Of all possible applications of solar energy, it appears that domestic water heating is the closest to being economical [1, 2] and the one likely to reach full commercialization first. As a result of this and the fact that solar water heating systems can be designed, assembled, and sold as packaged systems, the American Society of Heating, Refrigerating,and Air-Conditioning Engineers (ASHRAE) has recently formed a standards project committee to develop a standard testing procedure for such systems.

In order to support the work of this committee and to gain insight into performance of solar domestic water heating systems, the analysis outlined in this paper was undertaken. The primary objective was to examine different ways of correlating the primary performance factors of such systems and then to use any correlation technique found successful as a possible basis for the standard test.

The analysis involved simulating typical state-of-the-art systems using the University of Wisconsin computer program TRNSYS [3,4]. The simulations and associated analyses were successful in indicating a method of correlating the fraction of the hot water load supplied by solar energy with the primary independent variables governing the system performance. Actual test data for a commercially-available system were then used to substantiate the applicability of the correlation.