Unit 35MechanicalEngineeringDesignProcessText Thedecisionsmadebythedesignersofthebuilding'sheating,ventilating,andair-conditioning(HVAC)systemarecrucialindeterminingthermalcomfort,thequalityoftheindoorair,andtheefficiencyofenergyusebythebuilding.Airexchangeratesaffecttheamountofenergyusedtoheatorcoolfreshair,andtheenergylostwhenusedairisexhausted.TheAmericanSocietyofHeating,Refrigerating,andAir-ConditioningEngineers(ASHRAE)requirementsforventilationincludeminimumratesforreplacingpreviouslycirculatedairinthebuildingwithfreshair. Energycostscanbereducedoreliminatedbyimprovingbuildinginsulation,lightingdesign,andtheefficiencyofHVACandotherbuildingequipment.Buildingsthatallownaturalventilation,andthosethatemploysuchtechniquesasheatreclamation,thermal-storagesystems,andflexibleairhandlingandchillerunitslowerenergyuseandreducecosts.Thearchitectandengineersusuallymakethedecisionsonwhatsystemstoemploy,buttheresponsibilityforfindingappropriatesolutionsdependsoncreativityandintegratedeffortsoftheentiredesignteam,inwhichtheinteriordesignershouldplayasignificantrole.Text Themechanicalsystemsofthebuildinghavetheirownmodelcodes,whicharegearedtowardprofessionalmechanicalengineersandinstallers.Theyarebasedonthreemodelcodes:theBuildingOfficialsCodeAdministratorsInternational(BOCA)NationalMechanicalCode(NMC),theStandardNationalMechanicalCode(SMC),andtheUniformNationalMechanicalCode(UMC)."Thesemodelcodesarerevisedeverythreeyears.

Asaninteriordesigner,youwillrarelyneedtorefertothemechanicalcodes,butyoushouldbefamiliarwithsomeoftheirgeneralrequirementsandterms,especiallythoseaffectingenergyconservationrequirements.Inbuildingswherethereisaminimumofmechanicalwork,themechanicalengineerorcontractorwillworkdirectlyofftheinteriordesignersdrawings.Forexample,theinteriordesigndrawingsmaybethesourceforinformationinarenovationprojectwhereafewsupplydiffusersorreturngrillesarebeingaddedtoanexistingsystem.Inanyevent,youmayneedtocoordinateyourpreliminarydesignwiththemechanicalengineerorcontractortomakesureyouleaveenoughroomforclearancesaroundHVACequipment.Text Themechanicalengineer,liketheinteriordesigner,istryingtoachieveanenvironmentwherepeoplearecomfortable,andtomeettherequirementsofapplicablecodes.Bycalculatinghowmuchheatingorcoolingisneededtoachievecomfort,theengineerisabletodevelopdesignstrategiesthataffectboththearchitectureandthemechanicalsystemsofthebuilding,suchastheoptimalsizeofwindows,ortherelativeamountsofinsulationorthermalmass.TheengineerwillfigureouthowbigtheUVACsystemcomponentsshouldbetoprovideenoughheatingand/orcoolingforthemostextremeconditionsthebuildingislikelytoexperience.Theengineerwillcalculatetheamountofenergyusedfornormalconditionsinatypicalseasonandadjustthedesigntoreducelong-termenergyuse.Thenumberofpeopleusingthebuildingbothseasonallyandhourlyisalsotakenintoaccount. Theamountofheatgainedorlostfromtheoutsideenvironmentwillbeconsidered.Thematerials,areas,andratesofheatflowthroughthebuilding'senvelopeaffectthiscalculation.Theamountoffreshairintroducedintothesystemalsoinfluencesthesecalculations,sotheengineerwilllookatthevolumesofthespacesinthebuildingandtheratesoffreshairexchange.Theengineerwillsuggestwindowlocationsandotherdesignelementsthatminimizetheheatgainwithinthebuilding.TextPHASESOFTHEDESIGNPROCESS

