Government & Nonprofit

A study of air flow and heat transfer in building-wind tower passive cooling systems applied to arid and semi-arid regions of Mexico

Description
A study of air flow and heat transfer in building-wind tower passive cooling systems applied to arid and semi-arid regions of Mexico
Published
of 11
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Transcript
  EnergyandBuildings66(2013)211–221 ContentslistsavailableatScienceDirect Energy   and   Buildings  j   ournalhome   page:www.elsevier.com/locate/enbuild A   study   of    airflow   and   heat   transfer   in   building-wind   tower   passivecooling   systems   applied   to   arid   and   semi-arid   regions   of    Mexico V.A.   Reyes a ,   S.L.   Moya a ,J.M.   Morales a ,F.Z.Sierra-Espinosa b , ∗ a CentroNacionaldeInvestigacióny   DesarrolloTecnológico,CENIDET-DGEST,Prol.Av.Palmiras/n,Palmira,Cuernavaca,62490Morelos,Mexico b CentrodeInvestigaciónenIngenieríay   CienciasAplicadas,CIICAP,UniversidadAutónomadelEstadodeMorelos,Av.Universidad1001,Chamilpa,Cuernavaca,62209Morelos,Mexico a   r   t   i   c   l   e   i   nf   o  Articlehistory: Received14December2012Receivedinrevisedform23May   2013Accepted9July2013 Keywords: WindtowerPassivecoolingThermalcomfortConjugateCFDsolutionHeattransfer a   b   s   t   ra   ct Wind   towershavebeen   traditionallyused   as   passive   climatesolution   inMiddle   Eastcountries.   Theyare   massivestructures   that   capture   localwind   mainstreaminorder   to   force   fresh   airtocirculate   insidethe   buildingpromoting   thermal   comforttooccupants.This   work   analyzes   airflowdistribution   infivedifferent   configurationsof    coupled   systems   building-wind   tower.   Theobjective   isdemonstratingthisconceptis   technicallyfeasible   for   producing   thermal   comfortinpopularhouses   builtinaridand   semi-aridclimateconditionsinNorthernMexico.   Thestudy   isbased   onnumerical   simulations,   conducted   withRANSmethodon   a   commercial   programFluent.   Simulations   of    conjugatecoupled   solutions   betweenairflowand   heatconduction   through   ceiling,   floor   andwalls   were   carried   out   insteady   stateand   turbulentregime   with   appropriate   boundary   conditions.   Analysis   of    resultsfocused   onairflowcirculation   insidethe   buildinglead   toselecting   the   best   configuration,   which   wastested   byconjugated   flowdistributionandheat   transfer   in   buildingslocated   inMonterrey,   NuevoLeon.   Contours   of    velocityand   temperature   for   theselected   configuration   demonstrate   an   environmentofcomfortforthespecificsiteclimateconditions.Theremainderis   devoted   toemphasize   thatwind-tower   as   passive   cooling   methodenables   electricitysavings,   otherwisespent   inconventional   airconditioned   systems   inMonterrey.©2013   ElsevierB.V.   All   rights   reserved. 