Heat harvesting characteristics of building façades integrated photovoltaic /thermal-heat pump system in winter

The water temperature of building-integrated photovoltaic/thermal systems is an important indicator of building space heating. However, in the winter, this system's heat loss is significant, and the low-temperature water cannot meet building heating standards. Meanwhile, previous research on building envelopes integrated PV/T - heat pump systems have primarily focused on the performance of systems installed on limited roofs of buildings, which conflicts with the requirement for energy consumption in metropolitan high-rise buildings. This study proposes a photovoltaic/thermal-heat pump system (BIPV/T-HP) mounted on the building façade to solve this problem, and a numerical model is developed to assess the heating performance. The results showed that increasing the flow velocity from 0.05 m/s to 0.5 m/s reduces the mean outlet water temperature from 16.11 °C to 9.55 °C, but increases the operating times of the heat pump from 6 to 8 in January, and increases the heating capacity of the BIPV/T - HP system from 58.6 kWh to 90.5 kWh over the entire heating season. Meanwhile, higher temperature thresholds raise mean water temperature and increase heat loss, resulting in a reduction in heat pump output from 111.3 kWh to 50.2 kWh.