Geothermal potential of tunnel infrastructures – development of tools at the city-scale of Basel, Switzerland

This work presents preliminary evaluation elements for geothermal potential assessment and thermal influences of planned tunnel infrastructures for the urban agglomeration of Basel (Switzerland). In dependence of the tunnel type (motorway or railway) as well as its location related to the geological and hydrogeological settings different solutions for shallow geothermal energy systems (SGE) are investigated. ‘Passive’ and ‘active’ SGE have been evaluated, including heat-exchanging segments installed in tunnel lining structures and thermal exploitation of water circulating in culvert systems. First results suggest that thermal activation of a planned railway tunnel is most efficient where it is located within groundwater-saturated zones of the unconsolidated rock deposits. In summer, thermal power of 3.7 and 1.4MW can be exchanged from two 736 and 284 m-long tunnel sections, respectively. Accordingly, in standard heat pump operating conditions a thermal energy of 10.4 and 3.8 GWh can be delivered for ‘cooling’. In winter, thermal power of 1.9 and 0.7MW can be exchanged, respectively, and a thermal energy of 5.2 and 1.9 GWh can be delivered for ‘heating’. SGE within culverts reveals to be favorable in heating mode only and for sections where the motorway tunnel runs perpendicular to the regional groundwater flow field and where ambient groundwater temperatures are high. Under such conditions along a 320 m-long tunnel section thermal power of up to 0.4MW can be provided in summer and 0.8MW in winter, respectively, and thermal energy of 1.1 GWh in summer and 2.1 GWh in winter, can be delivered.