Heat transfer Model for a Closed Loop Geothermal System: Theoretical Calculation and Experimental Verification

Abstract

As a renewable energy source, geothermal energy (GE) plays an important role in achieving carbon peaking and carbon neutrality. As a form of downhole heat exchanger (DHE), the Closed Loop Geothermal System (CLGS) has the technical characteristics of heat exchange without extracting groundwater, making it a current research hot topic in the utilization of GE. However, there are few theoretical studies on CLGS, and there is a lack of public operating data to verify the practical heat extraction performance of geothermal wells. Based on Piecewise Analytical Solution, this paper established a operating mechanism-based heat transfer model for CLGS. The proposed model solves the problem that the Analytical Solution method lacks consideration of geothermal gradient, and can realize the calculation of fluid distribution in DHE. By comparing the simulated calculation data with the monitoring data in the actual project, it is found that the overall error is less than 3℃, and the average relative error achieves to 7.3%. The research results suggest that the proposed model can provide a simulation verification method for the analysis of the heat transfer characteristics of medium-depth geothermal wells, thereby contributing to the rational utilization of geothermal wells.