Simulation of earth-to-air heat exchangers in hybrid ventilation systems

Earth-to-Air Heat Exchanger (ETAHE) technology has been implemented in many mechanical ventilation systems. A literature review revealed that recent advancements in ETAHE modeling were focused on simulating heat conduction in soil. Air temperatures along the duct length were determined by calculating heat convection on the ETAHE duct surfaces using various empirical correlations. Comparison of the correlations for typical ETAHE in mechanical ventilation systems revealed that large discrepancy exists among them. A CFD simulation of an ETAHE applied to a hybrid ventilation building in Grong, Norway was conducted and the results confirmed field measurements. The convective heat transfer coefficient, obtained from the simulation, showed that the correlations significantly underestimate the heat convection in the ETAHE. Therefore, the existing models are not appropriate to simulate ETAHE in hybrid ventilation systems. Furthermore, a one-dimensional model was developed to predict the hybrid ventilation ETAHE system and provided satisfactory results.