GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.1 - POSTER GNGTS 2023 Methods and Results Due to the complex geological system and the articulated energy sources and in order to optimize the whole project, a holistic approach was applied taking into account both the energy needs on the side of the buildings and the hydrogeological, chemical and thermophysical characteristics of the subsoil, as well as the presence of other possible constraints. At the investigated site, we collected i) litho-stratigraphic, ii) hydrogeological, iii) hydrochemical and iv) thermophysical data acquired by means of in situ tests and analysed on the basis of integrated methods. All these tests allowed us to properly define the hydrodynamic and thermophysical behaviour of the underlying aquifers and the response of the subsoil to the thermal stresses applied. The performed cores and drilling document the following hydrostratigraphic succession. Up to a depth of 80 m there are two mainly sandy confined aquifers (A1, A2) separated by a clayey body about 10 m-thick. Chemical and isotopic analyses of the sampled waters also document the different composition and origin of the aquifers. Several thermal logs have been performed in the boreholes and probes either in undisturbed conditions as well as during and after thermal response tests allowing to clearly constrain the thermophysical characteristics of the subsoil and its vertical variations. Considering the long season of heat extraction for the district heating and the consequent energetic overexploitation of the subsoil, we planned to energetically balance the system by inverting during the summer the role of the geo-exchangers to provide cooling to the buildings by means of a dedicated heat-pump characterized by a high EER value. The complex geological conditions and the energy needs, lead us to design a hybrid shallow geothermal supply system, where static and dynamic closed-loop geo-exchangers have been integrated, and innovative monitoring methods have been installed. The investigated site also represented an occasion to test and properly evaluate the energy and environmental sustainability of the innovative dynamic closed loop exchangers.