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Higher College Of Technology June 16Cooling loadEstimation By 2012 -Cooling load calculationsMubarak Saeed Sayah Mubarak Al Dhaheri (200129413) report for subject:Mutlaq Abdulkareem Faraj A. Bin Amro (H00004658) Refrigeration and AirAhmed Mubarak Ismaeil Hashel Al Zaabi (H00098479) Conditioning System.Abdulrahman Mohamed A. Mohamed Al Marzooqi (H00089242) -MECH N440Saqer Saleh Abdulla Hussain Alahwal Al Mesaabi (H00100246) -Dr. Kamel AdrefWaleed Qassim Ali Ahmed Al Yafaie (H00089409)
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Cooling load Estimation 20121 Contents2 Introduction .......................................................................................................................................... 3 2.1 Occasion of the report .................................................................................................................. 3 2.2 Objectives...................................................................................................................................... 3 2.3 Terminology .................................................................................................................................. 33 Space heat gain ..................................................................................................................................... 5 3.1 The method of how the heat enters the space: ........................................................................... 5 3.2 Sensible heat ................................................................................................................................. 5 3.3 The factors involve the sensible heat load: .................................................................................. 6 3.4 Latent Heat Loads ......................................................................................................................... 6 3.4.1 The factors involve the sensible heat load: .......................................................................... 6 3.5 Space heat gain and cooling load (heat storage effect)................................................................ 6 3.6 Space cooling and cooling load (Coil)............................................................................................ 8 3.7 Components of cooling load ......................................................................................................... 84 CLTD/SCL/CLF METHOD OF LOAD CALCULATION ................................................................................. 9 4.1 External Cooling Load ................................................................................................................. 10 4.1.1 Roof ..................................................................................................................................... 10 4.1.2 Walls.................................................................................................................................... 13 4.1.3 Solar load through glass ...................................................................................................... 16 4.1.4 Partition, ceilings and floors ............................................................................................... 18 4.2 Internal Cooling Loads ................................................................................................................ 19 4.2.1 People ................................................................................................................................. 19 4.2.2 Lights ................................................................................................................................... 21 4.2.3 Appliances ........................................................................................................................... 22 4.2.4 Infiltration Air ...................................................................................................................... 235 References .......................................................................................................................................... 