1.Introduction Historically,societiesin   CentralandMiddleEasthavedevelopedcreativeandtraditionalarchitecturalsolutionsforfacinghightem-peraturehabitatconditions.Extremeclimateconditionsinaridandsemi-aridregionsleadtoconceptslikethewindtower[1–5].This isapassivecoolingsystemtypicallyusedin   placeslikeYazdinIran,amongothercities.Thewindtowerisa   massivestructuremadeof    materialsof    highspecificheatwiththepurposeofminimizingheattransfertowardbuildinginteriorenvironment.Ithasopenedwindowsorientedupstreaminordertocapturinglocalpredominantwindstreams.Onceairstreamcrossedthewindowsitpassesintooneor   morechannelsdesignedwithreducedcrosssectionareato   promoteanincrementof    itsvelocity.Thiseffectmakesiteasyforair   tocircu-latenaturallythroughthebuildingkeepingfreshandcomfortabletheenvironment,likea   passiveclimatesystem[6,7].Windtower producesthermalcomfortwithoutanyelectricor   mechanicalairconditioneddevice[1,2].   Itisa   conceptthatleadstosustainabledevelopmentbysavinglargeamountsofelectricalenergyduring ∗ Correspondingauthor.Tel.:+527773297084;fax:+527773297984. E-mailaddress: fse@uaem.mx(F.Z.Sierra-Espinosa). hotseasons[7–17].Awindtowerlocatedata   countryofMiddle-East,is   showninFig.1.Monitoringstudiesofbuildingsthatincorporatewindtowersto   providethermalcomfortwereconductedbyKarakatsanisetal.[18],ColesandJackson[19],AhmadrezaandNicol[20],   Bahadorietal.[21].   Mostof    themhaveconcludedfavorablytowardpropos-ingwindtowersaseffectivenaturalcoolingsystems,Kalantar[22].Inaddition,Bahadori[21]besidesShorbagy[23]andBansaletal. [24]haveproposednewdesignsof    windtowerincorporatingcom-binedsolarandgeothermaltechnologiesinorderto   producemoreefficientprototypes.However,despitetheseexamplesof    demonstratedfeasibilityof thisconcept,itis   stillneededtoprovideanswerto   basicquestionslikehowwindtowerperformsin   otherclimateconditions,includ-ingextremeweather,whichpresentslowandhightemperaturediurnaloscillations.Onealternativetorespondismakinguseofpowerfulcom-putersandtheoreticalalgorithmstosimulatetheoperationof    airdistributioninwindtowerscoupledtodifferentbuildingdesigns.Numericalsolutionscanbeobtainedbyresolvingcoupledmass,momentumandenergyequations.Thismethodologybelongsto   amoderntechniquecalledcomputationalfluiddynamics,CFD.CFDhasbeenusedinstudiescarriedoutbyMoyaetal.[25],Sami [26],Badran[3],   Narayan[27],   Kalantar[22],   Mahmoudi[28]and 0378-7788/$–seefrontmatter©2013ElsevierB.V.All   rightsreserved.http://dx.doi.org/10.1016/j.enbuild.2013.07.032  212 V.A.Reyesetal./    EnergyandBuildings66(2013)211–221 Fig.1. Wind-towerphotographintheMiddleEast. Reyes[29],whichhaveprovedthatCFDrepresentsoneaffordable optionforpredictingairflowbehaviorassociatedtoheattrans-ferinbuildings.Followingthistrend,thepresentworkmakesuseofacommercialprogramFluent[30]f orresolvingtheconserva- tionequationsofmass,momentumandenergythatgovernairflowdistributionandheattransferindifferentwindtower-buildingcon-figurations.Byanalyzingsimulationsresultsthebestconfigurationwaschosenconsideringasa   dependentvariabletheairstreamdis-tributionwithinthebuilding,assumingthisisanecessaryconditiontoensurethermalcomfortto   occupants.Theselectedconfigurationproducedthebestdistributionof    air   insidethebuilding.Furthermore,simulationsof    selectedconfigurationwereextendedtoconductathermalperformancestudyof    windtoweremployingmeasuredweatherdataofMonterrey,NuevoLeon,Mexicoasboundaryconditions.Theliteraturesurveydescribedaboveleadstorealizethatnoneof thesestudiesincludedananalysisof    severalconfigurations,withemphasisontheselectionofthebestdesignof    