cooling (Sometimes referred to as "Swamp
Coolers") is probably the best way to reduce
greenhouse temperature. The principle is simple.
As the exhaust fans blow air out of one end
of the greenhouse, they draw in moist air from
the other end. As the moist air moves through
the greenhouse, some of the water vaporizes,
absorbing heat in the process. Moisture is supplied
at the end opposite the fans with an evaporative
cooler that drips water through an absorbent
material such as aspen pads, cellulose or a
synthetic fiber media (commonly called “cooler
pads” or “wet pads”).
incoming air passes through this wet media.
Any water that drips through the pad media is
collected into the water pan at the bottom.
Water is recirculated by a small water pump
through a plastic line from the pump in the
water pan back to the top of the cooler pads.
needs to be a provision for replacing water
that is evaporated by the air passing through
the cooler pads. This is usually done with a
1/4" copper or plastic water line to the
float valve that is mounted in the cooler. This
line can be installed from a garden hose bibb
or sillcock located near the greenhouse to the
cooler float valve.
Evaporative cooling is more effective when the
air outside the greenhouse has a low relative
humidity. As the relative humidity of the outside
air increases, this technique becomes less effective.
But so long as the relative humidity is less
than 100 percent, this method will have some
cooling effect on the air.