The role of modelling in the planning strategies, the case study of Politecnico di Torino open-loop geothermal plant

Low-enthalpy open-loop geothermal systems (geo-exchange plants) are one of the most suitable renewable technologies for heating, especially in densely urbanised areas. They use water from a shallow aquifer to heat and cool buildings through a heat pump. The re-injection wells return the water to the aquifer at a different temperature and many environmental aspects have to be considered to minimise the impact on the shallow aquifer. In addition, in Italy, groundwater is protected by National Legislative Decree No. 152 of 2006, and in the Piedmont Region, there is the Water Protection Plan, which provides guidance for the authorisation of geothermal wells. Moreover, the authorities require the use of predictive models for at least three years of the geothermal plant's activity, and the final report must verify that there is no hydraulic and thermal feedback effect between the extraction and injection wells and, finally, that there is no overlap with other underground infrastructure and other installations plants. In the city of Turin there are 44 geothermal plants and the Politecnico di Torino has 12 geothermal wells scattered throughout the city. In this context, the role of modelling is crucial for the future sustainable development of open-loop geothermal plants and the management of water resources. The numerical model of the Politecnico di Torino, obtained with MODFLOW 6 and calibrated with PEST, includes other neighbouring geothermal plants and shows the actual situation in terms of dewatering and temperature of the shallow aquifer of a large area of Turin. In the future, numerical modelling will play an increasingly important role in the planning of geo-exchange plants and the assessment of their impact on water resources, and city-scale models will be necessary for both researchers and professionals working in this field.