Man and His Environment外文翻译.docx
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Man and His Environment外文翻译.docx
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ManandHisEnvironment外文翻译
ManandHisEnvironment
Bodyheatlosses.Thehumanbody,likeanyotherheatengine,consumesfuel(food)togenerateheat.Theheatleavesthebodyintheformofradiationandconvectionfromtheskin,evaporationofmoisturefromporesintheskin,andinthebreath.Radiationandconvectionoccuronlyiftheairtemperatureorthesurroundingsarebelowbloodheat.Ifapproachingorabovethiscondition,thesweatglandsexpandandheatisrejectedsolelybyevaporation.Highrelativehumiditycoupledwithhightemperaturerenderslifeincreasinglydifficult.
Atlowtemperatures,thebloodvesselsnearthesurfaceoftheskincloseup,leavingtheepidermisdryandactingasaninsulator.Shiveringisaprovisionofnaturetocausemuscularactivityandhenceincreasebloodcirculation.
Humancomfort.Fourfactorsaffectcomfort:
airtemperature,radiation,relativehumidity,andairmovement.Mostthermometersmeasureairtemperaturebutarenotinfluencedbyinfrared(long-wave)radiation,becausetheirglassenvelopesareopaquetosuchradiation.Thehumanbody,however,mayreceiveheatfromaradiantsource;ifso,airtemperaturemustbereducedifbodyheatreleaseistoremainnormal.Conversely,ifthebodyislosingheatbyradiationtoitssurroundings,suchastothecoldwallsofaroom,theairtemperaturemustberaisedforanequaldegreeofcomfort.
Thestudyofradianteffectsiscomplex.Themeanradianttemperatureinanenclosedspaceisthemeanofallthesurfacesboundingthespaceinproportiontotheirareasandtemperature,thelatterbeingcalculablefromtheknownconductivityofthematerialsandanassumedtemperaturedifferencebetweeninsideandoutside.Thiscalculationgivesonlyanapproximation;suchfactorsastheeffectofalargeareaofwindow,whichmaybecoldinwinterandhotinsummer,producevariationsindifferentpartsofaroom.Moreover,thebodyitselfissizeable,anditsresponsevariesaccordingtodifferencesofclothing.Thematterisfurthercomplicatedbytheintroductionofheatedsurfacestowarmthespaceandbytheentranceofheatthroughwindowsviasunshine.
Acloseapproximationtomeanradianttemperaturemaybeobtainedbytheuseofglobethermometer(Fif.1),consistingofanordinarythermometerinablackened,hollowmetalsphereaboutsixinches(15centimeters)indiameter.Ifsuspendedinanenclosureinwhichallsurfacesareatthesametemperatureastheair,theglobethermometerreadsthesameasanordinarythermometer,regardlessofairmovement;but,ifthesurfaceandairtemperaturesdiffer,theglobebecomeswarmerorcoolerinproportiontothepositiveornegativeradiationfallingonit.Giventheglobetemperatureandairtemperature,meanradianttemperaturemaybecalculated.
ResearchingreatBritainonfactoryworkersdoinglightsedentaryworkestablishedthatglobethermometertemperaturesof62-68°F(17-20°C)andairtemperaturesof60-68°F(16-20°C)wereregardedascomfortable.Personsseatedatrestrequiredtemperaturesafewdegreeshigher,asdidthosepersonswhowereusedtowarmerclimates.
Theabovecriteriatakenoaccountofhumidity.Incolderclimates,suchasinnorthernEurope,variationsinrelativehumiditywithintherange40-70percenthavelittleeffectoncomfort.Inwarmerclimates,inwhichsweatingplaysanimportantpartinheatrelease,humiditymustbetakenintoaccount.TheeffectivetemperaturescalewasdevelopedintheUnitedStatesinalongseriesofsubjectivetestsincarefullyconditionedrooms,fromwhichlinesofequalcomfortordiscomfort-effectivetemperaturelines-werederived.Limitswithinwhichindividualsfeelcomfortablemayalsobecharted,establishingwhatisknownasthe“comfortzone”,whichdiffersforsummerandwinter.
Theeffectivetemperaturescaletakesnoaccountofradiation.Thiscanbeincludedsimplybyusingaglobethermometerinsteadofanordinarythermometer.Thescalesoderivedisthecorrectedeffectivetemperaturescale,whichisnolongerwidelyused.Anotherscale,resultanttemperature,takesaccountofairtemperature,radiation,andairspeed.Itismeasuredbyasmallblackenedglobeandismoresensitivetoairtemperatureandmovementandlesstoradiationthantheglobethermometer.Thewetresultanttemperaturetakesaccountofhumiditybyusingawet-bulbthermometer–ausefuldevicefordeterminingrelativehumidity.Itconsistsofathermometerwiththebulbwrappedinclothkeptmoistenedbyasmallreservoirofwater.Evaporationcausescooling,theamountofcoolingdependingontherelativehumidity.
Anotherscaleisknownasenvironmentaltemperature;itisweightedinthatitisequivalenttotwo-thirdsmeanradianttemperatureandone-thirdairtemperature.Ittakesnoaccountofairmovementorhumidity.Itsapplicationisinthestudyofthethermalpropertiesofbuildings.
