New design method of ground heat exchangers by simultaneous estimation of ground and backfill thermal properties

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K14883
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 23020:Architectural environment and building equipment-related
• Research Institution: The University of Tokyo
• Principal Investigator: Choi Wonjun 東京大学, 生産技術研究所, 助教 (30817458)
• Project Period (FY): 2020-04-01 – 2022-03-31
• Keywords: 地中熱交換器 / 地中エネルギーシステム / 逆問題 / モンテカルロシミュレーション / ベイズ推定 / 不確かさ分析

Outline of Final Research Achievements

This study focused on the uncertainty of the thermal performance of the geothermal heat exchanger due to the uncertainties in ground thermal properties and geometric configuration of heat exchanger. The performance uncertainty was analyzed through Monte Carlo simulations. The results showed that the borehole thermal resistance, which represents the performance of the underground heat exchanger, can be changed in a wide range of 0.14 to 0.29 mK/W due to the uncertainty of the geometry and thermal properties.
In addition, a probabilistic estimation method based on Bayesian statistics was presented to estimate the thermal properties of grout. This method enables us to evaluate the uncertainty of estimated parameters. Through this, it was confirmed that it is more reasonable compared to the existing deterministic estimation method because it is possible to visually and numerically judge how reliable the estimated properties are.

Free Research Field

建築環境工学

Academic Significance and Societal Importance of the Research Achievements

本研究では、地中熱交換器の施工過程や熱物性情報の不足によって生じる性能不確実性の範囲を体系的に分析した。同じ構成で熱交換器を施工しても、その熱性能が二倍以上差があることを明確に示した。この結果は、既存の決定論的方法による設計は、非常に大きな不確実性を包含するために確率論的設計法と予測法の使用を必要であることを示唆す。そして、ボアホール構成要素の未知の熱物性推定をベイズ統計に基づいて確率論的に推定できる方法を開発した。今後行われる地中熱エネルギーシステムの確率論的設計方法の開発に寄与する成果だといえる。