- Kimya Shkohi
From ancient Egypt to the Persian Empire, over thousands of years people have been able to cool their homes thanks to an innovative way to “catch” the breeze. In the search for zero-emission cooling, can we rely on what used to be “wind traps” again?
Yazd, in the desert of central Iran, has long been a focal point for ingenuity and creativity. Yazd is home to a system of ancient engineering marvels that includes an underground cooling structure called “Yakhshal”, an underground irrigation system called “canats” or canals, and even a network of couriers called “Peradazes” that predated the US Postal Service by more than 2,000 years.
Among the ancient techniques that appeared in the city of Yazd was a tool for “catching” the wind, or what is called in Persian as “badger”. These magnificent structures still rise above the rooftops of Yazd are a familiar sight there, and are often rectangular towers, but may take circular, square or octagonal ornate shapes.
Yazd is said to have the largest number of wind traps in the world, although this idea may have first appeared in ancient Egypt. In Yazd, wind traps soon proved indispensable, so that life could be made in this part of the hot and arid Iranian plateau.
Although many of the city’s wind traps are no longer in use today, these structures are now attracting academics and architects to this desert city to see what role they can play in combating the ever-rising heat of climate change.
Because wind traps do not require electricity to operate, they are a low-cost and environmentally friendly form of cooling. Conventional mechanical air conditioning already consumes a fifth of total electricity production globally, so old alternatives such as wind traps are becoming an increasingly attractive option.
There are two main forces that push air through and down those structures: incoming winds and the change in air buoyancy depending on temperature, as warmer air tends to rise above cooler and denser air.
Initially, when air is captured through the hole in the wind trap, it is directed into the house below, depositing any sand or debris at the foot of the tower.
The air then flows throughout the interior of the building, sometimes over the aquifers for further cooling. Eventually, warm air will rise and leave the building through a tower or other opening, aided by the pressure inside the building.
It should be noted that the tower’s shape, along with other factors such as the layout of the house, the direction the tower faced, the number of openings in it, the ducts and the height of the tower, were carefully calculated to improve the tower’s ability to draw wind for the house below.
The history of using wind to cool buildings dates back to the periods when people began to live in hot desert environments. The oldest wind-catching techniques date back to Egypt 3,300 years ago, according to researchers Chris Soilberg and Julie Rich, from Webber State University in Utah.
The buildings consisted of thick walls, a few windows facing the sun, openings to draw air from the prevailing wind direction, and openings for wind to exit from the other side – known in Arabic as the “Malqaf”. However, some claim that Iran itself was the first to invent a wind trap method for cooling buildings.
Regardless of where this method was devised, wind traps have become widespread throughout the Middle East and North Africa. Variations of Iranian wind traps can be found in the so-called barjeel in Qatar and Bahrain, the malqaf in Egypt, the meng in Pakistan, and many other places, say Fatima Gomizadeh and colleagues at the University of Technology in Malaysia.
It is widely believed that the Persian civilization added structural differences to achieve better cooling – such as integrating these systems with the existing irrigation system to help cool the air before it was released throughout the house.
In the hot and dry climate of Yazd, these traps proved very effective, until the city became home to a huge number of tall ornate towers looking out for the desert winds.
UNESCO recognized the historic city of Yazd as a World Heritage Site in 2017, due in part to the spread of wind traps.
In addition to serving the functional purpose of cooling homes, these towers also had great cultural significance. In Yazd, wind traps are part of the city skyline, such as the Zoroastrian Fire Temple and the Tower of Silence, and perhaps the most notable of these is the Dowlatabad Gardens wind trap, said to be the highest in the world at 33 meters (108 ft) high, and one of the few wind traps that Still working now. This trap is located in an octagonal building, overlooking a fountain that stretches through rows of pine trees.
Some researchers argue that the effectiveness of wind traps in emission-free cooling may make people turn to them again.
Parham Khairkhah Sanghdeh studied the scientific application and culture surrounding wind traps in contemporary architecture at Ilam University in the Iranian capital, Tehran, and says that some inconveniences such as pests entering chutes and gathering dust have made many move away from using traditional wind traps, to be replaced by mechanical cooling systems, such as air conditioning units traditional.
Often, these systems are powered by fossil fuels and use refrigerants that act as potent greenhouse gases if released into the atmosphere.
Khirkhah Sangde also argues that the current lack of reliance on wind traps is partly due to people’s tendency to use technologies from the West. Energy. It starts with learning about the cultural history and understanding the importance of energy conservation.”
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