TO-82-07-2 -- Evaluation of the FCHART/SLR Solar Design Process

The actual heating requirements of 137 passive solar houses were compared to the requirements predicted by a typical design process that used the FCHART/SLR design tool. The calculation of the actual space-heating auxiliary energy needed by the houses during the 1979-1980 heating season was based on fuel bills and appliance use information. The prediction for each residence relied on site-specific weather data for that period, on owner-estimated occupancy patterns, and on measured building characteristics. FCHART/SLR was used with this information to predict the space-heating auxiliary. A statistical comparison of the actual and predicted auxiliaries showed that the design process over predicted the auxiliary requirement by 60% with 112% standard deviation. A simple heat-loss calculation that ignored the solar contribution proved as accurate a predictor of the heating requirement as the solar design process in some cases.