Comparative Heat Transfer Efficiency Study of Coaxial and U-loop Boreholes

Abstract—This paper presents the results of comparative heattransfer efficiency study based on in situ full scale tests conductedon conventional U-loop borehole heat exchangers (BHE) and acoaxial BHE. The results show that the coaxial BHE hasconsiderably higher heat transfer efficiency, while consuming lesspumping power than the U-loop’s. The implication of a highefficiency BHE on reducing borehole loop length and initialinvestment cost is also discussed. It is concluded that the higherefficiency coaxial BHE has the potential to reduce boreholelength 30% to 50%