Impact of shading on cooling and heating load

This paper explores the implications of shading the roof of a residence on the cooling and heating loads. This is done by simulating a thermal model of a hypothetical 2800 sq. ft house which takes into consideration direct and diffuse solar irradiation on its roof and walls. The simulation is performed for a home in the southwest portion of the United States, specifically, Phoenix. The simulation is performed twice: a) with half of the roof shaded with PV modules mounted on a rack, and b) with no PV modules. Even though the specific device used here to provide the shading is PV arrays, any other means would produce similar results. The dynamic thermal model of the house is implemented in TK-Solver. The simulation goes through every hour to determine the required cooling and heating load. It takes into consideration direct and diffuse solar irradiance. It uses the Sol-Air temperature approach to determine wall and roof temperatures. This approach modifies the outside skin temperature depending on direct and diffuse irradiation. Weather data for Phoenix, for the year 1990, is used in the simulation. The simulation results are used to perform an economic analysis, specifically, the impact on the payback period. The yearly cooling costs are reduced by $126, while the heating cost increases by $25. Thus the shading produced by the PV arrays has a net effect of reducing the yearly electric bill by approximately 11%. A major motivation for this study is to expose students to the tools and methodologies of modeling dynamic physical systems, especially in the energy area.