Review of calculation programs for supermarket DX refrigerating
Contents
1. The ORNL Supermarket Excele spreadsheets have been developed as tools to assist supermarket planners and engineers to compare the relative energy and refrigerant requirements for alternative designs of their refrigeration systems The program can accommodate both Direct Expansion DX and indirect systems An advantage for American users is that the program can be used with English units as well as with SI units The fact that the program is set up in Excel requires some basic knowledge of excel spreadsheets it also allows the more experienced Excel user to access the program code Concerning the target audience program developers tend to be optimistic as to whom would be the future users of the program Truth is that as soon as piping diameters defrost heating power and minimum condensing temperatures come into view the use of the program is quite restricted to refrigeration system engineers refrigeration consultants and of course researchers This is just as true for all of the three programs described here 3 Calculation methods When it comes to the calculation method for the energy consumption of a refrigeration system the basics are quite straightforward Condensing and evaporating conditions determine over the compressor characteristics the cycle efficiency The compressor energy consumption is then determined by total refrigeration load and cycle efficiency Condensing conditions Condensing conditions are dependent on2. 2 Scope of the programs The aim and target audience for the different programs as defined by their producers determine to a large extent what the user can expect from them Jaime Arias of KTH the Technical University of Stockholm describes his program as follows CyberMart is a user friendly computer model where different refrigeration system for a supermarket can be compared in detail with focus on energy usage environmental impact TEWI and LCC Life Cycle Cost In fact the Cybermart program encompasses much more than just a calculation of the refrigerating and freezing system it also takes account of the HVAC Heating Ventilation and Air Conditioning energy consumption of the supermarket It also accommodates pricing info on equipment so that an LCC Life Cycle Cost comparison can be made between two alternative system solutions There are a number of system configurations that can be used in Cybermart each of which is presented to the user by a system design drawing i Direct system DX for cooling and for freezing ii Completely indirect system Cooling and freezing indirect iii Partly indirect system DX on cooling and freezing side indirect condensers iv Cascade A or B sometimes referred to as Booster system freezer cascade condenser is load in the indirect cooling system v Parallel system with subcooling someties referred to as Booster system subcooling of freezer system is performed by cooling system vi D
3. Walk In Cooler Freezer 0 2365 0 3154 0 0079 0 2681 0 3469 0 2365 Evaporating conditions In the past it was quite common to use 10 C for medium temperature cabinets and 35 C for low temperature cabinets In recent years however requirements on energy efficiency have led to a more diversified landscape where manufacturers suggest higher evaporating temperatures for specific cabinets where possible In Cybermart and in Econu Koeling II the evaporating temperature is specified for each cabinet individually in Econu Koeling II default values of 10 C for 3M1 and 3M2 cabinets are used in the database when no specific manufacturer s details are available and 8 C for 3H cabinets When cabinets with different evaporating temperature requirements are connected to one rack Econu Koeling II sets the evaporating temperature to the lowest required temperature For the other cabinets with higher evaporating temperature requirements there is an option to specify the use of an evaporating pressure controller When this is used the cabinet will operate at it s prescribed evaporating temperature and no correction to the refrigerating capacity is made When the controller is not selected the program recalculates the cabinet data to operate at a lower evaporating temperature than described which means that the refrigerating capacity is increased due to lower circulating air temperatures and more air dehumidificat
4. Champaign Illinois USA July 22 23 2002 Proceedings ISBN 2 913149 27 8 Short Course SC12 Advances in Supermarket Refrigeration S Fischer et al 21st International Congress of Refrigeration Washington DC USA August 17 22 2003 Proceedings ISBN 2 913149 32 4 Experience with a voluntary energy labelling scheme for refrigerated display cabinets S M van der Sluis 20th International Congress of Refrigeration Sydney Australia September 19 24 1999 Proceedings ISBN 2 913149 06 5
