Performances Clean Technology and Business

As for geothermal applications in general, the interseasonal storage is best suited for heating and/or cooling efficient buildings , that is, buildings that require medium temperature levels. So dissiation means, such as heating/ cooling floors (10°C / 30°C regime), or buildings with active structure are most adapted to the system. Those working with higher temperature regimes (40°C / 70 °C) are put at a disadvantage.

The performance has to be evaluated on a given period of time, say one year. It accounts for the global performance of the installation (global Coefficient Of Performance, COP), which integrates all consumptions of the various equipments (heat pumps, circulating pumps, …). In our case, the COP is the ratio between the energy used by the building (Eu) and the energy actually consumed by the building (Ec) to provide Eu : COP = Eu/Ec. Traditional geothermal installation have a COP that is bound to heat pumps models, and generally have a COP ranging from 3 to 4 : for 1kwh of electrical power, they transfer from 3 to 4 kwh of thermal power.

In our case, stored energy is used to increase the COP. For example, on a “cooling + heating“ operation in an efficient building, the geocooling mode (direct cooling) offers a cost effective solution for cooling in summer, thanks to the cold stored during winter. Thus the COP in summer is all the higher, as heat pumps may be bypassed. The same way, heat stored in summer allows optimized consumption of heat pumps during winter, enhancing the COP.

It results an annual electrical COP that is greater than in a traditional geothermal installation. It is generally ranging from 5 to 7, allowing to divide by at least 2 the primary energy used by the building (following french standard definition : 1kWh electric = 2.58 kWh primary). In other words, a building designed to consume 100 kWhr/m2/year of primary energy for its thermal needs will effectively use less than 50 kWhr/m2/year (primary), and less than 20 kWh/m2/year (electrical).

However the performance can only be foreseen case by case, after a thorough study of the project.