Although the performance of solar domestic hot water (SDHW) systems has been well studied, there are several promising control alternatives that have not been thoroughly investigated. Reduced constant collector fluid flow rates, variable collector flow rates, and variable volume storage are several alternative strategies. This paper presents the results of an analytical study using the TRNSYS simulation program in which the thermal performance of SDHW systems utilizing alternative control strategies are compared while operating under realistic conditions in several different climates of the United States. The effects on system performance of time of year, collector area and quality, preheat storage tank volume and energy losses, occurrence of mixing the preheat storage tank, controller temperature deadbands, auxiliary set temperature, total daily usage, and load distribution are investigated.

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