standard 62 1 2010 User s Manual Atlanta GA ASHRAE 2010 Ventilation for Acceptable Indoor Air Quality ASHRAE Standard 62 1 2010 Atlanta GA ASHRAE Water Source and Ground Source Heat Pump Systems 207 208 ASHRAE and Illuminating Engineering Society of North America IESNA 2010 Energy Standard for Buildings Except Low Rise Residential Buildings BSR ASHRAE IESNA Standard 90 1 2010 Atlanta GA ASHRAE 2011 Standard 90 1 2010 User s Manual Atlanta GA ASHRAE Cleaver Brooks 2009 The Boiler Book http www boilerspec com Dow Chemical Company 2008 HVAC Application Guide Heat T
99. To maximize the energy related benefits of a boiler tower WSHP system the loop water temperature is typically allowed to float across a wide range between approximately 60 F 16 C and 90 F 32 C for example Water loop temperature control p 180 When communicating system level controls are used there is an opportunity to optimize the loop water temperature in an effort to minimize overall system energy use In the cooling mode the compressor in the WSHP uses less energy if the entering water temperature is cooler However making cooler water may require the cooling tower fans to use more energy and the cooler water decreases the efficiency of any compressors operating in the heating mode A system level controller can reset the loop temperature setpoint to minimize the combined energy consumed by the heat pumps and cooling tower under the current operating conditions Figure 128 Figure 128 Impact of loop temperature optimization 100 90 x 2 2 v E oO o 70 oO S 60 heat pumps cooling 50 tower 90 F optimal 32 C setpoint Water Source and Ground Source Heat Pump Systems 193 E TRANE System Controls 194 Coordination with other building systems System level control provides the opportunity to coordinate the operation of the HVAC system with other building systems such as lighting security and fire protection Following are some examples e A time of day schedule that is used to t
100. a cooling dominated application ground heat exchanger cooling tower or fluid cooler In this case the ground heat exchanger is sized based on the total heat to be extracted from the ground during the heating season Then the cooling tower is sized to reject the excess heat during the cooling season If the fluid temperature returning from the ground heat exchanger rises above a preset upper limit 90 F 32 C for example the cooling tower is activated to reject the excess heat 150 Water Source and Ground Source Heat Pump Systems SYS APM 010 EN S TRANE System Design Variations In a heating dominated application a small boiler is connected to the loop Figure 99 Figure 99 Hybrid GCHP system with supplemental heat addition for a heating dominated application ground heat exchanger boiler WSHPs DN N bypass valve i In this case the ground heat exchanger is sized based on the total heat to be This hybrid concept can also be used with jected to th d duri th li Th the boiler is sized Edaina svetaine I eae bulding galin rejected to the ground during the cooling season Then the boiler is size to loads have increased over time it may provide the supplemental heat during the heating season If the fluid cause an imbalance between heat temperature returning from the ground
101. a hot water boiler is used as the heat adder Figure 24 Components of water distribution loop cooling tower air separator and expansion tank O water circulating horizontal WSHPs Water circulating pumps Because a WSHP can only extract or reject heat while water flows through the refrigerant to water heat exchanger the water circulating pumps play a critical role in the operation of the system Centralized versus distributed pumping In a WSHP system that employs centralized pumping the water circulating pumps are typically installed downstream of the cooling tower and boiler and upstream of the heat pumps Figure 24 This helps to ensure positive water pressure throughout the system SYS APM010 EN S TRANE Primary System Components When centralized pumping is used the most common configuration is to use two pumps manifolded together see Figure 24 with each pump sized to meet the flow requirements of the entire system Only one of the pumps operates at any given time with the second available as a standby pump in case the operating pump was to fail In some systems operation of these two pumps is switched periodically to equalize the runtimes and starts sometimes called lead lag For example Pump 1 will be operated for the entire week with Pump 2 acting as the standby pump and during the following week Pump
102. a portion of the water from the pipe passes through the refrigerant to water heat exchanger to either extract heat from the refrigerant or reject heat to the refrigerant and then returns into the same pipe This piping configuration typically uses distributed pumping in that each heat pump contains a small pump that is sized to meet the flow and pressure drop requirements of only that heat pump Figure 27 In some cases a centralized pump may be used to circulate water through the main piping loop and through the heat rejection and heat addition equipment Figure 27 Single pipe system ground heat exchanger pumps g WSHPs ol eo e L 7 L X Y The primary advantage of this approach is reduced installed cost due to less piping However when many heat pumps are connected to the loop the heat pumps at the end of the pipe can receive water that is significantly warmer or colder than the heat pumps at the beginning of the pipe This impacts the efficiency of the heat pumps In addition flow rates and possibly pipe sizes must be larger because the fluid ATs near the end of the pipe will be smaller xa SYS APM010 EN Water Source and Ground Source Heat Pump Systems 37 eS TRANE Primary System Components For more information on sizing water piping refer to Chapter 22 Pipe Sizing in the 2009 ASHRAE Handbook Fundamentals www ashrae org Pipe siz
103. a variable flow system varies the speed of the pumps to maintain pressure in the piping at the desired setpoint Water distribution loop e Turns on cooling tower if needed to maintain the loop water temperature below the upper setpoint Turns on boiler if needed to maintain the loop water temperature above the lower setpoint 1 In some buildings outdoor air may be brought into the building during the morning warm up or cool down mode to dilute contaminants that have accumulated inside the building during the unoccupied mode This is often called a preoccupancy purge In this case the fan in the dedicated outdoor air unit is activated cooling dehumidification or heating is modulated to discharge air at the desired conditions and the central relief fan should modulate to maintain indoor to outdoor pressure difference at the desired setpoint Rather than simultaneously turning on all the heat pumps in the morning to warm up or cool down their respective zones a system level controller can be used to stagger the starting of the individual heat pumps to avoid a spike in the building electrical demand Of course this requires a longer period of time to bring all zones to desired occupied conditions Scheduling Determining the times at which to start and stop the HVAC system is typically based on assumptions regarding building usage Most building managers or operators want to avoid complaints from the occupants and the time ne
104. aces of the tubes Of course locating the tower inside the building requires extra floor space and the associated dampers and ductwork increase the system installed cost e Use an antifreeze solution Mixing in antifreeze such as glycol with the water in the closed distribution loop lowers the temperature at which the solution will freeze Given a sufficient concentration of glycol no damage will occur to the closed distribution loop The tower sump however must still be protected from freezing As the temperature drops below the glycol solution freeze point ice crystals begin to form Because the water freezes first the remaining glycol solution is further concentrated and remains a fluid The combination of ice crystals and fluid makes up a flowable slush The fluid volume increases as this slush forms and flows into available expansion volume Freeze protection indicates the concentration of antifreeze required to preventice crystals from forming at the given temperature Table 7 Burst protection indicates the concentration required to prevent damage to equipment e g coil tubes bursting Burst protection requires a lower concentration of glycol which results in less degradation of heat transfer SYS APM010 EN Water Source and Ground Source Heat Pump Systems 47 TRANE Primary System Components Table 7 Concentration required for freeze protection vs burst protection
105. al complaints can coexist e Use separate time of day schedules for areas with differing usage patterns For simplicity many building managers or operators define only one or a few time of day schedules to operate the entire building However if areas of the building have significantly different usage patterns this approach wastes energy since the entire building may be operating to maintain occupied temperature setpoints even though only part of the building is in use A more energy efficient approach is to create separate time of day operating schedules for areas of the building with significantly different usage patterns If the facility already has a BAS it probably includes a time of day scheduling function so the only additional costis the operator s time to set up the schedules To reduce the number of schedules that need to be created and maintained group zones with similar usage patterns together and create one schedule for each group Water loop temperature control Water source heat pumps can operate in either heating or cooling mode when the water loop temperature is maintained within the recommended range between about 60 F 162C and 90 F 322C for example Loop temperatures outside the recommended range can severely impact WSHP performance For this reason one of the primary functions of the system level controller is to monitor and maintain an acceptable temperature in the water loop The loop supply water
106. am of the cooling coil If a separate air to air heat exchanger is used for exhaust air energy recovery during warm weather it will pre cool the entering outdoor air reducing the amount of heat that can be transferred by the series air to air heat exchanger Auxiliary heat control If a WSHP is equipped with an internal electric resistance heater see Electric resistance heat in the WSHP boilerless system p 57 Section 6 4 3 5 requires that the unit level controller must prevent the electric heater from operating whenever the heat pump compressor is capable of offsetting the heating load Examples 6 X and 6 Y in the Standard 90 1 User s Manual discuss this requirement in more detail Opportunities to further reduce system energy use While local building codes might include requirements for minimum levels of energy efficiency many building owners desire even higher efficiency levels for their systems In addition programs like ENERGY STAR administered by the U S Environmental Protection Agency and Department of Energy DOE Rebuild America administered by the DOE and LEED Leadership in Energy and Environmental Design created by the U S Green Building Council a building industry coalition have encouraged higher levels of energy efficiency in buildings Table 26 contains a list of several system design options and control strategies that can help further reduce the energy use of a WSHP system This list is no
107. an 2 ft 600 mm from the walls or fixed airconditioning equipment building automation system BAS A centralized control and monitoring system for a building building diversity Calculated by dividing a building s block load by its sum of the peaks load also referred to as system diversity CA Conditioned Outdoor Air CDQ Trane s Cool Dry Quiet technology See series desiccant wheel circuit setter A device installed in the water pipe connected to a heat pump which is used to measure and adjust the water flow rate closed circuit cooling tower A type of cooling tower that keeps the fluid to be cooled separate from the water used in the evaporation process of the tower Coefficient of Performance See COP collection efficiency Describes how well a particulate filter removes particles of various sizes from the air stream combustion efficiency A measure of boiler efficiency that is calculated by dividing the fuel input to the boiler minus stack flue gas outlet loss by the fuel input to the boiler This value generally ranges from 75 to 86 percent for most non condensing boilers and from 88 to 95 percent for condensing boilers compressor A mechanical device used in the vaporcompression refrigeration cycle to increase the pressure and temperature of the refrigerant vapor Water Source and Ground Source Heat Pump Systems SYS APM010 EN condensate trap Device for collecting liquid formed by the cond
108. and Challenges 108 Why not just cool the outdoor air to a neutral dry bulb temperature without overcooling it to dehumidify to a low dew point To demonstrate the effect of this design choice consider if the same example classroom was served by a dedicated OA unit that cools the outdoor air to 74 F 23 3 C without overcooling it to dehumidify to a low dew point Although the dedicated OA unit eliminates the sensible cooling load associated with ventilation it only offsets part of the latent ventilation load because the dew point of the conditioned OA is still much higher than the dew point in the zone The remaining moisture in the conditioned OA must be removed from the classroom by the WSHP At the full load peak dry bulb condition the dedicated OA unit delivers conditioned OA CA that is at the same dry bulb temperature as the zone but at a much higher dew point Figure 80 This adds a significant latent load to the classroom moisture which must be removed by the WSHP The WSHP still needs to cool the recirculated air to 56 6 F DB 13 5 C DB to offset the zone sensible cooling load At this condition the resulting indoor relative humidity is 59 percent Figure 80 Dehumidification performance of neutral temperature conditioned air without overcooling to dehumidify at peak dry bulb condition 96 F DB fe fe 68 F DP an OA 59 9 F DB oe MA ogm a RA 74 F DB 55 so SEONG epuol aliiAuosyoer A
109. and avoids the periodic calibration and cleaning required to ensure proper sensor operation For the other zones occupancy sensors and or time of day schedules are used to reduce ventilation Reset dedicated OA leaving air temperature Many dedicated outdoorair systems are designed to dehumidify the outdoor air to a dew point that is drier than the zone and then reheat it to dry bulb temperature that is close to the zone setpoint neutral This control approach is simple because it allows the dedicated OA unit to operate independently of the local heat pumps However allowing the dedicated OA unit to deliver the conditioned outdoor air at a cold rather than neutral temperature can reduce both the installed cost and energy use of the overall system see Neutral versus cold air delivery p 64 Why reheat the dehumidified outdoor air to a neutral temperature on the hottest day of the summer when all zones need cooling However there are times during the year when it may be more efficient to reheat the dehumidified outdoor air to avoid overcooling the zones Following are some possible approaches for resetting the dry bulb temperature delivered by the dedicated OA unit The dew point of the conditioned air is controlled independently to meet the humidity control requirements of the zones Activate the reheat coil when it gets cold outside A very simple control approach would be to activate the reheat coil reheating the dehu
110. art load dehumidification performance 101 Methods for improving dehumidification performance 103 After hours dehumidification 0 00 00 e eee eee ee 109 Humidification 0 eee nent eee n eens 110 Energy Efficiency 0 c ccc ent e tee nes 111 Minimum efficiency requirements 000 ccc cece eee ee 111 Minimum equipment efficiencies 000 eee eee 112 Maximum allowable fan system power 2 005 113 ECONOMIZErS ausunu nananana nean 116 Demand controlled ventilation ss asasan aaea 119 WSHP distribution loop design and control 120 Cooling tower control 1 cece cee eens 121 Exhaust air energy recovery 00 cette 121 Auxiliary heat control 0 0 00 c eee 122 Opportunities to further reduce system energy use 122 ACOUSTICS iictdieeccdyeticautied ad Sane Ea a TR pes ad E e a eck don wh areca 125 Defining an acoustical model 000 cece eee 125 Specific acoustical recommendations 00 cece eee ees 128 WSHP console or unit ventilator models 128 WSHP horizontal models 0 0 00 cece eee ee 129 WSHP vertical Units 0 0 0 cece ene 131 WSHP vertical stack models 0 000 c eee eee 133 Cooling towers and other ancillary equipment 134 System Design Variations 0 cc ccc eee eee 135 Ground Source Heat Pump Systems 0
111. at a temperature warmer than the zone Tzone and zone air distribution effectiveness Ez can be 10 In such a case for this example the required system outdoorair intake flow Vot would be 3100 cfm 1 46 m3 s at either the cooling or heating design condition Calculating system intake airflow Vot for a dedicated outdoorair system when conditioned OA is supplied to a central conidor In some buildings a dedicated OA unit delivers conditioned OA to a central corridor The OA is then drawn into each zone underneath the door or through a grille in the door Figure 66 This configuration is most commonly used in dormitories barracks apartment buildings high rise condominiums extended care facilities and hotels As explained in example 6 H in the Standard 62 1 User s Manual the last two rows in the table of zone air distribution effectiveness Ez default values see Table 13 p 92 were included for this specific configuration When outdoor Water Source and Ground Source Heat Pump Systems 95 S TRANE System Design Issues and Challenges air is drawn into the breathing zone and enters the zone at a location that is near rather than on the opposite side of the room from the location of the exhaust outlet ASHRAE 62 1 prescribes the default value for Ez as 0 5 This suggests that a substantial amount of the outdoor air that is drawn in from the corridor will bypass the breathing zone and leave through the exhaust Table 16
112. ater distribution throughout the system Figure 26 Direct retum versus reverse retum piping arrangement direct return reverse return supply supply r M return return Though initially more expensive because of the additional length of return pipe a reverse return piping arrangement can reduce design layout time and system balancing requirements after installation With the reverse return arrangement the water supplied to each heat pump travels through essentially the same combined length of supply and return pipe Figure 26 In multiple story applications the risers are typically piped in a direct return arrangement while a reverse return arrangement is used to connect the heat 36 Water Source and Ground Source Heat Pump Systems SY S APM 010 EN For more information on single pipe ground source heat pump systems refer to the October 2009 ASHRAE Journal article One Pipe Geothermal Design Simplified GCHP System ANANN S TRANE Primary System Components pumps on each floor This arrangement avoids the expense of adding a third full sized riser Balancing valves and proper pipe sizing are used to ensure proper water flow to each floor Consider installing a drain valve at the base of each supply and return riser to permit system flushing during start up and maintenance Single pipe system In a single pipe system each WSHP is connected to a single pipe that serves as both supply and return In other words
113. ather preheating may be desirable Decide what amount of cross leakage is acceptable Many types of air to air energy recovery devices permit some degree of cross leakage Through fan configuration and properly adjusted seals the amount of leakage is usually less than 5 percent even for wheels in most applications Dedicated OA equipment types Depending on the climate the dedicated OA equipment may be used to cool dehumidify heat and or humidify the entering outdoor air This approach allows the heat pumps to handle only the zone cooling and heating loads not the ventilation load While there are many types and combinations of equipment that can be used following are a few examples of the types of dedicated OA equipment commonly used with WSHP systems Standalone air cooled DX unit packaged or split One of the most common types of dedicated OA equipment is a standalone air cooled direct expansion DX unit This might be a packaged unit or a split system comprised of two separate sections connected by refrigerant piping A packaged DX unit is typically installed on the roof of the building and contains a fan filter a gas fired burner or heating coil and all the components of a DX refrigeration system an evaporator cooling coil one or more compressors an air cooled condenser complete with propeller type fans and expansion devices Figure 50 In addition it may contain an air to air heat exchanger for exhau
114. ating Refrigerating and Air Conditioning Engineers Inc www ashrae org Consider if the same 7600 cfm 3600 L s rooftop style WSHP includes a total energy wheel with an effectiveness of 70 percent At design cooling conditions the outdoor airflow through the supply side of the wheel is 3000 cfm 1400 L s and the airflow through the exhaust side of the wheel is 2400 cfm 1100 L s For this example the pressure drop adjustment A is 136 bhp LO kW A 2 2 x0 70 0 5 in H20 x 3000 cfm 4131 2 2 x 0 70 0 5 in H20 x 2400 cfm 4131 136 bhp A 550 x 0 70 125 Pa x 1400 L s 650 000 550 x 0 70 125 Pa x 1100 L s 650 000 10 kW and the total allowable fan input power brake horsepower for the fan system is adjusted to 8 5 bhp 6 4 kW Allowable Fan Input Power 7600 cfm x 0 00094 1 36 8 5 bhp Allowable Fan Input Power 3600 L s x 0 0015 10 6 4 kW Water Source and Ground Source Heat Pump Systems 115 S TRANE System Design Issues and Challenges 116 Economizers Section 6 5 1 of ASHRAE 90 1 states that either an airside or waterside economizer is required on each cooling system that has a fan in which the rated cooling capacity is greater than or equal to the value listed in Table 23 below Table 23 Minimum heat pump size for which an economizer is required Minimum rated cooling capacity for which an Climate zone B economizer is required
115. ations indirect evaporative cooling is implemented using a standalone cooling tower or similar device and a separate coil located upstream of the conventional cooling coil However in a water source heat pump system because a water distribution system is already part of the system another approach may be to route the cool condenser water through a separate coil to pre cool the entering outdoor air before it passes through the conventional cooling coil This configuration is similar to a waterside economizer used in a water source heat pump see Figure 107 p 162 Evaporative cooling requires careful attention to water treatment periodic cleaning and routine maintenance to ensure safe and efficient operation Finally it consumes water which may be in limited supply in the arid climates where evaporative cooling provides the greatest energy saving benefit Air Distribution For water source heat pumps that are installed within or directly adjacent to the occupied zone such as console and vertical stack models air is typically supplied directly to and returned directly from the zone without the use of ductwork However for heat pumps that are installed outside of the occupied zone such as horizontal vertical and rooftop models a supply duct system is typically used to transport air from the WSHP to supply air diffusers for delivery to the zone Figure 60 shows an example of supply and return air ductwork connected to a horiz
116. be occupied but an occupancy sensor indicates that it is not presently occupied All or some of the lights can be shut off the temperature setpoints can be raised or lowered slightly and the outdoor airflow required can be reduced typically to the building related ventilation rate Ra optimal start An optimized morning warm up routine that determines the length of time required to bring the zone from its current temperature to the occupied setpoint temperature and then waits as long as possible before staring the system so the zone reaches the occupied setpoint just in time for scheduled occupancy outdoor air Air brought into the building from outside either by a ventilation system or through openings provided for natural ventilation perimeter zone A conditioned space with walls and windows that are exposed to the outdoors In most climates these spaces would require seasonal cooling and heating plenum The space between the ceiling and the roof or the floor above population diversity The ratio of the actual system population to the sum of the peak zone populations Water Source and Ground Source Heat Pump Systems SYS APM 010 EN pressure independent VAV control method that directly controls the actual volume of primary air that flows to the zone The position of the air modulation damper is not directly controlled and is simply a by product of regulating the airflow through the unit Since the airflow delivered to the zon
117. bes a limit to the allowable fan system power but this limit only applies if the fan system has a total motor nameplate power exceeding 5 hp 4 kW As defined by ASHRAE 90 1 fan system power is the sum of the power demand for all fans that are required to operate at design conditions to supply air from the heating or cooling source e g coils to the conditioned space s and return the air to the source or exhaust it to the outdoors According to this definition each WSHP is considered a separate fan system because each has a heating and cooling source the refrigerant to air heat exchanger This interpretation of the definition of fan system is confirmed by example 6 DDD in the Standard 90 1 User s Manual However the fan system includes not only the fan inside the WSHP but also the fan inside the dedicated OA unit and any central relief exhaust fans Individual exhaust fans with nameplate motor power of 1 hp 0 75 kW or less are exempt and do not need to be included in any calculations Example 6 DDD in the Standard 90 1 User s Manual clarifies that the fan in the dedicated OA unit and any central relief exhaust fans must be allocated to each WSHP on an airflow weighted basis In other words if the outdoor airflow delivered to a given zone is 5 percent of the total airflow delivered by the dedicated OA unit 5 percent of the dedicated OA unit fan motor power must be added to the fan motor power of the WSHP ser
118. bsorb moisture If humidification is needed for only a few specific zones within the building consider locating a humidifier in ductwork downstream of each WSHP serving those zones that require humidification This avoids the energy needed to humidify all the zones but does require space and maintenance near the occupied zones e Avoid oversizing the humidification equipment An oversized humidifier typically results in unstable control with large swings in humidity levels In an application where humidification is 110 Water Source and Ground Source Heat Pump Systems SYS APM010 EN For more information refer to ANSI ASHRAE IESNA Standard 90 1 Energy Standard for Buildings Except Low Rise Residential Buildings and the Standard 90 1 User s Manual both available for purchase at www ashrae org S TRANE System Design Issues and Challenges provided for comfort avoid the use of overly conservative assumptions or safety factors During cold weather adding too much moisture also increases the likelihood of moisture related problems in the building envelope where there are likely to be surface temperatures that are below the indoor dew point Sizing the humidifier can be particularly challenging if the WSHP includes an airside economizer as might be the case with a rooftop style WSHP Typically when the outdoor air is driest at the winter design condition for example the OA damper is closed to its minimum position But at o
119. but generally fall into the following categories e Airborne Sound follows the airflow path Supply airborne sound travels in the same direction as the supply air Return airborne sound travels against the direction of airflow back through the return air path e Duct breakout Sound passes through walls of the ductwork into the ceiling plenum and then through the ceiling into the occupied space e Radiated Sound radiated from the casing of the equipment travels through whatever is between the equipment and the receiver location e Structure borne This path differs from the others in that energy is transmitted through the framework of the building This energy may come directly from the vibration of the sound source a fan or compressor for example or may be airborne sound that is transferred to the structure Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Issues and Challenges An acoustical analysis consists of five basic steps Step 1 Set acoustical goals for the finished space It is critical to establish realistic acoustical goals for the occupied space at the outset of any project There are always implicit often subjective expectations and it is much easier if you understand these expectations before designing the HVAC system Sound goals will vary depending on how the space is expected to be used Once the sound goals are understood they can be stated using an approp
120. by hand evaporative cooling Sensible cooling obtained by latent heat exchange from water sprays or jets of water evaporator The component of the refrigeration system where cool liquid refrigerant absorbs heat from air causing the refrigerant to boil exhaust air Air that is removed from the conditioned space s and then discharged to the outdoors expansion device The component of the refrigeration system used to reduce the pressure and temperature of the refrigerant expansion tank A component of a closed piping system that accommodates the expansion and contraction of the water as temperature and therefore density changes expansion valve See expansion device face velocity Velocity of the air as it passes through a device airflow rate divided by the face area of the device fan performance curve A plot of a specific fan s airflow capacity at a given speed rpm versus the static pressure it generates fan speed control A method of supply fan modulation that affects a fan s capacity by varying its speed of rotation commonly accomplished using a variable speed drive on the fan motor Water Source and Ground Source Heat Pump Systems 199 200 flue gases Exhaust gases from a boiler or gas fired burner fluid cooler See closed circuit cooling tower four way valve See reversing valve glycol A liquid that is mixed with water to lower the freezing point of the solution grille A device used to direct a
121. ce that the equipment will be properly maintained Dedicated outdoorair system is typically required Because this system uses distributed equipment to provide cooling and heating the introduction of outdoor air for ventilation may bring a few challenges including insufficient dehumidification and or heating capacity of the WSHPs While the requirement for ventilation can be handled in various ways most WSHP systems use a dedicated outdoor air system to separately condition all the outdoor air required for ventilation and deliver it to the individual zones Common Building Types That Use WSHP Systems Water source heat pump systems are used in many building types but the most common applications are Commercial medical and government office buildings e Schools both K 12 and higher education e Hotels and motels e Apartment buildings and high rise condominiums e Dormitories and military barracks e Extended care facilities e Retail stores standalone strip malls and large malls Water Source and Ground Source Heat Pump Systems u TRANE 12 RO fan Primary System Components This chapter discusses the primary components of a typical water source heat pump system in greater detail For details on specific pieces of equipment consult the manufacturer Water Source Heat Pumps Typically each zone of the building is served by a separate water source heat pump WSHP A WSHP is a packaged heating and cooling unit
122. conditions all of the outdoor air required for ventilation see Dedicated OA equipment types p 73 As explained previously this configuration allows the cooling heating equipment to be distributed throughout the building often located very close to the dedicated OA unit that it is connected to This may be advantageous for buildings that are large in terms of floor area but are only one or two floors such as a K 12 school or an extended care facility An alternative approach is to use a centralized water cooled chiller which is also connected to the water distribution loop to serve multiple dedicated OA units Rather than connecting the water cooled chiller to a separate cooling tower the chiller condenser is connected to the same water distribution loop that is used by the heat pumps Figure 103 This configuration allows the cooling heating equipment used to condition the outdoor air to be centralized This may be advantageous for multi story buildings that include only a few dedicated OA air handling units such as an office building hotel or apartment building Other advantages include higher efficiency greater flexibility and centralized maintenance The chiller may be used for cooling only or it might be piped into the water distribution loop to allow it to be used for either cooling or heating In this latter configuration the chiller is sometimes referred to as a chiller heater This concept can be used with a
123. conomizer cycle could be implemented e If ventilation is provided by a dedicated OA system that system could be oversized to provide up to 100 percent of design supply airflow for cooling when economizing For most applications this is probably not desirable since it would require much larger ductwork and larger fans e A pre cooling waterside economizer coil see Figure 107 p 162 could be included in those heat pumps that have a rated cooling capacity of 54 000 Btu hr 16 kW or larger e And finally the design team could choose to comply using the Energy Cost Budget Section 10 method rather than following the prescriptive requirements of Standard 90 1 Water Source and Ground Source Heat Pump Systems SYS APM010 EN In June 2012 the Standard 90 1 committee issued an official interpretation IC 90 1 2010 15 to clarify that pre cooling waterside economizer coils can be used in WSHP systems to meet the requirements of Section 6 5 1 2 In this interpretation the committee confirmed that example 6 LL in the 2010 edition of the Standard 90 1 User s Manual is incorrect since it refers only to WSHP compressor energy use rather that overall building energy use and will be removed or corrected in future versions S TRANE System Design Issues and Challenges For a WSHP system some engineers are concerned that Section 6 5 14 Economizer Heating System Impact may not allow for the use of a pre c
124. correct plan of plenum system Though the ducts are not connected to the terminal units they discharge In this case outdoor air ventilation is provided to one near them with balancing means available to provide correct airflow to ventilation zone but not the other This could only meet the each requirement if it could be shown that sufficient air gets to the remote system perhaps by mixing between the zones Source ASHRAE 62 1 2010 User s Manual Figures 5 D and 5 E American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org 62 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Table 10 Comparison of different dedicated OA system configurations Conditioned OA delivered directly to each zone Advantages Disadvantages Makes it easier to ensure the required amount of outdoor air reaches each zone because separate ventilation diffusers allow easy airflow measurement and balancing Affords opportunity to cycle off the fan inside the heat pump reducing fan energy use when the compressor cycles off because outdoor air is not distributed to the zone by the WSHP fan Allows the dedicated OA system to operate during unoccupied periods for after hours humidity control or preoccupancy purge for example without needing to operate the fans inside the heat pumps Affords the opportunity to downsize local heat pumps reducing installed c
125. ct of a waterside economizer on the overall building heating energy use Table 24 illustrates the impact of a pre cooling waterside economizer on overall building heating energy use based on example 5 ton 18 kW water source heat pumps SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 117 S TRANE System Design Issues and Challenges 18 Table 24 Example impact of a pre cooling waterside economizer on overall building heating energy use Entering water temperature from loop 45 F 55 F 7 2 C 12 8 C i f 61 000 Btu hr 61 000 Btu hr Heating load in Zone 1 heating mode 17 9 kW 17 9 kW WSHP heating efficiency COP 3 70 4 04 WSHP compressor energy use 4 83 kW 4 43 kW heating load COP WSHP heat of compression 16 500 Btu hr 15 100 Btu hr heating load COP 4 8 kW 4 4 kW Heat extracted from loop 44 500 Btu hr 45 900 Btu hr heating load heat of compression 13 0 kW 13 4 kW r i F 5 000 Btu hr 5 000 Btu hr Cooling load in Zone 2 cooling mode 1 5 kW 1 5 kW Heat rejected to loop 5 000 Btu hr 5 000 Btu hr by waterside economizer coil 1 5 kW 1 5 kW Heat added to loop by boiler heat extracted from loop heat rejected to loop 39 500 Btu hr 11 6 kW 40 900 Btu hr 12 0 kW Boiler energy use heat added to loop by boiler 80 percent efficiency 49 400 Btu hr 14 5 kW 51 100 Btu hr 15 0 kw Building heating energy use
126. cted For an un ducted application see the recommendations related to the casing radiated sound path When return air is ducted to the WSHP inlet sound will travel opposite the direction of airflow from the WSHP to the occupied space A fully ducted return system uses ductwork to connect the return air grille directly to the WSHP inlet In a partially ducted system a section of return ductwork is connected to the WSHP inlet but it does not connect to the return air grille Avoid placing the return air grille near the WSHP inlet Moving the grille at least 6 ft 18 m away from the inlet will reduce the return airborne sound that enters the space All ducted returns will benefit from acoustical lining Size all return duct components for low velocity Partially ducted returns will benefit if the open end of the duct has no obstruction such as a grille and includes at least four equivalent duct diameters of straight duct prior to the WSHP inlet A partially ducted return may benefit by connecting an acoustically lined elbow to the return air grille with the opening facing away from the WSHP inlet WSHP vertical stack models Vertical stack water source heat pumps are typically installed in the occupied space so refer to the recommendations for console style heat pumps p 128 Return airborne sound can be reduced by installing a flush mounted return air door typically available as an optional accessory that recesses into the wall Figure
127. cts heat from the relatively warm water cooling the water and causing the liquid refrigerant to boil The refrigerant vapor travels back through the reversing valve to the compressor to repeat the cycle Water Source and Ground Source Heat Pump Systems 17 Se TRANE Primary System Components 18 ASHRAE Standard 90 1 2010 requires that each WSHP be equipped with a motorized two position isolation valve This isolation valve when combined with an automatic flow control device typically makes a water regulating valve unnecessary An isolation valve is less expensive opens quickly when the compressor turns on closes slowly when the compressor turns off to avoid water hammer and is a positive shutoff valve that ensures the valve is closed to prevent water flow See Isolation valves and flow control devices p 39 While a rare few applications may require the use of a water regulating valve the need for them has all but disappeared due to the common use of TXVs and less expensive isolation valves Water Source and Ground Source Heat Pump Systems Returning to the same example Table 1 p 17 in the heating mode this heat pump provides 71 MBh 21 kW of heating capacity while supplying 1700 cfm 0 80 m3 s of warm air The heat added to the air stream is comprised of heat extracted from the 15 gpm 0 95 L s of water flowing through the refrigerant to water heat exchanger plus the heat of compression This heat extrac
128. cts heat to the recirculated air The dedicated outdoor air system operates to provide the required amount of outdoor air to the zone for ventilation Water Source and Ground Source Heat Pump Systems 3 TRANE Overview of a Water Source Heat Pump System Zone is unoccupied Zone setpoints are typically relaxed when the zone is scheduled to be unoccupied allowing the temperature in the zone to either increase or decrease In fact this practice is required in many buildings by local codes or energy standards These new setpoints are often called setback temperatures and the result is a much wider deadband Figure 4 Figure 4 Unoccupied zone setback temperatures womomidhoccupied cooling setback temperature umn occupied cooling setpoint deadband occupied heating setpoint TTTS zone dry bulb temperature During unoccupied periods as long as the temperature in the zone is within this wider deadband the controller in the WSHP shuts off the fan and compressor If all zones served by the WSHP system are unoccupied and the zone temperatures are within the deadband the water circulation pumps can be shut off Because the building is unoccupied no ventilation is required and the fan in the dedicated outdoor air unit is also shut off Some systems incorporate a timed override button on the zone temperature sensor that allows the occupant to temporarily switch the zone into the occupied mode even thoug
129. currents have the potential to severely damage the heat exchanger Ground water heat pump systems A ground water heat pump GWHP system pumps water from a well and informati he desi For more information on te design ang then either returns the used water to the source through a separate well or layout of ground water heat pump systems refer to the ASHRAE manual dumps the water in a drain field or sewer system Figure 101 The water from Ground Source Heat Pumps Design of Gecticr a a E aad the well might be circulated directly through each heat pump an open Institutional Buildings and the March system but more commonly an intermediate heat exchanger is used to 2009 ASHRAE J ournal article titled separate the well water from the water that circulates throughout the building Commercial Open Loop Heat Pump d t Systems a closed system Figure 10L Ground water heat pump system heat pumps water circulating pumps SYS APM010 EN Water Source and Ground Source Heat Pump Systems 153 S TRANE System Design Variations 154 For a building site where an existing or proposed well can provide an ample supply of suitable quality water a GWHP system might be feasible A ground water system is typically the most efficient of any ground source system because fluid temperatures in the loop are typically cooler during the cooling season and warmer during the heating season than in a ground coupled system Also
