Effect of pipe material on the performance of earth pipe air heat exchangers

The Earth Pipe Air Heat Exchanger (EPAHE) is an innovative technique that leverages the earth's thermal storage capacity to provide heating or cooling for enclosed spaces by regulating the temperature of the air passing through a buried heat exchanger. This system uses long pipes buried at a depth of 1.5 m to 2 meters, where the earth's temperature remains relatively constant throughout the year. As the outdoor air passes through the heat exchanger, allowing heat transfer between the soil and the air, thereby adjusting the air's temperature based on external weather conditions. The entire system was modeled and analyzed in Ansys Fluent (CFD), with a 20-meter pipe of 0.1-meter diameter and 5mm wall thickness surrounded by thick soil. Mild Steel and Thermally Enhanced High-Density Polyethylene (TE-HDPE) were used as pipe materials, and air velocities of 6, 5, 4, and 3 m/s were simulated under steady-state conditions with a constant wall temperature. The study concluded that the performance of the EPAHE system is primarily dependent on the volume flow rate rather than the material of the pipe.