* KorneliaCabała,SebastianZaworski,M.Sc.Eng.JolantaGintowt,InstituteofMaterialsandBuildingStructures,FacultyofCivilEngineering,CracowUniversityofTechnology.

TECHNICAL TRANSACTIONSCIVIL ENGINEERING

5-B/2014

CZASOPISMO TECHNICZNEBUDOWNICTWO

KORNELIACABAŁA,SEBASTIANZAWORSKI,JOLANTAGINTOWT*

THEINFLUENCEOFFITTINGOFAWINDOWONAHEATTRANSFERCOEFFICIENTANDANENERGYBALANCE

OFABUILDING

WPŁYWMONTAŻUOKIENNASTRUMIEŃCIEPŁA IBILANSENERGETYCZNYBUDYNKU

A b s t r a c t

Theprojectconcernswindowsandtheirproperties.Fourwindowswereconsideredtoprovidecomputations.Twoofthemwerecommonwindowsandtheothertwo–passivewindows.Theanalysis focusesona roleofafitting inheat losses,explains importantaspectsofchoosingawindowandshowsmain typesofmethodsofmountingawindow.Thepaperproveshowbig the influenceoffittingawindowisonaheat transfercoefficientvalueandshowswhatthelossesstemingfrominproperfittingare.Theprojectsubmitsthatfittingfactorshouldbeconsideredwhilecalculatingtheheattransfercoefficientvalueandthatwindowsoughttobemountedinaninsulationtominimizeheatlosses.

Keywords: heat transfer, passive building, thermal bridges, montage, heat balance, window

S t r e s z c z e n i e

Analizadotyczymontażuokien.Obliczeniaprzeprowadzonodlaczterechtypówokien:dwóchpowszechniestosowanychidwóchpasywnych.Projektkoncentrujesięnarolimontażuwstra-tachciepła,wyjaśnia,cojestważneprzywyborzeoknaiokreśla,jakiesągłównekonsekwen-cje.Analizapodnosiżezagadnieniemontażuoknapowinnobyćbranepoduwagęnaetapieobliczeńwspółczynnikaprzenikaniaciepłaokna,aniedopieroprzyobliczaniuwartościwspół-czynnikaprzenoszeniaciepła.

Słowa kluczowe: przepływ ciepła, budynek pasywny, mostek termiczny, montaż, bilans energe-tyczny, okno

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Designations

Ag – surfaceglazing[m2]Af – surfaceframe[m2]U – theheattransfercoefficient[W/m2K]Uf – theheattransfercoefficientforaframe[W/m2K]Af – theareaofaframe[m2]Ψg – thelinearheattransfercoefficient(framebonding)[W/mK]Sg – thelengthof linearheattransfercoefficient(framebonding)[m],Sf – thelengthofathermalbridgealongwindowframe–wallbonding[m]Yf – thelinearheattransfercoefficientofathermal(wallbonding)[W/mK]lf – thelengthof linearheattransfercoefficient(wallbonding)[m]g – coefficientofasolarradiationpermeability(here:g=1)z – shadingcoefficient(here:z=1)ΔT – thetemperaturedifferencebetweeninsideandoutsidethebuilding(here:ΔT=35K)t – numberofhoursinamonth(here:t=720h)

1. Introduction

1.1.Topicoftheproject

Thetopicoftheprojectistheinfluenceoffittingawindowonaheattransfercoefficientandanenergybalanceofabuilding.Itisessentialforeachhousetochoosethebesttypeofawindowandtofititinaproperway.Itisnotenoughtochoosewindowswithhighinsulationpropertiesandgreatenergybalance–butthesurroundingofawindowanditsfittingarealsoimportant.Theyshouldbemountedinsuchawaythateliminatesthermalbridges[1,12,13]andthatmakesfittingconnectionsimpermeable[1–6].

Criteria of assessing the window: impermeability, fitting, heat transfer coefficient U[W/m2K],coefficientofasolarradiationpermeabilityg,shadingcoefficientz,heatlossQ[kWh].Theanalysisisconnectedwithtwofactorsmentionedabove:fittingandheatloss.

1.2.Meansofmountingawindow:

Althoughthefirstoneiscausingthegreatestheatlosses,itisthemostpopularwayofmountinginPoland[7–9,11,12].Itiscalled“traditionalfitting”,whereawindowislocatedoninternaledgeofthewall.ItisshowninFig.1a.Theamountofheatlossthroughthermalbridgeswill be smaller in case of “flushfitting”,where thewindow is located along theisolation,whichisnotcoveringtheframeofthewindowasitisshowninFig.1b.Windowsshouldbesituatedontheoutsideedgeofthewalltostayintheinsulatinglayer,whichisadditionally covering the frameof thewindow.This solution is recommended in passivebuildings[1,10,12].Inthiscasewindowsshouldnotbeopenable,asthesuitableamountofairisprovidedbyaspecialcirculatingsystem.Makingthewindowsopenablewouldalsocauseaproblemofstability.That iswhythesolutioncomeswithanchorswhichhelpthewindowstayintheinsulationasshowninFig.1c.

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Fig.1a)Traditionalfitting,b)Flushfitting,c)Fittinginaninsulation

2. Purpose of the project

ThepurposeoftheprojectistoshowtheinfluenceoffittingofawindowonthevalueofheattransfercoefficientandtoprovethataformulaforcalculatingtheheattransfercoefficientofthewindowwhichexistsinPolandshouldincludefittingandtakeintoaccountconsistentwith[10]amethodfordeterminingtheoutsidetemperature.