5. Swedish cities Dutch profile 237 USA cities Calculation Hourly values Temp intervals Temp intervals Condensing conditions Fixed T or floating Design Teo Temin T Temin T Capacity P fan Pran Subcooling Yes option Supply line T Indoor conditions Indoor temperature Choice day night and Fixed 19 C Not available winter summer Cabinets Predefined cabinets 180 Swedish cabs Eurovent directory Add user cabinets Possible txt file Possible program Cabinet DEC fan light def DEC 12h lighting fan light def heater Nightcovers All medium temp All Individual per cab z low temp cabs Additional lighting Brine system calc Evaporating conditions Evaporating temp Per rack automatic Per rack automatic User input per rack Superheat Not available 9K option EEV 5K Not available Suction line losses DX Suction line P Calculation Constant 2K Calculation Refrigerant circuit amp compressors of racks Unlimited 2 medium 2 low 3 medium 3 low max 10 loads rack Refrigerants R404A 7 refrigerants Not available Predefined Compres 1 Bitzer All Bock amp Bitzer 404A 1 Copeland Discus 2 Copeland 407C 507 Add user compressor Not available Data entry screens 144 tabulated values Reporting The reporting section in Cybermart is set up as a report on the whole supermarket energy situation inclu
6. energy consumption in the true sense is to make a calculation of energy consumption based on knowledge on location building and equipment without previous knowledge on measured values Then the calculation result is compared to actual measurements preferably for a number of supermarkets A validation in this sense has only been performed for Econu koeling II even though this program is explicitly intended for comparison of offers for refrigeration installations with regard to energy consumption and not for predicting actual energy consumption The validation for Econu Koeling II was performed on 3 supermarkets two in The Netherlands and one in Germany Supermarket 1 is a C1000 supermarket in Amsterdam with 1360 m sales area where energy consumption for refrigeration has been monitored for 4 years The market has 63 m positive temperature cabinets 20 m frozen display and 8 storage cells It has a floating condensing temperature minimum 24 C and active liquid subcooling for the freezer section Energy consumption calculated with Econu Koeling V2 for this supermarket was 351 MWh year which is 1 below the actual average measured value Table 4 Measured energy consumption data for 1360 m supermarket used for validation Measurement Period Energy Consumption kWh year April 2000 April 2001 353500 April 2001 April 2002 357500 April 2002 April 2003 353000 April 2003 April 2004 356000 Average 4
7. years 355000 The supermarket chain s advisor DN Consultancy used his own calculation method in projecting the installations and arrived at a yearly consumption of 360 000 kWh year which is also a quite accurate prediction of the actual measured energy consumption Supermarket 2 is a C1000 relatively new supermarket in Nieuwegein with 968 m2 sales area where energy consumption for refrigeration was monitored from may 2003 may 2004 The measured energy consumption over this period was 200 000 kWh In this case the supermarket chain s advisor had projected the installation at an energy consumption of 225 000 kWh year The consultant explained that this market was operated by an energy minded owner who consistently used the available night covers and operated at a low store temperature Econu Koeling calculated an energy consumption of 255 MWh year for this supermarket which is 28 above the actual measured value and 13 above the value predicted by the advisor It must be noted that Econu Koeling calculates energy consumption at fixed boundary conditions and does not take account of the actual situation such as a lower store temperature The last validation project for Econu Koeling V2 Supermarket 3 is a German Extra Markt located in Rheinberg For this market Econu Koeling V2 calculated a yearly energy consumption for refrigeration of 762 MWh year This value is within 1 of the actually measured energy
8. Review of calculation programs for supermarket DX refrigerating systems year round energy consumption S M van der Sluis M Sc IIR TIF D1 subcommission Refrigerated Display Cabinets Glasgow UK Meeting August 31 2004 1 Introduction Calculating the year round energy consumption of a complete supermarket refrigerating and freezing system is generally a tedious job First of all there are generally more refrigerating systems at various evaporation temperatures at least one for freezing and one for cooling possibly with different refrigerants Secondly varying outdoor temperatures throughout the year need to be taken into consideration for a realistic energy consumption estimation especially for systems with floating head pressure variable condensing temperature And last but not least numerous individual refrigeration loads display cabinets storage rooms and others must be taken into account for each of which proper data must be collected regarding refrigeration load and electrical power consumption as usually the electrical consumption for cabinet lighting fans defrosters etc is regarded as part of the refrigeration system energy consumption It is therefore quite helpful that computer programs have been developed to assist in the calculation of year round supermarket refrigeration system energy use Recently three such programs have been introduced to the refrigerating community for the calculation of year rou