thebuildingbasedonflowdistribution,becausethesewereorientatedtosimulateonlyoneexistingconfiguration.Furthermore,thepresentstudyproposesanenhanceddesignofwindtowerbasedinthemodi-ficationoftheinletsection,whichisdemonstratedthat   improvedtheairvelocitythatimpactsonthecomfortzonesizeinsidethemainroom.Theremainderisfocusedtoemphasizetheimportanceof    usingwindtowersinacitycharacterizedbytraditionalhighconsumptionofelectricitythroughconventionalairconditioningduringsummerseason,suchasMonterrey.Theresultsin   thispaperare   consid-eredthetechnicalfeasibilityofemployingwindtowersforthermalcomfortinaridandsemi-aridregionsofNorthernMexico. 2.Methodology  Thisworkis   dividedintotwo   sections:a   firstpartaddressespredictionsof    airflowdistributionthroughfivedifferentwindtower-buildingconfigurations(itiscalledflowdynamicsproblem).Ina   secondpart,itconductsconjugateflowdynamics-thermaltransportsolutions(calledthermal-dynamicproblem)ofoneselectedconfigurationfromthefivecasesmentionedbefore.All   simulationsassumedincompressiblesteadystateturbu-lent   flow,aswellasbi-dimensional.Thermophysicalpropertiesofbuildingmaterialsweretakenintoaccountintheconjugateconduction-convectionsolution,whichprovidedamorerealisticapproximation.Theoptionof    a   QUICKschemewas   adoptedincombinationwithSIMPLECalgorithmforcouplingvelocityandpressure.Thesimulationswereobtainedbynumericalsolutionof discretizedequationsin   ReynoldsaveragedNavier–Stokes,RANS,form.Thegoverningequationsmass,momentumandenergycon-sideredaregivenbelowbyEqs.(1),(2)–(3)and(4),   respectively: ∇    · (  ¯  V  ) =   0(1) ∇    · ( u i  V  )   =− ∂ ¯ P ∂x  +   ∇  · [(  ∇  u i )   + u ′ i u ′  j ](2) ∇    · ( u  j  V  )   =− ∂ ¯ P ∂y  +   ∇    · [(  ∇  u  j ) + u ′ i u ′  j ] −   gˇ (¯ T  − T  o )(3) ∇    · ( C   p T   V  ) = ∇  ·   (  ∇  ¯ T  ) + u ′ i T  ′ (4)  V   is   thevelocityvector,components( u i ,   u  j ),  is   density, P    accountsforpressure,while  g  ,  and ˇ aregravity,molecularviscosityandvolumetricthermalexpansioncoefficientof    air,respectively.InRANSapproachthestresstensorincludedin   Eqs.(2)and(3)leadstoa   closureproblemgiventhat   thewholeequationis   formu-latedin   termsof    anaveragevelocityplusa   fluctuatingone,suchas V  =  ¯ u +   u ′ [31].NewtermscalledtheReynoldsstresstensor,   ′ ij  = u ′ i  · u ′  j  appear.ThemethodRANShasbeenwidelyusedsinceitrepresentsoneof    thefewaffordablewaystoresolvetheproblemof    turbulencein   engineeringapplications[30,31].Oneapproachin thismethodis   basedontheBoussinesqassumption,whichmeansthattheReynoldsstressesare   proportionalto   theaveragegradientsofthevelocity: u ′ i  ·   u ′  j  ≡  T  ∂u i ∂x  j + ∂u  j ∂x i   (5)where  T  isa   turbulentviscosity.InthepresentstudytheReynoldsstresses u ′ i  ·   u ′  j  weremodeledusingthespecificdissipation  – ω model.It   hasbeendemonstratedthatthismodelperformsbet-tercomparedagainstthestandardmodel  – ε .The  – ω modelrenderedverygoodresultsin   previouscomputationsof    incom-pressibleflowinvolvingtwo   rectangularcavitieswithventilation[32].   