Effect of operation modes on the thermal performance of EAHE systems with and without PCM in summer weather conditions

This work reports a transient numerical study of the thermal performance of two earth-to-air heat exchanger systems (EAHE) in summer weather conditions in a desertic climate. One conventional EAHE and the other with a phase change material (PCM) in the entrance under four different modes of operation/recovery (continuous, intermittent, intermittent-PCM-natural convection, and intermittent-PCM-mixed convection) to find the system that guarantees the best thermal performance. A detailed validation was made by comparing it with experimental and numerical data reported in the literature, under similar climatic conditions. The EAHE-PCM systems were used to reduce the thermal saturation of the soil, bringing with it an increase in the thermal performance of the EAHE system. The behavior of temperatures of the cooled air, soil, and PCM for each system are presented and analyzed. Besides the coefficients of performance are compared for each EAHE. It was found that the PCM selection is completely dependent on the environmental conditions in which the EAHE-PCM system will be used, with the right PCM the air temperature that is in contact with the soil was decreased up to 2.65 °C. The thermal recovery through the night injection of air (colder than soil average temperature) is an effective way to achieve a colder outlet temperate during the useful hours of cooling, besides, night injection was able to decrease the saturation factor from 0.356 to 0.296. The case that shows the best-modified coefficients of performance (COP*) is the ones with PCM and only passive cooling during the recovery mode (328.16) because in this case, the air blower has less operation time, in the other hand, the worst COP is seen in the case without PCM and all-day force convection (158.16), the case with PCM and night injection shows a COP* of 268.43.