Heat transport modelling for the design of a low enthalpy open-loop system

Despite their high efficiency and ecological characteristics, the low enthalpy geothermal systems are still quite rare in Italy, mainly due to the disinformation about advantages and environmental rules too much severe (LO RUSSO & CIVITA, 2009) and authorization procedures quite long and complex. Particularly, the open loop systems (where groundwater is pumped out and then pumped into the aquifer, through 2 or more wells located along the groundwater flow direction) need a detailed hydrogeological study and often a numerical modeling too during the design phase. This paper presents an example of heat transport numerical modelling with SEAWAT 5.0 code (LANGEVIN, 2009) used to design a low enthalpy open-loop system for the cooling of an industrial plant in the northern part of Treviso Province (Veneto Region, Italy, Fig. 1). The low enthalpy system has a thermal power of 256 KWh. The use of the geothermal source allows to produce 245 KWh, to reduce the CO2 emissions of 12.6 tons/year and to save about 9400 €/year of electrical power. The local stratigraphy is made by alternances of gravel and sand layers with silt-clay layers of fluvial and glacial origin; as a consequence, 3 different confined aquifers occur in the first 75 meters below ground surface on the study site, separated by 3 aquitard layers of variable thickness. The third confined aquifer (25 m of thickness starting from 50 m b.g.l.) is the one exploited with the open-loop system and, despite che medium hydraulic conductivity (1.5E-05 m/s), it represents a good geothermal source thanks to the low variability of its temperature (mean value of 13.8 °C).