Applicability evaluation of cast-in-place energy piles based on two-year heating and cooling operation. (June 2021)

• Record Type: Journal Article
• Authors: Park, Sangwoo; Lee, Seokjae; Sung, Chihun; Choi, Hangseok
• Is Part Of: Renewable & sustainable energy reviews. Volume 143(2021)
• Publication Date: 2021-06
• Subjects: Cast-in-place energy pile -- Ground source heat pump system -- Ground heat exchanger -- Thermo-mechanical behavior -- Long-term monitoring; Renewable energy sources -- Periodicals; Power resources -- Periodicals; Énergies renouvelables -- Périodiques; Ressources énergétiques -- Périodiques; 333.794
• DOI: 10.1016/j.rser.2021.110906
• Languages: English
• ISSNs: 1364-0321

Abstract

Abstract: An energy pile is a type of ground heat exchanger (GHEX) that can reduce the initial construction cost by being installed in the existing foundation structure (i.e., pile). However, despite economic benefits, energy piles have not been globally employed owing to a lack of construction cases and appropriate design methods. Therefore, in this study, a design method applicable to large-diameter cast-in-place energy piles was developed and verified by conducting long-term monitoring on the heating and cooling operation. In addition, to evaluate the applicability of the cast-in-place energy piles, their thermo-mechanical behaviors and economic feasibility were analyzed using the long-term monitoring results. Although degradation of thermal performance and significant changes in the ground temperature were observed in the heating operation, it was concluded that the proposed design method could provide reliable design outcomes. The maximum thermal stress was estimated to be 2.38 MPa during the long-term monitoring, which is approximately 8.5% of the design strength criterion for cast-in-place concrete. Finally, compared with a conventional closed-loop vertical GHEX, the cast-in-place energy piles could reduce the initial investment cost by 25.31%, and the investment payback period was evaluated to be 1.61 years. Highlights: A novel design method was developed for cast-in-place energy piles. The developed design method was verified by long-term monitoring of heating and cooling operations in the test bed. The thermo-mechanical behavior and economic feasibility of cast-in-place energy piles were evaluated.