130. d Challenges 130 Sound paths and recommendations for this configuration are 1 Casing radiated Sound radiates from the casing of the heat pump and out through the return air inlet if un ducted into the ceiling plenum If the WSHP is placed directly over the occupied space the sound will travel through the ceiling and return air grille s into the occupied space The best way to reduce casing radiated sound is to place the WSHP over a non sound sensitive area a corridor for example Other options include adding a lined return duct to the inlet and or placing an acoustical barrier under the WSHP This barrier should be approximately twice the size of the WSHP footprint and have sufficient transmission loss to reduce the transmitted sound to acceptable levels Placing a layer of absorptive material on top of the barrier will also help 2 Supply airbome Sound leaving the discharge of the WSHP travels down the supply ductwork through the supply air diffusers and into the occupied space Supply airborne sound can be reduced by adding an acoustical liner to the supply ductwork Acoustical analysis can be used to determine the required lining thickness and length of ductwork that needs to be lined Another convenient way to add absorptive duct liner is to use lined flex duct as the final section that connects to the diffuser Figure 85 Pay careful attention to the attachment of the flex to the diffuser avoid sharp turns and pinched duc
131. d cost and adds more pressure loss that the fan needs to overcome So why do it Sometimes it is required to meet a local building code Sometimes it is done to allow easier cleaning of the return air path When designing the return air path for a WSHP consider the following general recommendations e Avoid undersizing return air grilles If the return air grilles are too small they will create too high a pressure drop and result in a significant pressure difference between the occupied space and the ceiling plenum A space to plenum pressure difference of no more than 0 02 to 0 03 in H20 5 0 to 75 Pa is acceptable under most conditions When a suspended T bar ceiling is used a high pressure difference between the occupied space and the ceiling plenum will typically cause some of the return air to be forced around the edges of the ceiling tiles This causes soiling of the tiles which increases the frequency of cleaning or replacement e Avoid undersizing return air openings within the ceiling plenum If the return air path must pass through an interior partition wall that extends from floor to floor make sure the opening through the wall is large enough to avoid an excessive pressure drop In addition the opening into the return air ductwork must be large enough to avoid an excessive pressure drop e Usean open ceiling plenum rather than a ducted return whenever possible Using an open ceiling plenum for the return air path
132. d off or for a rooftop style WSHP the outdoor air damper can be closed Allowing the indoor temperature to drift during the unoccupied mode often called night setback typically saves energy by avoiding the need to operate heating cooling and ventilation equipment Figure 117 SYS APM010 EN Figure 118 Zone temperature sensor with timed ovenide button S TRANE System Controls Figure 117 Energy saving potential of night setback 100 for A N HVAC energy consumption of baseline Atlanta Louisville Minneapolis without night setback baseline ia with night setback Table 31 describes the typical functions of the different system components during the unoccupied mode Table 3L Coordination of equipment during unoccupied mode e Fan is turned off unless the zone requires cooling or heating Positions the reversing valve and cycles the compressor s to bring the zone temperature to the unoccupied setpoint cooling or heating WSHP e Fan is turned off Dedicated outdoorsai unit e Central relief fan is turned off Water circulating pumps are turned off unless any zone requires cooling or heating if a variable flow system varies the speed of the pumps to maintain pressure in the piping at the desired setpoint e Turns on cooling tower if needed to maintain the loop water temperature below the upper setpoint Turns on boiler if needed to maintain the lo
133. d tube coil similar to a direct expansion DX refrigerant coil found in a packaged rooftop unit Figure 13 In the cooling mode this refrigerant to air heat exchanger is the evaporator and the air is cooled as heat is transferred from the air to the refrigerant inside the tubes In the heating mode it is the condenser and heat is transferred from the refrigerant to the air The refrigerant to water heat exchanger may be a tube in tube tube in shell or brazed plate design The example shown in Figure 13 is a tube in tube or coaxial heat exchanger It is constructed as a small tube running inside a larger tube The water flows through the inner tube and refrigerant flows through the outer tube In the cooling mode this refrigerant to water heat exchanger is the condenser and water flowing through the inner tube extracts heat from the refrigerant flowing through the outer tube In the heating mode it is the evaporator and the refrigerant extracts heat from the water The most common type of expansion device used in water source heat pumps is the thermal expansion valve TXV Some models however use electronic expansion valves EEV short orifices or capillary tubes All of these devices reduce the pressure and temperature of the refrigerant within the cycle Expansion valves such as the TXV shown in Figure 13 have the added capability of metering the quantity of refrigerant flowing through the cycle to match the load This enhances
134. de S TRANE System Design Variations could be added to the loop to help reject the excess heat see Hybrid ground coupled heat pump systems p 149 This example also demonstrates the risk associated with using a rule of thumb to determine borehole depth The same building located on the same plot of land with the same block cooling load required drastically different borehole depths depending on how that building is operated or used Fora typical office building schedule of 10 hours day and 5 days week the required borehole depth is 233 ft per ton of block cooling load 20 2 m kW But if operating for 24 hours day and 7 days week the required borehole depth increased to 582 ft ton 50 4 m kW If the borefield was designed using a rule of thumb like 300 ft per ton of block cooling load 26 m kW the ground heat exchanger would be oversized by about 25 percent for the typical operating schedule or undersized by almost 50 percent for the 24 7 operating schedule General recommendations for designing ground heat exchangers Other publications contain more complete details related to designing the ground heat exchanger but following are some general recommendations e Drill a test borehole prior to finalizing system design As mentioned previously this helps determine the actual soil thermal properties as well as drilling or trenching conditions at the site e Size the ground heat exchanger based on the block co
135. de of each WSHP Advantages Disadvantages Helps ensure the required amount of outdoor air reaches each unit because the OA is ducted directly to the supply side of each heat pump Avoids the cost and space needed to install additional ductwork and separate diffusers Affords the opportunity to downsize local heat pumps reducing installed cost and energy use if the conditioned outdoor air is delivered at a cold temperature rather than reheated to neutral Easier to ensure that outdoor air is adequately dispersed throughout the zone because outdoor air is distributed by the WSHP fan Measurement and balancing is more difficult than if the OA was delivered directly to the zone via separate diffusers May need to increase ventilation to account for Ez lt 1 0 during heating mode Fans inside the heat pumps typically must operate continuously to provide ventilation during scheduled occupancy rather than cycling off with the compressor unless a pressure independent VAV terminal is used to maintain outdoor airflow Conditioned OA delivered to the open ceiling plenum near each WSHP Advantages Disadvantages e Avoids the cost and space needed to install additional ductwork separate diffusers or field fabricated mixing plenums More difficult to ensure the required amount of outdoor air reaches each unit since the OA is not ducted directly to each heat pump May need to increase ventilation to account for Ez
136. dedicated OA unit should dehumidify the outdoor air to a dew point that is drier than the zone so that it will also offset the zone latent loads The heat pumps then only need to offset the zone sensible cooling loads Returning to the previous classroom example Figure 77 depicts a dedicated OA system that delivers 450 cfm 0 21 m s of outdoor air directly to the classroom The dedicated OA unit dehumidifies the entering outdoor air to a low dew point 52 F DP 111 C DP in this example and then reheats it to a neutral dry bulb temperature see Neutral versus cold air delivery p 64 71 F DB 217 C DB Meanwhile a console style WSHP in the classroom cools 1 500 cfm 0 7 m s of recirculated air from the zone to offset the zone sensible cooling load At the peak dry bulb condition Figure 78 the WSHP cools the recirculated air to 56 6 F DB 13 5 C DB Together with the dry outdoor air delivered to the zone by the dedicated OA unit the two air streams maintain the zone at the desired temperature and the resulting zone relative humidity is 50 percent 106 Water Source and Ground Source Heat Pump Systems SYS APM010 EN Whether the conditioned outdoor air CA is delivered at a cold temperature or reheated to neutral see Neutral versus cold air delivery p 64 the resulting indoor humidity level will typically be the same In either case the outdoor air is dehumidified to the same leaving air dew point
137. dedicated outdoorair system operates to provide the required amount of outdoor air to the zone for ventilation 2 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO10 EN S TRANE Overview of a Water Source Heat Pump System Zone is occupied but requires no cooling or heating As the cooling load in the zone decreases eventually the dry bulb temperature in the zone drops below the cooling setpoint If the temperature falls below the cooling setpoint but remains above the heating setpoint the WSHP compressor remains off The temperature range between the cooling and heating setpoints is called the deadband Figure 3 Figure 3 Occupied zone temperature setpoints OCCU pied cooling setpoint deadband occupied heating setpoint TT zone dry bulb temperature The dedicated outdoor air system continues to operate providing the required amount of outdoor air to the zone for ventilation Zone is occupied and requires heating When the temperature in the zone reaches the heating setpoint the controller in the WSHP activates the reversing valve to switch operation of the refrigeration circuit to the heating mode and cycles or varies the speed of one or more compressors to match the changing heating load in the zone As the heating load increases the compressor operates for a longer period of time between cycles Inside the WSHP the refrigeration circuit extracts heat from the water loop and reje
138. design does not need to be changed although it may be reviewed for potential cost reductions If the estimate exceeds the sound target the paths are reviewed to determine which paths are dominant Alterations to the source and or the path elements are then made to reduce the sound at the receiver location This is typically an iterative process comparing the acoustical effect of various alterations Once a design meets the acoustical goals for the project everyone on the team must understand the work and cost required to implement the design It may also be prudent to review the cost of meeting the acoustical goals and reconsider system layout alternatives or equipment options that were initially rejected due to cost Specific acoustical recommendations It is challenging to put together a list of specific acoustical practices that should be used on every project Nearly everything on the list increases the installed cost cost that may or may not be justified by the acoustical requirements For this reason an acoustical analysis is preferred to meet the acoustical goals at the lowest cost The following sections should be used to identify potential problems in WSHP systems Consider both source attenuation and path attenuation to determine the most cost effective way to achieve the acoustical goals Use flexible conduit and wiring connections to minimize vibration transmission to the building structure For ducted applications use canva
139. distribution effectiveness 92 Vaz VE NERA 9 breathing zone Note Occupant load or exit population is often determined for use in designing egress paths that comply with the fire code However this population is typically much larger than the expected zone population Pz used for designing the ventilation system and for calculating cooling loads Using occupant load rather than expected zone population to calculate ventilation requirements will often result in oversized HVAC equipment and excessive energy use Impact of zone airdistribution effectiveness In addition to defining the breathing zone outdoor airflow Vbz ASHRAE 62 1 also prescribes zone air distribution effectiveness Ez that accounts for how well the ventilation air which is delivered to the zone by supply air diffusers actually gets into the breathing zone Figure 64 The breathing zone outdoor airflow Vbz is divided by this effectiveness Ez to determine the outdoor airflow that must be delivered through the supply air diffusers Voz Table 13 is an excerpt from ASHRAE 62 1 and provides default values for Ez for air distribution configurations commonly used in WSHP systems It is based on the placement of supply air diffusers and return air grilles and the temperature of the air being supplied Table 13 Zone airdistribution effectiveness Ez Configuration of air distribution system Supply air
140. ducted or through a ceiling mounted return air grille and the open ceiling plenum ducted Sound data provided by AHRI Standard 260 Sound Rating of Ducted Air Moving and Conditioning Equipment is separated by sound path discharge inlet and casing radiated Sound paths and recommendations for this configuration are 1 Casing radiated Sound radiates from the casing of the heat pump and out through the return air inlet if un ducted into the closet In an un ducted return system the sound then travels through the door and return air grille into the occupied space For an application with a grille in the access door un ducted return locate the WSHP in a non sound sensitive portion of the occupied space Some attenuation may be provided by placing a line of sight barrier just inside the louver Figure 86 and adding absorptive materials to the inside of the closet SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 131 S TRANE System Design Issues and Challenges 132 avoid direct line of sight sound transmission through return air grille to the occupied space Figure 86 Recommendations for vertical models size ducts for low air velocity below 700 fpm 3 8 m s in main sections below 600 fpm 3 1 m s in runouts first section of duct should be straight for at least three duct diameters locate WSHP away from sound sensitive areas use flexible duct and conduit connections
141. dust 300 mm deep may use lofted MERV 9 40 to 45 e Auto emissions air laid or paper wet laid e Nebulizer drops media e Welding fumes MERV 8 30 to 35 3 0 to 10 0 um particles e Commercial buildings Pleated filters Disposable e Mold e Better residential buildings xtended surface 1 to 5 in 25 to MERV 7 25 to 30 e Spores e Industrial workplaces 123 mitti thick with cotton polyester blend media cardboard e Hair spray e Paint booth inlet air frame MERV 6 lt 20 e Fabric protector Cartridge filters Graded density e Dusting aids viscous coated cube or pocket MERV 5 lt 20 e Cement dust filters synthetic media e Pudding mix Throwaway Disposable e Snuff synthetic media panel filters e Powdered milk MERV 4 lt 20 gt 10 0 um particles e Minimum filtration Throwaway Disposable e Pollen e Residential buildings fiberglass or synthetic panel MERV 3 lt 20 e Spanish moss e Window air conditioners filters i Dust mites Washable Aluminum mesh latex coated animal hair or foam MERV 2 lt 20 e Sanding dust rubber panel filters e Spray paint dust Passive electrostatic MERV 1 lt 20 e Textile fibers electret Self charging Carpet fibers passive woven polycarbonate panel filter 1 Minimum Efficiency Reporting Value MERV is defined by ANSI ASHRAE Standard 52 2 1999 Method of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size HEPA ULPA classifications are defined by IEST RP CC0
142. e Cooling mode Heating mode Airflow 1700 cfm 0 80 m3 s 1700 cfm 0 80 m3 s Water flow rate 15 gpm 0 95 L s 15 gpm 0 95 L s Entering water temperature 90 F 32 C 60 F 16 C Leaving water temperature 99 F 37 C 53 F 11 C Capacity 54 MBh 16 kW 71 MBh 21 kW Heat rejected to the loop 69 MBh 20 kW Heat extracted from the loop 54 MBh 16 kW Assumes entering air conditions of 77 F 25 C dry bulb and 63 F 17 C wet bulb during cooling mode and 68 F 20 C during heating mode and 0 5 in H20 125 Pa of external static pressure WSHP operation during heating mode Figure 15 Hot high pressure refrigerant vapor is pumped from the compressor and diverted by the reversing valve to the refrigerant to air heat exchanger In the heating mode this heat exchanger functions as the condenser and heat is transferred from the refrigerant vapor to the lower temperature air passing over the outer surfaces of the tubes The air is heated and the refrigerant condenses into a liquid Figure 15 Operation of a WSHP in the heating mode expansion device refrigerant to air heat exchanger compressor reversing valve refrigerant to water heat exchanger This liquid refrigerant then flows through the expansion device and travels to the refrigerant to water heat exchanger that in the heating mode now functions as the evaporator Inside this heat exchanger the refrigerant extra
143. e elementary school may use a smaller central pump plus a separate pump serving each wing of the school building With this approach an entire wing of the building can be shut off when not in use reducing pumping energy use The distributed pumping concept discussed previously uses this same concept but in that case a separate pump is used for each heat pump When the heat pump compressor turns off the pump serving that heat pump also turns off to reduce overall pump energy use SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 35 eS TRANE Primary System Components Piping layout The water distribution loop should be designed to deliver the required water flow to each heat pump while minimizing pump energy use and noise problems Because piping can account for a large percentage of the total system installation cost careful planning of the piping arrangement is important Direct versus reverse retum arrangement A direct return piping arrangement minimizes the amount of piping by returning the water along the same path as it was supplied Figure 26 In other words the supply and return pipes for a particular heat pump will be similar in length Their combined length however will be different from that of other heat pumps The direct return arrangement while less costly requires strict attention to piping layout Flow control devices must be used to balance the individual heat pump flow rates to ensure proper w
144. e 10 Scalable capacity add it as needed 0 cc eee 10 Opportunity for individual tenant metering 00 cece eee 10 Drawbacks Challenges of WSHP Systems 00 cece eens 11 Equipment is located in or near the occupied spaces 11 Distributed maintenance sasaaa ea 11 Dedicated outdoor air system is typically required 11 Common Building Types That Use WSHP Systems 20005 11 Primary System Components 00 0 cece eee 12 Water Source Heat PUMPS 0 006 c ccs 12 Reversible direct expansion DX refrigeration circuit 12 Components of the DX refrigeration circuit 13 WSHP operation during cooling mode 005 16 WSHP operation during heating mode 005 17 Water regulating valves 0 cece ee 18 Water flow rate 2 0 2 eee 18 FON soba Seebeck ee cd eee Pee teed HORNS ww LE Vek a Peewee 19 Electronically commutated motor 0 0 00sec eee 20 Multiple speed fan operation 0 00 cece eee es 21 FIIterS asinine it eG a ee eae tae ed nee ee Oe Ree wad add we 22 Condensate management 606 0c cece 27 WSHP configurations 0 0 0 eee 28 AHRI SO rating standards 0 0 00 c ces 30 Water Distribution LOOP 0 ccc teas 32 Water circulating PUMPS 06 ee 32 Centralized versus distributed pumping 5 32 C
145. e in the water loop gets too hot or too cold As an example this might occur if a cooling tower fan belt were to break The controller should automatically enable all of the WSHP compressors after the system recovers and the loop water temperature returns to normal e Install a freeze protection sensor that will turn on the watercirculating pump or take some other action if the water in the loop approaches a temperature at which freezing might begin to occur Water Source and Ground Source Heat Pump Systems SYS APM010 EN For more information on the issues related to improper building pressure control refer to the Trane Engineers Newsletter Commercial Building Pressurization ADM APNOO3 EN and the Trane Engineers Newsletter Live broadcast Commercial Building Pressurization APP APV013 EN SYS APMO010 EN S TRANE System Controls Building pressure control In addition to providing conditioned outdoor air for ventilation the dedicated outdoor air system is also used to replace air that is exhausted locally from certain areas of the building such as restrooms kitchens and lab spaces and control the indoor to outdoor pressure difference During humid weather maintaining the pressure inside the building so that it is slightly higher than the pressure outside positive pressure may improve comfort and helps prevent humid outdoor air from leaking into the building envelope During cold weather the pressur
146. e inside the building should be equal to or even slightly less than the pressure outside This helps avoid forcing moist indoor air into the building envelope and helps minimize uncomfortable cold drafts due to infiltration In either case excessive building pressure whether negative or positive should be avoided Because most WSHP systems with a dedicated OA system bring in a constant quantity of outdoor air during occupied periods and do not use an airside economizer cycle maintaining proper building pressurization is typically thought of as an air balancing issue Even in a properly balanced system however the wind variable operation of local exhaust fans and stack effect can result in pressure fluctuations If an airside economizer or demand controlled ventilation is used the intake airflow varies during occupied periods This will also require varying relief exhaust airflow to avoid over pressurization or depressurization In most applications the dedicated OA system is turned off during unoccupied periods In some cases however local exhaust fans are allowed to operate either by design or as an oversight Because air is still being exhausted from the building but no air is being brought in by the ventilation system a negative pressure is created in the building with respect to the outdoors One solution may be to use the building automation system to turn off all local exhaust fans whenever the dedicated OA system is
147. e is directly controlled it is independent of inlet duct static pressure pressure temperature P T ports Self sealing orifices that allow insertion of a probe type thermometer or pressure gauge directly into the system water primary air Conditioned air delivered by a central supply fan to a terminal unit psychrometric chart A tool used to graphically display the properties of moist air pump Device for transferring a liquid or gas from a source or container through tubes or pipes to another container or receiver PVC Polyvinyl Chloride a plastic pipe material recirculated return air Air removed from the conditioned space and reused as supply air usually after passing through an air cleaning and conditioning system for delivery to the conditioned space reducer A transition that reduces the size of the air duct refrigerant A substance used to extract and transport heat for the purpose of cooling refrigerant to air heat exchanger A finned tube coil inside a water source heat pump In the cooling mode it acts like an evaporator and the refrigerant inside tubes extracts heat from the air flowing across the fins and tubes In the heating mode it acts like a condenser and the refrigerant rejects heat to the air refrigerant to water heat exchanger Typically a coaxial tube within a tube heat exchanger inside a water source heat pump In the cooling mode it acts like a condenser The water flowing through the ou
148. e optimum number of zones balances occupant comfort requirements with the budgetary limits of the project The first step is to determine the maximum number of potential zones ignoring cost Each room separated by physical boundaries should be a separate zone Larger open areas should be divided into several smaller zones The next step is to determine how many of these zones can be easily combined using the following criteria For perimeter zones or interior zones on the top floor of the building e Are there adjacent zones in which the perimeter wall and or roof have the same exposure east facing west facing and so on Ifso do these zones have the same percentage and type of glass Ifso do these zones have approximately the same density of occupants lighting and equipment and are the time of use schedules similar e If so will the occupants accept the temperature varying slightly For interior zones not on the top floor of the building e Are there adjacent zones that have approximately the same density of occupants lighting and equipment and are the time of use schedules similar e If so will the occupants accept the temperature varying slightly If adjacent zones meet these criteria they likely can be grouped together into a single zone without much sacrifice in occupant comfort In a WSHP system that uses horizontal style heat pumps installed in a ceiling plenum zone size is sometimes limited by ple
149. e part load dehumidification humidity pull down mode An operating mode for transition from the unoccupied mode to the occupied mode in which the HVAC system operates to lower the humidity inside the building to reach the desired occupied humidity setpoint by the time people enter the building IEEE Institute of Electrical and Electronics Engineers www ieee org IGSHPA International Ground Source Heat Pump Association www igshpa okstate edu Water Source and Ground Source Heat Pump Systems SYS APM 010 EN indirect fired burner A fuel burning device in which the products of combustion do not come into contact with the air stream being heated but are separated from the air stream through the use of a heat exchanger infiltration Leakage of air into a building or space through cracks crevices doors windows or other openings caused by wind pressure or temperature difference integrated economizer mode An operating mode of an airside economizer when the outdoor air is warmer than the current supply air temperature setpoint The outdoor air dampers remain wide open return air dampers are closed but the unit controller activates compressors to provide the balance of the cooling capacity needed to provide supply air at the desired setpoint interior zone A conditioned space that is surrounded by other conditioned spaces with no perimeter walls windows Typically requires some degree of cooling all year long to overcome the hea
150. eat exchangers adding an intermediate plate and frame heat exchanger offsets some or all of the performance advantage over a closed loop system Requires a method to re inject water into the ground or dispose of in a river or sewer system Typically subject to various local state and federal clean water and surface water codes and regulations 136 Ground coupled heat pump systems A ground coupled heat pump GCHP system uses a closed system of special high density polyethylene pipes that are buried in the ground at a depth that takes advantage of the earth s relatively constant temperature using the ground as the heat rejecter and heat adder Figure 88 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Variations Figure 88 Ground coupled heat pump system heat pumps water circulating pumps ground heat exchanger Most GCHP systems do not actually get rid of heat they store it in the ground for use at a different time During the cooling season heat rejected by the heat pumps causes the loop temperature to increase As the fluid flows through the buried pipes heat is transferred from the warm fluid to the cooler ground In a sense the heat is stored in the earth for use at a later time Conversely during the heating season heat extracted by the heat pumps causes the loop temperature to decrease The cool fluid flowing through the buried pipes extracts the stored heat f
151. eat in the WSHP boiler less system p 57 coordination of compressor and electric heater operation should be handled by the unit level controller to prevent simultaneous cooling and heating which wastes energy and is prohibited by many building energy codes In this configuration a temperature sensor is installed on the entering water pipe of the WSHP The heat pump operates the compressor in normal heating mode until the temperature of the entering water drops below a pre determined low limit 559F 13 C for example At that time the compressor is disabled and the electric resistance heater is energized to provide heat to the zone When the loop temperature rises SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 161 S TRANE System Controls 162 again to 60 F 16 C for example the electric resistance heater is disabled and the heat pump compressor is again allowed to operate in the normal heating mode Economizer control The energy consumed by a WSHP system can often be reduced through the use of a waterside or airside economizer A waterside economizer can provide an inexpensive means of cooling when used in systems that require perimeter heating and interior cooling During cold weather the heat pumps serving interior zones often operate in the cooling mode because of the heat generated by lights people and office equipment Simultaneously the heat pumps serving perimeter zones may be operat
152. eat pumps and water circulating pumps reflect the effect of the antifreeze solution Metal pipes and heat exchangers that are exposed to antifreeze solutions are vulnerable to corrosion so appropriate inhibitors must be added to the solution to prevent corrosion Because these inhibitors can degrade over time itis important to conduct a periodic chemical analysis to maintain proper antifreeze and inhibitor concentrations In addition a minimum percentage of antifreeze may be required to minimize the potential for microbial growth Consult the fluid provider Winterize the cooling tower With this approach a closed circuit cooling tower installed outside is winterized by insulating the casing of the tower adding an ice proof damper in the tower discharge adding insulation and heat tape to all exposed water piping including the make up water line and spray pumps and adding a sump heater if the sump will not be drained during the winter The addition of insulation and discharge dampers significantly decreases the amount of heat loss from the tower during cold weather 48 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE Primary System Components If an open cooling tower is used the intermediate heat exchanger should be located inside the building This usually eliminates the need to protect the closed water distribution loop from freezing One of the following approaches is typically us
153. ed to protect the tower sump from freezing e Drain the tower sump during winter In some systems an automatic drain valve opens to drain the water from the tower sump when the outdoor temperature drops below a pre determined limit such as 35 F 2 C In other systems building maintenance personnel manually drain the tower sump when the weather begins to get cold In either case the sump should be inspected periodically to ensure that leaves and debris do not clog the sump drain If some zones require cooling when the tower sump is empty there needs to be enough heat pumps operating in the heating mode extracting heat from loop to keep the temperature of the loop from getting too warm e Locate the tower sump inside the building With this approach after the water drops through the tower fill it drains by gravity into the sump which is located inside the building Of course locating the sump inside requires extra floor space and the associated piping increases the system installed cost Note Ground coupled heat pump systems can also experience temperatures below freezing These systems are generally protected by adding antifreeze to the loop water See Ground coupled heat pump systems p 136 Natural heat sink Some WSHP systems use a natural heat sink such as the ground or a lake as the heat rejecter For more information on ground coupled surface water and ground water systems see System Design Variations
154. eded to respond to those complaints For this reason they usually take a very conservative approach starting the system very early and stopping it very late This can be costly from an energy perspective since the entire building may be operating to maintain occupied temperature setpoints even though only a few spaces are occupied Following are a few simple solutions to minimize comfort complaints and avoid wasting energy e Use aggressive scheduling and equip zone temperature sensors with timed override buttons If a person wants to use a space during a time when it has been scheduled as unoccupied they simply press the timed override button see Figure 118 and the BAS switches that zone into the occupied mode This returns the temperature to the occupied setpoint and delivers ventilation air to that zone Typically the BAS automatically returns this zone to the unoccupied mode after a defined fixed period of time two hours for example Using the timed override feature affords the opportunity to be more aggressive with time of day operating schedules This avoids wasting energy by starting and stopping the HVAC system based on typical usage and allowing the timed override feature to handle the worst case or once SYS APM010 EN Water Source and Ground Source Heat Pump Systems 179 S TRANE System Controls 180 a year scenarios Once occupants are educated about using the timed override feature energy savings and minim
155. el without needing to modify the rest of the system Ease of installation The fact that the same piece of equipment is used to provide cooling and heating to the zone and that all the components of the WSHP are pre assembled at a factory makes installation fairly simple And even though a separate cooling tower and boiler may be included in the system only one set of water pipes is required In addition using pre engineered factory installed and factory commissioned controls simplifies installation and commissioning and can result in faster system start up Scalable capacity add it as needed For speculative buildings such as commercial office buildings retail strip malls or high rise condominiums individual watersource heat pumps can be installed and connected to the water distribution loop as areas of the building are fit out for lease to a tenant Of course the water distribution loop cooling tower and boiler must be installed earlier in the project and must have adequate capacity to serve the entire system This not only improves cash flow for the developer but also provides flexibility to accommodate the specific needs of future tenants Opportunity for individual tenant metering Because each zone is served by a separate WSHP this system offers the opportunity to meter individual units and bill the tenant for the operating costs for their space only This often makes a WSHP system an attractive option for condo
156. ely clean This improves system performance by keeping the refrigerant to air heat exchanger cleaner for example and keeps the air distribution system relatively clean Airborne particulates vary in size ranging from submicron to 100 microns um and larger Many types of particulate media filters are available Some are designed to remove only large particles while others high efficiency particulate air HEPA filters for example also remove particles with diameters less than one micron Particulate filter efficiency is typically expressed in terms of dust spot efficiency or minimum efficiency reporting value MERV Dust spot efficiency is defined by ASHRAE Standard 52 1 and relates to the amount of atmospheric dust that a filter captures MERV is defined by ASHRAE Standard 52 2 and relates to how efficiently a filter removes particles of various sizes from 0 3 to 10 micron Table 2 identifies common types of particulate filters and their typical applications It also approximates equivalent dust spot efficiencies for the various MERV levels 22 Water Source and Ground Source Heat Pump Systems SYS APM 010 EN Table 2 Applications guidelines for various filter types S TRANE Primary System Components Collection Dust spot Typical controlled Typical applications and z e efficiency efficiency contaminant limitations Typical air filter cleaner type IEST Type F n a lt 0 30 um particles e Cleanrooms HEPA ULPA
157. ems Non condensing versus condensing boilers Hot water boilers are classified by whether they are condensing or non condensing A conventional non condensing boiler is designed to operate without condensing the flue gases inside the boiler Only the sensible heat value of the fuel is used to heat the hot water All of the latent heat value of the fuel is lost up the exhaust stack This avoids corrosion of cast iron or steel parts Hot water systems with non condensing boilers are often operated to ensure that the return water temperature is no lower than 140 F 60 C to prevent condensing A condensing boiler on the other hand uses a high efficiency heat exchanger that is designed to capture nearly all of the available sensible heat from the fuel as well as some of the latent heat of vaporization The result is a significant improvement in boiler efficiency Condensing gas fired boilers have combustion efficiencies that range from 88 percent to over 95 percent while non condensing boilers have combustion efficiencies that range from 80 percent to 86 percent Condensing of the flue gases also allows for a lower return water temperature much lower than the 140 F 60 C limit that is common with non condensing boilers In fact the efficiency of a condensing boiler increases as the return water temperature decreases Figure 36 To maximize the efficiency of a condensing boiler therefore it is important that the rest of the heating sys
158. en needed to ensure minimum flow S TRANE System Controls limit 30 F 1 C for example a compressor is cycled off allowing the surface of the heat exchanger to warm back up and avoid condensate from freezing on the surface When the refrigerant temperature rises back up above the limit plus a deadband the compressor is allowed to turn on again This condition is most likely to occur in the integrated economizer waterside or airside mode if cool outdoor air is brought in directly through the WSHP unconditioned by a dedicated OA unit or if the dedicated OA system delivers the conditioned OA at a cold temperature directly to the intake of each WSHP Safeties The unit level controller for a water source heat pump typically includes several safeties that protect the equipment from harm Common examples include e Minimum on and off timers to prevent rapid cycling of the compressor s e Cutouts to avoid refrigerant pressures that are too low or too high e A condensate overflow float switch that turns off the compressor and closes the OA damper if equipped to prevent the drain pan from overflowing in the event that the condensate drain line is plugged A freeze protection sensor to turn off the compressor if the water leaving the refrigerant to water heat exchanger approaches a temperature at which freezing will occur below 35 F 2 C for example These are just examples Specific details on safeties
159. ensation of water vapor on a cooling coil as it travels out of the drain pan for the purpose of preventing the passage of air through the drain line condenser The component of the refrigeration system where refrigerant vapor is converted to liquid as it rejects heat to water or air condensing boiler A type of boiler that uses a high efficiency heat exchanger designed to capture nearly all of the available sensible heat from the fuel as well as some of the latent heat of vaporization The result is a significant improvement in boiler efficiency condensing pressure Pressure of the refrigerant vapor when it condenses into a liquid connected load The sum of the capacities of all heat pumps installed in the system constant volume system A type of airconditioning system that varies the temperature of a constant volume of air supplied to meet the changing load conditions of the zone controller The component of a control loop that compares the measured condition of the controlled variable to the desired condition Setpoint and transmits a corrective output signal to the controlled device cool down mode See morning cool down mode cooling tower An enclosed device for evaporatively cooling water by contact with air COP A dimensionless ratio of the rate of heat removal to the rate of energy input in consistent units for a complete refrigerating system or some specific portion of that system under designated operating condi
160. equires review of the electrical system before itis installed so that appropriate steps can be taken When necessary it is possible to alter the design of the system by oversizing the neutral wire for example and or reduce motor generated harmonics by adding a harmonic filter for example Water Source and Ground Source Heat Pump Systems SYS APM 010 EN SYS APMO010 EN S TRANE Primary System Components Multiple speed fan operation When the heat pump includes a two stage variable capacity or variable speed compressor or if itincludes more than one compressor the opportunity exists to use the ECM to change fan speeds at part load conditions For example when a two stage compressor or a heat pump with two compressors operates at 100 percent capacity the controller operates the fan at high speed but when the compressor operates at reduced capacity 67 percent for example the controller operates the fan at some reduced speed However in a heat pump equipped with a variable speed compressor as the load decreases the controller reduces fan speed at the same time that compressor capacity rotational speed is reduced Figure 18 Figure 18 Variable speed fan with a variable speed compressor 100 80 variable speed fan a 60 5 2 variable speed a compressor 40 p 20 design heating load space load design cooling load Note Assumes continuous not cycled fan operation In addition to reducing fa
