Figure 3From: Designing coaxial ground heat exchangers with a thermally enhanced outer pipe Comparison of borehole thermal resistance for U-pipe and coaxial GHEs. Properties of coaxial GHE only are varied on the x axis and are compared to U-pipe GHE resistances as reference cases. The GHE configuration belonging to each graphic line is shown in the legend with a cross section sketch of the pipes and borehole.Back to article page