Thermal Potential Improvement of an Earth-Air Heat Exchanger (EAHE) by Employing Backfilling for Deep Underground Emergency Ventilation

Backfilling can enhance the thermal potential of an earth-air heat exchanger (EAHE) system, but traditional researches are hindered by the shallow buried/horizontal conditions or the limitation of air temperature concerned only. This present research fills in an important research gap by investigating the effect of backfilling on both heat and mass transfer of an EAHE system for deep underground emergency ventilation. The advanced numerical model is established and the agreements with field test data are satisfactory. The effect of the backfilling system has been investigated and the possible improvement has been identified. The results show that the effect of the backfilling technology is of almost equal significance to the EAHE system in some cases, and the upper limit of application depth for the backfilling technology is found. Successful deployment of the backfilling system will assist the emergency ventilation on its process towards energy-efficiency and thermal comfort, and the backfilling system can further improve the thermal performance up to 100% on the basis of the original system. However, backfilling is not an appropriate method for EAHE system under 400 m depth. And there is no need for the thermal conductivity of backfilling materials to be higher than 2.5 W/(m·K).