Parametric analysis, response surface, sensitivity analysis, and optimization of a novel spiral-double ground heat exchanger

Abstract

This paper proposes a novel spiral-double ground heat exchanger (GHX) that decreases conventional construction costs, facilitates installation, promotes heat transfer, and reduces thermal resistance. In this study, a new and effective installation procedure was proposed. Three-dimensional, transient, and conjugated finite volume simulations were conducted to compare the thermo-hydraulic performance of the traditional single U-tube and spiral GHXs with the proposed spiral-double GHX under two different flow rates. Moreover, a parametric analysis was conducted to study the impact of the design, operating, and geological parameters on the thermal performance of the new spiral-double GHX. Finally, surface response and sensitivity analyses, as well as optimization, were carried out using the ANSYS workbench. The comparison revealed that the spiral-double GHX yields higher thermal effectiveness (E) and heat transfer rate (Q) than single-U tubes GHX by 40.8% and 44.1%, respectively. In addition, it has a lower thermal resistance of 75.3% than the single-U tube GHX under turbulent flow conditions. Furthermore, the parametric study and sensitivity analysis concluded that the spiral radius has the most significant impact, followed by flow velocity, tube diameter, and pitch distance. Moreover, the recommended fluid velocity does not exceed 0.21 m/s, pitch distance of 0.0625 m, a spiral radius of 0.2 m, and grout conductivity of 2.1 W/m.K.