The unconfined aquifers potential for the diffusion of the Open-Loop Groundwater heat pumps (GWHP) in the Piemonte Region (NW Italy)

The successful implementation of very low-enthalpy geothermal (T<50°C) open-loop groundwater heat pumps (GWHP) for heating and cooling buildings in several European countries has stimulated the investigation of the thermal and productive characteristics of the plain aquifers in the overall Piemonte region (NW Italy). These widespread systems can be frequently located near potential users (below and near buildings) and therefore no regional thermal energy transport infrastructure is required. GWHP typically withdraws groundwater to provide heat. In the winter, the GWHP extracts heat from the water to provide space heating. With reversible heat pumps, the heat-transfer process can be reversed in the summer and the groundwater absorbs heat from the living or working space and cools the air. Actually, the GWHP’s are suited to regions with extended shallow aquifers, from which it is relatively easy and not very expensive to extract groundwater. Generally, a highly productive, shallow aquifer would favour successful and efficient functioning of the GWHP. The most important consideration in GWHP design is to obtain a plentiful amount of groundwater with a very stable temperature. In Piemonte region there are extensive alluvial plain shallow aquifers which are suitable to be used for this aims. The vertical separation between the unconfined and deeper confined aquifers varies from a few meters to several tens of meters depending on local hydrogeological conditions. Deep, high-quality groundwater bodies are legally preserved for human consumption. To avoid potential alteration of the deeper aquifer, they should not be intersected by the wells to be used to operate the GWHP plant. Moreover, GWHP could be used only with shallow groundwater. Fortunately, the shallow groundwater temperatures are rather constant for the summer or winter seasons and also considering annual periods. Air-temperature influence (seasonal variability) seemed strictly connected to the depth to groundwater and it was negligible when the value was over 9.5 m. This element confirms that a strong implementation of GWHP could be considered suitable in the overall plain. At the end of 2012 more than 55 GWHP plants were requested to be authorized or are under construction in the whole Piemonte region plain.