Therelationbetweentheturbulentkineticenergy, k ,   anditsspecificdissipation, ω ,issuchthat:  T  =   ˛ ∗  kω  (6)Thesetwo   variablesaresolvedthrougha   coupleoftransportequationslistedbelow: ∇    · ( k ) + ∇    · ( ku i )   = ∇  ·   [   k ∇  k ] + G k  −   Y  k  + S k  (7) ∇    · ( ω ) + ∇  · ( ωu i ) = ∇  · [   ω ∇  ω ] + G ω  − Y  ω  +   S ω  (8)Thereaderisreferredtothespecializedliteratureformoredetailsaboutthe  – ω model,whichareoutof    thescopeofthepresentstudy[30,31].Thevalidationof    thenumericalmethodologyinthepresentstudywas   supportedbydirectcomparisonsto   reproducedcon-ditionsof    resultsreportedin   theliterature,withacceptable  V.A.Reyesetal./EnergyandBuildings66(2013)211–221 213 agreement.Thecomparisonswerereportedelsewhere[29].   HungandCheng[33],resolvedtheproblemof    naturalconvectioninasquarecavityforRayleighnumber,Ra=1 × 10 5 .Thiscasewasreproducedfindinggoodagreementin   therange0.57%forNus-seltnumberand2.63%formaximumvalueof    velocity, V  max .   Also,adirectcomparisonof    mapsof    isothermsagainsttheresultsgivenbyManz[34],forRa=   1 × 10 3 andRa=2.31 × 10 4 ,   showedgoodagreement.Finally,thesimulationreportedbyNarayan[27],   ofawindtower-buildingscheme,whichincludedheattransferanaly-sis,wasusedforcomparisonof    thepresentmethodologyintermsoftemperaturefieldssheddinggoodagreement.Theresultswerealsotestedforgridindependencethroughasensitivityanalysisbasedonfourgridssized4.5 ×   10 3 ,   3.8 × 10 4 ,9.4 × 10 4 and18.9 × 10 4 cells.Theanalysisshowedgridinde-pendenceensuringminimuminfluenceofcellsnumberonthenumericalresults,asshownin   Fig.2,   whichindicatesthatveloc-ityin   aregionafterthetowerinlet(seedottedlineintheimbibedframe)convergesforthetwofinestgrids,beingthe18.9 × 10 4 cellstheoneusedforsubsequentsimulations.  2.1.Geometryofbuildingwind-tower  Thecomputationaldomainof    coupledwind-towerbuildingisshowninFig.3a   andbwithmaindimensions.Configuration Fig.2.   Gridindependencetest. Fig.3. Wind-towerbuildingcomputationaldomainwithdimensionsandboundaryconditions;(a)Boundaryconditionsconsideredelsewhere[1];usedforflowdynamics study;(b)Boundaryconditionsconsideredforthermal-dynamicsstudy.  214 V.A.Reyesetal./    EnergyandBuildings66(2013)211–221  Table   1 Thermophysicpropertiesof    buildingmaterialsandair.MaterialandfluidDensity  (kg/m 3 )Specificheat C   p (J/kgK)Thermalconductivity, k   (W/mK)Dynamicviscosity,  (kg/ms)Thermalexpansioncoefficient ˇ (1/K)Air1.18401004.730.0261.8435 ×   10 − 5 0.003354Brick16008400.78Concrete230010001.74 calledbasiscaseshowninFig.3a   formspartof    fivedifferentgeometriesunderflowdynamicsstudy.InsteadFig.3bshowsa buildingimbibedintoa   controlvolume,whichenabledproperthermalboundaryconditionsnecessaryforthermal-dynamicanal-ysis.Thisconfigurationis   madeof    structured-no-structuredcellshybridmeshappropriateforrepresentingthisdomain,especiallyforbuilding’sinterior.Theno-structuredcellswereusedforrepre-sentingachannelof    curvedwalllocatedaftertheinletsection,aswellasforsectionslocatedoutof    thebuildingincludingtheendsofcontrolvolume.  2.2.Boundaryconditions Theboundaryconditionsusedforbothdomainsflowdynam-icsandthermal-dynamicsolutions,areshownalsoin   Fig.3aandb,   respectively.Airstreamexitwasdeclaredaspressureandsettoatmosphericpressure.Additionally,thenon-slipperyconditionwasappliedonallwalls(verticalwalls,floorandceiling).All   sim-ulationsconsiderrelativehumidityof    airasa   constant.Thisandotherpropertiesof    airat303K   aregivenin   Table1.   