engleski

Research into Shallow and Deep Geothermal Potential of the Zagreb Area (Croatia)

Urban areas represent the most important market for geothermal energy. The City of Zagreb is by far the largest urban agglomeration in Croatia with a population exceeding 800, 000, and population density higher of 1, 232 inhabitants per km2 (CROATIAN BUREAU OF STATISTICS, 2018), with heating season lasting 220 days annually, and a significant potential for both deep and shallow geothermal applications. Deep geothermal resources are aquifers comprising bioclastic (Lithotamnium) limestones of the Prečec Fm (M1-5) and dolostones, limestones and dolomitic limestones of the PT Fm (T2-3). Boreholes have penetrated the aquifer at depths generally ranging from 800 to 900 m in the central area of the geothermal field, and the water temperatures range from X to Y (Bošnjak, et al., 1998). Zagreb geothermal field had been investigated since 1980-s, but the utilisation level is poor considering the available resource inside densely populated area with existing district heating system. Vintage exploration data are currently being digitalised for the purpose of making a 3D model of the subsurface and thermal model in the scope of Horizon 2020 GeoERA project HotLime. Although thermal water occurrences are generally a spectacular phenomenon, 85% of the investment into geothermal in the EU is directed toward the shallow subsurface, i.e. heat pump utilisation (REF EGEC). Its advantages constitute almost omnipresent potential, lower investment risks and possibility of reversible regime (heating, but also cooling, which has high load in urban surroundings). In the alluvial part of Zagreb urban area it is more favourable to use groundwater heat pumps (GWHPs), while at the foothills of Medvednica Mt. ground source heat pumps (GSHPs) are successfully installed. Shallow geothermal potential of the area will be investigated in the scope of Horizon 2020 GeoERA project MUSE. The research will concentrate on GWHP applications because the same aquifer is utilised for water supply, and prospects for GSHP installation have been investigated by a previous project GeoMapping (Borović, et al., 2018, Soldo, et al., 2016). There exists a competition of multiple users in the shallow subsurface of urban areas (water supply and sewerage systems, geothermal systems, deep underground constructions like hydro-insulated underpasses, underground garages and deep foundations), which can become a conflict issue. That is why existing workflows must be adapted to the needs of local scale urban areas, which will represent the most important SGE market in the future and drive heating and cooling sector decarbonisation. Both of the mentioned projects have foreseen a wide outreach toward scientific, professional, and general public, as well as toward the regulatory bodies and decision makers, with the final aim to increase the uptake of this readily available resource in the common pilot area, as well as to transfer good practices to other urban areas. That will be achieved through knowledge and experience exchange between sixteen European geological survey organisations which participate in the projects and presented through web sites, GeoERA Information Platform (GIP-P), fact-sheets, workshops, and congress communications.

thermal water ; groundwater heat pump ; ground source heat pump ; urban area ; conflicts in subsurface utilisation

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