9. alk In Piping figure 5 refrigerant line characterization in the ORNL spreadsheets 1 main liquid line 2 branch liquid 3 branch suction 4 main suction 5 suction return Econu Koeling II takes a completely different approach suction line pressure drop is not calculated but quite simply an assumed value of 2K equivalent is used in all calculations Refrigerant circuit and compressors Development of the three programs has been started before the breakthrough of CO2 in supermarket refrigeration systems Therefore none of the programs is suited to make calculations for CO cascade or supercritical refrigeration systems Cybermart is at the moment limited in the choice for refrigerant and compressors it uses refrigerant R 404A and allows a choice out of three compressors Bitzer reciprocating Copeland reciprocating or scroll for the medium temperature system and for the low temperature system Info on compressor performance data is not accessible to the user Econu Koeling II allows a choice of refrigerants from a predefined list which includes the most commonly used refrigerants in supermarket refrigeration R404A R407C R507 R134a R290 R410A NH3 For each rack 2 medium temperature 2 low temperature the user can specify up to 4 compressors from a database and can indicate the configuration parallel compressors without or with frequency control The compressor database in Econu Koeling II is pre filled with Bock and Bitz
10. ambient conditions All three programs use a scheme in which the calculations are made at various ambient temperatures and the results are integrated over the occurring ambient temperatures Cybermart uses hourly values of ambient conditions in a format that is quite commonly used in HVAC system calculations Ambient conditions are available for a number of Swedish cities and for Amsterdam Ambient temperature distributions Cybermart 1200 e Stockholm s Amsterdam G teborg Frequency hours year Ambient temperatures C figure 2 example of Cybermart s ambient temperature distributions The condensing conditions can be specified in Cybermart inside the Heating and Air Conditioning input screen where there is a choice between heat recovery mode and floating condensing not diversified for cooling and freezing system In the heat recovery mode the user can specify a fixed condensing temperature In the floating condensing mode however there are no further input possibilities for condensing to ambient temperature difference or for minimum condensing temperature Subcooling of the refrigerant cannot be specified The total yearly energy consumption calculated by Cybermart is the sum of 8760 individually calculated hourly values each at the appropriate ambient condition Econu Koeling II has no choice of ambient conditions for all calculations the same distrib
11. consumption For the ORNL supermarket spreadsheets extensive measurements were made in a large supermarket with 6 refrigeration racks These measurements were however used for parameter fitting as well as for comparison of results and can therefore not be considered as a validation in the true sense The results are listed in the table below Table 4 ORNL supermarket spreadsheet validation after fitting Program Manuals The manual for Cybermart is available in PDF format and through the help function internal to the program The manual describes how to operate the program but gives no details concerning the calculation methods used The Econu Koeling If user manual gives a combination of operating instructions and description of the program It is available through the program s help function The ORNL supermarket spreadsheet manual is quite extensive and gives detailed information on the calculation rules used It is available as a separate PDF document For general use of the spreadsheets the manual is very complete for creative use of the spreadsheets with additional programming by the user it is necessary to have a good knowledge of Excel It is almost impossible to cover in a manual all the things a user might want to know It is therefore quite positive that in my experience the programmers have answered swiftly and helpful to questions posed by email or telephone Conclusions Which one of the three program
12. d certified by Eurovent by means of laboratory measurements 10 large manufacturers are participating in the certification scheme Currently the certified data is limited to positive temperature cabinets Table 1 Eurovent remote cabinet categories for details and definitions refer to www eurovent certification com M package Category Designation Family temperature te class Horizontal Chilled Serve over counter 3M1 no night cover RHC1 3M1 N List Horizontal Chilled Serve over counter 3M2 no night cover RHC1 3M2 N List Horizontal Chilled Open Wall site 3M1 no night cover RHC3 3M1 N List Horizontal Chilled Open Wall site 3M2 no night cover RHC3 3M2 N List Vertical Chilled Semi vertical 3M2 no night cover RVC1 3M2 N List Vertical Chilled Semi vertical 3M2 with night cover RVC1 3M2 Y List Vertical Chilled Semi vertical no night cover RVC1 H2 N List Vertical Chilled Semi vertical with night cover RVC1 H2 Y List Vertical Chilled Multi deck 3M1 no night cover RVC2 3M1 N List Vertical Chilled Multi deck 3M1 with night cover RVC2 3M1 Y List Vertical Chilled Multi deck 3M2 no night cover RVC2 3M2 N List Vertical Chilled Multi deck 3M2 with night cover RVC2 3M2 Y List Vertical Chilled Multi deck no night cover RVC2 H2 N List Vertical Chilled Multi deck with night cover RVC2 H2 Y List For cabinets not included in the Eurovent database Econu Koeling II of
