Geothermal engineering can provide a low-carbon, competitive solution for cooling or chilling buildings by transferring heat to the subsurface.
16 September 2020
Heat exchangers at BRGM's Geothermal platform

Heat exchangers at the BRGM Geothermal Platform (Orléans, 2009).


The period from January to July 2020 was the hottest period in France since scientists began recording temperatures. The increase in the mean global temperature could be from "6.5 to 7°C in 2100" compared to the pre-industrial era (1850 to 1899), according to the pessimistic scenario published by CLIMERI France. Heatwaves are also expected to increase in intensity and frequency. 

It is already indispensable to be able to cool or chill certain buildings in summer (such as hospitals, retirement homes, etc.). It will become crucial for current construction and renovation of buildings if they are not to become obsolete in 20 years' time due to unbearable temperatures. But how can we reconcile this need for comfortable coolness with the imperative of energy sobriety? 

How can cold be produced with geothermal energy? 

Surface geothermal energy (at a depth of less than 200 metres) makes it possible to create heat using a heat pump but also cold, with or without a pump. At these depths, it is not the high temperature of the subsurface that is valued, but rather its inertia over the seasons. Two systems are commonly used in this field: the heat pump in cooling mode to obtain active cooling, and geo-cooling to provide the cooling fluid. 

The first consists in removing heat from the building via the evaporator. The second, the compressor, then raises the temperature level in order to evacuate this heat, through an exchange with the cool subsurface.