“冷卻塔”外文文獻(xiàn)及譯文

本科畢業(yè)設(shè)計(jì)外文文獻(xiàn)及譯文文獻(xiàn)、資料題目：CoolingTowers文獻(xiàn)、資料來源：HVACEquipmentandSystems文獻(xiàn)、資料發(fā)表（出版）日期：院（部）：專業(yè)：班級(jí)：姓名：學(xué)號(hào)：指導(dǎo)教師：翻譯日期：山東XX大學(xué)外文文獻(xiàn)及譯文PAGE48-外文資料CoolingTowersIfachillerisusedtoprovidechilledwaterforbuildingairconditioning,thentheheatenergythatisabsorbedthroughthatprocessmustberejected.Thetwomostcommonwaystorejectthermalenergyfromthevaporcompressionprocessareeitherdirectlytotheairorthroughacoolingtower.Inacoolingtower,waterisrecirculatedandevaporativelycooledthroughdirectcontactheattransferwiththeambientair.Thiscooledwatercanthenbeusedtoabsorbandrejectthethermalenergyfromthecondenserofthechiller.ThemostcommoncoolingtowerusedforHVACapplicationsisthemechanicaldraftcoolingtower(Figure4.2.13).Themechanicaldrafttowerusesoneormorefanstoforceairthroughthetower,aheattransfermediaorfillthatbringstherecirculatedwaterintocontactwiththeair,awaterbasin(sump)tocollecttherecirculatedwater,andawaterdistributionsystemtoensureevendispersalofthewaterintothetowerfill.Figure4.2.14showstherelationshipbetweentherecirculatingwaterandairastheyinteractinacounterflowcoolingtower.Theevaporativecoolingprocessinvolvessimultaneousheatandmasstransferasthewatercomesintocontactwiththeatmosphericair.Ideally,thewaterdistributionsystemcausesthewatertosplashoratomizeintosmallerdroplets,increasingthesurfaceareaofwateravailableforheattransfer.Theapproachtothewet-bulbisacommonlyusedindicatoroftowersizeandperformance.Itisdefinedasthetemperaturedifferencebetweenthecoolingwaterleavingthetowerandthewet-bulboftheairenteringthetower.Theoretically,thewaterbeingrecirculatedinatowercouldreachthewetbulbtemperature,butthisdoesnotoccurinactualtoweroperations.FIGURE4.2.14Air/watertemperaturerelationshipinacounterflowcoolingtower.Therangeforachiller/towercombinationisdeterminedbythecondenserthermalloadandthecoolingwaterflowrate,notbythecapacityofthecoolingtower.Therangeisdefinedasthetemperaturedifferencebetweenthewaterenteringthecoolingtowerandthatleaving.Thedriveroftowerperformanceistheambientwet-bulbtemperature.Thelowertheaveragewet-bulbtemperature,the“easier”itisforthetowertoattainthedesiredrange,typically6°C(10°F)forHVACapplications.Thus,inahot,dryclimatetowerscanbesizedsmallerthanthoseinahotandhumidareaforagivenheatload.Coolingtowersarewidelyusedbecausetheyallowdesignerstoavoidsomecommonproblemswithrejectionofheatfromdifferentprocesses.Theprimaryadvantageofthemechanicaldraftcoolingtowerisitsabilitytocoolwatertowithin3–6°C(5–10°F)oftheambientwet-bulbtemperature.Thismeansmoreefficientoperationoftheconnectedchillingequipmentbecauseofimproved(lower)headpressureoperationwhichisaresultofthelowercondensingwatertemperaturessuppliedfromthetower.CoolingTowerDesignsTheASHRAESystemsandEquipmentHandbook(1996)describesover10typesofcoolingtowerdesigns.ThreebasiccoolingtowerdesignsareusedformostcommonHVACapplications.Baseduponairandwaterflowdirectionandlocationofthefans,thesetowerscanbeclassifiedascounterflowinduceddraft,crossflowinduceddraft,andcounterflowforceddraft.Onecomponentcommontoallcoolingtowersistheheattransferpackingmaterial,orfill,installedbelowthewaterdistributionsystemandintheairpath.Thetwomostcommonfillsaresplashandfilm.Splashfilltendstomaximizethesurfaceareaofwateravailableforheattransferbyforcingwatertobreakapartintosmallerdropletsandremainentrainedintheairstreamforalongertime.Successivelayersofstaggeredsplashbarsarearrangedthroughwhichthewaterisdirected.Filmfillachievesthiseffectbyforcingwatertoflowinthinlayersoverdenselypackedfillsheetsthatarearrangedforverticalflow.Towersusingfilmtypefillareusuallymorecompactforagiventhermalload,anadvantageifspaceforthetowersiteislimited.Splashfillisnotassensitivetoairorwaterdistributionproblemsandperformsbetterwherewaterqualityissopoorthatexcessivedepositsinthefillmaterialareaproblem.CounterflowInducedDraftAirinacounterflowinduceddraftcoolingtowerisdrawnthroughthetowerbyafanorfanslocatedatthetopofthetower.Theairentersthetoweratlouversinthebaseandthencomesintocontactwithwaterthatisdistributedfrombasinsatthetopofthetower.Thus,therelativedirectionsarecounter(downforthewater,upfortheair)inthisconfiguration.ThisarrangementisshowninFigure4.2.15.Inthisconfiguration,thetemperatureofthewaterdecreasesasitfallsdownthroughthecounterflowingair,andtheairisheatedandhumidified.Dropletsofwaterthatmighthavebeenentrainedintheairstreamarecaughtatthedrifteliminatorsandreturnedtothesump.Airandsomecarryoverdropletsareejectedthroughthefansandoutthetopofthetower.Thewaterthathasbeencooledcollectsinthesumpandispumpedbacktothecondenser.FIGURE4.2.15Counterflowinduceddraftcoolingtower.Counterflowtowersgenerallyhavebetterperformancethancrossflowtypesbecauseoftheevenairdistributionthroughthetowerfillmaterial.Thesetowersalsoejectairathighervelocitieswhichreducesproblemswithexhaustairrecirculationintothetower.However,thesetowersarealsosomewhattallerthancrossflowtypesandthusrequiremorecondenserpumphead.CrossflowInducedDraftAsinthecounterflowcoolingtower,thefaninthecrossflowtowerislocatedatthetopoftheunit(Figure4.2.16).Airentersthetoweratsideorendlouversandmoveshorizontallythroughthetowerfill.Waterisdistributedfromthetopofthetowerwhereitisdirectedintothefillandiscooledbydirectcontactheattransferwiththeairincrossflow(airhorizontalandwaterdown).Watercollectedinthesumpispumpedbacktothechillercondenser.Theincreasedairflowpossiblewiththecrossflowtowerallowsthesetowerstohaveamuchloweroverallheight.Thisresultsinlowerpumpheadrequiredonthecondenserwaterpumpcomparedtothecounterflowtower.Thereducedheightalsoincreasesthepossibilityofrecirculatingtheexhaustairfromthetopofthetowerbackintothesideorendairintakeswhichcanreducethetower’seffectiveness.CounterflowForcedDraftCounterflowforceddraftcoolingtowershavethefanmountedatornearthebottomoftheunitneartheairintakes(Figure4.2.17).Asintheothertowers,waterisdistributeddownthroughthetoweranditsfill,andthroughdirectcontactwithatmosphericairitiscooled.Thermaloperationofthistowerissimilartothecounterflowinduceddraftcoolingtower.Fanvibrationisnotassevereforthisarrangementcomparedtoinduceddrafttowers.Thereisalsosomeadditionalevaporativecoolingbenefitbecausethefandischargesairdirectlyacrossthesumpwhichfurthercoolsthewater.Therearesomedisadvantagestothistower.First,theairdistributionthroughthefillisuneven,whichreducestowereffectiveness.Second,thereisriskofexhaustairrecirculationbecauseofthehighsuctionvelocityatthefaninlets,whichcanreducetowereffectiveness.Thesetowersfindapplicationsinsmallandmedium-sizedsystems.MaterialsCoolingtowersoperateinacontinuouslywetconditionthatrequiresconstructionmaterialstomeetchallengingcriteria.Besidesthewetconditions