13. ding the HVAC system This implies that the refrigeration specific reporting details are quite minimal there is however an interesting plot of year round compressor power consumption which can be used to determine peak compressor power requirement Coamgasgion Pome Way prone imputar Pee ry mW m M1 a ee o 2 ee ee en ee ae Day figure 6 compressor power plot from Cybermart Econu koeling I provides only textual reporting of energy consumption per rack and the split up of energy use over compressors condenser fans direct cabinet consumption and others plug in cabinets The program can also print an extensive report of the complete calculation including all the input data with cabinet list compressor specs etc as well as results The ORNL supermarket spreadsheets provide reporting facilities in which 10 different runs calculated results can be easily compared in regard to energy consumption and refrigerant charge in a graphical representation The results are also available in tables the nature of the program Excel allows unlimited other representation forms Pewa Camump ka Complete Rahiye Syrum Lagani Besar Cosmeptiae SE recurs hme a ee l nniamin P Pome l bircyp Cae Fas Pee carer r ecm ee LEENT re woe EA DH HH HH figure 7 ORNL supermarket spreadsheet energy consumption display for 10 calculation runs Validation A validation of a calculation program for supermarket year round
14. e from the cabinet brand and type are presented more detailed data is not visible to the user during cabinet selection Length and refrigerating capacity of the cabinets are presented in an overview of selected cabinets also the overall capacity for freezing and cooling is presented Storage cells for medium or low temperature can be designated by size area and storage temperature Additional display cabinets can be created by the Cybermart user external to the program by specifying the detailed cabinet data in a text file The cabinet is then specified in terms of length refrigerating capacity evaporating temperature product temperature in out air temperatures direct electrical consumptions lighting fans defrost others in out brine temperatures and pressure drop It is possible to designate overall night cover usage in Cybermart for the low temperature cabinets and for the medium temperature cabinets in the system design screen Cybermart allows a quite precise designation of opening hours during weekdays and weekend days combined with store temperatures during opening and closing hours in winter and summer This allows for a perfect correlation of night cover use and store temperature Econu Koeling II comes with a database containing all cabinets from the Eurovent Directory of Certified Products www eurovent certification com The cabinet data in the Eurovent certification scheme is presented by the manufacturers an
15. er compressors for R404A R407C and R507 The user may add additional compressors to the database whereby the data to be supplied is data under standard test conditions There are easy to use input screens per manufacturer for data supply which reflect the terminology and representation as used in the manufacturer s technical documentation The compressor data available in the database at standard test conditions for example at 10 C 25 C suction gas temperature is recalculated by Econu Koeling II during run time to fit the actual conditions in the specified rack for example 12 C evaporating and 2 C suction gas temperature The ORNL supermarket spreadsheets use a polynomial to determine compressor COP based on saturated discharge condensing temperature and saturated suction evaporation temperature The polynomial used corresponds to the Copeland 4DT3 2200 Discus compressor Because of the spreadsheet nature of the program it is possible to make use of alternative compressor data which however requires that 2 tables capacity power with each 72 values are specified Table 3 Overview of calculation specific details Cybermart Econu Koeling II ORNL spreadsheets Units SI SI SI or English Units Systems DX Indirect z Indirect condenser Booster cascade Freezer subcooling District cooling Condensing conditions Ambient temperatures 16
16. fers the possibility to add cabinets in a second user database The data to be specified is equivalent to the Eurovent convention which closely relates to the European test standard and is defined in Eurovent recommendation REC 05 The user database contains a number of predefined cabinets which reflect European average cabinets Cabinet data is available for 2 50 meter length cabinets after selecting the appropriate brand and type from the list in Econu Koeling II the user only has to specify the actual cabinet length All cabinet data from the database is visible when selecting cabinets including the energy label designation A G for Eurovent cabinets 7 The data is presented at standard European test conditions climate class 3 room temperature 25 C 60 relative humidity Internally Econu Koeling II uses a fixed indoor temperature of 19 C which was a common choice by the Dutch suppliers and cannot be changed by the user This reflects the purpose of the program which is to compare the energy consumption of competing offers at fixed boundary conditions The cabinet data from the database specified at 25 C is internally adjusted for a room temperature Troom of 19 C Based on the internal circulation air temperature Terc in the cabinet the heat extraction rate is adjusted by Troom Tcirc 25 Teirc There is a further option in Econu koeling II to specify additional lighting for each individual cabinet as in the f
