Green Prophet looks to ancient Iran for some current alternative ideas to electricity-powered air con. Catch the wind with the bagdir wind tower!
The concept of “green building” has taken off in the Middle East over the last few years. The need for ecologically efficient housing and offices is becoming more urgent as the cost of heating and cooling skyrockets and water becomes ever more scarce.
But environmentally-conscious buildings have been around much longer than the modern environmental crisis. Outdating gas-guzzling air con units by generations, bagdirs – or windcatchers – have been cooling down the people of Yazd, Iran, since before the 19th century. These towers spike the skyline of the Iranian desert city like antiquated skyscrapers.
The stone structures channel wind down into a shaft which in turn cools or heats the rooms below, allowing them to remain comfortable all year with zero carbon impact.
As well as using smart technology, the windcatchers of Yazd’s success depends on effort from the building’s inhabitants too. People can reduce their energy use by occupant behaviour strategies, for instance, moving to warmer or cooler rooms throughout the day.
This contrasts to the approach of modern Western design where “the individual chooses the climate for a room:
While nomads in Iran migrate from summer climates, for those who remain in Yazd replace the long migration by a short intra mural migration, within the walls of a single house.
In the summer, when temperatures soar to over 40 degrees C, this means using the ground floor in morning and evening, while escaping to the roof at night – a popular pastime in cities like Tel Aviv. Other strategies include watering floors, wearing lighter or warmer clothes, or – my favourite – taking an afternoon nap in the heat of the day. In Morocco, men are known to sleep on the roofs of the apartments at night to catch the breeze.
How the wind catchers work
Iran is an extreme hot/cold and arid climate. It can get very hot in the daytime sun and then cool down completely at night. Before we had electric sockets and Iran was called Persia, people engineered windcatchers.
Windcatchers are very much a traditional Persian architectural design that creates natural or passive ventilation in buildings. The basic design illustrated below consists of a tower that emerges from the building below, with openings at the top.
Yazd, one of the largest cities in Iran, and which is home to hundreds of these windcatchers is also known as the City of Windcatchers. Yazd is located between the largest deserts of Iran: Dasht-e-Kavir and Dasht-e-Lut.
Today the tower of Dolat Abad is the tallest existing windcatcher in Iran.
But windcatchers weren’t built by themselves: the city of Yazd has a long network of qanats, or underground channels that bring well water to the surface. When you have a cool breeze running over water you can amplify the cooling effect. My friends in Beersheva, Israel, cool their home with a desert air conditioner which is borrowed from this idea: hot desert air that flows over water to cool the home, not refrigerate it. The modern air conditioners and the stark difference between inside and outside is sometimes unbearable.
How wind catchers work
Windcatchers work in a few ways: The first and most common is to cool the inside of a building. The tower has openings that are facing the wind and trap it inside creating a nice breeze inside the building, much like the way you feel in a wind tunnel between skyscrapers. When used with the qanat, air is pulled down, reaches the water and is drawn up the windcatcher to be dispersed in the building.
When there is no wind, the windcatchers are like a chimney, letting the hot air rise and escape. Ever spend some time in a camper fun in the heat of the summer sun? When the hot air can rise, flow is created and it escapes out of the chimney. Not so much in a camper van.
When built into adobe structures, low level spaces can remain very chill in the hottest parts of the day. And you can still find windcatchers in use in Iran, the Middle East and Persian Gulf.
But the bagdirs of Yazd do have their dark side. Though partly funded by the silk trade, most of the windcatchers owe their existence to local merchants who made their fortunes from the British opium trade to China during the Opium Wars.