An Optimal Open-Loop Flow Control for Double-Storage Solar Water Heaters

A considerable increase in the available energy from a double-storage solar water heater (SWH) can be achieved by an open loop control of the transfer flow rate (TFR) between the main water storage tank, which is attached to the collector, and a secondary storage tank. The optimal TFR profile, which is based on a priori-known load profile, weather, and solar radiation patterns, ensures minimal auxiliary energy requirement to meet load demands. The optimization is performed by comparing the evaluated system performance under various TFR profiles which are described by a sequence of step functions. Typical computations indicate that the utilized energy of a typical system may be increased by 10 to 30 percent while similar thermal efficiency optimization yields only a few percent improvement.