,recirculatingwatercouldhaveahighconcentrationofmineralsaltsduetotheevaporationprocess.Coolingtowermanufacturersbuildtheirunitsfromacombinationofmaterialsthatprovidethebestcombinationofcorrosionresistanceandcost.Woodisatraditionalmaterialusedincoolingtowerconstruction.Redwoodorfirareoftenusedandareusuallypressuretreatedwithpreservativechemicals.Chemicalssuchaschromatedcopperarsenateoracidcopperchromatehelppreventdecayduetofungiordestructionbytermites.FIGURE4.2.16Crossflowinduceddraftcoolingtower.FIGURE4.2.17Counterflowforceddraftcoolingtower.Galvanizedsteeliscommonlyusedforsmall-tomid-sizedcoolingtowerstructures.Hardwareisusuallymadeofbrassorbronze.Criticalcomponents,suchasdriveshafts,hardwaremountingpoints,etc.,maybemadefrom302or304stainlesssteel.Castironcanbefoundinbasecastings,motorhousings,andfanhubs.Metalscoatedwithplasticsarefindingapplicationforspecialcomponents.Manymanufacturersmakeextensiveuseoffiberglass-reinforcedplastic(FRP)intheirstructure,pipe,fanblades,casing,inletlouvers,andconnectioncomponents.Polyvinylchloride(PVC)isusedforfillmedia,drifteliminators,andlouvers.Fillbarsandfloworificesarecommonlyinjectionmoldedfrompolypropyleneandacrylonitrilebutadienestyrene(ABS).Concreteisnormallyusedforthewaterbasinorsumpoffielderectedtowers.Tilesormasonryareusedinspecialtytowerswhenaestheticsareimportant.PerformanceRejectionoftheheatloadproducedatthechillingequipmentistheprimarygoalofacoolingtowersystem.Thisheatrejectioncanbeaccomplishedwithanoptimizedsystemthatminimizesthetotalcompressorpowerrequirementsofthechillerandthetowerloadssuchasthefansandcondenserpumps.Severalcriteriamustbedeterminedbeforethedesignercancompleteathoroughcoolingtoweranalysis,includingselectionoftowerrange,water-to-airratio,approach,filltypeandconfiguration,andwaterdistributionsystem.Table4.2.6listssomeofthecommondesigncriteriaandnormallyacceptedrangesforcoolingtowers.MostcommonHVACapplicationsrequiringacoolingtowerwillusean“offtheshelf”unitfromacoolingtowermanufacturer.Manufacturerrepresentativesareusuallywellinformedabouttheirproductsandtheirproperapplication.AftertheprojectdesignprocesshasproducedtheinformationcalledforinTable4.2.6,itistimetocontactoneormorecoolingtowerrepresentativesandseektheirinputoncorrecttowerselection.ControlSchemewithChillersMostcoolingtowersaresubjecttolargechangesinloadandambientwet-bulbtemperatureduringnormaloperations.Foratypicalcoolingtower,thetowerfanenergyconsumptionisapproximately10%oftheelectricpowerusedbythechillercompressor.Thecondenserpumpsareabout2–5%ofthecompressorpower.Controllingthecapacityofatowertosupplyadequatelycooledwatertothecondenserwhileminimizingenergyuseisadesirableoperationalscheme.ProbablythemostcommoncontrolschemeemployedfortowersservinganHVACloadistomaintainafixedleavingwatertemperature,usually27°C(80°F).Fancyclingisacommonmethodtoachievethiscoolingtowercontrolstrategyandisapplicabletomultiunitandmulticelltowerinstallations.However,thiscontrolmethoddoesnotminimizetotalenergyconsumedbythechiller/coolingtowersystemcomponents.Loweringthecondensingwatertemperatureincreasesachiller’sefficiency.Aslongastheevaporatortemperatureisconstant,areducedcondensertemperaturewillyieldalowerpressuredifferencebetweentheevaporatorandcondenserandreducetheloadonthecompressor.However,itisimportanttorecognizethattheefficiencyimprovementsinitiallygainedthroughlowercondensertemperaturesarelimited.Improvedchillerefficiencymaybeoffsetbyincreasedtowerfanandpumpingcosts.Maintainingaconstantapproachatsomeminimumtemperatureisdesirableaslongasthecondensingtemperaturedoesnotfallbelowthechillermanufacturer’srecommendations.Sincemostmoderntowersusetwo-orthree-speedfans,anearoptimalcontrolschemecanbedevelopedasfollows(BraunandDiderrich,1990):?Towerfansshouldbesequencedtomaintainaconstantapproachduringpartloadoperationtominimizechiller/coolingtowerenergyuse.?Theproductofrangeandcondensingwaterflowrate,ortheheatenergyrejected,shouldbeusedtodeterminethesequencingofthetowerfans.?Developasimplerelationshipbetweentowercapacityandtowerfansequencing.DeSaullesandPearson(1997)foundthatsavingsforasetpointcontrolversusthenearoptimalcontrolforacoolingtowerwereverysimilar.Theircontrolschemecalledforthetowertoproducewateratthelowestsetpointpossible,butnotlessthanthechillermanufacturerwouldallow,andtocomparethatoperationtothesavingsobtainedusingnearoptimalcontrolasdescribedabove.Theyfoundthatthelevelofsavingsthatcouldbeachievedwasdependentontheloadprofileandthemethodofoptimization.Theirsimulationsshowed2.5to6.5%energysavingsforthesinglesetpointmethodwhilethenearoptimalcontrolyieldedsavingsof3to8%.Useofvariablespeedfanswouldincreasethesavingsonlyinmosttowerinstallations.Itismoreeconomicaltooperatemultiplecoolingtowerfansatthesamespeedthantooperateoneatmaximumbeforestartingthenextfan.Variablespeedfansshouldbeusedwhenpossibleincoolingtowers.ThesystemdesignershouldensurethatanynewlyinstalledcoolingtoweristestedaccordingtoASMEStandardPTC23(ASME1986)orCTIStandardATC-105.Thesefieldtestsensurethatthetowerisperformingasdesignedandcanmeettheheatrejectionrequirementsfortheconnectedchillerorrefrigerationload.SelectionCriteriaThecriterialistedinTable4.2.6areusuallyknownaprioribythedesigner.Ifnotknownexplicitly,thencommonlyacceptedvaluescanbeused.Thesecriteriaareusedtodeterminethetowercapacityneededtorejecttheheatloadatdesignconditions.Otherconsiderationsbesidesthetower’scapacityincludeeconomics,servicing,environmentalconsiderations,andaesthetics.Manyofthesefactorsareinterrelated,but,ifpossible,theyshouldallbeevaluatedwhenselectingaparticulartowerdesign.Becauseeconomicsisanimportantpartoftheselectionprocess,twomethodsarecommonlyused—life-cyclecostingandpaybackanalysis.Theseprocedurescompareequipmentonthebasisofowning,operation,andmaintenancecosts.Othercriteriacanalsoaffectfinalselectionofacoolingtowerdesign:buildingcodes,structuralconsiderations,serviceability,availabilityofqualifiedservicepersonnel,andoperationalflexibilityforchangingloads.Inaddition,noisefromtowerscanbecomeasensitiveenvironmentalissue.Iflocalbuildingcodesoundlimitsareanissue,soundattenuatorsattheairintakesandthetowerfanexitshouldbeconsidered.Aestheticscanbeaproblemwithmodernarchitecturalbuildingsoronsiteswithlimitedlandspace.Severaltowermanufacturerscanerectcustomunitsthatcancompletelymaskthecoolingtoweranditsoperation.Applications[1][1]節(jié)選自JamesB.Bradfordetal.