Conversion of tunnels and stations into geothermal systems

The Brussels Métro Nord (BMN) project consists in the extension of the current line 3 to the north of the region, with the construction of a new section linking the North station in Schaerbeek to the Bordet station in Evere. The aim of this intervention is to better connect the North and South districts of Brussels with its city center. The line has a total extension of 4.5 km and includes 3.8 km of tunnel and 7 stations. GEOEG has analyzed the feasibility of thermal activation of this tunnel line and its stations in collaboration with the partner Amberg Engineering.
Plan view of the considered infrastructure.
Equipping infrastructures such as tunnels with pipe heat exchangers allows to valorize their conventional and sole structural support role with an innovative clean thermal energy supply role. Turning infrastructures into heat exchangers specifically allows to harvest both renewable geothermal energy from the ground and waste thermal energy from the interior of the underground structure. In this manner, infrastructures turned into geothermal heat exchangers not only allow to represent a rational approach to harvest and reutilize clean thermal energy, but they also allow to reduce the ventilation costs and avoid/mitigate subsurface heat islands resulting from the operation of these infrastructures. The clean thermal energy harvested from tunnels can serve local heating and cooling uses in underground stations or other constructions located nearby, as well as district heating solutions.
Example of 3-D finite element model performed to design energy tunnels. © GEOEG
The analysis performed by GEOEG for the BMN consisted in assessing the feasibility and estimating the potential associated with the thermal activation of the considered infrastructure. Multiple thermal activation scenarios for tunnel segments and/or stations were considered to provide a solution that together with complementary vertical geothermal heat exchangers operating underneath the stations can supply heating and cooling to real estate development projects in the vicinity of the metro line.
Cross-section examples of the BMN depicting the potential of turning selected portions of such underground infrastructure into an energy infrastructure.

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