24 2 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20122 Introduction2.1 Occasion of the reportTo complete the requirements of the course refrigeration and air conditioning system.2.2 Objectives To calculate the cooling load needed to remove the amount of heat energy from a class roomby the HVAC equipment to maintain the room at indoor design temperature when worst caseoutdoor design temperature is being experienced.2.3 Terminology Before we go further in cooling load calculations, we need to define and understand someimportant terminology.Space: is either a volume or a site without a partition or a partitioned room or group of rooms.Room: is an enclosed or partitioned space that is usually treated as single load.Zone: is a space or group of spaces within a building with heating and/or cooling requirementssufficiently similar so that comfort conditions can be maintained throughout by a singlecontrolling device.Cooling Load Temperature Difference (CLTD): an equivalent temperature difference used forcalculating the instantaneous external cooling load across a wall or roof.Sensible Heat Gain: is the energy added to the space by conduction, convection and/or radiation. 3 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012Latent Heat Gain: is the energy added to the space when moisture is added to the space by meansof vapor emitted by the occupants, generated by a process or through air infiltration from outsideor adjacent areas.Radiant Heat Gain: the rate at which heat absorbed is by the surfaces enclosing the space and theobjects within the space.Space Heat Gain: is the rate at which heat enters into and/or is generated within the conditionedspace during a given time interval.Space Cooling Load: is the rate at which energy must be removed from a space to maintain aconstant space air temperature.Space Heat Extraction Rate: the rate at which heat is removed from the conditioned space and isequal to the space cooling load if the room temperature remains constant.Temperature, Dry Bulb: is the ordinary temperature of the air.Temperature, Wet Bulb: is the temperature of the air with consisting of moisture.Temperature, Dewpoint: is the temperature to which air must be cooled in order to reachsaturation or at which the condensation of water vapor in a space begins for a given state ofhumidity and pressure.Relative humidity: describes how far the air is from saturation. It is a useful term for expressingthe amount of water vapor when discussing the amount and rate of evaporation. One way toapproach saturation, a relative humidity of 100%, is to cool the air. It is therefore useful to knowhow much the air needs to be cooled to reach saturation.Relative humidity: is a term used to describe the amount of water vapor in a mixture of air andwater vapor.Space heat gain: the amount of heat is entering the space. 4Space cooling load: the amount of energy must be removed from the space to keep temperatureand relative humidity constant. Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012Space heat extraction: the amount of the energy that is removed by the HVAC.Cooling load (coil): how much energy is removed by the cooling coil serving various spacesplus any loads external to the spaces such as duct heat gain, duct leakage, fan heat and outdoormakeup air.3 Space heat gain It’s the rate of heat gained when heat enters the space or heat generated within a space.3.1 The method of how the heat enters the space:Solar radiation through the window or any transparent surfaces.Heat conduction through walls, roof and windows of the class.Heat conduction through interior partitions, ceilings and floors.The generated heat by the occupants such as lights, appliances, equipment and processes.The loads that are results of ventilation and infiltration of outdoor air.Other miscellaneous heat gains.Table 1, shows how the heat goes into the mechanical engineering class.3.2 Sensible heat It’s about heat at which a substance absorbs. During rising the temperature of the substance,the substance doesn’t change state. Sensible heat gain is directly added to the conditioned spaceby conduction, convection, and radiation. Note that the sensible heat gain entering theconditioned space does not equal the sensible cooling load during the same time interval becauseof the stored heat in the building envelope. Only the convective heat becomes cooling loadinstantaneously. 5 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20123.3 The factors involve the sensible heat load:Heat transmitted thru floors, ceilings, walls.Occupant’s body heat.Appliance & Light heat.Solar Heat gain thru glass.Infiltration of outside air.Air introduced by Ventilation.Table 2 shows factors influencing the total of heat load.3.4 Latent Heat Loads Latent heat gain occurs when moisture is added to the space either from internal sources (e.g.vapor emitted by occupants and equipment) or from outdoor air as a result of infiltration orventilation to maintain proper indoor air quality.3.4.1 The factors involve the sensible heat load:Moisture-laden outside air form Infiltration & Ventilation.Occupant Respiration & Activities.Moisture from Equipment & Appliances.Table 3 shows factors influence the total