Possible applications of ground coupled heat pumps in high geothermal gradient zones

Abstract

• Ground source heat pump in geothermal basins is investigated. • TRT has been done to describe the ground properties. • Improvement of the heat pump performance is found. • GHE directly coupled with building is the best case in term of primary energy need. Geothermal energy is increasingly being used to heat and cool buildings. However its use has been slow to catch on due to the high installation costs of the most common Borehole Heat Exchangers (BHE), which constitute the major cost item of an air geothermal conditioning system. In areas where the shallow subsoil temperature is higher than normal (geothermal basins), the average temperature of the carrier water in the BHE is higher than in systems located in areas with a normal geothermal gradient, thus improving heat pump Coefficient Of Performance (COP). This paper investigates a range of solutions that use geoexchange systems coupled with BHE in anomalous geothermal zones. This study evaluates a residential building's heating system when it is directly coupled with BHEs and compares the results with a range of thermal plant solutions. In Northern Italy, as in many other parts of the world, there are places where the ground's thermal conditions are anomalous, with temperatures reaching around 35–85 °C, instead of normal values of about 13–15 °C. The energy of the building was analyzed by means of the TRNSYS, coupled with the CaRM model—designed by the authors—which provides detailed thermal behaviour readings for Ground Heat Exchangers (GHE).