3. Theses of the project

Aninappropriatefittingofawindowcauseslargeamountsofheatlossesandatthesametimeincreasesthecostofheating.Balancinggainsandlossesthroughwindowsforpassivehouses,nearlytozero-energybuildings,shouldbecalculatedaccordingtotheformulaPHI[10].

4. Subject matter

Thesubjectmatterare fourwindows: twocommonwindows (Aluplast IDEAL® 4000 [14]andAluplastENERGETO® 4000[15])andtwopassivewindows(InternormHF®200[16]andOknoplastWINERGETICPLUS®[17]).

5. Methods of analyses

Theheattransfercoefficientcalculationsweredonebasingonthefollowingformulas:

UA U A U l

A AWg g f f g g

g f

=+ +

+∑∑∑

∑∑Ψ

(1)

Inagreementwith[12]

UU A U A s s

A Ag g f f g g f f

g f

=⋅ + ⋅ + ⋅ + ⋅

+ψ ψ

(2)

Inagreementwith[10]

a)b)c)

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Bothformulasconsiderglazing,frameandbondingglazing–frameofawindow.Theydifferfromeachotherinawaythatoneofthemdoesnotconsidertheinfluenceoffitting.

Theformulaforaheatlosscalculation:

Q U A g z s T tw w f f= ⋅ ⋅ ⋅( ) + ⋅( ) ⋅ ⋅ ⋅ −ψ ∆ 10 3 (3)

Accordingto[12]

Q U A g z T tW W= ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ −∆ 10 3 (4)

Accordingto[10]

Thecalculationsofaheat loss forcommonwindowsweredonebasingon thefirstofthe formulas. That is because in Poland fitting is considered in calculations only at thisstage. Incomputationforpassivewindows thesecondformulawasused.Additionally, toshowsignificant influenceoffittingonaheat loss itwasassumedthatcommonwindowsaremountedinawall,asitisgenerallydoneinPoland.Ontheotherhanditwasassumedforpassivewindowsthattheyaremountedinaninsulation,accordingtorulesforpassivebuildings.

Forthepurposesofcomparison,thedifferenceincalculationofaheatbalanceresultingfrom the different outside temperatures has been omitted (computational temperature isselectedfrom:thecoldestandwarmestsunny/cloudyday)in[12]and[10].

6. Results

6.1.Thevalueofaheattransfercoefficient

Thechartbelowshowsavalueofaheattransfercoefficientofawindow.Itisdividedaccordingtoawindowmodel(firsttwoofthemarecommonwindowsandtheothertwoarepassivewindows)andalsoaccording toa formofacalculationformula.ThewhitecolorrepresentstheformulawhichisinlinewiththePolishnorm,whichdoesnotconsiderfitting.LightanddarkbluecolorsrepresenttheformulaaccordingtoPHPP.“Properfitting”shouldbeunderstoodasfittingwhichfulfillsrequirementsofpassivebuildings.Inturnan“improperfitting”isfittingfailingtomeetthoserequirementsofpassivebuildings.Inturnabadmontageisamontagewhichdonotsatisfythatdemands.

Analyzing the chart, one should notice that an improperly-mounted passive window(OknoplastWinergeticPlus®)hascomparablevalueofaheattransfercoefficientasawell-mountedcommonwindow(AluplastEnergeto®4000).OneAbigdifferencebetweenawell-andbadly-mountedwindowisalsoclear.Inthiscaseitequals0.432[W/m2·K](Internorm® HF200).Bothfactorsmentionedaboveshowthesignificanceofinfluenceoffittingonaheattransfercoefficientofawindow.

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Fig.2.HeattransfercoefficientU[w/m2K]T a b l e 1

Window – U coefficient

Window PN-ENISO10077-1 AccordingtoFig.1c AccordingtoFig1a

AluplastIDEAL® 4000 1.360 1.375 1.807

AluplastENERGETO® 4000 1.234 1.249 1.680

OknoplastWINERGETICPLUS® 0.800 0.815 1.246

InternormHF®200 0.699 0.714 1.146

6.2.Comparativeanalysisoftheheatlossthroughwindows

Thechartshowsaheatlossthroughananalyzedwindowinaperiodofonemonth. Time intervaladoptedforthepurposesofthisanalysisseemstobesufficient.Oneshouldnoticethatthedifferencebetweenapassivewindowmountedininsulationandacommonwindowmountedinawallisalmosttripledandequals91.11[kWh].Itshowshowgreatthelossescreatedbyabadfittingare.ItisshowninFig.3a.Thedifferenceresultingfromtheuseof[10]and[12]forthecalculationoftheheatdemandisapproximately 25%.(Anonlylossassociatedwithheattransferthroughwindows).Thisisavaluethatshouldnotbeignored.ThisisshowninFig.3b.

Fig.3a)Theheatdemandforheating-window[kWh],b)PHPPandPN13789methods

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7. Conclusions

Tominimizeheatlossesandtoeliminatethermalbridgeswindowsshouldbemountedinaninsulation.Thefittingshouldbeconsideredinaformulaforaheattransfercoefficientbecause fitting considerably influences its value. It seems that the use of a formula forcalculating the heat demand for passive houses, nearly-zero buildings, plus building,proposedbythePassiveHouseInstituteinDarmstadt,andenteredinthePHPP,isjustified.

R e f e r e n c e s

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