Algorithms for modeling secondary solar heat gain

This report details the development of algorithms for modeling the interreflected solar heat gain from neighboring structures (secondary solar heat gain) and implementation of the algorithms in a building energy simulation program. The algorithms account for the contribution from unobstructed and interreflected solar radiation on the solar heat gain through opaque and transparent surfaces. The algorithms are an adaptation of a freeware ray-tracing program which models specularly and diffusely reflecting surfaces under varying sky conditions. The surfaces may be nonplanar and have anisotropic transmittance and reflectance characteristics, which makes it possible to model such objects as venetian blinds and trees. The authors demonstrate implementation of the algorithms in a building energy simulation program to show the necessary steps to accomplishing this task in other building simulation programs.