Research on the thermal balance of a novel independent heat extraction-release double helix energy pile in long-term operation

Ground source heat pump buried pipes offer potential in civil defense due to their concealment and reliability, yet face thermal imbalance issues. This paper adopts a double helix energy pile with independent heat extraction-release capacity and develops an experiment to compare the performance of independent operation versus joint operation. Furthermore, a verified 2D model facilitated extensive simulations for long-term thermal balance, integrating refrigeration load, principles of water use in an underground engineering, and heat pump model. Comparative experiments show that joint operation can effectively alleviate soil heat accumulation by more than 20%. Extended simulations reveal that as accumulated heat is removed, the unit's performance is improved, and soil heat accumulation can boost heat extraction. However, under domestic water heat extraction, the heat-extracting pipe shows low flow rates, leading to thermal accumulation, necessitating the use of water for equipment or additional feed water to improve heat extraction. Compared to uniform enhancement heat extraction, centralized enhanced heat extraction boosts overall heat extraction capacity by 35.1%, which can more effectively mitigate thermal imbalances and improve unit performance, and achieving thermal balance in the geotechnical area requires an enhanced extraction flow rate above 10.5 L/h, with over 56 m3 of water passing through the heat-extracting pipe.