Geothermal probes are used to transfer the heat from the ground : U-tubes made of materials with high thermal transmittance, in which a liquid absorbs heat and brings it to the surface or into the subsoil. The probes can be of three types:

• vertical

• horizontal

• compact

In the first case the probe goes down into the ground going to higher temperatures and requires special machines for the soil coring; in the second case, a sufficiently flat ground is necessary in which the pipes are laid following a simple excavation at a shallow depth but also on the bottom of an artificial or natural lake, exploiting, in this case, the water heat. In the third case, the probes are made by horizontal or vertical structures embedded in the ground at depths varying between 4 and 8 meters, exchanging heat through high surfaces made by special structural solutions.