Thermal performance comparison and sensitivity analysis of elliptical and conventional single U-tube borehole heat exchangers: Numerical approach

Abstract

Borehole heat exchangers (BHEs) are critical components of ground-coupled heat pump (GCHP) systems, and their thermal performance is consequently significant for GCHP system design and operation. This paper investigates the heat transfer characteristics of an elliptical BHE and compares it to conventional single U-tube BHE. All numerical simulations are carried out using a 3D numerical model, and all of the models under consideration have the same heat transfer area. The experimental data is used to validate the numerical simulations. The sensitivity analysis was carried out and the effects of several operating and design parameters on heat exchange were investigated. The influence of the elliptical U-tube geometry parameters on the BHE's thermal performance is evaluated using the shape's slope angle and shape's factor. The results show that the average and maximum heat transfer rate of the elliptical BHE can be raised by 11.55% and 22.09% compared with the conventional single BHE. Furthermore, the sensitivity analysis demonstrated that flow rate, BHE materials, BHE depth, and cross-section tube area have the most influence on elliptical tube BHE. These findings could be used as a guideline for future BHE research, particularly in terms of heat transfer and pressure drop performance perspectives.