A Projection And Clipping Method To Calculate Direct, Diffuse, And Reflected Irradiation

Various approaches are used to determine direct, sky diffuse, and reflected contributions to the solar irradiance on building surfaces. Among these are ray tracing, pixel counting, and projection and clipping. Projection and clipping is closest to an exact solution but it is often considered as too slow. This paper presents an improved projection and clipping method to determine the direct and the sky diffuse contribution to the irradiance. In a second step a projection and clipping approach is applied to calculate the view factors between building surfaces, so that the reflected contribution can be obtained. The presented approach delivers results which are comparable to those obtained by EnergyPlus in acceptable computation time. This shows that modern building simulation tools can benefit from an approach that applies fewer approximations than common raytracing or pixel counting techniques.