Heat GainsCooling Load ComponentsSensible and Latent GainsTime of Peak Cooling LoadSunlit SurfacesTime LagStorage Effect (thermal lag)Conduction – Sunlit SurfacesRoofsCLTD Correction - RoofLatitude Month AdjustmentRoof TypesSunlit WallsWall GroupsCorrecting CLTD - WallsRoof CalculationSlide 17Wall CalculationCLTD Correction - WallsSunlit GlassGlass - ConductionSolar Heat Gain FactorsTypes of Shading DevicesGlass – Solar GainSHGFSCCLFCLF with interior shadingWindow CalculationLightingLighting EstimatesLight CLFSpace versus Plenum LoadsCLF Design Values (Coefficients)Lighting CalculationPeopleEquipment - OfficeEquipment -RestaurantHeat Gain in DuctworkSystem Heat GainsSample Form Heat GainHeat Gain Assignment“Rules of Thumb”Balancing the SystemNext TimeHeat GainsHVAC 7abCNST 305 Environmental Systems 1Dr. BerrymanCooling Load Componentsroofrooflightslightsequipmentequipmentfloorfloorexteriorexteriorwallwallglass solarglass solarglassglassconductionconductioninfiltrationinfiltrationpeoplepeoplepartitionpartitionwallwallSensible and Latent Gainssensibleloadlatentloadconduction through roof, walls, windows, and skylightssolar radiation through windows, skylightsconduction through ceiling, interior partition walls, and floorpeoplelightsequipment/appliancesinfiltrationventilationsystem heat gainscooling load componentsTime of Peak Cooling Loadheat gainheat gainroofeast-facingwindow12 6 12 6 1212 6 12 6 12noonnoona.m.a.m.p.m.p.m.midmidmidmidSunlit Surfacessunrayssunrayssolar angle changes throughout the daysolar angle changes throughout the dayTime Lagsolar effectsolar effect12 6 12 6 1212 6 12 6 12noonnoona.m.a.m.p.m.p.m.midmidmidmidAABBtime lagtime lagStorage Effect (thermal lag)Conduction – Sunlit SurfacesA factor called the cooling load temperature difference (CLTD) is used to account for the added heat transfer due to the sun shining on exterior walls, roofs, and windows, and the capacity of the wall and roof to store heat. The CLTD is substituted for T in the equation to estimate heat transfer by conduction.BH = U  A  TCLTDRoofsBased on:•Solar radiation at 40o lat on July 21•Dark surface•OA 95oF•Outdoor mean of 85oF•Daily Range of 21oF•No VentilationCLTD Correction - RoofCLTDcorr = [(CLTD + LM)k + (78 – tR) + (tO – 85)]fto = OA – (DR/2)Latitude Month AdjustmentRoof TypesSelect closest construction•Weight•ConstructionCompare U valuesAdditional insulation•Use a CLTD whose roof weight and heat capacity are approximately the same•Find peak gain during the day•For each R-7 above selected roof type•Move value 2 hours later•29oF is the lowest adjustment value you can useSunlit WallsBased on:•Solar radiation at 40o lat on July 21•Dark surface•OA 95oF•Outdoor mean of 85oF•Daily Range of 21oFWall Groups•Select closest wall group•Compare U-values•Move up one wall group for each R-7G F E D C B AEach R-7Correcting CLTD - WallsCLTDcorr = (CLTD + LM)k + (78 – tR) + (tO – 85)to = OA – (DR/2)Roof CalculationEXAMPLEGiven:•New Orleans, LA•OA DB=93oF WB=77oF•IA 77oF 40% RH•30o N. Latitude – June 22•Daily Range of 16oF •5000 SF light colored steel sheet roof w/ drop ceiling – rural area•No attic ventilation•Rtotal = 21Find peak cooling load:Closest roof type: 1 Peak: 1500 hrs CLTDuncorr: 78oFCorrect for insulation:R=7.5 vs 21 (+4 hrs) CLTDuncorr: 42oFCorrect CLTD:next slideCLTD Correction - RoofCLTDcorr = [(CLTD + LM)k + (78 – tR) + (tO – 85)]f42oF 2oF 0.5 77oF 1.093oF 16oFtO = 85oFtO = (OA – (DR/2)Average outside temperature85oFCLTDcorr = 23oFHeat gain through roof:BH = U  A  CLTD(1/21)(5000)(23oF) = 5476 BHEXAMPLEWall CalculationGiven:•New Orleans, LA•OA DB=93oF WB=77oF•IA 77oF 40% RH•30o N. Latitude – June 22•Daily Range of 16oF •12x100’ light colored metal curtain wall – rural area – West facing•Rtotal = 19Determine Wall Group:Type G Metal Curtain WallCorrect for insulation:Correct CLTD:next slideR values 5.6 - 12.3 vs 19 (up 1 wall group)Use Type F Wall GroupCLTD Correction - WallsCLTDcorr = (CLTD + LM)k + (78 – tR) + (tO – 85)28oF 0oF 0.65 77oF 85oFCLTDcorr = 19.2oFHeat gain through wall:BH = U  A  CLTD(1/19)(12’ x 100’)(19.2oF) =1213 BTUHsun rayssun rayssun rayssun raysreflectedreflectedenergyenergyreflectedreflectedenergyenergytransmittedtransmittedenergyenergytransmittedtransmittedenergyenergyglassglasswindowwindowglassglasswindowwindowconductionconductionsolar gain solar gain (radiation)(radiation)Sunlit GlassBH = solar gain + conductionBH = solar gain + conductionGlass - ConductionBHconduction = U  A  CLTDBased on:•IA = 78oF•OA = 95oF•Daily Avg – 85oF•DR = 20oFCalculate CLTDcorr like roof/wallsCLTDcorr = CLTD + (78 – tR) + (tO – 85)Solar Heat Gain FactorsDirection that the window facesTime of dayMonthLatitudeConstruction of interior partition wallsType of floor coveringExistence of internal shading devicesTypes of Shading DevicesinteriorinteriorblindsblindsinteriorinteriorblindsblindsexteriorexteriorfinsfinsexteriorexteriorfinsfinsGlass – Solar GainThe equation used to predict the solar heat gain (radiation) through glass is:BHglass = SHGF x A x SC x CLF where,- BH = heat gain by solar radiation through glass, Btu/hr- SHGF = solar heat gain factor, Btu/hr•ft2 - A = total surface area of the glass, ft2 - SC = shading coefficient of the window, dimensionless-CLF = cooling load factor, dimensionlessSHGFSolar energy through fenestrationfor Sunlit Glass* *use N(shade) for non-sunlit glassSCBlinds or drapes absorb the solar energy before it can strike the floor causing a rapid response in the cooling load82% Solar Reduction82% Solar ReductionCLFWithout interior shadingWhen shading is absent: Energy is absorbed by the more massive elements of the spaceHeavier construction = larger heat gain delayCLF with interior shadingReduction in the amplitude of the solar heat gain due to the constructionsWindow CalculationEXAMPLEGIVEN:•New Orleans, LA•OA DB=93oF WB=77oF•IA 77oF 40% RH•30o N. Latitude – June 22•Daily Range of 16oF •Light venetian blinds•30 40 DH Clear Glass•R = 2•West facing at 1400 HRSConductionSolar GainBH = U  A  CLTDBH = SHGF x A x SC x CLF(½)(3 x 4)(15oF)CLTDcorr= 14oF+(78oF–77oFF) + (85oF–85oF)= 90 BH(214 BH)(12)(0.58)(.53)= 790 BHBHtotal = 880LightingBHlight = watts  3.41  ballast factor  CLF1 watt = 3.4 BTUH-BH =