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1. Low Intensity Applications eee XE b og mm 8 NOTE Values and equations quoted in this handbook are from reliable sources and apply to most applications Actual results are subject to several variables so results may vary HEAT TRANSFER There are three modes of transferring heat They are Convection Conduction and Radiation CONVECTION The dictionary defines convection as follows Transference of heat by moving masses of matter as by currents in gases or liq uids caused by differences in density and the action of gravity When a difference in density occurs the mass of the specific unit volume changes causing a change in weight When air is heated its density changes in that its mass becomes less per unit volume When air comes in contact with a hot surface it heats and be comes less dense Due to the change in mass the heated less dense air rises An example of heat transfer by convection is the old potbellied stove or in more modern times the finned tube used in residential hot water heating systems Cooler air when it comes in contact with the finned tube warms and becomes less dense It then rises and as it does creates a void into which more cool air moves This continuing process creates a circular air pattern across the finned tube warming all the air in the space Modern gas fired convection heating equipment does not depend solely on gravity but uses an air mover in the form of a fan or blower
2. REZNOR INFRARED HEATING HANDBOOK FORWARD This handbook has been prepared by Reznor to assist in the selection sizing installation and service of both low and high intensity infrared heating appliances In addition to this information general data on fuel gases heat transfer and the combustion process is included We believe that this booklet will be most helpful to students or individuals who are apprentices in the heating industry Additionally engineers and architects may find the information helpful in the selection and specification of infrared systems As a primer to this manual it is suggested that you read Reznor s SPACE HEATING HAND BOOK which is available from most Reznor distributors or directly from a Reznor representa tive TABLE OF CONTENTS MI ooo EE 0 Page Atmospheric Aeration 5 Gas Characteristics is secasctenstcondacaahstateeiedrctpecapesesteads 3 Aeration Atmospheric essere SMEIDG Boer NEU 28 Aeration Building ese piss UOGHMEES S rom 29 Aeration Induced DES ouo aspe paa mayas 2 HeatLoss Study 20 Aeration Pilot Burner rE S Heat TSC 2 Black Induced Dra Aeration Luise aiias 5 Boltzimart Stefan diia order eedioseaaciactseasncsiees B NAM 12 Boltzman Ludwig Thermodynamic Radiation T
3. 19 fiofiof 9 9 s Fe e 7 8 P 8 8 7 135717 posne 2 e EG zafo 5 rs po sz as anne Fiss po sa 66 ai 53 27 22 18 spa po ps pose pe sioe opis nju H HEIGHT FT w etre gt gt Fi 24 27 28 26 i9 v i5 ria is por 27 2 2 19 18 16 14 Fu 14 i7 8 18 is 17 6 14 13 H HEIGHT FT 8 in 13 15 15 15 15 14 13 12 6 911215 131 13 13 12 11 5 7 8 10 i pnmo fo 7 8 1010 10 10 9 Most infrared units have standard reflector systems that serve to delineate the radiation pattern and in effect provide a better con centration of BTU intensities Fig 21 illustrates the long axis pat tern while Fig 22 illustrates the short axis pattern The maximum spread of 12 feet is typical but will vary with unit size Also the manufacturer has selected these dimensions based on acceptable intensity levels for the average installation Intensities beyond these dimensions exist but in many cases are considered fringe BTU s that do not figure into considerations for spot heating LONG AXIS FIG 21 LINE OF SIGHT PATTERN SHORT AXIS FIG 22 LINE OF SIGHT BTUH FT intensity tables are determined based on extensive test ing The values and boundaries are considered by the manufac turer to be the most useful i
4. determine the most favorable mounting height from the recommended mini mum mounting height chart and the floor coverage required A simple rule to follow in floor coverage is that the coverage of a horizontal unit is two times the mounting height At a 30 angle the length of dispersion extends to four times the mounting height However the distance intensity relationship not only applies to the mounting height but also affects the intensity pattern of the infrared dispersion or floor coverage The first step in spot heating with high intensity infrared is to determine what BTU level is needed Most spot heating is installed to provide comfort for people With this in mind let s take a look at how the BTU requirements vary under different ambient condi tions and also as the activity of the people changes Fig 19 isa SURFACE HEAT LOSS NOMOGRAPH showing BTU levels that would be necessary to provide comfort conditions for people as they work within the confines of a given area Note that the activity level with ambient temperature air movement and cloth ing affect the BTU s lost from a person s body The greatest influ ence is the activity level As the level rises less comfort BTU s are required since the body will be generating much of its own heat requirements As the activity level decreases more comfort BTU s must be added These variations are displayed in the small inset upper right on the chart and must be added or
5. CALCULATIONS To help in understanding the heat loss calculation process more fully the following sample heat loss study is offered Commercial 200 L x 150 W x 20 H equals 600 000 ft Thirty 30 double insulated windows with steel sash 48 x 48 each U Factor 15 70 refer to Figure 31 1 Surface area equals 4 x 4 x 30 windows or 480 ft to be deducted from sheet metal wall surface area Three 3 Insulated steel service doors THx4 W x 1 75 thick with foam core and thermal break U Factor is 20 Figure 31 2 Total surface area equals 7H x W x 3 doors or 84 ft 3 Surface area below 5 H to be deducted from brick wall surface area equals 5 H x 4 W x 3 doors or 60 fe 4 Surface area above 5 H to be deducted from sheet metal wall surface area equals 27H x 4 W x3 doors or 24 ft Two 2 Steel rollaway doors 12 W x 16 1 75 thick U Factor is 59 Figure 31 5 Total surface area equals 16 H x 12 W x 2 doors or 384 square feet 6 Surface area below 5 H to be deducted from brick wall surface area equals 5 H x 12 W x2 or 120 f 7 Surface area above 5 H to be deducted from sheet metal wall surface area equals 11 12 W x2 doors or 264 ft Building Windows Doors Walls Bottom wall Split Construction 5 H consist of 2 rows of 4 wide common brick 8 thick total U Factor is 41 Figure 31 8 Surface area for the side walls equals 5 H x
6. a proper mix of oxygen and methane are heated to the point of ignition we obtain a flame This heating may occur by any one of several processes The one we are most familiar with is the use of a match Presently many gas fired appliances are initially ig nited through the use of a spark or hot surfaces energized by electricity may also be used to heat gas air mix for ignition Once ignition takes place the burning process gives off carbon dioxide If the mix of air and gas is not within the proper ratio carbon monoxide will also issue from the flame and can reach unaccept able levels Gas air mixes may not even ignite if the ratio of air to gas is not within a certain range It is important that these mixes are at an acceptable level for the most efficient burning character istics Such mixes are controlled in the design of the pilot burner internal passageways aeration methods orifices and gas pres sures Therefore it would be detrimental to the safety of the user if modification of any kind beyond those prescribed by the manu facturer were made on any of these gas heating products Fig 2 shows the effects of carbon monoxide at various levels given in PPM parts per million Carbon dioxide concentrations up to 5000 PPM may be present in a given space with no ill effect on humans Incomplete Combustion 100PPM Safe for continuous exposure 200PPM Slight effect after six 6 hours 400PPM Headache after three 3 hours 900PPM He
7. calculations When heating with infrared we will be able to reduce the calcu lated heat loss by 15 and we will be sizing the units based on their INPUT rating Therefore 643 468 x 85 546 948 BTUH The 15 reduction is permissible due to the fact that with infrared we will be avoiding direct radiation against the ceiling and outside walls This in effect keeps the AT at a minimum That is why it is so important to avoid directing the infrared rays against outside walls windows and doors Of course with the reflectors no infra red energies should contact the ceiling or roof 20 200 3 Service Doors Tx4 30 Windows 4 x 4 15 Sheet Metal 5 Brick HEAT LOSS CALCULATION RADIATIONAL LOSS Surface Area FT x AT x U Factor BTUH LOSS Windows 480 f x 58 F x 70 U 19 488 BTUH Service doors 84 ft x 58 F x 20 U 974 BTUH Rollaway doors 384 ft x 58 F x 59 U 13 140 BTUH Brick wall 3 320 58 F x 41 U 78 950 BTUH Sheet metal wall 9 732 ft x 58 F x 21 U 118 536 BTUH Roof 30 000 f x 58 F x 05 U 87 000 BTUH TOTALE RADIATIONS LLOSSES einean 318 088 BTUH INFILTRATION Volume f x Air Change x 018 x AT BTUH LOSS 600 000 f x 1 2 x 018 x 58 F 313 200 BTUH SLAB EDGE LOSS Lineal Feet x AT x U F
8. constructed of coated or stainless steel For many years now pilots operate on secondary air only therefore the flame is disbursed through the use of a specially designed head This makes it necessary to use stainless steel in the con struction of the burner head due to the high flame temperatures involved Figure 6 illustrates one of these pilots and demonstrates the exclusive use of secondary air for flame support This design was introduced some 30 40 years ago and was selected because it eliminated the need for primary air Older pilot designs used both primary and secondary air but it was found that primary air tended to create buildups of dust within the pilot gas air passageways and consequently was a source of constant service problems Buildup of dust within a burner is not nearly as critical since most burners have large chambers that will permit dust accumulation Nevertheless it is good practice to clean burners and pilots on a regular basis to prevent buildups that may alter or disrupt the normal flame patterns THIS IS ESPECIALLY IMPORTANT WITH HIGH INTENSITY INFRARED BURNERS Stainless Steel Burner Head Secondary Air Slot Pilot Orifice FIG 6 Secondary air pilot PILOT BURNER AERATION During the design of gas heating appliances the most critical de sign consideration is in properly aerating the combustion zone Too little air can result in gas rich air gas mixtures that can result in undesirable combustion resul
9. gas burning equipment both in the pilot burner configurations and in the design of the combustion air and flue gas passageways found in and around each gas heating appli ance Further we will discuss pilot burner aeration by means of either atmospheric pressures or by power assist using blowers or ex hausters FLAME There are three ingredients needed to create a flame They are Fuel air and heat Fuel is required to supply the carbon air is required to supply the oxygen and heat is required to raise the mix to its ignition temperature Natural gas is composed primarily of methane having a chemical formula of CH C Carbon and H Hydrogen Each molecule of methane consists of one atom of carbon and four atoms of hydro gen Thus methane in natural gas can provide the carbon re quired to create a flame Air which consists of 21 oxygen pro vides the second ingredient required to create a flame These two gases natural gas and air contain other ingredients but for the purpose of illustrating the resultant chemical formula when com plete combustion occurs only carbon hydrogen and oxygen will be used Fig 1 shows the chemical transition that occurs when methane burns Note that the combustion effluents contain car bon dioxide CO and water H O m Combustion Products Carbon Dioxide SOO 221 7 Vapor Oxygen OO 0 0 6 m 9 0 9 FIG 1 Complete combustion forms only water and carbon dioxide When
