Abstract: This invention relates to a greenhouse climate control system for controlling the air exchange rate, temperature, and relative humidity (RH) level in a greenhouse. The system has at least one air processing unit that obtains return air from the greenhouse, processes the air, and returns the processed air as supply air back into the greenhouse. Return air is obtained from a location in the greenhouse above the canopy of a crop grown in the greenhouse, and supply air is returned to the greenhouse through perforated distribution tubes located in the vicinity of the crops.