Shallow geothermal systems include vertical and horizontal borehole heat exchangers, and geothermal baskets. The principle of these closed-loop technologies is to use a heat carrier fluid that circulates in a piping network embedded in a borehole to harvest or store thermal energy from or into the ground, respectively.
GEOEG has designed and performance-tested a variety of shallow geothermal systems. These activities have allowed to push to the limits the economic profitability of such systems.
Designs based on advanced optimization of the piping network, materials, and thermo-hydraulic operational parameters employed for geothermal heat exchangers (e.g., coaxial vs. 2-U shaped pipe) can save significant costs during the exploitation of such systems and ensure earlier return of investment, as low as 2 to 3 years. These optimizations have been developed through the use of cutting edge numerical software and techniques that can simulate the operation of the modeled systems over any time-scale (e.g., hours and days to several decades) by accounting for the actual flow of the heat carrier fluid circulating in the pipes of such heat exchangers. An example of the modeling results achievable through these simulations is reported below with reference to the design of more than 200 vertical borehole heat exchangers with a length of 300 m.
In situ tests, including thermal response tests and thermal performance tests, have been performed by GEOEG to experimentally quantify crucial variables for the design, the quality control of construction, and the operation of shallow geothermal systems. In the former case, these variables include the undisturbed ground temperature of sites, the thermal conductivity of the ground, and the thermal resistance of the tested heat exchangers. In the latter case, these variables include the thermal power harvested by the tested geothermal heat exchangers during the experimental testing of their dynamic operation.