Thermal Performance Enhancement of a Novel Inner Pipe for Medium-Deep Coaxial Borehole Heat Exchangers

The medium-deep coaxial borehole heat exchanger (CBHE) has been demonstrated to exhibit excellent heating performance. To further investigate the efficient heat transfer characteristics of novel inner-tube materials, a numerical simulation approach based on OpenGeoSys was employed. This approach was used to systematically examine and compare the thermal performance of novel and conventional pipes under various operational scenarios during both short- and long-term operation. The results show that the novel geothermal pipe was found to possess superior thermal insulation performance over the conventional pipe. During operation, an increase in thermal resistance of 0.5 m·K/W (approximately a 30.5% improvement) and a higher pressure drop of 0.4 MPa (approximately a 12.3% rise) were observed. This contributed to an outlet temperature approximately 1 °C higher (approximately a 2.5% improvement) and a temperature drop 2.5 °C lower (approximately a 19.2% reduction). Over a 20-year simulation, the novel pipe achieved a heat exchange capacity approximately 3.5 kW greater than that of the conventional pipe (approximately a 1.5% improvement).