Comparative study of straight and spiral earth air tunnel heat exchanger system operated in cooling and heating modes

Thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) system is found to be highly dependent on thermal properties of soil and soil with poor thermal properties require longer buried pipe for desired heat exchange between air and sub-soil. In densely populated country like India, EATHE systems are rarely used due to the limited ground space (higher aspect ratio in terms of length) in most of the residential and commercial applications. Therefore, in this paper, problem of space limitation for the installation of straight EATHE system is attempted by proposing new spiral shaped EATHE system. The developed EATHE systems were used to determine cooling and heating potential individually and COP were 5.94 and 6.24 in summer; 1.92 and 2.11 in winter for straight and spiral respectively. A transient numerical model has been developed to investigate the performance of both systems. The COP were 4.23 and 4.48 in summer; 5.0 and 5.16 in winter for straight and spiral respectively. The experimental and numerical results suggested that the thermal performance of these two systems are comparable can be interchanged based on available site conditions.