Performance enhancement of borehole ground source heat pump using single U-tube heat exchanger with a novel oval cross-section (SUO) and a novel spacer

Abstract

This study introduces a new, efficient, and cost-effective spacer to maintain the space between the upward and downward U-tube legs of a single U-tube with an oval cross-section. Therefore, short-term and long-term transient numerical simulations were performed to compare the thermal and energy performance of the ground source heat pump system with both a single U-tube with an oval cross-section coupled with a novel spacer, and a conventional single U-tube with a circular cross-section. The impact of using different spacer cross-sections (circular cross-section, oval cross-section, and an oval cross-section with fins, double spacers with circular cross-section), materials, and length on the thermal performance was examined. Finally, a straightforward economic study was implemented to examine the feasibility of utilizing the proposed spacer. A single aluminum spacer with oval and fins cross-section decreases the borehole thermal resistance (Rb) by 25 % and 28 % compared with single U-tube with an oval cross-section and single U-tube with a circular cross-section, respectively. Furthermore, it improves the coefficient of performance (COP) in winter by 9.5 % compared with single U-tube with circular cross-section. Thus, it saves 497 kW·h operating energy. Finally, the economic study shows that the simple payback period for using the single aluminum spacer with oval and fins cross-section of length 50 m is 3.8 y.