During the summer, greenhouses can be cooled by using evaporative cooling systems. The most common is the pad and fan system. Water drips down a pad (usually a honeycombed paper) to keep it continuously wet. It is located opposite to an exhaust fan that draws outside air across the wet pad.

Evaporative cooling is related to the outside dewpoint, so it works best in areas with low humidity.

Photo of pad and fan cooling in a greenhouse. Photo of an evaporative cooling system.