of sensible heat load.3.5 Space heat gain and cooling load (heat storage effect) The heat that is collected from the heat sources (conduction, convection, solar radiation,lightning, people, equipment, etc...) doesn’t go directly to heating the room. However, only somepart of the heat sources that is absorbed air in the conditioned space (class), leading to a quickchange in its temperature. Most of the radiation heat especially from sun, lighting, people is firstabsorbed by the internal surfaces, which include ceiling, floor, internal walls, furniture etc. Dueto the large but finite thermal capacity of the roof, floor, walls etc., their temperature increasesslowly due to absorption of radiant heat. The radiant portion introduces a time lag and also adecrement factor depending upon the dynamic characteristics of the surfaces. Due to the time 6lag, the effect of radiation will be felt even when the source of radiation, in this case the sun isremoved. Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012Figure 1 shows differences between Space Heat Gain and Space Cooling Load.As you can see from figure (1) that shows difference between immediate heat gain and coolingload is due to heat storage affect.The relation between heat gain and cooling load and the effect of the mass of the structure (light,medium & heavy) is shown below. From figure (2) it is evident that, there is a delay in the peakheat, especially for heavy construction. Figure 2 shows actual cooling load and solar heat gain for light, medium and heavy construction. 7 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20123.6 Space cooling and cooling load (Coil) Space cooling is the rate at which heat must be removed from the spaces to maintain airtemperature at a constant value. Cooling load, on the other hand, is the rate at which energy isremoved at the cooling coil that serves one or more conditioned spaces in any central airconditioning system. It is equal to the instantaneous sum of the space cooling loads for all spacesserved by the system plus any additional load imposed on the system external to the conditionedspaces items such as fan energy, fan location, duct heat gain, duct leakage, heat extractionlighting systems and type of return air systems all affect component sizing.3.7 Components of cooling load The total class room cooling load consists of heat transferred through the class roomenvelope (walls, roof, floor, windows, doors etc.) and heat generated by occupants, equipment,and lights. The load due to heat transfer through the envelope is called as external load, while allother loads are called as internal loads. The percentage of external versus internal load varieswith class room type, site climate, and class room design. The total cooling load on any buildingconsists of both sensible as well as latent load components. The sensible load affects the dry bulbtemperature, while the latent load affects the moisture content of the conditioned space. 8 Figure 3 shows the external loads and internal loads. Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012 Class room may be classified as externally loaded and internally loaded as you can seefrom figure (3). In externally loaded class room, the cooling load on the class room is mainly dueto heat transfer between the surroundings and the internal conditioned space. Since thesurrounding conditions are highly variable in any given day, the cooling load of an externallyloaded building varies widely. In internally loaded class room, the cooling load is mainly due tointernal heat generating sources such as occupants, lights or appliances. In general the heatgeneration due to internal heat sources may remain fairly constant, and since the heat transferfrom the variable surroundings is much less compared to the internal heat sources, the coolingload of an internally loaded class room remains fairly constant. Obviously from energyefficiency and economics points of view, the system design strategy for an externally loadedclass room should be different from an internally loaded building. Hence, prior knowledge ofwhether the building is externally loaded or internally loaded is essential for effective systemdesign.4 CLTD/SCL/CLF METHOD OF LOAD CALCULATION CLTD is a theoretical temperature difference that accounts for the combined effects of insideand outside air temp difference, daily temp range, solar radiation and heat storage in theconstruction assembly/building mass. It is affected by orientation, tilt, month, day, hour, latitude,etc. CLTD factors are used for adjustment to conductive heat gains from walls, roof, floor andglass. CLF accounts for the fact that all the radiant energy that enters the conditioned space at aparticular time does not become a part of the cooling load instantly. The CLF values for varioussurfaces have been calculated as functions of solar time and orientation and are available in theform of tables in ASHRAE Handbooks. CLF factors are used for adjustment to heat gains frominternal loads such as lights, occupancy, power appliances. 