You saw off the bottoms of liter soda bottles and insert the remaining neck in a board, which is then placed "big side out" in a window.
With the wider part facing outside, hot air is drawn into the funnel created. Air pressure changes as the air passes through the neck into the room and cooled air is released. This can cool a room by five degrees Celsius in a short amount of time.
Maybe this wouldn't be "cool" in Phoenix, but it sure makes a difference in some countries where electricity is not available or is on and off.
For blueprints, check out www.grey.com.
