Long-term performance simulation analysis of solar-assisted borehole thermal energy storage combined with a heat pump heating system

Borehole thermal energy storage can avoid the diurnal and seasonal mismatch between energy supply and demand, making it an effective way to utilize renewable energy for heating. This study proposes a heating solution that integrates solar-assisted borehole thermal seasonal energy storage (SABTES) with a heat pump system, which targets the dynamic thermal load demands of buildings in cold regions. Parameters such as the collector area, circulation flow rate, and thermal storage volume are selected. A model is established via TRNSYS for simulation analysis. The simulation results indicate that the collector area is positively correlated with the overall operating temperature of the borehole heat exchanger. With a unit circulation flow rate of 0.03 m³/(h·m²) in the collector and pump operating/stopping temperature differentials set at 10 °C/2 °C respectively, the solar collector module demonstrates the collector efficiency of 45.2 %. A larger borehole spacing can achieve greater thermal storage efficiency, with an average decrease in the BHE center temperature of approximately 6.68 °C/m as the borehole spacing increases. With the SABTES-GSHP configuration, an instantaneous average system COP is over 2.80. Compared with the SABTES heating system, the thermal storage volume can be reduced by 72 % while still meeting 45 °C, reducing the initial construction cost by 56.7 %.