Numerical investigation of serpentine earth-to-air heat exchanger for passive building heating systems by recovery criteria

This paper investigates the performance of the earth-to-air heat exchanger (EAHE) system in the winter for Mashhad. A three-dimensional model of novel serpentine geometry for use in the passive building heating system is proposed. A new and visual method of recovery analysis is performed for regaining the soil energy by considering a period of time to stop the system. The thermal performance of the system is evaluated by analyzing the derating factor, knee point, and heat transfer evaluation criteria for a serpentine model of EAHE. Results demonstrate that the thermal conductivity of the soil and the duration of EAHE's continuous operation has a significant impact on its transient thermal performance. By employing soil thermal conductivities of 1, 2, and 4 W/m.K, the temperature of the outlet reduced 21 %, 12 %, and 6 %, respectively. Finally, the results indicate the highly better performance of the system in soils with higher thermal conductivity during long-term. The temperature of the outlet air in the 24-hours operation mode decreases compared with the 1-hour operation mode. A new method of recovery analysis is performed for regaining soil energy. This paper aims to develop a new model of EAHE system to maximize the energy use of buildings.