17. ield extra lighting is often installed This extra lighting has an influence both on the Direct Electrical Consumption DEC and the refrigeration load as most of the dissipated heat is removed over the refrigeration system The ORNL supermarket spreadsheets contains 5 predefined low temperature and 8 predefined medium temperature loads in terms of refrigerating capacity For each of these predefined loads the refrigerating load can be set to low average or high Because the ORNL program is a spreadsheet program the user can access these predefined settings sheet central manager display case energy use to use his own data set or to account for night cover use differing indoor temperatures and such All direct electrical consumptions fans lighting heaters and defrost have to be supplied individually per cabinet by the user which is quite some work for larger numbers of loads Table 2 ORNL Supermarket spreadsheet loads data Medium Temperature Low Temperature ORNL Loads data kW m or kW m kW m or kW m Average High Low Average High Low Deli Cheese and Pizza 0 4326 0 6008 0 3365 Meat and Seafood 0 2884 0 6008 0 0961 Multi Deck w Doors 0 5768 0 6248 0 5287 0 5768 0 7931 0 3365 Open Multi Deck 1 5138 1 9226 0 9613 1 3698 1 3698 1 3698 Other Display Cases 0 8892 1 5861 0 4326 0 7450 0 9613 0 5287 Produce 0 6729 0 9373 0 3605 Tub or Coffin 0 2644 0 3124 0 2403 0 4806 0 6729 0 2644
18. ion All three programs have an option to use more than one compressor rack From an energy efficiency viewpoint it is advisable to group cabinets per compressor rack according to their evaporating temperature In this way cabinets which allow high evaporating temperatures can also be operated efficiently at these high temperatures and are not operated at a too low evaporating temperature that may be required by other cabinets in the same group In the ORNL supermarket spreadsheets the user can specify the evaporating temperature per rack The cabinet superheat in DX systems is set to a default value of 9K in Econu Koeling IL There is an option per rack to reduce this value to 5K to reflect the use of electronic expansion valves Suction line losses Cybermart has been developed for applications with indirect cabinets and has a program module to calculate the pressure drop in the brine system Also for DX applications a pressure loss module is used For each compressor rack the geometry data length diameter elbows others has to be supplied for liquid suction and discharge lines Velocity pressure drop en temperature are then calculated by the program The ORNL spreadsheets use the same approach but to a greater detail Here for each single cabinet or other load the individual branch piping lengths have to be specified as well Due to this setup the number of loads per compressor rack is limited to 10 Display Case and W
19. istrict cooling cascade condenser to district cooling system figure 1 Cybermart system design presentation Cascade system B In The Netherlands supermarket equipment investors wanted a tool to compare offers from different suppliers not only concerning price but also concerning energy costs The program has been set up based on agreement on methodology between the major Dutch refrigeration system suppliers Carrier Fri Jado Elficold Smeva Linde and Veld Koeltechniek Arneg Econu Koeling II is an instrument to compare offers for supermarket refrigeration installations from different suppliers in a uniform manner Econu Koeling I calculates the year round energy consumption based on details given in the offer The basic idea is that of a post processor which transforms an offer received from a supplier into an energy consumption figure The program is explicitly not intended for system design studies and does not accommodate any exotic system designs It is mostly suited for DX systems and booster systems where the freezer cascade condenser is a load to the refrigeration system and it can accommodate indirect systems The program background was presented at the NTCR 2001 conference 5 Steve Fischer presented his spreadsheet calculation program during the international congress of refrigeration in Washington 2003 during a workshop at which free copies of the spreadsheets were distributed 6 He wrote
