World Geothermal Congress
May 21-26, 2021

Shallow Geothermal Potential with Borehole Heat Exchangers (BHEs): Three Case Studies in the Alps

Dusan RAJVER, Alessandro CASASSO, Pietro CAPODAGLIO, Charles CARTANNAZ, Joerg PRESTOR, Charles MARAGNA, Jernej JEZ

[Geological Survey of Slovenia, Slovenia]

In view of increasing the number of shallow geothermal installations, the assessment and mapping of shallow geothermal potential can contribute to identify the most suitable areas for each technology (closed/open loop). In the framework of the Interreg project GRETA, a study of geological and geothermal characteristics in three alpine pilot areas was carried out, namely Aosta Valley (Italy), Parc Naturel des Bauges (France) and municipality of Cerkno (Slovenia), with the aim of defining the geothermal potential for closed-loop systems (borehole heat exchangers or BHEs). Previous studies on closed-loop shallow geothermal potential assessment have identified two main key parameters: thermal conductivity and undisturbed temperature of the ground. In particular, the greatest challenge is the identification of lithologies in different scales in order to assign thermal property values correctly. While the Aosta valley is characterized by metamorphic rocks with some granite, the studied areas of Cerkno and Parc des Bauges predominantly consist of sedimentary rocks with rapid changes in geological units (sequences) and, consequently, various geothermal properties of rocks. Thermal conductivity (TC) of rock samples was determined with laboratory measurements using the thermal conductivity scanning (TCS) method. The mean values of TC range from 2.8 to 4.0 W/(m∙K) for rocks from the Aosta Valley, from 2.4 to 3.5 W/(m∙K) (with one exception of 1.3 W/(m∙K)) for sedimentary rocks from Parc des Bauges, and in a range of 1.8 to 5.6 W/(m∙K) for the rocks from the Cerkno area. With this input, the shallow geothermal potential – i.e. the annual amount of energy sustainably exchangeable with the ground by a single borehole - was determined using the G.POT method for a standard 100 m deep BHE. The G.POT method is based on the fitting of analytical ground heat transport equations and can account for several input parameters: thermal properties of the ground, plant characteristics and usage profile (BHE length, threshold temperature of the heat carrier fluid, duration of the heating/cooling season, and simulated lifetime). Worth to note, the G.POT method allowed to correctly take into account the ground temperature, which strongly varies in the wide elevation ranges characterizing all the three case studies analysed. The resulting maps show that spatial distributed potential for Cerkno ranges from 8 to 15 MWh/y for a 100 m long BHE; for the Aosta Valley from 5 to 17 MWh/y, with over 70% of the mapped territory exceeding 10 MWh/y; for Parc des Bauges, the potential ranges from 5.5 to 15 MWh/y, with the lowest values (

        Topic: Geothermal Heat Pumps Paper Number: 29031

         Session 4I: Geothermal Heat Pumps 2 -- Urban and Industrial Applications [Friday 21st May 2021, 03:00 pm]
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