Reply #72: They use Swap Coolers ...

[aggiesal]

You'll see one on just about every roof.

Simple motor turns the fan to suck air in through the 4 panels.
A motor siphons/pumps COLD water from a reservoir (bottom 3-4 inches)
to the top of the unit where it is split 4 ways to dump over the
top of each 4 panels through what looks like straw inserts.

When the fan sucks air through the panels the cold water stored
in the straw inserts convert the air to cold air.

They break down constantly. If you get really good at servicing them
you can make a pretty decent living. If you don't mind heights.