Study On The Thermal Properties Of External Windows With Inside Curtains

Building energy consumption in China accounts for about30%of the total socialenergy consumption. Among them, the heating energy consumption is the maincomponent of building energy consumption. However, the heat loss through thewindows and doors accounts for30%to50%of heating energy consumption. Atpresent, the outside windows of heating building are most equipped with heatpreservation curtains. But in heat load calculation, the heat preservation effect ofcurtains is always as a more security, not as a heat load calculation. So, it is notadvisable for building energy saving. Moreover, because thermal resistance of thebuilt-in curtain is relevant to some factors, curtain type, window type and the curtainfolds, so the research results are less.In this paper, the physical model of outside window hanging curtain inside issimplified, from the vertical and horizontal directions. And the heat-transfermechanism of the outside window physical model is analyzed form three aspects, heatconduction, convection and radiation. Based on determination of the space and theflow pattern, the mathematical formulas used in the process of calculating the modelare established, and then the calculation method of total thermal resistance of outsidewindow with inside curtains have been gained. Next，for the air layer formed byoutside window and internal curtain, analysing the convection and radiation heattransfer process, the calculation method of air layer’s thermal resistance have beengained. After optimizing and analysing the air layer thickness, we can find that theoptimal gap between curtain and window, or curtain and curtain, is about0.06m to0.08m. Making use of the physical model and the calculation method established before,the curtain’s additional thermal resistance had been calculated, at situations of differentcurtain type and different window type. The results show that: the thermal resistanceproduced by double curtains is greater than the thermal resistance produced by singlecurtains; the thermal resistance produced by thick and heavy curtains is greater thanthe thermal resistance produced by light and thin curtains. For single window,equipped with single cotton curtain, single linen cloth curtain, single gauze curtain anddouble curtains, the additional thermal resistance is respectively about0.22m~2·K/W，0.19m~2·K/W，0.18m~2·K/W，0.43m~2·K/W，and the total thermal resistance of outsidewindow respectively increased about55%，54%，50%，70%; For double window,equipped with various curtain above, the thermal resistance are about0.21m~2·K/W，0.17m~2·K/W，0.16m~2·K/W，0.40m~2·K/W, and the total thermal resistance of outsidewindow respectively increased about40%，32%，30%，50%. The additional thermalresistance of the calculation method established in this paper can also be applied toother built-in curtain thermal resistance calculation.