Cold storage scheme for energy tunnels to improve the ground thermal accumulation around subway tunnels

Over the long-term operation of subway systems, there is potential for thermal accumulation in the ground surrounding the tunnels. In this paper, a novel solution for thermal accumulation improvement by utilizing the cold storage system of energy tunnels is proposed. During cold seasons, segment heat exchangers are activated to store cold energy in the surrounding ground, which is used to reduce the ground temperature during hot seasons. Feasibility analysis results show that within 3.5 m from the segment, the ground temperature at the start of June and the end of September decreases 0.56–2.18 °C and 0.12–0.95 °C, respectively. The long-term cumulative temperature increase in ground is suppressed. The impacts of ground thermophysical properties on the ground temperature reduction are small, and the long-term impact of the subway opening date is limited, whereas the daily cold storage duration has a significant impact. After cold storage, the temperature of the ground in contact with the segment decreases by more than 11 °C in a 24-h daily cold storage scenario, while that decreases by less than 4 °C in an 8-h scenario. The proposed solution facilitates seasonal energy utilization and offers a new approach for controlling subway tunnel thermal environments under long-term operation.