Small greenhouses need the larger amount. Also, the light intensity may be too great for the plants. During the summer, evaporative cooling, shade cloth or paint may be necessary. Shade materials include roll-up screens of wood or aluminum, vinyl netting and paint. Small package evaporative coolers have a fan and evaporative pad in one box to evaporate water, which cools air and increases humidity.
Heat is removed from the air to change water from liquid to a vapor.
Moist, cooler air enters the greenhouse while heated air passes out through roof vents or exhaust louvers. The evaporative cooler works best when the humidity of the outside air is low. The system can be used without water evaporation to provide the ventilation of the greenhouse. Size the evaporative cooler capacity at one to one and a half times the volume of the greenhouse. Thermostats can be used to control individual units or a central controller with one temperature sensor can be used.