Optimizing the beam and sky diffuse radiation calculations under random obstructions of urban environments

Solar radiation is important in studies of the energy and environment of buildings. Calculations of the direct beam and sky diffuse radiation, however, usually rely on numerical approaches, which can lead to notable calculation burdens. This research evaluates the update interval of the daily solar position series and the skydome discretization densities as they affect the estimation accuracies of the direct beam and sky diffuse radiation, respectively. Additionally, an approach is proposed for studying the direct beam radiation using a number of representative sun directions, the density of which is optimized for efficient radiation studies under external obstructions. Field measurements and simulations show that 61 sky elements can be sufficient for diffuse radiation estimations in low-latitude regions. For the direct beam, on the other hand, more than 1100 representative sun directions are necessary. The accuracy is comparable to that of the approach in which the sun position is updated in the calculation interval every 2–10 days. The representative sun direction approach and the results of the optimized day interval and sky discretization density are essential to efficient building simulations conducted at high frequencies.