10. includes either or both of these functions then the following rules should be observed Ifthe infiltration rate CFM is greater than the exhaust CFM and or ventilation CFM then calculate only the infiltration losses Infil tration CFM may be calculated by dividing the volume of infiltra tion FT by 60 Minutes Ifthe infiltration rate CFM is less than the exhaust and or venti lation CFM then calculate the losses associated with these func tions and add to the radiational losses determined earlier Be sure to omit the infiltration losses Exhaust and ventilation BTUH losses may be calculated using the following formula CFM x 1 085 x AT BTUH loss LOSS BY CONDUCTION Conductive losses occur at grade and are most prominent in build ings that use a slab rather than a basement It is important that the slab edges are adequately insulated to guard against excessive losses at this point This is particularly important when using infra red as a heat source since the object with infrared is basically to heat the slab In order to calculate the BTUH loss for the edges of the slab use the following Slab with uninsulated edge 81 BTUH x Lineal feet x AT Slab with insulated edge 30 BTUH x Lineal feet x AT This quantity is then added to the radiational infiltration or ex haust and ventilation losses determined earlier The total repre sents the hourly building BTU loss at design conditions HEAT LOSS STUDY AND SAMPLE
11. that were gradually harnessed by mankind are Oil Electricity Liquefied Petroleum Gases Nuclear Geothermal and finally Solar Energy Back to the sun BRIEF HISTORY OF NATURAL GAS At this point we want to expand somewhat on the history of natu ral gas since most infrared heaters are fueled by this particular gas and to a lesser degree LP gases Modern natural gas began in United States in 1821 when William Hart dug the first gas well a depth of 27 feet near Fredonia New York The gas was distributed for use in illumination of homes and offices For the next 35 to 40 years wells sprung up throughout the eastern states and by 1900 there were gas wells in 17 states The gas industry had essentially begun Today nearly all of the lower 48 states and Alaska have gas wells and all have immense distribution networks to supply natural gas to nearly every vil lage town and city in the USA Natural gas in addition to being the most economical form of fuel energy also has clean effluents and is the most dependable of all the fuels Supplies of natural gas are in such quantities that it will be reliable as a source of energy well into the 21st century In addition to active fields there are huge quantities yet to be tapped which should fill our requirements beyond the middle of the 21st century Add to this the increasing availability of liquefied natural gas LNG from foreign producers and it appears that natural gas will be our majo
12. the gas burns The reason for this is so the flame is contained within the port to heat the clay or ceramic to an extremely high temperature usually between 1650 F and 1850 F for maximum surface temperature and optimum heat radiation Obviously with the flame withdrawn into the ports no secondary air is available to the combustion process Orifice Mixing Section Ceramic Block with Minute Drilled Ports FIG 12 High intensity burners have these basic parts FIG 13 A reflector type radiant heater RADIANT HEATING As mentioned earlier radiant heat was the earliest form of comfort heating Early man found that fire provided warmth in the absence of the sun and this warmth was absorbed through radiation Then fireplaces appeared in buildings and were the sole source of heat in the bitterest cold These too offered radiation and it was soon discovered that the rays would heat other objects within the room which would reradiate to other objects Then as all the objects warmed they would convect heat and eventually the room or en closure would become quite comfortable Fireplaces while still in use generally for their esthetic value gave way to stoves of various shapes and sizes These stoves were fired with wood and eventually coal and provided for the most part radiant heat However because of their design and their location within the building they were also capable of delivering heat through conduction cooking and al
13. when 1 the pressure in the building is negative 2 the atmosphere is dirt laden 3 the atmosphere contains any substance that will cause toxic gas when passed through the flame or 4 the heater is installed in a tightly closed room that does not provide required air for combustion Consult the heating equipment manufacturer and their installation instructions for requirements on drawing combustion air from out doors BURNERS Modern burner designs operate similar to the Bunsen Burner ex cept that in most current burner designs the gas is introduced in a horizontal direction and the flame port design is different to ac commodate the overall design of the heat exchanger Fig 11 illustrates a typical horizontal burner Again you will see the two distinct flame patterns cones which are derived from the use of both primary and secondary air Also a venturi is shown and as mentioned earlier this persuades more primary air to enter with the gas jet stream allowing for much higher input ratings in the indi vidual burner designs Fig 12 illustrates a burner used in HIGH INTENSITY infrared units Of extreme importance is the port arrangement on these burners Port diameters are small but by comparison to Fig 11 there are many more of them This fact points out the importance of air gas velocity in such a design The flame must occur within the port therefore this velocity must closely match the velocity of oxidation as
14. 200 L x 2 walls or 2 000 fe 9 Surface area for the end walls equals 5 H x 150 W x 2 walls or 1 500 f 10 Total brick wall surface area equals 3 500 f less surface area for doors lines 3 and 6 above 11 3 500 ft 60 ft 120 f 3 320 f 15 H consist of sheet metal with 1 expanded polystyrene U Factor is 21 Figure 31 12 Surface area for the side walls equals 15 H x 200 L x 2 walls or 6 000 ft 13 Surface area for the end walls equals 15 H x 150 W x2 walls or 4 500 f 14 Total sheet metal wall surface area equals 10 500 2 less surface area for windows and doors lines 1 4 and 7 above 15 10 500 f 480 f 24 f 264 f 9 732 ft Flat built up with 6 R19 insulation U Factor is 05 Figure 31 16 Surface area equals 200 L x 150 W or 30 000 ft Slab on grade with edge insulation U Factor is 30 Figure 31 17 Lineal feet equals length of four walls 200 150 200 150 or 700 lineal feet Top wall Roof Floor For convection type heating this is the amount of heat that must be supplied to the building under design conditions of 10 F out doors and 68 F indoors The convection type heaters would have to be sized based on their BTUH OUTPUT rating which is listed in the manufacturer s specifications Outdoor design 10 F Indoor design 68 F AT 58 F Infiltration Rate air change per hour Figure 35 shows the sample building layout and the final heat loss
15. Single glass with metal sash 1 23 2 C Double insulated glass with wood sash 2 D Double insulated glass with metal sash 3 0 DOOR CONSTRUCTION FACTOR ee 0 ROOF CONS TRUCTION FACTOR Wood built up with deck insulation R 1 39 Above with acoustical tile 5 Above with 6 R 19 blanket insulation 1 C Above with acoustical tile 5 and R 19 blanket 0 04 insulation Above with 3 5 R 11 blanket insulation 0 07 1 E Above with acoustical tile and 3 5 R 11 blanket insulation Above with 3 5 R 11 blanket insulation 0 06 2 Steeloraluminumoversheathinghollowbacked 069 3 Concrete builtup S Above with suspended ceiling 75 panels 0 19 Above with 3 5 R 11 blanket insulation Above with 6 R 19 blanket insulation IN NN ceiling per 3 A ceiling per 3 A DEM Sloped 45 wood with Gypsum wallboard 5 and asphalt shingles Above with 3 5 R 11 blanket insulation 0 06 ee 0 FLOOR CONSTRUCTION FACTOR Slab on Grade is 4 inch concrete with sand 0 30 aggregate 140 Ib sq ft and 1 inch edge insulation Over a heated basement 1 3 Ifbasement heat loss is required it must be calculated separately For the portion of the wall below grade use the following U values A B Concrete Basement Floor The annual fuel consumption for each insulation may be computed using the following formula or Annual fuel consumption BTU Where HL Hourly heat loss for area studied DD An
16. VE LENGTH Heat may be lost from a body even though no substance is in contact with the body Such energy is sent from the surface in every direction Picture the sun theoretically in contact with no matter and throwing off heat which is ultimately intercepted by the earth The heat cannot be seen nevertheless it is transmitted mil lions of miles by electromagnetic waves Most of this passage is through a vacuum outer space Infrared ultraviolet rays gamma rays x rays radio and visible light are transported in the same manner However these energies all travel in different WAVE LENGTHS impulses A WAVE LENGTH is the distance measured in the progression of a wave from one point to the next point much the same as the waves in the ocean as they travel across the surface of the water Infrared wave lengths are measured in microns A micron is 0 000001 or 1 1 000 000 ofa meter By comparison visible light travels in wave lengths of 4 to 8 microns while infrared travels within a range of 8 to 400 microns From a practical standpoint infrared heating wave lengths are found in the 2 to 20 micron range however infrared heating devices oper ate most efficiently within the 2 to 7 micron range Infrared rays do not lose their energy until they are intercepted by liquids or solids Air does not absorb the rays therefore none of the energy is lost to air This would explain the fact that when infrared heating is in use it can
17. actor BTUH LOSS 700 ftx 58 F x 30 U 12 180 BTUH HOURLY HEAT LOSS 643 468 BTUH FIG 35 Sample building layout and heat loss calculations INFRARED APPLICATION FOR TOTAL BUILDING HEATING The first consideration in selecting infrared heaters is the available mounting height Low mounting heights dictate that larger num bers of small high intensity units may be required or low intensity units High mounting heights may require large high intensity units in lesser quantities and will possibly rule out low intensity units The one thing to remember is that the most effective application will allow the intensity patterns of adjacent units to overlap If you allow voids between unit patterns the results will be less than ideal Let s continue with the sample heat loss above and make our unit selections The ceiling height as you recall was 20 feet however this does not mean that the units will be installed at or even near this height First of all clearances from combustibles must be ex amined If we find that in the built up roof some combustible mate rial exists then we must be certain that we observe the manufacturer s recommended clearances and this would be the closest we dare install the selected units Fire hazard clearances are clearly stated and will vary for each Manufacturer and for each individual unit These dimensions must be known before planning any unit selections or installations Let s assu
18. adache and nausea after one 1 hour 1000PPM Death on long exposure 1500PPM Death after one 1 hour Most codes specify that CO Concentrations shall not exceed 50 PPM FIG 2 Effects of carbon monoxide EXPLOSIVE LIMITS When natural gas and air are joined together the mix may or may not oxidize For instance if natural gas in the mix is between 4 and 14 there is potential for explosion or burning depending how the mix is handled In a heating appliance the combination of burner pilot and aeration design will cause the mix to burn under controlled conditions If the mix is simply in a space such as a room and it by some means is ignited it most likely will explode When the mix is outside the 4 to 14 limits there will be no ignition consequently no flame or explosion This points out the importance of creating a proper mix within the gas burning appli ance and also points out the hazards of allowing gas to escape indiscriminately into a confined area Fig 3 Natural Gas no combustion not enough gas combustion no combustion not enough oxygen FIG 3 Flammability limits of natural gas Propane gas acts in the same way but the percentage of gas in the mix changes somewhat and is shown in Fig 4 Propane Gas no combustion not enough gas combustion no combustion not enough oxygen FIG 4 Flammability limits of propane gas PRIMARY AND SECONDARY AIR In the design of pilots and burn
