Regional-scale assessment of the thermal potential in a shallow alluvial aquifer system in the Po plain (northern Italy)

The Milan Metropolitan Area is one of the most densely populated regions in Italy and Europe and, consequently, has an extremely high thermal power demand. In this study a regional scale assessment of the potential of a shallow alluvial aquifer to host low enthalpy geothermal systems is presented. The study area lies on a layered phreatic aquifer complex and presents advantageous hydrogeological characteristics that make low enthalpy geothermal supply an attractive heating/cooling solution from a carbon footprint and an economical point of view. In this context, different analytical solutions were used to estimate the thermal potential of closed- and open-loop systems based on the distribution of hydraulic and thermal parameters of the shallow aquifers. The thermal potential of closed-loop systems (ground-coupled heat pumps - GCHP) was estimated through the ASHRAE analytical equation considering the hydraulic and thermal parameters of the ground, the groundwater temperature, and the characteristics of the system. The thermal potential of open-loop systems (groundwater heat pumps - GWHP) was estimated by considering the local regulation on the abstraction and the conservation of the quantity and the quality of the groundwater as well as preventing excessive groundwater table drawdown or rising and thermal short-circuit. The results were compared with heat demand rates of the buildings in the municipalities of the study area and, finally, the most profitable shallow geothermal system configuration is discussed.