Improvement of thermal performance through window surface with interior blind by analyzing detailed heat transfer

Generally, the cooling loads of buildings with interior blinds are greater than those of buildings with exterior blinds. This is caused by convective and infrared heat gain from the blind and the air gap between the blind and the window’s inner surface. The aim of this study is to determine the optimum thermal properties of an interior blind that can generate the minimum window heat gain. Therefore, we analyzed the detailed window heat gain with several variables of window blinds. In addition, we found the best performance case in terms of the combination of the solar reflectance and the infrared emissivity that has the minimum window heat gain according to the different slat angles. We used the EnergyPlus software V.8.1 verified according to the ANSI/ASHRAE standard 140-2011 to analyze the detailed window heat gain. The results of this study informed the following conclusions. Increasing the solar reflectance of both sides of the blind slat is advantageous to reduce the window heat gain with the interior blind, regardless of the blind slat angle. Moreover, increasing the infrared emissivity of both sides of the blind slat is the best way to reduce the window heat gain in the case of the blind slat angle of 0°. However, in other cases, the best way to reduce the window heat gain is to increase the infrared emissivity of the front side of the blind slat and decrease the infrared emissivity of the back side of the blind slat.