Application of simple sky and building models for the evaluation of solar irradiance distribution at indoor locations in buildings

Abstract

Solar radiation is a key element that has a large impact on the indoor thermal environment. It is therefore important to incorporate the impact of indoor solar irradiance when evaluating the thermal environment within a real building. This paper proposes a real-time estimation method for solar irradiance reaching multiple occupant locations within a building from global irradiance data measured at a single point outside. First, Watanabe's decomposition model and Perez's transposition model are selected and applied to calculate direct and diffuse irradiance incident on a tilted facade. Then, the sky view factor (SVF), horizontal view factor (HVF), and unshaded fraction (Fu) are applied to calculate reductions in diffuse solar irradiance incident on the window area. The sunlit factor (Fsunlit) is applied to determine whether the direct solar beam incident on the occupant location is blocked or not. To calculate these four factors, a method of generating a simple sky model and a building model is presented for application to existing buildings. An experiment is performed to verify the accuracy of the calculation method. The indoor irradiance at a target location was measured by a pyranometer and also estimated by the calculation method. The measured and estimated indoor irradiance values were compared, and the results show a high estimation performance of the calculation method with a coefficient of determination of 0.95. This paper discusses the applicability of the proposed calculation method to the real-time evaluation of an indoor environment and to the control of building passive systems.