Evaluation of heat pumps: combination of virtual and real
It is a genuine field of geothermal boreholes, arranged in a double U and at a depth of 20 metres. This equipment can extract energy from the ground or inject energy into the ground. This borehole field is connected to CSTB's semi-virtual laboratory, the PEPSY (Platform for the Evaluation of Performances of dynamic SYstems). These two platforms can be used to evaluate the behaviour and performances of the global system of a geothermal heat pump. Geothermal boreholes can be connected to a virtual heat pump and a virtual building, or they can be coupled to a real heat pump itself connected to the hydraulic network of a virtual building. In this case, part of the system to be tested (heat pump, storage tank, pumps, regulation, etc.) is actually installed in the laboratory, while the building or the house (with its distribution and heat emissions, occupants, equipment, climate and geothermal exchangers) is simulated numericallly. The boundary between the “real” and “virtual” parts can be freely determined as a function of the product to be tested … (See diagram).
Adaptability at the service of a complete system
This adaptability is the main advantage of this experimental platform; the behaviour and performances of the heat pump are evaluated based on a complete system combining geothermal boreholes, heat pumps and buildings. Unlike conventional tests, performances are annual or seasonal rather than nominal (for example for heating, the COP (Coefficient of Performance) is an annual or seasonal COP and is not a nominal COP). The robustness of product control is also tested at the same time, which is not the case at the moment with standard tests. Therefore data on the heat source, emission, heat pump and auxiliaries are included with data characterising the inertia of the global system, building regulation, etc. The result is an analysis and a global performance calculation including all relevant parameters i.e. equipment, climate, typology, building use, etc. It offers a genuine advantage for manufacturers who wish to optimise their industrial products or improve prototypes; only a short period and a few tests are necessary to optimise a particular heat pump for a set of climates, buildings or different soil types, while guaranteeing results close to reality.
Saving time and money
Very low temperature
The different projects under way at CSTB only apply to so-called "very low temperature" geothermal heating, in other words a temperature at which a heat pump is necessary. The use of the term "geothermal" is slightly abusive for part of the geothermal exchangers such as horizontal collectors or spiral heat exchangers); heat stored in the ground at this level is mostly due to solar energy or runoff of rainwater rather than originating from the depths of the earth's crust.