Solar-Load-Ratio Statistics for the United States and Their Use for Analytical Solar Performance Prediction

This paper presents a new analytical method for estimating the annual auxiliary space heating energy requirements of passively heated solar buildings. It features closed-form, analytical expressions for solar system performance that are amenable for use with an inexpensive, programmable calculator. The method is applicable to direct gain, water storage wall, and masonry storage (Trombe) wall passive solar space heating systems and does not restrict the user to a particular “reference” system. It permits the rapid assessment of the performance effects of variations in such system features as south glazing, thermal storage mass, and fenestration insulation. Site specific data for its implementation are included for twenty-six cities in the United States. Also, the method is illustrated with examples. Auxiliary energy estimates from this model are compared with measured auxiliary energy use data from owner-occupied, passively heated solar houses. Statistically significant agreement is demonstrated between predicted and measured results in the 1981–1982 space heating season. While this does not constitute a complete validation of the method, it does demonstrate its viability when applied to actual residences.