Thesametablecontainspropertiesforsolidmaterialsconsideredintothermal-dynamicsimulations.Averagedailyvaluesoftemperaturewereobtainedfroma   threeyeardatabasisfroma   weatherstationlocatedinMonterrey[35,36].AsummaryisprovidedinTable2.Datafromthistablewereused asboundaryconditions,whichareshowninFig.3b.Temperature  Table2 Weatherconditionsof    buildinglocation(threeyear’s   data).ConditionSpringSummerWinter T  AV  (K)299.35   301.25298.25Rel.Hum.(%)   61.865.172.9Velocity(ms − 1 ) 1.30 1.27 1.14Hot   time/day(h) 3.6 7.6 2CeilingNorthwallEastwallSouthwallWest   wallT(K)317303306304305 valuesusedforwallandceilingsurfaceconditionsweredefinedfollowinga   standardprocedure[30].Thedynamicproblemwassolvedbyapplyingfourdifferentcon-ditionstoairincome-exitorientationinthetower:(a)airinletlocatedonthelefthandsideof    windtowercombinedwithoppo-sitewindowopened;alsoreferredto   asthebasiscase,Fig.3a;   (b)air   inletlocatedonthelefthandsideof    windtowercombinedwithoppositewindowclosed;(c)airinletlocatedontherighthandsideofwindtowercombinedwithoppositewindowopened;and(d)airinletlocatedontherighthandsideof    windtowercombinedwithoppositewindowclosed.Theresultsofall   thesecaseswereusefulfordefiningwhichconfigurationofairdistributioninsidethebuild-ingwasthebestto   investigate.However,theyallarenotshowninthispaperbecauseofa   lackofspace.Instead,wefocustheattentionondiscussionthebasiscase. Fig.4. Fivedifferentconfigurationsunderflow   dynamicstudy;(a)   typicalcase,configuration1;(b)variationof    innerwallposition;(c)endof    towerwithhorizontaldeviator;(d)   curvedfloorandlargeinnerwall;(e)dividedinnerwall,configuration5.  V.A.Reyesetal./EnergyandBuildings66(2013)211–221 215 Fig.5. Numericaldifferentsolutionsof    velocityvectorsforflowdynamicstudy;(a)typicalcase,configuration1;(b)variationof    innerwallposition;(c)endoftowerwithhorizontal   deviator;(d)curvedfloorandlargeinnerwall;(e)dividedinnerwall,configuration5.  2.3.Descriptionofcoupledbuildingwind-tower  Specificdifferencesofeachconfigurationunderflowdynamicstudyareshownin   Fig.4.Atypicalcaseis   showninFig.   4aandhasbeenusedinIranianwindtowers[6,13];Geometry2,Fig.4b, isproposedinthisworkin   orderto   avoidaccumulationofairintheupperpartof    building’sinterior.Case3isalsoproposedin   thiswork.Thisconfigurationhasthepurposeof    promotinga   horizontalairstreamaroundoccupant’sbody,especiallyin   chestandup.Thisisbecauseaccordingto   literaturesuchcontactaugmentsthermalcomfort[16].Configurationshownin   Fig.4dhasbeenproposedbyBahadori[6],lookingforcapturinganytraceofdustcontainedin   airfrominlet.Thedustiscapturedin   a   concavitylocatedintheground.Thisdesignlooksalsoforreducingtheair   temperaturethroughitscontactwithfloor,whichnormallyremains10 ◦ Ccolderthansurroundingair   in   average.Finally,thetypicalcasewas   modifiedtoleadto   anotherconfiguration,5,   byincludinga   shortdividingwallintheflooratroom’sinlet,whichimprovedtheairdistributionaswillbediscussedinnext   section[29]. 3.Resultsanddiscussion  3.1.Flowdynamicsproblem Theresultsof    simulationsare   firstanalyzedthroughvelocityvectorsfordescribingairflowbehaviorwithinthewindtowerandinsidethebuilding.ResultsforthebasiscaseareshowninFig.5a   whereitisobservedthatairmainstreamincreasesits Fig.6. Resultsof    velocityvectorsunderdynamicstudy.(a)   Forchosencase;(b)proposedconfigurationwithcurvedinletwall.
Search
Similar documents
View more...
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks