Thermal performance assessment of closed-loop geothermal heat exchangers with vertical, inclined, and curved boreholes

Abstract

Accurate sizing of closed-loop geothermal heat exchangers is crucial to ensuring the energy efficiency and cost-effectiveness of shallow geothermal HVAC systems. One common design limitation is the restricted surface area available for borehole drilling. To address this constraint, inclined and curved borehole configurations offer an alternative to conventional vertical ones, allowing a greater underground exchange volume without increasing the ground footprint. However, inclined —and especially curved—boreholes involve higher drilling costs, raising the question of whether thermal performance justifies the investment. This study assesses the thermal behavior of closed-loop geothermal heat exchangers with vertical, inclined, and curved borehole configurations. Results show that inclined configurations represent the best balance between thermal efficiency and economic feasibility among the three.