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Vengono descritte le indagini geologiche eseguite in quattro aree italiane finalizzate alla realizzazione di mappe del potenziale di geoscambio, le analisi eseguite su un set rilevanti di Ground Response Test (GRT) e i test effettuati utilizzando due sonde geotermiche a circuito chiuso rispettivamente con configurazione a singola e doppia U installate nel campo sperimentale RSE.
The low enthalpy geothermal energy is a renewable source that can provide a valuable contribution to reduce greenhouse gases emissions and to save energy. The use of technologies related to the low enthalpy geothermal regards the exploitation of the subsoil temperatures (lower than 40°C) and can be used for heating/cooling, buildings air-conditioning, domestic or industrial hot water production. For a proper design of complex geothermal plants, it is important to know the ground thermal response in order to properly size the number of vertical probes related to energy that must be provided or disposed. Geological surveys were performed on test areas to quantify the ground heat exchanger. In four different Italian areas it was possible to map of geothermal heat pump capacity; they are: Isola Bergamasca, a northern area located at the confluence of Brembo river into the Adda river, Nocera Inferiore and Solofra municipalities, two south-central areas in the Sarno basin (Campania) and a Calabria area on the south bank of the Tyrrhenian Sea. The ground heat exchanger can be experimentally estimated by the Ground Response Test (GRT) that, with dedicated equipment and applied to a pilot probe, introduces a known quantity heat fluid in the probe and measures the temperature variations of the transfer heat fluid returning from the ground. Processing inlet and outlet temperatures of the heat transfer fluid and knowing the thermal power used, it can evaluate the soil thermal conductivity and the well thermal resistance by reverse mathematical procedures. A relevant set of GRTs has been analyzed with also the tests performed in the RSE test field in Milan where two 100 meter deep wells were made with a single and double U geothermal probes configuration. The experimental values have been compared with the theoretical ones based on the local site stratigraphy. The values estimated by using the GRT were more favorable than the theoretical ones, and it must be emphasized that the difference is consistent for a relevant set of cases. A potential cause of this difference may be due to ground aquifers that can generate convective effects in the heat geothermal conductivity and that, from the supposed stratigraphy, it is difficult to quantify the real deep aquifer contribution. This analysis shows how important it is to run the GRT because the ground thermal exchange depends on the local geological configuration and often the theoretical values may not reflect the real situation.
31 Dicembre 2013
Energia elettrica da fonti geotermiche (ENERGEOTER2013)