Numerical investigation of the saturating soil layers' effect on air temperature drops along the pipe of Earth-Air Heat Exchanger systems in heating applications

Abstract

The study investigates the performance of an Earth-Air Heat Exchanger (EAHE) system, which uses underground pipes to pre-condition incoming air by leveraging the stable temperatures of the earth, thereby enhancing energy efficiency in buildings. A key challenge in heating applications is the heat loss experienced by air as it exits the pipe, which leads to a temperature drop. This study addresses this issue by exploring the impact of different soil layer configurations on reducing the outlet air temperature drop. A numerical analysis was conducted, to simulate various arrangements of soil layers to determine their effect on the outlet air temperature. The soils used include typical soil and sand-bentonite mixtures with moisture contents of 0 %, 10 %, and 20 %. The results indicate that the optimal configuration consists of two layers: an upper layer of one meter of dry typical soil and a lower layer of wet sand-bentonite soil with 20 % moisture content. This configuration yields an outlet air temperature of 20.2˚C, representing a 15.9 % increase compared to a single-layer model. This study provides novel insights by demonstrating that specific soil layer arrangements can significantly enhance the thermal performance of EAHE systems, offering a potential solution to minimize temperature drops in heating applications.