Experimental and theoretical study of the efficiency of a dual-function solar collector

A design of solar collector that is able to provide both hot water and hot air has been proposed to increase annual thermal conversion ratio of solar energy. By modifying the conventional flat-plate solar water heater, the collector with L-shape fins can also function as a double-flow solar air heater. Experiments have been conducted to investigate the dual functions of the collector. It is shown that the thermal efficiency of the collector reached 50% in water heating, and varied from 41% to 55% in air heating depending on the ambient condition and flow rate. Mathematical model has been presented for the collector working in air heating mode. The theoretical results are in good agreement with the experiment results. Theoretical results show that the air flow rate is a dominant factor to determine the efficiency. The enhancement of the L-shape fins on the performance of the collector in air heating is also proved from the theoretic results.