The underground temperature at a depth of about three to four meters is almost constant during the year. As a result in summer the underground is cooler than the ambient temperature. This potential is considered for greenhouse cooling by using an Earth-to-Air Heat Exchanger (EAHE). In this research the effects of two parameters were investigated: a) the area of greenhouse in three levels
of 9, 18, 27 m2 and b) the percent of vegetation coverage inside the greenhouse in three levels of 0%, 50%, 100% on the performance of EAHE. The experimental design was factorial experiment in a randomized complete block design. The parameters of greenhouse’s inside temperature, thermal energy exchange and coefficient of performance (COP) were considered in cooling mode. As one of the remarkable results it was observed that the closed loop utilization of the system was infeasible in cooling mode. This was mainly due to the occurrence of vapor distillation inside the underground pipes and hence the blockages of the air flow. Also the effect of area and the percent of vegetation coverage were significant on the performance of EAHE. The highest average temperature difference between the temperature of testimonial greenhouse and the temperature of greenhouse was observed in treatment of 100% vegetation coverage and 9 m2 floor area which was measured as 9.6°C. The least average temperature difference in the treatment without vegetation coverage and 27 m2 floor area was measured as 5.2 °C. Considering thermal energy exchange in cooling greenhouse with open loop, the best treatment determined for EAHE in this research was the one with 9 m2 floor area and 100% of vegetation coverage.