Thephasesoftheengineeringdesignprocessaresimilartothoseofarchitectsandinteriordesigners:preliminarydesign,designdevelopment,designfinalizationandspecification,andtheconstructionphase.Duringthepreliminarydesignphase,theengineerconsidersthemostgeneralcombinationsofcomfortrequirementsandclimatecharacteristics.Thescheduleofactivitiesthatwilltakeplaceinthespaceislisted,alongwiththeconditionsrequiredforcomfortduringperformance.Theengineeranalyzesthesite'senergyresourcesandlistsstrategiestodesignwiththeclimate.Buildingformalternativesareconsideredanddiscussedwiththearchitect.Availablesystemsarereviewed,includingbothpassive(nonmechanical)andactivealternatives.Thentheengineerfiguresoutthesizeofoneormorealternativesystemsusinggeneraldesignguidelines. Insmallerbuildings,thearchitectmaydothesystemdesign.Forlarger,morecomplexbuildings,themechanicalengineerwillworkasateamwitharchitects,landscapearchitects,andtheinteriordesigner.Theteamapproachhelpstoassessthevalueofavarietyofdesignalternativesarisingfromdifferentperspectives.Whenmutualgoalsareagreeduponearlyinthedesignprocess,thisteamapproachcanleadtocreativeinnovations.TextThemorethatthesiting,layout,andorientationofthebuildingreducesheatloss,thelessenergythehealingandcoolingequipmentconsumes.OpportunitiesmayariseforthedesignoftheHVACsystemtobeexpressedintheformofthebuilding.Creativeteamworkcanleadtonewdesignsthatofferbetterenvironmentswithlessenergyuse,andthatcanbeappliedtomanyotherbuildingslateron. Duringthedesigndevelopmentphase,onealternativeisusuallychosenaspresentingthebestcombinationofaesthetic,social,andtechnicalsolutionsforthebuilding'sprogram.Theengineerisgiventhelatestsetofdrawingsandprogramminginformationforthebuilding.Thearchitectandengineerthenestablishthedesignconditionsbylistingtherangeofacceptableairandsurfacetemperatures,airmotions,relativehumidities,lightinglevels,andbackgroundnoiselevelsforeachactivitytotakeplaceinthebuilding.Ascheduleofoperationsforeachactivityisalsodeveloped. Byconsideringtheseactivitiesandtheirschedule,theamountofheatthatwillbegeneratedbytheactivities,andthebuilding'sorientation,theengineerthendeterminestheHVACzonesforthebuilding.Eachofthesezoneshasitsownsetoffunctional,scheduling,andorientationconcernsthatdeterminewhenandhowmuchheating,cooling,orventilationisneeded.TextForeachzone,theengineerestablishesthethermalload(theamountofheatgainedorlost)fortheworstwinterandsummerconditions,andforaverageconditionsduringthemajorityofthebuilding'soperatinghours.Anestimateofthebuilding'sannualenergyconsumptionmayalsobemadeatthistime. Withallthisdetailedinformationinplace,theengineernextselectstheHVACsystems.Morethanonesystemmaybeusedtomeetdifferentconditionsinalargebuilding.Forexample,onesystemmayservezonesthatarecompletelywithintheinteriorofthebuilding,withaseparatesystemforperimeterzones. Next,theengineeridentifiesthecomponentsoftheHVACsystem,andlocatesthemwithinthebuilding.Mechanicalrooms,distributiontrees(verticalchasesandhorizontalrunsofductwork),andcomponentslikefan-coilunits(FCUs)underwindowsandairgrilleswithinspecificspacesallhavetobeselectedandlocated.Sizesforthesecomponentsarealsospecified. Oncetheengineerlaysoutthesystem,itistimetocoordinateconflictswithotherbuildingsystems,suchasthestructure,plumbing,firesafety,andcirculation.TextBydrawingsectionsthroughthebuilding,architectsandengineerscanidentifyclearanceproblemsandseeopportunitiestocoordinatetheHVACsystemwithotherbuildingsystems. Theprocessofdesignfinalizationinvolvesthede-signeroftheHVACsystemverifyingtheloadoneachcomponentandthecomponentsabilitytomeetthisload.Thenthefinaldrawingsandspecificationsarecompleted.Duringconstruction,theengineermayvisitthesitetoassurethatworkisproceedingaccordingtodesign,andtodealwithunanticipatedsiteconditions.TextTHERMALCOMFORTZONES Thewayzonesforheatingandcoolingaresetupbythemechanicalengineerhasimplicationsforthearchitectureandinteriordesignofthespace.Zonesmayoccupyhorizontalareasofasinglefloor,ormaybeverticallyconnectedbetweenfloors.Thefunctionofaspaceaffectsbothitsverticalandhorizontalzoning(Fig.1).Somefunctionsmaytoleratehighertemperaturesthanothers.Somefunctionsrequiredaylight,whichmayaddheattothespace,whileothersarebetteroffawayfromthebuilding'sperimeter.Insomeareas,suchaslaboratories,airqualityandisolationisamajorconcern.Theinputoftheinteriordesignercanbeanimportantcomponentinmakingsurethattheclient'sneedsaremet.Fig.35.1 Thermalzonesbasedonactivitypatterns.Text