161. er modulates its capacity to supply hot water at the desired temperature typically between 140 F 60 C and 180 F 82 C and the mixing valve modulates to blend in some of this hot water from the boiler to keep the loop temperature above the lower setpoint 172 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE System Controls Figure 115 Boiler control using a three way mixing valve hot water boiler boiler mixing valve water circulating pumps This piping configuration is simple and is suitable for a wide range of packaged boilers For example non condensing boilers require that the return water temperature be no lower than 140 60 C to prevent condensing Since the loop water temperature is well below this limit this decoupled piping configuration diverts hot water leaving the boiler and mixes it with cooler water from the loop to keep the temperature of the water entering the boiler warm enough to prevent condensing and minimize the risk of boiler shock When variable flow pumping is used it may be necessary to ensure constant water flow through the boiler to prevent the leaving water temperature from getting too hot This piping configuration employs a small constant volume pump and bypass line to decouple the constant flow boiler from the variable flow water distribution loop Figure 115 Sensor location can be critical for proper boiler control Ensure that the
162. er that is sprayed over the tubes is kept separate from the water that flows inside the tubes and through the refrigerant to water heat exchangers of the individual heat pumps This prevents clogging corrosion and scaling inside the WSHP heat exchangers A primary advantage of this configuration is that the tower is a single factory assembled package Unlike an open cooling tower the heat exchanger and circulating pump are an integral part of the tower so there is no need to design and install an intermediate heat exchanger or separate pump and piping to pump water through the intermediate heat exchanger and cooling tower see Figure 34 Another advantage is the fan in a closed circuit cooling tower is typically capable of generating higher static pressures than open towers This provides the opportunity to install the tower indoors reducing the risk of freezing and minimizing heat loss during cold weather see Freeze protection p 46 In an open cooling tower relatively warm water is sprayed over the fill inside the tower while a fan draws outdoor air upward through the fill Figure 34 The movement of air through the spray causes some of the water to evaporate a process that cools the remaining water before it falls into the tower sump This cooled water is pumped from the sump through a separate heat exchanger where heat is transferred from the warm water returning from the heat pumps to the cooler water coming from the coolin
163. et one of the exceptions listed in the standard When required the exhaust air energy recovery device must result in a change in the enthalpy of the outdoor air supply equal to 50 percent of the difference between the outdoor air and return air enthalpies at design conditions SYS APM010 EN Water Source and Ground Source Heat Pump Systems 121 S TRANE System Design Issues and Challenges 122 However like other requirements in the standard there are several exceptions provided The following exceptions are the most likely to apply to a typical WSHP system e Exception h If the building has been designed with multiple exhaust locations where the largest source of air exhausted at a single location in the building is less than 75 percent of the design outdoor airflow exhaust air energy recovery is not required This exception acknowledges the impracticality of recovering heat from multiple exhaust sources for a single outdoor air intake e Exception i Ifthe dedicated OA system is needed for dehumidification as would bethe case in a climate that experiences humid weather and the dedicated OA unit includes an air to air heat exchanger than is configured in series with wrapped around the cooling coil the system is not required to also provide exhaust air energy recovery The series configuration relies on the warm entering outdoor air to be the source of heat that is transferred to reheat the cold dehumidified air downstre
164. ey likely have drilled or trenched in soil conditions similar to those of the project site System design variables can be changed to reduce the installed cost of a ground coupled heat pump system Table 28 However these changes are not without side effects Changing a system design variable often impacts the energy use or some other aspect of system operation Table 28 Impact of various ground heat exchanger design decisions System design variable Impact on installed cost Other impacts Increase the upper temperature limit for water entering the GSHP during cooling mode Reduces the required length of the ground heat exchanger GSHP will be less efficient during cooling mode Decrease diameter of U tube piping Reduces the cost of the ground heat exchanger Increases the required length of the ground and simplifies installation heat exchanger Increase the separation distance between boreholes Reduces the required length of the ground heat Increases the amount of land required and exchanger increases length of header piping Install a cooling tower to supplement heat rejection hybrid ground coupled system Reduces the required length of the ground heat Requires seasonal maintenance and operation exchanger of the cooling tower uses energy Assume movement of groundwater in design of ground heat exchanger Reduces the required length of the ground heat Requires hydrological survey to confirm or r
165. filters 2 99 999 on 0 1 to 0 2 um particles IEST Type D Virus unattached Carbon dust Radioactive materials Pharmaceutical n a manufacturin 2 99 999 on 0 3 um Seasalt as particles e All combustion smoke e Carcinogenic materials IEST Type C e Radon progeny e Orthopedic surgery 2 99 99 on0 3pm a particles IEST Type A 2 99 97 on 0 3 um n a particles MERV 16 n a 0 3 to 1 0 um particles e Hospital inpatient care Bag filters Nonsupported e All bacteria e General surgery flexible microfine fiberglass or MERV 15 gt 95 Most tob k Smoking synthetic media 12 to 36 in 300 o e Most to ccorsmo e e Smo ing ounges l to 900 mm deep 6 to 12 pockets e Droplet nuclei sneeze e Superior commercial m nae Box filters Rigid style cartridge MERV 14 90 to 95 e Cooking oil buildings filters 6 to 12 in 150 to e Most smoke 300 mm deep may use lofted MERV 13 80 to 90 e Insecticide dust air laid or paper wet laid e Copier toner media e Most face powder e Most paint pigments MERV 12 70 to 75 1 0 to 3 0 um particles e Superior residential Bag filters Nonsupported e Legionella buildings flexible microfine fiberglass or MERV 11 60 to 65 e Humidifier dust e Better commercial buildings synthetic media 12 to 36 in 300 x x to 900 mm deep 6 to 12 pockets e Lead dust e Hospital laboratories F f Box filters Rigid style cartridge MERV 10 50 to 55 e Milled flour filters 6 to 12 in 150 to e Coal
166. frequently and when it does occur that the system flow rate will likely be relatively low assuming variable flow pumping is used So any pump energy savings is minimal e Installing the bypass valve adds a risk that somebody will control it improperly in the future e Keeping the fluid flowing through the ground heat exchanger helps even out the ground temperature throughout the borefield which improves system performance over the long term 182 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Controls Preheat for moming warm up On a Monday morning following a cold weekend the temperature in many zones of the building may have drifted so that a large number of the WSHPs will need to operate in morning warm up mode prior to occupancy To avoid overwhelming the boiler the loop water temperature can be preheated above the lower setpoint before the system enters the occupied mode Figure 122 Figure 122 Loop preheat 100 scheduled occupied hours 9 mp upper supply w setpoint g 8 y 80 2 D w gt 70 Q 2 loop water temperature a ie 2 60 a as cal a lower supply setpoint 50 6 a m Noon 6 p m To avoid the unnecessary use of energy during mild weather the system level controller can be used to disable the loop preheat sequence if the outdoor temperature is warm above 40 F 4 C for example Precool loop for moming cool do
167. g thermostat control system level controller water source heat pump P gt gt ain communicating thermostat e em 00000 20000 o0000 This configuration allows basic information about the zone to be shared with a centralized system level controller For example any zone can request after hours operation of the system to maintain setback temperatures and the system level controller can be used to centralize system scheduling However since the individual unit controllers do not communicate with the system level controller this approach does not provide for centralized alarms troubleshooting or trend logging of equipment operation e Networked unit controllers with zone sensors Achieve more functionality including the potential for greater energy savings by using a communicating controller on each WSHP All the controllers are connected to a network communicating with a centralized system level controller Figure 106 The unit controllers may be more expensive but the zone temperature sensors will likely be less expensive than either communicating or non communicating thermostats SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 159 eS TRANE System Controls Figure 106 Networked unit controllers with zone sensors Wireless communications eliminates the wires between the zone temperature
168. g tower This intermediate heat exchanger is used to keep the two water loops separate preventing clogging corrosion and scaling inside the refrigerant to water heat exchangers of the individual heat pumps Figure 34 Open cooling tower with intermediate heat exchanger O NN N f 2 lt T n a a TA i N 7 ji propeller fan water distribution Ea loop outdoor alr gt Sigs sump tower circulating plate and frame heat pump exchanger A primary advantage of this configuration is that the cooling tower can be located outside while the heat exchanger is located inside This still reduces the risk of freezing and minimizes heat loss during cold weather because only the tower sump must be protected from freezing see Freeze protection p 46 Less space inside the building is required to house the heat exchanger than to accommodate a closed circuit cooling tower Water Source and Ground Source Heat Pump Systems 43 E TRANE Primary System Components Another advantage is an open cooling tower typically uses less fan energy than a closed circuit tower However this configuration requires design and installation of an intermediate heat exchanger and a separate pump and piping to pump water through the intermediate heat exchanger and open cooling tower Sizing the cooling tower Because all heat pumps on the loop are not likely to be operating in the cooling mode at the exact same time the coolin
169. g tower should be sized to account for system load diversity The 2008 ASHRAE Handbook HVAC Systems and Equipment p 8 17 defines system load diversity as the maximum instantaneous cooling load of the system divided by the installed cooling capacity For a WSHP system the installed cooling capacity is the sum of all the individual heat pump cooling capacities Table 6 shows an example eight zone WSHP system serving a small office building This system is comprised of 15 heat pumps connected to a common water distribution loop Table 6 Sizing the cooling tower for a WSHP system example office building Nominal cooling Water flow rate Heat rejected to loop capacity tons kW gpm L s tons kW South offices 5 18 15 0 95 5 8 20 West offices 5 18 15 0 95 5 8 20 South conf room 2 4 ton 14 kW 24 1 5 9 1 32 East offices 5 18 kW 15 0 95 5 8 20 South interior offices 4 5 ton 18 kW 60 3 8 23 81 North interior offices 4 5 ton 18 kW 60 3 8 23 81 North offices 4 14 12 0 76 4 5 16 North conf room 5 18 15 0 95 5 8 20 Sum 72 250 216 13 7 83 290 Assumes 90 F 32 C entering water temperature 1520 cfm 0 72 m3 s of airflow for each 4 ton 14 kW unit and 1700 cfm 0 80 m3 s for each 5 ton 18 kW unit entering air conditions of 77 F 25 C dry bulb and 63 F 17 C wet bulb and 0 5 in H2O 125 Pa of external static pressure loss Foll
170. guration where the fan is located downstream and draws air through the cooling coil dust spot efficiency A rating value defined by ASHRAE Standard 52 1 that depicts the amount of atmospheric dust a filter captures Water Source and Ground Source Heat Pump Systems SYS APM 010 EN SYS APMO10 EN ECM Electronically commutated motor A brushless DC motor that combines a permanent magnet rotor wound field stator and an electronic commutation assembly to eliminate the brushes EER Energy Efficiency Ratio The ratio of net cooling capacity in Btu hr to total rate of electric input in watts at any given set of rating conditions in watts per watt electronic air cleaner Particulate filter that uses electrostatic attraction either passively charged electret or actively charged electrostatic precipitators to enhance collection efficiency Energy Star A program administered by the U S Environmental Protection Agency and Department of Energy that helps reduce energy costs and protect the environment through energy efficient products and practices www energystar gov enthalpy Describes the total amount of heat energy both sensible and latent in one pound of air at a given condition enthalpy wheel See total energy wheel equal friction duct design method A method of designing an air duct system that results in an equal static pressure drop per foot meter of duct Equal friction duct systems can be easily designed
171. h Open Office Area and South Open Office Area require 10 tons 35 kW each the grouping of private offices along the west side of the building require a total of 8 tons 28 kW and the grouping of rooms in the core of the building require a total of 12 tons 42 kW Figure 8 Heat recovery in a VRF system S TRANE Overview of a Water Source Heat Pump System With a maximum size for a heat recovery outdoor unit of 20 tons 70 kW the East Open Office Area would be served by a dedicated system refrigerant circuit While heat can be transferred between the many indoor VRF terminals connected to that 20 ton 70 kW outdoor unit it cannot be transferred to zones that are not served by that system In this example the most likely implementation of heat recovery would be to connect the indoor VRF terminals serving the group of offices on the west side of the building and those serving the rooms in the core of the building to a common heat recovery outdoor unit When the VRF terminals serving the interior zones operate in the cooling mode the heat rejected can be used for heating the offices along the west perimeter While this would provide some energy savings heat recovery is only applied to 43 percent of total floor area The big difference between a WSHP system and a VRF system is that a WSHP system can recover heat from any zone in the building and use it in any other zone in the building AVRF system however can on
172. h it is scheduled to be unoccupied After a fixed period of time two hours for example the zone automatically returns to unoccupied mode In addition an occupancy sensor can be used to indicate that a zone is actually unoccupied even though it is scheduled to be occupied This unoccupied signal can be used to switch the zone to an occupied standby mode in which all or some of the lights can be shut off and the temperature setpoints can be raised or lowered slightly And in some cases the outdoor air delivered to that zone can be reduced When the occupancy sensor indicates that the zone is again occupied the zone is switched back to the normal occupied mode Water Source and Ground Source Heat Pump Systems SYS APM 010 EN SYS APMO010 EN S TRANE Overview of a Water Source Heat Pump System Seasonal operation of the water loop During warm weather when most or all of the heat pumps are operating in cooling mode heat removed from the air is transferred to the water loop This causes the temperature of the water in the loop to increase making it necessary to remove heat from the water Figure 5 A heat rejecter such as a closed circuit cooling tower or fluid cooler is used to reject heat from the loop maintaining a leaving water temperature of approximately 90 F 322C Figure 5 System operation during warm weather summer cooling tower on water circulating D pumps on 90 F
173. he cooling season The total energy wheel cools and dehumidifies the entering outdoor air to 76 F dry bulb and 63 F dew point 24 C DB and 17 C DP by transferring both sensible heat and water vapor to the exhaust air stream The cooling coil then dehumidifies the air to the desired leaving air dew point of 52 F 11 C When necessary the fixed plate heat exchanger transfers sensible heat recovered from the exhaust air stream to reheat the dehumidified air to 70 F dry bulb and 52 F dew point 21 C DB and 11 C DP SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 79 eS TRANE Primary System Components Figure 56 Example performance of a dedicated OA unit with total energy recovery and a fixed plate HX 180 t bulb t F 45 wet pu emperature 160 40 140 amp 3 2 e oa 120 lt lt a AEA 100 Q 2 80 z 60 9 Qa lt 15 40 20 0 30 40 50 60 70 80 90 100 110 dry bulb temperature F By using heat recovered from the exhaust air stream the fixed plate heat exchanger pre cools the air entering the exhaust side of the wheel This increases the heat recovery capacity of the wheel resulting in more pre cooling of the entering outdoor air and less cooling energy required f f 7 3 As another example the air handling unit depicted in Figure 57 includes a For more information on using a series 7 f desiccant wheel inma dedicatediOA total energy wheel and a series desiccant wheel used for improved sy
174. he heat pump when the compressor is operating as the overall system flow rate and pressure change see Isolation valves and flow control devices p 39 Note In a ground source heat pump system consider installing a bypass valve and pipe to avoid pumping water through the ground heat exchanger whenever the temperature of the loop is within the desired range Figure 121 p 182 This lowers the pressure drop that the pump must overcome and reduces pump energy use 34 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Because it is unlikely that all compressors will need to operate simultaneously water does not need to flow through all heat pumps simultaneously This zone by zone load variation throughout the day called system load diversity see sidebar on p 45 affords the opportunity to downsize the water circulating pumps Table 6 p 44 shows an example eight zone WSHP system serving a small office building This system is comprised of 15 water source heat pumps totaling 72 tons 250 kW of installed cooling capacity connected to a common waterdistribution loop For this example system the load calculation software indicates the block cooling load to be 61 tons 210 kW so system load diversity is 0 85 D 61 72 tons or 210 250 kW If constant flow pumping is used the watercirculating pumps must be sized to deliver the sum of the individual heat pump wa
175. he outdoor airflow that must be delivered to the breathing zone Vbz using the prescribed rates in Table 6 1 of the standard 2 Determine the zone airdistribution effectiveness Ez which depends on the location of supply air diffusers and return air grilles using the default values in Table 6 2 of the standard 3 Calculate the outdoor airflow required for the zone typically at the supply air diffusers by dividing the breathing zone outdoor airflow by the zone air distribution effectiveness Voz Vbz Ez Minimum ventilation required in breathing zone Vpz Table 6 1 of ASHRAE 62 1 prescribes two ventilation rates for each occupancy category one for people related sources of contaminants and another for building related sources For step 1 determine the occupancy category for the zone using Table 6 1 and identify the corresponding ventilation rates The people related ventilation rate Rp is quantified in terms of cfm person L s person and the building related ventilation rate Ra is quantified in terms of cfm ft2 L s m2 Then determine the number of people expected to occupy the zone during typical usage Pz and the occupiable floor area Az Finally solve the following equation to find the minimum outdoor airflow required for the breathing zone Vpz Vbz Rp xPz Ra XAz SYS APM010 EN Water Source and Ground Source Heat Pump Systems 91 E TRANE System Design Issues and Challenges Figure 64 Impact of zone air
176. he requirement to employ demand controlled ventilation DCV attempts to reduce system intake airflow during periods of partial occupancy When intake airflow is reduced exhaust air energy recovery provides less benefit SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 119 E TRANE System Design Issues and Challenges 120 e Exception c Small systems in which the design system level intake airflow is less than 1200 cfm 0 6 m3 s are exempt from this requirement e Exception d Small zones in which the design supply airflow is less than 1200 cfm 0 6 m3 s are also exempt from the DCV requirement WSHP distribution loop design and control ASHRAE 90 1 contains several requirements that impact the design and control of the water distribution loop When the water loop of a WSHP system contains both a heat rejecter such as a cooling tower and a heat adder such as a hot water boiler Section 6 5 2 2 3 requires that the temperature deadband used for loop temperature control must be at least 20 F 12 C For example if the boiler is activated whenever the loop water temperature drops below 60 F 15 6 C the cooling tower cannot be activated until the loop water temperature rises to at least 80 F 26 6 C A smaller temperature deadband is allowed however if a system level controller is used to optimize loop temperature control to minimize overall system energy use based on real time operating conditions see
177. heat exchanger drops below a preset rejected to the ground and heat so z P p A acon Sai hoh Ge Sn NEY lower limit 25 F 4 C for example the boiler is activated to provide have been balanced when originally supplemental heat designed After years of operating with such an imbalance the result of the increased cooling loads will likely be a warmer fluid temperature returning from the ground heat exchanger during the cooling season By installing a small heat rejection device and operating it at night or in the spring or fall the excess cooling load can be rejected restoring the balance between heat rejected to the ground and heat extracted SYS APM010 EN Water Source and Ground Source Heat Pump Systems 151 S TRANE System Design Variations For more information on the design and layout of surface water heat pump systems refer to the ASHRAE manual Ground Source Heat Pumps Design of Geothermal Systems for Commercial and Institutional Buildings submerged heat exchanger Surface water heat pump systems Rather than burying the heat exchanger underground a surface water heat pump SWHP system submerges the heat exchanger in a pond or lake Figure 100 In a cooling dominated application a moderately sized pond or lake can provide enough heat rejection and heat addition to maintain proper temperatures in the water loop without the need for a cooling tower or boiler Figure 100 Surface water heat pump system
178. heat pump includes a two stage variable capacity or variable speed compressor or if it includes more than one compressor there may be an opportunity to automatically change fan speeds at part load conditions see Adjustable fan speed p 103 SYS APMO010 EN S TRANE System Design Issues and Challenges Figure 67 Part load dehumidification cycling compressor constant speed fan sensible Re evaporation provides sensible cooling as coil surface warms O Time delay before condensate falls into drain pan Moisture re evaporates from coil surface Ime minutes Source Shirey D H Henderson and R Raustad 2003 DOE NETL Project DE FC26 01NT41253 Notice that several minutes elapse after the compressor starts before the water vapor that condenses on the coil surface actually falls into the drain pan below The droplets of condensation on the coil fins must accumulate enough mass for gravity to overcome surface tension and fall into the drain pan When the compressor stops sensible cooling drops off dramatically meanwhile latent cooling dehumidification not only falls to zero but actually becomes negative As the fan continues to operate condensate on the coil surface re evaporates into the supply air stream water vapor is added to the air stream not removed This evaporation takes some time during which the evaporation has the effect of sensibly cooling the air Figure 68
179. his mixture is then either cooled or heated by the WSHP before it is supplied to the zone Assuming negligible duct leakage all intake air reaches all supply diffusers so the system intake airflow at the dedicated OA unit must equal the sum of the zone outdoor airflows Vot Voz For this example at the cooling design condition the required system outdoorair intake flow Vot is 3100 cfm 146 m s Table 14 100 OA system ventilation calculations for example office building cooling design Rp cfm p Pz qty Ra cfm ft Az ft2 Vbz cfm Ez E Voz cfm South offices 5 18 0 06 2000 210 1 0 210 West offices 5 20 0 06 2000 220 1 0 220 South conf room 5 30 0 06 3000 330 1 0 330 East offices 5 20 0 06 2000 220 1 0 220 South interior offices 5 50 0 06 10000 850 1 0 850 North interior offices 5 50 0 06 10000 850 1 0 850 North offices 5 16 0 06 2000 200 1 0 200 North conf room 5 20 0 06 2000 220 1 0 220 System totals ce Voz 94 Water Source and Ground Source Heat Pump Systems SY S APM 010 EN S TRANE System Design Issues and Challenges When a WSHP is operating in the heating mode it will likely be supplying air to the zone at a temperature that is warmer than the zone As mentioned earlier supplying warm air to the zone through ceiling mounted diffusers may result in a zone air distribution effectiveness Ez that is less than 10 How does this impact system intake airflow Table 15
180. ibed in Dedicated OA system configurations p 59 conditioned outdoor air CA is then either 1 Ducted directly to each zone 2 Ducted to thesupply side of each WSHP where it mixes with supply air from the heat pump before being delivered to the zone 3 Ducted to the intake of each WSHP where it mixes with recirculated air from the zone 4 Ducted to the ceiling plenum near the intake of each WSHP where it mixes with recirculated air from the zone before entering the WSHP In any of these configurations since the outdoor air is delivered to each zone or to each zone level WSHP this is not considered a multiple zone recirculating ventilation system Rather it is considered a 100 percent outdoor air system because one unit delivers only outdoor air to one or more ventilation zones Accordingly per Section 6 2 4 of ASHRAE 62 1 the system level intake airflow Vot delivered by the dedicated OA unit should be the sum of the calculated zone outdoor airflows Voz Vot 2 Voz Figure 65 shows an example eight zone office building The three step zone level ventilation calculations have already been completed Table 14 see Zone level ventilation requirements p 91 In this case each zone is served by a water source heat pump and outdoor air is delivered directly to the intake of each ceiling mounted heat pump by a dedicated OA unit The preconditioned outdoor air mixes with locally recirculated air from the zone and t
181. ic pressure 0 in H20 0 Pa 0 in H20 0 Pa 0 in H20 0 Pa Liquid flow rate specified by the manufacturer Entering liquid temperature 86 F 30 C 77 F 25 C 59 F 15 C Heating mode Airflow rate specified by the manufacturer Entering air dry bulb temperature 68 F 20 C 68 F 20 C 68 F 20 C Entering air wet bulb temperature 59 F 15 C 59 F 15 C 59 F 15 C External static pressure 0 in H20 0 Pa 0 in H20 0 Pa 0 in H20 0 Pa Liquid flow rate specified by the manufacturer Entering liquid temperature 68 F 20 C 32 F 0 C 50 F 10 C Notice that neither the airflow rate nor the liquid flow rate is specified by the standard Rather they are left to the discretion of the manufacturer Since these factors can significantly impact the performance of a WSHP use caution when comparing the performance of one manufacturer to another As an example one manufacturer s 3 ton 11 kW heat pump may be rated at a liquid flow rate of 8 4 gpm 0 53 L s while another manufacturer may rate the same size unit using 9 gpm 0 57 L s The heat pump will operate more efficiently with the higher flow rate but system pumping energy will also increase While the 0 6 gpm 0 04 L s difference in this example may seem small this 7 percent increase in flow adds up when you consider that the system may be comprised of 5
182. ikely be more efficient to allow the heat pumps to operate in the heating mode e Monitor loop water temperature and modulate reheat capacity to avoid activating the boiler Ifthe cold conditioned outdoor air causes only afew heat pumps to operate inthe heating mode they will extract heat from the water loop reducing the amount of heat that must be rejected by the cooling tower This likely improves system efficiency rather than degrading it In addition the remaining zones where the heat pumps are operating in the cooling mode continue to benefit from the sensible cooling provided by the cold conditioned outdoor air However if enough heat pumps are operating in the heating mode that the temperature of the water loop approaches the lower setpoint 60 F 16 C for example and the source of reheat energy in the dedicated OA unit is recovered from another part of the system hot gas reheat or an air to air heat exchanger for example it will likely be more efficient to reheat the dehumidified outdoor air to avoid the need to activate the hot water boiler For an application in which very few zones require cooling during the colder months of the year it may be desirable to heat the outdoor air to a temperature near the desired zone temperature before delivering it directly to the zones Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE System Controls Loop temperature optimization
183. iler as the heat adder is to install an electric resistance heater in the WSHP Figure 39 or in the downstream ductwork In this configuration the heat pump operates the compressor in normal heating mode until the temperature of the water loop drops below a pre determined low limit 55 F 132C for example At that time the compressor is disabled and the electric resistance heater is energized to provide heat to the zone Figure 39 Electric resistance heat in WSHP for a boiler less system water loop electric strip heater In a cooling dominated application it is likely that many heat pumps in the system will still be operating in the cooling mode adding heat to the water loop When the loop temperature rises again to 60 F 16 C for example the electric resistance heater is disabled and the heat pump compressor is again allowed to operate in the normal heating mode Table 9 summarizes the advantages and disadvantages of this boilerless approach SYS APM010 EN Water Source and Ground Source Heat Pump Systems 57 Se TRANE Primary System Components Table 9 Advantages and disadvantages of a boiler less WSHP system Advantages Disadvantages Electric resistance heaters in the WSHPs typically result in a lower installed cost than a centralized boiler Avoids space required to install a centralized boiler Affords the opportunity to bill each tenant for all electricity used
184. includes calculations for this same example system at the heating design condition with several zones having a zone air distribution effectiveness of 0 8 For this example at the heating design condition the higher required zone outdoor airflows Voz increase the required system outdoor air intake flow Vot to 3450 cfm 163 m s Table 15 100 OA system ventilation calculations for example office building heating design Rp cfm p Pz qty Ra cfm ft2 Az ft2 Vbz cfm Ez Voz cfm South offices 5 18 0 06 2000 210 0 8 263 West offices 5 20 0 06 2000 220 0 8 275 South conf room 5 30 0 06 3000 330 0 8 413 East offices 5 20 0 06 2000 220 0 8 275 South interior offices 5 50 0 06 10000 850 1 0 850 North interior offices 5 50 0 06 10000 850 1 0 850 North offices 5 16 0 06 2000 200 0 8 250 North conf room 5 20 0 06 2000 220 0 8 275 System totals ne Z Voz Figure 66 Hotel guest room with outdoor air drawn in from a conidor exhaust air restroom corridor induced outdoor air for ventilation SYS APM010 EN guest room Consider however if the dedicated OA system was designed to deliver conditioned OA directly to each zone through separate ventilation diffusers at either a cold or neutral air temperature Since outdoor air is not delivered to the zone by the WSHP which is used to provide heating for the zone the outdoor air does not need to be delivered
185. ing In addition to the pipe sizing methods described by the ASHRAE Handbook Fundamentals ASHRAE Standard 90 1 2010 defines a maximum water flow rate for various pipe sizes Table 5 The maximum allowable flow rate depends on the annual system operating hours and whether constant or variable flow pumping is used In order to use the variable flow variable speed column the system must include a two position isolation valve at each WSHP and a VFD on the water circulating pump Since the water circulating pumps in a WSHP system operate during both cooling and heating seasons the combined number of pump operating hours should be used Table 5 Maximum allowable flow rate for various pipe sizes gpm L s Annual system operating hours lt 2000 hrs yr gt 2000 and lt 4400 hrs yr gt 4400 hrs yr mmm ther E pee Other Var CPE sa Other TEE ee 2 V2 75 120 8 180 11 85 5 130 8 68 4 110 7 3 90 180 11 270 17 140 9 210 13 110 7 170 11 4 110 350 22 530 33 260 16 400 25 210 13 320 20 5 140 410 26 620 39 310 20 470 30 250 16 370 23 6 160 740 47 1100 69 570 36 860 54 440 28 680 43 8 225 1200 76 1800 114 900 57 1400 88 700 44 1100 69 10 280 1800 114 2700 170 1300 82 2000 126 1000 63 1600 101 12 315 2500 158 3800 240 1900 120 2900 183 1500 95 2300 145 For pipe sizes larger than 12 in 315 m
186. ing Such zones require cooling in the summer it is warm outside the sun is shining through the windows people are occupying the zone and the lights are turned on In the winter these zones can require heating to offset the heat loss through the exterior walls and windows even though some heat is generated in the zone by people lights and equipment Water Source and Ground Source Heat Pump Systems SYS APMO10 EN S TRANE System Design Issues and Challenges Interior zones are typically surrounded by other zones at the same temperature so they do not experience the same heat gain and heat loss fluctuations as a perimeter zone Therefore many interior zones require year round cooling due to the relatively constant amount of heat generated by people lights and equipment and the absence of heat loss through the building envelope Interior zones on the top floor of a building might need to be treated as a perimeter zone if they experience a significant amount of heat loss through the roof Optimizing the number of zones If a WSHP system is designed with too few thermal zones it may result in undesirable temperature variations in the areas that are farther away from the zone temperature sensor A smaller zone is typically better able to closely control temperature which contributes to better occupant comfort However increasing the number of independently controlled zones also raises the installed cost of the system Therefore th
187. ing dehumidification performance constant speed compressor on off If the dehumidification performance of a conventional heat pump in this basic constant volume mixed air configuration is not acceptable the system can be altered to enhance dehumidification performance Adjustable fan speed A WSHP that combines a multiple speed fan with a two stage variable capacity or variable speed compressor or more than one compressor reduces supply airflow at part load see Multiple speed fan operation p 21 This results in a lower supply air temperature and improves dehumidification Figure 73 Variable speed WSHP at In the previous classroom example the WSHP delivers 1 500 cfm 0 7 m s of part load unconditioned supply air to offset the design space sensible cooling load As the sensible OA cooling load in the space decreases the WSHP responds by simultaneously reducing fan speed and compressor capacity POF At the same example part load mild rainy day condition the reduced Ay 850 cfm 974 F supply airflow from 1 500 cfm 0 7 m s to 850 cfm 0 4 m s results in a zone lOWer supply air temperature than if a constant speed fan was used a ee a Figure 74 Reducing the airflow allows the coil to remove more moisture 695E WBT DA ee and lengthens the compressor runtime both of which improve the R D ral Fer aE dehumidification performance of the system At this condition the relative humidity in the space improves
188. ing in the heating mode extracting heat from the loop and lowering the water temperature This cool loop water can be circulated through a waterside economizer coil in a WSHP that serves an interior zone providing free cooling without the need to operate the heat pump compressor In the example shown in Figure 107 a temperature sensor is installed on the pipe entering the WSHP When the entering water temperature is below the economizer enable setpoint 50F 10 C for example the unit level controller positions a three way valve to divert the cool loop water through the waterside economizer coil to cool the entering air This water then passes through the refrigerant to water heat exchanger This piping configuration allows the economizer coil to be bypassed when not in use which reduces pump energy use It also allows the waterside economizer to operate in the integrated economizer mode whereby both the economizer and compressor are used simultaneously to satisfy the cooling load Figure 107 Waterside economizer in a horizontal WSHP refrigerant to water heat exchanger waterside economizer coil three way valve water loop airflow Water Source and Ground Source Heat Pump Systems SYS APM010 EN Unlike waterside economizers that are used with other types of HVAC systems the waterside economizer in a WSHP system requires no use of cooling tower energy to create the colder water for free cooling The
189. ing individual heat pumps to the loop piping Figure 32 Other hydronic accessories There are typically several other accessories included in the water distribution loop e A strainer is typically installed upstream of each water circulating pump to protect it from debris flowing inside the water distribution loop Figure 24 p 32 Strainers must be inspected and cleaned periodically to avoid pump cavitation or wasted pump energy use In some systems for example when each WSHP is equipped with an automatic or self balancing flow control valve it may also be desirable to install a strainer in the entering water pipe for each WSHP to protect the flow control valve from debris if SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 41 eS TRANE Primary System Components For more information on sizing the expansion tank refer to Chapter 12 Hydronic Heating and Cooling System Design in the 2008 ASHRAE Handbook HVAC Systems and Equipment www ashrae org e Air entrained in the loop water can separate and become pocketed inside the system during pump shutdown While proper piping design and venting can minimize air entrainment an air separator is typically installed upstream of the water circulating pump s to remove any air that does become entrained in the loop Figure 24 p 32 e An expansion tank accommodates the expansion and contraction of the water as temperature and therefore dens
190. ing mode this situation likely improves system efficiency As those heat pumps operating in the heating mode extract heat from the water loop they reduce the amount of heat that must be rejected by the cooling tower In addition the rest of the zones in which the heat pumps are still operating in the cooling mode continue to benefit from the sensible cooling provided by the cold conditioned outdoor air However if enough heat pumps are operating in the heating mode that the temperature of the water loop approaches the lower setpoint 60 F 16 C for example and the source of reheat energy in the dedicated OA unit is recovered from another part of the system hot gas reheat or an air to air heat exchanger for example it may be more efficient to reheat the dehumidified outdoor air to avoid the need to activate the boiler During cold weather it may be desirable to heat the outdoor air to a temperature near the desired zone temperature before delivering it directly to the zones SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 69 eS TRANE Primary System Components Figure 49 Total energy wheel in a 70 dedicated outdoorair unit In applications where zone sensible cooling loads differ greatly at any given time In hotel guest rooms or dormitories the sensible cooling loads can be drastically different from zone to zone The result is that if the conditioned OA is delivered cold it may be more like
191. ing mode may cause the loop water temperature to drop to the point where the boiler must be activated The energy used by the boiler may exceed the energy saved by turning off the compressors and using the airside economizer in the heat pumps operating in cooling mode Therefore consider disabling the airside economizer if the temperature of the water loop drops too far below 65 F 18 C for example Hot gas reheat for humidity control As mentioned in Methods for improving dehumidification performance p 103 hot gas reheat can be a cost effective method of controlling zone humidity As long as the zone relative humidity is less than the desired upper limit 60 percent for example the WSHP operates in the standard cooling mode and the compressor cycles on and off to maintain zone temperature When the SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 165 S TRANE System Controls 166 humidity sensor indicates that the zone relative humidity is too high the reheat valve diverts hot refrigerant vapor from the compressor through the reheat coil Figure 110 This allows the compressor to keep operating to dehumidify the air while warming the supply air to avoid overcooling the zone Figure 110 Hot gas reheat for humidity control expansion device water loop refrigerant to air heat exchanger reheat coil reversing valve refrigerant to water heat exchanger reheat val
