Improved Design Method of Open Loop Geothermal System and its Applications

Abstract

In recent years, the utilization of geothermal energy for buildings has increased significantly. Among the existing geothermal energy systems, open loop systems show better efficiency than closed loop systems because of the direct heat exchange with groundwater or surface water. On the other hand, there are a lack of technical and institutional standardized procedures for the design of open loop systems. Therefore, this study proposes an improved design method of an open loop geothermal system using the borehole thermal resistance based on the result of a numerical study using a commercial finite element program (COMSOL Multiphysics). The borehole thermal resistance obtained using the numerical study was 43% lower than that calculated using the existing method. Consequently, the proposed design method can reduce the design length of a ground heat exchanger by approximately 5%. Similar trends of a lower borehole thermal resistance (42%) and shorter design length of the ground heat exchanger (2%) were also observed in the application of the proposed design method to the open loop system in a military facility.