Performance improvement of the phase change material-assisted earth-air heat exchanger in summer

Abstract

Studies confirmed that phase change material (PCM) can improve the cooling potential of an earth-air heat exchanger (EAHE). However, the poor utilization of the PCM unit’s latent heat storage (LHS) capacity and insufficient understanding of energy efficiency hinder its applications in EAHE. To solve these problems, this study made a structural improvement to the PCM unit and proposed a centrally located hollow cylindrical PCM-assisted EAHE (CHCPCM-EAHE). Then, numerical simulations were conducted on this CHCPCM-EAHE through a 3-D model built on the ANSYS FLUENT, and its cooling performance in Chongqing (China) summer was comparatively studied. The results found that the LHS performance of the PCM unit in this CHCPCM-EAHE was improved despite the significant reduction in material volume. Compared to the PCM unit in the previous PCM-assisted EAHE, the maximum liquid fraction and average charged latent heat in all charge–discharge cycles of the PCM unit in this CHCPCM-EAHE were increased by 56.82 % and 10.46 %∼56.43 %, respectively. The results also found that the CHCPCM-EAHE performed better in cooling potential and coefficient of performance (COP). Compared to the conventional EAHE and previous PCM-assisted EAHE, its average cooling capacity increased by 60.12 %∼70.75 % and 4.05 %∼10.96 %, and average COP increased by 47.22 %∼49.02 % and 6.88 %∼8.18 %, respectively.