- Kimiya Shokoohi
- BBC Future
From Ancient Egypt to the Persian Empire, an ingenious method of capturing and directing the wind has refreshed people for millennia. In the quest for emission-free cooling, the “wind catcher” may come to help us again.
The city of Yazd, in the desert of central Iran, has long been a center of creativity. Yazd is home to one of the wonders of ancient engineering — a system that includes an underground cooling structure called the yakhchal, an underground irrigation system called the qanats, and even a messenger network called pirradazis, created more than 2,000 years before the US Postal Service .
Among the ancient technologies of Yazd is the wind catcher, or bâdgir, in Persian.
These remarkable structures are commonly found towering over the roofs of Yazd. They are often rectangular towers, but they also exist in circular, square, octagonal, and other ornate shapes.
Yazd is said to be the city with the most wind pickups in the world. They may have originated in Ancient Egypt, but at Yazd, the wind catcher soon proved indispensable, making life possible in that hot, barren part of the Iranian plateau.
While many of the desert city’s wind picks have fallen into disuse, their structures are now drawing the attention of academics, architects and engineers to study the role they could play in keeping us cool in a rapidly warming world.
Since wind sensors don’t need electricity to run, they are a cheap, green form of cooling. With conventional mechanical air conditioning already accounting for one-fifth of the world’s total electricity consumption, older alternatives such as wind traps are becoming an increasingly attractive option.
There are two main forces that drive the air through the structures: the entry of wind and the change in the thrust of the air depending on the temperature — warm air tends to rise over cold air, which is denser.
First, when air is captured by the opening of a wind sensor, it is channeled down to the building, depositing any fragments or sand at the foot of the tower. The air then flows throughout the entire interior of the building, sometimes over underground pools of water for better cooling. Finally, the heated air will rise and leave the building through another tower or opening, with the aid of pressure inside the building.
The tower’s shape and other factors — such as the design of the house, the direction the tower is facing, the number of openings, its fixed internal vane configuration, channels, and height — are all properly defined to increase the tower’s capacity. channel wind down into the building.
The story of the use of wind to cool buildings began at almost the same time that people began to live in the hot environment of deserts.
One of the first wind-capture technologies dates back to 3,300 years ago, in Egypt, according to researchers Chris Soelberg and Julie Rich, from Weber State University in Utah, in the United States. In this system, buildings had thick walls, few windows facing the sun, air intake vents in the main wind direction, and an exhaust vent on the other side—known in Arabic as malqaf architecture.
But there are those who argue that the wind sensor was invented in Iran itself.
In any case, wind pickups spread across the Middle East and North Africa. Variations of Iranian windpickers can be found with local names, like the barjeels of Qatar and Bahrain, the malqaf of Egypt, the mungh of Pakistan and many others, according to Fatemeh Jomehzadeh of the Malaysia University of Technology and his colleagues.
The Persian civilization is believed to have added structural variations to allow for better cooling, such as combining it with existing irrigation systems to help cool the air before it is released throughout the house.
In the hot, dry climate of Yazd, these structures became increasingly popular, until the city became an oasis of tall ornate towers in search of desert wind. Yazd is a historic city that was recognized as a UNESCO World Heritage Site in 2017 — in part, for its large number of wind pickups.
In addition to fulfilling the functional purpose of cooling the houses, the towers also had a strong cultural importance. Wind pickups are part of the Yazd landscape, as are Zoroaster’s Fire Temple and Tower of Silence.
Then there’s the wind pickup at the Jardim de Dowlat Abad, which is believed to be the tallest in the world (at 33 meters high) and one of the few still in operation. Housed in an octagonal building, it faces a fountain and a lake that stretches along rows of pine trees.
With the effectiveness of the cooling provided by these emission-free wind picks, some researchers argue that they deserve a resurgence.
Researcher Parkham Kheirkhah Sangdeh has carefully studied the scientific application and local culture of wind catchers in contemporary architecture at Ilam University in Iran. that many people abandoned traditional wind sensors.
Instead, mechanical cooling systems such as conventional air conditioning units are used. Often these alternative systems are powered by fossil fuels and use refrigerants that act as powerful greenhouse gases when released into the atmosphere.
The advent of modern cooling technologies has long been blamed for the deterioration of traditional methods in Iran, as Iranian architectural historian Elizabeth Beazley wrote in 1977.
Without constant maintenance, the hostile climate of the Iranian plateau has eroded many structures, from wind catchers to ice storage houses. Kheirkhah Sangdeh also notes that the abandonment of wind pickups was in part due to the public’s tendency to adopt technologies from the West.
“There needs to be a change of cultural perspective to use these technologies. People need to look at the past and understand why energy conservation is so important”, says the researcher, “starting with the recognition of cultural history and the importance of conservation power”.
Kheirkhah Sangdeh hopes Iran’s wind traps will be retrofitted to provide energy-efficient cooling to existing buildings. But he encounters many barriers to this work, such as existing international tensions, the covid-19 pandemic and the current lack of water. “The situation is so bad in Iran that [as pessoas] take one day at a time,” he says.
Non-fossil fuel cooling methods and systems, such as wind catchers, may well deserve their resurgence, but to the surprise of many, they are already present—though not as grand as the Iranians—in many Western countries.
In the UK, around 7,000 variations of wind sensors were installed in public buildings between 1979 and 1994. They can be seen in buildings such as the Royal Chelsea Hospital in London and in supermarkets in Manchester.
These modern wind picks bear little resemblance to Iranian tower-shaped structures. In a three-story building on a busy street in north London, small hot pink painted ventilation towers provide passive ventilation. Perched on top of a shopping center in Dartford, UK, conical ventilation towers rotate to capture the breeze with the aid of a rear wing that keeps the tower facing downwind.
The United States has also embraced wind pickup-inspired designs with enthusiasm. One such example is the visitor center at Zion National Park in southern Utah.
The park sits on a high desert plateau, with a climate and topography comparable to the Yazd region, and the use of passive cooling technologies such as the wind pickup has almost completely eliminated the need for mechanical air conditioning. Scientists recorded a temperature difference of 16°C between the outside and the inside of the visitor center, despite the many people who regularly pass through the site.
As the search for sustainable solutions to global warming deepens, more opportunities arise that favor the construction of wind sensors. In Palermo, Italy, researchers found that the prevailing weather and wind conditions make the city a hotspot for an Iranian version of the wind pickup.
In October, the wind sensor was prominently displayed at the Expo Dubai fair, in the United Arab Emirates, as part of a network of conical constructions in the Austrian pavilion. The Austrian architecture firm Querkraft was inspired by the barjeel to create it – the Arabic version of the wind sensor.
While researchers like Kheirkhah Sangdeh argue that the wind pickup has much more to offer for cooling homes without using fossil fuels, this ingenious technology has already migrated to other parts of the world — more than one might imagine. Next time you find a tall ventilation tower on top of a supermarket, building, or school, examine it carefully. You may be looking at the legacy of Iran’s magnificent wind catchers.
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