19. all cases when the heat from the infrared units is directed into the floor slab the heated floor in turn provides heat to the space For this reason it is advantageous to have a slab that has ample edge insulation to limit the conduc tion of heat from the slab into the surrounding grade FULL BUILDING HEAT LOSS Like all applications of heating apparatus a determination of the BTU H needs must be made when infrared heating is planned For buildings such information is very often available from the Archi tect or Engineer who was instrumental in the original design of the building In cases where it is not available from these sources you will be required to develop it on your own or enlist the aid of someone knowledgeable in heat loss studies to make these deter minations With the aid of the following data you should be able to generate much of your own heat loss information for commercial and indus trial buildings BUILDING HEAT LOSSES Buildings lose their internal heat by radiation convection con duction and by infiltration outside air leaking into the building These losses occur when the outdoor temperature is lower than the indoor temperature DESIGN TEMPERATURE When determining heat loss through a wall roof or other parts of a building enclosure the design temperature difference DT will be used in the final calculation The outdoor temperature at winter design conditions is needed Fig 33 is a short list o
20. be noted that upon start up the air in the space is slow to heat The air is finally warmed as the heated objects within range of the infrared source give off some of their heat through convection Fig 18 is an illustration of the effects that wave length has on the emitting power of a black body Note that a black body at 2200 degrees Rankin 1740 F has peak radiation BTU HR OUTPUT at a wave length of approximately 2 3 microns Also note that the peak output of a given temperature is at a lower micron level The shaded portion of the graph is the ultraviolet range Note that the output level descends sharply when the ultraviolet range is ap proached This means that wave lengths that fall into the ultravio let range are not effective for providing heat EMISSIVITY EMISSIVITY is the relative power of a surface to emit heat by radiation The emissivity of a surface is rated based on its ability to radiate compared to a black body By comparison a black body has an emissivity value of 1 The emissivity value of 1 serves as a basis for all studies relating to the emitting power of a given surface and et HERUM M AN AAA RELATIVE INFRARED OUTPUT FIG 18 MATERIAL Aluminum Polished Aluminumalloy Asbestos board Brick Rough red Glass Gravel Iron cast Iron Rusted Lacquer Flat black Lacquer Flat white Marble Plaster Sand stone Sawdust late Steel galvanized Steel sheet Steel 18 8 stain
21. ble mounting height 20 ft max no min Available mounting space sse 20 ftx 40 ft Air velocity in building essione 2MPH Light clothing consists of undershirt cotton shirt shorts and cotton trousers Heavy clothing would be double this amount Every person loses body heat even when asleep As activities increase the body generates additional heat which warms the indi vidual even under extremely cold conditions Most of this body heat is lost through convection radiation and perspiration It is when the activity level is reduced and the sur rounding temperature is below 70 F that some type of heat must be added or the individual must be in some way protected against the cold It is the intent of SPOT HEATING to provide the heat that the body is not generating so that comfortable conditions exist By referring to the surface nomograph Fig 24 the surface cloth ing loss for our example can be determined Follow the 35 F tem perature line down vertically from the HEAV Y CLOTHING line at the top When this line intersects the 2 MPH line move directly horizontal to the BTU FT line and read the value at that location You should read 25 BTUH By referring to the Activity Adjustment table you will note that for light bench work there is no BTU ad justment Had the subject in our example been engaged in heavy Work there would be no need for heat whatsoever since 36 BTUH must be deducte
22. by electromagnet waves REFLECTION When infrared energies bounce offa surface are deflected SECONDARY AIR Air that is introduced into the flame after igni tion has occurred SHORT AXIS Imaginary center of infrared source that runs across the width of a radiating surface SPECIFIC GRAVITY The weight of gas when compared to the weight of air Weight of air given as 1 0 SPOT HEATING Supplying heat to a specific area located in a building that is essentially unheated U FACTOR Amount of heat that will move through one square foot of a specifically defined surface in one hour with one degree F of temperature difference between the two sides VENTILATION The introduction of fresh air into a building un der power and exhausting a like amount back to the atmosphere Fi 2001 Thomas amp Betts Corporation Printed in U S A All rights reserved homas amp Betts Reznor is registered in at least the U S 15M 6 01 YL FORM RZ NA IRHB Version 0 1
23. d and this results in more continuity of pattern from one unit to the next The installation of units in either mode is solely depen dent upon the building character and use This must be examined carefully before any final decision on location and deflection mode is made i ct HORIZONTAL 30 ANGLE MOUNTING HEIGHT 11 FEET HORIZONTAL 30 ANGLE ZS FIG 39 Sample layout of eight 75 000 BTUH 40 ft low intensity tubular units 24 MOUNTING HEIGHT FEET DISTANCE FT FIG 40 Centerline to wall distance for low intensity infrared heater with reflector positioned for 30 angle UNIT LOCATION SUMMARY When using either high or low intensity infrared units for full build ing heating keep in mind that the best heating job is the one that provides infrared energies over the greatest portion of the perim eter The manufacturer s technical data regarding intensity pat terns is the key to providing such an application Here are a few guidelines that should be considered when plan ning a full building heating application 9 Never anticipate significant intensities beyond those expressed in the technical data Make every attempt to get full perimeter coverage of the slab Add units oversize as a last resort to get full coverage 30 angle tilt is recommended to simplify installation and to provide further assurance that the outside walls windows and doors are not impinged upon Horiz
24. d from the 25 BTUH value we have just deter mined Conversely if our subject would be at rest we would be adding 19 BTU to the 25 BTU already determined For SAFETY OF DESIGN multiply the 25 BTUH by 120 giving a BTU FT value of 30 as our target intensity requirement Therefore 30 BTUH FT must be directed at the subject in our example at a point 3 feet above the floor approximately belt height for person standing If the person were seated the distance above the floor would be 2 feet Ideally an attempt should be made to cover the subject from all four sides however spot heating may be adequately provided by using only two infrared units installed as illustrated in Fig 25 SURFACE HEAT AIR amp SURROUNDING TEMP FOR HEAVY CLOTHING 20 10 0 10 20 30 40 50 60 70 ACTIVITY At rest Light bench work Mod heavy work Heavy work a SURFACE HEAT LOSS BTUH FT a o o o 20 10 0 10 20 30 40 50 60 70 AIR amp SURROUNDING TEMP FOR NORMAL CLOTHING FIG 24 Surface heat loss nomograph High intensity infrared used in spot heating is most often installed at an angle Most infrared units are certified for both angular or horizontal installation According to the recommended minimum mounting height chart a Size 30 000 BTUH heater at a 30 angle should be installed at a minimum mounting height of 10 feet When spot heating is being used to heat a person or persons in addition to the activity and c
25. d that most tube type units have a much higher input rating than would be necessary on a small spot heating job such as described in the example above Tube type units could best be used in an application where the spot to be heated is un usually long and where the mounting height may be relatively low Some examples of this would be an assembly line or a service counter Fig 31 Care should be used in the selection of unit size due to restrictive mounting heights A sample of a recommended minimum mounting height chart by size and reflector position is printed below Recommended Minimum Mounting Height feet Reflector Reflector at Reflector at 30 degree Angle 1 Horizontal 45 degree Angle Hn 9 oo n 216 11 12 13 15 16 17 18 of 7 S 15 0 11 13 14 15 16 Consideration should also be given to the use of the U tube configuration for low intensity units because of the wide tempera ture difference that exists from burner end to exhaust end If flux density BTUH FT data is available for low intensity tube type infrared units design applications using that precise test generated information FIG 31 Service Counter Heating with Low Intensity Tubular Units 5 In the absence of flux density test information select the tubular infrared size based on mounting height BTU input and unit length Tubular units are usually equipped with reflectors wh
26. deducted from the Surface Heat Loss determined on the left column A sample appli cation later will put this chart to use Figure 20 illustrates examples of BTUH per square ft tables As was explained BTUH per square ft tables display the radiating capability and provide the mounting heights based on testing of specific heaters These tables are for specific Reznor Models of high intensity infrared heaters Each table is based on testing of the heater installed in the most common spot heating application a 30 angle measuring the BTUH intensity 3 feet above the floor FIG 20 The charts to the right show the BTUH FT Heat Delivery at point B in the illustration above for three different sizes of Reznor Radiant Heaters These values are valid for heaters mounted at height H at a distance D from point B when a standard reflector is used and the heater is mounted at a 30 angle Example A 60 000 BTUH radiant heater Model RIH60 mounted at a 30 angle 17 feet off the ground H at a distance of 8 feet D will deliver 18 BTUH FT to point B as shown in the table to the right MODEL RIH60 60 000 BTU s D DETANCECD 2 46 8 10 12 14 16118 201221241 29 22 117113 10 8 7 w 39 H HEIGHT FT nsmscrm 2a rol ie pisqepspspos is eror se o se sofos a pra pensa Fs 5e 38 3r spa is is 2 9 12 14 15 puri pe pep Es 7 9 10
27. dy characteristics but for the most part these materi als fall short ofthe BLACK BODY rating of 1 DO NOT confuse radiation with reflection As stated earlier a BLACK BODY has an emissivity of 1 which means that it absorbs ALL the thermal radiation directed at it none bounce off reflect Conversely a black body can send or radiate all those energies away On the other hand a sheet of polished aluminum is highly reflective It rejects a good portion ofthe infrared energies directed at it because the infrared rays bounce off Polished aluminum does absorb a small quantity of these energies If we assumed that the polished aluminum reflected 95 of the infrared impinged upon it we can then say the same material absorbs 596 of those energies thereby disposing of 100 of the energy with which it comes in contact For the reason of its reflectiveness polished aluminum is used extensively in conjunction with both high and low intensity infrared units Panels of this material are used to deflect the infra red rays for a more compact or more concentrated pattern giving much more definition to the area which these units are able to cover Black bodies are only theoretical however many surfaces are ca pable of absorbing a large percentage of the infrared energies di rected at them while others like the polished aluminum will reflect a high percentage of this energy You should keep this in mind when working in the infrared heating field WA
