Ground source heat pumps: should we use single U-bend or coaxial ground exchanger loops?

Ground source heat pumps are becoming more common as traditional energy costs rise. Innovative pipe loop configurations promise increased performance and efficiency. The coaxial ground loop is among these new systems. The working fluid flows through a pipe to the depth of the system and returns to the surface through a larger annulus surrounding the delivery pipe. This study compares the coaxial and the single U-bend. By use of numerical CFD modelling, it was found that the coaxial performs both better than the U-bend but also exhibits a smaller pressure loss over equal lengths. It was found that the residence time of the fluid in the loop affects the heat transfer greatly, but the U-bend was affected more than the coaxial. Thus, coaxial ground loops are essential for efficient design and performance