Potentiality of the low-enthalpy open-loop groundwater heat pumps (GWHP) diffusion in the Piemonte Region (NW Italy)

Groundwater heat pumps have potential advantages in terms of energy efficiency and environmental impact. The diffusion of such technology in the urban areas potentially represents one important task for the European development in the renewable energy. The Groundwater Heat Pump (GWHP) system is an open-loop system that withdraws water from a well or surface water, passes it through a heat exchanger and discharges the water into an injection well or nearby river. Depending on the use mode (heating or cooling), energy may be extracted or injected. As an efficient use of natural energy, this system utilizing the relatively stable temperature of groundwater can achieve a higher coefficient of performance and offers a more energy saving solution than the conventional Air-Source Heat Pump (ASHP) system. This study is aimed to highlight the hydrogeological potential for the Piemonte regional territory to supply clean energy by the diffusion of GWHPs and therefore contribute to reducing greenhouse gas (GHG) emissions starting from the regional analysis of (1) the hydrogeological plain setting and (2) the spatial distribution and temporal variability of the shallow groundwater temperature. Focusing on the GWHP, the groundwater temperatures trend and the productivity characteristics of the shallow aquifers in the alluvial plain of the Piemonte region were examined. The distribution of mean groundwater temperatures ranged from a minimum of 10.3°C to a maximum of 17.0°C with a mean of 14.0°C. Differences among diverse areas were slight according with the modest variations in the general climatic condition. Air-temperature influence (seasonal variability) seemed strictly connected to the depth to groundwater in the measure point and it was negligible when the value was over 9.5 m. 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. Environmental conditions and the widespread distribution of a suitable shallow aquifer in the entire Piemonte plain encourage the use of GWHPs. Energy demand is concentrated in the urban and industrial areas, which are located preferentially in the plain where low-enthalpy geothermal energy associated with the shallow aquifer is ready available. Future diffusion of GWHP could be favoured by the great number of existing groundwater wells used for various purposes throughout the region that could limit additional installation costs especially for small buildings. 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.