Fig. 1From: Impact of operational temperature changes and freeze–thaw cycles on the hydraulic conductivity of borehole heat exchangersLeft: schematic sketch of a typical double U-pipe BHE system (only one of the two congruent U-pipes is depicted). The borehole penetrates two aquifers and is filled with grout. Right: schematic view in horizontal section (modified after Sass et al. 2016)Back to article page