The effect of operation modes on the thermal performance of a novel multi-tubular phase change material-filled earth-air heat exchanger

The phase change material (PCM)-filled earth-air heat exchanger (PAHE) represents a technology aimed at reducing energy consumption in outdoor air pretreatment. This study develops a two-dimensional numerical model of the proposed multi-tubular PCM-filled earth-air heat exchanger using the finite difference method, with a computational program implemented in MATLAB. The model's accuracy is validated against experimental data. The results indicate that the proposed system exhibits superior performance overall during the four-month operation in Chongqing, China, achieving a maximum temperature drop of 5.26 degrees C during the nine-day investigation period. Furthermore, the operating modes (Conditions 3, 4, and 5), when combined with night purging, enhance the cooling performance and temperature drop of the proposed system, while the liquid fraction of the PCM is distributed more uniformly throughout the daily cycle. The soil and PCM units in condition 5 exhibited the least thermal accumulation and the highest coefficients of performance during the nine-day examination period. The findings of this study enhance the understanding of the impact of operating modes on the thermal performance of PAHE systems.