28. e Angle 20 000 50 000 60 000 Some high intensity infrared heater manufacturers publish flux den sity graphs that can be interpreted to accurately determine the desired mounting height The most complete information provided is when the manufacturer further interprets the flux density graph information and publishes a BTUH per square ft table See Figure 20 These tables not only provide specific mounting heights based on the BTU s required at the floor or at a specified height but also the horizontal distance in an easy to interpret format However to generate the information required to publish flux density graphs or BTUH per sq ft tables testing is required on each specific Model size and potential variation ofthe heater Unfortunately therefore this type of specific information is most often not available When 00 000 18 SURFACE HEAT AIR amp SURROUNDING TEMP FOR HEAVY CLOTHING 10 60 70 LOSSES 30 20 0 10 20 30 40 50 400 ACTIVITY At rest Light bench work Mod heavy work Heavy work 50 a o k T 5 m o l lt I w Q uu s 5 o l 20 10 0 20 30 40 60 70 AIR amp SURROUNDING TEMP FOR NORMAL CLOTHING FIG 19 Surface heat loss nomograph flux density graphs or BTUH per sq ft tables are available use them to determine the mounting height for the heat required When this specific test generated information is not available
29. e of 1 F However since most buildings are constructed with partitions much thinner than 12 inches and very often are constructed of various layers of differing materials the factor is not a very practical or efficient tool for determin ing heat loss Fig 33 Outdoor Design Temperature Degrees F Annual Degree Days 4348 Another measure of the resistance of heat flow is the R factor The R factor is a rating assigned to insulation which identifies by number the power of the insulation to resist the flow of heat The higher the number the greater the resistance However the R factor alone is insufficient for computing heat loss Please turn to page 18 Outdoor Design Temperature Degrees F Annual Degree Days 10 ty 5 30 10 5634 6599 AA L gt Milwaukee 5 7062 N 10 3254 10 5882 6351 10 15 10 10 10 10 35 20 10 25 10 10 25 acksonville ty Lansing Casper Dallas Lansing 20 7410 Ci Los Angeles Oklahoma City hiladelphia Rapid City St Louis Washington D C ty 79 E 10 25 10 20 5 5 10 35 35 15 10 This is a select list of cities For other cities consult ASHRAE or other sources 17 The U Factor The U factor is a value that is expressed in and represents the amount of heat that in one hour will flow through one square foot
30. e rays are generally at a right angle to this area Since the earth is spherical in shape the rays from the sun tend to deflect off the earth s surface as they approach the north and south poles Consequently with less heat absorption colder climates result In the gas heating industry radiation has been in use for a much longer time than convection As early as the 1920 s gas heaters were used for spot heating in residences and commercial build ings Heat was supplied by a gas flame and was reflected from polished surfaces designed to broadcast the heat rays through out the space These polished surfaces were soon replaced by clay blocks with highly irregular surfaces which when heated did a more efficient job of distributing the heat rays through radia tion This handbook will deal primarily with radiation principles and radiant heating appliances FUELS Over the centuries man has used many forms of fuel to provide heat for his own comfort Beginning with prehistoric man we would have to assume that his preference for fuels would most likely have been wood The next prominent fuel would have been coal It may surprise you to know however that natural gas was discov ered and used by the Chinese 2500 years ago Although we are not certain of its use we do know that they transported the natu ral gas through bamboo poles and can assume that the flame may have found some ritualistic use in their villages Other energies
31. e shortest CLD Also remember there is a limit to the mounting height in our example building 18 Therefore we will proceed with this size and style using the greater number of units to hopefully get total coverage of the perimeter The mounting height and the centerline distance from the wall must be deter mined Selecting a 15 ft mounting height Fig 36 shows the units should be installed at a distance of 7 9 from the wall Fig 37 is a sketch showing a proposed layout for the 30 000 BTUH high intensity infrared units This size has been selected for opti mum perimeter coverage Larger units would result in considerable pattern voids because of the limited mounting height and greater CLD o x 9 Z gt 695 20 18 16 14 12 10 8 FIG 36 Minimum unit centerline to wall distance feet for a high intensity infrared heater installed at a 30 angle As mentioned earlier this would provide less than ideal heating characteristics Note that liberties were taken with unit placement so that a concentration of heat is available at the rollaway doors Otherwise the CLD of 38 9 Ft was observed and the units are set at a 30 angle facing the center of the building Two adjacent infrared heaters at 38 9 feet CLD will provide intense coverage to the floor over at about 30 feet of the CLD This will leave 8 9 feet of diminished intensity void In this case we could rely on t
32. each differ ent construction type listed When the AT U factor and surface area are known the surface losses can be calculated as follows Area x AT x loss for area studied The sum of all surface area losses will be the total radiational and conventional losses for the building under study INFILTRATION In all buildings there is a certain amount of infiltration of outside air This unheated air enters through cracks usually around win dows and doors but also can seep through loosely constructed walls and joints Such leakage adds considerably to the total heat loss Determining the amount of infiltration is very difficult and time consuming Devices are in existence which can provide mea surement of such leakage but at considerable cost An accurate assessment of infiltration is best compiled by the Architect or Engineer If this information is unavailable most estimators will arbitrarily enter an infiltration rate based on the volume of the building For small buildings less than 100 000 cubic feet an infil tration rate of one air change hr is generally used For larger build ings the air change rate is lower but is never less than the vol ume of the building A more exacting method of determining infiltration rates is avail able from the ASHRAE guides and other sources In these studies lineal feet measurements of all window and door edges are neces sary Considerations must be given to the ty
33. ed or damaged gt Clogged or damaged exhaust outlet 2 Unit lights but goes out prematurely Vented to space gt Unit not straight Inadequate radiation gt Gas pressure low 28 gt Lack of adequate ventilation Correct ventilation volume CFM Clean Replace gt gt 1 c c n n Correct vent rate GLOSSARY ANNUAL DEGREE DAYS The total number of outdoor degrees F below the indoor design temperature 65 Using the average de viation for each day over a 365 day period ANSI American National Standards Institute ASHRAE American Society of Heating Refrigeration and Air Conditioning Engineers BLACK BODY Matter which absorbs all the infrared energies impinged upon it BTU British Thermal Unit The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit BTU FT British thermal unit per square foot BTU FT British thermal unit per cubic foot BTUH British thermal unit per hour BUTANE Fuel gas that 1s a derivative of oil cracking process COMBUSTION Rapid oxidation of fuel when mixed with oxygen and ignited CONDUCTION Heat being transmitted by physical contact CONVECTION Transference of heat by moving masses of mat ter as by currents in gases or liquids caused by differences in density and the action of gravity DELTA T AT Temperature difference DENSITY Mass per specific unit volume DRAFT HOOD Device used to balance combusti
34. ers considerations are given to the practicality of aeration of the pilot and burner Primary air is air that is introduced with the gas directly downstream from the ori fice The gas jet entrains air as it moves from the orifice into the burner chamber A venturi design within the burner creates a vacuum which causes air to be sucked into the burner along with the gas providing the gas air mix that is necessary for proper ignition and combustion Secondary air is air that is introduced into the flame after the burner ports Fig 5 is an illustration of a Bunsen Burner showing both primary and secondary air Note that there are two distinct flame patterns PILOTS In many gas fired heating appliances ignition of the main burner is accomplished through the use of a pilot burner whose flame is located adjacent to the main burner Pilots generally burn far less gas than the individual burners they are required to ignite This 4 Outer Mantle Incandescent Products of Complete Combustion Outer Cone Complete Combustion of Intermediate Products Secondary gt Air _ gt Inner Cone Zone of Partial Combustion Unburned Mixture of Gas and Primary Air Burner Port Burner Body Primary Air Shutter Primary Air Opening Gas Orifice Orifice Spud Gas Supply FIG 5 Bunsen burner eliminates the hazard of large accumulations of gas air mix while in the initial trials for pilot ignition Pilots are usually
35. esses GAS CONNECTIONS Flexible gas connections at the unit are recommended providing local codes do not prevent this practice Use a C S A certified stainless steel connector with a maximum length of 24 and mini mum size of 2 O D Be aware of gas pressure drop through the connector Gas lines should never be routed in full view of the radiation pattern nor should they be located directly above the infrared units All manufacturers supply gas pipe sizing informa tion for all gases Use this information so as not to undersize supply piping Undersized piping will result in total dissatisfaction and system condemnation even when unit sizing and placement is correct in every detail TROUBLESHOOTING The following troubleshooting information covers some ofthe application and startup related problems that may arise Consult manufacturer s literature for specific information HIGH INTENSITY UNITS PROBLEM CAUSE CORRECTION 1 Darkened radiating surface Adjust pressure gt Dirt or dust accumulation inside burner Clean with air nozzle 2 Black spot on radiating surface gt Broken ceramic or part missing Replace ceramic 3 Unit ignites but extinguishes after short run 5 Spark or pilot on no ignition or delayed ignition il flame around ceramic burner head 6 Burner roars no glow gt Cracked or missing ceramic LOW INTENSITY UNITS PROBLEM CAUSE 1 Tube glows gt Gas pressure too high gt Combustion air inlet clogg
36. ext other provisions for combustion air are available for infrared units High intensity infrared units generally are unvented This means the products of combustion are released into the space in which they are installed For this reason ventila tion of the space is necessary to carry these products from the building Since these gases are initially hot they rise by convec tion to the top of the building They will stratify at this point unless they are free to escape from the building If these gases remain in this zone they most likely will condense when they come in contact with the cold roof or cold roof supports Such condensa tion and resultant dripping is generally intolerable Therefore it is necessary to provide an escape route for these gases Fig 44 illus trates how such ventilation can be provided Either gravity or power may be enlisted to assure adequate ventilation High intensity unvented infrared units require approximately 4 to 6 CFM of ventilation Check manufacturer s specifications for each 1000 BTUH of installed heaters Low intensity infrared units because of the power draft may be aerated directly from the outside of the building and conversely may be vented back to the outside However they may also receive their air from the space in which they are installed Also venting into the space is permissible providing adequate ventilation is provided to the building The ventilation rate for these units is 4 t
37. f 5 feet to 7 feet will be re quired beneath low intensity units Screened gt Opening Do not attempt to install infrared units without first determining these clearances Each unit is unique and will have its own require ments Be certain you know what they are before proceeding with an application SPECIAL WARNING Very often when NON combustible ceilings are involved the specifier or contractor will plan on installing ex tremely close to this surface possibly for headroom considerations There is no problem in doing this except when the noncombustible material has electrical wiring or other heat sensitive equipment or devices imbedded within High intensity infrared units will exhaust very hot flue gases that can heat the noncombustible surface By conduction these high temperatures may reach the wiring con duits or other devices in the area causing melting and other related failures If you discover these conditions exist be sure to observe the manufacturer s TOP clearance requirements Vent Gravity or Power Preferably at Highest Point Vent ABOVE Units Grilled Opening Fresh Air Openings BELOW Units FIG 44 Ventilation system TEMPERATURE CONTROL Unlike most heating equipment infrared heaters are often con trolled using a manual switch This is particularly true when spot heating The reason should be obvious In spot heating an at tempt is made to provide warmth for a confined space withi
38. f cities throughout the USA and Canada along with their winter outdoor design temperatures Annual de gree day information that can be used to estimate fuel consump tion is also shown for each city Such data is also available from the nearest US weather station or from ASHRAE The indoor temperature is a matter of choice or possibly is depen dent upon the use of the building As mentioned earlier some warehouses are unheated Others are maintained at a temperature just above freezing for the protection of materials or equipment stored within However for comfort conditions most building own ers or users currently observe an indoor design temperature of 68 F which offers adequate heating while providing the most eco nomical fuel costs By subtracting the outdoor temperature from the indoor temperature we obtain the AT temperature difference to be used in the heat loss determinations SURFACE LOSSES By convection and radiation The outside surface of all buildings will lose the heat stored inside The construction of the building dictates at what rate this will occur All building materials have a certain resistance to the flow of heat For computing heat losses the heat flow rate through the outer shell must be known Heat flow rates are expressed in several ways A K factor is the flow of heat expressed in BTUH through one square foot of a specific material that is 12 inches thick and is based on a temperature differenc
39. hat a compromise height has been determined due to interference with other equipment Also we have set up 6 locations based on 30 angle position of the reflec tors and two locations using horizontal reflector positions Our mounting height is 11 feet The low intensity tubular units may also be installed with the re flectors in the horizontal position However they must be located further from the wall when doing this The following chart gives these recommended distances depending on mounting height and unit input HL DISTANCE TO THE WALL FT Horizontal Reflector Oo oB oe 23 25 27 28 i SS SS SS Se ae 280 indicates height not compatible with unit size Some tubular infrared units have optional shields that allow for closer to wall placement of units with horizontal reflectors Con sult manufacturer s information Fig 41 shows a layout of eight 75 000 BTUH tubular units with the reflectors in the horizontal position The mounting height is 13 feet By changing to this strategy the centerline distance is re duced which will tend to lessen any voids that may have existed between units In either case of high or low intensity the coverage may be im proved using horizontal deflection when the unit numbers are inadequate to provide full perimeter coverage Of course by using horizontal deflection the wall dimensions are theoretically com presse
40. he line of sight intensities to provide a small amount of heat to this area As an alternate we may elect to use more heaters for a shorter CLD A better solution however is to close the CLD by changing units to HORIZONTAL POSITION This necessitates moving further from the wall By referring to the following chart the recommended distance between heater and wall is 18 when the unit is installed at 14 feet high SUGGESTED LONG HORIZONTAL AXIS DISTANCE MOUNTING HEIGHT FT FROM WALL Fig 38 illustrates how the layout would appear Note that on the 200 walls there will be no intensity voids The 150 walls however will have voids of foot which we could plan on allowing the line of sight intensities to cover Therefore there are three choices of installation They are as fol lows 1 18 units 30 tilt with 8 9 feet of void between units Since the number of units matches the heat load we may elect to rely on the line of sight intensities to fill the voids Mounting height is 15 feet 2 24 units 30 tilt with no voids This would require 6 additional units which would represent a 33 increase in input beyond the calculated heat loss Mounting height is 15 feet 3 20 units HORIZONTAL installation This represents a 11 increase in capacity over the calculated heat loss 2 additional units Mounting height is 14 feet If all three systems are acceptable insofar as their locations are concerned it
41. he most popular gaseous fuels HEAT CONTENT SPECIFIC FUEL BTU FT GRAVITY Natural gas 1020 BTU 65 Propane gas 2550 BTU 1 52 Butane gas 3200 BTU 1 95 The specific gravity is the weight of the gas as compared to air Specific gravity of air 1 Therefore you will note that the LP gases are heavier than air and that Natural gas is lighter than air This is important to know because should the gas inadvertently escape during service installation or the remote possibility of control failure knowledge of the fuel characteristics is helpful in determining suitable purging to clear the space of potential explo sive conditions Specific gravity is also important along with BTU content and gas supply pressure to properly size the main burner orifices The manufacturer will publish correct orifice sizes for each unit in a service manual making it unnecessary to do these calculations in the field Further to this each gas fired appliance has the proper gas orifice when it leaves the factory providing that correct gas characteristics have been supplied to the manufacturer by the purchaser COMBUSTION Combustion by definition is the rapid oxidation of solids gases or liquids It is therefore safe to assume that combustion cannot take place without the presence of oxygen In the following text we will deal with the controlled use of air oxygen for proper combustion of gaseous fuels Such control is accomplished in the design of the
42. heory 9 Liquified Petroleum LP 2 British Thermal Unit BTU 3 Natural Gas History MR os 2 Building Heat Loss NES o com 4 6 Pilot Burner Aeration 5 Clearances from Combustibles 27 Pim y 4 OmU DOT usu dst 3 Radiant Heathi saisit dotem taped ird dans 7 Products of Combustion sss S ENTER MOTOR 2 2 Secondary Ait rasis a TUR slide dis 4 Conduction Heat LOSS ZU SpotHeat Sample ausser cu aperti n ater HERE 13 2 SpotHeating with High Intensity Infrared 10 Design Temperature 16 Spot Heating with Low Intensity Infrared 15 Ibidem 6 tertie e Olde 17 9 Suspension Methods ssiccessscessisassesiercsadeccdeessecasssioies 26 19 Technical Words and Phrases for Radiant Heating 8 Explosive 4 Temperature CODIEOL 28 FEES 3 Thermodynamic Radiation Theory 9 PUEIS wr EN buie nitus 28 Full Building Heating 16 LU PACTS ee rA aeS 18 Applications for Infrared Heaters sss 21 Unit Location SU ROO 25 acciri b aracic bbea vd aio issues 25 High Intensity Applications eee 22 ME MEO 19
43. ich fasten directly to the emission tube These reflectors may be rotated be tween 0 and 45 in order to direct the rays as needed Remember if you are supplying heat to people the best way to do this is with rays directed from a 30 angle in order to strike the subject on the side rather than the top Also for a complete spot heating applica tion you should direct the rays against at least two sides or front and back of the person s within the target range of the units Fig 32 illustrates how low intensity tubular infrared units may be used to supply spot heating for the 8 x 30 work area There are several details that should be noted BURNER 5 0p 25 85 ee Fig 32 1 Mounting height is 13 Based on our earlier selection of two 30 000 BTUH units per side select one 75 000 BTUH tubular unit per side 2 Reflectors are positioned at 30 facing target 3 Centerline distance between units is 12 and is obtained from Fig 26 4 Burners are located at opposite ends Actual intensity patterns show greater BTU production at the burner end of the unit By locating as shown a better intensity balance will be obtained 5 Unit length is 30 FULL BUILDING HEATING WITH INFRARED All types of commercial and industrial buildings may be heated very successfully with infrared units Placement number and size of the units are extremely important to guarantee a good applica tion We will be discus
44. ke certain the tubing is STRAIGHT AND LEVEL Fig 43 is a typical manufacturer s sketch showing the correct and incorrect implementation of the turnbuckle It also shows a variety of chain supports that may be considered Tubular infrared units will expand lengthen when they are heated and will contract when they are cooled For this reason chain sup ports as illustrated in Fig 43 are recommended Also due to ex pansion and contraction special arrangements and hardware are suggested by the manufacturer for inlet air electrical supply and gas connection This is a very important facet of installation and should be completed based on total adherence to the manufacturer s instructions When installing either a high and low intensity infrared unit refer to the manufacturer s installation data for specific information re garding suspension techniques and requirements AERATION As pointed out earlier the combustion process requires air In most buildings air for combustion is available from the infiltration How ever ANSI American National Standards Institute establishes a minimum building volume as follows 50 FT of building volume is required for each 1000 BTUH of total heat capacity When a building s volume is less than this ratio provisions must be made to introduce air for combustion Instructions to this effect are found in the manufacturer s installation brochure Fortunately as you will see in the following t
