A fast and simple numerical model for a deeply buried underground tunnel in heating and cooling applications

Underground tunnels used in underground constructions serve as huge ventilation pipes that conduct outside fresh air into a cavern. Predicting the heat and mass transfer is critically important in order to exploit the relatively constant underground soil temperature for heat transfer, and to ensure sufficient ventilation for occupational safety. This paper presents a numerical model developed to describe the simultaneous heat transfer between air and the tunnel surface, taking into account the condensation phenomena inside the tunnel. The soil surrounding the tunnel is treated as an equivalent long annulus and divided into several cross-section slices. With appropriate assumptions, a set of discrete numerical equations and its solution is proposed. The developed model is validated against field measurements which showed good agreement between the simulated results and measurement data. The model is then applied to an underground tunnel operating for a ten-year-period.