192. inimize airflow through the space between adjacent filters 24 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE Primary System Components Filter located in each water source heat pump In most WSHP configurations recirculated return air passes through a particulate filter to remove airborne particulate contaminants Locating these filters upstream of the refrigerant to air heat exchanger Figure 19 helps keep it cleaner for a longer period of time and allows the system to operate more efficiently Figure 19 Particulate filter installed in a horizontal WSHP i F water loop expansion device connections condensate drain line P puen Bian o pan E Y N ea compressor p 1 f 5 E A i N E 2 BS gt 4 2 25 oT Oo Pc E a vO oY 56 ow g x lt Dp v o Eo Ds DL Ep a og control box ooo a filter Lp reversing valve ASHRAE Standard 62 1 2010 Section 5 8 requires that a filter with a MERV rating of at least 6 be installed upstream of all wet surfaces including cooling coils In general this requirement can be met with standard throwaway or pleated filters see Table 2 p 23 To maintain the desired level of cleanliness and minimize system energy use never operate a WSHP without the filter in place especially during construction or renovation Filters used duri
193. ious safeties to protect the equipment In addition alarms and diagnostic messages assist the building operator or service personnel in responding to or preventing problems with the equipment While this section identifies many of the unit level control functions for the primary components of a WSHP system specific details should be obtained from the manufacturer of the equipment Extended discussions in this section will be limited to those unit level control issues that require decisions to be made by the HVAC system designer or system operator 160 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Controls Water source heat pump Typically each water source heat pump is equipped with a dedicated unit level controller This controller typically performs the following functions Zone temperature control A sensor in each zone measures the dry bulb temperature in that zone The unit level controller compares this measured temperature to the desired setpoint If the zone requires cooling the controller responds by cycling the compressor to match the changing cooling load in the zone As the cooling load decreases the compressor operates for a shorter period of time between cycles If the zone requires heating the controller activates the reversing valve to switch operation of the refrigeration circuit to the heating mode and then cycles the compressor to match the changing heating load in the zone
194. ir out of the conditioned space into the ceiling plenum or return duct system GSHP Ground source heat pump ground coupled system A type of ground source heat pump system that uses a closed system of looped polyethylene pipes that are buried in the ground in a vertical horizontal or spiral pattern ground heat exchanger A closed system of looped polyethylene pipes that are buried in the ground in a vertical horizontal or spiral pattern ground source system A type of watersource heat pump system that takes advantage of the earth s relatively constant temperature and uses the ground or surface water as the heat rejecter and heat adder ground water system A type of heat pump system that supplies water from a well directly to each heat pump and then returns it to the source or a drain field heat of compression Energy in the form of heat created from the pressurization of a refrigerant vapor by a compressor heat pump A device that transfers heat from one substance to another substance It includes the basic refrigeration components of a compressor condenser evaporator and expansion device The difference is that it can also reverse the refrigeration cycle to perform heating as well as cooling HEPA High efficiency particulate air filter hot gas reheat A process where hot high pressure refrigerant vapor is diverted from the compressor through a separate reheat coil located downstream of the cooling coil to improv
195. ired n trea ired 226 000 cfm 212 000 cfm 25000 cfm 24000 cfm BSR q q 12271 L s 5663 L s 2360 L s 1888 L s 6b 211000 cfm 25500 cfm 24500 cfm 23500 cfm 22500 cfm 21500 cfm 5191 L s 2596 L s 2124 L s 1652 L s 1180 L s 708 L s la 2a 3a 4a 5a 25500 cfm 24500 cfm 23500 cfm 22000 cfm 21000 cfm 20 cfm 6a 2596 L s 2124 L s 1652 L s 944 L s 472 L s 0 L s 7 8 22500 cfm 21000 cfm 20 cfm 20 cfm 20 cfm 20 cfm 1180 L s 472 L s 0 L s 0 L s 0 L s 0 L s Excerpt from Table 6 5 6 1 of ASHRAE Standard 90 1 2010 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org If outdoor air is brought directly into the WSHP as might be the case with a rooftop style model the percent of outdoor air would need to be at least 30 percent before exhaust air energy recovery might be required Then it depends on climate zone and design supply airflow In most WSHP systems however the outdoor air required for ventilation is typically conditioned and delivered by a dedicated 100 percent outdoorair system In this case for some climate zones 1a 2a 3a 4a 5a 6a 7 and 8 exhaust air energy recovery is required for any size dedicated OA system For the other climate zones the minimum system size for which energy recovery is required is relatively small The likely impact is that most dedicated OA units will be required to use exhaust air energy recovery unless they me
196. isks exchanger under performance of the heat exchanger Source Ground Source Heat Pumps Design of Geothermal Systems for Commercial and Institutional Buildings Table 4 12 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org 148 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Variations Hybrid ground coupled heat pump systems While eliminating both the cooling tower and boiler likely results in the For more information on the design and f i P controller hybrid Ground coupled heat greatest overall energy savings for many applications it requires a larger pump systems refer to the Energy Center and more expensive ground heat exchanger to account for the imbalance of Wisconsin publication Hybrid Ground between heat rejected to the ground and heat extracted Source Heat Pump Installations Experiences Improvements and Tools For example in a cooling dominated climate a large amount of heat must be rejected to the ground during the cooling season but a much smaller amount of heat is extracted from the ground during the heating season This imbalance can cause the temperature of the ground surrounding the heat exchanger to increase over time Conversely in a heating dominated climate a relatively small amount of heat is rejected to the ground during the cooling season but a much larger amount of heat must be extracted from
197. ity changes While closed or bladder type tanks can be located anywhere in the system they are typically installed upstream of the water circulating pump s where the water pressure is lowest Figure 24 p 32 Heat Rejection A heat rejecter is used to maintain the temperature of the water in the loop below a pre determined upper limit such as 909F 322C for a boiler tower WSHP system Cooling tower In a boiler ftower WSHP system the heat rejecter is typically either a closed circuit cooling tower or an open cooling tower with an intermediate heat exchanger Either method helps prevent the WSHP heat exchangers from getting clogged with debris In a closed circuit cooling tower Sometimes called a fluid cooler warm water from the water distribution loop travels through closed tubes inside the tower while air is drawn or blown over these tubes by a fan Figure 33 Water is pumped from the tower sump and sprayed over the tube surfaces As the air passes over the tubes it causes a small portion of the water on the outer tube surfaces to evaporate This evaporation process extracts heat cooling the water inside the tubes Figure 33 Closed circuit cooling tower fluid cooler outdoor air LE RRA SAS j water distribution loop lt spray pump 42 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE Primary System Components In a closed circuit cooling tower the wat
198. ive Air Cooling Equipment in the 2008 ASHRAE Handbook HVAC Systems and Equipment www ashrae org 82 Water Source and Ground Source Heat Pump Systems may be practical to recover the needed heat from the condenser of a water chiller A small inexpensive electric heater is another option Alternatively a total energy wheel can be added to the system Figure 57 and Figure 58 When high RH conditions occur the total energy wheel will transfer water vapor from the entering outdoor air OA to the exhaust air EA thus lowering the relative humidity of the air before it enters the regeneration side of the series desiccant wheel OA In such cases adding a total energy wheel reduces and often eliminates the need to add regenerative preheat Of course this requires exhaust air to be ducted back to the dedicated OA unit Evaporative cooling Using an evaporative process to cool the air can reduce the energy used by mechanical cooling equipment Any cooling energy saved is offset somewhat by the increased fan energy use as the evaporative media increases the airside pressure drop that the fan must overcome Direct evaporative cooling introduces water directly into the air stream usually with a spray or wetted media The water evaporates as it extracts heat from the passing air stream which lowers the dry bulb temperature of the air Evaporation of the water however also raises the dew point of the air Figure 59 Figure 59
199. kge K 0 24 If a fluid other than pure water is used these factors will be different 46 Water Source and Ground Source Heat Pump Systems If constant flow pumping is used in this example the system water flow rate is 216 gpm 13 7 L s and the cooling tower range is 79 F 4 4 C Range 24 x71 tons 216 gpm 7 9 F Range 0 24 x 250 kW 13 7 L s 4 4 C If variable flow pumping is used the sum of the individual heat pump water flow rates is multiplied by system load diversity D and range is calculated using 184 gpm 116 L s as the system water flow rate 216 gpm x 0 85 or 13 7 L s x 0 85 In this case the resulting cooling tower range is 9 3 F 5 2 C Range 24 x71 tons 184 gpm 9 3 F Range 0 24 x 250 kW 16 L s 5 2 C Note Even if system load diversity has not been used to downsize the water circulating pumps and piping in a variable flow system it is important to apply diversity to the water flow rate used to select the cooling tower This avoids selecting a larger than necessary tower The fourth step is to use the manufacturer s catalog or selection software to select the cooling tower using the design outdoor wet bulb temperature the system water flow rate the design leaving water temperature and the calculated range For this example system assuming variable flow pumping is used the cooling tower should be selected based on e Design ambient wet bulb temperature 78 F 26 C e Design
200. l allow it to be used for either cooling or heating Geothermal Systems SYS APM009 EN A water to water heat pump is a small reversible cycle water chiller that contains one or more compressors a thermal expansion valve a reversing valve and two refrigerant to water heat exchangers see Figure 22 p 29 Figure 52 depicts a water to water heat pump which is connected to the water distribution loop serving an airhandling unit that conditions all of the outdoor air required for ventilation This system uses a dedicated water circulating pump Ps to draw water from the main loop Figure 52 Water to water heat pump connected to loop loop return loop supply PS source side heat load side heat exchanger exchanger When it is hot or humid outside cold water leaving the load side refrigerant to water heat exchanger is pumped through the cooling coil in the AHU to cool and or dehumidify the entering outdoor air Figure 53 and Table 12 p 79 Water from the loop flows through the source side heat exchanger to extract heat rejected from the heat pump SYS APMO010 EN Water Source and Ground Source Heat Pump Systems 77 Se TRANE Primary System Components g a S 2 a 8 78 loop supply loop supply Figure 53 Operation of water to water heat pump in cooling mode 74 F DB 23 C DB 52 F DP aico 2000 cfm 0 94 m3 s 84 F DB 29 C DB 76 F DP 24 C DP VR Ki 95 9 F
201. lating dampers to reduce fan airflow This approach not only provides freeze protection but results in closer temperature control and less tower fan energy use In addition for projects where a small part of the building needs to operate before the remainder of the building is completed the tower can operate at reduced heat rejection capacity without excessive cycling of the fan Loss of flow protection is very important in a system with a closed circuit cooling tower that is not protected by antifreeze If the pump fails the water remaining inside the tower heat exchanger can freeze rapidly Therefore it is essential that the controls respond quickly to protect the tower from freezing in the event of flow loss Open cooling tower Open cooling towers are usually controlled to achieve a desired leaving water sump temperature A typical sequence for controlling an open cooling tower Figure 114 is Stage 1 Start the tower circulating pump This circulates water from the sump through the intermediate heat exchanger If the temperature of the water in the sump is cooler than the water in the closed loop heat will be rejected from the loop After passing through the heat exchanger the sump water is sprayed over the fill inside the tower Air moves through the tower via natural convection and a small amount of heat will be rejected from the water No tower fan energy is used but the amount of heat rejected is limited typically to about
202. ling mode at the same time other units operate in the heating mode Because of these characteristics and the fact that these types of buildings can have drastically different occupancy patterns the use of rules of thumb should be avoided for commercial or institutional buildings as they can lead to severe oversizing or undersizing of the ground heat exchanger While some HVAC design engineers have developed their own rules of thumb for sizing the ground heat exchanger they are typically only applicable to a limited geographical area with similar weather conditions and soil types and to a specific type of building with similar occupancy patterns and distribution of loads Test project specific soil conditions Prior to finalizing the system design a test bore should be drilled to determine the actual soil thermal properties and drilling conditions at the project site For several reasons this is often the greatest cost saving task that can be performed First the actual drilling or trenching conditions can be described in the bid documents aiding the contractor in developing the most accurate bid Unknown soil conditions typically result in the contractor increasing the bid price as a safety margin Visiting the project site to drill a test bore also helps to determine how difficult it will be for heavy excavation or drilling equipment to access the site Second the thermal properties of the soil influence the necessary length
203. livered directly to the zone the sensible cooling load in the zone is unchanged so supply airflow is unaffected Figure 48 and the WSHP cannot be downsized Also since the local fan is tasked with delivering the outdoor air into the zone it cannot cycle off without interrupting ventilation Figure 48 Conditioned OA delivered directly to the intake of each WSHP Classroom 101 450 cfm at 71 F 0 21 m3 s at 22 C 1380 cfm at 55 F 0 65 m3 s at 13 C Neutral Air r e a IOS System RO 450 cfm at 52 F a ae 0 21 m3 s at 11 C 1380 cfm at 55 F 0 65 m3 s at 13 C Cold Air E System 1380 cfm 0 65 m3 s SYS APM010 EN For many applications another approach to avoid overcooling is to implement demand controlled ventilation see Demand controlled ventilation p 188 This control strategy reduces the quantity of outdoor air delivered to a zone when there are fewer people in that zone This often avoids overcooling altogether and reduces the energy used to condition and deliver that air S TRANE Primary System Components If the conditioned OA is delivered at a cold temperature it lowers the enthalpy of the mixed air entering the WSHP thereby reducing the cooling load that must be offset by the heat pump compressor However the packaged nature of water source heat pumps means that they are typically only available with pre matched components fans compressors heat exchangers etc Thi
204. lounge rest storage office room central relief fan vestibule corridor conf room reception area office computer room elevators Direct control of building pressure requires a differential pressure sensor to monitor the indoor to outdoor pressure difference A common approach is to use an electronic transducer to convert the pressure difference into an electrical signal which is sent to the controller of the central relief fan Two sensing tubes one measuring indoor pressure and the other measuring outdoor pressure are attached to the transducer Proper location of these pressure sensing tubes is important e The indoor sensor is typically located on the ground floor because the effects of over or under pressurization are most noticeable at the external doors Many design engineers locate the sensor in a large open space near the door while others isolate the indoor sensor from the door ina central hallway for example to dampen the effect of rapid pressure changes caused by door operation In either location the indoor pressure sensor should include sufficient signal filtering to minimize the effects of high speed pressure changes Itis also important to avoid perimeter locations that can be influenced by wind induced pressure fluctuations e Many design engineers place the outdoor sensor on the roof of the building Others use multiple sensors one at each corner of the building at least 15 ft 4 6 m above the roof and ave
205. low rate of 90 gpm 5 7 L s dividing the U bends into three separate groups allows each group to be served by a 2 in 50 mm header pipe Figure 94 Some design engineers or contractors prefer to locate the isolation valves inside the building routing the separate header pipes from that location to each group of U tubes in the borefield as shown in Figure 94 Others prefer to locate the isolation valves in a vault or pit that is located near the borefield and then install a single larger set of pipes to connect the heat exchanger to the building loop 142 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Variations Centralized versus dedicated ground heat exchangers Many ground coupled heat pump systems are designed to connect all the heat pumps to a common water distribution loop which is then connected to a centralized or shared ground heat exchanger Figure 88 p 137 and Figure 94 p 142 However in one or two story buildings with large footprints an alternate approach could be to connect each heat pump to a dedicated ground heat exchanger Figure 95 In this case a small water circulating pump serves each heat pump and heat exchanger and turns on and off along with the compressor Using dedicated heat exchangers typically requires more overall length of pipe for the ground heat exchanger because this approach is not able to benefit from load diversity And it is more diffic
206. lternative approach is a strategy called optimal start The system level controller is used to determine the length of time required to bring each zone from its current temperature to the occupied setpoint temperature Then the controller waits as long as possible before starting the system so that the temperature in each zone reaches the occupied setpoint just in time for occupancy Figure 125 Figure 125 Optimal start optimal starting time occupied heating a setpoint ae scheduled Zong l occupied hours temperature unoccupied heating setpoint 6 a m Noon 6 p m The optimal starting time is determined using the difference between the actual zone temperature and the occupied setpoint temperature heating or cooling It compares this difference with the historical performance of how quickly the zone has been able to warm up or cool down Some systems also compensate for the current outside temperature SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 187 S TRANE System Controls For densely occupied zones demand controlled ventilation may be required by ASHRAE Standard 90 1 see Demand controlled ventilation p 119 This strategy reduces the number of system operating hours and saves energy by avoiding the need to maintain the indoor temperatures at occupied setpoint even though the building is unoccupied This may require many of the heat pumps to operate at full capacity simultaneously
207. ly and simplicity in design and installation especially when a packaged unit is used The selection and performance of the standalone unit is independent of the water source heat pumps and other components of the water distribution loop Additionally the dedicated OA unit can be operated to control indoor humidity after hours for example without requiring the pumps and possibly the boiler or cooling tower to operate The drawbacks of this approach include limited flexibility especially when a packaged unit is used lower efficiency and installation of some or all of the equipment outside 74 Water Source and Ground Source Heat Pump Systems SYS APMO10 EN S TRANE Primary System Components As for efficiency air cooled condensing is typically not as efficient as water cooled condensing And while an air source heat pump could be used in this application heat pump operation is typically limited or ineffective when it is cold outside Water cooled DX unit packaged or split connected to the water loop Because of the water distribution loop some WSHP systems use a water cooled DX unit for the dedicated OA equipment Instead of an air cooled condenser this type of equipment uses a water cooled condenser allowing it to be connected to the water loop Figure 51 Figure 51 Packaged water cooled DX unit connected to the loop cooling tower pumps F Q Q boiler water cooled DX
208. ly that some zones will experience overcooling For these applications it may be simpler to deliver the conditioned OA at a neutral dry bulb temperature because the benefit of delivering the air cold occurs less frequently In classrooms or offices however sensible cooling loads in the zones are relatively high during daytime hours In fact for some climates classrooms may never reach the pointwhen overcooling occurs during occupied hours especially if demand controlled ventilation is used to reduce outdoor airflow when zone population decreases These applications are typically well suited for delivering the conditioned OA at a cold temperature e In applications that require lower than normal dew points If an application has very high indoor latent loads or requires a lower than normal dew point the outdoor air may need to be dehumidified to a very low dew point In this case the corresponding dry bulb temperature of the air leaving the cooling coil may be colder than the HVAC design engineer is willing to discharge directly into an occupied zone below 45 F 7 C for example In this case the dehumidified OA could be reheated to a more traditional supply air temperature 55 F 13 C for example but not reheated all the way to neutral To avoid condensation when conditioned OA is delivered to the ceiling plenum In some applications the dedicated OA system delivers the conditioned outdoor air CA to the ceiling plenum
209. ly transfer heat between zones that are served by a given outdoor unit not throughout the entire building This significantly limits the energy saving benefit of heat recovery especially since the maximum size for a heat recovery outdoor unit is currently 20 tons 70 kW 10 ton 35 kW unit Office 101 North Open Office Area Office 102 12 ton unit 42 kW 20 ton 70 kW unit a Dining Break combine on a single s Room 20 ton 70 kW heat recovery unit East Open o Office Area Conf 106 Conf 108 A Lobby Conf Conf Ao unit for west offices Hallway Office 104 South Open n Office Area Office 103 10 ton 35 kW unit SYS APM010 EN Water Source and Ground Source Heat Pump Systems 9 S TRANE Overview of a Water Source Heat Pump System 10 Limits impact of equipment failure Because each zone is served by a separate WSHP that can provide either cooling or heating if one WSHP fails and needs to be replaced it does not impact the remaining zones within the building Some building operators keep a few spare units on site so if a unit fails it can quickly be replaced For this same reason the system can typically adapt easily if the use of a zone changes due to a change in space layout or a new tenant for example As long as the water distribution loop and dedicated outdoor air system have sufficient capacity the WSHP serving the affected zone can be replaced with a larger or smaller mod
210. m the standard specifies a maximum allowable velocity gt 12 315 8 5 ft s 2 6 m s 13 0 ft s 4 0 m s 6 5 ft s 2 0 m s 9 5 ft s 2 9 m s 5 0 ft s 1 5 m s 7 5 ft s 2 3 m s Source Table 6 5 4 5 from ASHRAE Standard 90 1 2010 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org Pipe insulation For a conventional boiler tower WSHP system typical loop water temperature ranges from about 60 F 16 C to 90 F 32 C At 60 F 16 C the outer surfaces of the piping is typically not cold enough for condensation to form and at 90 F 32 C the amount of heat loss from the water piping is relatively small Therefore in most applications insulation is added only to those sections of the water loop piping that pass through unheated areas or outside of the building Note This practice is consistent with the requirements of ASHRAE 90 1 Section 6 4 4 L3 of this standard requires piping to be thermally insulated and includes a table defining minimum insulation thickness However exception b in this section excludes Piping that conveys fluids having a design operating temperature range between 60 F 16 C and 105 F 41 C inclusive As mentioned above if the loop water temperature in a WSHP system is within this range Standard 90 1 does not require the piping to be insulated 38 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary Syste
211. m instantaneous heat rejection required of the cooling tower As explained earlier system load diversity is the maximum instantaneous or block cooling load of the system which is typically determined with building load calculation software divided by the total installed cooling capacity For this example system the load calculation software indicates the block cooling load to be 61 tons 210 kW so the system load diversity is 0 85 D 61 72 tons or 210 250 kW Using the sum of heat rejected to the loop as estimated by a manufacturer s selection software Table 6 the maximum instantaneous heat rejection required of the cooling tower is calculated to be 71 tons 250 kW Qrejection 83 tons x 0 85 71 tons Qrejection 290 kW x0 85 250 kW The third step is to calculate the range of the cooling tower The range is the difference AT between water temperatures entering and leaving the cooling tower Range 24 x Qrejection tons system water flow rate gpm Range 0 24 x Qrejection KW system water flow rate L s Water Source and Ground Source Heat Pump Systems 45 eS TRANE Primary System Components In the equations for Range 24 and 0 24 are not constants but are derived from properties of water Density 8 33 gallons ft3 998 kg m3 Specific heat 1 0 Btu Ibe F 4 18 kJ kge K 12000 Btu hr ton 8 33 gallons ft x 1 0 Btu Ibe F x 60 min hr 24 1000 L m3 998 kg m3 x 4 18 kJ
212. m Components Isolation valves and flow control devices An isolation valve is a motorized two position spring return water valve that is installed in the water pipe leaving the WSHP Figure 28 The isolation valve opens whenever the WSHP compressor turns on allowing water to flow through the refrigerant to water heat exchanger When the compressor turns off the valve closes slowly to shut off water flow This provides the opportunity to reduce pump energy use because the pump will only need to move the amount of water required by the operating WSHPs Figure 28 Isolation valve installed in the retum water pipe ifj two position isolation valve M it gt return WSHP supply me An isolation valve should open quickly to avoid the compressor tripping off on a Safety and should close slowly to avoid water hammer The electric solenoid in an isolation valve ensures it remains closed to prevent water flow when not desired If every heat pump is equipped with an isolation valve ensure that some isolation valves in the system are open before starting the pump or include a bypass pipe with a pressure actuated valve in the piping system Historically water regulating valves were used to modulate water flow through the refrigerant to water heat exchanger to maintain proper condensing head pressu
213. m chart in Figure 69 shows this same data plotted on a unconditioned OA psychrometric chart Note that the coil curves on the Trane psychrometric chart provide a good depiction of the part load dehumidification performance of a cycling DX system with a constant speed fan eo Full load versus part load dehumidification performance of a sor 1500 cfm onr conventional constant speed WSHP unconditioned OA 450 cfm constant EE First consider if the outdoor air enters the WSHP directly and is not PoE VAT TAPIN ai preconditioned by a dedicated outdoor air system Figure 70 In this basic MA constant volume mixed air configuration the heat pump mixes outdoor air l D Cra ae with recirculated air and supplies a constant volume of air to a single thermal constant speed zone The mixture passes through the refrigerant to air heat exchanger to be compressor on off SYS APM010 EN Water Source and Ground Source Heat Pump Systems 101 E TRANE System Design Issues and Challenges 102 Design condition OA RA MA SA Full Load cooled and dehumidified When the supply air reaches the zone it extracts sensible heat and moisture latent heat To demonstrate the dehumidification performance of a WSHP in this basic constant volume mixed air configuration consider a 10 000 ft3 283 m3 classroom in J acksonville FL that accommodates 30 people During cooling mode the zone temperature setpoint is 74 F 23 3 C dry bulb
214. m the zone The WSHP conditions this mixture of outdoor and recirculated air and delivers it to the zone through a shared duct system and diffusers Figure 42 Conditioned OA delivered to the intake of each WSHP Conditioned OA delivered to the supply side of each WSHP The example configuration shown in Figure 43 delivers the conditioned outdoor air CA directly to the supply side of each WSHP where it mixes with supply air from the heat pump before being delivered to the zone The WSHP conditions only recirculated air RA Figure 43 Conditioned OA delivered to the supply side of each WSHP SYS APM010 EN Water Source and Ground Source Heat Pump Systems 61 Se TRANE Primary System Components Conditioned OA delivered to the open ceiling plenum near each WSHP The example configuration shown in Figure 44 delivers the conditioned outdoor air CA to the ceiling plenum near the intake of each WSHP The outdoor air mixes with recirculated air RA in the plenum before being drawn in through the WSHP intake The WSHP conditions this mixture of outdoor and recirculated air and delivers it to the zone through a shared duct system and diffusers Figure 44 Conditioned OA delivered to the open ceiling plenum near each WSHP i DOES NOT COMPLY dividing wall dividing wall A A return air return air inlet to ceiling inlet to ceiling plenum plenum Correct plan of plenum system with discharge near terminal ends In
215. m totals H E Voz Consider however if the dedicated OA system ducted the outdoor air directly to each guest room rather than requiring itto be drawn into each room from the corridor Assuming the outdoor air is never delivered at a temperature warmer than the zone the zone airdistribution effectiveness Ez would be LO and the required zone outdoor airflow Voz would be only 25 cfm 0 012 m3 s for each guest room For the example in Table 16 this would reduce the required system outdoorair intake flow Vot to 324 cfm 0 15 m s 96 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Issues and Challenges Calculating system intake airflow Vot for a single zone system In some WSHP configurations such as rooftop console or larger vertical models outdoor air may be brought in through the WSHP itself and then delivered to the zone When one WSHP delivers a mixture of outdoor air and recirculated air to only one ventilation zone ASHRAE 62 1 defines this as a single zone system For this type of ventilation system Section 6 2 3 of ASHRAE 62 1 requires that the system level intake Vot needs to equal the calculated zone outdoor airflow Voz Vot Voz Returning to the example office building in Figure 65 p 94 assume that the South Conference Room is served by a rooftop style WSHP that brings in outdoor air mixes it with recirculated air from that zone and then deliver
216. may be all a design engineer needs to create an installation that is free of noise problems However this may also unnecessarily inflate the installed cost of some projects and may not provide sufficient attenuation on others On projects where acoustics is critical or prior experience is lacking the proper approach is to conduct an acoustical analysis early in the design process Even a simple acoustical analysis can help achieve occupant satisfaction while minimizing installed cost Defining an acoustical model A simple acoustical model consists of a source receiver and path Source The source is where the sound originates The primary sound source in a WSHP system is the heat pump itself However secondary sources include the dedicated outdoorair unit water circulating pumps hot water boilers and cooling towers This section will focus on the heat pumps however a quick review of the other equipment is recommended Each source has a unique sound quality and level and all of them play a role in determining the sound the receiver hears The foundation of an acoustical analysis is the equipment sound data An accurate analysis depends on accurate sound data for the equipment Indoor sound data for air moving equipment should be measured in accordance with AHRI Standard 260 Sound Rating of Ducted Air Moving and Conditioning Equipment This will ensure that the sound data accurately reflects the contributions of all the sound sou
217. mental Design LEED Green Building Rating System Washington D C USGBC http Awww usgbc org Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APM010 EN Index A acoustics 125 134 ADPI 85 after hours dehumidification 109 AHRI Standard 260 125 AHRI ISO Standard 13256 30 112 AHU See air handling unit air distribution 83 92 air separator 32 42 air handling unit 74 airside economizer 111 119 162 165 185 air source heat pump 75 air to air heat exchanger 69 73 122 antifreeze 47 49 139 148 ASHRAE Standard 52 1 22 ASHRAE Standard 52 2 22 ASHRAE Standard 62 1 25 91 93 96 98 174 176 ASHRAE Standard 90 1 38 111 120 123 automatic flow control device 41 auxiliary heat control 122 B balancing valve 37 40 ball valve 40 block cooling load 147 boiler 32 76 137 149 151 163 192 condensing 50 electric 54 55 173 hot water 49 57 172 173 non condensing 50 boiler less system 57 58 76 borehole 141 brake horsepower 114 115 breathing zone outdoor airflow 92 building pressure control 185 C carbon dioxide CO2 sensors 189 centralized pumping 32 circuit setter 40 closed circuit cooling tower 42 43 control 170 coefficient of performance COP 8 collection efficiency 24 communicating thermostat 159 communicating thermostat control 159 compressor 13 compressor capacity modulation 14 143 condensate drain line 1 12 27 167 overflow 167 trap 27 condensing boiler 50 console WS
218. midified outdoor air to a neutral dry bulb temperature whenever the outdoor temperature drops to the point where the sensible cooling loads in some of the zones are expected to be low enough that the cold outdoor air may cause overcooling For example when the outdoor temperature drops below 65 F 18 C but this limit could be adjusted after a few months of experience in operating the system e Monitor the zone temperatures and modulate reheat capacity in the dedicated OA unit to avoid overcooling An even more effective way to implement this strategy is to use a building automation system BAS to monitor the current zone temperature for all Water Source and Ground Source Heat Pump Systems 191 S TRANE System Controls 192 the heat pumps to determine the zone where the temperature is closest to its heating setpoint This is the zone that is most at risk of overcooling Based ona signal from the BAS the dedicated OA unit could then modulate its reheat capacity resetting the leaving air dry bulb temperature upward just enough to prevent overcooling any of the zones This strategy delivers the conditioned OA at a temperature that offsets as much of the zone sensible cooling loads as possible without overcooling any zone avoiding the need for any heat pumps to operate in the heating mode Of course this is only a benefit if the dedicated OA unit uses recovered energy for reheat If it uses new energy for reheat it would l
219. miniums apartment buildings retail strip malls and leased office space If a dedicated outdoor air system is used however individual metering of energy used to condition outdoor air for ventilation is more difficult Water Source and Ground Source Heat Pump Systems SYS APMO10 EN S TRANE Overview of a Water Source Heat Pump System SYS APM010 EN Drawbacks Challenges of WSHP Systems The following section discusses some of the primary drawbacks or challenges of using a WSHP system along with some potential ways to address those challenges Equipment is located in or near the occupied spaces Typically WSHPs are located in or very close to the occupied space This requires the use of floor space or ceiling space throughout the building And because this equipment contains both a compressor and a fan achieving acceptable noise levels in the space can be challenging and needs to be considered during system design Distributed maintenance Because the WSHPs are distributed throughout the building maintenance must be performed within the occupied spaces or in the ceiling or closet near the occupied spaces This can be disruptive to occupants or may lead to neglecting proper equipment maintenance Proper maintenance of WSHPs requires that they be located in accessible areas In anew building this requires close coordination with the architect Additionally selecting units that are designed for easy access increases the chan
220. mp compressor turns off e Pump failure only impacts one heat pump rather than the entire system although using a standby centralized pump minimizes this concern Constant versus variable flow pumping The water circulating pumps can be either constant or variable flow pumps Constant flow pumps operate whenever the system is on delivering a constant flow of water throughout the loop This approach is simple and inexpensive to install because no method of pump capacity control is used However a constant flow pump consumes a constant amount of pump energy regardless of building load Variable flow pumps take advantage of the fact that not all of the WSHP compressors in the system are operating at the same time For example when a zone needs neither cooling nor heating the compressor turns off When the compressor turns off a motorized two position valve can be used to shut off water flow to that heat pump so less total water flow is required in the loop A variable frequency drive VFD on the circulating pump allows the pump to unload saving energy by delivering only the amount of water required by the operating heat pumps While variable flow pumping reduces system energy use it requires some method to control pump capacity see Water circulating pump s p 167 In a variable flow system consider installing an automatic balancing flow control valve for each heat pump This device helps ensure proper water flow through t
221. ms manual balancing may be impractical And in systems that use variable flow pumping manual balancing does not adjust for the variations in system pressure that occur as isolation valves open and close An automatic balancing or self balancing flow control valve installed in the leaving water pipe for each WSHP Figure 31 automatically adjusts to provide a constant water flow rate over a wide range of system pressures It also eliminates the need for the iterative re adjustments associated with manual flow control devices Figure 3L Automatic flow control device for water balancing automatic flow control isolation valve valve a D Yt as ______ return a TE MEC supply strainer with blow down manual ball valve with valve and hose connector NY pressure temperature port Figure 32 Examples of hose kits used Manual shut off valves are often installed in both the entering and leaving with WSHPs water pipes for each WSHP to allow for easy removal or service Sometimes the flow control valve can be used for this purpose Because a WSHP system typically contains many WSHPs that need to be connected to the water distribution piping factory provided hose kits are often used as a convenient means for connect
222. n ASHRAE Standard 62 1 and its procedures for calculating zone level and system level outdoor airflow requirements for a WSHP system refer to the Trane Engineers Newsletter Live broadcast DVD titled ASHRAE Standard 62 1 Ventilation Requirements APP CMC023 EN or the following ASHRAE Journal articles e Stanke D Addendum 62n Single zone and dedicated OA systems ASHRAE Journal 46 October 2004 12 20 Available at www ashrae org or www trane com e Stanke D Addendum 62n Single path multiple zone system design ASHRAE Journal 47 January 2005 28 35 Available at www ashrae org or www trane com S TRANE System Design Issues and Challenges effectiveness is only 0 8 When supplied and returned overhead the buoyancy of this hot air tends to cause some of the air to bypass from the supply air diffusers to the return air grilles without reaching the actual breathing zone Therefore this configuration is less than 100 percent effective at delivering outdoor air from the diffusers into the breathing zone For zones that require heating employ one of the following strategies e If Tsa gt Tzone 15 F 8 C increase the outdoor airflow delivered through the diffusers Voz Vbz 0 8 during the heating mode to compensate for the zone air distribution effectiveness Ez 0 8 of using ceiling mounted return air grilles Alternatively locate the return air grilles in the floor or at the base of a side wall E
223. n energy use operating the fan at a reduced speed can provide acoustic and dehumidification benefits at part load conditions During the cooling mode reducing airflow when the compressor unloads results in a colder discharge air temperature at part load It also allows the compressor to operate for longer continuous periods of time without needing to cycle off quickly to avoid over cooling the zone The colder drier air and lengthened compressor run time typically improves part load dehumidification performance see Dehumidification impact of compressor cycling and constant speed fan p 98 Water Source and Ground Source Heat Pump Systems 21 eS TRANE Primary System Components For more information on the various types of particulate filters refer to Chapter 28 Air Cleaners for Particulate Contaminants in the 2008 ASHRAE Handbook HVAC Systems and Equipment www ashrae org or the NAFA Guide to Air Filtration www nafahq org During the heating mode reducing airflow when the compressor unloads results in a warmer discharge air temperature at part load The warmer air can sometimes improve occupant perception of comfort When a multiple speed fan is used take care to ensure that the zone receives the proper quantity of outdoor air required for ventilation requirements regardless of fan speed Filters Another requirement of the HVAC system is to ensure that the air delivered to the conditioned space is relativ
