Evaluation of the Potential Use of Geothermal Heat Exchangers in the CEVA Tunneling Project

Abstract

The CEVA railway connection is planed in Geneva, Switzerland. Along the pathway, houses, schools and commercial centers will also be built and integrated into a general energy scheme and energy supply. Since considerable parts of railway lines are running in tunnels, the utilization of geothermal energy can be of major interest along sections near well-developed infrastructure. As such heating of buildings in winter and cooling in summer using a heat pump could be performed. The objective of this concept study is to quantify the energy balance obtained from the use of absorber elements integrated into the lateral walls and bottom slab of the CEVA tunnel. The potential of the produced power has been calculated for different tunnel sections and different utilization scenarios. At first, a one-dimensional analytical approach of the system is presented for sensitivity analyses of various parameters variations. Further on, the temperature field is computed in 2D Finite Element models applying the geometry of typical 100 m long tunnel section and using the numerical code FRACTure. Different scenarios for energy utilization and installation variants have been considered. Typical usage of the system (mean temperature of the energy piles is -1°C in winter and 30°C in summer, for combined heating and cooling use) result in total annual energy of 560 MWh for heating and 480 MWh for cooling. The results strongly depend on the temperature level in the tunnel, which in turn depends on the railway transit and the air condition of the trains. Optimum results are obtained for balanced heat load profiles.