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Earth-to-air heat exchangers (EAHE) can reduce the energy consumption required for heating and cooling of buildings. The composition and the thermal characteristics of the soil influence the heat exchange capacity, and the soil moisture can furthermore affect thermal performance of EAHE. The aim of this study was to compare the thermal performance of EAHE in dry and artificially wetted soil. Tests were carried out in the Basra Province (Iraq), in a semi-desert area. Two experimental EAHE were built in a poultry barn and tested from June 2013 to September 2013. The pipe exchangers were buried at 2 m deep. One heat exchanger operated in dry soil (DE), while the other one operated in artificially wetted soil (WE). In the WE system, a drip tubing placed 10 cm above the air pipe wetted the soil around the exchanger. Air temperatures at the inlet and at the outlet of both the exchangers as well as soil temperature at 2 m deep were continuously monitored. The experimental results confirmed that wetting the soil around EAHE improves the general heat exchange efficiency. The coefficient of cooling performance (COP) of the earth-to-air heat exchangers system was evaluated on the basis of the ratio between the heat removed from the air or added to the air and the energy input. During the day, with an average COP of 6.41, the WE system cooled the air more than the DE system, which reported a value of 5.07. On average, in the hottest hours of the day, the outlet temperature of the WE was 37.35°C while in the DE it was 38.91°C. Moreover, during the nighttime, the WE system warmed the air more than the DE system. [ABSTRACT FROM AUTHOR]