Keeping with this month's "cities" theme, I want to share a rather cool passive building design that has been around for centuries. Long before LEED Platinum ratings and green building programs, ancient persian architects were developing ways to keep cool in crowded cities baking under the sun. Wind catchers - or "barjeels" as they are called in Arabic - are both a defining architectural fixture among cities across the Middle East and a clever, natural form of air conditioning.

Before modern air conditioning systems existed - with their pumps, refrigerants, and heat exchangers - ancient designers and engineers made use of the natural differences in pressures and temperatures to cool down buildings and make them habitable.

Wind catchers are tall, box-like towers that rise up and out of buildings like large chimneys. By allowing the sides of the tower to heat up in the sun, air inside the tower is warmed and rises. Warm air then passes out of the opening at the top of the tower, drawing in cooler air, typically from underground where temperatures are cooler than outside air.

I find the wind catchers charming because they are an elegant solution to a problem that is still a major design consideration in modern buildings (air conditioning represents approximately 8 percent of all energy used in commercial buildings). And many green building practices used today can be traced back to designs similar in nature to wind catchers. Use of natural sunlight, water reclamation, and natural material selection are hardly new or novel ideas and have their roots in ancient building design.

While ancient societies were not as technologically advanced by today's standards, they demonstrated a clever mastery of the natural environment and limited resources to improve living standards, which is as relevant today as ever.

Photos courtesy of Pedram Veisi and birdfam on Flickr. For those interested in seeing more photos of wind catchers, there is a nice photo group on Flickr you can check out.