Modelling and thermo-hygrometric performance study of an underground chamber with a long vertical earth-air heat exchanger system

A study of an underground building ventilated by a long vertical earth-air heat exchanger (EAHE) system is especially of interest because it shows a mechanism to alter the thermal characteristics in the building. However, studies on this thermal configuration are rare. In this paper, based on the free-falling equation of water film and the heat and mass transfer equations of airflow, a coupled numerical solution method is proposed to predict the thermo-hygrometric performance of the system. The Heat Index (HI) is chosen as the thermal evaluation index. According to the numerical results, the long vertical EAHE system can significantly reduce the indoor air temperature in summer while it only has a lag effect on the air humidity ratio, causing a high relative humidity and making it the main reason for the indoor thermal discomfort. The indoor HI decreases by approximately 1 degrees C for every 6 m(3)/(h.p) (p is short for per person) increase of the ventilation volume, but the reduced rate gradually slows down; the diameter of ventilation pipe less than 0.25 m is not conducive for the thermal control; the EAHE system is more suitable for application with a buried depth less than 200 m.