45. le air is available to support complete burning of the mix In order to control the quantities of air entering the combustion zone care is taken in the appliance design to meter proper amounts of air for clean and efficient combustion This fur ther emphasizes the fact that alterations of the unit in any way could at minimum adversely affect the total efficiency of the unit or at worst could create extremely hazardous conditions INDUCED DRAFT AERATION In order to more closely control primary and secondary air and to also provide more flexibility in the combustion air introduction and venting of gas fired appliances a trend of design over the past several years has been to do this through the use of power induc ers blowers or impellers This method of aeration has been instru mental in providing units with extremely high efficiencies The bulk of the improvements occur in the vent process where much smaller quantities of room air are required to support the combustion and venting processes Venting will be covered later in this section With INDUCED DRAFT an electrically powered exhauster is lo cated at the discharge of the unit and is used to draw off the products of combustion under controlled metering As the prod ucts of combustion are drawn off a void is established in the combustion zone which entices more air to enter the system Fig 8 Powered Exhauster Heat Exchanger Combustion Zone Burners Combus
46. less tonework Varnish Glossy Water Wood planed oak 0 IVITY 93 REFLECTIVENES S 093 007 09 01 0 0 1 096 00 08 02 e 093 00 066 034 09 0 is used in formulating not only the emission rates but also the ability of a surface to absorb radiated heat As the emissivity of a material decreases from 1 the reflecting quality of the same mate rial increases For instance if a material has an emissivity of 9 it will reflect 10 of the infrared energies impinging upon it No material has an emissivity greater than 1 If a material with an emissivity of 8 has been found to radiate 25 000 BTUH then that same material contains heat in the amount of 31 250 BTUH Conversely if the same material is impinged upon by 31 250 BTUH it will absorb 80 of this quantity or 25 000 BTUH 20 6250 BTUH will reflect bounce away from the material Following is a list of various materials and their approximate emis sivity value In general a rough surface with no sheen whatsoever will have a comparably high emissivity rate while a smooth sur face that is highly polished will have a relatively low emissivity rate Both emissivity and reflectiveness are shown for each mate rial STEFAN BOLTZMAN Stefan Boltzman suggested that the total radiation from a heated body is proportional to the 4th power of its absolute temperature Ludwig Boltzman furthered this theory through ther
47. lothing you should also consider the normal position of the person If the subject is standing the infrared heat should be directed at a point three feet above the floor See Figure 25 If the subject is seated use a point two feet above the floor For our example we are using a 13 3 mounting height from the floor with the heater at a 30 angle INFRARED UNIT AT 30 ANGULAR MOUNTING REGRESS HEIGHT FT From the target level 123 45 6 7 8 91011 12 13 14 15 16 DISTANCE FROM TARGET FT FIG 26 With the mounting height determined refer to Figure 26 to deter mine the distance horizontally that the unit must be located from the subject From the 1074 ft height line left column move right until you intersect the sloped 0 line From this point drop verti cally down to the horizontal dimension line You should read ap proximately 6 feet This dimension when doubled gives you cen ter to center distance 12 ft between the two infrared units and they will be located as illustrated in Fig 27 13 1 4 FT FIG 27 End view two unit application If you wish to guarantee coverage for all four sides of the subject and have elected to use four units rather than two refer to Fig 28 for a plan view ofthe four unit layout Remember the same height of 13 1 4 feet is used with either 2 or 4 units TARGET MOUNTING HEIGHT REMAINS AT 13 1 4 FEET Floor to Radiant Surface FIG 28 Plan View four unit a
48. lows R10 70x 10 000 x 1 70 000 BTUH loss R19 70x 10 000 x 0526 36 820 BTUH loss U WALL CONSTRUCTION FACTOR 1 Wood frame 4 thick with wood siding 5 sheathing and 5 Gypsum wallboard 1 A Above with 3 5 R 11 Blanket insulation 2 Common brick 8 4 double row 2 A Above with 5 R 1 1 Gypsum wallboard 3 Concrete block cinder aggregate 8 3 A Above with face brick 4 3 B Above with 5 Gypsum wallboard 3 C Above with face brick 4 and 5 Gypsum wallboard 4 Concrete block stone aggregate 8 4 A Above with face brick 4 4 B Above with face brick 8 4 C Above with face brick 4 and 5 Gypsum wallboard 4 D Above with face brick 8 and 5 Gypsum 0 16 wallboard 5 Steel sheet over sheathing hollow baked 0 69 5 A Steel sheet w 375 insulating board 5 B Steel sheet w 375 insulating board w foil back 5 B Steel sheet w 1 expanded polystyrene 5 D Steel sheet w 3 mineral fiber blanket insulation 6 Poured concrete 6 A Lightweight aggregates 120 Ib cu ft 4 thick 6 B Lightweight aggregates 80 Ib ft 4 thick 6 C Lightweight aggregates 40 Ib cu ft 4 thick 6 D Gypsum fiber concrete 87 5 Gypsum 12 596 0 42 wood chips 4 ER WINDOW CONSTRUCTION FACTOR 1 Vertical in walls 1 A Single glass with wood sash 0 99 1 B Single glass with metal sash 1 C Double insulated glass with wood sash 1 D Double insulated glass with metal sash 2 Horizontal skylights a 2 A Single glass with wood sash 2 B
49. me that 24 top clearance is required for high intensity units and 12 top clearance for low intensity units We know from this that the maximum mounting height for high intensity units will be 18 and will be 19 for low intensity units This dimension is measured from the floor to the top of the unit Remember our ex ample building has 700 lineal Ft of wall With this as a beginning we can now commence to analyze for our equipment selections Most high intensity infrared units are available in sizes of 30 000 BTUH input to 160 000 BTUH input with three or four sizes in between Low intensity units are generally available in sizes of 50 000 BTUH input up to 200 000 BTUH input with four or five sizes in between You should determine exactly what sizes are avail able from the manufacturer For our example let s see how many of the largest and smallest units we might need We can also determine what initial centerline distance CLD between units might be needed 24 HIGH INTENSITY 546 948 30 000 I8UNITS 700 18 389FtCLD 546 948 100 000 6UNITS 700 6 116 6FtCLD 546 948 150 000 4UNITS 700 4 175 0FtCLD LOW INTENSITY 546 948 50 000 IIUNITS 700 11 63 6FtCLD 546 948 75 000 8UNITS 700 8 875FtCLD 546 948 150 000 4UNITS 700 4 I75FtCLD 546 948 200 000 3UNITS 700 3 2333FtCLD HIGH INTENSITY APPLICATION Of the above unit types the 30 000 BTUH high intensity infrared units has th
50. modynamic reasoning Thus the following formula may be reliably adapted e bb Where e bb emissive power of a black body Stefan Boltzman constant 172 10 00000000172 T Absolute temperature R F 460 Example Determine the emission rate btu ft h of a black body having an area of square foot and at a temperature of 1600 F e bb KT e bb 00000000172x 1600 460 e bb 30 974 btub fe Using the Stefan Boltzman constant and adding the emissivity value of a material the following can be used KT xE emissive power e Where e emissivity value 96 ofthe Tl T2 D2 DI material Ifthe material in the example above had an emissivity of 8 then e would be 30 974 x 8 or 24 779 btu ft hr SPOT HEATING WITH HIGH INTENSITY INFRARED When a high intensity infrared has reached peak temperature the surface glows brightly since the material has reached a temperature of approximately 1650 to 1850 F A close observation of this appli 102 20 T2 10 102 400 T 100 ance indicates that the intensity 1s so great near the surface that it is impractical or even dangerous to expose objects or materials at close distance It is when you draw away from this surface that more acceptable levels of radiation are found The intensity dimin ishes as the inverse square of the distance and can be calculated using the following formula Where TI Known BTUH FT intensi
51. n an unheated area Consequently any temperature sensing thermo stat that would be located in the spot heating area will be not only subject to heat requirements in that area but will be influenced by the lower temperature of the surrounding space This situation becomes untenable Therefore the worker in the space is best suited to determine when heat is needed and when it is not and should be permitted to control on off of units from a manual switch located at his work station With full building heating thermostats are certainly acceptable as means of controlling the building temperature However here are a few rules that should be observed when controlling in this manner 1 When locating the thermostat on an outside wall you must provide an insulating board on which to mount the thermostat and also be sure to provide an air gap between the board and the outside wall 2 Avoid installing the thermostat where line of sight intensities exist 3 Ifline of sight intensity cannot be avoided provide radiational shields reflectors for the thermostat 4 Control no more than 4 or 5 units from one thermostat Electri cal load may be a limiting factor so check the manufacturer s literature for multiple unit wiring 5 Do not install thermostat in front of doors where they may be affected by incoming cold winds or drafts 6 Avoidlocating thermostat where it may sense heat that is being generated by machinery or other proc
52. n applying infrared However the infra red pattern extends beyond these boundaries by simple line of sight considerations If you can see the glowing surface then there will be energies however small radiated to the point of sight ing Fig 23 depicts the typical line of sight pattern for both long and short axis Intensities are small but nevertheless do exist Keep this in mind when selecting a room thermostat location LINE OF SIGHT PATTERN MANUFACTURER S RECOMMENDED PATTERN LONG AXIS LINE OF SIGHT PATTERN LINE OF SIGHT PATTERN MANUFACTURER S RECOMMENDED PATTERN SHOR FIG 23 T AXIS 12 SPOT HEAT SAMPLE Remember spot heating is most often used for people comfort in buildings which have either partial or no heating Many warehouses fall into this category because very often warehouses are unheated or only partially heated to guard against freezing of product or sprinkler systems We will use such a building for our example The spot heating requirement stems from the fact that a worker en gaged in packaging of product in preparation for shipment is lo cated in a small section of the warehouse Here is the pertinent design criteria Building esas Medium sized warehouse Surrounding temperature sssrin irin iinis 35 F Work area ane an KEE a 8 ftx 8 ft People isses ee ndn eis One Standing Clothing antes HR RR RETE RES Heavy ceina acar din ale Light bench work Availa
53. nual degree days EFF Efficiency of heating equipment AT Temperature difference at design 70 F For this example we will use 9096 heater efficiency Therefore 70 000 x24 x6 000 160 000 000 BTU 90 x70 and R19 36 820 24 6 00 _ 160 000 BTU 90 x 70 To determine the fuel costs divide the annual BTU used by BTU per unit of fuel 1 000 000 BTU 1 unit of natural gas 160 000 000 1 000 000 160 units 84 160 000 1 000 000 84 16 units If the cost per unit is 8 37 then multiply the units by this value 160 8 37 1 339 20 forR10 84 16x 8 37 704 42 forR19 DIFFERENCE 634 78 At this point a decision on which insulation to use will be made based on insulation cost difference vs fuel cost during years of amortization SURFACE AREA The best way to develop surface area for an entire building is to first list all of the various construction types found in the shell of the building This would include Wall construction There may be several different types of con struction employed so be sure to list them all Type of glass List each type separately Ceiling or roof construction Doors List each size or type separately Basement or slab Next for each of the various surfaces or edges measure carefully so that accurate areas or lineal dimensions can be developed Be sure to deduct windows and door areas from the wall surface Next review Fig 34 and find the proper U factor for
