Research on seasonal soil thermal energy storage strategies of a photovoltaic/thermal - coupled ground source heat pump system in severe cold regions

In severe cold regions, the long-term operation of ground source heat pump (GSHP) systems can cause soil thermal imbalances, potentially leading to system shutdown. To address this critical issue, this study proposes a hybrid system that couples photovoltaic/thermal (PV/T) collectors with a GSHP. Two control strategies for the transition season, namely direct thermal storage and indirect thermal storage, are introduced to actively regulate and restore soil heat. A dynamic simulation model of the system was developed using TRNSYS, with a focus on analyzing the long-term effects of different thermal storage modes on soil temperature and system performance. Simulation results indicate that the system maintains an annual soil temperature fluctuation within 0.5 °C, with average heat pump COP of approximately 4.0 and 7.3 during the heating and cooling seasons, respectively. Comparative analysis showed that the direct thermal storage mode increased the thermal storage duration by 3% and soil heat gain by 9.22% compared with the indirect mode. A 10-year simulation confirmed soil temperature stability at 9.0-9.16 °C, demonstrating the effectiveness of transition season thermal storage strategies in thermal recovery. This study not only demonstrates the simulation-based feasibility and application potential of the PV/T-GSHP hybrid system in severe cold regions but also offers a potentially replicable solution for low-carbon and efficient building energy systems in such areas through the innovative integration of multi-energy complementarity and cross-seasonal thermal storage control.