Otherinfluencesaffectingcomfort.Itispossibletoenumeratehereonlyafewoftheotherfactorsaffectingcomfort.
Qualityofheatradiation.Ithaslongbeenknownthatthehumanbodyderivesgreatercomfortwhentheairtemperatureislowerthanthatofthesurroundingwallandothersurfaces.Thisprobablyaccountsforthecomfortofthepaneledroomcommoninthe18thand19thcenturies;eventhoughthesourceofheatwasnomorethananopenfire,thesurfacesofthetimberpanelingwerequicklywarmedbyradiation,whiletheairdrawninbythelargeflueensuredalowreadingofthethermometer.
Radiantheatingmakesuseofextendedsurfacesofwallorceilingheatedtosome100°F(38°C)orfloorto75°F(24°C).Airtemperaturemaythenbesome5°F(3°C)belowthatrequiredwithaconvectivesystem.Unfortunately,theeffectoflow-temperatureradiationontheskin,coupledwiththelackofairmovementfromconvectioncurrents,producesanenervatingcondition.Consequently,ithasbeensuggestedthataventilationsystemaccompanythisformofheatingtostimulateafresheningatmosphere.
Radiantheatsourcesemployinghighertemperatures,suchasinfraredpanelsorluminousreflectorelementselectricallyheated,presenttheproblemofdirectionaleffects;acertainintensityacceptableonthefeetmaybeuncomfortableifdirectedatthehead.Atanairtemperatureof50°F(10°C)orunder,itisbelievedimpossibletocreateafeelingofcomfort,nomatterhowgreatthesupplyofradiantheat.Thesetwoconsiderationsareboundupinone,namelythatasameansofdistributionofwarmth,veryhigh-temperatureradiantheatsourcesareinherentlyunsatisfactory.
Theeffectofradiantheatsourcesonthehumanbodyrequiresspecialattention.Thegreatmeritoftheopencoalfirewasitswiderangeandconstantvariationofradiantwavelength,fromthehighincandescentpartsofthefuelandflamestothedull,low-temperatureradiationfromthesurroundingfirebrickandcast-ironortiledecoration.Althoughthefireplaceisdecriedasaninefficientitemofheatingequipment,itdoeshavebeneficialeffects,onalimitedscale,roombyroom.Itisopentoquestion,however,whethertheeffectsofvariouswavelengthsofradiationonthehumanskinandonthestimulationofthesensesasawholehavebeenthoroughlyexplored.
Theunrelievedmonotonyofacertainlimitedrangeofwavelengths,asfromagasfireorelectricheater,cancausedrynessandintenseirritationoftheskin.Thehumansystemseemstoneedstimulationfromconstantlyvaryingconditions.
Temperaturegradients.Becausehotairrises,asystemofheatingrelyingonwarmingofairforheatdistributionresultsinahighertemperatureattheceilingthannearthefloor.Anexceptionisafloor-heatingsystem,inwhichconvectionfromthefloorisbalancedbyradiationatthefloorlevel.
Inthecaseofalargeopenspace,suchasafactory,asystemthatminimizestemperaturegradientismoreefficientthanoneinwhichtheeffectisdisregarded.Thus,theoncecommonuseofoverheadpipesproducedinordinatelyhightemperaturegradientsandhighrooflosses.
Radiant-heatingsystemsingeneralminimizetemperaturegradients.Forced-convectionsystemsarepreferabletonaturalconvection.Radiatorsemployingextendedsurfacesbelowwindowsgivelowerairtemperaturerisethanthoseconcentratedoninnerwalls.
Uniformityofcondition.Inanair-conditionedbuilding,airtemperaturesdifferlittlefromthoseofsurroundingsurface.Thus,astateofthermometricuniformitymayexist,exceptinsofarasairmovementisconcerned.Comfort,asdefinedbyacertainrangeofeffectivetemperature,islikelytobeachieved,butitispossiblethatthehumanbodycontinuouslysoenvelopedmaysufferfromnotonlyphysiologicalbutalsopsychologicalenervation.
Airmovement.Theeffectivetemperaturedependsonairvelocity.Thehighertheairmotion,thelowertheeffectivetemperatureforagiventemperatureandrelativehumidity.Aneffectivetemperatureof70°F(21°C)withanairspeedof30feet(ninemeters)perminute,forinstance,fallsto60°F(16°C)atanairspeedof600feet(180meters)perminute.Thevariationdiminisheswithincreasingtemperatureuntil,atbloodheat,airmotionceasestohaveanyeffect.Itisforthisreasonthatinhot,crowedatmospheresfanningseemstogivelittlealleviation.
Airmovementupto50feet(15meters)perminuteinanoccupiedspaceisusuallyconsideredacceptableanddesirable,risinglocallyperhapsto60feet(18meters)perminuteandproducingsomedegreeofturbulence.Theseisamuchstrongerriskofdraftsathigherairspeeds.
Theproblemfortheair-conditioningengineerisoftentofindwaysofintroducinglargequantitiesofairintoaspacewhilekeepingvelocitiesintheoccupiedregionwithinacceptablelimits.Raisingtherela
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