Geothermics in use
This section focuses on the uses of very shallow and shallow geothermal systems. They can meet the energy needs of a variety of building types (residential, office, industrial, etc.), by providing either heating (including hot water) or cooling. These systems can also store heat in the ground, where it can be reused during the following season.
The Earth is an excellent natural heat reservoir, as the ground temperature at depths above 10 metres is not influenced by atmospheric conditions and therefore remains stable. At 150 metres below the surface, the ground temperature is around 14 °C, which can be used for heating in the winter and cooling in the summer.
A shallow geothermal system can capture this heat and carry it to the surface using either a heat transfer fluid running through a closed loop, or water collected directly from an aquifer. Regardless of the transfer medium, its temperature must then be increased before it can be used to heat the building. A heat pump can transfer the Earth's heat to the building at a higher temperature. Among a building's various energy needs, many can be covered by very shallow or shallow geothermics.
A main use of geothermics is heating. While geothermal techniques can be used with any type of heating, they are especially well suited to underfloor heating. This is because they require a water temperature of 35 °C, which is lower than the 60 °C required by traditional radiators, allowing the heat pump to run more efficiently.
Geothermics can also be used to produce hot domestic water. To this end, the water must be heated to a higher temperature (around 60 °C, which is the minimum threshold to prevent Legionella growth) by the heat pump.
One of the main benefits of geothermics is that it can meet the increasing need for cooling in office buildings during the summer. Cooling is based on the same principles as heating, but the process is reversed. During the summer, the ground is used as a natural source of cold, which can be captured and carried to the surface using an open or closed geothermal system. The building is then cooled using a simple heat exchanger if only passive cooling (geocooling) is needed, or using a reversible heat pump if both heating and cooling are required.
More generally, geothermics can be used for seasonal heat storage. The idea is to use the Earth's thermal inertia to inject excess heat into the ground in the summer, and reuse it in the winter; conversely, excess cold can be stored in the winter, then used to cool the building in the summer.