Energy performance of a Swiss thermo-active underground train station

© 2019 EPFL

© 2019 EPFL

The Laboratory of Soil Mechanics (LMS) of EPFL is leading the energy performance evaluation of the first energy underground train station in Switzerland. This project has been developed in the context of the CEVA project in Geneva. The project is being developed for the Services Industriels de Genève (SIG) in collaboration with BG Ingénieurs Conseils.

The under-construction railway line CEVA will connect the city centre of Geneva (Switzerland) to Annemasse (France). A portion of the underground infrastructure, located at Lancy-Bachet station, in the south-western part of Geneva, is equipped with energy geostructures (energy walls and slabs) for a total surface area of around 5000 m2 of heat exchangers embedded in the geostructural elements. To our knowledge, this is the first “energy station” in the country.

Energy geostructures, such the energy walls and slabs implemented in this project, is a technology that provides renewable thermal energy to the built environment, by injecting and extracting heat to/from the ground. Taking advantage of the quasi-constant ground temperature at shallow depths, energy geostructures satisfy both the heating and cooling energy needs of buildings. The energy geostructures concept adopt heat exchanger loops, usually made by plastic pipes, fixed to the steel cage of reinforced concrete geostructures (e.g. retaining walls, piles, slabs, etc…). A heat carrier fluid is circulated into them, exchanging heat with the surrounding materials. Heat exchangers are connected to a heat pump and to the heating/cooling circuit of the served building, forming a ground source heat pump system. Energy geostructures installed at Lancy-Bachet train station aim to serve the nearby neighborhood which is currently under development.

Under the leadership of Prof. Laloui, the LMS-EPFL is a world leader group in the area of energy geostructures with twenty years of research and technology transfer.

On January 2020, the construction of the energy station will be concluded. We are now initiating energy performance evaluations by the thermal activation (heating, cooling and cyclic operation) of a portion of the thermo-active walls. This will allow for the validation of the amount of energy that the station will provide as well as the structural behavior through a series of thermo-mechanical energy-wall tests. The goals of this stage of the project are related to the multidisciplinary nature of energy geostructures and encompass the analysis of the thermal and mechanical behavior of energy walls. On one hand, it is essential to quantify the energy potential of the installed energy geostructures and to define scenarios for future energy exploitation. To do so, one of the main challenges is to define the role of each heat exchange mode within the materials around the energy walls, with particular emphasis on understanding the hydro-thermal interactions among the energy wall and the airflow in the train tunnel. On the other hand, the preliminary quantification of the thermally-induced mechanical effects will be key for defining analysis and design rules of such energy geostructures.

An initial phase is dedicated to conventional thermal response tests (TRT), a second phase will present constant, one-way heating followed by one-way cooling tests, and a third phase foresees the simulation of the real heat pump functioning. A thermomechanical monitoring system is installed on the wall facing the train tunnel.

With this project, LMS-EPFL provides the needed support for the development of this renewable energy technology in Switzerland.

Contacts for further information:

June, 2019.