They stand towering, working noiselessly to keep the locals of Yazd cool during summer. Like square-shouldered sentinels, they break the dust-blown horizon, jutting vertically across the skyline. These were the air conditioners of ancient times.
For centuries, tall ceramic towers with ports mounted up high have kept—and still keep—people brisk by capturing wind to condition indoor air. Termed badgirs, literally wind-catchers in Farsi, they were used in places like Yazd, Iran, one of the world’s hottest, driest cities. Part of city infrastructure, these towers helped cool the insides of homes and buildings. They kept perishables frigid, pumping cold air into underground ice houses.
In some ways, these ancient AC units were better than those of today. Badgirs ran passively, without a power source, even when the wind wasn’t blowing. And they made no noise. Yet today, badgirs have mostly been outmoded by noisy and costly modern types.
Perhaps the ingenuity and simplicity of such ancient cooling solutions deserve a second glance. They might even inspire new breakthroughs to come. Were the power grid ever to fail us modern folks, badgirs would not leave us dangling in the wind.
The Ancients Had Free Freezers
In modern cities, particularly in summer, AC is essential in many parts of the world. It’s loud, clunky, and, for some, unaffordable. Yet a simple solution may be found in the remote past. As passive cooling units, badgirs use wind and convection currents, rather than electricity, to cool down living spaces.These chimney-like towers were used in desert climates as early as 3,000 B.C. In arid regions such as Yazd on the Iranian plateau, average temperatures reach 100 degrees Fahrenheit (38 degrees Celsius) in July, while precipitation averages 1.9 inches (49 millimeters) annually. Yet, even here, cooler drafts may be found blowing above. That’s where wind towers come in.
Prevailing winds differ from place to place. They may be unidirectional, bidirectional, or multi-directional. Badgirs were faced windward accordingly, tailored to local climes. In Yazd, for instance, where badgirs are most abundant with hundreds still existing—and working—there are one-sided, two-sided, four-sided, or octagonal versions. They feature distinct right angles to direct gusts downward instead of allowing air to flow around.
The higher the air is, the less dusty it is. Yet particles that enter the wind scoops are deposited as the air drops down and slows. Many wind-catchers in Yazd are equipped with filters that remove dust. Doors were also sometimes installed to keep buildings warm in winter.
Reverse Chimney Stacks
The Western world knows the hearth and chimney stack as the center of a home, providing warmth, allowing hot air to escape above. This principle operates in reverse in the form of wind towers, which scoop colder air from above, allowing it to descend into the building, as cooler air does, due to temperature gradations.
Similar to a chimney stack, air inside the badgir is channeled vertically, often penetrating belowground into ice houses or underground canals. Although wind pressure helps push the air down, other forces such as convection, buoyancy, and gravity assist in this. This passive downward force is, fittingly, called the chimney effect. It allows badgirs to operate even when the wind isn’t blowing.
Capturing the Cool of Underground
Just like people today, during summer heatwaves especially, the ancients had to store cold drinks and perishables someplace chilly. Lacking modern refrigeration, though, they dug down underground. Here, the soil or underground canal would maintain a constant frosty temperature, regulated by thermal inertia. At such depths, the chill from the previous winter never entirely thaws. Thus, the cold carries over into summer, resulting in a year-round deep freeze.
How Ancient Cities Kept Their Cool
The composite parts of ancient cities were an integrated system. In Yazd, for instance, the mainly ceramic buildings are pressed tightly together with high ceilings designed to maximize shaded area. There are buildings called tekhtubush, similar to Roman atriums, which incorporated heavily shaded central courtyards to keep ground-level cool. There were centrally located fountains which were, in effect, quite literally reverse chimneys, cooling their surroundings. Stone walls, meanwhile, served to passively regulate heat—using thermal inertia to carry over frigid nighttime temperatures, typical in the deserts of Iran, into the daytime climates. Additionally, the countless domed roofs throughout Yazd help keep indoor air circulating.Incorporating badgirs into this system, the product is a total infrastructure design. It creates a passive, quiet, and free air conditioned climate.
Badgirs were the standard for air conditioning in ancient times. They were even considered status symbols for those who could afford them. Although hundreds still survive—in places like Iran and Egypt—they have largely been neglected by architects in the late 20th century. Meanwhile, the noisier, more electricity-thirsty modern variety has prevailed.
Yet, lately modern designers have taken a page from history. Looking back to wind-catchers they found inspiration for new designs. Pittsburgh’s PNC PLAZA and its solar chimney, for instance, make use of ancient concepts of thermodynamics, like those found in badgirs. With today’s increasing demand for eco-friendly solutions in architecture, badgirs could, just maybe, catch a second wind.
