Evaluation of cold water temperature and tank size impacts on a PVT-assisted heat pump system performance for hot water applications

This study evaluated the performance of an indirect-expansion photovoltaic-thermal assisted heat pump (IDX-PVT-AHP) system designed for hot water production under the tropical climate of Chiang Mai, Thailand. The system comprised a 5.7 kW heat pump using R134a refrigerant, which extracted heat from a cold water storage tank thermally coupled with parallel photovoltaic-thermal (PVT) modules. Each 550 Wp PVT module generated electricity primarily to operate the compressor, while also supplying auxiliary thermal energy. Auxiliary heating was employed if the hot water tank temperature failed to reach 60 °C by 6:00 p.m. Mathematical models were developed to assess the effects of cold water temperature and storage tank capacity on electricity consumption, PVT module requirements, and system payback period. Maintaining the cold water tank at 18 °C minimized energy use but resulted in prolonged condensation on PVT surfaces, posing degradation risks. Conversely, aligning the tank temperature with real-time dew point conditions reduced condensation to just 7 h annually, while preserving energy efficiency. Increasing the number of PVT modules reduced reliance on auxiliary heating, but appropriate cold tank size was critical to avoid excessive cooling. The appropriate configuration, three PVT modules, a 1500 L cold tank, and a 1000 L hot tank, achieved a favorable 3.36-year payback period.