空调系统中英文翻译、外文文献翻译、外文翻译

PAGEPAGE4AirConditioningSystemsAirconditioninghasrapidlygrownoverthepast50years,fromaluxurytoastandardsystemincludedinmostresidentialandcommercialbuildings.Airconditioninghasalsogrownrapidlyincommercialbuildings.From1970to1995,thepercentageofcommercialbuildingswithairconditioningincreasedfrom54to73%.Airconditioninginbuildingsisusuallyaccomplishedwiththeuseofmechanicalorheat-activatedequipment.Inmostapplications,theairconditionermustprovidebothcoolinganddehumidificationtomaintaincomfortinthebuilding.Airconditioningsystemsarealsousedinotherapplications,suchasautomobiles,trucks,aircraft,ships,andindustrialfacilities.However,thedescriptionofequipmentinthischapterislimitedtothosecommonlyusedincommercialandresidentialbuildings.Commercialbuildingsrangefromlargehigh-riseofficebuildingstothecornerconveniencestore.Becauseoftherangeinsizeandtypesofbuildingsinthecommercialsector,thereisawidevarietyofequipmentappliedinthesebuildings.Forlargerbuildings,theairconditioningequipmentispartofatotalsystemdesignthatincludesitemssuchasapipingsystem,airdistributionsystem,andcoolingtower.Theresidentialbuildingsectorisdominatedbysinglefamilyhomesandlow-riseapartments/condominiums.Thecoolingequipmentappliedinthesebuildingscomesinstandard“packages”thatareoftenbothsizedandinstalledbytheairconditioningcontractor.Thechapterstartswithageneraldiscussionofthevaporcompressionrefrigerationcyclethenmovestorefrigerantsandtheirselection,followedbypackagedChilledWaterSystems.1.VaporCompressionCycleEventhoughthereisalargerangeinsizesandvarietyofairconditioningsystemsusedinbuildings,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.2.RefrigerantsUseandSelectionUpuntilthemid-1980s,refrigerantselectionwasnotanissueinmostbuildingairconditioningapplicationsbecausetherewerenoregulationsontheuseofrefrigerants.Manyoftherefrigerantshistoricallyusedforbuildingairconditioningapplicationshavebeenchlorofluorocarbons(CFCs)andhydrochlorofluorocarbons(HCFCs).Mostoftheserefrigerantsarenontoxicandnonflammable.However,recentU.S.federalregulations(EPA1993a;EPA1993b)andinternationalagreements(UNEP,1987)haveplacedrestrictionsontheproductionanduseofCFCsandHCFCs.Hydrofluorocarbons(HFCs)arenowbeingusedinsomeapplicationswhereCFCsandHCFCswereused.Havinganunderstandingofrefrigerantscanhelpabuildingownerorengineermakeamoreinformeddecisionaboutthebestchoiceofrefrigerantsforspecificapplications.Thissectiondiscussesthedifferentrefrigerantsusedinorproposedforbuildingairconditioningapplicationsandtheregulationsaffectingtheiruse.TheAmericanSocietyofHeating,RefrigeratingandAirConditioningEngineers(ASHRAE)hasastandardnumberingsystem,foridentifyingrefrigerants(ASHRAE,1992).ManypopularCFC,HCFC,andHFCrefrigerantsareinthemethaneandethaneseriesofrefrigerants.Theyarecalledhalocarbons,orhalogenatedhydrocarbons,becauseofthepresenceofhalogenelementssuchasfluorineorchlorine(King,1986).ASHRAEgroupsrefrigerantsbytheirtoxicityandflammability(ASHRAE,1994).GroupA1isnonflammableandleasttoxic,whileGroupB3isflammableandmosttoxic.Toxicityisbasedontheuppersafetylimitforairborneexposuretotherefrigerant.Iftherefrigerantisnontoxicinquantitieslessthan400partspermillion,itisaClassArefrigerant.Ifexposuretolessthan400partspermillionistoxic,thenthesubstanceisgiventheBdesignation.Thenumericaldesignationsrefertotheflammabilityoftherefrigerant.ThelastcolumnofTable4.2.1showsthetoxicityandflammabilityratingofcommonrefrigerants.Refrigerant22isanHCFC,isusedinmanyofthesameapplications,andisstilltherefrigerantofchoiceinmanyreciprocatingandscrewchillersaswellassmallcommercialandresidentialpackagedequipment.ItoperatesatamuchhigherpressurethaneitherR-11orR-12.RestrictionsontheproductionofHCFCswillstartin2004.In2010,R-22cannotbeusedinnewairconditioningequipment.R-22cannotbeproducedafter2020(EPA,1993b).R-407CandR-410AarebothmixturesofHFCs.BothareconsideredreplacementsforR-22.R-407Cisexpectedtobeadrop-inreplacementrefrigerantforR-22.ItsevaporatingandcondensingpressuresforairconditioningapplicationsareclosetothoseofR-22(Table4.2.3).However,replacementofR-22withR-407Cshouldbedoneonlyafterconsultingwiththeequipmentmanufacturer.Ataminimum,thelubricantandexpansiondevicewillneedtobereplaced.Thefirstresidential-sizedairconditioningequipmentusingR-410AwasintroducedintheU.S.in1998.SystemsusingR-410Aoperateatapproximately50%higherpressurethanR-22(Table4.2.3);thus,R-410Acannotbeusedasadrop-inrefrigerantforR-22.R-410Asystemsutilizecompressors,expansionvalves,andheatexchangersdesignedspecificallyforusewiththatrefrigerant.Ammoniaiswidelyusedinindustrialrefrigerationapplicationsandinammoniawaterabsorptionchillers.ItismoderatelyflammableandhasaclassBtoxicityratingbuthashadlimitedapplicationsincommercialbuildingsunlessthechillerplantcanbeisolatedfromthebuildingbeingcooled(Toth,1994,Stoecker,1994).Asarefrigerant,ammoniahasmanydesirablequalities.Ithasahighspecificheatandhighthermalconductivity.Itsenthalpyofvaporizationistypically6to8timeshigherthanthatofthecommonlyusedhalocarbons,anditprovideshigherheattransfercomparedtohalocarbons.Itcanbeusedinbothreciprocatingandcentrifugalcompressors.Researchisunderwaytoinvestigatetheuseofnaturalrefrigerants,suchascarbondioxide(R-744)andhydrocarbonsinairconditioningandrefrigerationsystems(Bullock,1997,andKramer,1991).CarbondioxideoperatesatmuchhigherpressuresthanconventionalHCFCsorHFCsandrequiresoperationabovethecriticalpointintypicalairconditioningapplications.Hydrocarbonrefrigerants,oftenthoughtofastoohazardousbecauseofflammability,canbeusedinconventionalcompressorsandhavebeenusedinindustrialapplications.R-290,propane,hasoperatingpressuresclosetoR-22andhasbeenproposedasareplacementforR-22(Kramer,1991).Currently,therearenocommercialsystemssoldintheU.S.forbuildingoperationsthatuseeithercarbondioxideorflammablerefrigerants.3.ChilledWaterSystemsChilledwatersystemswereusedinlessthan4%ofcommercialbuildingsintheU.S.in1995.However,becausechillersareusuallyinstalledinlargerbuildings,chillerscooledover28%oftheU.S.commercialbuildingfloorspacethatsameyear(DOE,1998).Fivetypesofchillersarecommonlyappliedtocommercialbuildings:reciprocating,screw,scroll,centrifugal,andabsorption.Thefirstfourutilizethevaporcompressioncycletoproducechilledwater.Theydifferprimarilyinthetypeofcompressorused.Absorptionchillersutilizethermalenergy(typicallysteamorcombustionsource)inanabsorptioncyclewitheitheranammonia-waterorwater-lithiumbromidesolutiontoproducechilledwater.4.OverallSystemAnestimated86%ofchillersareappliedinmultiplechillerarrangementslikethatshowninthefigure(BitondoandTozzi,1999).Inchilledwatersystems,returnwaterfromthebuildingiscirculatedthrougheachchillerevaporatorwhereitiscooledtoanacceptabletemperature(typically4to7°C)(39to45°F).Thechilledwateristhendistributedtowater-to-airheatexchangersspreadthroughoutthefacility.Intheseheatexchangers,airiscooledanddehumidifiedbythecoldwater.Duringtheprocess,thechilledwaterincreasesintemperatureandmustbereturnedtothechiller(s).Thechillersarewater-cooledchillers.Wateriscirculatedthroughthecondenserofeachchillerwhereitabsorbsheatenergyrejectedfromthehighpressurerefrigerant.Thewateristhenpumpedtoacoolingtowerwherethewateriscooledthroughanevaporationprocess.Chillerscanalsobeaircooled.Inthisconfiguration,thecondenserwouldbearefrigerant-to-airheatexchangerwithairabsorbingtheheatenergyrejectedbythehighpressurerefrigerant.5.VaporCompressionChillersThenominalcapacityrangesforthefourtypesofelectricallydrivenvaporcompressionchillers.Eachchillerderivesitsnamefromthetypeofcompressorusedinthechiller.Thesystemsrangeincapacitiesfromthesmallestscroll(30kW;8tons)tothelargestcentrifugal(18,000kW;5000tons).ChillerscanutilizeeitheranHCFC(R-22andR-123)orHFC(R-134a)refrigerant.Thesteadystateefficiencyofchillersisoftenstatedasaratioofthepowerinput(inkW)tothechillingcapacity(intons).Acapacityratingofonetonisequalto3.52kWor12,000btu/h.Withthismeasureofefficiency,thesmallernumberisbetter.centrifugalchillersarethemostefficient;whereas,reciprocatingchillershavetheworstefficiencyofthefourtypes.Theefficiencynumbersprovidedinthetablearethesteadystatefull-loadefficiencydeterminedinaccordancetoASHRAEStandard30(ASHRAE,1995).Theseefficiencynumbersdonotincludetheauxiliaryequipment,suchaspumpsandcoolingtowerfansthatcanaddfrom0.06to0.31kW/tontothenumbersshownChillersrunatpartloadcapacitymostofthetime.Onlyduringthehighestthermalloadsinthebuildingwillachilleroperatenearitsratedcapacity.Asaconsequence,itisimportanttoknowhowtheefficiencyofthechillervarieswithpartloadcapacity.arepresentativedatafortheefficiency(inkW/ton)asafunctionofpercentagefullloadcapacityforareciprocating,screw,andscrollchillerplusacentrifugalchillerwithinletvanecontrolandonewithvariablefrequencydrive(VFD)forthecompressor.Thereciprocatingchillerincreasesinefficiencyasitoperatesatasmallerpercentageoffullload.Incontrast,theefficiencyofacentrifugalwithinletvanecontrolisrelativelyconstantuntiltheloadfallstoabout60%ofitsratedcapacityanditskW/tonincreasestoalmosttwiceitsfullyloadedvalue.In1998,theAirConditioningandRefrigerationInstitute(ARI)developedanewstandardthatincorporatesintotheirratingspartloadperformanceofchillers(ARI1998c).Partloadefficiencyisexpressedbyasinglenumbercalledtheintegratedpartloadvalue(IPLV).TheIPLVtakesdatasimilartothatinFigure4.2.3andweightsitatthe25%,50%,75%,and100%loadstoproduceasingleintegratedefficiencynumber.Theweightingfactorsattheseloadsare0.12,0.45,0.42,and0.01,respectively.TheequationtodetermineIPLVis:MostoftheIPLVisdeterminedbytheefficiencyatthe50%and75%partloadvalues.Manufacturerswillprovide,onrequest,IPLVsaswellaspartloadefficiencies.Thefourcompressorsusedinvaporcompressionchillersareeachbrieflydescribedbelow.Whilecentrifugalandscrewcompressorsareprimarilyusedinchillerapplications,reciprocatingandscrollcompressorsarealsousedinsmallerunitarypackagedairconditionersandheatpumps.

空调系统过去50年以来，空调得到了快速的发展，从曾经的奢侈品发展到可应用于大多数住宅和商业建筑的比较标准的系统。中央空调在商业建筑物中也得到了快速的发展，从1970年到1995年，有空调的商业建筑物的百分比从54%增加到73%。建筑物中的空气调节通常是利用机械设备或热交换设备完成。在大多数应用中，建筑物中的空调器为维持舒适要求必须既能制冷又能除湿，空调系统也用于其他的场所，例如汽车、卡车、飞机、船和工业设备，然而，在本章中，仅说明空调在商业和住宅建筑中的应用。商业的建筑物从比较大的多层的办公大楼到街角的便利商店，占地面积和类型差别很大，因此应用于这类建筑的设备类型比较多样，对于比较大型的建筑物，空调设备设计是总系统设计的一部分，这部分包括如下项目：例如一个管道系统设计，空气分配系统设计，和冷却塔设计等。居住的建筑物被划分成单独的家庭或共有式公寓，应用于这些建筑物的冷却设备通常都是标准化组装的，由空调厂家进行设计尺寸和安装。本章节首先对蒸汽压缩制冷循环作一个概述，接着介绍制冷剂及制冷剂的选择，最后介绍冷水机组。1.蒸汽压缩循环虽然空调系统应用在建筑物中有较大的尺寸和多样性，大多数的系统利用蒸汽压缩循环来制取需要的冷量和除湿，这个循环也用于制冷和冰冻食物和汽车的空调，在1834年，一个名叫帕金斯的人在伦敦获得了机械制冷系统的第一专利权，在1857年，詹姆士和赛博生产出第一个有活力的商业系统，除了蒸汽压缩循环之外，有两种不常用的制冷方法在建筑物中被应用：吸收式循环和蒸发式冷却，这些将在后面的章节中讲到。对于蒸汽压缩制冷循环，有一种叫制冷剂的工作液体，它能在适当的工艺设备设计压力下蒸发和冷凝。每个蒸汽压缩制冷系统中都有四大部件，它们是压缩机、冷凝器、节流装置和蒸发器。压缩机提升制冷剂的蒸汽压力以便使制冷剂的饱和温度微高于在冷凝器中冷却介质温度，使用的压缩机类型和系统的设备有关，比较大的电冷却设备使用一个离心式的压缩机而小的住宅设备使用的是一种往复或漩涡式压缩机。冷凝器是一个热交换器，用于将制冷剂的热量传递到冷却介质中，制冷剂进入冷凝器变成过冷液体，用于冷凝器中的典型冷却介质是空气和水，大多数住宅建筑的冷凝器中使用空气作为冷却介质，而大型系统的冷凝器中采用水作为冷却介质。液体制冷剂在离开冷凝器之后，在膨胀阀中节流到一个更低的压力。膨胀阀是一个节流的装置，例如毛细管或有孔的短管，或一个活动的装置，例如热力膨胀阀或电子膨胀阀，膨胀阀的作用是到蒸发器中分流制冷剂以便当它到压缩机吸入口的时候，制冷剂处于过热状态，在膨胀阀的出口，制冷剂的温度在介质(空气或水)的温度以下。之后制冷剂经过一个热交换器叫做蒸发器，它吸收通过蒸发器的空气或水的热量，如果空气经过蒸发器在流通，该系统叫直接膨胀式系统，如果水经过蒸发器在流通，它叫冷却设备，在任何情况下，在蒸发器中的制冷剂不直接和空气或水接触，在蒸发器中，制冷剂从一个低品位的两相液体转换成在正常的工艺条件下过热的蒸汽。蒸汽的形成要以一定的足够速度被压缩机排出以维持在蒸发器中低压和保持循环进行。2.制冷剂的使用和选择直到20世纪80年代中叶，制冷剂的选择在大多数的建筑物空调设备中不是一个问题，因为在制冷剂的使用上还没有统一的的标准，在以前，用于建筑物空调设备的大多数制冷剂是氟氯碳化物和氟氯碳氢化物，且大多数的制冷剂是无毒的和不可燃的，然而，最近的美国联邦的标准(环保署1993a；环保署1993b)和国际的协议(UNEP，1987)已经限制了氟氯碳化物和氟氯碳氢化物的制造和使用，现在，氟氯碳化物和氟氯碳氢化物在一些场合依然被使用，对制冷剂的理解能帮助建筑物拥有者或者工程师更好的了解关于为特定的设备下如何选择制冷剂，这里将讨论不同制冷剂的使用并给出影响它们使用的建筑空调设备和标准。美国社会的供暖、制冷和空调工程师学会(ASHRAE)有一个标准的限制系统用来区分制冷剂，许多流行的氟氯碳化物，氟氯碳氢化物和氟碳化物的制冷剂是在甲烷和乙烷的制冷剂系列中，因为卤素元素的存在他们被叫作碳化卤或卤化的碳化氢，例如氟或氯。ASHRAE组制冷剂根据它们的毒性和易燃性(ASHRAE，1994)划分的。A1组合是不燃烧的和最没有毒的，而B3组是易燃的和最有毒的，以空气为媒介的制冷剂最高安全限制是毒性，如果制冷剂在少于每百万分之400是无毒的，它是一个A级制冷剂，如果对泄露少于每百万分之400是有毒的，那么该物质被称B级制冷剂，这几个级别表示制冷剂的易燃性，表4.2.1的最后一栏列出了常用的制冷剂的毒性和易燃的等级。制冷剂22属于HCFC，在多数的相同设备中被用，也是在多数往复和螺旋式冷却设备和小型商业和住宅的集中式设备中的首选制冷剂，它可以在一个更高的压力下运行，这一点要优于R-11或R-12中的任何一个。从2004开始，HCFCs的制造将会受到限制。在2010年，R-22不能在新的空调设备中被使用。2020年之后，R-22不允许生产(环保署，1993b)。R-407C和R-410A是HFCs的两种混合物，两者都是R-22的替代品，R-407C预期将很快地替换R-22，在空调设备中，它的蒸发和冷凝压力接近R-22(表格4.2.3)。然而，用R-407C来替换R-22应该在和设备制造者商议之后才能进行，至少润滑油和膨胀装置将需要更换。在1998年，第一个使用R-410A的空调设备的住宅在美国出现。使用R-410A的系统运作中，压力大约比R-22高50%(表4.2.3)；因此，R-410A不能够用于当作速冻制冷剂来替代R-22。R-410A系统利用特定的压缩机、膨胀阀和热交换器来利用该制冷剂。氨广泛地被在工业的冷却设备和氨水吸收式制冷中用，它具有可燃性并且毒性等级为B，因此在商业建筑物中使用受到限制，除非冷却设备的制造工厂独立于被冷却的建