Thermo-physical properties of groundwater in sedimentary deposits of Umbria-Marche succession and their role for low enthalpy geothermal plants

To realize the EU Strategy for Sustainable Development, improving the quality of life on planet Earth of both present and future generations through the use of renewable energy, the geothermal energy plays certainly an important role. In particular, in the last years, the interest towards the exploitation of low enthalpy geothermal resources to produce heating, sanitary warm water and cooling for private and public buildings is notably increased. In this regard, our project is oriented on a detailed knowledge of the subsoil through a multidisciplinary approach (geological, hydrogeological, structural and geophysical data) that permit a correct evaluation of geo-exchange potential of heat at depth, corresponding to specific lithologies. We focus our attention on the seasonal monitoring of the thermo-physical properties of groundwater at depths (temperature and thermal conductivity above all), under different conditions of elevation and morphology, and within specific lithologies, belonging to sedimentary deposits of the Umbria-Marche succession. Information so obtained, together with other parameters taken from literature, are fundamental to acquire the Pèclet Number (Pe)1, a dimensionless number used in the study of transport phenomena in fluid flow that permit to know the amount of heat transfer by conduction, and to compare it with the heat transfer by convection. Introducing the Pèclet Number (Pe) within the equations that define the heat and mass transfer2, it is possible to obtain a better knowledge about the processes that rule the geo-exchange of heat in the subsoil3. This improves the understanding of the correct amount of thermal energy available for building energy needs, and it is very important in order to favourite a correct use of the resources supported by a technological optimization of low enthalpy geothermal plants. First results in the studied area show that in fractured limestones with significant groundwater circulation the thermal energy that define the geo-exchange of heat is in the order of 70 W/m, higly different with respect to alluvial deposits. References: 1) Miranda, J.M.; Campos, J.B.L.M. International Journal of Heat and Mass Transfer 2004, 47, 775-785. 2) Martin, S. O.; Hydrogeology Journal 2011, 19, 31-52 3) Sonney, R.; PhD Thesis 2010, 364 p.