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By Eloisa Di Sipio
Galgaro A., Di Sipio E., Teza G., Destro E., De Carli M., Chiesa S., Zarrella A., Emmi G., Manzella A. 2015. Empirical modeling of maps of geo-exchange potential for shallow geothermal energy at regional scale. Geothermics, 57, 173-186 doi.org/10.1016/j.geothermics.2015.06.017
In the frame of the economic crisis occurring since 2008 in Europe, the use of renewable energy resources is expected to increase in order to overcome the economic dependence on fossil fuels and ensuring energy supply for the European economic development.
Therefore, in the next future the use of geothermal resource both for power and heat generation is likely to increase, given its ability to meet part of the global energy needs and to produce low levels of greenhouse-gas emissions (GHG), reducing significantly CO2 emissions in the atmosphere.
To assess the geothermal energy exchanging ability of closed-loop Ground Source Heat Pump (GSHP) systems, a specific procedure able to combine ground and GSHP parameters was developed.
The methodology is based on different input parameters: i) the thermal conductivity of the ground, ii) the undisturbed ground temperature at 50 meters depth b.g.l. and iii) the monthly energy loads of the building considering a standard case study. The maximum energy requirements in a year has been estimated for a reference residential building (100 m2) with standard insulation and transmittance, according to the normative UNI EN ISO 6946, and usual requirements on heat pump efficiency (coefficient of heating performance COP =4.5 and cooling energy efficiency ratio EER = 4.0). The parameter adopted to link the ground thermal properties to the building thermal requirements is the total length (Ltot) of the group of vertical borehole heat exchangers (BHE) required to satisfy the energy building needs of the reference building.
Since the modeling has empirical character, it was applied to four regions of Southern Italy within the VIGOR Project (http://www.vigor-geotermia.it/). The obtained geo-exchange potential maps are conceived for energy planning purposes at regional scale and, due to the complexity of the different system components (house type, geological conditions, heating/cooling needs), provide a first and rough estimation of the geo-exchange potential of the areas taken into consideration. They do not replace detailed site-specific analyses, which, instead, are necessary for GSHP design purposes.
However, the proposed methodology can be easily exported in other contexts were use of shallow geothermal resources is planned. In fact the maps show the thermal energy that could be exchanged through the unit area by BHEs for a recent or a recently renovated building, taking into account the local geological and climatic conditions. Higher values of the geo-exchange potential identify more suitable place for shallow geothermal exploitation, implying a lower total length of the BHE field required for the GSHP system and then lower installation costs.
Eloisa Di Sipio is currently a post-doctoral researcher at the Institute of Geosciences and Earth Resources (IGG) of the National Research Council (CNR), Italy. Awarded in 2015 of a Marie Sklodowska Curie (MSC) fellowship, she will start the research cooperation with the Friedrich-Alexander-Universität, Germany, in November 2015. Main research interests concern shallow geothermal energy resources, hydro-geological topics and petrophysical characterization of lithological materials. She is involved also in dissemination and outreach activities addressed to general public. Eloisa is currently chair of the Early Career Hydrogeologist Network – Italy (ECHN-Italy) and member of the International Geothermal Association (IGA).
For more information, you can contact her at email@example.com, or follow her on the LinkedIn or ResearchGate pages.