Fig. 2From: The deeper the better? A thermogeological analysis of medium-deep borehole heat exchangers in low-enthalpy crystalline rocksThe borehole heat exchangers modelled in this study. a A 600-m-deep open-loop coaxial borehole heat exchanger, b a 600-m-deep U-tube borehole heat exchanger, and c a 1- to 3-km-deep open-loop coaxial borehole heat exchanger with casing in the topmost 300Ā m (green). Arrows indicate the direction of working fluid circulationBack to article page