Experimental evaluation of a “U” type earth-to-air heat exchanger planned for narrow installation space in warm climatic conditions

Abstract

The thermal performance of a “U” type earth-to-air heat exchanger is presented in this experimental study. The device has a serial-connected vertical configuration. The wells where tubes were installed have a depth of fewer than 3 m and are separated every 1.5 m, using an installation area of 3m². The experimentation was carried out in March in Morelos, Mexico when the environmental temperature reaches 35 °C during the day. The performance of the device was measured and compared to the requirements of an office for cooling purposes within a university campus to reproduce the space restrictions found in urbanized areas. By using a small land surface, it is feasible for urbanized areas. The air temperature inside the “U” type earth-to-air heat exchanger, the surrounding soil temperature, the airspeed, and the power consumed by the fan were measured. The air temperature and the fan's power consumption data were obtained by modifying the airspeed in four constant values, from 1.3 m/s to 6.6 m/s. Results show that the device evaluated in this work has adequate thermal performance for cooling purposes compared to the requirements of an office. A decrease in air temperature was recorded in a range of 5.1 °C to 9.4 °C. Over 70% of the total temperature difference was reached in the first well, where the average soil thermal disturbance at 5 cm was 2.8 °C. The device achieved a maximum COP of 12.8 and a maximum effectiveness of 88.4%. With these results, it is concluded that the system is suitable for cooling purposes in areas with space restrictions. This work is novel since the dimensions available for installation in urbanized areas are considered and compared with the thermal requirements of an office. In addition to the fact that there are no published works with vertical heat exchangers connected in series.