9 SCL factors are used for adjustment to transmission heat gains from glass. Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20124.1 External Cooling Load4.1.1 Roof If the roof is exposed directly to the sun, it absorbs maximum heat. If there is other roomabove the air-conditioned room, then the amount of heat gained by the roof reduces. The heatgained by the partitions of the room depends upon the type of partition. Roof calculation formulais given below:Q = U * A * (CLTD)Where• Q = cooling load.• U = Coefficient of heat transfer roof or wall or glass.• A = area of roof.• CLTD = cooling load temperature difference.Since the ASHRAE tables provide hourly CLTD values for one typical set of conditions i.e.outdoor maximum temperature of 95°F with mean temperature of 85°C and daily range of 21°F,the equation is further adjusted to apply correction factors for conditions other than thementioned base case. Thus,Q Roof = U * A * CLTD Roof Corrected4.1.1.1 The typical steps to calculate the Roof load are as follows in table (4):Step 1 Determine roof construction and overall heat transfer coefficient (U) (Table A24-4, A29- 5).Step 2 Select roof no. from ASHRAE Table 31 or Text table 7-34 which is closest to matching actual roof construction.Step 3 Select CLTD Roof for time of interest, typically on an hourly basis (Table A28-32, A28-34).Step 4 Corrections: CLTD ROOF Corrected= [CLTD Roof+ (25.5 – TR) +(TM – 29.4)]Step 5 Calculate roof area (A) 10Step 6 Q Roof = U * A * CLTD Roof CorrectedTable 4 shows steps of calculating the roof load. Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20124.1.1.2 Roof View in Auto CadFigure 4 shows the Auto Cad top view. 11 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012 4.1.1.3 Roof sectionFigure 5, shows the roof sectioning of the class room. Order Section Color 1 Foresealing 2 Hungers 3 Sandwich 4 Insulation 5 Paint Figure 6 shows the coding of the sections and its order. 4.1.1.4 Results of the calculating the roof load Hour 12pm 1pm 2pm 3pm 4pm 5pm Q watt 426.6 534.6 642.6 750.6 831.6 939.6 Table 5 shows the product of the roof load through the five hours. 12 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20124.1.2 Walls The walls of the room gain heat from the sun by way of conduction. The amount of heatdepends on the wall material and its alignment with respect to sun. If the wall of the room isexposed to the west direction, it will gain maximum heat between 2 to 5 pm. The southern wallwill gain maximum heat in the mid-day between 12 to 2 pm. The heat gained by the wall facingnorth direction is the least. The heat gained by the walls in day-time gets stored in them, and it isreleased into the rooms at the night time thus causing excessive heating of the room. If the wallsof the room are insulated the amount of heat gained by them reduces drastically.The cooling load from walls is treated in a similar way as roof:Q Wall = U * A * CLTD Wall CorrectedWhere• Q Wall = Load through the walls.• U = Thermal Transmittance for walls.• A = area of walls.• CLTD = Cooling Load Temperature Difference for walls. 13 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20124.1.2.1 The typical steps to calculate the Wall load are as follows:Step1 Determine wall construction and overall heat transfer coefficient (U) Table A24-4, A29-5).Step 2 Select wall type from ASHRAE Table 33 which is closest to matching actual wall construction.Step 3 Select CLTD Wall for time of interest, typically on an hourly basis (Chapter 28 ASHRAE Table A28-32, A28-34).Step 4 Corrections: CLTD Wall Corrected= [CLTD Wall+ (25.5 – TR) +(TM – 29.4)] Where TR = indoor temperature TM = outdoor temperature =maximum outdoor temp – Daily Range/2Step 5 5- Calculate walls area. Wall area you have. exclude windows and door and count only wall area.Step 6 U * A * CLTD Wall CorrectedTable 6 shows the procedure of wall load calculations.Figure 7 shows the back view. 14 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012 4.1.2.2 Section of the wall Figure 8 shows the wall sectioning of the class room. Order Section Color 1 Paint 2 Gypsum 3 Insulation 4 Wood 5 FinishFigure 9 shows the code of the sectioning and its order. 