Field experiments on the cooling capability of earth-to-air heat exchangers in hot and humid climate

In this study, full-scale experiments were performed to investigate the cooling capability of earth-to-air heat exchangers in a hot and humid climate. Four pipes with different configuration parameters were employed; the variations in the air temperature, relative humidity, cooling capacity, coefficient of performance and the soil thermal response and recovery rate were investigated. The results demonstrate that although the temperature and moisture content of the inlet air vary from 21.5 to 41.2 °C and from 11.2 to 20.52 g/kg, respectively, the temperature and moisture content of the outlet air are relatively stable for all four pipes. For an earth-to-air heat exchanger with a 0.075 m diameter and 3 m depth, the maximum reductions in the air temperature and moisture content are approximately 22.13 °C and 7.41 g/kg, respectively. It is observed that increasing the buried depth and decreasing the pipe diameter contribute to decreasing both the outlet air temperature and moisture content. The air temperature decays exponentially along the pipe length and the air temperature reduction increases linearly with the inlet air temperature. Moreover, the time-averaged sensible cooling capacity of earth-to-air heat exchangers accounts for 60.5%–82.82%, whereas the time-averaged latent cooling capacity accounts for 17.18%–39.5% of the total cooling capacity. The maximum total cooling capacity and coefficient of performance occur in the earth-to-air heat exchanger with a 0.16 m diameter and 3 m depth; these are 2987.94 W and 31.79, respectively. Further, the thermal recovery rates of the soil temperature are lower than the corresponding response rates.