Thermal and electrical performance optimization of photovoltaic/ thermal air Heaters: Comparative analysis of upper, double, and lower flow channel designs

To further the thermal and electrical efficiencies of PV/T air heaters, mathematical models of three types of the PV/T air heaters (upper channel, double channel, and lower channel) were established. The established mathematical models were validated by comparisons of the predicted temperature and Nusselt number and the experimental ones. The relative deviations of the temperature and Nusselt number were less than 2 % and 15 %, respectively. The results of the numerical simulations showed that the natural air convection occurred in the upper air channels resulted in the upper channel PV/T air heater achieving a superior convective heat transfer coefficient. The double channel PV/T air heater recorded the highest thermal efficiency of 57.39 % ∼ 73.87 %, which was 5.06 % ∼ 7.19 % and 46.45 % ∼ 50.60 % higher than that of the upper channel and lower channel PV/T air heaters, respectively, as the double channel configuration enlarged the effective heat transfer area between the airflow and PV modules. Although the lower channel PV/T air heaters recorded the highest electrical efficiency, the high thermal efficiency of the double channel PV/T air heater contributed to the fat that the double channel PV/T air heater achieved the highest overall efficiency compared to the other PV/T air heater.