54. o 26 a i Wall Mount I Beam Mount Wall Mount Wall Mount FIG 42 Methods of mounting infrared heaters on walls and other vertical surfaces ALL TUBE HANGING CHAINS MUST BE PLUMB AND VERTICAL IN ALL DIRECTIONS WHEN INITIALLY INSTALLED OVERALL EXPANSION 2 4 IN 60 0 FIG 43 Typical support installation tubular low intensity infrared heater 6 CFM per 1000 BTUH input of natural gas and 5 to 7 CFM per 1000 BTUH input of propane gas For the most part these units are unique due to their power system which makes them most attrac tive for using closed circuit ventilation The combustion air inlet and exhaust outlet are connected directly to the out of doors In all cases however consult the manufacturer s installation manual for recommended aeration volume CLEARANCES FROM COMBUSTIBLES In previous text we discussed required clearances above these units There are other clearances that also must be observed Each unit regardless of design has a hazard potential from high heat High intensity units may reach temperatures of 1850 F while low intensity units may reach temperatures in excess of 1000 F For these reasons clearances from combustibles are necessary on all sides top and particularly beneath these devices For instance many of the high intensity units require from 6 to 15 feet clearance between the radiating source and any combustibles that may be located beneath the unit Distances o
55. of a material having a specific thickness and fur ther is based on a 15 MPH wind effect on the cold side The values are scientific expressions that advise the anticipated loss when there is a temperature difference AT between the two sides amount ing to 1 F All U factors are given for not only individual materi als but for specific wall and roof construction which may or may not include insulation Therefore the U factor provides the cor rect heat flow information for computing heat loss Fig 34 is a list of construction configurations with the U factors shown in the right hand column For materials not listed here you may have to refer to the ASHRAE guide or other sources FIG 34 U Factors The R Factor The factor discussed above can be converted to U value by simply dividing R number into 1 Example 19 1 19 05 BTUH FT F However since insulation is never singularly used in construction you should only use this information to make comparisons between insulations for the purpose of studying fuel consumption For instance let s assume that a ceiling having a surface area of 10 000 FT is under study to choose the most cost effective insulation R10 and R19 are being considered First con vert the R factors to BTUH FT R10 1 10 1 BTUH FT R19 1 19 2 0526 BTUH FT With a AT of 70 F indoor 70 F outdoor 0 F calculate the BTUH loss for each as fol
56. on over a com bustion zone and stabilize unit efficiency in the face of varying vent conditions ELECTROMAGNETIC WAVE An electrical impulse that trans mits radio signals infrared visible light and other such energies EMISSIVITY The power ofa matter to emit heat EXHAUST GASES Products of combustion FLUX DENSITY A measure of infrared intensity at a given dis tance from the infrared source FORCED DRAFT Furnishing burner aeration by pushing air into the combustion zone under power 29 INDUCED DRAFT Evacuating a combustion zone under power thereby causing fresh air to enter the combustion zone INFILTRATION Air that enters a building indiscriminately through cracks in the building shell K FACTOR A measure of the amount of heat BTU FT that passes through one square foot of material that is 12 thick in one hour with one degree Fahrenheit difference between the two sides LONG AXIS Imaginary center of infrared source running the length of the infrared radiating surface METHANE A colorless odorless gas that constitutes the major portion of all fuel gases NATURAL GAS Fuel gas containing methane and other elements PRIMARY AIR Air introduced with the gas before the flame PROPANE A fuel gas that is derived from the petroleum cracking process R FACTOR A measure of the resistance to the flow of heat The greater the factor number the higher the resistance RADIATION The flow of heat transmitted
57. ontal deflection is certainly acceptable but very often due to the distances from the wall there are various interfer ences to contend with that may prohibit their location in these zones Always suspend units within the mounting height recommen dations suggested by the manufacturer Carefully select unit size based on available mounting height and if available manufacturer s intensity pattern information Never install infrared units where combustibles might be stacked within the required fire hazard clearance dimensions Be sure that the long axis is parallel to the nearest wall 10 Be careful that the infrared unit is not put into a position to activate fire alarms or sprinkler systems MOUNTING HEIGHT 13 FEET FIG 41 Sample layout of eight 75 000 BTUH tubular infrared heaters horizontal position 25 SUSPENSION METHODS High intensity infrared units are installed in a myriad of ways Pipes rods chains and various support mechanisms are used Figure 42 illustrates a few methods that have been used to suspend high intensity units The important consideration is that the unit be at its prescribed attitude That is when horizontal a level unit is the most effective When at a 30 angle care should be taken to assure the angle is accurate otherwise the planning and location will have been wasted Low intensity units are generally suspended with combination chains and turnbuckles The turnbuckle is used to ma
58. pe of joints used in the construction of the building and to potential wind velocities and prevailing wind directions Later you will find that certain amounts of ventilation are required in order to support combustion in the heating equipment selected Many times the infiltration rate will more than exceed these re quirements ANSI requires a minimum of 50 FT of building vol ume for each 1 000 BTUH of firing rate regardless of infiltration rate If volume is less than this amount some means of introduc ing fresh air for the combustion process will be necessary This will be covered later page 27 If you elect to use the air change method then simply multiply the building volume FT x 018 x DT This will give the BTUH loss for one air change of infiltration If you elect to use other than one air change or if you elect to use the ASHRAE method you must make this adjustment before completing above calculation See example heat loss study for air change The infiltration loss will be added to the total radiational losses determined earlier EXHAUSTS AND VENTILATION Many industrial and commercial buildings are equipped with ex hausters to get rid of unwanted contaminants Also many of these buildings require ventilation Both exhaust and ventilation are sup plied under power to assure that the volume is as prescribed Flow rates are expressed in CFM Cubic feet per minute If the building you are evaluating for heat loss
59. permits the de signer to reduce the size of the heat exchanger Such miniaturiza tion of the heat exchanger allows for small diameter piping that can reach up to 60 feet in length covering a much larger area of radia tion and at the same time using a minimum amount of space in the building FIG 17 Two types of low intensity tube type infrared heaters Some LOW INTENSITY infrared units may be operated with in duced draft rather than forced draft The products of combustion are drawn off using powered exhaust The results are much the same However as is the case with most induced draft systems high temperatures found in the flue gas present design problems which very often add cost to the unit TECHNICAL WORDS AND PHRASES Because some of the words and phrases associated with infrared may be new to you this section will define those that you should be familiar with Here are a few that will be covered BLACK BODY WAVE LENGTH and EMISSIVITY BLACK BODY A BLACK BODY is any material which theoretically can absorb all the thermal radiation impinging upon it reflecting none of these energies Please remember a BLACK BODY is not necessarily black Ifa list of BLACK BODIES could be generated among those materials nearing such characteristic could be a whitewashed wall While the color is far from black this material absorbs infrared energies at very near the black body rate There are other materials that may be near black bo
60. pplication LARGER WORK AREA If we find that the work area in our example is larger and accommo dates more workers we must first determine the coverage area Let s assume that we will have 3 workers doing the same work and that the area will be expanded from 8 x8 to 8 x30 Now we must plan on at least two units on each side of the work ers Also we must be careful not to create too much intensity by overlapping the focus of the two units Remember our original determinations required 30 BTUH FT2 intensity at a recommended minimum of 10 feet We are using 1073 plus 3 for standing work ers or a mounting height of 1373 Figuring that the coverage measured at 3 above the floor is ap proximately twice the mounting height Figure 29 illustrates two heaters with a centerline distance of 20 feet Since the coverage overlaps the average of the total BTU s radiated will increase al lowing for a slightly higher mounting height to achieve the same comfort level By referring back to Figure 26 you will note also that if the mounting height changes the distance from the target will also change See Figure 30 for an example of a plan view using the four units FIG 29 TARGETS WORKERS MOUNTING HEIGHT 13 10 5 8 FLOOR TO RADIANT SURFACE FIG 30 4 Unit 2 Bank Application SPOT HEATING WITH LOW INTENSITY INFRARED While spot heating with low intensity tube type infrared units is feasible you will fin
61. r fuel source for many years to come LIQUEFIED PETROLEUM GASES One of the by products of oil refining is LP gas This fuel is ex tracted during the cracking process It is then pressurized until it becomes a liquid It is in this liquid form that LP gases are trans ported to the end user The most common of these liquid gases is propane although butane is sometimes available and is restricted for use in warmer climates When the storage vessel or tank is tapped the gas vapor over the liquid is released for use in the gas burning process The pressure within the vessel maintains most of the gas in liquid form but as the vapors are drawn off the liquid will boil and generate more gas Therefore the demand rate determines the size of the storage vessel that will be needed for each application BTU BRITISH THERMAL UNIT A British Thermal Unit BTU is defined as the amount of heat required to raise one pound of water one degree Fahrenheit Here are a few expressions that refer to BTU s and will be found in the following text BTUH British Thermal Unit per Hour BTU FT British Thermal Unit per cubic foot BTUH FT British Thermal Unit per hour per square foot BTUH FT F British Thermal Unit per hour per square foot per degree Fahrenheit GAS CHARACTERISTICS In order to properly size gas piping and orifices the characteris tics of the gas in use must be known Here then is the pertinent data as it relates to t
62. sing these considerations in the following text When heating with infrared bear in mind that floors slabs and stationary objects will be heated and that they in turn will radiate conduct and convect their accumulated heat to the space So it is important that the infrared rays are wisely directed and that they are not wasted on walls particularly outside walls or windows Placement angle of installation and intensity patterns will be very important in making sure that the heat is put to its very best use 16 Another noteworthy facet of infrared full building heating is start up It must be recognized that by heating the floor slab and other stationary objects time must be given to generate this buildup particularly from a cold start If start up heating is initi ated during the winter months it may require one or two full days of heating with infrared before such a buildup heat sink is ob tained However once the heat sink has been established com fortable conditions should prevail throughout the remainder of the heating season with normal cycling of the heating equipment The heat sink infrared method is best appreciated in buildings where doors are opened frequently or in buildings that due to their construction permit high levels of infiltration leaks of outside air into the space to occur Other buildings that come to mind are those that have walls with high rates of heat loss such as uninsulated steel buildings In
