Multiobjective Numerical Analysis of Thermal and Fluid Dynamics Performance of a Vertical Helical Earth–Air Heat Exchanger Using the TOPSIS Method

Abstract

The present work numerically investigates an Earth–Air Heat Exchanger (EAHE) of the vertical helical (VH) type, with regard to the prevailing climate and soil attributes of Rio Grande city, in southern Brazil, through the variation of its pitch between the helicoids (P_h), with constant air flow and soil conditions. The goals are to maximize the Thermal Potential (TP) and minimize the Pressure Drop (PD) of the EAHE-VH, that is, it is a problem involving multiobjectives. The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is employed for multiobjective evaluation, and its application is assessed in relation to the results of the Coefficient of Performance (COP) and the Energy Performance Indicator (EPI). The problem is numerically solved using ANSYS FLUENT package, through verified and validated computational models of thermal and fluid dynamics approaches. Among the evaluated P_h values, the configuration with P_h = 100 mm delivered the best TP for both cooling and heating, achieving gains of up to 20% compared with the least favorable geometry (P_h = 400 mm), thereby highlighting the significant influence of the helical pitch on system performance. Conversely, the configuration with P_h = 400 mm demonstrated the best performance in terms of PD, with a reduction of approximately 65.33%. The TOPSIS method effectively identified the optimal geometry with a balanced performance between TP and PD, with P_h = 300 mm being ideal when both are equally prioritized. In contrast to the evaluations based on COP and EPI, the TOPSIS method demonstrated superior comprehensiveness and flexibility, enabling the identification of optimal configurations aligned with distinct operational priorities.