224. n of the refrigeration circuit to transfer heat from the source side to the load side heat exchanger In this manner a water to water heat pump can provide either cold or warm water Water to water heat pumps are commonly used to serve radiant heating and or cooling systems snow or ice melting systems and air handling units as part of a dedicated OA system see Dedicated OA equipment types p 73 They are also used for heating service water for restrooms showers laundry or kitchens The availability of these multiple configurations allows a single WSHP system to be used in a building that has various types of zones For example in a hotel building vertical stack units might be used in the guest rooms horizontal units might be used in the smaller meeting rooms vertical units might be used in the larger meeting rooms and banquet halls rooftop units might be used for the lobby and restaurant and water to water units might be used to serve the dedicated OA units All of these different WSHP configurations can be connected to the same water loop Figure 23 SYS APM010 EN Water Source and Ground Source Heat Pump Systems 29 TRANE Primary System Components Figure 23 Example WSHP system serving a hotel using various unit configurations SN N N rooftop LA WSHP qH
225. n the pressure outside and air and condensate are pushed out through the condensate drain line This eliminates concerns for wetting the interior of the unit but results in conditioned air leaking out of the unit wasted energy In either a draw thru or blow thru configuration the condensate drain line must include a properly designed drain seal to allow condensate to properly flow out of the drain pan and maintain the air seal Although other sealing devices are sometimes used a simple P trap is used in the majority of installations Follow the manufacturer s recommendations for the design and installation of this condensate trap Note that the design of the trap differs depending on whether the refrigerant to air heat exchanger is a draw thru or blow thru configuration Remember even a well designed trap if plugged causes the drain pan to overflow Inspect traps regularly for blockage Clean and prime the trap if necessary especially just prior to the cooling season e Include a condensate overflow float switch in each heat pump This switch turns off the compressor and closes the OA damper if equipped to prevent the drain pan from overflowing if the condensate drain line is plugged A unit controller can simultaneously send an alarm or diagnostic message to the building automation system indicating the need to service SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 27 Se TRANE Primary System Components
226. n the pump motor Similar to the supply fan in a variable air volume VAV system the pump is often controlled to maintain a set pressure at some location in the piping system A challenge in a WSHP system is deciding where to locate the differential pressure sensor since the isolation valves on the individual heat pumps are two position open or closed rather than modulating Some design engineers locate the differential pressure transducer between the supply and return piping ata location far from the pump Figure 111 Other design engineers install a small bleed line ata location in the piping that is far from the pump and measure the pressure difference across this bleed line A controller compares the measured pressure difference to a setpoint and pump capacity is modulated to generate enough pressure to maintain the desired pressure difference at the location of the transducer Figure 11L Pump capacity control in a variable flow system Figure 112 depicts an exaggerated example to illustrate this control loop When a WSHP compressor turns off its isolation valve closes to shut off water flow through that heat pump Closing the valve forces more water to flow through the remaining open valves increasing the pressure drop head through the system In response the pump begins to ride up the constant speed rpm performance curve from the design operating point A trying to balance with this new part load system resis
227. nality is limited Figure 104 Non communicating thermostat control standalone control panel water source heat pump non communicating i mE programmable thermostat With no communication between the individual heat pumps and loop control panel the water circulating pumps are often operated continuously To avoid this adaisy chained wirecan beused to connectto arelay in each heat pump allowing the centralized loop control panel to disable the heat pumps and turn off the water circulating pumps based on a time of day schedule Unoccupied operation to maintain setback temperatures can be enabled using either a single temperature sensor in a representative zone ora second set of relays can be daisy chained to allow any zone to request after hours operation of the system Of course when wires need to be pulled to connect the individual heat pumps it may be more beneficial to use communication wire and take advantage of using networked unit controllers 158 Water Source and Ground Source Heat Pump Systems SYS APMO10 EN S TRANE System Controls e Communicating thermostat control One step up in functionality is to use a communicating thermostat to control each WSHP Figure 105 Communicating thermostats are more expensive than non communicating thermostats but likely less expensive than networked communicating unit controllers with zone temperature sensors Figure 105 Communicatin
228. nameplate power will likely be smaller than 5 hp 4 kW making them exempt from the current ASHRAE 90 1 limit on fan power For larger heat pumps however the fan power limitation may apply When the maximum allowable fan power limit does apply the 2010 version of ASHRAE 90 1 includes two options for compliance Table 21 depending on whether the fan system is constant or variable volume Historically most WSHPs have been equipped with a constant speed fan so they would be classified as constant volume fan systems However today some models are equipped with an electronically commutated motor that can be used to vary airflow delivered to the zone see Electronically commutated motor p 20 These would be considered variable volume fan systems Table 2L Fan power limitation Constant volume Variable volume A hp lt CFMsupply x 0 0011 hp lt CFMsupply x 0 0015 Option 1 Allowable nameplate motor power KW lt L ssupply x 0 0017 kW lt L Scuppy x 0 0024 y bhp lt CFMsupply x 0 00094 A bhp lt CFMsuppiy x 0 0013 A Option 2 Allowable fan input brake power KWi lt Liscupply x 0 0015 A KWi lt L Ssuppiy x 0 0021 A Excerpt from Table 6 5 3 1 1A of ASHRAE Standard 90 1 2010 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org Option 1 is based on nameplate motor power Itis easier to apply but not as flexible To comply using Option 1 the
229. ncentration in the zone is lower than it actually is the system will reduce ventilation to under ventilate that zone degrading indoor air quality On the other hand if the sensor signals that the CO2 concentration is higher than it actually is the system will increase ventilation to over ventilate that zone wasting energy Therefore CO2 sensors should not be used indiscriminately Rather they should be installed only in those zones where they provide the best return on investment and are worth the risk S TRANE System Controls In most cases the best value is achieved by combining all three DCV approaches using each where it best fits Those zones that are densely occupied and experience widely varying population such as conference rooms auditoriums and gymnasiums are typically good candidates for CO2 sensors However zones that are less densely occupied or have a population that varies only minimally such as private offices many open plan office spaces and many classrooms are probably better suited for occupancy sensors and or time of day schedules Zones with predictable occupancy patterns such as cafeterias are good candidates for time of day schedules Combining these various zone level DCV strategies can ensure that each zone is properly ventilated without requiring a CO2 sensor in every zone CO2 sensors are used only in those zones where they will bring the most benefit This minimizes installed cost
230. nd Source Heat Pump Systems 147 S TRANE System Design Variations Minimize the use of antifreeze Because the header piping and U tubes are installed well below grade the fluid inside the heat exchanger is not exposed to ambient temperatures The ground heat exchanger design software will typically estimate the minimum expected loop temperature which would then indicate whether or not antifreeze should be added to the water inside the loop In many climates ground heat exchangers for commercial or institutional buildings likely require little or no antifreeze because annual cooling loads are greater than annual heating loads and because the quantity of heat rejected to the loop during the cooling mode is typically higher than the quantity of heat extracted from the loop during the heating mode Lay out piping and headers to simplify field fabrication and flushing Beyond drilling boreholes or digging trenches fabricating the heat exchanger at the project site involves fusing each U tube to the header and connecting the header pipes to the building loop This part of the project is labor intensive and typically occurs in a deep trench The use of pre assembled headers and simple layouts can reduce installation cost and minimize risk Hire contractors that are experienced with the installation of ground heat exchangers Experienced contractors have developed their own proven methods of installing U tubes and headers In addition th
231. nd level sometimes oversizing the unit and operating the fan at a slower speed helps or choosing a different style WSHP that allows for greater flexibility in sound attenuation If more than one heat pump serves the same area moving them further away from each other may also help However avoid placing a WSHP in the corner of the room since this would reduce the area for the sound to radiate WSHP horizontal models Horizontal water source heat pumps are typically installed in a ceiling plenum with supply air ducted to diffusers and air returning from the space through a return air grille and the open ceiling plenum Figure 85 Figure 85 Recommendations for horizontal models use flex duct for final connection to supply air diffusers being careful to avoid sharp turns or pinched ducts use flexible duct and avoid close coupled fittings separate fittings with straight duct of at least four to five duct diameters in length locate WSHP above a non sound sensitive area size ducts for low air velocity below 700 fpm 3 8 m s in main sections below 600 fpm 3 1 m s in runouts locate WSHP inlet at least 6 ft 1 8 m away from return air grille Sound data provided by AHRI Standard 260 Sound Rating of Ducted Air Moving and Conditioning Equipment is separated by sound path discharge inlet and casing radiated Water Source and Ground Source Heat Pump Systems 129 S TRANE System Design Issues an
232. ndbook HVAC Systems and Equipment www ashrae org during after hours dehumidification If the dedicated OA unit includes exhaust air energy recovery it likely already has a return air path and may only require the addition of a return air damper to allow for after hours humidity control Figure 82 Dedicated OA system used for after hours dehumidification dedicated OA unit Adding a 100 recirculated air recirculation path also allows for use of exhaust air energy recovery WSHP off WSHP off If the dedicated OA unit is connected to the water distribution loop as would be the case for a water cooled DX unit or a water to water heat pump for example the water circulating pump and possibly the cooling tower would also need to operate to provide after hours dehumidification Humidification Some buildings or specific areas within a building require maintaining minimum humidity levels for comfort or process requirements If a building with a WSHP system requires humidification consider the following e Location of the humidifier If humidification is needed for comfort consider locating the humidifier in the dedicated outdoor air system downstream of the heat source During cold and dry weather outdoor air brought in for ventilation does not have much capacity to hold additional moisture After the outdoor air has been warmed by a gas fired burner or heating coil ithas a much greater capacity to a
233. near the intake of each WSHP see Figure 44 p 62 The outdoor air mixes with recirculated air RA in the plenum before being drawn in through the WSHP intake In this configuration the dedicated OA unit should reheat the dehumidified OA to a dry bulb temperature that is above the expected dew point temperature of the air within the ceiling plenum If cold air is dumped into the ceiling plenum it could cool surfaces structural beams electrical conduit ceiling framework At night when the dedicated OA unit is off wind or operating exhaust fans may cause humid outdoor air to leak into the plenum which may lead to condensation on these cold surfaces Exhaust air energy recovery A dedicated outdoorair system often makes it more feasible to implement exhaust air energy recovery if exhaust air from the building can be routed back to the dedicated OA unit The energy recovery device transfers sensible heat or sensible heat and water vapor between the outdoor air OA and exhaust air EA streams As an example Figure 49 shows a total energy wheel used to precondition the entering outdoor air During the cooling season this desiccant coated wheel revolves between the outdoor and exhaust air streams removing both sensible heat and water vapor from the entering outdoor air and rejecting it to the exhaust air During the heating season the wheel recovers both Water Source and Ground Source Heat Pump Systems SYS APM 010 EN For more inf
234. ng 1000 Btu 1000 Btu 1000 Btu hr 1000 Btu hr January ass08 jo 420 592 o February j395g2 p i O jaso ot March 20483 jo 408 113 0 April 5920 24447 383 037 307 036 May fo 84806 0 587 508 June jo 117234 0 689 039 July fo 122485 0 756 753 August fo fizie45 0 22774 September 0 74816 0 632896 October e233 hz 33403 239 723 November fasso o eos 400 263 138 5235 December 52051 fo 422 196 0 Typically the design engineer uses this type of software to design the ground heat exchanger so that it will maintain the loop temperature entering the building between the minimum and maximum temperatures for which the heat pump can operate To briefly demonstrate the utility of such design software consider a small office building located in St Louis Missouri The building is operated for ten hours a day five days a week The design block cooling load is 66 tons 230 kW For this example the borefield is arranged as an 8 by 8 rectangle containing 64 boreholes of U tubes that are constructed of 0 75 in 19 mm HDPE pipe SDR 11 and spaced 15 ft 4 6 m apart The design software determines the required depth of each borehole to maintain the loop temperature entering the building between the user specified minimum and maximum temperatures For this example to maintain loop temperatures between 20 F 7 C and 90 F 32 C each borehole must be 240 ft 73 m deep The software also simulates the operation of the
235. ng construction should be replaced prior to building occupancy Some WSHP models have an option for two return air intake openings Figure 20 The increased filter media surface area means the filters can hold more dirt and be replaced less frequently Water Source and Ground Source Heat Pump Systems 25 Se TRANE Primary System Components Earning LEED credit One of the requirements for earning the Indoor Chemical and Pollutant Source Control credit Indoor Environmental Quality section of LEED 2009 is to install a MERV 13 or higher filter to clean the outdoor air before it is introduced to any occupied space In most WSHP systems this would involve installing a MERV 13 filter in the dedicated outdoor air unit Note In 2010 this credit changed from requiring MERV 13 filtration of outdoor and recirculated air to requiring it for only outdoor air Figure 20 Two retum air intake openings increase filter surface area return air intake 1 supply gt air V S return air intake 2 Se Filter located in the dedicated outdoor air unit When the WSHP system uses a dedicated outdoor air system to condition all the outdoor air OA required for ventilation the dedicated OA unit typically includes a particulate filter to remove airborne particulate contaminants entering the building If the dedicated OA unit contains a cooling coil Section 5 8 of ASHRAE 62 1 requires a filter with a M
236. ng used and there is a benefit in avoiding a higher electrical demand when all the heat pumps start in the morning then the storage tank should be large enough to provide any heat that the loop by itself is unable to provide Qtank Qextracted Qloop Forthesame example a storage tank sized for 225 000 Btu 240 000 k plus the 150 000 Btu 155 000 kJ provided from the loop itself would be sufficient to provide the total heat required for the morning warm up period Using the equation above this corresponds to a 900 gallon 3400 Liter tank However if the intent is to simply avoid the need to oversize the boiler to be able to provide enough heat for morning warm up then the storage tank could be smaller since the boiler will also be operating during the morning warm up period Qtank Qextracted Qloop Qboiler For this example assuming that the boiler has a capacity of 100 000 Btu h 107 000 kj h and the morning warm up period lasts one hour a storage tank sized for 125 000 Btu 133 000 kj would be needed This size of tank plus the 100 000 Btu h 107 000 kJ h from the boiler plus the 150 000 Btu 155 000 kj provided from the loop itself would be sufficientto provide the total heat required for the morning warm up period This corresponds to a 500 gallon 1900 Liter tank Alternatively the tank could be sized to store excess heat during the day for use later at night Many newer buildings designed and constructed in acco
237. not operating This may require a manual override to allow for after hours cleaning processes If some exhaust fans are required to operate at all times then a solution may be to operate the dedicated OA system at a reduced airflow during unoccupied periods to maintain building pressure 24 7 This indoor to outdoor pressure difference can be controlled by adjusting either the quantity of air brought into or exhausted from the building In most WSHP systems the quantity of outdoor air brought into the building is based on the minimum ventilation requirements of a local building code so controlling building pressure typically involves varying the quantity of air exhausted from the building When a dedicated OA system is used this might involve controlling the capacity of a central relief fan to maintain a desired static pressure difference between indoors and outdoors Figure 124 A differential pressure sensor monitors the indoor to outdoor pressure difference Its signal is used to Water Source and Ground Source Heat Pump Systems 185 S TRANE System Controls 186 adjust relief airflow directly controlling building pressure Capacity control can be accomplished by either a modulating the relief damper and allowing the relief fan to ride the fan curve or b equipping the relief fan with a variable speed drive Figure 124 Direct control of building pressure using a central relief fan differential pressure sensor
238. num height That is the distance between the top of the ceiling structure and the bottom of the roof SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 89 S TRANE System Design Issues and Challenges Figure 63 Wireless zone sensor 90 or floor above may limit the size capacity of the heat pumps used for the project and this might dictate the maximum zone size Locating the zone sensor The zone temperature sensor should be installed in a representative location within the zone If the zone consists of more than one room place the sensor in the room where tighter temperature control is most important The temperature in the other rooms may vary more than in the room with the temperature sensor Follow these general guidelines when locating the zone sensor Do not place the zone sensor where it will be affected by air discharged from a supply air diffuser e Make certain that only the WSHP that is connected to the zone sensor can influence the temperature being measured by that sensor Do not place the zone sensor directly on a wall with a large amount of heat gain or loss or where solar radiation will create a false reading generally this means placing the sensor on an interior wall e Do not place the zone sensor directly above heat generating equipment such as a copy machine computer terminal or coffee maker Using wireless technology In the HVAC industry the use of wireless technology can
239. occupy the building Figure 119 When the building must be heated prior to occupancy this is called morning warm up When the building must be cooled it is called morning cool down Figure 119 Moming warm up system on system off occupied heating setpoint scheduled zone occupied hours temperature unoccupied heating setpoint 6 a m Noon 6 p m The morning warm up cool down mode typically occurs as a transition from the unoccupied mode to the occupied mode The system attempts to return the temperature inside the building to the occupied setpoint as rapidly as possible In this mode the building does not typically require ventilation because it is not yet occupied Table 32 describes the typical functions of the different system components during the morning warm up or morning cool down modes Water Source and Ground Source Heat Pump Systems SYS APM 010 EN S TRANE System Controls Table 32 Coordination of equipment during moming warm up or cool down mode Activates the fan until zone temperature reaches the occupied heating for warm up or occupied cooling for cool down setpoint then the fan is turned off Positions the reversing valve and cycles the compressor s to bring the zone temperature to the occupied setpoint cooling or heating WSHP e Fan is turned off Dedicated outdoor air unit CERAI e Central relief fan is turned off Turns on water circulating pumps if
240. of the ground heat exchanger Using actual soil properties specifically the thermal conductivity thermal diffusivity and undisturbed ground temperature helps avoid oversizing or undersizing the heat exchanger The test report should indicate the type of soil or rock found at different depths Finally the site evaluation can also reveal potential problems that could occur during installation where coordination between trades is critical On smaller construction sites waiting for building materials to be moved so that the drilling or trenching area can be accessed may result in project delays or cost overruns SYS APM010 EN Oe yet Uae Dla aal Sietom u mm a a a Bb errcte Orare barem Then News wee baha Searing Sok type nmerdy arreend Themed Comatety a te pase Vasse beat capacity d Oe parsi Uncenated gourd meme iial P a orere Tatai ee ate ia e Geen Phat Tyee More wae bar ie bgtu S TRANE System Design Variations Sizing the ground heat exchanger Typically the ground heat exchanger is designed using computer software that was developed specifically for this purpose Figure 96 These software programs can typically model various borefield configurations and account for soil properties and grout conductivity fluid properties if not pure water borehole diameter and spacing and size and type of piping used Figure 96 Example of ground heat exchanger design software U hae Dawi U Tide Con
241. of pumping energy e Typically has a higher installed cost than the other types of ground source systems because of the amount of drilling or trenching required and the limited availability of certified loop contractors in some regions Surface water heat pump system Advantages Disadvantages High thermal conductivity makes a body of water a good heat rejection heat absorption medium Closed system means that no water treatment is required and is not reliant on a constant supply of water from a well Typically requires less total length of pipe than a closed loop ground coupled heat exchanger Less expensive because no drilling and less trenching is required Requires a large body of water for submerging the heat exchanger Typically experiences lower heat pump efficiencies due to wider temperature variation than a ground heat exchanger or ground water Risk of damage to submerged heat exchanger Ground water heat pump system Advantages Disadvantages Higher heat pump efficiencies due to better thermodynamic performance than closed loop systems Typically provides highest return on investment because cost to drill wells does not rise linearly with capacity Land required for drilling wells is much smaller than required for ground coupled systems Well drilling contractors are widely available Sufficient quantity of water is needed Requires high quality water to minimize fouling or scaling of heat pump h
242. often result in an overall lower installed cost when compared to traditional wired sensors especially in historical or difficult to wire buildings renovations or in locations with high labor rates By eliminating the wires between a zone temperature sensor and a water source heat pump the sensor Figure 63 can be easily placed in the best location to accurately measure the zone temperature This might be ona cubicle wall a concrete or brick wall or some other difficult to wire location A wireless zone sensor is easy and inexpensive to move when the layout or use of the zone changes or if the initial placement of the sensor turns out to be a poor location Furthermore wireless communication eliminates the wires between the unit controller on each water source heat pump and the centralized system level controller Benefits include faster project completion and easier relocation when space layout or use changes in the future Wireless communication also makes it easier to upgrade an older system to reap the benefits of networked unit controls see System Controls p 158 To ensure reliable operation make sure the wireless technology adheres to the Institute of Electrical and Electronics Engineers IEEE Standard 802 15 4 This standard was created to minimize the risks of interference with other wireless devices In addition ensure that the wireless sensor has a long battery life at least five years and a visible low battery
243. oling season the cooling tower could be operated during off peak hours to decrease the temperature of the water inside the loop and storage tank This would allow the heat pump compressors those operating in the cooling mode to operate more efficiently during on peak hours and use less electricity This strategy can also delay or avoid the need to operate the cooling tower during the on peak period at which time the outdoor wet bulb temperatures would likely be higher e During those times in the year when it is warm during the day and cool at night the addition of a storage tank allows the loop to store more heat that is rejected from heat pumps operating in the cooling mode during daytime hours This delays and may even avoid the need to operate the cooling tower The heat stored in the water can then be used to offset the nighttime heating loads High temperature storage If the electric utility has a time of day utility rate with a high on peak electrical demand charge the use of high temperature storage might be a more attractive approach Figure 38 In this case the storage tank is installed downstream of the boiler During off peak hours when the cost of electricity is lower a heating element in the storage tank is used to increase the temperature of the water inside the tank typically up to 180 F 82 C or higher By storing the water at a much warmer temperature a given tank size can store significantly more hea
244. oling load rather than summing installed heat pump capacities In asystem with multiple heat pumps zone by zone load variation throughout the day called system load diversity see sidebar on p 45 results in an instantaneous cooling load that is less than summing the peak cooling loads of all zones Sizing the ground heat exchanger based on the block cooling load typically results in a smaller heat exchanger e Separate boreholes by at least 20 ft 6 m to help avoid long term changes in ground temperature Spacing the boreholes further apart also allows for a reduced overall length of the heat exchanger which can result in shallower or fewer boreholes e Size boreholes with as small a diameter as possible and use a grout with high thermal conductivity This minimizes the use of grout which often has poorer thermal conductivity than the surrounding ground When possible use thermally enhanced grouts with higher thermal conductivity e Design for a total system flow rate of 2 5 to 3 0 gpm per ton of block cooling load 0 045 to 0 054 L s per kW Due to the pressure drop through the ground heat exchanger excessive pump energy use can drastically reduce the energy savings benefit of a ground coupled system To avoid over pumping the overall system flow rate should account for system load diversity and be based on the block load rather than by summing installed heat pump capacities Water Source and Grou
245. oling mode on on g g reheat as needed heating heating mode on on full bypass The primary advantages of using a water to water heat pump connected to the loop are piping simplicity and the fact that the cooling heating equipment can be distributed throughout the building often located very close to the dedicated OA unit that it is connected to With this equipment configuration the air handling unit may be installed indoors or outdoors and contains a fan filter chilled water cooling coil heating coil or gas fired burner and possibly one or more air to air heat exchangers An air handling unit typically provides more flexibility and has more options for fans air cleaning devices air to air energy recovery devices and sound attenuation for example than packaged equipment For example the AHU depicted in Figure 55 includes a total energy wheel to precondition the entering outdoor air See Exhaust air energy recovery p 70 and a fixed plate heat exchanger to recover heat for reheating the dehumidified air when necessary Figure 55 Dedicated OA unit with total energy recovery and a fixed plate HX AY EA MERECEN supply fan oa exhaust fan ym ABiaua e 109 yeayaid 109 Buljooo fixed plate heat exchanger Figure 56 shows an example performance of this AHU configuration during t
246. olyethylene HDPE with a factory attached 180 degree fitting U bend at the bottom underfloor air distribution A method of air distribution in which conditioned air is delivered to the zones under a raised floor and floor grilles unoccupied mode The typical nighttime operating mode of a system The building does not require ventilation because it is not occupied and the zone temperatures are allowed to drift to unoccupied setpoints variable frequency drive VFD See variable speed drive variable speed drive VSD A device used to vary the capacity of afan pump or compressor by varying the speed of the motor that rotates the drive shaft ventilation The intentional introduction of outdoor air into a zone through the use of the HVAC system in the building warm up mode See morning warm up mode water chiller A refrigerating machine used to transfer heat between fluids water regulating valve A type of valve used to vary the flow rate of water through the refrigerant to water heat exchanger in a WSHP for the purpose of controlling the refrigerant pressure within a desired range waterside economizer A method of free cooling that diverts cool water from the loop through a separate heat exchanger to precool the entering air before it reaches the refrigerant to air heat exchanger water source heat pump A type of heat pump that transfers heat from air to water and vice versa water to water heat pump A type of heat pump
247. om air circulation divided by the air discharged from the outlet Also called entrainment ratio attenuation The reduction in the sound level as it travels along the path from a source to the receiver block cooling load Calculated by finding the single instance in time when the sum of the space cooling loads is the highest blow thru A configuration where the fan is located upstream and blows air through the cooling coil Water Source and Ground Source Heat Pump Systems 195 196 boiler A pressure vessel that typically consists of a water tank or tubes with water flowing through them a heat exchanger fuel burners exhaust vents and controls Its purpose is to transfer the heat generated by burning fuel to either water or steam boiler less system A WSHP system that does not include a centralized hot water boiler connected to the water distribution loop Rather if the loop temperature gets too cold the heat pump activates an external heat source such as an electric heater installed inside the heat pump borehole A narrow shaft bored in the ground either vertically or horizontally in which a U tube is inserted as part of a ground heat exchanger brake horsepower bhp Actual rather than theoretical power required to drive a fan or that is applied to the shaft of a pump or compressor breathing zone The region within an occupied space between planes 3 in and 72 in 75 mm and 1800 mm above the floor and more th
248. ome cases also results in reduced energy use during part load conditions Figure 12 compares the part load performance of these different methods of compressor capacity modulation in an example 4 ton 14 kW water source heat pump e At part load conditions a single on off compressor will operate for a period of time cycle off for a period of time and then cycle back on again Hot gas bypass HGBP diverts some of the hot refrigerant vapor to the low pressure side of the system This allows the compressor to continue operating at part load conditions but it is inefficient because the compressor pumps refrigerant that never is used for the cooling e A two stage scroll compressor can operate at either 100 percent capacity or some reduced capacity 67 percent for example This ability to operate at partial capacity results in improved efficiency EER at part load conditions e At part load conditions a Digital scroll compressor continues to operate at a constant speed but the two scrolls are periodically separated to release the compressor refrigerant vapor and reduce the capacity of the compressor to better match the changing load While this approach is able to more closely match capacity to the load it does not improve efficiency at part load conditions e When two compressors are manifolded together on the same circuit either both compressors operate together one compressor operates while the other is off or both compre
249. onstant versus variable flow pumping 5 34 SYS APMO10 EN Water Source and Ground Source Heat Pump Systems iii eS TRANE Table of Contents PIDINGUAYOUE escent se eee a dente Rebs Hoes hae eee eaten eee aces 36 Direct versus reverse return arrangement 2 4 5 36 Single pipe system 0 0 0 eee 37 PIPE SIZING cece bows eee eae dba bade de yee eee ee eee 38 Pipe insulation eari cgi peas OR eee eee es 38 Isolation valves and flow control devices 0 00c cece eee 39 Other hydronic accessories 0 000 eee 41 Heat Rejection 6 ent e nent eee n eens 42 Cooling OWErF gti cis maana bee ra aa deal edhe Ream ae Ra Ae 42 Sizing the cooling tower 0 cece eee 44 Freeze protection 0 ett ee 46 Natural heat Sink seemi iesakam ia aiaa eaae a a e aaa a 49 Heat Addition xiwiiek iu thaws bee Ree OA Ree ee Ree Re ae wee ipid 49 Hot water boiler 40 8e0s cade vedas oka ee eee eS 49 Non condensing versus condensing boilers 50 Sizing the boiler in a system with night setback 51 Sizing the boiler in a system without night setback 52 Hot water Storage orcs rras ariaa ENE EEEE ee 53 Low temperature storage cece ees 53 High temperature storage 0 cece ee 54 Sizing the storage tank 2 0 cette 55 Electric resistance heat in the WSHP boiler less system 57 Natural heat source 0 0 0
250. ontal water source heat pump that is installed in the ceiling plenum SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 83 Se TRANE Primary System Components For more information on best practices for the design and layout of duct systems Figure 60 Air distribution components of a WSHP system horizontal water source heat pump Q ee S CG return duct SS L return air grille ie supply duct supply air diffuser Supply duct system Supply ductwork is typically routed through the ceiling plenum above the occupied zone A successful design of the supply duct system achieves the refer to the Sheet Metal and Air following Conditioning Contractors National g i 48 A Association SMACNA manual HVAC e Supplies the required quantity of air to each supply air diffuser without Systems Duct Design 84 excessive noise e Minimizes the static pressure and associated power requirements of the fan e Minimizes the installed cost without great sacrifices in system efficiency e Accommodates space limitations without excessive pressure drop Other publications contain more complete details related to duct design but following are a few general recommendations e Keep the duct layout as simple and symmetrical as possible Uselow pressure drop duct fittings and follow the best practices published by the Sheet Metal and Air Conditioning Contractors National Association SMACNA for designing and in
251. ooling waterside economizer coil to meet this requirement for an economizer Section 6 5 14 states that HVAC system design and economizer controls shall be such that economizer operation does not increase the building heating energy use during normal operation In order for a pre cooling waterside economizer coil to provide enough capacity to meet the requirements of Section 6 5 12 the loop water temperature may need to be allowed to drift colder than normal below 60 F 16 C for example While this colder loop temperature will allow for waterside economizing in those zones that require cooling the colder loop water will decrease the efficiency of any WSHP compressors that are operating in the heating mode But Section 6 5 14 explicitly refers to the overall building heating energy use not just energy used by those heat pump compressors operating in the heating mode For a WSHP system the building heating energy use is the sum of the energy used by compressors operating the heating mode plus any energy used by the boiler connected to the water distribution loop When a zone is cooled by a water source heat pump that is equipped with a pre cooling waterside economizer the heat removed from the zone is rejected to the water distribution loop This heat rejected to the loop reduces the amount of heat that the boiler must add to the loop This corresponding reduction in boiler energy use must be considered when evaluating the impa
252. op water temperature above the lower setpoint Water distribution loop Some systems incorporate a timed override feature which allows the occupant to switch the system into the occupied mode during hours when it is scheduled to be unoccupied The most common means for enabling this function is a timed override button located on the zone sensor Figure 118 Typically pressing this button directs the system to operate in the occupied mode for only a fixed period of time two hours for example After this time period expires the BAS automatically returns the zone to unoccupied mode Finally in some cases it may be important to control humidity in addition to temperature when the building is unoccupied to avoid damage to the building structure and furnishings The BAS can monitor indoor humidity levels and take action if the humidity rises above a maximum limit see After hours dehumidification p 109 or drops below a minimum limit SYS APM010 EN Water Source and Ground Source Heat Pump Systems 177 E TRANE System Controls 178 Moming warm up or cool down mode As mentioned previously the temperature inside a building is typically allowed to drift when unoccupied usually for the purpose of saving energy This generally requires the HVAC system to start prior to occupancy and operate long enough for the temperature inside the building to reach the desired occupied setpoint by the time people are expected to
253. oplets in an air stream SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 201 202 morning cool down mode A typical operating mode for transition from the unoccupied mode to the occupied mode during the cooling season It establishes the zone occupied comfort conditions because they were allowed to drift from the occupied setpoint during the unoccupied mode usually to save energy morning warm up mode A typical operating mode for transition from the unoccupied mode to the occupied mode during the heating season It establishes the zone occupied comfort conditions because they were allowed to drift from the occupied setpoint during the unoccupied mode usually to save energy night setback See setback Noise Criteria NC A single number used to describe sound in a occupied space It uses a series of curves for plotting sound pressure by octave band and determining the NC value non condensing boiler A conventional boiler designed to operate without condensing the flue gases inside the boiler Only the sensible heat value of the fuel is used to heat the hot water All of the latent heat value of the fuel is lost up the exhaust stack occupied mode The typical daytime operating mode of a system The building must be ventilated and the comfort cooling or heating temperature setpoints must be maintained in all occupied zones occupied standby mode A daytime operating mode of a system when a zone is expected to
254. or air to 52 F 11 C dew point then reheats the air to 71 F 22 C dry bulb before delivering it directly into the classrooms The dew point of this conditioned OA is low enough to offset the latent load in the classrooms but because it is delivered at a dry bulb temperature that is near the desired zone temperature which is 74 F 23 C in this example it offsets only asmall portion of the sensible cooling load in the classrooms For Classroom 101 the design sensible cooling load in the zone is 29 800 Btu hr 8 7 kW When the 450 cfm 0 21 m3 s of outdoor air required for that zone is delivered at a neutral dry bulb temperature 71 F 22 C in this example the conditioned OA offsets only 1 470 Btu hr 0 43 kW of the zone sensible cooling load The local WSHP must be sized to offset the remaining 28 330 Btu hr 8 3 kW of sensible load with a supply airflow of 1380 cfm 0 65 m3 s assuming the WSHP cools the air to 55 F 13 C Table 1 Example of cold air versus neutral air delivery Classroom 101 Classroom 102 Classroom 103 Classroom 104 Zone outdoor airflow Voz 450 cfm 0 21 m3 s 450 cfm 0 21 m3 s 480 cfm 0 23 m3 s 440 cfm 0 21 m3 s Zone sensible cooling load Qzone sensible 29 800 Btu hr 8 7 kW 26 800 Btu hr 7 9 kW 26 900 Btu hr 7 9 kW 28 300 Btu hr 8 3 kW Zone cooling setpoint Tzone 74 F 23 C 74 F 23 C 74 F 23 C 74 F 23 C
