Vertical geothermal solutions for the tertiary sector

A construction project combining energy innovation and heritage

The municipality’s specifications were clear: conserving the historical building, creating an extension that fits naturally into its environment, ensuring the whole is exemplary from a sustainable development viewpoint (BBC) and remains consistent with the surrounding ecodistrict.

We opted for geothermal technology because the building had to be exemplary with regard to its thermal shell, and for the opportunity to have heating and cooling installed ahead of the expected climate changes. We wanted renewable energy and to keep our carbon and environmental footprint as small as possible. Finally, the return on investment for this building being lower than the probable lifespan of a public building, this type of installation was viable.


Project type=> Renovation and extension
Building type => Tertiary
Construction time => 15 months
Net surface area => 1,887 m2
Cost of construction => €5,385,147
Proportion of geocooling cost => < 2.0%
Cost/m² =>  €2,854/m2

Operating feedback

Terrendis vertical geothermal probes were selected as part of this public building renovation project because they are suitable for an existing building as well as new constructions.

This vertical geothermal probe solution was adopted for heating and cooling for the entire building, except from the server room, which requires what we call “process operation” rather than a comfort approach.

For this project, Elydan supplied the Double U vertical geothermal probes, designed to recover heat from the ground. A liquid coolant recovers the heat energy from the ground via the probe and converts it using a thermodynamic (heat pump) system than can be used to heat or cool the building.

Made from High-Density Polyethylene (PE 100 RC) and compliant with standard NFX 10960, the geothermal probes are produced from start to end then tested in the Rhône-Alpes region, at the plant in Saint-Etienne-de-Saint-Geoirs.  Heating and cooling is then possible, via the ground, over the predefined surface area. Now, the project’s total cooling energy requirements are provided by the heat pump.

Number of probes => 11 units at 100m

Thermal output => 89 MW

Cold output => 50 MW

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