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AirConditioningSystemsAirconditioninghasrapidlygrownoverthepast50years,fromaluxurytoastandardsystemincludedinmostresidentialandcommercialbuildings.In1970,36%ofresidencesintheU.S.wereeitherfullyairconditionedorutilizedaroomairconditionerforcooling(Blue,etal.,1979).By1997,thisnumberhadmorethandoubledto77%,andthatyearalsomarkedthefirsttimethatoverhalf(50.9%)ofresidencesintheU.S.hadcentralairconditioners(CensusBureau,1999).Anestimated83%ofallnewhomesconstructedin1998hadcentralairconditioners(CensusBureau,1999).Airconditioninghasalsogrownrapidlyincommercialbuildings.From1970to1995,thepercentageofcommercialbuildingswithairconditioningincreasedfrom54to73%(JacksonandJohnson,1978,andDOE,1998).Airconditioninginbuildingsisusuallyaccomplishedwiththeuseofmechanicalorheat-activatedequipment.Inmostapplications,theairconditionermustprovidebothcoolinganddehumidificationtomaintaincomfortinthebuilding.Airconditioningsystemsarealsousedinotherapplications,suchasautomobiles,trucks,aircraft,ships,andindustrialfacilities.However,thedescriptionofequipmentinthischapterislimitedtothosecommonlyusedincommercialandresidentialbuildings.Commercialbuildingsrangefromlargehigh-riseofficebuildingstothecornerconveniencestore.Becauseoftherangeinsizeandtypesofbuildingsinthecommercialsector,thereisawidevarietyofequipmentappliedinthesebuildings.Forlargerbuildings,theairconditioningequipmentispartofatotalsystemdesignthatincludesitemssuchasapipingsystem,airdistributionsystem,andcoolingtower.Properdesignofthesesystemsrequiresaqualifiedengineer.Theresidentialbuildingsectorisdominatedbysinglefamilyhomesandlow-riseapartments/condominiums.Thecoolingequipmentappliedinthesebuildingscomesinstandard“packages”thatareoftenbothsizedandinstalledbytheairconditioningcontractor.Thechapterstartswithageneraldiscussionofthevaporcompressionrefrigerationcyclethenmovestorefrigerantsandtheirselection,followedbypackagedChilledWaterSystems。1.1VaporCompressionCycleEventhoughthereisalargerangeinsizesandvarietyofairconditioningsystemsusedinbuildings,mostsystemsutilizethevaporcompressioncycletoproducethedesiredcoolinganddehumidification.Thiscycleisalsousedforrefrigeratingandfreezingfoodsandforautomotiveairconditioning.ThefirstpatentonamechanicallydrivenrefrigerationsystemwasissuedtoJacobPerkinsin1834inLondon,andthefirstviablecommercialsystemwasproducedin1857byJamesHarrisonandD.E.Siebe.Besidesvaporcompression,therearetwolesscommonmethodsusedtoproducecoolinginbuildings:theabsorptioncycleandevaporativecooling.Thesearedescribedlaterinthechapter.Withthevaporcompressioncycle,aworkingfluid,whichiscalledtherefrigerant,evaporatesandcondensesatsuitablepressuresforpracticalequipmentdesigns.Thefourbasiccomponentsineveryvaporcompressionrefrigerationsystemarethecompressor,condenser,expansiondevice,andevaporator.Thecompressorraisesthepressureoftherefrigerantvaporsothattherefrigerantsaturationtemperatureisslightlyabovethetemperatureofthecoolingmediumusedinthecondenser.Thetypeofcompressoruseddependsontheapplicationofthesystem.Largeelectricchillerstypicallyuseacentrifugalcompressorwhilesmallresidentialequipmentusesareciprocatingorscrollcompressor.Thecondenserisaheatexchangerusedtorejectheatfromtherefrigeranttoacoolingmedium.Therefrigerantentersthecondenserandusuallyleavesasasubcooledliquid.Typicalcoolingmediumsusedincondensersareairandwater.Mostresidential-sizedequipmentusesairasthecoolingmediuminthecondenser,whilemanylargerchillersusewater.Afterleavingthecondenser,theliquidrefrigerantexpandstoalowerpressureintheexpansionvalve.Theexpansionvalvecanbeapassivedevice,suchasacapillarytubeorshorttubeorifice,oranactivedevice,suchasathermalexpansionvalveorelectronicexpansionvalve.Thepurposeofthevalveistoregulatetheflowofrefrigeranttotheevaporatorsothattherefrigerantissuperheatedwhenitreachesthesuctionofthecompressor.Attheexitoftheexpansionvalve,therefrigerantisatatemperaturebelowthatofthemedium(airorwater)tobecooled.Therefrigeranttravelsthroughaheatexchangercalledtheevaporator.Itabsorbsenergyfromtheairorwatercirculatedthroughtheevaporator.Ifairiscirculatedthroughtheevaporator,thesystemiscalledadirectexpansionsystem.Ifwateriscirculatedthroughtheevaporator,itiscalledachiller.Ineithercase,therefrigerantdoesnotmakedirectcontactwiththeairorwaterintheevaporator.Therefrigerantisconvertedfromalowquality,two-phasefluidtoasuperheatedvaporundernormaloperatingconditionsintheevaporator.Thevaporformedmustberemovedbythecompressoratasufficientratetomaintainthelowpressureintheevaporatorandkeepthecycleoperating.Allmechanicalcoolingresultsintheproductionofheatenergythatmustberejectedthroughthecondenser.Inmanyinstances,thisheatenergyisrejectedtotheenvironmentdirectlytotheairinthecondenserorindirectlytowaterwhereitisrejectedinacoolingtower.Withsomeapplications,itispossibletoutilizethiswasteheatenergytoprovidesimultaneousheatingtothebuilding.Recoveryofthiswasteheatattemperaturesupto65°C(150°F)canbeusedtoreducecostsforspaceheating.Capacitiesofairconditioningareoftenexpressedineithertonsorkilowatts(kW)ofcooling.Thetonisaunitof