Unmanaged conflicts and potential synergies between shallow geothermal systems in a Swiss urban aquifer

The use of shallow geothermal systems (SGS) as an efficient technology to provide clean thermal energy has become increasingly widespread, especially in urban settings: this is leading to a significant systems density and to the more frequent risk of thermal interactions between neighboring systems. This work presents a holistic 3D numerical model of the urban aquifer of Locarno (Switzerland), simulating mutual interactions between open and closed-loop SGS. Results show that the high amount of installed SGS in limited space is progressively creating mutual hydraulic and thermal interferences: negative, with a reduction of SGS efficiency and sustainability or (rarely) positive, when an accidental and unmanaged synergic effect is established due to favorable exploitation patterns and SGS locations. Moreover, the presence of underground structures affects the thermal conditions of the subsurface and consequently the operation of SGS. Neglecting an underground holistic vision of the hydro/thermogeological processes in urban areas could result in long-term efficiency losses and thermal issues for SGS solutions, also given the increasing exploitation of shallow geothermal energy for building conditioning.