that looks like an overgrown air conditioner
that's used to cool
by evaporating water
. Evaporative coolers are usually found in the West
climates. They're also called swamp cooler
The big advantage to an evaporative cooler is that they use considerably less electricity than a compressor-based air conditioner, and work better the drier it is, while adding a little humidity to the air in dry climates can make people more comfortable. Their big disadvantage is that they consume water--up to 20 gallons a day--and thus are not good if an area is experiencing drought conditions, and may be problematic as water rights issues become more prominent in the American West.
Evaporative coolers have large pads over vents and a fan to blow air over them, which cools the air, and forces the air into a house. There are window and whole house evaporative cooling units.
Generally evaporative coolers are seen more in lower income homes, although they would be a good supplement to regular air conditioning in any home in a dry climate. Also see how to use less air conditioning for other cooling tips.