Evaluation of vertical closed loop system performance by modeling heat transfer in geothermal probes

Abstract

This study aims to develop and validate the heat transfer models for evaluating the performance parameters of closed loop geothermal systems, considering in detail probe internal geometry, heat exchange between the tubes, surrounding medium, and its depth-dependent temperature. The developed models are based on numerical solutions of differential equations that govern heat transfer in tubes, with refining the thermal resistance coefficients of probe elements. The models allow to calculate performance parameters, first of all, the fluid output temperature and system thermal capacity, for vertical single, double U-shaped and coaxial probes contacting either soil or mine water. We validated the models using the experiments performed in-situ at three sites in Germany and Turkey demonstrating high agreement between calculated and measured parameters. In addition, we proposed and tested the criterion to optimize the geothermal system operation regarding the technology features.