Closed-loop heat-exchanging systems in geothermal anomaly areas: the case of the Euganean Thermal Basin, Italy

The Euganean Thermal Basin is the most important thermal field in northern Italy. It is located in the Veneto alluvial plain, south-west of Padua, close to the north-eastern edge of the Euganean Hills. Abano Terme is the largest town of the Basin (which includes a few other smaller towns) and is one of the most important thermal and mud-therapeutic resorts and in the world. Its very well structured hotels’ system offers hospitality to more than 250000 tourists every year. Almost every hotel and spa owns a well to extract thermal water at a temperature in the range 60-87°C from the fractured carbonatic bedrock found at a depth of about 150-200 m. To preserve this fundamental resource, the local legislation does not allow extracted thermal water to be used for purposes other than therapeutic ones. For this reason, this thesis work wants to analyse the feasibility and sustainability of a technique which does not require the extraction (and re-injection) of thermal water: closed-loop heat-exchangers, also known as Borehole Heat Exchangers (BHE). By circulating a refrigerant liquid in a closed loop of pipes installed vertically in a 400 m deep well, there is no fluid exchange between refrigerant and groundwater, but only heat transfer. The refrigerant accumulates heat when in contact with the hot groundwater, and releases it to a receiving body on the surface. An actual application of such technique to provide heat to the “Kursaal” building of Abano Terme is analysed in terms of its thermal impact on underground and groundwater temperature. Several hotels are present in the Kursaal’s surroundings and it must be verified that heat extraction by the BHE does not hinder the temperature of groundwater extracted by their wells. The analysis is carried out using the software FEFlow 6.1, using input data from another software called EED. It will be shown how according to the model there is absolutely no impact caused by the BHE on the extracted thermal water. Finally, it is estimated that such application may reduce CO2 production by 95% and paid back in 5.5 years