Zonesalsotakeintoconsiderationthescheduleofuseofthespace.Spacesthatgainheatfromdaylightorelectriclightingduringthedayonlymaybeabletoflushthatheattoanotherspaceforuseatnight.Anisolatedactivitywithadifferentschedulefromtherestofthebuildingmayneedaseparatemechanicalsystem. Thebuilding'sorientationwillalsoaffecttheHVACzones.Exposuretodaylightdirectsun,andwindallcreatespecificheatingandcoolingrequirements.Perimeterspaceshavedifferentneedsfrominteriorspaces. Inmultistorybuildings,interiorspacesoninter-mediatefloors—thosespacesnotatthebuilding'sperimeteroronthetoporgroundfloors—maybeabletouseventilationairastheironlyheatingloadsource.Theseareasaresowellshieldedfromthebuilding'sexteriorthattheymaynotneedadditionalheal,andcanbeservedonlybycooling.Theamountofelectricallygeneratedheat,plusthatproducedbyhumanactivityandotherheat-generatingsources,usuallyoutweighthecoolingeffectoftheamountofoutdoorairsuppliedbyminimalventilation,eveninwinterweather.Inthesummer,mostoftheinteriorcoolingloadsaregeneratedinsidethebuilding.Theperimeterareasofthebuildingaremuchmoreweathersensitive.TextHEATINGANDCOOLINGLOADS Heatingandcoolingloadsaretheamountsofenergyrequiredtomakeupforheatlossandheatgaininthebuilding(Fig.2).Therateofflowofhotorcoldaircomingintothebuildingfromventilationandinfiltrationinfluencestheamountofheatingorcoolingload.Itisalsodependentuponthedifferenceintemperatureandhumiditybetweentheinsideandoutsideair.Theamountofoutsideaircominginisexpressedinliterspersecond(cubicfeetperminute,orcfm).Fig35.2 Heatgainsandlossesinbuildings.TextHeatLossandHeatingLoads Aheatingloadiscreatedwhenabuildinglosesheatthroughthebuildingenvelope.Coldoutsideairenteringabuildingthroughventilation,suchasanopenwindow,orasaresultofinfiltration,aswhenairleaksthroughcracksinthebuildingenvelope,alsoaddtotheheatingload. Convection,radiation,orconductionofheatthroughthebuilding'sexteriorwalls,windows,androofassembliesandthefloorsofunheatedspacesarethemainsourcesofheallossincoldweather.Windpassingthebuildingbothdrawswarmairoutandforcescoldairin.Infiltrationofcoldairthroughcracksintheexteriorconstruction,especiallyarounddoorsandwindowscontributessignificantheatloss.Thisheatlossplacesaheatingloadonthebuildingsmechanicalsystem,whichmustmakeupheatinspacesthatloseitthroughcracksandpoorlyinsulatedareas. Energyauditorsuseequipmenttolocateairleaksandareaswithinadequateinsulation.Theyknowwhattolookforinnewandolderbuildings,andthecostofanenergyauditisagoodinvestmentforabuildingowner.Someutilitieswillsupplybasicenergyauditsforfree.Trainedexperts,sometimescalledhousedoctorsorhomeperformancecontractors,lookatthebuildingasasystemandevaluatesafety,comfort,energyefficiency,andindoorairquality.Youcangetalistingofqualified,trainedenergyauditorsfromyourstaleenergyofficeorcooperativeextensionservice.Text Themostcommonsourcesofairleaksarewhereplumbing,wiring,orachimneypenetratesthroughaninsulatedfloororceiling,oralongthesillplateorbandjoistontopofthebuilding'sfoundationwall,fireplacedampersandatticaccesshatchesareotherlikelysuspects. Anywherethatwallsandceilingsorfloorsmeetorwhereopeningspiercethebuilding'sexteriorisanopportunityforairtoinfiltrate.Aircanleakwherethetopsofinteriorpartitionwallsintersectwiththeatticspaceandthroughrecessedlightsandfansininsulatedceilings.Missingplasterallowsairtopassthroughawall,asdoelectricaloutletsandswitchesonexteriorwalls.Window,door,andbaseboardmoldingscanleakair,ascandroppedceilingsabovebathtubsandcabinets.Aircanalsoleakatlowwallsalongtheexteriorinfinishedattics,especiallyataccessdoors,andatbuilt-incabinetsandbureaus. Gapsunder4mm(1/4in.)widecanbescaledwithcaulk,whichisavailableinavarietyoftypesfordifferentmaterials.Specifycaulkswith20-yearflexibilitylifetimesandselecteithercoloredorpaintablecaulkforvisibleuse.Avoidusingthecheapestcaulks,astheydon’tholdupwell.Largercracksandholesthatareprotectedfromthesunandmoisturecanbefilledwithexpandingone-partpolyurethanefoamsealant.Lookforasafe-for-ozonelabelforfoamsealantswithoutchlorofluorocarbons(CFCs).Text Forevenlargercracksandforbackingindeepcracks,specifybackerrodorcrackfiller,usuallyintheformofaround4-to25-mm(1/4-1-in.)diametercoilmadeofaflexiblefoammaterial.Thecrackisthenscaledwithcaulk.Rigidfoaminsulationorfiberglassinsulationwrappedinplasticcanbeusedforverylargeopeningslikeplumbingchasesandattichatchcovers.Avoidusingplasticinplaceswithhightemperatures,asitmaymelt.Metalflashingwithhightemperaturesiliconesealantsmaybepermittedaroundchimneybysomebuildingcodes.HeatGainsandCoolingLoads Buildingsgainheatfromoccupantsandtheiractivities.Coolingloadsaredefinedasthehourlyrateofheatgaininanenclosedspace,andareexpressedinBtuperhour.Coolingloadsareusedasthebasisforselectinganair-conditioningunitoracoolingsystem.

