Technical performance comparison between U-shaped and deep borehole heat exchangers

The geothermal industry is fronted to a fundamental decade to grow and become an energy supplier in transitioning to a sustainable energy system. The introduction of Closed-Loop Geo-thermal energy systems (CLG) can overcome a negative social response and increase the attrac-tiveness of geothermal developments. The present work aims to investigate and compare the performance of CLG systems. For the comparison, the case study of Campi Flegrei has been chosen. The maximum depth has been fixed at 2000 m, and the two configurations have been set up to analyse the performance and evaluate the best operational configuration. Both CLG configurations show decay in the output temperature of working fluid during production time. For a U-shaped design, it is possible to find a working condition that allows constant thermal power over time. The DBHE specific power is always more significant, up to 350 kW/m, compared to the U-shaped, which attains a maximum of 300 W/m (15%). The comparison with Beckers et al. [33] highlights the similarity of results for their base case. The consideration of the CLG system's length is related to heat exchange and investment costs. For longer exchangers, higher investments and less specific power.