Thermal activation of tunnel infrastructures: city-scale solutions for Basel, Switzerland

As open space in urban areas is very rare and mobility requirements are constantly increasing, new infrastructures are being planned and constructed in the subsurface. These underground infrastructures may additionally be used as Shallow Geothermal Energy systems (SGE) to exchange and store heat. For real-world tunnel set-ups in the urban agglomeration of Basel (Switzerland), optimal closed and open SGE systems were evaluated depending on the type of tunnel infrastructure (motorway or railway) as well as geological and hydrogeological settings. This contribution illustrates strategies for seasonal Thermal Energy Storage (TES) in solid rock layers at depth of approx. 25 and 35 m by combination of Tunnel Absorber Segments (TAS), and very shallow Borehole Heat Exchangers (BHE). Investigations focus on the efficiency of the TES systems where the BHE extracts heat injected by TAS. First results suggest that thermal energy of up to 290 W could be recovered by the simulated double-Uloop BHE. Furthermore, TES system efficiency can reach values of up to 10.2%. The here presented performance analysis provides preliminary evaluation elements of SGE combined use as a further step for spatiotemporal thermal management in realistic urban settings.