Energy Efficiency of External Perforated Window Solar Screens in Desert Environments: Effect of Screen Surface Reflectance

In hot-arid desert environments, solar radiation passing through windows increases buildings energy consumption. Shading of windows can reduce these loads. Previous research proved that external deep perforated solar screens can achieve up to 30% energy savings. Solar screen colors should be taken into consideration as the lighter the color, the more transmitted proportion of radiation due to increased reflectance, hence affecting daylighting and buildings thermal performance. This paper investigated the influence of surface reflectance on the energy saving capacity of solar screens in the hot arid desert environment. The relation between screen surface reflectance and other configuration parameters was examined. Series of experiments were performed using the EnergyPlus simulation software for a range of solar screen colors ranging from white screens having a visible reflectance of one, to black screens with a visible reflectance of zero. Simulations were conducted for a screen fixed in front of a window of a typical residential living room space in the Kharga Oasis, located in the Egyptian desert. It was found that light colored screens reduce lighting and heating energy. However, they significantly increase the cooling energy, and thus overall energy consumption. Results scientifically confirm the effectiveness of the traditionally used colors of the old "Mashrabeya" solar screens, which were typically dark. Conclusions prove that screens visible reflectance could reduce energy savings up to 14%. Optimum ranges of screen visible reflectance were recommended.