15 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012 4.1.2.3 Results Hour 12pm 1pm 2pm 3pm 4pm 5pm Q watt 836.57 856.82 897.32 937.60 1038.56 1098.30 Table 7 shows the results of wall load. 4.1.3 Solar load through glass Solar load through glass has two components: 1) Conductive and 2) Solar Transmission The absorbed and then conductive portion of the radiation through the windows is treated like the roof & walls where CLTD values for standard glazing are tabulated in ASHARE fundamentals handbook. For solar transmission, the cooling load is calculated by the cooling load SCL factor and shading coefficient (SC).Figure 10 shows the window view of the class room. Figure 11 shows the AutoCad view of the door in the class room. 16 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012The cooling load equations for glass are:Conductive Q Glass Conductive = U * A * CLTD Glass CorrectedSolar Transmission Q Glass Solar = A * SC * SCLWhere• Q Conductive = Conductive load through the glass.• Q Solar = Solar transmission load through the glass.• U = Thermal Transmittance for glass.• A = area of glass.• CLTD = Cooling Load Temperature Difference for glass.• SC = Shading coefficient.• SCL = Solar Cooling Load Factor.4.1.3.1 Steps for conductive calculationsStep 1 For the glass types used, select from ASHRAE tables the overall heat transfer coefficient (U).Step 2 Select CLTD Glass for time of interest, typically on an hourly basis Table 34.Step 3 Corrections: CLTD Glass Corrected= [CLTD Glass+ (25.5 – TR) +(TM – 29.4)].Step 4 Calculate glass area (A).Step 5 Q Glass = U * A * CLTD Glass CorrectedTable 8 shows procedure of conductive calculations4.1.3.2 Results Hour 12pm 1pm 2pm 3pm 4pm 5pm 17 850.8036 995.0076 995.0076 1067.11 1067.1096 995.0076 Q wattTable 9 shows the results of the glaze conductive calculations. Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20124.1.3.3 Steps for solar transmission calculations:Step 1 Determine shading coefficient (SC) from, Table 11.Step 2 Determine zone type from, Table 35 B.Step 3 Determine solar cooling load factor (SCL) from, Table A28-36.Step 4 Calculate glass area (A).Step 5 Q Glass Solar = A * SC * SCLTable 10 shows the procedure of solar transmission calculations.4.1.3.4 Results Hour 12pm 1pm 2pm 3pm 4pm 5pm 1984.2 2624.4 3183.6 3966 4489.4 4546.6 Q wattTable 11 shows the product of the glazing solar calculations.4.1.4 Partition, ceilings and floorsThe various internal loads consist of sensible and latent heat transfers due to occupants, products,processes appliances and lighting. The lighting load is only sensible. The conversion of sensibleheat gain (from lighting, people, appliances, etc.) to space cooling load is affected by the thermalstorage characteristics of that space and is thus subject to appropriate cooling load factors (CLF)to account for the time lag of the cooling load caused by the building mass. The weightingfactors equation determines the CLF factors.CLF = Q cooling load / Q internal gainsNote that the latent heat gains are considered instantaneous. 18 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20124.2 Internal Cooling Loads The various internal loads consist of sensible and latent heat transfers due to occupants,products, processes appliances and lighting. The lighting load is only sensible. The conversion ofsensible heat gain (from lighting, people, appliances, etc.) to space cooling load is affected by thethermal storage characteristics of that space and is thus subject to appropriate cooling loadfactors (CLF) to account for the time lag of the cooling load caused by the building mass. Theweighting factors equation determines the CLF factors.CLF = Q cooling load / Q internal gainsNote that the latent heat gains are considered instantaneous.4.2.1 People Human beings release both sensible heat and latent heat to the conditioned space when theystay in it as you can see the figures in the table (11). You might have noticed that when a smallroom is filled with people, it tends to become warmer. People emit heat primarily throughbreathing and perspiration, and, to a lesser extent, through radiation. This heat translates into anincreased cooling load on your cooling systems. The heat gain by the occupants in the building isseparated into sensible and latent heat. The number of people, the type of activity they areperforming, and the CLF determines sensible and latent heat. The CLF is determined by the timethe occupants come into the building and for how long they stay in the building. 19 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012The heat gain from the occupancy or people is given be equation:Q sensible = N (QS) (CLF)Q latent = N (QL)Where• N = number of students in space (class room).• QS, QL = Sensible and Latent heat gain from occupancy is given in Table 3.