空調(diào)系統(tǒng)中英文翻譯、外文文獻翻譯、外文翻譯

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.

空調(diào)系統(tǒng)過去50年以來，空調(diào)得到了快速的發(fā)展，從曾經(jīng)的奢侈品發(fā)展到可應用于大多數(shù)住宅和商業(yè)建筑的比較標準的系統(tǒng)。中央空調(diào)在商業(yè)建筑物中也得到了快速的發(fā)展，從1970年到1995年，有空調(diào)的商業(yè)建筑物的百分比從54%增加到73%。建筑物中的空氣調(diào)節(jié)通常是利用機械設備或熱交換設備完成。在大多數(shù)應用中，建筑物中的空調(diào)器為維持舒適要求必須既能制冷又能除濕，空調(diào)系統(tǒng)也用于其他的場所，例如汽車、卡車、飛機、船和工業(yè)設備，然而，在本章中，僅說明空調(diào)在商業(yè)和住宅建筑中的應用。商業(yè)的建筑物從比較大的多層的辦公大樓到街角的便利商店，占地面積和類型差別很大，因此應用于這類建筑的設備類型比較多樣，對于比較大型的建筑物，空調(diào)設備設計是總系統(tǒng)設計的一部分，這部分包括如下項目：例如一個管道系統(tǒng)設計，空氣分配系統(tǒng)設計，和冷卻塔設計等。居住的建筑物被劃分成單獨的家庭或共有式公寓，應用于這些建筑物的冷卻設備通常都是標準化組裝的，由空調(diào)廠家進行設計尺寸和安裝。本章節(jié)首先對蒸汽壓縮制冷循環(huán)作一個概述，接著介紹制冷劑及制冷劑的選擇，最后介紹冷水機組。1.蒸汽壓縮循環(huán)雖然空調(diào)系統(tǒng)應用在建筑物中有較大的尺寸和多樣性，大多數(shù)的系統(tǒng)利用蒸汽壓縮循環(huán)來制取需要的冷量和除濕，這個循環(huán)也用于制冷和冰凍食物和汽車的空調(diào)，在1834年，一個名叫帕金斯的人在倫敦獲得了機械制冷系統(tǒng)的第一專利權，在1857年，詹姆士和賽博生產(chǎn)出第一個有活力的商業(yè)系統(tǒng)，除了蒸汽壓縮循環(huán)之外，有兩種不常用的制冷方法在建筑物中被應用：吸收式循環(huán)和蒸發(fā)式冷卻，這些將在后面的章節(jié)中講到。對于蒸汽壓縮制冷循環(huán)，有一種叫制冷劑的工作液體，它能在適當?shù)墓に囋O備設計壓力下蒸發(fā)和冷凝。每個蒸汽壓縮制冷系統(tǒng)中都有四大部件，它們是壓縮機、冷凝器、節(jié)流裝置和蒸發(fā)器。壓縮機提升制冷劑的蒸汽壓力以便使制冷劑的飽和溫度微高于在冷凝器中冷卻介質(zhì)溫度，使用的壓縮機類型和系統(tǒng)的設備有關，比較大的電冷卻設備使用一個離心式的壓縮機而小的住宅設備使用的是一種往復或漩渦式壓縮機。冷凝器是一個熱交換器，用于將制冷劑的熱量傳遞到冷卻介質(zhì)中，制冷劑進入冷凝器變成過冷液體，用于冷凝器中的典型冷卻介質(zhì)是空氣和水，大多數(shù)住宅建筑的冷凝器中使用空氣作為冷卻介質(zhì)，而大型系統(tǒng)的冷凝器中采用水作為冷卻介質(zhì)。液體制冷劑在離開冷凝器之后，在膨脹閥中節(jié)流到一個更低的壓力。膨脹閥是一個節(jié)流的裝置，例如毛細管或有孔的短管，或一個活動的裝置，例如熱力膨脹閥或電子膨脹閥，膨脹閥的作用是到蒸發(fā)器中分流制冷劑以便當它到壓縮機吸入口的時候，制冷劑處于過熱狀態(tài)，在膨脹閥的出口，制冷劑的溫度在介質(zhì)(空氣或水)的溫度以下。