• Energy Research

In view of the decarbonisation of the thermal sector, the use of ground source heat pumps (GSHP) plays a key role. The geothermal system coupled with heat pumps, is the most energy efficient and environmentally sustainable heating and cooling system because the ground temperature is constant all year round, unlike traditional air-source heat pumps (ASHP). A comparative life cycle assessment of a pilot GSHP system, operating in the ENEA Casaccia Research Centre (Italy), and a conventional ASHP was performed. In accordance with ISO standard, the impacts on the four damage criteria were evaluated for each phase of the entire life cycle (production, installation, operation and end-of-life), using the SimaPro 9.0 software. The GSHP system has significant impacts compared to the other ASHP system components during manufacturing and installation. In contrast, slightly higher impacts of the ASHP system are recorded during the operational phase. It should be considered that the geothermal probe circuit has a useful life of 100 years, which allows for multiple operational life cycles of the geothermal plant. Therefore, the paper highlights that the GSHP system, as a whole, is more energy efficient and has a lower long-term environmental impact, compared to a traditional air conditioning system.

Abstract A system for capturing thermal energy is planned for installation at the ENEA-Casaccia centre (Italy). Costs, primary energy requirements, pollutant emissions and seasonal electricity consumption were estimated. The configuration based on four boreholes of different depths and the sizing of the vertical loop (double-U) were performed according to the ASHRAE method. This pilot plant, the first under construction within an Italian research centre, is part of a long-term research project funded by the Italian Ministry of Economic Development. The results of this research could be applied throughout the Italian Tyrrhenian Apennine margin, which is geologically characterised by highly conductive lithotypes.

The thermal characterisation of a geosonde field, consisting of four boreholes at the ENEA-Casaccia Research Centre (Rome, Italy), was carried out by processing the temperature values measured by DTS (Distributed Temperature Sensing) fibre optics positioned vertically in each well. By correlating the vertical temperature profiles, it was possible to estimate the thermal conductivity of each stratigraphic level and the contribution of the groundwater on the heat exchange between ground and geothermal probes. The theoretical model has been confirmed by the experimental data obtained through direct measurement of thermal conductivity on soil/rock samples collected at different depths. In the first 10 m of depth, temperature variations are influenced by seasonal climatic fluctuations, the amplitude of which decreases with depth, to regularise and assume a linear trend, compatible with the movement of groundwater. The work carried out has shown that the area investigated is affected by the upwelling of hydrothermal fluids from the deep aquifer, which infiltrate the fractured lavas reaching the most superficial layers of the subsurface. The results of this research could be useful for estimating the geothermal potential of the areas within the ‘Cesano geothermal field’, whose lithotypes belong to the Sabatini volcanic province.