HVAC暖通空调外文文献

1MeasuringSoundPowerinDuctedHeating,Ventilating,andAir-conditioning(HVAC)SystemsforUseinVerifyingAcousticalPredictionMethodsStevenR.RyherdandLilyM.WangArchitecturalEngineeringProgram,UniversityofNebraska—Lincoln,PKI,1110S.67thSt.,Omaha,NE68182;PH(402)554-2065;FAX[phone];email:[e-mail]ussesissuesregardingin-situmethodsofobtainingsoundpoweratapointinaheating,ventilatingandair-conditioning(HVAC)ductsystem.Suchamethodisbeingusedaspartofalargerinvestigationonacousticalpredictionmethodstoallowforcomparisonofmeasureddatatoresultsfromattenuationpredictionsofindividualductelements,suchaselbowsordampers.SoundpropagationinHVACductworkiscomplex.Anymeasurementsofsoundenergyintheductmustaddressthecharacteristicsofsoundpropagationinducts,endreflections,andairturbulence.Investigationsarebeingconductedtounderstandtheextentstowhichtheseacousticalissuesaffectmeasurementresults.ThestudyprovidesabetterunderstandingofsoundpropagationinHVACductsforfutureinvestigationofacousticalpredictionmethods.IntroductionThestudyoutlinedinthispaperispartofalargerinvestigationofacousticalpredictionsoftwareforheating,ventilating,andair-conditioning(HVAC)systems.TheauthorshavepreviouslyinvestigatedpredictionsoftwareforHVACsystemsalongentireacousticalpathsfromthefansourcetothereceiverinaroom(Ryherd&Wang,2005).Suchverificationofthepredictionsoftwarerequiredcontrolledenvironmentswithwell-documentedinformationabouttheactualsoundsourcepower,ductelements,andreceivingroomcharacteristics.Inanattempttoverifythealgorithmsusedagainstactualdatameasuredinfieldinstallations,though,itisdesiredtolimitotherpotentialsourcesoferror.Thispaperpresentstheissuessurroundinganin-situmethodofinvestigatingtheacousticalinfluenceofeachelementintheductpathseparately.Toverifyeachductelement’scontribution,theremustbedependablemeansofobtainingasoundpowerlevelattheinletandoutletofthespecifiedelement.Thesesoundpowerlevelscouldthenbecomparedtotheexpectedattenuationofthatelement,ascurrentlyCopyrightASCE2006AEI2006BuildingIntegrationSolutionsDownloadedfromascelibrary.orgbyHuazhongUniversityofScience&Technologyon12/26/13.CopyrightASCE.Forpersonaluseonly;allrightsreserved.2projectedinHVACnoisepredictionsoftware.However,in-situmeasurementsofthiskindarenotcommon,especiallyininstalledHVACsystems.BackgroundSoundpredictionsoftwarefornoiseinHVACsystemsutilizeacollectionofalgorithmsthatcalculatetheattenuationcontributionsofeachelementofasystem.Ingeneral,thealgorithmisanempiricalblackboxthattakesanincomingsoundpowerlevelandcharacteristicinformationoftheelementtoproduceanoutputsoundpowerlevel.Forexample,ifafanisusedasthesoundsourceatthebeginningofalengthofduct,thesoundpowerlevelsateachoctavebandareputintothealgorithmforthespecifictypeofduct(e.g.rectangular,circular,etc.)alongwiththeductdimensions,ductlengthandamountofabsorption.Thealgorithmcalculatestheamountofsoundattenuationandprojectstheoutputsoundpowerlevel.ThisprocesscontinuesdownthepathoftheHVACsystemforeachelementofthepath(silencers,elbows,branches,etc.)untilthesoundreachesthereceiverroom.Atthereceivingroom,correctionfactorsareappliedtotheestimatedsoundpowerleveltocalculatetheequivalentsoundpressurelevelperceivedbyareceiverinthespace.Althoughtheexampleissimplystated,theprocessofpredictingthenoiseinHVACsystemsiscomplexwithmanypotentialsourcesoferror.Thereisinherenterrorwhenalgorithmsbasedonempiricaldatamadeincontrolledenvironmentsareusedforin-situapplications;andunfortunately,usersofsoftwareprogramsoftenarenotabletoaccessevenwhatalgorithmisbeingusedtoknowifitsapplicationisappropriate.Additionally,theinitialsourcedatafromafanisnotalwaysreliableandmayvarybasedonoperatingconditionsandinstallation.Ultimately,anyinaccuraciesatonepointintheanalysisofthesystemcancompounderrorsfurtherdownthesystempath.ToimproveacousticalpredictionsalongHVACductwork,oneshouldfirstbesuretounderstandsoundpropagationinducts.RelationshipofSoundPressureandSoundPowerInacousticsofbuildingmechanicalsystems,soundenergyisoftenrepresentedasoneoftwoquantities:soundpressurelevelsorsoundpowerlevels.Soundpressurelevelisthemostcommonformofdescribingthehumanresponsetoairbornesound,andmeasuresthechangesinpressurewithrespecttostaticpressure.Thisquantityisdependentuponthedistanceofthereceivertothesourceandtheenvironmentinwhichitismeasured.However,anotherquantity,soundpowerlevel,isindependentofdistancetothesourceandtheenvironmentalcharacteristicsofthespace.Soundpowerdescribestherateatwhichsoundenergyisproducedbyasourceandisusedtoquantifythesoundenergyrelatingtomechanicalequipment.Usinganacousticalpredictorthatisindependentoftheenvironmentallowsforsimplecomparisonofacousticalcharacteristicsofmechanicalequipment.CopyrightASCE2006AEI2006BuildingIntegrationSolutionsDownloadedfromascelibrary.orgbyHuazhongUniversityofScience&Technologyon12/26/13.CopyrightASCE.Forpersonaluseonly;allrightsreserved.3Althoughsoundpowerisacommondescriptorofacousticalenergy,thereisnoeasywaytomeasuresoundpowerdirectly.Acollectionofsoundpressuremeasurementscanbeusedtocalcu