Coolingloadsrepresenttheenergyneededtooffsettheheatgainedthroughthebuildingenvelopeinhotweatherorfromhotairenteringbyinfiltrationorventilation.People'sbodyheal,showering,cooking,lighting,andappliancesandequipmentusealsocreatecoolingloads.Text Theheatgeneratedbylightingisoftenthegreatestpartofthetotalcoolingloadinabuilding.Alltypesofelectriclightingconvertelectricalpowerintolightplusheat.Eventually,thelightisalsoconvertedtoheatwithinthespace(thinkaboutalampshiningonadeskandthedeskbecomingwarmer).Alltheelectricalpowerthatentersalightingfixtureendsupasheatinthespace. Someoftheheatfromlightingisconvertedfromthelightingfixturetothesurroundingairandbecomespartofthecoolingload.Therestisradiatedtosurroundingsurfaces,exceptforasmallamountthatisconductedtoadjacentmaterial.Thisradiatedandconductedheatisthenconvertedtotheair,becomingpartofthecoolingload.Recessedfixturestendtohealthesurroundingstructure,whilehangingfixturesconveyheatmoredirectlytotheair.Somefixturesaredesignedsothatairreturnsthroughthem,absorbingheatthatwouldotherwisegointothespace. Electric,gas,orsteamappliancesandequipmentinrestaurants,hospitals,laboratories,andcommercialspacessuchasbeautysalonsandrestaurantsreleaseheattointeriors.Hoodsoverkitchenappliancesthatexhaustairmayreduceheatgain,buttheexhaustedairmustbereplacedwithoutdoorair,whichmayneedtobecooled.Steamorhotwaterpipesthatrunthroughair-conditionedspacesandhotwatertankswithinspacescontributetothecoolingload.Text Inwarmorhotweather,buildingsgainheatbyconvection,radiation,andconductionthroughtheexteriorwallsandwindowandroofassemblies.Theamountofheatgainvarieswiththetimeofday,theorientationoftheaffectedbuildingpartstothesun,theexposuretothewind,andtheamountoftimeittakesfortheheattoreachtheinteriorofthebuilding(thermallag).Theheatgainfromsunshiningonwindowsvarieswiththeorientationtothesunandthewaysthewindowsareshaded. Inhotweather,warmmakeupairenterswhenspacesareventilatedtoremoveodorsorpollutants.Theuseofadehumidifiertolowerrelativehumidity(RH)inaspaceaddstoheatgain,duetothelatentheatreleasedintothespacewhenmoistairiscondensedandtheheatproducedbyrunningthedehumidifier'scompressor.MeasuringHeatingandCoolingLoads Adegree-dayisaunitusedincomputingheatingandcoolingloads,sizingHVACsystems,andcalculatingyearlyfuelconsumption.Itrepresentsonedegreeofdifferenceinmeandailyoutdoortemperaturefromastandardtemperature.Aheatingdegree-dayisonedegree-daybelowthestandardtemperatureof18°C(65°F),andisusedinestimatingfuelorpowerconsumptionbyaheatingsystem.TextAcoolingdegree-dayisonedegree-dayabovethestandardtemperatureof24°C(750F),andhelpsincalculatingenergyrequirementsforair-conditioningandrefrigerationsystems.Degree-dayinformationisusuallypublishedindailynewspapers. Systemsareratedintonsofrefrigeration,whichisthecoolingeffectobtainedwhenatonoficeat0°C(32°F)meltstowaterwhileatthesametemperatureoveraperiodof24hours.Itisequalto3.5kW(12,000Btu/hr). Theenergy-efficiencyratingisanindexoftheefficiencyofarefrigeratingunit.ItexpressesthenumberofBtusremovedperwattofelectricalenergyinput.ventilate vt.使通風(fēng)；給…裝通風(fēng)設(shè)備insulation n.絕緣；隔離，孤立employvt.使用，采用；雇用；使忙于，使從事于reclamation n.開墾；收回；再利用；矯正integrated adj.綜合的；完整的；互相協(xié)調(diào)的contractor n.承包人；立契約者renovation n.革新；修理；恢復(fù)活力diffusern.[機(jī)]擴(kuò)散器；散布者；[航][機(jī)]擴(kuò)壓器finalization n.終結(jié)，結(jié)束；終止化aestheticadj.美的；美學(xué)的；審美的，具有審美趣味的humidity

