暖通空调专业外文翻译.docx

上传人:b****5 文档编号:12217112 上传时间:2023-04-17 格式:DOCX 页数:20 大小:35.66KB
下载 相关 举报
暖通空调专业外文翻译.docx_第1页
第1页 / 共20页
暖通空调专业外文翻译.docx_第2页
第2页 / 共20页
暖通空调专业外文翻译.docx_第3页
第3页 / 共20页
暖通空调专业外文翻译.docx_第4页
第4页 / 共20页
暖通空调专业外文翻译.docx_第5页
第5页 / 共20页
点击查看更多>>
下载资源
资源描述

暖通空调专业外文翻译.docx

《暖通空调专业外文翻译.docx》由会员分享,可在线阅读,更多相关《暖通空调专业外文翻译.docx(20页珍藏版)》请在冰豆网上搜索。

暖通空调专业外文翻译.docx

暖通空调专业外文翻译

暖通空调专业外文翻译

英文文献

AirConditioningSystems

Airconditioninghasrapidlygrownoverthepast50years,fromaluxurytoastandardsystemincludedinmostresidentialandcommercialbuildings.In1970,36%ofresidencesintheU.S.wereeitherfullyairconditionedorutilizedaroomairconditionerforcooling(Blue,etal.,1979).By1997,thisnumberhadmorethandoubledto77%,andthatyearalsomarkedthefirsttimethatoverhalf(50.9%)ofresidencesintheU.S.hadcentralairconditioners(CensusBureau,1999).Anestimated83%ofallnew

homesconstructedin1998hadcentralairconditioners(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.Theresidentialbuildingsectorisdominated

bysinglefamilyhomesandlow-riseapartments/condominiums.Thecoolingequipmentappliedinthesebuildingscomesinstandard“packages”thatare

oftenbothsizedandinstalledbytheairconditioningcontractor.

Thechapterstartswithageneraldiscussionofthevaporcompressionrefrigerationcyclethenmovestorefrigerantsandtheirselection,followedbypackagedChilledWaterSystems。

1.1VaporCompressionCycle

Eventhoughthereisalargerangeinsizesandvarietyofairconditioningsystemsusedinbuildings,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,suchasacapillarytubeor

2

shorttubeorifice,oranactivedevice,suchasathermalexpansionvalveorelectronicexpansionvalve.Thepurposeofthevalveistoregulatetheflowofrefrigeranttotheevaporatorsothattherefrigerantissuperheatedwhenitreachesthesuctionofthecompressor.

Attheexitoftheexpansionvalve,therefrigerantisatatemperaturebelowthatofthemedium(airorwater)tobecooled.Therefrigeranttravelsthroughaheatexchangercalledtheevaporator.Itabsorbsenergyfromtheairorwatercirculatedthroughtheevaporator.Ifairiscirculatedthroughtheevaporator,thesystemiscalleda.Ifwateriscirculatedthroughdirectexpansionsystem

theevaporator,itiscalledachiller.Ineithercase,therefrigerantdoes

notmakedirectcontactwiththeairorwaterintheevaporator.Therefrigerantisconvertedfromalowquality,two-phasefluidtoasuperheated

vaporundernormaloperatingconditionsintheevaporator.Thevaporformedmustberemovedbythecompressoratasufficientratetomaintainthelowpressureintheevaporatorandkeepthecycleoperating.

Allmechanicalcoolingresultsintheproductionofheatenergythatmustberejectedthroughthecondenser.Inmanyinstances,thisheatenergyisrejectedtotheenvironmentdirectlytotheairinthecondenserorindirectlytowaterwhereitisrejectedinacoolingtower.Withsomeapplications,itispossibletoutilizethiswasteheatenergytoprovidesimultaneousheatingtothebuilding.Recoveryofthiswasteheatattemperaturesupto65?

C(150?

F)canbeusedtoreducecostsforspaceheating.

Capacitiesofairconditioningareoftenexpressedineithertonsorkilowatts(kW)ofcooling.Thetonisaunitofmeasurerelatedtotheabilityofaniceplanttofreezeoneshortton(907kg)oficein24hr.Itsvalueis3.51kW(12,000Btu/hr).ThekWofthermalcoolingcapacityproducedbytheairconditionermustnotbeconfusedwiththeamountofelectricalpower(alsoexpressedinkW)requiredtoproducethecoolingeffect.

2.1RefrigerantsUseandSelection

Upuntilthemid-1980s,refrigerantselectionwasnotanissueinmost

3

buildingairconditioningapplicationsbecausetherewerenoregulationsontheuseofrefrigerants.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).

Zeotropesandazeotropesaremixturesoftwoormoredifferentrefrigerants.Azeotropicmixturechangessaturationtemperaturesasitevaporates(orcondenses)atconstantpressure.Thephenomenaiscalledtemperatureglide.Atatmosphericpressure,R-407Chasaboiling(bubble)pointof–44?

C(–47?

F)

andacondensation(dew)pointof–37?

C(–35?

F),whichgivesitatemperature

glideof7?

C(12?

F).Anazeotropicmixturebehaveslikeasinglecomponent

refrigerantinthatthesaturationtemperaturedoesnotchangeappreciablyasitevaporatesorcondensesatconstantpressure.R-410Ahasasmallenoughtemperatureglide(lessthan5.5?

C,10?

F)thatitisconsidereda

near-azeotropicrefrigerantmixture.

ASHRAEgroupsrefrigerantsbytheirtoxicityandflammability(ASHRAE,1994).GroupA1isnonflammableandleasttoxic,whileGroupB3isflammableand

4

mosttoxic.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,thelubrican

展开阅读全文
相关资源
猜你喜欢
相关搜索

当前位置:首页 > PPT模板 > 节日庆典

copyright@ 2008-2022 冰豆网网站版权所有

经营许可证编号:鄂ICP备2022015515号-1