“HVACEquipmentandSystems”.HandbookofHeating,Ventilation,andAir-Conditioning.Ed.JanF.Kreider.BocaRaton,CRCPressLLC.2001Unlikechillers,pumps,andairhandlers,thecoolingtowermustbeinstalledinanopenspacewithcarefulconsiderationoffactorsthatmightcauserecirculation(recaptureofaportionofwarmandhumidexhaustairbythesametower)orrestrictairflow.Apoortowersitingsituationmightleadtorecirculation,aproblemnotrestrictedtowetcoolingtowers.Similarrecirculationcanoccurwithair-cooledcondensingequipmentaswell.Withcoolingtowerrecirculation,performanceisadverselyaffectedbytheincreaseinenteringwet-bulbtemperature.Theprimarycausesofrecirculationarepoorsitingofthetoweradjacenttostructures,inadequateexhaustairvelocity,orinsufficientseparationbetweentheexhaustandintakeofthetower.Multipletowerinstallationsaresusceptibletointerference—whentheexhaustairfromonetowerisdrawnintoatowerlocateddownwind.Symptomssimilartotherecirculationphenomenonthenplaguethedownwindtower.Forrecirculation,interference,orphysicallyblockingair-flowtothetowertheresultislargerapproachandrangewhichcontributetohighercondensingpressureatthechiller.Bothrecirculationandinterferencecanbeavoidedthroughcarefulplanningandlayout.Anotherimportantconsiderationwhensitingacoolingtowerinstallationistheeffectoffogging,orplume,andcarryover.Foggingoccursduringcoolerweatherwhenmoistwarmairejectedfromthetowercomesintocontactwiththecoldambientair,condenses,andformsfog.Fogfromcoolingtowerscanlimitvisibilityandcanbeanarchitecturalnuisance.Carryoveriswhensmalldropletsofentrainedwaterintheairstreamarenotcaughtbythedrifteliminatorsandareejectedintheexhaustairstream.Thesedropletsthenprecipitateoutfromtheexhaustairandfalltothegroundlikealightmistorrain(inextremecases).Carryoverordriftcontainsmineralsandchemicalsfromthewatertreatmentinthetowerandcancausestainingordiscolorationofthesurfacesitsettlesupon.Tomitigateproblemswithfogorcarryover,aswithrecirculation,thedesignershouldconsidernearbytrafficpatterns,parkingareas,prevailingwinddirection,largeglassareas,orotherarchitecturalconsiderations.OperationandMaintenanceWinterOperationIfchillersorrefrigerationequipmentarebeingusedincoldweather,freezeprotectionshouldbeconsideredtoavoidformationoficeonorinthecoolingtower.Capacitycontrolisonemethodthatcanbeusedtocontrolwatertemperatureinthetoweranditscomponents.Electricimmersionheatersareusuallyinstalledinthetowersumptoprovideadditionalfreezeprotection.Sinceicingoftheairintakescanbeespeciallydetrimentaltotowerperformance,thefanscanbereversedtode-icetheseareas.Ifthefansareoperatinginextremelycoldweather,icecanaccumulateontheleadingedgesofthefanblades,whichcancauseseriousimbalanceinthefansystem.Instrumentationtodetectout-of-limitsvibrationoreccentricityinrotationalloadsshouldbeinstalled.Aswithanyoperationalequipment,frequentvisualinspectionsduringextremeweatherarerecommended.WaterTreatmentThewatercirculatinginacoolingtowermustbeatanadequatequalityleveltohelpmaintaintowereffectivenessandpreventmaintenanceproblemsfromoccurring.Impuritiesanddissolvedsolidsareconcentratedintowerwaterbecauseofthecontinuousevaporationprocessasthewateriscirculatedthroughthetower.Dirt,dust,andgasescanalsofindtheirwayintothetowerwaterandeitherbecomeentrainedinthecirculatingwaterorsettleintothetowersump.Toreducetheconcentrationofthesecontaminants,apercentageofthecirculatingwaterisdrainedorblown-down.Insmallerevaporativelycooledsystems,thisprocessiscalledableed-offandiscontinuous.Blow-downisusually0.8to1.2%ofthetotalwatercirculationrateandhelpstomaintainreducedimpurityconcentrationsandtocontrolscaleformation.Ifthetowerisservedwithverypoorwaterquality,additionalchemicaltreatmentsmightbeneededtoinhibitcorrosion,controlbiologicalgrowth,andlimitthecollectionofsilt.Ifthetowerinstallationpresentscontinuingwaterqualityproblems,awatertreatmentspecialistshouldbeconsulted.LegionellosisLegionellosishasbeenconnectedwithevaporativecondensers,coolingtowers,andotherbuildinghydroniccomponents.Researchershavefoundthatwell-maintainedtowerswithgoodwaterqualitycontrolwerenotusuallyassociatedwithcontaminationbyLegionellapneumophilabacteria.InapositionpaperconcerningLegionellosis,theCoolingTowerInstitute(CTI,1996)statedthatcoolingtowersarepronetocolonizationbyLegionellaandhavethepotentialtocreateanddistributeaerosoldroplets.Optimumgrowthofthebacteriawasfoundtobeatabout37°C(99°F)whichisaneasilyattainedtemperatureinacoolingtower.TheCTIproposedrecommendationsregardingcoolingtowerdesignandoperationtominimizethepresenceofLegionella.TheydonotrecommendfrequentorroutinetestingforLegionellapneumophilabacteriabecausethereisdifficultyinterpretingtestresults.Acleantowercanquicklybereinfected,andacontaminatedtowerdoesnotmeananoutbreakofthediseasewilloccur.MaintenanceThecoolingtowermanufacturerusuallyprovidesoperatingandmaintenance(O&M)manualswithanewtowerinstallation.Thesemanualsshouldincludeacompletelistofallpartsusedandreplaceableinthetowerandalsodetailsontheroutinemaintenancerequiredforthecoolingtower.Ataminimum,thefollowingshouldalsobeincludedaspartofthemaintenanceprogramforacoolingtowerinstallation.?Perioddiciinspeectioonofftheeenttireunitttoensuureiitissingooddreppair..?Compleetepperioodicdraiiningganddcleeaninngoffalllwetttedsurffacessinthetoweer.TThisgiveesthheoppporttunittytorremovveacccumuulatiionsofddirt,,sliime,scalle,aandaareasswheereaalgaeeorbactteriaamigghtddevellop.?Perioddicwwaterrtreeatmeentfforbbioloogicaalanndcoorrossionconttrol..?Continnuoussdoccumenntatiionoonopperattionandmainntenaanceoftthettowerr.ThhisddevellopsthebaseelineeforfutuureOO&Mddecissionssanddisveryyimpportaantfforaaproopermainntenaancepoliicy.4.2.4PPackaagedEquiipmenntCentrallHVAACsyystemmsarrenootallwaysstheebesstapppliccatioonfoorapartticullarccooliingoorheeatinnglooad.Inittialcosttsfoorceentraalsyystemmsarreussualllymuuchhhigheerthhanuunitaaryoorpaackaggedssysteems.Therremaayallsobbephyssicallconnstraaintssonthesizeeofthemechhaniccalccompoonenttsthhatccanbbeinnstallledintthebbuildding..Unittaryorppackaagedsysttemscomeefacctoryyasssemblledaandpproviideoonlycoollingorccombiinedheattingandcoolling..Theesessysteemsaaremmanuffactuuredinaavarrietyyofconffigurratioonstthatalloowthhedeesignnerttomeeetalmoostaanyaappliicatiion.Cabiinetorsskid--mounntedforeasyyinsstalllatioon,ttypiccaluunitssgenneralllycconsiistoofaneevapooratoor,bbloweer,ccomprressoor,ccondeenserr,annd,iifacombbineddsysstem,,ahheatiingssectiion.Thecapaacitiiesofttheuunitssranngesfrommappproxiimateely55kWto4460kkW(11.5tto1330toons)..Typpicalluniitaryysysstemssareesinggle-ppackaagedunitts(wwindoowunnits,,roooftoppuniits),,spllit-ssysteempaackaggeduunitss,heeatppumpsysttems,,andwateersoourceeheaatpuumpssysteems.Unittarysysttemsdonnotllastasllong(onlly8to115yeears))ascenttralHVACCequuipmeentaandaareooftennlessseffficiient..Unitaryysysstemssfinndapppliccatiooninnbuiildinngsuuptooeigghtsstoriiesiinheeightt,buutthheyaaremmoregeneeralllyuseddinone--,twwo-,ortthreee-stoorybbuilddingssthaathaavessmalllerccooliinglloadss.