n.[氣象]濕度；濕氣ductwork

n.管道系統(tǒng)plumbing

n.水管設(shè)施perimeter

n.周長(zhǎng)；周界multistory

adj.多層的；有多層樓的infiltration

n.滲透；滲透物convection

n.[流][氣象]對(duì)流；傳送caulk

n.填補(bǔ)物polyurethane

n.聚氨酯；聚亞安酯sealant

n.[機(jī)]密封劑NewWordsandPhrasesattic n.閣樓；頂樓silicone n.硅樹脂；[口腔]硅酮recessed adj.嵌壁式的；深底的dehumidifier n.減濕劑；干燥器latent adj.潛在的；潛伏的；隱藏的NewWordsandPhrasesNotes（1）Asaninteriordesigner,youwillrarelyneedtorefertothemechanicalcodes,butyoushouldbefamiliarwithsomeoftheirgeneralrequirementsandterms,especiallythoseaffectingenergyconservationrequirements. 作為一個(gè)室內(nèi)設(shè)計(jì)師,你很少需要參考機(jī)械代碼,但你應(yīng)該熟悉一些他們的一般要求和條件,特別是那些影響節(jié)能的要求。（2）Thephasesoftheengineeringdesignprocessaresimilartothoseofarchitectsandinteriordesigners:preliminarydesign,designdevelopment,designfinalizationandspecification,andtheconstructionphase. 在工程設(shè)計(jì)過程中的各個(gè)階段都與建筑師和室內(nèi)設(shè)計(jì)師相似：：初步設(shè)計(jì)，設(shè)計(jì)開發(fā)，設(shè)計(jì)定型和規(guī)范，以及施工階段。（3）Coldoutsideairenteringabuildingthroughventilation,suchasanopenwindow,orasaresultofinfiltration,aswhenairleaksthroughcracksinthebuildingenvelope,alsoaddtotheheatingload. 通過通風(fēng)進(jìn)入建筑物的外面冷空氣，如打開的窗口，或者由于滲透，或者通過建筑圍護(hù)結(jié)構(gòu)裂縫的空氣泄漏，都增加了熱負(fù)荷。Notes（4）Coolingloadsrepresenttheenergyneededtooffsettheheatgainedthroughthebuildingenvelopeinhotweatherorfromhotairenteringbyinfiltrationorventilation. 制冷負(fù)荷代表需要抵消通過建筑圍護(hù)結(jié)構(gòu)在炎熱的天氣或熱空氣進(jìn)入浸潤(rùn)或通風(fēng)獲得的熱量的能量。（5）Theamountofheatgainvarieswiththetimeofday,theorientationoftheaffect