Heat Pumps Energy Transfert

The calories extracted from the ground are transmitted to the building via heat pumps, usually electric ones. Heat pumps carry out a thermodynamic transfer of calories coming from the geothermal probes toward the building. They are characterized by a coefficient of performance (COP) which is defined as the number of kWh provided to the building per (electric) kWh consumed by the pump. The COP is not constant: it depends on the temperature level in the fluid coming from the probes, and on the temperature level required by the building. Heat pumps are designed to function optimally (i.e. with high COP) within fixed temperature limits. Outside this range the COP goes down.

In the event of thermal imbalance of the ground (cooling, for example), the heat pumps can be brought to work on ill-suited temperature ranges, therefore with a lower (or even mediocre) efficiency.

Unbalanced geothermal systems are characterized in the long run by a lowering COP, as the ground is getting cooler. The consumption of primary energy raises in time, with a direct impact on environmental and economic performances of the installation.