Thheyaaremmostofteenussedforretaailsspacees,ssmallloffficebuilldinggs,aandcclasssroomms.UUnitaaryeequippmenttisavaiilablleonnlyiinprreesttabliisheddcapaacityyinccremeentswithhsettperrformmanceechaaractterissticss,suuchaastootalL/s(cfmm)deeliveeredbytheunitt’saiirhaandleer.SSomedesiignerrscoombinneceentraalHVVACssysteemswwithpackkageddequuipmeentuusedonpperimmeterrbuiildinngzoones..Thiiscoompossitecansolvvehuumidiityaandsspaceetemmperaatureereqquireementtsbetttertthanpackkagedduniitsaalonee.Thhisaalsoworkksweelliinbuuildiingswherreittisimprractiicalforpackkageddunittstooserrveiinterriorspacces.Table44.2.77lisstsssomeofttheaadvanntageesannddiisadvvantaagesofppackaagedandunittaryHVACCequuipmeent.Table44.2.88lisstseenerggyeffficiiencyyrattingss(EEERs)fortypiicalelecctriccairr-anndwaater--coolledssplittanddsinnglepackkageunittswiithccapaccitygreaaterthann19kW((65,0000BBtuh)).Typicallly,commmerciialbbuilddingssuseeuniitaryysysstemsswitthcooolinngcaapaciitiessgreeaterrthaan188kW(5toons)..Insomeecasses,howeever,,dueetospaccereequirremennts,physsicalllimmitattionss,orrsmaallaaddittionss,resiidenttial--sizeedunnitarrysyystemmsarreussed.Ifaauniitaryysysstemis110yeearsoroolderr,ennergyysavvingsscannbeachiieveddbyrepllacinngunnitarrysyystemmswiithppropeerlysizeed,eenerggy-effficiientmodeels.aElecttricair--anddwatter-ccooleedspplitsysttemaandssingllepaackaggeunnitswithhcappacittyovver119kWW(65,,000Btuhh)arrecoovereedheere.bEER,oreenerggyeffficiiencyyrattio,isttheccooliingccapaccityinkkW(BBtu/hh)offtheeuniitdiivideedbyyitsselecctriccaliinputt(innwattts)atsstanddard(ARII)coondittionssof35°CC(95°°F)fforaair-ccooleedeqquipmment,,and29°CC(85°°F)eenterringwateerfoorwaater--coolledmmodells.cBaseddonARI210//240testtprooceduure.dSEER(seaasonaalennergyyeffficieencyratiio)iisthhetootalcoollingoutpputkkW(BBtu)provvideddbytheunittduriingiitsnnormaalannnuallusaagepperioodfoorcooolinngdiivideedbyytheetottaleenerggyinnput(inWh)ddurinngthhesaamepperiood.eSplittsysstemandsinggleppackaageuunitsswitthtootalcapaacityyundder119kWW(655,0000Btuuh)aareccoverredheree.Thhisaanalyysisexclludesswinndowunittsanndpaackaggedttermiinalunitts.FIGURE4.2..18CompparissonbbetweeenTTXVaandsshortt-tubbeorrificcesyystemmscaapaciityfforaaranngeoofchhargiingccondiitionnsand95°FF(35°°C)ooutdooorttempeeratuure.(FroomRoodriqquezetaal.,19966).AswithhanyyHVAACeqquipmment,,proopermainntenaanceandoperratioonwiilleensurreopptimuumpeerforrmancceandlifeeforrassysteem.SSplitt-sysstemaircondditioonerssanddheaatpuumpsarethemosttcommmonunittsappplieedinnresiidenttialandsmalllcoommerrciallappplicaationns.TTheseeuniitsaarettypiccallyyshiippeddtotheconsstrucctionnsitteasssepaarateecommponeents;;aftterttheccondeenserr(ouutdooorunnit)andtheevapporattor((indoooruunit))areemouuntedd,therefrrigerrantpipiingiiscoonnecctedbetwweenthemm.Thheaiircoondittioniingttechnniciaanmuusteensurrethhatttheunittispropperlyychaargeddwitthreefriggeranntanndchheckforpropperooperaationn.Ifftheesysstemisuunderr-orroveerchaargedd,perfformaancecanbeaadverrselyyafffecteed.RRodriiquezzetal.(19996)ffounddthaatpeerforrmancceoffanaircondditiooninggsysstemequiippeddwitthashorrttuubeoorifiicewwasaaffecctedbyiimproopercharrge((Figuure44.2.118).TheplootinnFiggure4.2..18cclearrlysshowssthaatfoora20%undeer-chhargeeinrefrrigerrant,,auunitwithhasshortttubeeoriifice