255. or some other device that provides a comparable reduction in pump power at reduced water flow rates Water Source and Ground Source Heat Pump Systems SYS APM 010 EN S TRANE System Design Issues and Challenges Cooling tower control If a cooling tower is equipped with a motor of 7 5 hp 5 6 kW or larger Section 6 5 5 2 requires the fan be capable of operating at two thirds of full speed or less and must have controls to automatically change fan speed to control the leaving fluid temperature In many cases this is accomplished by equipping the cooling tower fan with a variable speed drive Exhaust air energy recovery Section 6 5 6 1 of ASHRAE 90 1 states that exhaust air energy recovery is required on each fan system in which the system design airflow is greater than or equal to the value listed in Table 25 For example in climate zone 4a if the system brings in 30 percent outdoor air exhaust air energy recovery is required if the system design airflow rate is 5500 cfm 2596 L s or higher Table 25 Exhaust air energy recovery requirement Percent outdoor air at design airflow 230 and 240 and 250 and 260 and 270 and gt 80 lt 40 lt 50 lt 60 lt 70 lt 80 eae Climate zone Minimum system design airflow at which energy recovery is required 4 25000 cfm 25000 cfm 3b 3c 4b 4c 5b not required not required not required not required 2360 L s 2360 L s 1b 2b 5c not requ
256. ormance when delivering cool air to the zone adsorption Process by which fluid molecules are concentrated on a surface by chemical or physical forces AHRI Air Conditioning Heating and Refrigeration Institute www ahrinet org air cooled condenser A type of condenser in which refrigerant flows through the tubes and rejects heat to outdoor air that is drawn across the tubes air source heat pump A type of heat pump that transfers heat from indoor air to outdoor air and vice versa air diffusion Distribution of air within a conditioned space by an outlet discharging supply air in various directions and planes air handling unit AHU A piece of equipment used to move clean and condition heat cool humidify dehumidify air air separator A component of a closed piping system that removes air that is entrained in the water distribution system airside economizer A method of free cooling that involves using cooler outdoor air for cooling instead of recirculating warmer indoor air air to air energy recovery The transfer of sensible heat or sensible plus water vapor latent heat between two or more air streams or between two locations within the same air stream ANSI American National Standards Institute www ansi org ARI Former Air Conditioning amp Refrigeration Institute See AHRI ASHRAE American Society of Heating Refrigerating and Air Conditioning Engineers www ashrae org aspiration ratio Total ro
257. ormation on air to air energy recovery including application and control in a dedicated outdoor air system refer to the Trane application manual Air to Air Energy Recovery in HVAC Systems SYS APM003 EN S TRANE Primary System Components sensible heat and water vapor from the exhaust air and transfers it to the outdoor air being brought into the building for ventilation Sensible energy recovery devices transfer only sensible heat Common examples include coil loops fixed plate heat exchangers heat pipes and sensible energy rotary heat exchangers also known as sensible energy wheels or heat wheels Total energy recovery systems not only transfer sensible heat but also water vapor or latent heat Common examples include total energy rotary heat exchangers also known as total energy wheels or enthalpy wheels and fixed membrane heat exchangers In many climates and building types exhaust air energy recovery is an effective means of reducing the energy required to cool dehumidify heat or humidify the entering outdoor air It also reduces the required cooling and heating capacity of the dedicated OA unit However adding an air to air energy recovery device increases the static pressure drop in both the outdoor and exhaust air paths which impacts fan energy use The energy saved by preconditioning the outdoor air must exceed any increase in fan energy use In addition routing most of the exhaust air back to the energy
258. ortant system level control functions is to coordinate the water source heat pumps cooling tower boiler and other pieces of equipment during the various modes of operation The primary system level control modes in a water source heat pump system are e Occupied mode e Unoccupied mode e Morning warm up or cool down mode Typically a time of day schedule in the building automation system is used to define when the system is to operate in these various modes Occupied mode When the building is occupied the heat pumps must maintain the temperature in each occupied zone at the desired setpoint cooling or heating and provide the required amount of outdoor air for ventilation Table 29 describes the typical functions of the different system components during the occupied mode Table 29 Coordination of equipment during occupied mode e Activates the fant WSHP e Positions the reversing valve and cycles the compressor s to maintain zone temperature at the occupied setpoint cooling or heating Activates the fan to bring in the required amount of outdoor air for ventilation e Modulates cooling dehumidification or heating to discharge air at the desired conditions e Modulates the central relief fan to maintain indoor to outdoor static pressure difference at the desired setpoint Dedicated outdoor air unit e Turns on water circulating pumps if a variable flow system varies the speed of the pumps to maintain press
259. ose of humidity control it lists several exceptions for which reheat is allowed Exception E allows for the unlimited use of reheat for humidity control if at least 75 percent of the energy for reheating is site recovered energy such as heat recovered from the refrigeration circuit or hot gas reheat As long as the zone humidity level is less than the desired upper limit 60 percent RH for example the heat pump operates in the standard cooling mode and the compressor cycles on and off to maintain zone temperature When the humidity sensor indicates that zone humidity is too high and the zone temperature is at setpoint the compressor remains on to continue dehumidifying the air and the reheat valve diverts hot refrigerant vapor from the compressor through the reheat coil warming the supply air to avoid overcooling the zone Using the previous classroom example the WSHP always delivers 1 500 cfm 0 7 m3 s of air to the zone For comparison purposes assume the humidity sensor is set to keep the zone humidity at or below 62 percent RH At the same example part load condition mild rainy day the compressor operates for a longer portion of the hour to dehumidify the air CC and maintain zone humidity at 62 percent RH and the hot gas reheat coil warms the supply air SA to avoid overcooling the zone Figure 76 Figure 76 Constant speed WSHP with HGRH at part load unconditioned OA mild rainy OA 70 F DB 69 F WB MA
260. ost and energy use if the conditioned outdoor air is delivered at a cold temperature rather than reheated to neutral Requires installation of additional ductwork and separate diffusers May require multiple diffusers to ensure that outdoor air is adequately dispersed throughout the zone Conditioned OA delivered to the intake of each WSHP Advantages Disadvantages Helps ensure the required amount of outdoor air reaches each unit because the OA is ducted directly to each intake Avoids the cost and space needed to install additional ductwork and separate diffusers Easier to ensure that outdoor air is adequately dispersed throughout the zone because outdoor air is distributed by the WSHP fan Measurement and balancing is more difficult than if the OA was delivered directly to the zone via separate diffusers May need to increase ventilation to account for Ez lt 1 0 during heating mode Typically requires a field fabricated plenum or section of duct to connect the outdoor air duct and mix it with recirculated air prior to entering the heat pump Fans inside the heat pumps must operate continuously to provide ventilation during scheduled occupancy rather than cycling off with the compressor If the dedicated OA system operates during unoccupied periods e g for after hours humidity control or preoccupancy purge the fans inside the heat pumps typically must operate also Conditioned OA delivered to the supply si
261. owei Tube botei Dunan itt TE inga teaceg td D 2 ar U Tae ae Da O 5 RSG at Bre Bo l tent bates S UTi Cpyate Ouna DIY 7 OF ww vibama Fome pe tarwa ih Fit F ter Cur ma Sewer betas RECTANGULAR COMIGURATION G4 a E itar Optieme tat ipec ping the Ihat Convection oefen Fiemora Pore Cet Taher How Core 1 nes Now Hea Asp Semai Ta GHAN OCET 0 Pw The Trane TRACE 700 software has the capability to export both peak and monthly loads that can then be imported into GLHEPRO a ground heat exchanger design software program After running GLHEPRO specific characteristics about the ground heat exchanger design can be imported back into TRACE for a more accurate simulation of system energy use SYS APM010 EN Water Source and Ground Source Heat Pump Systems be Sa Dar Pisom J cm In addition the software program requires the peak heating and cooling load in Btu hr kW for example for each month of the year as well as the total quantity of heat in Btu kWh for example rejected to and extracted from the ground during each month of the year Figure 97 Some software programs have the capability to import this data from HVAC load calculation software 145 E TRANE System Design Variations 146 Figure 97 Monthly heating and cooling loads Month Total Heating Total Cooling Peak Heating Peak Cooli
262. ower needs to operate Figure 7 In this manner a WSHP system provides a form of heat recovery Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Overview of a Water Source Heat Pump System Figure 7 System operation during mild weather spring and fall cooling tower off water circulating pumps on Q nm boiler off 70 F 21 C eiki JZE L heat pumps in heating mode In applications such as office buildings heat generated by lights people and office equipment may require year round cooling in the interior zones of the building In these applications the benefit of this heat recovery further reduces boiler operation during the winter months Benefits of WSHP Systems heat pumps in cooling mode The following section discusses some of the primary benefits of using a WSHP system Provides multiple zones of comfort control Water source heat pump systems are capable of controlling the temperature in many zones with dissimilar cooling and heating requirements This is accomplished by providing a separate WSHP and temperature sensor for each independently controlled zone When the sun is shining against the west side of the building in the late afternoon the WSHPs serving the zones on that side of the building can operate in the cooling mode while the WSHPs serving the zones along the east exposure can cycle their compresso
263. owing is a process for sizing the cooling tower L Sum the heat rejection from all heat pumps connected to the loop 2 Apply system load diversity to estimate the maximum instantaneous heat rejection required of the cooling tower 3 Calculate the cooling tower range 4 Select the cooling tower using the design ambient wet bulb temperature design system water flow rate design leaving water temperature and range 44 Water Source and Ground Source Heat Pump Systems SYS APM010 EN Failing to account for system load diversity when selecting the cooling tower will likely result in a larger than necessary tower This increases installed cost and energy use while providing little added benefit to system performance If load calculation software has not been used to determine the block cooling load consider using the following conservative estimates e For a system water flow rate greater than 200 gpm 13 L s assume 90 percent system load diversity For a system water flow rate between 200 gpm 13 L s and 300 gpm 19 L s assume 85 percent system load diversity For a system water flow rate greater than 300 gpm 19 L s assume 80 percent system load diversity Depending on the building type and climate system load diversity may be as low as 65 or 70 percent SYS APMO010 EN S TRANE Primary System Components The first step is to sum the heat rejected from all heat pumps that are connected to the loop The mos
264. pace in the building This section discusses three types of ground source systems including A ground coupled heat pump system which is a closed system that uses special high density polyethylene pipes that are buried in the ground as a heat source and heat sink A surface water heat pump system which is similar to a ground coupled heat pump system except that the pipes are submerged in a pond or lake A ground water heat pump system in which water is pumped from a well and then either returns to the source through a separate well or is directed to a drain field or sewer system Typically an intermediate heat exchanger separates the well water from the water circulated throughout the building While this section focuses primarily on closed loop ground coupled systems because they are the most common the other two types of systems certainly should be considered when feasible Table 27 summarizes the advantages and drawbacks of these three types of GSHP systems SYS APM010 EN Water Source and Ground Source Heat Pump Systems 135 S TRANE System Design Variations Table 27 Comparison of ground source heat pump systems Ground coupled heat pump system Advantages Disadvantages Simpler to design than the other types of ground source systems Closed system means that no water treatment is required and is not reliant on a constant supply of water from a well Typically requires the least amount
265. pen Loop Heat Pump Systems ASHRAE J ournal March pp 52 62 Sheet Metal and Air Conditioning Contractors National Association SMACNA 2006 HVAC Systems Duct Design Chantilly VA SMACNA Water Source and Ground Source Heat Pump Systems SYS APM 010 EN Shirey D H Henderson and R Raustad 2003 Understanding the Dehumidification Performance of Air Conditioning Equipment at Part Load Conditions DOE NETL Project DE FC26 01NT41253 Florida Solar Energy Center Cocoa FL Stanke D 2004 Addendum 62n Single zone amp Dedicated OA Systems ASHRAE J ournal October pp 12 20 Stanke D 2005 Addendum 62n Single Path Multiple Zone System Design ASHRAE J ournal J anuary pp 28 35 Stanke D 2006 Standard 62 1 2004 System Operation Dynamic Reset Options ASHRAE J ournal December pp 18 32 Trane 2004 Trane CDQ Desiccant Dehumidification CLCH PRB0O20 EN La Crosse WI Trane Bradway B Hallstrom A Stanke D and Bailey N 1998 Managing Building Moisture SYS AM 15 La Crosse WI Trane Cline L and J Harshaw 2010 Central Geothermal Systems SYS APMOO9 EN La Crosse WI Trane Guckelberger D and Bradley B 2006 Acoustics in Air Conditioning ISS APMO01 EN La Crosse WI Trane Murphy J and Bradley B 2002 Air to Air Energy Recovery in HVAC Systems SYS APMO03 EN La Crosse WI Trane Murphy J and Bradley B 2002 Dehumidification in HVAC S
266. perature 52 F 11 C versus 74 F 23 C it offsets a significant portion of the sensible cooling load in the SYS APMO010 EN Water Source and Ground Source Heat Pump Systems 65 Se TRANE Primary System Components classrooms This reduces the sensible load that must be offset by the local heat pumps allowing them to be sized for less airflow and less cooling capacity than in a neutral air system For Classroom 101 when the 450 cfm 0 21 m3 s of outdoor air is delivered at a cold dry bulb temperature 52 F 11 C in this example the conditioned OA offsets 10 740 Btu hr 3 1 kW of the zone sensible cooling load The local WSHP need only be sized to offset the remaining 19 100 Btu hr 5 6 kW of sensible load which corresponds to a supply airflow of only 930 cfm 0 44 m3 s Figure 46 and Figure 47 Figure 46 Conditioned OA delivered directly to each zone Classroom 101 450 cfm at 71 F 0 21 m3 s at 22 C Neutral Air System 1380 cfm at 55 F 0 65 m3 s at 13 C 1830 cfm 0 86 m3 s 450 cfm at 52 F 0 21 m3 s at 11 C Cold Air n ON 1380 cfm 0 65 m3 s 66 Water Source and Ground Source Heat Pump Systems SY S APM 010 EN S TRANE Primary System Components Figure 47 Conditioned OA delivered directly to the supply side of each WSHP Classroom 101 450 cfm at 71 F 0 21 m3 s at 22 C Neutral Air System 1380 cfm at 55 F 0 65 m3 s at 13 C
267. pied While the outdoor airflow delivered to the breathing zone Vbz can be reset as zone population Pz varies per Section 6 2 7 the system must deliver at least the building related or base ventilation rate Ra whenever the zone is expected to be occupied see Minimum ventilation required in breathing zone Vbz p 91 To reduce installation costs some WSHP systems use simple residential style thermostats with no system level controls A non programmable thermostat causes the heat pump to maintain the same temperature whether the zone is occupied or not Use of a programmable thermostat allows a zone to vary the temperature setpoint based on time of day and day of the week But they also allow occupants to override these setpoints or ignore the schedule altogether by using the hold feature of the thermostat thus thwarting any potential for energy savings A more sustainable approach may be to equip each heat pump with a DDC controller that is connected to a zone temperature sensor and then use a system level controller that coordinates the operation of all components of the system This system level controller contains a time of day schedule that defines when the building is expected to be unoccupied During these times the system is shut off and the temperature in each zone is allowed to drift away from the occupied setpoint often called night setback Allowing the indoor tempera
268. pment operators and technicians may also find this publication of interest because it addresses system layout and control Trane in proposing these system design and application concepts assumes no responsibility for the performance or desirability of any resulting system design Design of the HVAC system is the prerogative and responsibility of the engineering professional Trademarks Trane and the Trane logo are trademarks of Trane in the United States and other countries All trademarks referenced in this document are the trademarks of their respective owners 2013 Trane All rights reserved Water Source and Ground Source Heat Pump Systems SYS APM010 EN Table of Contents PremaCe sicuvdh scence eset awkena naike i Gane ited a a E a EE ii Overview of a Water Source Heat Pump System 1 Basic System Operation 0 0c cect 2 Zone is occupied and requires cooling cece cece eee eee 2 Zone is occupied but requires no cooling or heating 3 Zone is occupied and requires heating ccc cece eee ee eee 3 Zone is unoccupied 1 eee 4 Seasonal operation of the water loop 0 000 e eee eee 5 Benefits of WSHP Systems 0 0 ects 7 Provides multiple zones of comfort control ccc eee ees 7 Opportunity to save energy ccc cee eee eens 8 Limits impact of equipment failure 0 0 0 c eee ee 10 Ease of installation 0 0 0 0 c cett
269. ptimized WSHP system reduced the overall HVAC energy use by 20 percent for the building in Atlanta by 15 percent in Louisville and by 8 percent in Minneapolis If the system is converted to a ground coupled heat pump system the energy savings increases to 37 percent in Atlanta 40 percent in Louisville and 24 percent in Minneapolis There is a real potential to save energy in WSHP systems through optimized system design and control strategies This savings reduces operating costs for the building owner and can help in achieving points toward LEED certification Water Source and Ground Source Heat Pump Systems SY S APM 010 EN S TRANE System Design Issues and Challenges Acoustics HVAC equipment creates sound and in a well designed application that a a a sound provides a positive effect on occupant comfort That is it provides an in general refer to the Trane application appropriate level of background sound for speech isolation or permits clear manual Acoustics in Air Conditioning communication in a classroom However it is also possible for the sound GSS ARMOO TEN from HVAC equipment to be considered noise because it disrupts the intended function of the building Equipment sound levels play a role in proper room sound levels but a larger role is played by how the equipment is applied One common approach to addressing HVAC acoustics is to use a fixed set of design practices on every project With sufficient experience this
270. r and lessens and may even eliminate the need for frost prevention Total energy recovery devices generally have a higher effectiveness than most sensible energy recovery devices so they save more heating energy and may permit greater downsizing of the heating equipment SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 71 TRANE Primary System Components For more information on methods used for capacity control and frost prevention with various air to air energy recovery devices refer to the Trane application manual Air to Air Energy Recovery in HVAC Systems SYS APM003 EN Water vapor transferred by a total energy recovery device humidifies the entering outdoor air during the heating season which helps keep the space from becoming too dry Free humidification also reduces the energy used by the mechanical humidification system if installed and may allow this equipment to be downsized Most heating climates also include a cooling season Applying a total energy recovery device enables a larger reduction in cooling capacity than a sensible energy recovery device which can offset some of the first cost premium for energy recovery Strive for balanced airflows Duct as much of the exhaust airflow to the energy recovery device as possible The less disparity between the outdoor and exhaust airflows the more energy can be recovered If demand controlled ventilation DCV is being used the amount
271. r opportunity for fan energy savings However even if a zone may not bea good candidate for this type of motor based solely on energy savings the decision to use an ECM may be based on other benefits listed below e Self balancing An ECM is capable of maintaining a relatively constant airflow regardless of filter loading or future changes to downstream ductwork e Gradually changing sound levels The soft start nature of the ECM allows the fan to ramp up slowly when activated and ramp down slowly when turned off This minimizes the distraction of the fan cycling on and off especially when the heat pumps are located in spaces where people are sleeping such as hotels motels apartments condominiums dormitories barracks and extended care facilities Potential drawbacks include e Higher installed cost An ECM requires a power transistor to drive the stator windings ata specified motor current and voltage level This addition coupled with electronic commutation controls currently make them more expensive to purchase than their AC counterparts e Potential for disruptive harmonic currents Harmonic currents are created when AC power is converted to DC power In some cases these currents can overheat conductors and connectors interfere with the operation of sensitive equipment and in severe cases burn out transformers and motors Determining whether harmonic currents will cause a problem in a particular building r
272. r of pipe buried in the ground using a trenching machine However land requirements have been reduced with the advent of multiple layer horizontal loops While less land and trenching is required a multiple layer loop requires more total length of piping than a single layer loop Each closed loop pipe is placed in a trench which is typically 6 ft 18 m deep and spaced 6 to 15 ft 18 to 4 6 m apart Trench length can range from 100 to 400 ft per block cooling ton 8 7 to 34 7 m kW for a single layer loop Advantages of horizontal loops include e Trenching costs are typically lower than the drilling costs associated with vertical loop installation e In cooler climates horizontal loops may not build up as much heat over time as vertical loops because the pipes are closer to the surface where heat can be dissipated to the atmosphere Drawbacks include e Horizontal loops require a larger area of land than vertical loops e Atthis shallower depth ground temperatures are subject to seasonal temperature variations rainfall and snow melting Obtaining the same loop temperatures as a vertical loop requires a more complicated design with longer pipe lengths e The longer pipe lengths also require more antifreeze solution when necessary and more pumping energy than vertical loops e The pipe is at greater risk of damage during backfilling of the trenches SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 139
273. r static pressure drop e Dirt holding capacity Dirt holding capacity is an indication of how much dirt the filter will hold at the dirty or final pressure drop This indicates how often the filter will need to be replaced In general a filter with more media surface area will hold more dirt and will need to be replaced less frequently This varies with the brand of filter e Available space In general filters with a higher collection efficiency lower airside pressure drop and or greater dirt holding capacity require more space than filters that perform more poorly in these categories e Available budget Filters with more media surface area generally cost more than filters with less surface area This impacts both the installed cost and maintenance replacement cost of the filter system It is important to maintain and replace filters as recommended by the manufacturer The replacement filters should have similar performance characteristics as the filters originally specified by the design engineer Critical characteristics include efficiency MERV rating for example airside pressure drop at the desired operating airflow and physical size In addition air bypass can reduce the effectiveness of the filtration system During replacement the filter assembly should be carefully inspected to identify any areas that can allow air to bypass around the filters These areas should be sealed with gasketing for example to m
274. r to be exhausted from C to E so that it is high enough to overcome the pressure loss associated with the relief damper and force the excess air out of the building Adding the relief fan allows the system to exhaust air that is to be replaced by fresh outdoor air and does so without increasing the pressure inside the building see Building pressure control p 185 SYS APM010 EN Water Source and Ground Source Heat Pump Systems 19 Se TRANE Primary System Components Electronically commutated motor Figure 17 Electronically commutated Some smaller water source heat pumps use an electronically commutated 20 motor ECM GE Industrial Systems motor ECM for the fan An ECM is a brushless DC motor that combines a permanent magnet rotor wound field stator and an electronic commutation assembly to eliminate the brushes Figure 17 Some benefits of using an ECM on the heat pump fan include e Energy savings ECMs are typically more efficient than the single speed fractional horsepower motor technologies that have traditionally been used in smaller water source heat pumps This efficiency difference often allows ECMs to offer substantial energy savings compared to conventional motor technologies When the heat pump includes a two stage variable capacity or variable speed compressor or if itincludes more than onecompressor the ECM can be used to change fan speeds at part load conditions This provides anothe
275. rage their signals In any case select sensors that will minimize wind effect and keep water out of the sensing tube and locate them to minimize the effects of wind Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Controls System optimization When there is a building automation system BAS that provides system level coordination of the various pieces of equipment the next logical step is to optimize the control of that system For this discussion optimization is defined as minimizing the cost to operate the entire HVAC system while still maintaining acceptable comfort In other words this means maximizing the efficiency of the entire system not just an individual component Optimal start The morning warm up or cool down mode was discussed previously in this chapter In some buildings a simple time clock or a time of day schedule is used to start and stop the HVAC system In this case the time at which the morning warm up or cool down mode begins is typically set to ensure that the indoor temperature reaches the desired occupied setpoint prior to occupancy on the coldest or warmest morning of the year In other words the system is programmed to start early enough so that the building will warm up or cool down fast enough on the worst case morning As a result for most days the system starts earlier than it needs to This increases the number of operating hours and increases energy use An a
276. ransfer Fluids for HVAC and Refrigeration Systems www dow com heattrans Hackel S and A Pertzborn 2011 Hybrid Ground Source Heat Pump Installations Experiences Improvements and Tools Madison WI Energy Center of Wisconsin Henderson H 1998 The Impact of Part Load Air Conditioner Operation on Dehumidification Performance Validating the Latent Capacity Degradation Model Proceedings of ASHRAE IAQ and Energy 1998 pp 115 122 Institute of Environmental Sciences and Technology IEST 2006 HEPA and ULPA Filters IEST RP CCOOL4 Mt Prospect IL IEST International Ground Source Heat Pump Association IGSHPA 1988 Closed Loop Ground Source Heat Pump Systems Installation Guide Stillwater OK IGSHPA www igshpa okstate edu Mescher K 2009 One Pipe Geothermal Design Simplified GCHP System ASHRAE J ournal October pp 24 40 Morris W 2003 The ABCs of DOAS Dedicated Outdoor Air Systems ASHRAE J ournal May pp 24 29 Murphy J 2006 Smart Dedicated Outdoor Air Systems ASHRAE J ournal J uly pp 30 37 Murphy J 2009 Using Time of Day Scheduling To Save Energy ASHRAE J ournal May pp 42 48 National Air Filtration Association NAFA 2007 NAFA Guide to Air Filtration 4th Edition Virginia Beach VA NAFA New Buildings Institute NBI 1998 Gas Boilers Advanced Design Guideline Fair Oaks CA NBI http Awww newbuildings org Rafferty K 2009 Commercial O
277. rces and accounts for the effects of the cabinetry Receiver The receiver is simply the location where the sound will be heard and judged against some defined criteria This could be a private office a conference room an open office area a classroom a hotel guest or dormitory room and so on Typically a building will have many indoor receiver locations but often these can be grouped by similarity e g a school may have many classrooms that use the same equipment and are dimensionally similar SYS APM010 EN Water Source and Ground Source Heat Pump Systems 125 S TRANE System Design Issues and Challenges 126 return airborne Path The path is the route the sound travels from the source to the receiver Sound from a single source may follow more than one path to the receiver location Figure 84 For example sound from the fan inside the WSHP follows the supply ductwork and enters the occupied space through the supply air diffuser That fan sound also travels back out through the WSHP inlet against the direction of airflow and then through the ceiling into the space Figure 84 Typical sound paths in a WSHP system water source heat pump ow ceiling transmission radiated from casing supply airborne For each sound source it is necessary to determine the path that the sound travels from the equipment to the receiver location These sound paths are dependent on the type and location of the equipment
278. rdance with current building and energy codes experience a net cooling load during daytime operation even at cold ambient temperatures In such a case the heat rejected to the loop during daytime hours or during a mild winter day could be stored for use when the building requires heat during the cold nighttime hours or during a colder winter day The process for sizing the tank is the same as above except that Step 1 is used to calculate the total amount of heat extracted from the loop during the nighttime unoccupied hours While the storage tank can be sized to provide all of the nighttime heat required it should also be verified that there is sufficient excess heat rejected to the loop during the daytime hours to re charge the loop and tank 56 Water Source and Ground Source Heat Pump Systems SYS APM 010 EN S TRANE Primary System Components Of course budgetary constraints available space and ability to support the weight of the tank are also factors that can dictate the maximum storage tank size that can be installed in a given building After calculating the required tank size the design engineer can evaluate the installed cost versus the operating cost savings to determine the optimal tank size Electric resistance heat in the WSHP boilerless system For applications where the heat pumps are not expected to operate in the heating mode for many hours during the year an alternative to using a centralized bo
279. re While a rare few applications may still require their use the need for water regulating valves has all but disappeared due to the commonplace use of TXVs and less expensive isolation valves see Water regulating valves p 18 A flow control valve is used to facilitate water balancing at system start up and to optimize WSHP performance by ensuring the proper water flow rate when the compressor operates Too little flow can increase compressor energy use and may even damage equipment or shorten equipment life while too much flow can result in excessive pump energy use SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 39 Se TRANE Primary System Components 40 Some common approaches used to provide for flow control include e Manual ball valves In simple constant flow pumping systems manual ball type balancing valves can be installed in the water pipes for each WSHP Figure 29 During system balancing pressure and temperature measurements via the ports on the ball valves are used to manually adjust one of the valves to allow more or less water flow through the WSHP While only one valve is needed for balancing valves are typically installed in both the entering and leaving pipes to allow for easy removal or service of the WSHP Figure 29 Manual ball valves for water balancing isolation valve y return manual ball valve with pressure temperature port
280. re can be differences Advantages of vertical loops include e They typically require the least amount of land of the three configurations Vertical loops typically require anywhere from 60 to 275 ft2 of ground surface per block cooling ton L6 to 73 m2 kW e They typically require less total piping than the other two configurations because the ground temperature is more constant at greater depths e When piped in a parallel reverse return configuration this pattern typically requires the least amount of pumping energy of the three configurations 138 Water Source and Ground Source Heat Pump Systems SYS APM010 EN Figure 90 Horizontal heat exchanger S TRANE System Design Variations Drawbacks include e Drilling costs are frequently higher than the trenching costs associated with horizontal or spiral loops e Grouting and backfilling of the boreholes require special attention to fill material and to ensuring that the pipes and surrounding earth remain in contact e Ifthe boreholes are spaced too close together there is a potential for long term heat build up in the ground that may be undesirable for a cooling dominated application e Installation requires the knowledge and availability of a certified loop contractor with proper drilling equipment Horizontal loops Horizontal loops are often considered when adequate land is available Figure 90 Historically horizontal loops often consisted of a single laye
281. recovery device often requires the installation of additional ductwork Note An advantage of a coil loop is that it can be used to transfer heat between air streams that are physically separated by some distance making it particularly advantageous in retrofit situations Also a coil loop can be used to recover heat from multiple separate exhaust air streams using multiple exhaust side coils When using air to air energy recovery to precondition the entering outdoor air consider the following general recommendations e Sensible or total energy recovery In most climates a total energy recovery device allows for greater downsizing of the cooling and heating equipment and usually provides the best payback because it recovers both sensible heat and water vapor latent heat The most notable exception is in warm dry climates where itis often unnecessary to mechanically dehumidify the outdoor air In this case a sensible energy recovery device likely provides the best value There is a common misperception that only hot humid climates justify the need for total energy recovery When compared with sensible energy recovery however total energy recovery devices can provide advantages in climates where heating operation prevails Frost forms on atotal energy recovery device at a much colder outdoor temperature than it does on a sensible energy recovery device This allows total energy recovery to recover more heat during cold weathe
282. refer to building To prevent water related problems within the WSHP itself follow the Trane application manual Managing i j Building Moisture SYS AM 15 these basic practices e Provide access suitable for regular inspection and cleaning Ensure that the WSHP includes removable panels to allow regular inspection and cleaning Poor location of the WSHP or limited service clearance can also discourage inspection and cleaning e Use sloped drain pans and clean them regularly A flat drain pan retains water and stagnant water can provide a habitat for microbial growth A sloped pan improves drainage considerably and eliminates standing water Be sure that the drain connection is located at the lowest pointin the pan and install the WSHP within the manufacturer s tolerance for levelness e Properly install condensate traps and periodically clean them out If the refrigerant to air heat exchanger and its associated drain pan are located upstream of the supply fan draw thru configuration the pressure inside the WSHP unit casing at the location of the drain pan is less than the pressure outside so air can be drawn in through the condensate drain line from outside This results in the wetting of the interior of the unit and may even allow water to leak into the building If the refrigerant to air heat exchanger and drain pan are located downstream of the supply fan blow thru configuration the pressure inside the casing is greater tha
283. riate descriptor such as Noise Criteria NC or Room Criteria RC for indoor environments or dBA for classrooms or outdoor environments Remember the following when defining the desired sound levels e As a general rule lower sound levels cost more to achieve e The entire building does not have the same acoustical requirements Restrooms and hallways do not need to be as quiet as executive offices and conference rooms A low cost quiet installation takes advantage of this point e Successful acoustics requires a team effort including the owner HVAC design engineer architect equipment manufacturer and installing contractor Step 2 Identify each sound path and its elements Paths are defined by the end points the source location and the receiver location There may be many receiver locations depending on the installation but the number can be reduced by determining the critical receiver locations In general sound diminishes with distance so the space closest to the unit will typically be the loudest If adjacent spaces have sound targets that are considerably below the level required in the space closest to the unit these spaces should also be analyzed Common examples include conference rooms executive offices hotel guest or dormitory rooms and classrooms After the critical receiver locations are defined the sound paths from the source to each receiver can be identified Step 3 Perform a path by path analysis i
284. rom warmer ground GCHP systems offer the potential for reduced energy use when compared to a traditional boiler tower WSHP system because they can reduce or eliminate the energy needed to operate a cooling tower and or boiler Eliminating the cooling tower and boiler also has architectural and maintenance advantages and may free up floor space in the building In addition the loop may operate at cooler temperatures during the cooling season than in a conventional boiler tower system This results in the heat pump compressors operating more efficiently The installation costs associated with this system however must be considered to determine the economic viability In general the largest portion of the installation cost is due to the ground heat exchanger Installation requires excavation trenching or boring and in some locales there are very few qualified contractors for installing the ground heat exchanger SYS APM010 EN Water Source and Ground Source Heat Pump Systems 137 S TRANE System Design Variations Figure 89 Vertical heat exchanger In a perfectly balanced system the amount of heat rejected to the ground over the year would equal the amount of heat extracted eliminating the need for a cooling tower and boiler In most applications however there is an imbalance between heat rejected to the ground and heat extracted This imbalance requires the ground heat exchanger to be larger to prevent the ground temperature from
285. round piping may cause the loop water temperature to decrease below the low temperature safety limit This could trip the WSHP controller and prevent the compressor from starting until the diagnostic is cleared manually To prevent this from occurring consider installing asmall boiler or water heater sized only to offset any expected heat loss through the tower and exposed or underground piping Natural heat source Some WSHP systems use a natural heat source such as the ground or a lake as the heat adder For more information on ground coupled surface water and ground water systems see System Design Variations p 135 Dedicated OutdoorAir System Most building codes require a minimum quantity of outdoor air OA be provided to each zone for ventilation This outdoor air can be brought into the building locally or centrally A rooftop style WSHP includes an outdoor air damper that allows outdoor air to be brought into and conditioned by each heat pump Similarly a console type WSHP may include an optional OA damper that allows outdoor air to be brought into the heat pump through an opening in the perimeter wall of the building However in most WSHP systems particularly those that use horizontal vertical console or vertical stack models the outdoor air required for ventilation is typically conditioned and delivered by a dedicated outdoorair system Water Source and Ground Source Heat Pump Systems SYS APM010 EN
