Cool towers use gravity to move cool air without any fans, although fans may be used to reduce the size of the towers. The most common cool towers do this by having a wet pad medium in the top of the tower. Since cool air is heavier than warm air, it will fall, creating its own airflow. Wind is not required, but will improve the airflow in a cool tower.
Generally cool towers without fans are from 20 to 30 feet tall and between 6 and 10 feet square (6'x 6', to 10' x 10'). Typically cool towers of this size will require from 10 to 150 watts, and will cool 1,000 to 2,500 square feet. Airflow for these cool towers will range from 2,500 to 8,000 CFM (cubic ft. per minute).
Passive ventilation systems rely on the movement of air through buildings to equalize pressure. The pressure difference can be caused by Wind or the Buoyancy effect created by stratified warm air. In either case, the amount of ventilation will depend critically on the size and placement of openings in the building.
Evaporating water is what creates the cooling and makes evaporative coolers and cool towers work. Rain water is the perfect source for the water used in cool towers because it does not have dissolved salts or minerals. Well water can contain dissolved minerals. As the water evaporates from the cooler pads, whatever minerals it contains are left behind. This buildup can eventually clog the pads and block air flow.
Source: thefarm.orgAdded: 9 September 2009