• CLF = Cooling Load Factor, by hour of occupancy in Table 37.4.2.1.1 Results Internal Gains Number Gain/unit CLF Q People 30 70 0.91 1911Table 12 shows the sensible heat gain. INTERNAL LOADS Number Gain/unit Ql= People 30 45 1350Table 13 shows the latent heat gain. 20 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20124.2.2 Lights Table 14 shows actual cooling load from fluorescent lights. The primary source of heat from lighting comes from light-emitting elements. Table (13),indicate and explain more about the lights effects on the heat gain when it’s off or on.Calculation of this load component is not straightforward; the rate of heat gain at any givenmoment can be quite different from the heat equivalent of power supplied instantaneously tothose lights. Only part of the energy from lights is in the form of convective heat, which ispicked up instantaneously by the air-conditioning apparatus. The remaining portion is in the formof radiation, which affects the conditioned space only after having been absorbed and re-releasedby walls, floors, furniture, etc. This absorbed energy contributes to space cooling load only aftera time lag, with some part of such energy still present and reradiating after the lights have beenswitched off. 21 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012Generally, the instantaneous rate of heat gain from electric lighting may be calculated from:Q = 3.41 x W x FUT x FSACooling load factors are used to convert instantaneous heat gain from lighting to the sensiblecooling load; thus the equation is modified to:Q = 3.41 x W x FUT x FSA x (CLF).Where:• W = Watts input from electrical lighting plan or lighting load data.• FUT = Lighting use factor, as appropriate.• FSA = special ballast allowance factor, as appropriate.• CLF = Cooling Load Factor, by hour of occupancy, Table 38.4.2.3 AppliancesIn a cooling load estimate, heat gain from all appliances-electrical, gas, or steam-should be takeninto account. Because of the variety of appliances, applications, schedules, use, and installations,estimates can be very subjective. Often, the only information available about heat gain fromequipment is that on its name-plate. 22 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 2012Q Sensible = Qin x Fu x Fr x (CLF)Q Latent = Qin x FuWhere• Qin = rated energy input from appliances. See Table 5 thru 9 or use manufacturer’s data. Forcomputers, monitors, printers and miscellaneous office equipment, see 2001 ASHRAEFundamentals, Chapter 29, Tables 8, 9, & 10.• Fu = Usage factor. See 1997 ASHRAE Fundamentals, Chapter 28, Table 6 and 7.• Fr = Radiation factor. See 1997 ASHRAE Fundamentals, Chapter 28, Table 6 and 7.• CLF = Cooling Load Factor, by hour of occupancy. See 1997 ASHRAE Fundamentals, Chapter28, Table 37 and 39.4.2.4 Infiltration AirQ sensible = 1.08 x CFM x (To – Ti)Q latent = 4840 x CFM x (Wo – Wi)Q total = 4.5 x CFM x (ho – hi)Where• CFM = Infiltration air flow rate. See 1997 ASHRAE Fundamentals, Chapter 25, fordetermining infiltration• To, Ti = Outside/Inside dry bulb temperature.• Wo, Wi = Outside/Inside humidity ratio.• ho, hi = Outside/Inside air enthalpy. 23 Dr. Kamel Adref | HCT, Abu Dhabi
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Cooling load Estimation 20125 References"Cooling Load Estimation." Cooling Load. N.p., 23 May 2010. Web. 16 June 2012.<http://me.lsu.edu/~meniki/me4643/downloads/COOLING%20LOAD%20%20%20LECTURE%20OUTLINE.pdf>."Thread: Cooling Load Calculation Formulas." Refrigeration-Engineer.com Forums. N.p., n.d. Web. 16June 2012. <http://www.refrigeration-engineer.com/forums/showthread.php?14289-cooling-load-calculation-formulas>."Cooling Load Calculations." Cooling Load Calculations. N.p., n.d. Web. 16 June 2012.<http://www.iklimnet.com/expert_hvac/cooling_load.html>."HEAT GAIN – COOLING LOAD ESTIMATE." Environmental Technology I. N.p., Spring 2003. Web. 16 June2012. <http://web.dcp.ufl.edu/mgold/ET1/2003_SPRING/Homeworks_03/HeatGain_Example.pdf>.Tongshoob, Taperit, and Chirdpun Vitooraporn2. "Cooling Load Calculation." Mechanical EngineeringDepartment, Chulalongkorn University, 2 July 2004. Web. 16 June 2012.<http://www.ashraethailand.org/download/ashraethailand_org/journal_2004-2005_10_a%20probabilistic%20approach%20for%20cooling%20load%20calculation.pdf>.Burdick, Arlan. "Accurate Heating and Cooling Load Calculations." Building Technologies Program. USDepartment Of Energy, 3 June 2011. Web. 16 June 2012.<http://www.nrel.gov/docs/fy11osti/51603.pdf>."Cooling Load Calculation." Cooling Load Calculation. N.p., n.d. Web. 16 June 2012.<http://personal.cityu.edu.hk/~bsapplec/cooling.htm>. 24 Dr. Kamel Adref | HCT, Abu Dhabi
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