Investigating the effect of Soil Moisture Around the Pipe in an Earth–Air Heat Exchanger (EAHE) System on its Performance Indicators

In order to investigate the effect of soil moisture and air transfer tube lenth on the performance indicators of a geothermal system, two factorial experiments were conducted based on a complete randomized block design in three replications in a greenhouse equipped with Earth–Air Heat Exchanger(EAHE)system located in the city of Arak in early August and September 2022. Two soil moisture levels, a1=10% and a2=25%, were considered as the first factor and three pipe lengths of b1=17, b2=34, and b3=51 m, were considered as the second factor in both experiments. The air was circulated by a fan through two PVC pipes with a diameter of 200 mm, which were buried at three meters deep from the ground surface. An irrigation tape with a diameter of 16 mm was used to increase the soil moisture around the pipe. The results showed that with the increase of soil moisture from 10% to 25%, the temperature of the outlet air decreases from 25.5°C to 23.5°C. The average efficiency at soil moistures of 25% and 10%, was 0.82 and 0.69 respectively. The produced cooling power was 2.7 kW and 2.2 kW, at two levels of soil moisture respectively. The best treatment from the point of performance indicators was obtained with a tube length of 34 meters and soil moisture of 25%. The outlet air temperature, system efficiency , cooling power and coefficient of performance for this treatment were 23.7°C, 0.90, 2.8 kW and 3.7 respectively.