Numerical modelling and optimization of the finite-length overhang for passive solar space heating

Overhangs are usually used with direct gain solar heating to reduce gains during times when heat is not wanted in the building. As these energy-saving devices may partially shade absorbing surfaces during periods when collection is desired, analysis of their effect on the absorbed radiation is necessary. In this article, a detailed mathematical model was developed to simulate the solar thermal energy transfer through a window with finite overhang. The effects of the finite overhang on the solar energy components (i.e. beam and diffuse) received by the aperture is considered in detail for various shadow patterns. A simulation was carried out to analyse the energy saving. In the practical applications, the use of these shading devices in the building can be beneficial at certain times of the year; however, they are counter-productive at some other times. Therefore, a multi-objective optimization was needed for optimal sizing to maximize the total annual energy saving through the building during cold and hot periods. The modified solar radiation synthetic energy-savings coefficient objective function was used to calculate optimal shading.