286. rs to avoid overcooling or operate in the heating mode if necessary SYS APMO010 EN Water Source and Ground Source Heat Pump Systems 7 S TRANE Overview of a Water Source Heat Pump System Note In the heating mode a water source heat pump is typically capable of supplying air up to about 100 F 38 C depending on airflow and operating conditions This is typically warmer air than can be supplied by an air source heat pump when operating during cold weather Opportunity to save energy Several characteristics of a WSHP system make it an energy efficient system choice First as explained previously during some parts of the year a WSHP system provides heat recovery because the heat rejected by WSHPs serving zones that require cooling can be used to provide heat for those zones that require heating This saves energy by reducing the need to operate the cooling tower or boiler Second using a heat pump for heating is typically more efficient than using electric resistance heat or a gas fired burner When operating in the heating mode the coefficient of performance COP of a water source heat pump might be somewhere between 3 0 and 6 0 depending on model and operating conditions This is significantly higher than a COP of 10 for electric resistance heat Third when operating in the cooling mode the refrigeration cycle of a WSHP is water cooled Water cooled condensing is typically more efficient than air cooled condensing
287. s duct connectors to prevent vibration transmission to steel ducts To avoid vibration transmission from ducts to the ceiling do not attach ceiling wires to or through ducts Finally to minimize vibration transmission to the floor install floor mounted WSHPs on rubber or cork pads or on rubber backed carpeting with padding thickness of 3 8 to 1 2 in 9 5 to 13 mm WSHP console or unit ventilator models From an acoustical perspective console style water source heat pumps are simple to model but difficult to attenuate Sound data provided by AHRI 128 Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN S TRANE System Design Issues and Challenges Standard 350 Sound Rating of Non Ducted Indoor Air Conditioning Equipment is for the entire unit discharge inlet and casing sound are combined The sound path is simply the room correction that accounts for the size and absorptivity of the room where the WSHP is located Units placed in exceptionally hard rooms i e rooms with an absorptivity factor less than 0 20 may benefit from adding absorptive materials to the walls and ceiling A typical acoustically hard or live room is characterized by a tile floor and masonry or gypsum board walls and ceiling Since very little is typically done to change the acoustical character of the room the most effective ways to reduce sound in the occupied area are to choose a WSHP with a lower sou
288. s the cooled or heated mixture to the zone through ceiling mounted supply air diffusers Air returns from the zone through ceiling mounted return air grilles Assuming negligible duct leakage all intake air reaches the supply air diffusers so the system intake airflow for this single zone WSHP must equal the calculated zone outdoor airflow Vot Voz For this example at the cooling design condition Table 17 the required system outdoor air intake flow Vot is 330 cfm 0 16 m3 s Table 17 Single zone system ventilation calculations for example office building cooling design Rp cfm p Pz qty Ra cfm ft Az ft Vbz cfm Ez Voz cfm South conf room 5 30 0 06 3000 330 1 0 330 330 System total Vot Voz When the WSHP is operating in the heating mode it will likely be delivering air to the zone at a temperature that is warmer than the zone As mentioned earlier supplying warm air to the zone through ceiling mounted diffusers may result in a zone air distribution effectiveness Ez that is less than LO For this example at the heating design condition Table 18 a zone air distribution effectiveness of 0 8 results in a higher zone outdoor airflow Voz increasing the required system outdoorair intake flow Vot to 413 cfm 0 19 m3 s Table 18 Single zone system ventilation calculations for example office building heating design Rp cfm p Pz qty Ra cfm ft2 Az ft2 Vbz cfm
289. s include hotels apartment buildings high rise condominiums and dormitories A rooftop WSHP is designed for installation outside typically on the roof of the building with supply air ducted to the zone They are commonly used for very large zones such as cafeterias and gymnasiums or to replace existing packaged rooftop equipment in a renovation A variation of the water source heat pump called a water to water heat pump contains one or more compressors two refrigerant to water heat exchangers no refrigerant to air heat exchanger an expansion device and a reversing valve Figure 22 The refrigeration circuit is pre engineered and assembled in a factory so no field installed refrigerant piping is required 28 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Figure 22 Water to water heat pump load side source side water connections water connections a refrigerant to water heat exchanger compressor Like a WSHP a water to water heat pump is connected to the common water loop but rather than cooling or heating air this type of heat pump is used to cool or heat water in a separate loop In the cooling mode the refrigeration circuit transfers heat from the water flowing through the load side heat exchanger to the water flowing through the source side heat exchanger In the heating mode the reversing valve changes the operatio
290. s limits their selection to a finite cfm ton m3 s kW range of application When cold conditioned outdoor air is delivered to the intake of a heat pump supply airflow cfm m3 s is unaffected but the lowered mixed air enthalpy reduces the required cooling capacity tons kW This raises the cfm ton m3 s kW required of the heat pump possibly above the maximum allowed for the equipment In this case it may be necessary to reheat the dehumidified outdoor air to allow proper selection of the heat pumps but may not require reheating the air all the way to neutral When should the conditioned OA be reheated While the conditioned outdoor air should be delivered cold whenever possible there are situations when the dedicated OA unit should reheat the dehumidified outdoor air e To avoid overcooling at part load conditions As explained earlier delivering the conditioned OA at a dry bulb temperature colder than the zone temperature offsets part of the sensible cooling load in the zone As the zone sensible cooling load decreases due to changes in outdoor conditions solar heat gain and or internal loads it is possible that the cold conditioned OA may provide more sensible cooling than the zone requires As a result the temperature in the zone begins to drop and the WSHP eventually switches to operate in the heating mode While this may appear strange to the building operator if only a few heat pumps are operating in the heat
291. ses At this example part load peak outdoor dew point condition the compressor runtime is shortened resulting in less dehumidification and zone relative humidity rises to 67 percent Figure 71 An even more challenging part load condition is a mild rainy day At this example condition the only sensible load in the classroom is from people and lights so the compressor cycles off for an even greater portion of the Water Source and Ground Source Heat Pump Systems SYS APM 010 EN S TRANE System Design Issues and Challenges hour The conventional WSHP continues to supply a constant volume of air to the zone and zone humidity rises to 72 percent Figure 71 and Figure 72 Figure 72 Conventional constant Section 5 9 of ASHRAE 62 1 requires that systems be designed to limit the speed WSHP at part load relative humidity in occupied spaces to 65 percent or less at the design unconditioned OA outdoor dew point condition and at the peak indoor latent load The basic constant volume system matches sensible capacity to the sensible 66 F cooling load while dehumidification capacity is coincidental As the zone A oii sensible cooling load decreases the compressor operates for less of the 74 F hour Some dehumidification may occur but only if the zone sensible cooling aem contani Zens load is high enough to keep the compressor operating long enough higher 69 F WBT speed fan runtime MA eee ly D lt j cfm Methods for improv
292. should be obtained from the equipment manufacturer Water circulating pump s The simplest approach to controlling the water circulating pump is to turn on a constant flow pump whenever the building is expected to be occupied A simple time clock or a time of day schedule in the building automation system may be used to turn on the pump at the beginning of the scheduled occupied period and turn it off at the end of the occupied period This approach is simple and inexpensive to install because no method of pump capacity control is needed However a constant flow pump consumes a constant amount of pump energy regardless of building load Variable flow pumping takes advantage of the fact that all the WSHP compressors in the system are not always operating at the same time For example when a zone needs neither cooling nor heating the compressor turns off When the compressor turns off a motorized two position isolation valve can be used to shut off water flow to that heat pump so less total water flow is required in the loop SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 167 S TRANE System Controls 168 While variable flow pumping reduces system energy use it requires some method to modulate pump capacity The most common method used in a variable flow system is to vary the speed at which the pump impeller rotates This is commonly accomplished using a variable speed drive or variable frequency drive VFD o
293. shows this same data plotted on a psychrometric chart with the dots indicating the condition of the air leaving the evaporator in 15 second intervals When the compressor is on the leaving air is cold and dry But when the compressor stops the leaving air quickly warms up and condensate from the coil surface begins to evaporate back into the air stream The result is that the humidity ratio or dew point of the air leaving the coil is higher than when it entered As water on the coil surface continues to evaporate the condition of the leaving air travels along a constant wet bulb line until all the water has evaporated Water Source and Ground Source Heat Pump Systems 99 E TRANE System Design Issues and Challenges 100 Figure 68 Effect of compressor cycling on condition of the air leaving the evaporator leaving air E compressor off ee Maing R z Te 15 sec intervals 3 entering air S Ea A 3 ofo leaving air lt n compressor on ine kil Bear in mind that the test data in Figure 67 and Figure 68 was based on 45 minute on off cycles In actual operation compressor off time depends on the zone sensible cooling load and may last only a few minutes too briefly to permit the coil to dry completely between compressor starts To better mimic real world operation the same researchers varied compressor runtime to determine the effect on net dehumidification capacity top chart in Figure 69 Ne
294. sing boilers must be vented with a corrosion resistant stack However since most of the heat has been removed from the combustion gases the stack for a condensing boiler is usually smaller than for a non condensing boiler In addition it can often be constructed out of PVC pipe although stainless steel may be required in some cases and can often be directly vented through an exterior wall of the building Sizing the boiler in a system with night setback Zone setpoints are typically relaxed when the zone is scheduled to be unoccupied allowing the temperature in the zone to either increase or decrease see Zone is unoccupied p 4 a practice often called night setback While this strategy reduces energy use during unoccupied periods night setback can impose an additional heating load on the system during morning warm up mode When night setback is used all heat pumps on the loop might need to operate in the heating mode at the exact same time during the morning warm up mode In this case the boiler must be sized to offset the heat extracted by all the units connected to the loop Table 8 includes an example eight zone WSHP system serving a small office building This system is comprised of 15 heat pumps connected to a common water distribution loop Table 8 Sizing the boiler for a WSHP system example office building Nominal Heating Heat extracted i Water flow rate cooling capacit
295. sing the ground heat exchanger In some ground source heat pump systems a bypass valve and pipe are included to avoid pumping water through the ground heat exchanger whenever the temperature of the loop is within the desired range Figure 121 Water Source and Ground Source Heat Pump Systems 181 E TRANE System Controls Figure 12L Bypass of the ground heat exchanger air separator and expansion tank O ground heat exchanger WSHPs 4 bypass valve During mild weather heat rejected to the loop by heat pumps serving zones that require cooling may be nearly equal to the heat extracted from the loop by heat pumps serving zones that require heating In such a case the loop temperature may remain within a reasonable temperature range requiring no heat rejection to or heat extraction from the ground When the fluid temperature upstream of the ground heat exchanger is within a reasonable range the valve diverts flow to bypass the ground heat exchanger This lowers the pressure drop that the pump must overcome and reduces pump energy use It also avoids unwanted heat transfer to or from the ground when some zones requires cooling while other simultaneously need heating While some design engineers include this bypass pipe others suggest that it provides little benefit The proponents of no bypass pipe claim the following e Thatthe balanced load condition occurs in
296. ssors are off Because the individual compressors are selected at optimal points their motors are often operating at a high efficiency and part load performance is pretty good e Finally a variable speed compressor changes the rotational speed of the compressor to vary capacity as the load changes This approach results in the greatest efficiency improvement at part load conditions Compressor technologies used in heat pumps will continue to evolve For the most recent information contact the equipment manufacturer The decision on which type of compressor capacity modulation is best suited for a given project depends on available budget range of heat pump capacities needed maintenance capabilities and energy use targets Figure 12 Part load compressor performance for a 4 ton 14 kW water source heat pump 30 3 variable speed scroll 25 MIT EYON EENE OAN PE AEE EREE EAE dual manifolded scrolls eM 20 EER Digital scroll MULL TE t Mitts Dy 1 0 mi scroll with we HGBP 5 0 25 50 75 100 load 14 Water Source and Ground Source Heat Pump Systems SYS APMO10 EN Figure 13 Components of the DX refrigeration circuit refrigerant to air heat exchanger coaxial refrigerant to water heat exchanger thermal expansion valve reversing valve SYS APMO010 EN S TRANE Primary System Components The refrigerant to air heat exchanger is a finne
297. st air energy recovery see Exhaust air energy recovery p 70 SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 73 eS TRANE Primary System Components Figure 50 Packaged air cooled DX dedicated OA unit reheat coil intake hood propeller type condenser fans compressors cabinet for energy recovery device optional return air direct drive or belt drive damper evaporator coil plenum fan w stainless steel drain pan indirect gas fired burner A split DX system is comprised of a condensing unit which contains one or more compressors and an air cooled condenser with propeller type fans and an air handling unit AHU which contains the evaporator coil and expansion devices along with a fan filter heating coil or gas fired burner and possibly an air to air heat exchanger The condensing unit is typically installed on the roof or on the ground next to the building while the AHU can be installed indoors or outdoors The two components are connected by field installed refrigerant piping to complete the refrigeration circuit A packaged unit typically offers less flexibility in selection and fewer options while a split DX system increases flexibility since the AHU typically has more options for fans air cleaning devices air to air energy recovery devices and sound attenuation The primary advantages of using air cooled DX equipment as the dedicated OA unit are lower installed cost typical
298. st case heating load Qheating minus the heat of compression Qcompressor which can be determined using the estimated heating COP Qextracted Qheating Qcompressor Qheating X 1 1 COPheating For this same example system Table 8 load calculation software indicates the design heating load to be 890 MBh 260 kW From the manufacturer s catalog the rated heating COP for the 5 ton 18 kW heat pump is 5 0 Therefore the heat extracted is estimated to be 710 MBh 210 kW Qextracted 890 MBh x 1 1 5 0 710 MBh Qextracted 260 kW x 1 1 5 0 210 kW In this case the boiler should be selected with 710 MBh 210 kW of capacity 52 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Hot water storage As mentioned previously the use of night setback might require the selection of a larger capacity boiler because all the heat pumps on the loop might need to operate in the heating mode at the exact same time during the morning warm up mode One approach to reducing the required boiler capacity is to install a hot water storage tank in the water distribution loop During the unoccupied mode the boiler is operated for a brief period of time to increase the temperature of the water inside the loop and storage tank When morning warm up mode begins the heat stored in the water is extracted to offset some of the heating loads allowing for the installation of a smaller boiler
299. stalling duct systems e Use atleast three diameters of straight duct for the first section downstream of the discharge from the WSHP Satisfactory fan performance and distribution of air throughout the system requires unrestricted and relatively uniform airflow from the discharge of the WSHP This first section of supply ductwork should be straight for at least three duct diameters to allow a uniform velocity profile to develop conversion of fan energy from velocity pressure to static pressure However when jobsite conditions dictate that an elbow be installed near the WSHP discharge the loss of fan capacity and static pressure can be somewhat minimized by installing turning vanes within the elbow Water Source and Ground Source Heat Pump Systems SYS APM 010 EN For more information on space air diffusion refer to e 2009 ASHRAE Handbook Fundamentals Chapter 20 www ashrae org e ASHRAE s Designer s Guide to Ceiling Based Air Diffusion www ashrae org SYS APMO010 EN occupied space S TRANE Primary System Components When possible locate ceiling mounted WSHPs above a hallway or other unoccupied area Figure 61 This will typically simplify installation and maintenance and help minimize sound radiated to the occupied space Figure 6L Horizontal WSHP located above hallway i supply ductwork supply ductwork WSHP return ductwork return ductwork
300. stem Figure 46 and Figure 47 For zones that require year round cooling the WSHP may need to be sized based on the warmest temperature expected to be delivered by the dedicated OA unit SYS APM010 EN Water Source and Ground Source Heat Pump Systems 67 E TRANE Primary System Components 68 Water Source and Ground Source Heat Pump Systems Less supply airflow and less cooling capacity allows for the selection of smaller heat pumps which can lower the system installed cost and requires less space Alternatively selecting the same sized WSHP cabinet and operating the fan at a lower speed can provide an acoustical benefit Finally if the outdoor air is delivered directly to each zone see Figure 40 p 59 the fan inside the heat pump is no longer required to operate to ventilate the zone This affords the opportunity to cycle the local fan on and off along with the compressor reducing fan energy use If the outdoor air is delivered to the supply side of each heat pump see Figure 43 p 61 the fan inside the heat pump could cycle on and off if a pressure independent VAV terminal is used to maintain required outdoor airflow What happens if conditioned outdoor air is delivered to the intake of each WSHP rather than directly to each zone If the conditioned OA is delivered to the intake of each WSHP it mixes with recirculated air from the zone before entering the heat pump Because the conditioned outdoor air CA is not de
301. stem refer to the Trane Engineers dehumidification Newsletter Advances in Desiccant Based Dehumidification ADM APN016 EN and the Trane engineering bulletin Trane CDQ Desiccant Dehumidification series desiccant total energy CLCH PRB020 EN wheal wheel Figure 57 Dual wheel dedicated OA unit preheat coil supply fan exhaust cooling fan coil In this series configuration the desiccant dehumidification wheel adsorbs water vapor from the process air downstream of the cooling coil and then 80 Water Source and Ground Source Heat Pump Systems SY S APM 010 EN SYS APMO010 EN 30 S TRANE Primary System Components releases the collected moisture upstream of that coil enabling the AHU to deliver drier supply air at a lower dew point without lowering the coil temperature In addition the moisture transfer occurs within a single air stream a separate regeneration air stream is not needed Figure 58 shows the performance of this AHU configuration Air leaves the cooling coil CA at a dry bulb temperature of 52 F 11 C and a dew point of 51 F 10 7 C The series desiccant wheel adsorbs water vapor drying the conditioned outdoor air CA to a dew point of 45 F 7 C Sensible heat added by the adsorption process raises the dry bulb temperature of this air to 56 F 13 C The wheel rotates into the air upstream of the cooling coil OA where water vapor released from the wheel passes into the
302. such as a hot water boiler or ground heat exchanger and water circulating pumps Water Source and Ground Source Heat Pump Systems 1 S TRANE Overview of a Water Source Heat Pump System Figure 2 Primary components of a water source heat pump system dedicated oa outdoor air unit exhaust fan cooling tower water source heat pump system level controller hot water boiler water circulating pumps Typically outdoor air required for ventilation is conditioned and delivered by a separate dedicated outdoorair system Each WSHP is equipped with a unit controller that regulates cooling and heating for the zone it serves A system level controller coordinates the operation of the individual WSHP unit controllers so they operate together as an efficient system Basic System Operation The following section describes in a very simple manner how a WSHP system operates For a more detailed discussion see System Controls p 158 Zone is occupied and requires cooling A sensor in each zone compares the dry bulb temperature in the zone to a setpoint and the controller in the WSHP cycles or varies the speed of one or more compressors to match the changing cooling load in the zone As the cooling load decreases the compressor operates for a shorter period of time between cycles Inside the WSHP the refrigeration circuit extracts heat from the recirculated air and rejects heat to the water loop The
303. sult might be overcooling the zone unless the WSHP is equipped with hot gas reheat Also this requires turning on the water circulating pump and possibly the cooling tower If a dedicated OA system is used when after hours dehumidification is needed the dedicated OA unit could be turned on to deliver dehumidified air to the zone s Because there is typically very little sensible cooling load in the zone the dehumidified air may need to be reheated to avoid overcooling the zone If the dedicated OA system delivers the conditioned outdoor air directly to each zone Figure 40 p 59 it could be used for after hours humidity control without needing to operate the local water source heat pump s If the conditioned OA is ducted directly to the intake of each WSHP then the fan in the WSHP may need to operate in conjunction with the dedicated OA unit If the dedicated OA unit includes a recirculating air path the outdoor air damper could be closed and the return air damper opened Figure 82 This avoids the energy penalty associated with conditioning unneeded outdoor air SYS APM010 EN Water Source and Ground Source Heat Pump Systems 109 S TRANE System Design Issues and Challenges For more information on the various types of humidification equipment including sizing and application refer to the ASHRAE Humidity Control Design Guide for Commercial and Institutional Buildings and Chapter 21 Humidifiers in the 2008 ASHRAE Ha
304. system depends on climate building usage and utility costs Building analysis software tools can be used to analyze these strategies and convert energy savings to operating cost dollars that can be used to make financial decisions Figure 83 shows the potential energy savings of using various strategies in an example office building with a WSHP system The baseline WSHP system complies with ASHRAE 90 1 so it includes night setback control variable flow pumping with a VFD and a total energy wheel on the dedicated outdoorair unit Water Source and Ground Source Heat Pump Systems 123 S TRANE System Design Issues and Challenges 124 Figure 83 Example energy savings versus a baseline WSHP system So o a o A N o HVAC energy consumption of baseline o Atlanta Louisville Minneapolis I 90 1 compliant WSHP system baseline optimized WSHP system i optimized GSHP system The optimized WSHP system adds optimal start and loop temperature optimization to the system level controls and the conditioned outdoor air is ducted directly to each zone rather than to the inlet of each WSHP Delivering the OA directly to each zone allows it to be delivered cold rather than reheated to neutral during the cooling season and allows the fan in each heat pump to cycle off with the compressor when that zone does not require either cooling or heating For this example the o
305. system water flow rate 184 gpm 116 L s Design leaving water temperature 90 F 32 C e Range 9 3 F 5 2 C Freeze protection Because the water loop operates all year long freeze protection during winter months is important In a tower boiler WSHP system freeze protection depends on the type of cooling tower used If a closed circuit cooling tower is used one of the following approaches is typically used for freeze protection e Locate the cooling tower inside the building With this approach dampers are typically installed in the tower discharge and in either the intake ductwork or behind the louvers of an intake plenum Figure 35 Both sets of dampers close whenever the tower is off minimizing heat loss and preventing water inside the tower sump and heat exchanger tubes from freezing SYS APM010 EN S TRANE Primary System Components Figure 35 Closed circuit cooling tower with intake and discharge dampers discharge damper intake dampers gt Using a modulating damper in the tower discharge provides more precise temperature control during cold weather which might eliminate the need to drain the tower sump for winter operation If a two position rather than a modulating damper is used the tower sump should be drained when the outside temperature is below freezing conditions The tower is still able to operate but it will operate as a dry cooler with no water flowing over the outside surf
306. t high limit shutoff As the weather warms and the zone requires cooling the linked outdoor and return air dampers modulate to bring in more of the cool outdoor air Figure 109 This is called modulated economizer mode In this mode the outdoor air is cool enough to provide all the needed cooling capacity to maintain zone temperature at setpoint without needing to operate the WSHP compressor As the cooling load increases the outdoor air damper eventually opens to 100 percent and the return air damper closes completely To provide the extra cooling capacity needed to maintain the zone temperature at setpoint the compressor is cycled on This is called integrated economizer mode 100 percent outdoor airflow provides part of the required cooling capacity and mechanical cooling provides the balance Figure 109 At some point the outdoor air becomes so warm that it provides little or no cooling benefit When the outdoor air condition reaches the high limit shutoff setting the unit controller disables airside economizer operation and the outdoorair damper is closed to a minimum position to bring in only the quantity of outdoor air required for ventilation Figure 109 At this point the compressor provides all cooling capacity needed to maintain zone temperature at setpoint The three most common high limit shutoff strategies used to control the airside economizer in a WSHP are e Fixed dry bulb control uses a sensor
307. t or a much smaller size can be used to store the same amount of heat as a larger low temperature storage tank Figure 38 High temperature storage tank added to the loop supplemental heat storage tank boiler 54 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components During morning warm up mode or whenever heat must be added to the loop during the day hot water from the storage tank is mixed into the loop maintaining the loop temperature at either the lower limit or at some higher temperature that would allow the heat pump compressors those operating in the heating mode to operate more efficiently during on peak hours Sizing the storage tank As mentioned the most common use of hot water storage in a WSHP system is to reduce or eliminate the need to operate the hot water boiler during the morning warm up mode This often allows for the installation of a smaller boiler and can reduce peak electrical demand if an electric boiler is used l1 Calculate the total amount of heat that must be extracted from the loop during morning warm up The total amount of heat extracted during morning warm up mode depends on the difference between the unoccupied and occupied heating setpoints the thermal capacitance of the building and the COP of the heat pumps First calculate the total amount of heat Qwarm up in Btu k needed to raise the indoor temperature from the unocc
308. t accurate approach is to use a manufacturer s catalog or selection software to determine the performance of each heat pump including heat rejected to the loop at the project specific operating conditions such as airflow entering air conditions water flow rate and entering water temperature The eight zone system in this example is comprised of 15 water source heat pumps Table 6 The sum of the heat rejected from each heat pump is 83 tons 290 kW An alternate approach is to sum the nominal cooling capacities of all the heat pumps and then estimate total heat rejected to the loop using an estimated value for cooling COP Coefficient of Performance The total heat rejected to the loop Qrejected equals the cooling capacity Qcooling plus the heat of compression Qcompressor which can be determined using the estimated cooling COP Qrejected Qcooling Qcompressor Qcooling x 1 T 1 COPcooling For this example the sum of the nominal cooling capacities for all 15 heat pumps is 72 tons 250 kW From the manufacturer s catalog the rated cooling EER for the 5 ton 18 kW heat pump is 14 8 which equates to a COP of 4 34 COP EER x 0 293 Therefore using this alternate approach the heat rejection for all heat pumps is estimated to be 89 tons 310 kW Qrejection 72 tons x 1 1 4 34 89 tons Qrejection 250 kW x 1 ate 1 4 34 310 kW The second step is to apply system load diversity D to estimate the maximu
309. t dehumidification capacity equals all of the water vapor that condenses on the coil while the compressor is on minus the water that re evaporates after the compressor turns off Notice that as the compressor operates for a smaller percentage of the hour this system constant speed fan cycling compressor provides little or no net dehumidification benefit The compressor is not operating for a long enough period of time to allow condensate to build up and fall into the drain pan And the compressor remains off for longer periods of time which allows more water to re evaporate from the coil Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Issues and Challenges Figure 69 Net dehumidification as a function of compressor run time T T no dehumidification unit SHR sensible capacity total capacity 3 OO ea ee Os ee 0 7 fa a eee a 0 20 40 60 80 100 compressor run time of hour Source Henderson H 1998 Proceedings of ASHRAE Energy and IAQ Conference entering air z e coil curves 6C leaving air compressor i i run time of hour 100 80 60 40 20 0 Note This chart can also demonstrate what happens when constant volume DX equipment is oversized If the equipment is oversized the compressor operates for a smaller percentage of the hour and less dehumidification occurs Figure 70 Conventional constant speed WSHP at full load The botto
310. t generated by people lighting or equipment ISO International Organization for Standardization www iso org latent heat Heat that causes a change in the moisture content of the air with no change in dry bulb temperature LEED Leadership in Energy and Environmental Design A building rating system created by the U S Green Building Council a building industry coalition www usgbc org linear slot diffuser A type of supply air diffuser in which jets are formed by slots or rectangular openings with a large aspect ratio See Coanda effect makeup water Water added to the cooling tower to compensate for the volume of water lost through drift loss evaporation and blow down i e water wasted from the system to the sewer to reduce the concentration of solids makeup air unit See dedicated outdoor air unit MERV Minimum Efficiency Reporting Value A rating value defined by ASHRAE Standard 52 2 that depicts how efficiently a filter removes particles of various sizes mixed air A mixture of outdoor air and recirculated return air modulated economizer mode An operating mode of an airside economizer when the outdoor air is cool enough to handle the entire cooling load and the compressors are off The controller modulates the positions of the outdoorair and return air dampers so that the mixture of outdoor and return air provides supply air at the desired setpoint moisture carryover Retention and transport of water dr
311. t intended to be all encompassing but focuses on those energy savings strategies that are of specific interest to designers of typical WSHP systems Water Source and Ground Source Heat Pump Systems SYS APM 010 EN For more information on the Trane s TRACE 700 or System Analyzer building analysis software programs visit www tranecds com SYS APMO010 EN S TRANE System Design Issues and Challenges Table 26 Potential energy savings strategies for water source heat pump systems Water source heat pumps High efficiency WSHPs p 14 Multiple speed fan operation p 21 Cycle WSHP fan with compressor p 68 and p 161 Waterside or airside economizer p 162 Water distribution loop Variable flow pumping p 34 Increase pipe sizes to reduce pressure loss p 38 Heat rejection heat addition Condensing boiler p 50 VFD on cooling tower fan s p 170 and p 171 Thermal storage p 53 Ground source system p 135 Dedicated outdoor air system Deliver conditioned OA cold rather than neutral directly to spaces p 64 Precondition outdoor air with air to air energy recovery p 70 System level controls Night setback p 176 Occupancy sensor to enable occupied standby mode p 176 Optimal start p 187 Demand controlled ventilation p 188 Loop temperature optimization p 193 The impact of any energy saving strategy on the operating cost of a specific
312. t signal to the controller series desiccant wheel A dehumidification device in which the downstream process side of the desiccant wheel is located downstream of the cooling coil and the upstream regeneration side of the wheel is located upstream of the cooling coil setback The practice of changing the temperature setpoint of the zone during unoccupied hours in an effort to save energy setpoint The desired condition of the controlled variable in a control loop silencer A device installed in an air distribution system to reduce noise SMACNA Sheet Metal and Air Conditioning Contractors National Association www smacna org specific gravity SG Weight of a volume of material compared to the weight of the same volume of water specific heat Quantity of heat required to raise the temperature of a definite mass of a material a definite amount compared to that required to raise the temperature of the same mass of water the same amount expressed in units of Btu lb F J kg K stack effect When indoor air is warmer than outdoor air the less dense column of air inside the building results in a negative pressure in the lower floors and a positive pressure in the upper floors This pressure difference induces outdoor air to enter the lower floors and indoor air to leave the upper floors while air flows upward within shafts and stairwells strainer A component of the water distribution loop installed prior to the inlet of
313. t the part load peak dew point condition the dedicated OA unit continues to cool the outdoor air to the same 74 F DB 23 3 C DB temperature still adding a significant latent load to the classroom Because the sensible cooling load in the zone is lower however the compressor in the WSHP cycles to maintain zone temperature and provides less dehumidification The resulting zone humidity is 70 percent RH Figure 81 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Issues and Challenges Figure 8L Dehumidification performance of neutral temperature conditioned air without overcooling to dehumidify at peak dew point condition 74 0 F DB 71 5 F DP P OA CA 84 F DB 76 F DP 65 5 F DB MA RA SA 74 F DB 63 F DB 70 RH epuoj4 a IAUosyoer The preceding example demonstrates that supplying conditioned OA ata neutral dry bulb temperature without subcooling it to reduce its moisture content provides less dehumidification than a system without a dedicated OA unit to begin with see Figure 71 p 102 After hours dehumidification Controlling humidity is not only a priority when the building is occupied When indoor humidity rises too high during unoccupied periods after hours one option could be to turn on the WSHP serving the affected zone and dehumidify recirculated air However there is typically very little sensible cooling load in the zone during unoccupied periods so the re
314. tail in System Controls p 158 Specific details should be obtained from the equipment or controls manufacturer Figure 62 Control of a WSHP system exhaust fan water source heat pumps boiler system level controller SYS APM010 EN Water Source and Ground Source Heat Pump Systems 87 S TRANE 88 Definition of a thermal zone A space or group of spaces within a building with similar heating and cooling requirements served by a single temperature sensor to maintain the desired temperature System Design Issues and Challenges This chapter proposes solutions to several common challenges of designing a water source heat pump system This is not an exhaustive list of all challenges or all solutions but is meant to cover the most common Thermal Zoning In a WSHP system each thermal zone has a heat pump that is controlled to maintain the temperature in the zone it serves Defining the zones in a WSHP system is often more of an art than a science and requires judgment by the system design engineer An individual zone might be either of the following A single room separated by physical boundaries walls windows doors floor and ceiling The individual offices in an office building or individual classrooms ina school could each be a separate zone In this case each office or classroom would be served by an individual WSHP and zone temperature sensor e A group of several rooms Several of
315. tance curve Water Source and Ground Source Heat Pump Systems SYS APM010 EN In a variable flow system consider installing an automatic flow control device for each heat pump This device helps ensure proper water flow through the heat pump when the compressor is operating as the overall system flow rate and pressure changes see Isolation valves and flow control devices p 39 S TRANE System Controls Figure 112 Variable flow pump modulation part load system 100 resistance curve full load system resistance curve Q D O pump head 20 10 20 30 40 50 60 70 80 90 100 water flow rate of design flow As a result the pump delivers less flow at a higher pressure The pressure transducer senses this higher pressure difference and the controller sends a signal to reduce pump capacity The VFD reduces the speed rpm at which the pump impeller rotates which reduces the system water flow rate until the system balances at an operating point B that brings the pressure difference at the location of the transducer back down to the desired setpoint As the VFD reduces the flow rate that the pump produces it also reduces pump energy use A standby pump is often installed to minimize the risk of flow loss in the water loop in the event that one pump fails In this case the controller often rotates operation of the two pumps to equalize runtimes and starts For example pump 1 would be operated for
316. ted from the loop 54 MBh 16 kW in this example lowers the water temperature from 60 F 16 C entering the heat exchanger to 53 F 11 C leaving heat extracted from loop heat added to air heat of compression Water regulating valves Historically water regulating valves were used to modulate water flow through the refrigerant to water heat exchanger to maintain the condensing head pressure high enough for the refrigeration system to operate properly as water temperature in the loop decreased This was necessary because the water source heat pumps typically used a capillary tube or fixed orifice as the refrigerant expansion device To operate properly these types of expansion devices required that the entering water temperature be maintained between 60 F 16 C and 90 F 32 C in both the cooling and heating modes Today most water source heat pumps use a thermal expansion valve TXV see Figure 13 p 15 rather than a capillary tube or fixed orifice The operating range for a typical TXV is between 45 F 7 C and 120 F 49 C in the cooling mode and between 25 F 4 C and 86 F 30 C in the heating mode For this reason very few applications require the use of a water regulating valve In fact the use of water regulating valves is discouraged because it competes with the TXV to ensure proper compressor operation If the loop temperature is expected to drop below 45 F 7 C when some heat pumps need to
317. tem be designed to operate at these lower return water temperatures Figure 36 Impact of retum water temperature on boiler efficiency 100 NS natural gas 1050 Btu ft 39 MJ kg 98 aN 96 stoichiometric air 17 24 Ib lb of fuel N 17 24 kg kg of fuel 94 92 x gt non condensing mode oO Co aMi Cc i 2 90 D dew point 88 al 8 V 86 dendi d 1D condensing mode 6 excess Ir 84 82 80 60 100 140 180 220 16 38 60 82 104 inlet water temperature F C Source 2008 ASHRAE Handbook HVAC Systems and Equipment Chapter 31 Figure 6 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org SYS APM010 EN One way to reduce the boiler capacity needed to satisfy morning warm up mode is to add a storage tank see Hot water storage p 53 Alternatively the building automation system could be used to stagger the morning warm up mode for different parts of the building thus warming only part of the building at a time This can also reduce required boiler capacity A potential secondary benefit is lowering the electrical demand during this staggered startup S TRANE Primary System Components Because of the potential for corrosion a condensing boiler must be constructed of special materials that will resist the corrosive effects of the condensing flue gases This typically results in a higher first cost Finally conden
