Method of Calculating Solar Heat Transmitted Through Shaded Windows for OTTV in Consideration of Diffuse Radiation Diminished

Abstract

The energy used in the buildings in hot climate conditions is mainly for the cooling load requirements for air conditioning in summer. To reduce the energy consumption for air conditioning, the threshold value for OTTV (Overall Thermal Transfer Value) is regulated in energy standards for air-conditioned buildings of some subtropical and tropical countries. To ensure a satisfactory OTTV value, the top priority of building envelope designing is reasonable Window to Wall Ratio (WWR) with appropriate sun shading devices to reduce the heat penetrated through window glass into the buildings. Therefore, the accurate calculation of solar radiation through window glass with shading devices is very important to properly determine the cooling load of the air conditioning system in the summer and the energy efficiency of the architectural facade solutions. The research aims to calibrate the reduced solar radiation coefficient of the shading device (β) from the original method of calculating the solar heat transmitted through window glass with sun-shading devices, thereby completing the OTTV evaluation method with high accuracy. The calculation is based on the sunlight projection to determine the window’s shaded area created by shading devices of any shapes with consideration of diffuse radiation diminished. The results of β calculated showed that in tropical climate, the total solar radiation transmitted through the window glass calculated by the proposed method is much lower than the previous method. A computer software built from the proposed theory helps the designer easily choose the optimal sun shading solutions. The research conducts the calculation as an example for horizontal-inclined and the combined of horizontal and left/right vertical shading devices (accepted as EKE).