Numerical Analysis of the Thermal Performance of a Novel Dual-Purpose Solar Air-Water Heater

Abstract

Flat plate solar water heaters (SWHs) are well-known thermal systems for their simplicity and efficiency in heating water. Enhancing their functionality, dual-purpose solar air-water heaters (SAWHs) integrate both water and space heating, thereby reducing energy costs while maintaining minimal installation complexity. These systems harness solar energy to efficiently transfer heat to both air and water, presenting a versatile solution for sustainable energy applications. This research investigates the thermal performance of a new design of dual-purpose SAWH under solar irradiation of 1100 W/m. In this innovative design, the water tubes feature a semi-circular cross-section to maximize contact area with the absorber. The study examines the effect of varying inlet water temperatures (32, 37, and 42°C) on heat transfer, temperature distribution, and thermal efficiency. Additionally, the effects of different air mass flow rates have been investigated. Results indicate that as the inlet water temperature increases, the heat transfer rate on the waterside decreases from 788 to 695 W due to the reduced temperature difference between the water tubes and the absorber. Conversely, the air-side heat transfer rate increases from 120 to 157.6 W, benefiting from enhanced heat transfer facilitated by higher temperature difference. Thermal efficiency shows a slight decline, dropping from 82.5% to 77.5% with higher inlet water temperatures. The effect of air mass flow rates (0.01–0.026 kg/s) and water mass flow rates (0.015–0.06 kg/s) on thermal efficiency were investigated, showing a 1.77% improvement in efficiency for air and a 5.13% increase in water flow rates. These findings emphasize the advantages of dual-purpose solar air water heater systems, achieving an average thermal efficiency of about 80%, which is significantly higher than the 77.6% and 27.8% efficiency of a comparable single-purpose solar air heater (SAH) and solar water heart, respectively.