318. temperature Tsa Ez cooler than zone 1 0 warmer than zone 0 8 supply from ceiling return from ceiling 2Tzone 15 F 8 C warmer than zone 1 0 lt Tzone 15 F 8 C i cooler than zone 1 0 supply from ceiling return from floor warmer than zone 1 0 supply from floor return from ceiling cooler than zone 1 2 thermal displacement ventilation warmer than zone 0 7 supply from floor return from ceiling cooler than zone 1 0 underfloor air distribution warmer than zone 0 7 supply from floor return from floor warmer than zone 1 0 outdoor air drawn into the room 0 8 opposite of the exhaust or return outlet outdoor air drawn into the room 0 5 near the exhaust or return outlet Excerpt from Table 6 2 of ANSI ASHRAE Standard 62 1 2010 In many WSHP systems the supply air diffusers are located in or near the ceiling When cool air Tsa lt Tzone is delivered to the zone through these ceiling mounted diffusers the system is 100 percent effective at getting the outdoor air into the actual breathing zone that is Ez 10 This is the case whether the return air grilles are located in or near the ceiling or in or near the floor However when hot air Tsa gt Tzone 15 F 8 C is delivered to the zone through the same ceiling mounted diffusers and then leaves the zone through ceiling mounted return air grilles the zone airdistribution Water Source and Ground Source Heat Pump Systems SYS APM010 EN For more information o
319. ter flow rates 216 gpm 13 7 L s in this example However if variable flow pumping is used the pumps might be able to be sized to deliver 15 percent less flow 184 gpm 116 L s in this example because the sum of the individual heat pump water flow rates is multiplied by system load diversity 216 gom x0 85 13 7 L s x0 85 Some HVAC design engineers choose NOT to account for system load diversity when sizing the water circulating pumps This allows the pumps to deliver the design water flow rate through each heat pump in case all the heat pumps need to operate simultaneously during morning warm up or cool down modes for example This avoids the risk of a nuisance trip due to low water flow and because the pumps are equipped with a VFD there is no energy penalty associated with the higher system design water flow rate However other design engineers DO account for system load diversity when sizing the pumps because it allows for the installation of smaller pumps smaller VFDs and electrical service and smaller main header piping Their argument is that it is highly unlikely that all of the heat pumps will ever need to operate simultaneously and even if they did the use of automatic flow control devices and preheating or precooling the water loop will minimize the risk of nuisance trips A variation on the variable flow system is to have a separate pump serving different sections of the building As an example a fingerstyl
320. ter tube extracts heat from the refrigerant flowing through the inner tube In the heating mode it acts like an evaporator and the refrigerant extracts heat from the water return air Air that is removed from the conditioned space s and either recirculated or exhausted return air grille See grille reverse return piping A type of piping arrangement where the water being supplied to each coil travels through essentially the same distance of supply and return pipe reducing system design and balancing time SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 203 204 reversing valve The component of a heat pump that allows it to perform heating as well as cooling In the heating mode refrigerant vapor from the compressor is diverted by the reversing valve to the refrigerant to air heat exchanger Room Criteria RC A single number used to describe sound in an occupied space It uses a series of curves and reference lines for plotting sound pressure by octave band and determining the RC value and a descriptor of the sound quality i e hiss rumble sensible energy recovery The transfer of sensible heat between two or more air streams or between two locations within the same air stream sensible heat Heat that causes a change in the dry bulb temperature of the air with no change in moisture content sensor The component of a control loop that measures the condition of the controlled variable and sends an inpu
321. that transfers heat from one water loop to another water loop and vice versa WRV See water regulating valve WSHP Water source heat pump zone One occupied space or several occupied spaces with similar characteristics thermal humidity occupancy ventilation building pressure zone air distribution effectiveness Ez A measure of how effectively the air delivered to the zone by the supply air diffusers reaches the breathing zone Water Source and Ground Source Heat Pump Systems SYS APM010 EN SYS APMO010 EN TRANE References Air Conditioning Heating and Refrigeration Institute AHRI 2001 Sound Rating of Ducted Air Moving and Conditioning Equipment AHRI Standard 260 2001 Arlington VA AHRI 2008 Sound Rating of Non Ducted Indoor Air Conditioning Equipment AHRI Standard 350 2008 Arlington VA AHRI AHRI ASHRAE and International Organization for Standardization ISO 1998 Water Source Heat Pumps Testing and Rating for Performance Part 1 Water to Air and Brine to Air Heat Pumps ISO Standard 13256 1 1998 Switzerland ISO 1998 Water Source Heat Pumps Testing and Rating for Performance Part 2 Water to Water and Brine to Water Heat Pumps ISO Standard 13256 2 1998 Switzerland ISO American Society of Heating Refrigeration and Air Conditioning Engineers Inc ASHRAE 2011 ASHRAE Handbook Applications Atlanta GA ASHRAE 2009 ASHRAE Handbook Fundamentals Atlanta GA ASH
322. the offices or classrooms along the west facing perimeter of the building could be grouped together as one zone In this case one WSHP could be used to serve the entire group of rooms and a zone temperature sensor would typically be installed in only one of the rooms e A subsection of a large open area An office building might include a large open area that is divided into cubicles The interior portion of this open area might be separated into several zones to provide better temperature control If the area is bounded by a perimeter wall the outer 15 ft 4 6 m of this area might be its own zone due to the impact of heat gain and loss through the building envelope In all cases rooms that are grouped together as a single thermal zone should have similar heating and cooling requirements and operating schedules Whenever possible a zone should have definite physical boundaries walls windows doors floor and ceiling Loss of temperature control can result if air can be supplied to the zone by a WSHP other than the one connected to the zone temperature sensor Perimeter versus interior zones For simplicity a typical building can be described as having two types of zones perimeter and interior As mentioned earlier each zone is typically served by an individual WSHP allowing independent control of cooling and heating In many climates perimeter zones with walls and windows exposed to the outdoors require seasonal cooling or heat
323. then estimate total heat extracted from the loop using an estimated value for heating COP The total heat extracted from the loop Qextracted equals the heating capacity Qheating minus the heat of compression Qcompressor which can be determined using the estimated heating COP Qextracted Qheating Qcompressor Qheating x 1 ors 1 COPheating For this example the sum of the heating capacities for all 15 heat pumps is 1014 MBh 300 kW From the manufacturer s catalog the rated heating COP for the 5 ton 18 kW heat pump is 5 0 Therefore using this alternate approach the heat extracted by all heat pumps is estimated to be 810 MBh 240 kW Qextracted 1014 MBh x 1 1 5 0 810 MBh Qextracted 300 kW x 1 1 5 0 240 kW In this case the boiler should be selected with 810 MBh 240 kW of capacity Note If other cooling equipment such as water cooled computer room air conditioning equipment is connected to the loop and operates during the morning warm up mode the heat rejected by this equipment can be used to reduce the size of the boiler Sizing the boiler in a system without night setback In some applications particularly those buildings that operate 24 hours a day 7 days a week night setback is not used so there is no morning warm up mode where all heat pumps will operate in the heating mode simultaneously In this case the total heat extracted from the loop Qextracted equals the building s wor
324. ther times during the year the airside economizer may open the OA damper further when it is relatively cold and dry outdoors While the outdoor air may not be as dry as it is at the winter design condition the system is introducing a larger quantity of outdoor air The design engineer should estimate the humidification load at both conditions e Follow the manufacturer s recommendations for downstream absorption distance and maximum relative humidity If the moisture is not fully absorbed by the air stream it can cause downstream surfaces to get wet The humidifier should be far enough upstream of elbows junction sensors or dampers to allow for sufficient absorption Absorption distances are shorter with lower air velocities Energy Efficiency Decisions made solely or primarily based on installed first cost often ignore such factors as energy use maintenance requirements or expected life of the equipment Life cycle cost includes the total cost of owning and operating the HVAC system over a given period of time This includes installed cost energy cost maintenance cost replacement cost and any other known and expected costs As mentioned in other parts of this manual WSHP systems are in many ways inherently energy efficient A heat pump is an efficient method of heating and when some zones require cooling at the same time other zones require heating the heat recovery nature of the system saves energy by reducing the opera
325. ting time of the cooling tower and boiler In addition various control strategies and design options including ground coupling provide the opportunity to further reduce the energy use of this type of system Minimum efficiency requirements Many state and local building codes include requirements for minimum levels of energy efficiency Some of these requirements relate to the efficiency of specific equipment such as water source heat pumps cooling towers or boilers while others relate to the design and control of the overall HVAC system ANSI ASHRAE IESNA Standard 90 1 Energy Standard for Buildings Except Low Rise Residential Buildings is the basis for many of these local codes Its purpose is to establish the minimum energy efficiency requirements for buildings and as such it addresses the entire building The HVAC section of SYS APMO10 EN Water Source and Ground Source Heat Pump Systems u S TRANE System Design Issues and Challenges ASHRAE 90 1 includes a large number of requirements related to system design control and construction However this section of the manual will focus on only a few of the HVAC related requirements that are of specific interest to designers of typical WSHP systems Note Because ASHRAE 90 1 is under continuous maintenance it can change frequently This manual is based on the 2010 published version of the standard Refer to the most current version for specific requirements Minimum eq
326. tions O O O configuration configuration configuration It is typically recommended to group 10 to 12 U tubes on a single header and isolate each group with valves Figure 94 This allows for easier flushing of the U tubes to purge air and debris And if a leak occurs the affected section of the borefield can be shut off to fix the leak while the remaining sections of the field remain in operation 141 S TRANE System Design Variations Figure 94 Example layout of well field only supply side piping shown o U tube 2 in 50 mm supply header pipe isolation building valves a Source Ground Source Heat Pumps Design of Geothermal Systems for Commercial and Institutional Buildings Figure 5 6 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org The final benefit of this approach is simpler installation Smaller header pipes can often be purchased in a roll which simplifies installation by greatly reducing the number of field fabricated thermally fused joints Larger pipe sizes however often need to be purchased in straight sections increasing the number of joints fabricated in the field As an example a 2 in 50 mm HDPE SDR 11 header pipe will convey 30 gpm 19 L s at an acceptable pressure drop approximately 2 3 ft of H2O per 100 ft of piping 0 23 kPa m For a 30 ton 106 kW system with a total system f
327. tions A higher COP designates a higher efficiency CPVC Chlorinated Polyvinyl Chloride a plastic piping material cycling The practice of alternating a compressor on and off to match the system load damper A device used to vary the volume of air passing through a confined cross section by varying the cross sectional area deadband The temperature range between the cooling and heating setpoints dedicated outdoor air system DOAS A system that uses a dedicated air handling unit to cool heat dehumidify or humidify all of the outdoor air brought into the building for ventilation This system then delivers this conditioned outdoor air directly to the conditioned spaces or to HVAC equipment SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 197 198 dedicated outdoor air unit An airhandling unit used to cool heat dehumidify or humidify all of the outdoor air brought into the building for ventilation This conditioned outdoor air may be delivered directly to the zone s or to other air handlers or terminal equipment Also called a makeup air unit or 100 percent outdoor air unit demand controlled ventilation DCV A control strategy that attempts to dynamically reset the system outdoor air intake based on changing population in the zone desiccant Adsorbent or absorbent liquid or solid that removes water or water vapor from an air stream or another material dew point temperature DPT The temperature
328. to the unit level controller on a VAV terminal unit indicating whether that zone should be considered occupied or unoccupied When the sensor indicates the zone is occupied the VAV terminal unit modulates to deliver the design outdoor airflow for that zone When the sensor indicates the zone is unoccupied the damper closes to shut off outdoor airflow to that zone If an occupancy sensor is used in combination with a time of day schedule the building may be scheduled as occupied while the sensor indicates the zone is unoccupied Table 33 In this mode called occupied standby the zone is supplied with a less than design base outdoor airflow typically the building related ventilation rate Ra Table 33 Combining occupancy sensors with time of day schedule Time of day schedule Occupancy sensor reads indicates Operating mode Ventilation setpoint design outdoor occupied occupied occupied airflow pase outdoor occupied unoccupied occupied standby airflow less than design unoccupied n a unoccupied no outdoor airflow Occupancy sensors are relatively inexpensive do not need to be calibrated and are already used in many zones to control the lights Zones that are less densely occupied or have a population that varies only minimally such as private offices many open plan office spaces and many classrooms are good candidates for occupancy sensing Carbon dioxide CO2 sensors
329. trolled ventilation refer to the Trane Engineers Newsletter CO2 Based Demand Controlled Ventilation with ASHRAE Standard 62 1 ADM APNO17 EN and to the Trane Engineers Newsletter Live broadcast DVD CO2 Based Demand Controlled Ventilation APP CMC024 EN S TRANE System Controls Time of day schedules A time of day schedule can be created in the building automation system BAS to indicate when each zone is occupied versus unoccupied For any hour that a zone is scheduled to be unoccupied even though other zones served by the dedicated OA system are scheduled to be occupied outdoor airflow for that zone is reduced to zero or to the building related ventilation rate Ra see Zone level ventilation requirements p 91 This approach may be well suited for many classrooms where occupancy is predictable and the number of occupants does not vary greatly Alternatively a time of day schedule can be used to estimate the actual number of people in a zone for any given hour This variation in population is then communicated to the unit level controller on a VAV terminal unitand used to reset the outdoor airflow delivered to the zone for that hour This approach may be well suited for densely occupied zones that have a predictable occupancy pattern such as a cafeteria Occupancy sensors An occupancy sensor such as a motion detector can be used to detect the presence of people in a zone and send a binary signal
330. ts at and near the diffuser Sizing ductwork for low velocity and low static pressure loss will reduce the sound produced by the fan As a general rule maintain the velocity in main duct sections below 750 fpm 3 8 m s and below 600 fpm 3 1 m s in runout duct sections Avoid close coupled fittings in the ductwork as these create high pressure loss and turbulence that generates sound When possible separate turns or fittings with straight duct sections that are at least four to five duct diameters in length Figure 85 Check the static pressure drop against the static capability of the fan Finally remember that supply air diffusers generate sound that will be added to the sound coming from the WSHP Select diffusers at least 10 NC points below the desired NC level for the space Avoid turbulence at the diffuser by placing the balancing damper near the duct take off rather than near the diffuser 3 Supply breakout Sound traveling down the ductwork can also travel though the duct walls into the ceiling plenum and then through the ceiling into the occupied space This is generally only a problem on the main supply duct near the WSHP When breakout sound is a problem it can be reduced by routing the main duct over a non sound sensitive area a corridor for example splitting the Water Source and Ground Source Heat Pump Systems SYS APM 010 EN S TRANE System Design Issues and Challenges main duct into multiple smaller ducts
331. ture to drift during unoccupied periods saves energy by avoiding the need to operate heating cooling and ventilation equipment Figure 117 shows the potential energy savings of using night setback in an example office building that has a typical boiler tower WSHP system Night setback reduced the overall HVAC energy use by 10 to 15 percent for this example building 176 Water Source and Ground Source Heat Pump Systems Occupied standby mode As mentioned earlier a time of day schedule in the BAS is typically used to define when a zone is to operate in the occupied versus unoccupied mode In addition when an occupancy sensor is used in combination with a time of day schedule this sensor can be used to indicate if the zone is actually unoccupied even though the BAS has scheduled it as occupied This combination can be used to switch the zone to an occupied standby mode see example in Table 30 In this mode all or some of the lights in that zone can be shut off and the temperature setpoints can be raised or lowered by 1 F to 2 F 0 5 C to 1 C The purpose of these actions is to reduce energy use In addition if the dedicated outdoorair system is capable of varying the outdoor airflow delivered to individual zones the ventilation delivered to that zone can be reduced typically to the building related or base ventilation rate Ra required by ASHRAE Standard 62 1 see Minimum ventilation required in breathing zone
332. uipment efficiencies Section 6 4 of ASHRAE 90 1 contains minimum efficiency requirements for various types of HVAC equipment including water source heat pumps boilers and cooling towers Table 20 includes the minimum efficiency requirements for water source heat pumps based on operating conditions defined by AHRI ASHRAE ISO Standard 13256 1 1998 Water Source Heat Pumps Testing and Rating for Performance Part 1 Water to Air and Brine to Air Heat Pumps ASHRAE 90 1 includes minimum efficiency requirements for heat pumps used in conventional boiler tower systems as well as for ground coupled ground source and ground water systems For heat pumps meeting both the cooling and heating efficiencies is mandatory whether the prescriptive or Energy Cost Budget ECB method of compliance is used For example a water source heat pump with a capacity less than 17 000 Btu hr 5 kW or about 14 tons must have a cooling efficiency of 1 2 EER 3 28 COP or higher In addition the heating efficiency must be 4 2 COP or higher Table 20 Minimum equipment efficiencies for water source heat pumps from ASHRAE 90 1 2010 Equipment type Size category Entering water temperature Minimum efficiency water source heat pump cooling mode lt 17 000 Btu hr 5 kW 86 F 30 C 11 2 EER 3 28 COP gt 17 000 Btu hr 5 kW and lt 65 000 Btu hr 19 kW 86 F 30 C 12 0 EER 3 51 COP gt 65 000 Btu hr
333. ult to add supplemental heat rejection or heat addition equipment for a hybrid approach see Hybrid ground coupled heat pump systems p 149 However using dedicated ground heat exchangers requires less piping inside the building and reduces the need for headers isolation valves and valve vaults Figure 95 Example of a dedicated ground heat exchanger for each pump two or three loops per classroom return water circulating pump heat pumps diffuser classroom classroom classroom corridor classroom classroom classroom L L Source 2011 ASHRAE Handbook HVAC Applications Chapter 34 Figure 18 American Society of Heating Refrigerating and Air Conditioning Engineers Inc www ashrae org Avoid using rules of thumb For a residential building it is common to size of the ground heat exchanger based on a rule of thumb typically in terms of feet m of heat exchanger per installed ton kW of capacity These estimates are typically based on the rated or nominal capacity of the heat pump 3 tons 10 6 kW for example Sometimes the term connected load is used which has the same meaning in this context But in a residential application only one heat pump is typically connected to the loop And since the building cooling and heating loads are primarily SYS APMO10 EN Water Source and Ground Source Heat Pump Systems 143 144 S
334. unities are enacting legislation that limits allowable sound levels for outdoor equipment Even if legislation does not exist people who live and work near a tower installation may object if the sound intrudes on their environment To assess the acceptability of cooling towers or other ancillary equipment follow the five step acoustical analysis process outlined at the beginning of this section p 127 Using the acoustical modeling process to identify potential problem areas so they can be addressed prior to construction will save considerable time cost and the aggravation of addressing problems after the project is installed Water Source and Ground Source Heat Pump Systems SYS APM010 EN TRANE System Design Vanations This chapter explores several variations to the typical water source heat pump system design including ground source heat pump systems and several hybrid WSHP system configurations Ground Source Heat Pump Systems While much of the system is the same as in a conventional boiler tower WSHP system a ground source heat pump GSHP system uses the relatively constant temperature of the earth for heat rejection and heat addition GSHP systems offer the potential for saving energy because they can reduce or eliminate the energy needed to operate a cooling tower and or boiler Eliminating the cooling tower and or boiler also has architectural no cooling tower outside and maintenance advantages and may free up floor s
335. upied heating setpoint to the occupied heating setpoint This calculation should assume that the dedicated outdoorair system is shut off and should take credit for heat generated by lights or any other heat producing equipment that will be operating during the morning warm up period Then calculate the amount of heat that must be extracted from the loop Qextracted This equals the total amount of heat needed to warm up the building Qwarm up minus the heat of compression which can be approximated using the average heating COP of the heat pumps Qextracted Qwarm up X 1 1 COPheating As an example consider a building where the total amount of heat needed for morning warm up Qwarm up is 500 000 Btu 527 000 kj Assuming an average heating COP of 4 0 the total amount of heat that must be extracted from the loop Qextracted is 375 000 Btu 395 000 kj 2 Calculate the amount of heat stored in the loop water without storage The amount of heat stored in the water loop depends on the volume of fluid in the loop properties of that fluid and the difference between the temperature in the loop at the beginning of the morning warm up period and the lower temperature limit at which the boiler will be activated First calculate the volume of water in gallons Liters inside the loop Then assuming that the loop is preheated prior to the start of the morning warm up period calculate the heat stored by the water in the loop Qloop
336. upply of water The water flow rate through a WSHP is typically between 1 5 and 3 gpm ton 0 027 and 0 054 L s kW In a commercial or institutional building with many heat pumps this adds up to a significant quantity of water often causing a ground water heat pump system to be subject to local water resource restrictions The final consideration is determining an acceptable way to discharge this large quantity of water after it returns from the heat pumps The water is typically either re injected into the ground through a separate well or separate pipe in the same well or discharged into a river lake or sewer system Local codes and regulations may limit some of these practices Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE System Design Variations Hybrid WSHP System Configurations The WSHP system is often viewed solely as an alternative to other types of HVAC systems Hybrid systems comprised of water source heat pumps and other types of HVAC equipment however may be best suited to meet the specific requirements of a given building While there are many possible combinations this section includes two examples Water cooled self contained VAV systems serving interior zones The example hybrid WSHP system shown in Figure 102 uses a variable air volume VAV self contained air conditioner to serve the interior zones on each floor of a multi story building and water source heat pumps to serve
337. ure in the piping at the desired setpoint Water distribution loop e Turns on cooling tower if needed to maintain the loop water temperature below the upper setpoint Turns on boiler if needed to maintain the loop water temperature above the lower setpoint 1 Assumes outdoor air is introduced to the occupied zone through the WSHP and thus requires the fan inside the WSHP to operate to ventilate the zone If a dedicated outdoor air system delivers outdoor air directly to the zone the fan inside the WSHP could be configured to cycle off whenever the compressor is off 2 Ifthe WSHP is equipped for waterside economizing see Economizer control p 162 the WSHP unit controller may open the waterside economizer valve if the loop water temperature is suitable to provide free cooling If the WSHP is equipped for airside economizing the WSHP unit controller may open the outdoor air damper further if the condition of the outdoor air is suitable to provide free cooling In many buildings the occupied mode occurs during daytime hours and the unoccupied mode occurs at night Depending on building usage however the occupied mode could extend into the evening SYS APM010 EN Water Source and Ground Source Heat Pump Systems 175 E TRANE System Controls Section 8 3 of ASHRAE Standard 62 1 2010 states the following Systems shall be operated such that spaces are ventilated in accordance with Section 6 when they are expected to be occu
338. ure of the refrigerant At this lower pressure a small portion of the refrigerant boils or flashes cooling the remaining liquid refrigerant to the desired evaporator temperature The resulting mixture of cool liquid and vapor travels to the refrigerant to air heat exchanger that in the cooling mode functions as the evaporator Inside this heat exchanger the refrigerant extracts heat from the relatively warm air passing over the outer surfaces of the tubes cooling the air and causing the liquid refrigerant to boil or evaporate The resulting refrigerant vapor is then pumped back to the compressor which increases its pressure and temperature to repeat the cycle Table 1 shows the example performance of a water source heat pump In the cooling mode this heat pump provides 54 MBh 16 kW of cooling capacity while supplying 1700 cfm 0 80 m3 s of cooled air The heat removed from the air stream plus the heat of compression is rejected to the 15 gpm 0 95 L s of water flowing through the refrigerant to water heat exchanger This heat rejected to the loop 69 MBh 20 kW in this example raises the water temperature from 90 F 32 C entering the heat exchanger to 99 F 37 C leaving heat rejected to loop heat removed from air heat of compression 16 Water Source and Ground Source Heat Pump Systems SYS APMO10 EN SYS APMO010 EN S TRANE Primary System Components Table L Example WSHP performanc
339. urn the HVAC system on and off could also be used to turn lights on and off inside or outside the building In addition an occupancy sensor could be used to indicate that a zone is actually unoccupied even though the BAS has scheduled it as occupied see Occupied standby mode p 176 and turn off all or some of the lights and or plugged in equipment When the occupancy sensor indicates that the zone is again occupied the lights are turned back on e An occupancy sensor that is used to turn on and off lights in a private office could also be used to slightly raise or lower the zone temperature setpoints and to reduce the outdoor airflow delivered to that zone when it is unoccupied see Occupied standby mode p 176 A card access security system could be used to turn on lights start the HVAC system and increase outdoor airflow delivered to a secure work area when the occupants card in for the day e A point of sale ticket system at a theater could be used to vary the outdoor airflow delivered to an individual theater based on the number of people that purchased tickets for the show e Activation of a fire alarm could enlist the help of the fans in the dedicated OA unit to perform a smoke control function Water Source and Ground Source Heat Pump Systems SYS APM 010 EN SYS APMO010 EN TRANE Glossary ACH Air changes per hour ADPI Air Diffusion Performance Index A measure of a supply air diffuser s perf
340. usted proportionally between the base and design airflows Figure 127 Varying zone outdoor airflow based on CO2 concentration zone outdoor airflow nuasnnnnnnnnnnnnnnnnnnnnnnnnnnn design Terre 3 D x CO2 min CO2 ssssss base CO2 concentration in zone It takes some time for the indoor concentration of CO2 to decrease when people leave a room An occupancy sensor can be used in combination with a CO2 sensor to reduce zone ventilation more quickly thus saving energy When all the people have left a room the occupancy sensor will indicate that the zone is unoccupied and this signal can be used to reduce zone outdoor airflow to the base outdoor airflow even though the measured CO2 concentration is still decreasing and has not yet reached the minimum CO2 limit CO2 based DCV requires a CO2 sensor in each zone where it is used which requires periodic calibration and cleaning to ensure proper operation Zones that are densely occupied and experience widely varying population such as conference rooms auditoriums and gymnasiums are typically good candidates for CO2 sensors Water Source and Ground Source Heat Pump Systems SY S APM 010 EN SYS APMO010 EN CO2 sensors increase the installed cost of the system but they also increase risk These sensors need to be maintained and calibrated or periodically replaced to maintain accuracy If the sensor goes out of calibration and signals that the CO2 co
341. ve When the zone relative humidity drops back below this upper limit minus some offset the reheat valve returns to its original position and the WSHP operates in the standard cooling mode again Evaporator freeze protection When the heat pump is operating in cooling mode and the air entering the refrigerant to air heat exchanger is cooler or drier than normal the temperature and pressure of the refrigerant inside the heat exchanger operating as the evaporator in the cooling mode can drop to the point where the coil surface temperature falls below 32 F 0 C When this occurs water vapor that condenses out of the air will begin to freeze on the surface of the heat exchanger A common approach to prevent this is to attach a temperature sensor to the refrigerant to air heat exchanger and monitor the refrigerant suction temperature inside the evaporator If this temperature drops below a desired Water Source and Ground Source Heat Pump Systems SY S APM 010 EN Before starting the pump ensure that some isolation valves in the system are open to avoid dead heading the pump or include a bypass pipe with a pressure actuated valve in the piping system Also the pump may require a minimum flow rate or speed to sufficiently cool the pump motor A bypass pipe with a pressure actuated valve can be used to ensure the minimum required flow rate or the system level controller can be used to open the valves at several heat pumps wh
342. ventilation p 188 Humidity Control While humidity control is apt to imply special applications such as museums or printing plants managing humidity should be a key design consideration in any HVAC application Dehumidification A conventional watersource heat pump typically supplies a constant airflow at all load conditions and the compressor cycles on and off as needed to maintain zone temperature at setpoint When the zone cooling load is higher the compressor operates for a greater portion of the time When the zone cooling load is lower the compressor operates for a shorter portion of the time Dehumidification impact of compressor cycling and constant speed fan Recent research has demonstrated how compressor cycling affects part load dehumidification performance when the fan operates at a constant speed In Figure 67 the X axis depicts time and the Y axis depicts capacity When the compressor starts the coil surface quickly becomes cold enough to provide both sensible cooling and latent cooling or dehumidification 98 Water Source and Ground Source Heat Pump Systems SYS APM010 EN Fan cycling If the fan in the heat pump is controlled to cycle on and off along with the compressor rather than continue to operate at a constant speed when the compressor is off part load dehumidification will likely be improved If the fan turns off it minimizes the re evaporation of condensate from the coil surface If the
343. ving that zone For example consider a wing of an elementary school building that contains eight classrooms Each classroom is served by a separate WSHP each equipped with a 3 4 hp 0 56 kW fan motor The dedicated OA system delivers 500 cfm 0 24 m3 s of conditioned outdoor air for a total of 4000 cfm 1 9 m3 s directly to each classroom The dedicated OA unit is equipped with a5 hp 3 7 kW supply fan motor and a 1 hp 0 75 kW exhaust fan motor As explained previously each WSHP is considered a separate fan system The power of the two fans in the dedicated OA unit must be allocated to each heat pump on an airflow weighted basis For each classroom 12 5 percent 500 4000 cfm 0 24 19 m3 s of the dedicated OA unit fan power must be added to the fan power for each WSHP 0 75 hp 0 125 x5 hp 0 125 x1 hp L5 hp 0 56 KW 0 125 x 3 7 kW 0 125 x 0 75 KW 11kW For this example system even with the dedicated OA unit fans allocated the total fan motor nameplate power for each WSHP fan system is L5 hp L1 kW which is less than the 5 hp 4 kW threshold in Section 6 5 3 Therefore this system does not need to comply with the maximum allowable fan power defined by Section 6 5 3 1 SYS APMO10 EN Water Source and Ground Source Heat Pump Systems u3 E TRANE System Design Issues and Challenges For most horizontal vertical console vertical stack and smaller rooftop WSHP configurations the total fan system motor
344. with a vertical WSHP installed in the adjacent closet exhaust air outdoor air classroom 101 K 1 corridor In this example layout there is an added cost to install extra ductwork and diffuser s versus simply dumping the conditioned outdoor air into the closet where the WSHP is located However if the conditioned OA is delivered ata cold rather than neutral temperature most of the heat pumps can typically be downsized since they deliver less airflow with less cooling capacity see Neutral versus cold air delivery p 64 This reduces not only the cost of the heat pumps but less supply airflow means that the supply SA and return RA ductwork can be smaller And smallercapacity heat pumps require less water flow which results in smaller piping valves and pumps and smaller electrical service Finally delivering the conditioned OA at a cold temperature directly to each space provides cooling and fan energy savings and allows the local fans to cycle or reduce speed Be sure to consider all the cost impacts and energy savings when considering the benefit of this approach 60 Water Source and Ground Source Heat Pump Systems SYS APM010 EN S TRANE Primary System Components Conditioned OA delivered directly to the intake of each WSHP The example configuration shown in Figure 42 delivers the conditioned outdoor air CA directly to the intake of each WSHP where it mixes with recirculated air RA fro
345. wn During the hot summer months outdoor temperatures in the early morning hours may be cool enough that the cooling tower can be activated to precool the loop water temperature below the upper setpoint before the system enters the occupied mode Figure 123 SYS APM010 EN Water Source and Ground Source Heat Pump Systems 183 E TRANE System Controls 184 Figure 123 Loop precool 100 scheduled occupied hours SS ee eae upper supply 0 gt AN A setpoint a V loop water temperature 70 loop supply water temperature F 60 m m all l lower supply setpoint 50 6 a m Noon 6 p m This can reduce building energy use by operating the cooling tower during cooler drier conditions in the morning rather than during the hot humid hours of the day This can also help avoid overwhelming the cooling tower when a large number of the WSHPs will need to operate in morning cool down mode prior to occupancy Safeties The system level controller can also include several safeties that protect the equipment from harm Examples include e Sending a signal to disable all WSHP compressors if the water circulating pump fails resulting in the loss of water flow Of course the controller should also attempt to start the standby or back up pump and then automatically enable all of the WSHP compressors after water flow resumes e Sending a signal to disable all WSHP compressors if the temperatur
346. y m L s capacity from loop tons kW gp MBh kW MBh kW South offices 5 18 15 0 95 71 21 55 16 West offices 5 18 15 0 95 71 21 55 16 2 4 ton South conf room 14 kW 24 1 5 108 32 86 25 East offices 5 18 15 0 95 71 21 55 16 i 4 5 ton South interior offices 18 kW 60 3 8 284 84 220 64 3 i 4 5 ton North interior offices 18 kW 60 3 8 284 84 220 64 North offices 4 14 12 0 76 54 16 43 13 North conf room 5 18 15 0 95 71 21 55 16 Sum 72 250 216 13 7 1014 300 790 230 Assumes 60 F 16 C entering water temperature 1520 cfm 0 72 m3 s of airflow for each 4 ton 14 kW unit and 1700 cfm 0 80 m3 s for each 5 ton 18 kW unit 68 F 20 C entering air temperature and 0 5 in H2O 125 Pa of external static pressure loss SYS APM010 EN Water Source and Ground Source Heat Pump Systems 51 eS TRANE Primary System Components The most accurate approach for determining the heat extracted by the heat pumps is to use a manufacturer s catalog or selection software to determine the performance of each heat pump including heat extracted from the loop at the project specific operating conditions such as airflow entering air conditions water flow rate and entering water temperature For this example the sum of the heat extracted by all the heat pumps is 790 MBh 230 kW An alternate approach is to sum the heating capacities of all the heat pumps and
347. ystems SYS APM004 EN La Crosse WI Trane Trane 2000 Cooling and Heating Load Estimation TRG TRC002 EN Air Conditioning Clinic series La Crosse WI Trane 2001 Fundamentals of HVAC Acoustics TRG TRCOO7 EN 2000 Water Source Heat Pump Systems TRG TRCO15 EN 2002 HVAC System Control TRG TRCO17 EN Trane Guckelberger D and Bradley B 2004 Brushless DC Motors Setting a New Standard for Efficiency Trane Engineers Newsletter 33 4 Guckelberger D and Bradley B 2000 Sound Ratings and ARI Standard 260 Trane Engineers Newsletter 29 1 Hsieh C and Bradley B 2003 Green Growing Here to Stay Energy and Environmental Initiatives Trane Engineers Newsletter 32 3 SYS APM010 EN Water Source and Ground Source Heat Pump Systems 209 210 Murphy J and Bradley B 2002 Using CO2 for Demand Controlled Ventilation Trane Engineers Newsletter 31 3 Murphy J and Bradley B 2005 CO2 Based Demand Controlled Ventilation with ASHRAE Standard 62 1 2004 Trane Engineers Newsletter 34 5 Murphy J and Bradley B 2005 Advances in Desiccant Based Dehumidification Trane Engineers Newsletter 34 4 Murphy J and J Harshaw 2007 Energy Saving Strategies for Water Source Heat Pump Systems Trane Engineers Newsletter 36 2 Schwedler M and Bradley B 2001 The Three E s of Geothermal Heat Pump Systems Trane Engineers Newsletter
348. z L0 during both cooling and heating modes e Design the system so that the supply air temperature Tsa during the heating mode is less than 15 F 8 C above the zone temperature Tzone and select the supply air diffusers to achieve a velocity of 150 fpm 0 8 m s within 4 5 ft L4 m of the floor With this design a zone air distribution effectiveness Ez of 10 can be achieved even with overhead supply of warm air and overhead return e Ifa dedicated OA system is being used consider delivering the outdoor air directly to each zone through separate ventilation diffusers at either a cold or neutral air temperature Since outdoor air is not delivered to the zone by the WSHP which is used to provide heating for the zone the outdoor air does not need to be delivered at a temperature warmer than the zone Tzone and zone air distribution effectiveness Ez can be 1 0 Note The only configuration that has a zone airdistribution effectiveness greater than LO is when cool air is delivered to the zone using low velocity thermal displacement ventilation TDV However if this system is used to deliver warm air through its floor mounted diffusers and return air through ceiling mounted grilles zone air distribution effectiveness is only 0 7 System level ventilation requirement ASHRAE Standard 62 1 also defines procedures for calculating the outdoor airflow needed at the system level intake Vot to make sure the required

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