The first purpose of this experiment was to measure the thermal performance of two solar heated domestic hot water systems under actual weather conditions. The second purpose was to compare the observations with the performance that would have been predicted by the "F" chart method.

An underlying concern was that the averaging techniques used in "F" chart would underpredict the daily performance during the hot summer periods and cause a safety or system related problem. The system chosen therefore combined the highest performance collectors commercially available with conventional closed loop design and a double walled heat exchanger having an effectiveness of 0.35. This combination would accentuate any potential for high temperatures in the collector loop that might lead to system related difficulties.