Assessment of an earth-air heat exchanger (EAHE) system for residential buildings in warm-summer Mediterranean climate

Abstract

Open-loop earth-air heat exchangers (EAHE) can be used as a passive contribution to reduce the energy demand of buildings for heating and cooling, by providing a thermal pre-conditioning of the required ventilation air. This paper aims to numerically assess the influence of three parameters on the overall thermal performance of an EAHE system for residential buildings in warm-summer Mediterranean climate: spacing between pipes, pipes diameter and flowing air velocity. ANSYS-CFX® was used to simulate the EAHE transient behaviour during heating and cooling operation modes, and to evaluate the influence of each parameter on the outlet air temperature and soil-air heat transfer rate. The numerical results were validated against experimental data and compared with previously obtained analytical results. It was concluded that for a certain pipe diameter and distance between adjacent pipes, the higher the air velocity the lower the thermal performance of the system, mainly for cooling. Results also showed that for a certain air velocity and pipe diameter, the distance between pipes can be reduced from 1.0 m to 0.5 m without compromising the EAHE performance, thus allowing a reduction of the land area needed for the EAHE pipes up to ca. 50%.