之后制冷劑經(jīng)過一個熱交換器叫做蒸發(fā)器，它吸收通過蒸發(fā)器的空氣或水的熱量，如果空氣經(jīng)過蒸發(fā)器在流通，該系統(tǒng)叫直接膨脹式系統(tǒng)，如果水經(jīng)過蒸發(fā)器在流通，它叫冷卻設備，在任何情況下，在蒸發(fā)器中的制冷劑不直接和空氣或水接觸，在蒸發(fā)器中，制冷劑從一個低品位的兩相液體轉(zhuǎn)換成在正常的工藝條件下過熱的蒸汽。蒸汽的形成要以一定的足夠速度被壓縮機排出以維持在蒸發(fā)器中低壓和保持循環(huán)進行。2.制冷劑的使用和選擇直到20世紀80年代中葉，制冷劑的選擇在大多數(shù)的建筑物空調(diào)設備中不是一個問題，因為在制冷劑的使用上還沒有統(tǒng)一的的標準，在以前，用于建筑物空調(diào)設備的大多數(shù)制冷劑是氟氯碳化物和氟氯碳氫化物，且大多數(shù)的制冷劑是無毒的和不可燃的，然而，最近的美國聯(lián)邦的標準(環(huán)保署1993a；環(huán)保署1993b)和國際的協(xié)議(UNEP，1987)已經(jīng)限制了氟氯碳化物和氟氯碳氫化物的制造和使用，現(xiàn)在，氟氯碳化物和氟氯碳氫化物在一些場合依然被使用，對制冷劑的理解能幫助建筑物擁有者或者工程師更好的了解關于為特定的設備下如何選擇制冷劑，這里將討論不同制冷劑的使用并給出影響它們使用的建筑空調(diào)設備和標準。美國社會的供暖、制冷和空調(diào)工程師學會(ASHRAE)有一個標準的限制系統(tǒng)用來區(qū)分制冷劑，許多流行的氟氯碳化物，氟氯碳氫化物和氟碳化物的制冷劑是在甲烷和乙烷的制冷劑系列中，因為鹵素元素的存在他們被叫作碳化鹵或鹵化的碳化氫，例如氟或氯。ASHRAE組制冷劑根據(jù)它們的毒性和易燃性(ASHRAE，1994)劃分的。A1組合是不燃燒的和最沒有毒的，而B3組是易燃的和最有毒的，以空氣為媒介的制冷劑最高安全限制是毒性，如果制冷劑在少于每百萬分之400是無毒的，它是一個A級制冷劑，如果對泄露少于每百萬分之400是有毒的，那么該物質(zhì)被稱B級制冷劑，這幾個級別表示制冷劑的易燃性，表4.2.1的最后一欄列出了常用的制冷劑的毒性和易燃的等級。制冷劑22屬于HCFC，在多數(shù)的相同設備中被用，也是在多數(shù)往復和螺旋式冷卻設備和小型商業(yè)和住宅的集中式設備中的首選制冷劑，它可以在一個更高的壓力下運行，這一點要優(yōu)于R-11或R-12中的任何一個。從2004開始，HCFCs的制造將會受到限制。在2010年，R-22不能在新的空調(diào)設備中被使用。2020年之后，R-22不允許生產(chǎn)(環(huán)保署，1993b)。R-407C和R-410A是HFCs的兩種混合物，兩者都是R-22的替代品，R-407C預期將很快地替換R-22，在空調(diào)設備中，它的蒸發(fā)和冷凝壓力接近R-22(表格4.2.3)。然而，用R-407C來替換R-22應該在和設備制造者商議之后才能進行，至少潤滑油和膨脹裝置將需要更換。在1998年，第一個使用R-410A的空調(diào)設備的住宅在美國出現(xiàn)。使用R-410A的系統(tǒng)運作中，壓力大約比R-22高50%(表4.2.3)；因此，R-410A不能夠用于當作速凍制冷劑來替代R-22。R-410A系統(tǒng)利用特定的壓縮機、膨脹閥和熱交換器來利用該制冷劑。氨廣泛地被在工業(yè)的冷卻設備和氨水吸收式制冷中用，它具有可燃性并且毒性等級為B，因此在商業(yè)建筑物中使用受到限制，除非冷卻設備的制造工廠獨立于被冷卻的建