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The shade effect of a rooftop photovoltaic (PV) collector on a roof is usually ignored in building energy simulation in Transient System Simulation (TRNSYS) software. This disregard is due to either the unavailability of a suitable shading component in the simulation software or to an assumption that the shade on opaque surfaces, such as roofs, has small impact on the indoor temperature and the subsequent heating and cooling energy usage. However, for a relatively large collector area, ignoring the collector shadow on the roof may produce inaccurate results.

In this paper, a novel component is developed in MATLAB to simulate the shade effect of a collector using TRNSYS. The component is based on an isotropic diffuse sky model to calculate the beam and diffuse radiation blocked by the collector. The preliminary results show that 782 degree-hours of cooling can be saved, however, 1649 degree-hours of additional heating is required. The results indicate that for a large collector area the collector shade on the roof should be considered to be able to accurately estimate a dwelling's heating and cooling energy usage.

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