Experimental analysis of an innovative geo-exchange system installed on the island of Ischia, in southern Italy

Abstract

The need to use efficient and eco-friendly air conditioning systems is a fundamental requirement for today’s society. In this context, low and medium enthalpy geothermal energy plays a crucial role. The research and development activities carried out in the present work have made it possible to successfully design and analyze an innovative technology capable of supplying thermal energy to environments without pumping fluid from the subsoil. The proposed system is based on the use of a downhole heat exchanger (DHE). The authors have developed an innovative system for the sustainable use of low and medium enthalpy geothermal energy, installed on the island of Ischia, near Napoli, in southern Italy. The proposed system is based on the use of an ad hoc designed DHE, capable of optimizing the heat transfer with the subsoil, without the need to withdraw fluid from the aquifer. A numerical finite element model was developed to study the interaction between the DHE, the well and the surrounding aquifer. The experimental set-up consists of the heat exchanger and an above ground system, necessary to test the efficiency of the exchanger. The DHE is inserted inside a geothermal well made with a steel casing, equipped with a filtering section in correspondence of the DHE, in order to increase the heat transfer performance due to increased convection with the surrounding aquifer. The experimental data show that the DHE allows to exchange more than 40 kW with the ground, obtaining overall heat transfer coefficient values larger than 450 W/m2 K.