Long-term assessment of thermal sustainability of thermoactive geostructures

Thermoactive geostructures represent an original and efficient technique for fulfilling the energy demand of buildings and infrastructure, in terms of both cooling and heating. Thermal and mechanical aspects have to be considered to achieve a proper design of such structures. This paper focuses only on thermal aspects and deals with the development of an original approach based on the analysis of thermal flux and volumetric thermal power to assess the thermal sustainability of a thermoactive geostructure. This approach is firstly applied to a simple three-dimensional geometry to validate some numerical implementation issues. A case study based on a Grand Paris Express metro station is then presented and analysed in terms of temperature variations and heat exchanges. The consideration of the groundwater flow and the thermal exchanges by conduction and advection provides a new and better insight on the thermoactive geostructure energy assessment. Furthermore, the obtained numerical results show the zones of the geostructures where the heat exchanges are the most significant and where the risk of temperature drift is the highest. This analysis can be used to improve the design of the thermoactive metro station.