YOU CAN WATCH THIS PRESENTATION IN MUSIC HERE (You have a link on the first slide): http://www.authorstream.com/Presentation/michaelasanda-1371522-yazd2/
The existence of special ventilation structures, called Badgirs, on the roofs is a distinctive feature of the architecture of this city (A Badgir is a high structure on the roof under which, in the interior of the building, there is a small pool). All about the simplest towers, which ranges from standard two-sided models to more elaborate six-sided variety, consist of at least for parts : the body or trunk that contains the shafts; air shelves that are used to catch some of the hot air and prevent it from entering the house; flaps which redirect the circulation of the wind; and the rood covering. The currents that enter the house do so above a pool of cool water, thereby cooling the air, while the warm air continues its circular path, redirected upward through a different shaft.
If you stand directly beneath a badgir, the air is appreciably cooler, and while not quite as cold as modern air-con, it's a whole lot healthier.