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Thermal Response Tests and effects of geological heterogeneity

pubblicazioni - Articolo

Thermal Response Tests and effects of geological heterogeneity

La risposta termica del sottosuolo è stata studiata con l’esecuzione di cinque test e l’analisi di un secondo significativo set di 15 prove sperimentali ed è stata stimata la conducibilità e resistenza termica dei pozzi attrezzati con sonde geotermiche configurate a singola e doppia U. I risultati ottenuti indicano le difficoltà oggettive a valutare l’influenza dell’acqua e delle falde in movimento specialmente nelle potenti coltri alluvionali recenti.

The low enthalpy geothermal energy is a technology that can significantly limit the use of fossil fuels and to contribute effectively to reduce greenhouse gas emissions. The closed-loop geothermal probes are easy to install, they have a simplified authorization procedure and combined with heat pumps in the GSHP-Ground Source Heat Pumps systems provide a real support to energy efficiency. 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.

The ground thermal exchange can be estimated by means of the TRT-Thermal Response Test that allows a direct measurement of the subsoil thermal conductivity and thermal resistance of the boreholes. A relevant set of experimental response tests have been analyzed with also the tests performed in the experimental field in Milan where two 100 meters deep borehole have been drilled with single U and double U closed-loop geothermal probes configuration. The experimental values have been compared with the theoretical ones based on the local site stratigraphy.

In general, the experimental values estimated by using the Thermal Response Test were more favorable than the theoretical ones, and it must be emphasize that the difference is consistent for a relevant set of cases. Certain thermal conductivity values are particularly high if compared to the expected ones from the local geology and it could be due to ground heterogeneity and groundwater flow can facilitated the heat exchange between borehole and ground.

These experimental results seem to indicate that in complex and heterogeneous sedimentary basins as Po plain, it is really difficult to quantify the real deep aquifer contribution in the estimation of ground thermal response.

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