Comparison of Borehole Heat Exchangers (BHEs): State of the Art vs. Novel Design Approaches

P. Oberdorfer, F. Maier, and E. Holzbecher
Applied Geology
Geoscience Centre
Georg-August-University Göttingen
Göttingen, Germany
Published in 2011

The efficiency of borehole heat exchangers (BHEs) for geothermal purposes depends not only on material properties but also on their geometrical design. These days most used design consists of two parallel arranged U-shaped pipes which are embedded in a high-conductive shell filling out the borehole. Another common design is a pipe inside of another pipe, with fluid flowing down inside and up outwards (coaxial design).

These two are compared to a new design approach consisting of a down flow pipe surrounded by six (twelve) up flow pipes, promising a better efficiency because of the larger surface compared to the double U pipes. All four designs are calculated with COMSOL Multiphysics using symmetries and numerical simplifications.