Study on heat-exchange efficiency and energy efficiency ratio of a deeply buried pipe energy pile group considering seepage and circulating-medium flow rate

• Published in: Renewable energy 2023-11, Vol.216, p.119020, Article 119020
• Main Authors: Chen, Zhi, Lian, Xingwei, Tan, Jinjia, Xiao, Henglin, Ma, Qiang, Zhuang, Yan
• Format: Article
• Language: English
• Subjects: Circulating-medium flow rate; Deeply buried pipe energy pile group; Heat accumulation; Seepage velocity; Thermal migration
• ISSN: 0960-1481
• DOI: 10.1016/j.renene.2023.119020

Seepage and circulating-medium flow rate are both primary factors affecting the heat-exchange efficiency and energy efficiency ratio of underground energy structures. In this study, a thermal-seepage coupled model of a deeply buried pipe energy pile group is developed, and the effects of circulating-medium flow rate, seepage velocity, and thermal migration caused by seepage on heat-exchange efficiency and energy efficiency ratio are analyzed. The results show that increasing the circulating-medium flow rate can improve heat-exchange efficiency, but aggravate heat accumulation, resulting in energy efficiency ratio reduction. Seepage can eliminate the heat accumulation as well as improve the heat-exchange efficiency and energy efficiency ratio. The heat accumulated around upstream piles will migrate along the seepage direction, generating thermal disturbance to the downstream piles. An increase in the circulating-medium flow rate of upstream deeply buried pipe energy piles will aggravate thermal disturbance. This phenomenon is slightly retarded if seepage velocity is increased. Additionally, when the circulating-medium flow rate of the deeply buried pipe energy pile group under seepage is within the optimal range, slightly reducing the circulating-medium flow rate of the upstream deeply buried pipe energy piles can reduce thermal disturbance to the downstream piles without affecting the overall heat-exchange efficiency.