Traditional Middle Eastern architecture uses tall towers to funnel passing breezes down to a courtyard. Often ponds or fountains are built in the enclosed area to further cool the air through evaporation. In the southwestern United States evaporative coolers are a common means of relief from the heat. These cooling devices use a fan to disperse a cool water vapor. The hydro unit that caps the tower structure is a cube with cellulose pads exposed on four vertical sides.
Water is conveyed through hoses up the tower to the hydro unit where it saturates the pads.
As air comes into contact with the wet pads the water evaporates. The exchange of energy between the air and the water results not only in vaporized water, but in cooler air. The cool air is now denser than the surrounding air, and it falls down the tower creating a breeze that escapes out of a vent at the bottom. The falling air pulls more warm air through the pads perpetuating the evaporation process. Troughs around the base of the hydro unit catch excess water, and a pump recirculates the runoff water through the pads.