A simplified method to determine the comprehensive heat transfer quantity in subway tunnels

Abstract Thermal environments influence the comfort and energy consumption in subway tunnels and are mainly controlled by environmental control systems (ECSs). The comprehensive heat transfer quantity in surrounding rock/soil and retaining structure (CHTQSR) of a subway tunnel is one of the essential factors to determine the thermal load of a subway ECS, and it has significant influences on the investment of subway projects, operation energy consumption, and the long-term stability of environmental control effects. The current investigation outlined a straight-forward and simplified analytical solution to calculate the internal face temperature and heat transfer quantity in a subway tunnel based on an unsteady hollow cylindrical heat transfer model. With appropriate simplification, a simplified formalism of CHTQSR was obtained. Moreover, the analytical solution was validated by numerical simulation and physical model experiment, and a satisfactory agreement was achieved. Furthermore, the thermal environment evolution process, the heat transfer characteristics and influencing factors of the surrounding rock/soil and retaining structure were analyzed, and different measures to enhance its heat transfer capacity were put forward. This study not only provide supports for the optimal design of ECS, but also provide references for the researches of energy tunnel, energy geostructure and waste heat recovery system which are both economically and environmentally friendly.