A procedure of testing for rating solar domestic hot water (SDHW) systems is currently under consideration by a project committee of the ASHRAE Standards Committee. The procedure requires that the entire SDHW system be assembled in the laboratory and that the system be subjected to specific diurnal variations of the environmental conditions controlling the system performance, such as incident solar radiation and ambient temperature, while the system supplies hot water at specified temperature, times, and draw rate throughout the day. The test continues until the system performance is near-identical for successive days. It is proposed that the rating be the daily "fractional energy savings" under this quasi-steady-state condition. The actual collector array can be used and irradiated with a solar simulator. Alternately, the collector module comprising the array can be tested separately following ASHRAE Standard 93-77, the results used to compute the thermal output of the array under the specified system test conditions, and this thermal output supplied to the system during the system test using a conventional energy source.

The purpose of this paper is to describe the proposed test procedure, suggest alternate ways the simulation of the collector array thermal output can be accomplished in the laboratory, and report on progress being made at the National Bureau of Standards to validate the procedure.