* Kornelia Cabała, Sebastian Zaworski, M.Sc. Eng. Jolanta Gintowt, Institute of Materials and Building Structures, Faculty of Civil Engineering, Cracow University of Technology. TECHNICAL TRANSACTIONS CIVIL ENGINEERING 5-B/2014 CZASOPISMO TECHNICZNE BUDOWNICTWO KORNELIA CABAŁA, SEBASTIAN ZAWORSKI, JOLANTA GINTOWT * THE INFLUENCE OF FITTING OF A WINDOW ON A HEAT TRANSFER COEFFICIENT AND AN ENERGY BALANCE OF A BUILDING WPŁYW MONTAŻU OKIEN NA STRUMIEŃ CIEPŁA I BILANS ENERGETYCZNY BUDYNKU Abstract The project concerns windows and their properties. Four windows were considered to provide computations. Two of them were common windows and the other two – passive windows. The analysis focuses on a role of a fitting in heat losses, explains important aspects of choosing a window and shows main types of methods of mounting a window. The paper proves how big the influence of fitting a window is on a heat transfer coefficient value and shows what the losses steming from inproper fitting are. The project submits that fitting factor should be considered while calculating the heat transfer coefficient value and that windows ought to be mounted in an insulation to minimize heat losses. Keywords: heat transfer, passive building, thermal bridges, montage, heat balance, window Streszczenie Analiza dotyczy montażu okien. Obliczenia przeprowadzono dla czterech typów okien: dwóch powszechnie stosowanych i dwóch pasywnych. Projekt koncentruje się na roli montażu w stra- tach ciepła, wyjaśnia, co jest ważne przy wyborze okna i określa, jakie są główne konsekwen- cje. Analiza podnosi że zagadnienie montażu okna powinno być brane pod uwagę na etapie obliczeń współczynnika przenikania ciepła okna, a nie dopiero przy obliczaniu wartości współ- czynnika przenoszenia ciepła. Słowa kluczowe: przepływ ciepła, budynek pasywny, mostek termiczny, montaż, bilans energe- tyczny, okno
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.
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.
Thechartshowsaheatlossthroughananalyzedwindowinaperiodofonemonth. Time intervaladoptedforthepurposesofthisanalysisseemstobesufficient.Oneshouldnoticethatthedifferencebetweenapassivewindowmountedininsulationandacommonwindowmountedinawallisalmosttripledandequals91.11[kWh].Itshowshowgreatthelossescreatedbyabadfittingare.ItisshowninFig.3a.Thedifferenceresultingfromtheuseof[10]and[12]forthecalculationoftheheatdemandisapproximately 25%.(Anonlylossassociatedwithheattransferthroughwindows).Thisisavaluethatshouldnotbeignored.ThisisshowninFig.3b.
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.