20. nd energy consumption of supermarkets These are in alphabetical order Cybermart created by KTH in Sweden 1 Econu Koeling created by TNO in The Netherlands 2 The ORNL Supermarket Spreadsheets by ORNL USA 3 These programs are available for free and can be run on a normal desktop computer with Windows operating systems The ORNL spreadsheets further require the availability of Excel as a platform to run them The programs currently still bear national characteristics such as weather databases component data and or language used but are expected to outgrow this stage in the near future At the Ecole des Mines in Paris another program called Clim Top 4 was developed by M Orphelin and D Marchio but regrettably this program has not been released for use by the general public Although the task of calculating energy consumption may look quite straightforward and the general approach taken in these three programs is similar the programs are quite different in their actual use depending on the various aims and target audiences for which the programs have been developed For the end user this also means that the choice for the right program for the right job should be made on the basis of knowledge of the ins and outs of the different programs This review intends to present the three programs in such a way that the user can decide which program is most suited for his specific purposes
21. number of American cities for which climatic conditions are available It is possible to supply the minimum condensing temperature and the condenser approach temperature for low temperature freezing and medium temperature cooling systems separately Dry Bulb Yearly Temperature distribution Olympia ORNL Econu NI Probability 20 0 10 0 0 0 10 0 20 0 30 0 40 0 Temperature Celcius figure 4 example ambient temperature distribution from the ORNL spreadsheets Olympia USA and the Econu Koeling II temperature distribution Loads Cabinet selection Loads in a supermarket environment are refrigerated cabinets freezer cabinets storage cells and sometimes other loads such as air conditioning loads Generally many individual loads are present in the form of individual display cabinets Here a distinction is made between plug in cabinets with an integrated refrigeration system discharging heat into the supermarket and remote cabinets which are connected to the central refrigeration systems Plug in cabinets are irrelevant in the refrigeration calculations but both Cybermart and Econu koeling II allow their specification whereby the direct electric energy consumption is added to the total yearly energy consumption Cybermart comes with a database of some 180 cabinets including minor variations in length and temperature of brands Carrier and Wyca To choos
22. s for calculation of supermarket yearly energy consumption is most suitable depends highly on the users purpose In the design stage when one wants to make an energy efficient system choice for the supermarket as a whole including the HVAC system Cybermart is definitely the right choice For time saving calculations to compare energy use of standard DX systems with minimum need for user input of technical data Econu Koeling II is very well suited By nature the ORNL supermarket spreadsheets offer maximum flexibility and are thus best suited when special features need to be calculated as the spreadsheets allow access to every formula used Literature 1 2 3 4 5 6 7 Cybermart Beta Version Jaime Arias KTH Sweden July 2004 Econu Koeling V2 test version Sietze M van der Sluis TNO and Henk Stijnen DWA for NOVEM and CBL The Netherlands August 2004 The ORNL Supermarket spreadsheets Steve Fischer Oak Ridge National Laboratory CD ROM distributed during the 21st International Congress of Refrigeration Washington DC USA August 17 22 2003 Computer aided energy use estimation in supermarkets M Orpelin amp D Marchio Centre d Energ tique de l Ecole des Mines de Paris Proceedings of Building Simulation 97 Volume 2 213 220 A Method for Comparing Refrigeration Offers for Supermarkets S M van der Sluis IIR Conference New Technologies in Commercial Refrigeration University of Urbana
23. ution of ambient temperatures is used which is a reflection of the program s purpose to compare different solutions at identical boundary conditions The outdoor temperature distribution used is a typical long term average for the Netherlands The ambient temperature spectrum is divided in a number of 2 C intervals each with it s own number of occurrences in a year The energy calculations are made at the central temperature of each interval and then multiplied with the number of occurrences In Econu Koeling II the condenser of each installation cooling or freezing must be specified at the design point Furthermore the minimum condensing temperature must be specified in case of constant condensing pressure such as would be used with condenser heat recovery the minimum value is chosen equal to the design value In the calculations the actual temperature difference is related to the ratio between actual condensing load and design condensing capacity Econu Koeling II condensing curves ee Full load design example g j Te min 20 C Condensing temperature C Ambient temperature 2C figure 3 example of Econu Koeling II condensing temperature curves The ORNL supermarket spreadsheets use the same approach as Econu Koeling IL using temperature intervals with occurrence distribution when it comes to the treatment of varying outdoor conditions However the user can choose from a large
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