Research on capillary energy wall system of subwaystations in loess areas

In this paper, a new capillary energy wall system is proposed. This system lays a capillary grid in the cavity between the off-wall wall and the structural wall as a heat exchanger to transfer the condensation heat of the station to the surrounding soil, replacing the traditional cooling tower. Given the widely distributed unsaturated soil conditions in the loess area, a coupled heat and moisture transfer model is established in this study, and the thermal insulation measures and heat transfer performance of the system are studied by the numerical simulation method. The results show that extruded polystyrene (XPS) has excellent thermal insulation and moisture resistance, and it is recommended to give priority to the insulation material of energy walls. When the thickness of the thermal insulation layer is designed to be 8 cm, it can take into account both the thermal insulation effect and economic benefits. The radiative heat transfer of the walls on both sides of the cavity has little effect on the total heat transfer on the station side, and from the perspective of economy, there is no need to reduce the emissivity of the wall. The recommended water velocity of the branch pipe of the capillary grid is 0.05-0.13 m/s, and the spacing between the branch pipes is recommended to be 2-4 cm. The water temperature of the main inlet should be increased as much as possible to achieve the optimal heat transfer effect. When the system is in stable operation in summer, the heat transfer per unit buried pipe area can reach 31 W/m2, indicating high potential for application.