Comparative experimental investigation of air space height effects on a finned PV/T-assisted heat pump system

The air space height in photovoltaic/thermal (PV/T) air collectors governs the interaction among airflow velocity, convective heat transfer, hydraulic resistance, and photovoltaic cooling. However, the combined effect of air space height on performance of finned PV/T-assisted heat pump under real outdoor conditions has not yet been sufficiently investigated. This study experimentally investigates a finned air-based PV/T-assisted heat pump at three air space heights of 5, 7, and 10 cm. Each configuration was compared with a reference PV operating simultaneously under the same environmental conditions, while thermo-electrical, thermo-hydraulic, and exergy performance of PV/T system and the performance of the heat pump were systematically evaluated. Reducing the air space height enhanced convective heat transfer and PV cooling but increased hydraulic resistance, revealing a clear performance trade-off. The 5 cm configuration achieved the largest PV rear-surface temperature reduction of 23.22% and the highest average electrical and thermal efficiencies of 17.98% and 49.55%, respectively. In contrast, the 7 cm configuration yielded the highest relative improvements in electrical power and electrical efficiency, reaching 4.35% and 4.30%, respectively, while also producing the highest average thermal power of 591.08 W. Furthermore, PV/T air preheating increased heating COP of the heat pump by 5.06–5.11% compared with operation without PV/T assistance. These findings demonstrate that air space height is a critical design parameter governing the coupled performance of finned PV/T-assisted heat pumps and that operation requires balancing PV cooling, heat recovery, electrical performance, and hydraulic resistance rather than simply maximizing heat transfer.