63. so through convection Natural gas while originally used for lighting eventually was put to use providing comfort heating The earliest heating device was in fact a reflector heater quite similar to the one illustrated in Fig 13 The gas was encouraged to burn with a yellow flame The re FIG 14 An early clay type radiant heater flection from this flame was then directed into the space through the use of a highly polished irregular faced metal reflector As in most technical development better ways to broadcast heat were continually sought The reflector gave way to a more sophis ticated surface which was constructed of hardened clay The burner was positioned to heat the clay to an orange glow creating a more intense source of heat This was the early beginnings of infrared radiational heating Fig 14 represents just one of these units and illustrates the ornamental design employed for period esthetics Vent Pipe Radiating Fins FIG 15 Most of these units were unvented and this eventually obsoleted such designs In the days they were in use the techniques in home building were such that great quantities of infiltration leaks of outside air into the building permitted operation of these units without vents As building designs improved to reduce infiltra tion the need for venting increased So too did the design of the units change Fig 15 illustrates a LOW INTENSITY radiant heater that was put into wide
64. tion Air FIG 8 Induced draft system FORCED DRAFT works in much the same way except the powered device usually a blower or impeller is located at the entrance to the combustion zone and under metered conditions supplies air to the pilot burner Fig 9 This method is used widely in the design of low intensity infrared appliances and will be covered later Heat Exchanger Combustion Zone Burners Combustion Air Powered Blower FIG 9 Forced draft system In either case of INDUCED OR FORCED DRAFT the exhaust gases are under positive pressure and may be directed to the outdoors through vent pipes that are by comparison much smaller than the pipes used to vent atmospheric units Combustion Gases FIG 10 Typical draft hood DRAFT HOODS Atmospheric units rely solely on convection to vent the flue gases to the outdoors However if you would connect a vent flue pipe directly to an atmospheric unit the combustion can be at the mercy of the surrounding conditions High winds negative or positive pressures in the building and even surrounding temperatures can change the amount of air passing through the combustion zone For these reasons atmospheric units are equipped with draft hoods These devices are always supplied with atmospheric units and may be factory or field installed Fig 10 shows a typical draft hood As can be seen in the illustration room air is used to balance the amount of draft over the combus
65. tion zone Also the draft hood is designed to guard against the effects of downdrafts which are situations usually caused by unusual wind currents or wind pres sures at the outside terminus of the vent system Unfortunately room air is lost through the draft hood to the vent during normal exhausting or even when the burner is turned off Such losses must be considered in the overall efficiency of the heating appliance because the air passing through the draft hood is heated room air The induced draft system shown in Fig 8 creates a positive vent pressure that is not affected by wind or wind pressure conditions Room air is no longer lost in the venting process since the induced draft system requires no draft hood The forced draft system shown in Fig 9 enjoys the same venting advantages as the induced draft system Consequently induced draft or forced draft systems show a much more favorable total efficiency than does the atmospheric system because far less room air is used Secondary Cone Primary Air Secondary Air FIG 11 Typical horizontal burner IMPORTANTNOTE ON COMBUSTION AIR Provisions forcom bustion air must be met according to the National Fuel Gas Code ANSI Z223 1 and the manufacturer s installation instructions when the combustion air is being drawn from the indoor space Some infrared heating equipment have provisions for drawing the combustion air from outdoors Combustion air from outdoors is normally recommended
66. to circulate the air hasten ing warm up of the space CONDUCTION The transmission of heat through a conductor When two objects are in contact with each other and barring any other phenom enon the two objects should be the same temperature If they are not the heat from the hottest flows to the object that is the coolest until both objects attain the same temperature From this we might say that heat flows down hill Heat always flows toward the coolest objects While conduction is not normally used in the heating industry it does appear in the appliances that are used to supply heat For example conduction very often is used to convey heat to sensing devices within the appliance that provide such things as high heat limiting of the appliance temperature A good example of conduction is in cooking utensils where heat is applied to one side of the utensil and the surface then conducts this heat to the food inside for proper preparation A more dra matic example of conduction is found when one touches a hot surface with the bare finger The transfer of heat through conduc tion is very vivid to the individual owning the finger RADIATION The transmission of heat through rays emitting from a hot surface The best example of radiation is the sun The extreme tempera tures of the sun emits rays which travel through space and are absorbed by Earth The earth s proximity to the sun results in extreme warmth at the equator because th
67. ts ranging from poor efficiency to hazardous effluents containing dangerous amounts of carbon mon oxide On the other hand if too much air is introduced into the air gas mix total appliance efficiencies fall to unacceptable levels and there is also a potential for undesirable combustion effluents since the air gas mix may not burn totally Excessive air very often dis torts the flame causing carbon monoxide to form It can be seen then that the air in the combustion zone must be controlled at all times and this is done in the engineering design of the appliance ATMOSPHERIC AERATION The most common method of pilot burner aeration is to in some way persuade the air to enter the combustion process without the need for powered air moving devices The high velocity gas jet emitting from the orifice is capable of entraining air along with the gas and directing the mix into the burner This method of inducing air into the mix is usually enhanced by the use of a venturi as shown in Fig 7 Mixing Burner Head Tube Venturi Burner Ports Gas Orifice Mixer Face Primary Air Openings Air Shutter Secondary Air Opening FIG 7 Basic burner Secondary air is induced into the combustion zone when the hot flue gases lift as in convection upward to escape from the com bustion zone As they rise a void is generated which in turn in spires more air to enter the zone This continual action during com bustion insures that amp
68. ty DI Distance at which T1 was measured T2 New BTUH FT intensity D2 New distance For example let s assume an intensity of 102 BTUH FT has been measured beneath an infrared unit at a distance of 10 feet from the surface We know that if we measure the intensity again at a dis tance of 20 feet the BTUH FT2 will have fallen off In order to calculate the new intensity we can use the formula 10200 400 26 T2 26 BTUH As you can see the intensity recedes as you move away from the source However this does not indicate a reduction of total output What it does demonstrate is that as the distance increases the focus widens Consequently the BTU s are spread over a larger area thereby reducing the temperature at the greatest distances from the source while the original output remains constant 10 When you recognize the distance intensity relationship of infra red heat it is easier to understand the importance of the correct mounting height Because BTU intensities vary with the size sur face temperatures and infrared patterns of the heater specific mounting height versus BTU intensity can only be determined through testing of a particular model and size of heater For this reason mounting height information varies with manufacturers with the most common being a recommended minimum mounting height chart such as the one illustrated below Recommended Minimum Mounting Height Heater Position TUH Size Horizontal 30 degre
69. use in the late 1940 s and early 1950 s Note that the burner is enclosed within the shell of the heater and that the outer walls have been embellished with fins to create a much larger sur face from which radiation could be emitted Also the material and color ofthe radiant surface was dark to enhance its emitting power Emission emissivity will be covered later FIG 16 High intensity infrared heater Additionally draft hoods were put into use so the unit could be vented from the space Fig 16 illustrates a HIGH INTENSITY infrared heater which is found in today s market Such designs employ the high surface tempera ture approach of the earlier clay radiant unit but with greater uni formity of surface temperature Also the clay radiant was replaced with a ceramic material that is more acceptable to the high tempera tures and much less susceptible to breakage and erosion through flame impingement Ironically these units for the most part are unvented That is they have no provisions for attaching a flue pipe However as you will find in later text ventilation of the build ing in which they are used is of extreme importance Fig 17 shows modern LOW INTENSITY infrared units These de signs operate in much the same fashion as the unit depicted in Fig 15 however the burner is supported by a FORCED AIR DRAFT fan allowing for a more uniform temperature between 600 F and 1000 F of the radiant surface but more important
70. would appear that strategy number 3 should be se lected to guarantee solid perimeter coverage MOUNTING HEIGHT 15 FEET 7 9 4 gt gt _ gt BE gt 38 11 38 11 38 11 FIG 37 Sample layout of 18 30 000 BTUH high intensity at 30 angle 200 0 28 6 MOUNTING HEIGHT 14 FEET 28 6 FIG 38 Sample layout of 20 30 000 BTUH high intensity units installed horizontally 23 LOW INTENSITY APPLICATION Fig 39 is a sketch showing a proposed layout for size 75 000 BTUH low intensity infrared units Because of its design this unit is avail able in 20 30 40 50 60 and 70 Ft lengths For our example we have selected the 40 Ft length Note that there are voids in the patterns but that the units have been located at the points of highest loss centered in front of doors Also two units have been angled across opposite corners of the building to help reduce the voids at the perimeter The reflectors will be positioned horizontally on these two units only The determination for a mounting height for the low intensity unit is based solely on the recommendations of the manufacturer For example the 75 000 BTUH unit in Fig 39 has a recommended mini mum mounting height of 10 Ft when the reflector is positioned for a 30 angle The recommendation changes to 12 feet when the reflector is positioned horizontally For our example we will assume t

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