Numerical investigation of high capacity ground-coupled heat exchanger performance for water cooled chillers services

Ground coupled heat exchanger (GCHE) has received considerable attention with the increased demand on energy efficiency to combat global warming. Among other applications, GCHE has a promising potential as a heat rejection method for chillers especially in hot and humid climates where cooling towers are not very effective such as the case of the Gulf countries. In this work, a transient axisymmetric numerical model to simulate the heat transfer and turbulent flow through coaxial borehole ground heat exchanger is developed. The present study is aimed at improving our understanding of the parameters controlling the heat transfer from the GCHE to serve large capacity chillers under hot and wet climate condition. Parameters such as borehole size, exchanger depth and inner‒outer pipe diameter ratio are optimized to maximize the heat transfer. For validation, the present results of a deep small diameter heat exchanger are compared with experimental and numerical data reported in the literature.  For further enhancement of the performance, a novel idea, helical digging threading fins configuration (HDTFC), is employed with GCHE to enhance the heat rejection into the ground using the extended surfaces (fins) and to facilitate the ground digging process for the heat exchanger installment.