Abstract
During the past decades, large windows and glazed façades have become an important part of modern architecture and they are designed frequently in both public and residential buildings. However, besides the positive effect of such a design on building occupants, large windows may cause thermal discomfort. Cold inner window surface may generate draught in the occupied zone. Thermal comfort in rooms is usually assessed by measuring air temperature, relative humidity, air velocity and heat transfer due to radiation. In this study computational fluid dynamics (CFD) methods have been used to investigate these phenomena. Air movement caused by cold vertical window surfaces was evaluated and its impact on thermal comfort conditions in rooms have been outlined. Windows of different constructions and having different heat transmission coefficients were modelled (2.4, 1.6 and 1.0 W/m2K). CFD predictions showed that even in cases of low window thermal transmittance coefficient (U value), thermal discomfort conditions may appear in the room if the height of the window is more than 2.0 meters. Santrauka Dideli langai ir stiklo fasadai tapo neatsiejama šiuolaikiškos architektūros dalis. Jie projektuojami ne tik visuomeniniuose, bet ir individualiuose namuose. Nekalbant apie teigiamus tokios architektūros aspektus, didelių matmenų langai gali tapti šiluminio diskomforto priežastis. Už patalpos orą vėsesnis vidinis stiklo paviršius sukelia žemyn nukreiptą oro srautą, kuris tam tikru greičiu patenka į žmonių gyvenamąją arba darbo zoną. Vėsių stiklo paviršių sukeltų oro srovių intensyvumas priklauso nuo lango šiluminių savybių, jo konstrukcijos bei šildymo prietaisų įrengimo vietų. Dažniausiai mikroklimato sąlygos patalpose vertinamos matuojant oro temperatūrą, santykinį drėgnį, oro judrumą ir šilumos mainus spinduliavimu. Straipsnyje pristatomas tyrimas, kuriam buvo pasitelktas kompiuterinis oro judėjimo modeliavimas (skaitiniai skysčių ir dujų dinamikos metodai). Buvo tiriama oro judėjimo patalpose priklausomybė nuo langų bei stiklo fasadų konstrukcijų ir šiluminių savybių. Modeliuojant įvertinti trys langų tipai, kurių šilumos perdavimo koeficientų vertės: 2,4; 1,6 ir 1,0 W/m²K. Rezultatai parodė, kad net ir mažiausiai šilumai laidūs langai gali sukelti neleistiną oro judėjimą patalpose, jei jų aukštis viršija 2 metrus.
Highlights
Human thermal comfort is influenced by a combination of physical, physiological and psychological factors
computational fluid dynamics (CFD) predictions showed that even in cases of low window U value (1.0 W/m2K) thermal discomfort conditions may appear in the room, if the height of the window is more than 2.0 metres
CFD predictions showed that even in cases of low window U value (1.0 W/m2K), thermal discomfort conditions may appear in the room if the height of the window is more than 2.0 m
Summary
Human thermal comfort is influenced by a combination of physical, physiological and psychological factors. Glazed part of a building envelope has a significant effect on microclimate and building energy consumption Windows may cause both local and overall body thermal discomfort leading to occupants’ dissatisfaction and health problems. As it is well known, window replacement is a key action solving building refurbishment problems (Pikutis and Šeduikytė 2006). In this paper only thermal conditions and air movement caused by natural convection were considered Such factors as solar radiation and air leakage of the window are neglected. Ge and Fazio (2004) found that large tall windows may generate air speed up to 1 m/s (close to the surface) This problem is usually solved by installing heating devices below the windows. An analysis was carried out in several cases with high rooms having glazed façades (up to 5 m height) with and without convector heaters below the windows
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