Quantitative Evaluation of Summer Performance of an Underground Earth Tube System Based on Field Measurements

Abstract

Earth tube systems utilizing geothermal energy have attracted increasing attention as an effective natural energy technology for reducing outdoor air loads in buildings. However, most previous studies have focused on buried pipe-type systems, and quantitative evaluations of earth tube systems that utilize underground building spaces remain limited. In particular, there is a lack of detailed assessment of operational conditions, such as start-up and operation timing, and performance variations under different outdoor air conditions. To address this gap, this study conducts a field-based evaluation of the summer operation of an underground space-type earth tube system installed at the Osaka Institute of Technology Umeda Campus, with the aim of quantitatively clarifying its cooling load reduction effect. In addition, the appropriateness of the enthalpy threshold used as the start-up condition is examined, and the influence of outdoor air conditions and operational timing on system performance is analyzed. Through this investigation, the study seeks to identify effective operational conditions for summer use and to provide practical insights for improving the operation of earth tube systems.