Natural Convection Heat Transfer in Roofs with Above-Sheating Ventilation

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1、NaturalConvectionHeatTransferinRoofswithAbove-SheathingVentilationWilliamMiller,PhDMajidKeyhani,PhDTimothyStovallAdamYoungquistMemberASHRAEABSTRACTAnalgorithmwasdevelopedforpredictingtheratesofairflowandheatflowinaninclinedairspaceheatedfromaboveorfrombelow.Thealgorithmyieldsthema

2、ssflowrateandthetemperatureriseofthethermallyinducedflowrate.Theflowandconvectiveheattransferareverysimilartothoseoccurringininclinedcoolingductsformedbyoffsetroof-mountedphotovoltaicinstallations.Thealgorithmisusefulforpredictingthefreelaminarconvectionheattransferprevalentinroof

3、selevatedfromtheroofdeck.Theroutinewasimplementedinanatticsimulationcodeandvalidatedagainstthermalfielddataforstone-coatedmetalroofsequippedwithabove-sheathingventilation.INTRODUCTION(Rose1995)providedapathfornaturalventilationabovethesheathing.Theoldadage“keepingaroofoverone’shea

4、d”aptlyPlacingtileandstone-coatedmetalroofsonbattenanddescribesthebasichumanneedforshelter.Aroofprovidescounter-battensupportsprovidesexcellentthermalperfor-protectionfromthesun,wind,andrain.Itisdesignedtomance,althoughitisnotthecurrentpracticeusedinFloridapreventorlimittheflowofm

5、assandenergy,dependingontheorinCaliforniabecauseofconcernsaboutwindupliftduringenvironmentaldifferencesbetweentheconditionedspaceandstorms.Counter-battenconstructionprovidesanairspacetheoutdoorambient.Craftsmenatsomepointduringthebetweentheexteriorfaceoftheroofsheathingandtheunder

6、-evolutionofbuildingdiscoveredthewater-sheddingqualitiessideoftheroofcoversothataclear,albeitcomplex,airpath-ofdifferentmaterials,includingoverlappedslateandstonewayexistsbeneaththeroofcoverfromthesoffittotheridgeslabs.Wherenaturalslabswerescarce,claywasused,andtheoftheroof.Solari

7、rradianceabsorbedattheroof’ssurfaceisfirstsingle-laprooftilesweremoldedbyhandandshapedoverconductedthroughtheroofandconvectedasheattotheair.thethighsoffemaleartisans.Eventoday,someSpanishtileThewarmer–andtherefore,morebuoyant–airmovesupthehavethischaracteristicshape,wideatoneendan

8、dnarrowatinclinedairpassage.Mille