Soil Heat Deficit Regulation-Based Cross-Seasonal Heat Storage of Medium-Deep Borehole Heat Exchanger

Medium-deep borehole heat exchanger (MBDHE) is a clean building heating solution that offers improved indoor thermal comfort, but it risks heat extraction capacity deterioration due to insufficient geothermal heat flux recovery. Cross-seasonal heat storage can mitigate heat extraction capacity deterioration. However, previous studies focused on optimizing the heat storage parameters without considering the mutual inhibition between geothermal heat flux recovery and the heat storage. This paper proposes a soil heat deficit regulation-based cross-seasonal heat storage method, which expands the soil heat deficit to enhance the geothermal heat flux recovery and heat storage simultaneously for improved heating performance of the MDBHE. The effectiveness of the proposed method is demonstrated by using an MDBHE model validated against actual engineering data. The results show that the flow rate-based soil heat deficit regulation is more effective than the temperature-based soil heat deficit regulation. Expanding the soil heat deficit by lowering the heat extraction temperature effectively increases the heat extraction capacity of MDBHE by up to 44.82% with a relatively stable heat storage efficiency. Expanding the soil heat deficit by increasing the heat extraction flow rate increases the heat extraction capacity by up to 55.93% and improves the heat storage efficiency by up to 18.71%. Furthermore, the robustness of the soil heat deficit regulation is verified under different heat storage conditions. Therefore, the proposed method can effectively improve the heating performance of MDBHE, enhancing indoor thermal comfort and contributing to the advancement of low-carbon building heating.