Análises paramétricas de trocadores de calor solo-ar acoplados a estruturas galvanizadas

Abstract

Earth-air heat exchangers (EAHE) connect buried ducts to the ventilation system of a building. They aim to take advantage of the ground thermal inertia, which makes it hotter or colder than ambient air at different times. Studying this technology is valuable because EAHE use a renewable thermal energy source and consume little electricity. The heating and cooling capabilities of EAHE depend on many factors such as local climate, soil properties, and facility design. This research seeks to evaluate the thermal performance of EAHE, considering the ducts coupled to galvanized fins (with high thermal conductivity) to improve thermal exchanges with the surrounding soil. In particular, this work adopts the soil and climate conditions (subtropical) from the south Brazilian city of Viamão. The data comes from the literature about an experimental installation built in that location. The simulations use a validated analytical model, known by the acronym GAEA, which depends on estimates of soil temperatures without the ducts. In this dissertation, such temperatures are calculated numerically by solving the energy conservation equation, in the transient regime and two-dimensional domains, through a combination of finite element and finite difference methods. The research started by assessing recent literature suggestions for fin configurations; in each case, estimating the annual root mean square value (RMS) of the soil thermal potential. Thus, the best result was considered the one that produced the highest RMS value and needed less galvanized material. In general, adopting fins caused a significant increase (over 90%) in the annual efficiency of EAHE. Hence, the second part of the work took a parametric study to verify the possibilities of minimizing the duct size, keeping efficiency rates above 70%. In this sense, the results show that the installation size can be reduced by almost half. Finally, to better understand the phenomenology, this work analyzes the soil thermal conductivity enrichment around the duct and how it affects the EAHE thermal potential. The study shows that an indiscriminate increase in soil thermal conductivity may not be beneficial to EAHE performance. Therefore, this topic demands further investigations such as those taken in this manuscript.