Even at a depth of only ten metres, the temperature of the ground is almost constant, between 10 and 15 degrees Celsius. Concrete geothermal piles, sunk into the ground to a depth of up to several score metres, have a dual purpose, as the building’s foundations on unstable ground and as a means of heating or cooling it.
The exchange of heat takes place through the pile’s reinforced concrete wall, via a fluid circulating in a system of flexible exchanger tubes fixed to each pile’s armature cage.
At the top of the piles these tubes converge on a heat pump, which transfers the energy into the building, heating it in the winter and cooling it in the summer.
Network of exchanger tubes in the armature cage
© Pinto
Geothermal pile foundations
For the system to work efficiently, the ground has to have good thermal conductivity and be saturated with water.
Geotechnical investigation is therefore necessary to determine the feasibility of installing geothermal piles.
The expansion and contraction caused by the heating or cooling of the fluid circulating in the piles has to be taken into account for their design, in order not to affect the building’s stability.
Heat exchanger tubes can also be installed in other types of foundations with armature cages. The Odéon Tower in Monaco has 20 kilometres of tubes in its diaphragm walls and pile foundations.