Numerical Simulation of Vertical Helical Earth-Air Heat Exchangers Multiobjective Performance Assessment

In the present study, a numerical evaluation of the thermal behavior of Vertical Helical Earth-Air Heat Exchangers (EAHE-VH) installations was conducted under representative climate and soil conditions of the city of Rio Grande, in southern Brazil. The Rectilinear Horizontal Earth-Air Heat Exchanger (EAHE-HR), traditionally employed, was used as a reference. The evaluated geometric variable was the pitch between the helicoids ( P h ), and the performance was quantified by the thermal potential of the system, allowing for quantitative comparisons between the different EAHEs through statistical indicators. Comparisons were also made with the Vertical Earth-Air Heat Exchanger with 3 U-shaped ducts (EAHE-V3U). As a result, the option of EAHE-VH with a pitch of 100 mm achieved superior performance of up to 20 % compared to the other helical geometries studied. Additionally, it reached the result closest to the EAHE-HR considered as a reference. When compared to the EAHE-V3U, it showed lower results related to the annual thermal potential. However, it stood out for the need for a smaller volume of soil for its installation, with a reduction of 51.5 % compared to the EAHE-V3U and 79.1 % compared to the EAHE-HR. The multiobjective analysis showed the ability of the EAHE-VH to simultaneously meet the objectives related to thermal potential and required volume for installation, making it the most viable option among the evaluated EAHE construction models when both purposes are equally important.