Evaporative
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”).
All
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.
There
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.
