Significance evaluation of performance factors on horizontal spiral-coil ground heat exchangers

Abstract

Ground-coupled heat pump systems using horizontal spiral-coil ground heat exchangers (HSGHE) are being utilized for an increasing number of applications due to the efficiency in terms of thermal performance. To optimize design accuracy and thermal performance, significant design factors of HSGHEs should be identified. Thus, this study investigates the effects of influential factors on the thermal performance of HSGHEs through sensitivity analysis. Numerical models were established with respect to the operation of HSGHEs using the finite element method. Variance-based sensitivity analysis was conducted using the numerical results to quantitatively evaluate the overall effects, which include the main effects as well as interaction effects between the design factors. Furthermore, case studies of two different regions were applied to the sensitivity analysis to compare the effects of regional climate factors on the order of significance of the input factors. As a result, ground thermal conductivity, installation depth, and inlet fluid temperature were determined as major design factors. On the other hand, the order of significance of the major factors was found to be dependent on regional climate factors. This result implies that it is necessary to consider different critical factors of HSGHE design according to the ambient conditions of the installation region.