One method of greenhouse cooling that has not been recommended, in years past, is the use of misting and fogging systems.  These systems are said to achieve a very small drop in temperature, and that they produce too much water pressure to consistently produce a proper sized drop of water.  This problem caused unnecessary plant wetness and has lead to unwanted insects, molds and diseases on greenhouse crops.  Now there is a system that creates a 4.2 micron water droplet, as opposed to a 10-20 micron water droplet.  These droplets fully evaporate regardless of the temperature reduction of at least 20 degrees Fahrenheit.  For information on this system go to www.fruittek.com.