Heat transfer and energy performance of a parallel multi-pipe earth–air heat exchanger

Earth–air heat exchanger (EAHE) systems offer a sustainable means of reducing building heating and cooling demand by utilizing the thermal stability of the ground. This study presents a three-dimensional computational fluid dynamics analysis of a dual-manifold, parallel multi-pipe EAHE for the climatic conditions of Malatya, Türkiye. The numerical methodology was validated against the published experimental measurements for PVC and steel pipes. The resulting mean absolute error and root mean square error were 0.86 °C and 0.99 °C for PVC and 1.38 °C and 1.49 °C for steel, respectively. A steady-state parametric investigation was then conducted to examine the effects of airflow velocity (1–9 m/s), pipe length, pipe diameter, pipe material, and soil type on outlet temperature, heat-transfer rate, pressure drop, fan power, and system performance factor (SPF). Pipe material had a negligible influence on thermal performance under the investigated conditions. Among the examined velocities, 6 m/s provided the most favorable thermal–energy trade-off, yielding a heat-transfer rate of 250 W and an SPF of 46.38. Increasing pipe length increased the SPF to 48.16, whereas increasing pipe diameter reduced it to 32.14. Moist clay provided the highest performance, producing a 50.0% higher heat-transfer rate than dry soil and an SPF of 52.21. Steady-state simulations under monthly representative inlet-air and ground-temperature conditions yielded the highest SPF of 50.93 in November. The results demonstrate the influence of geometric, operating, and soil parameters on the performance of parallel multi-pipe EAHEs and provide guidance for their thermally efficient design.