Air source heat pumps (ASHP) experience performance degradation at low outdoor temperatures, resulting in a significant decrease in their COP. To address this limitation, this study proposes a hybrid operation that integrates a heat pump with a photovoltaic-thermal (PVT) system. A PVT-heated storage tank can offer a more stable heat source; however, under low-temperature thermal storage conditions, the operation of an auxiliary boiler may be necessary, leading to performance variations based on the chosen control strategy. Using TRNSYS 18, we compared two operation modes: Case 1, where a boiler reheats the tank before the water-to-water heat pump operates, and Case 2, where a dual-source heat pump automatically switches to air-source mode. Results showed that Case 1 achieved a higher seasonal COP (3.86) than Case 2 (3.65), indicating that boiler intervention effectively prevents performance degradation. In terms of energy consumption and CO₂ emissions, Case 1 recorded lower CO₂ emissions (1,572 ㎏CO₂) than Case 2 (1,607 ㎏CO₂). Moreover, Case 1’s PVT system generated 5,488.9 ㎾h during the heating season, exceeding the heat pump’s consumption (3,102.8 ㎾h) and enabling energy self-sufficiency. The annual CO₂ reduction reached 4,247 ㎏CO₂, offsetting system emissions and providing additional mitigation. These findings demonstrate that under low-temperature storage conditions, Case 1 represents the optimal strategy for both heating performance and environmental benefits when integrated with PVT.
Lee et al. (Tue,) studied this question.