Among one the Middle East’s most ancient technologies is the windcatcher, or bâdgir in Persian. These remarkable structures are a common sight soaring above the rooftops of Persia. They are often rectangular towers, but they also appear in circular, square, octagonal and other ornate shapes.
How a windcatcher works
There are two main forces that come into play with the structures: the incoming wind and the change in buoyancy of air depending on temperature – with warmer air tending to rise above cooler, denser air. First, as air is caught by the opening of a windcatcher, it is funneled down to the dwelling below. This air flows throughout the interior of the building, sometimes over pools of water for further cooling. Eventually, warmed air will rise and leave the building through another tower or opening, aided by the pressure within the building that is elevated by the incoming airflow.
The shape of the tower, the direction the tower is facing, how many openings it has, its configuration of fixed internal blades, and height are all finely tuned to improve the tower’s ability to draw wind down into the dwellings below.
Some of the earliest wind-catching technology comes from Egypt 3,300 years ago
Using the wind to cool buildings has a history stretching back almost as long as people have lived in hot desert environments. Some of the earliest wind-catching technology comes from Egypt 3,300 years ago, according to researchers Chris Soelberg and Julie Rich of Weber State University in Utah. In Egypt, buildings had thick walls, few windows facing the Sun, openings to take in air on the side of prevailing winds, and an exit vent on the other side of the structure.
Constructing a windcatcher
The first consideration is placement of the windcatcher structure. It should face the prevailing winds. If wind directions vary, the wind tower may have radial internal walls which divide the vertical structure into sections (like multiple chimneys inside a single box). Windcatchers can be built taller to harness higher winds.
If wind tends to blow from one side only, then it will be built with one downwind opening. This is the simplest design.
These windcatchers tend to be more efficient for airflow circulation and have better performance. They serve two functions – to blow and suck air into a building.
These tend to be either four, six or eight-sided windcatchers, and are bigger and taller than the other types. The exact height and structure of each opening depends upon the specific region’s climate.
This is the most technical form of windcatcher and achieves better performance than the other types.
The following components comprise a typical windcatcher:
Includes a moving column opened and closed either manually or electronically. This helps prevent rainwater ingress.
Fixed in place and can be installed on a rooftop (flat or inclined) using bolts.
Installed at the lower end of the column to control airflow.
Can be installed to detect the wind direction.
Using upward airflow
In environments that experience minimal wind, or where a qanat is impractical, a windcatcher can be used to function as a solar chimney which allows hot air to travel upwards and escape from the top of the building. In this way, large buildings – especially those constructed with thick adobe to provide good heat transmission resistance – can be kept at chilled temperatures during hot periods.
Mesh can be used to filter the air. However, it is common for dirt and dust to be deposited at the bottom of the windcatcher.
Windcatchers can be designed to draw air over a basin of water, making the structure a sort of evaporative cooler.
Windcatcher picture gallery
Image CreditsA windcatcher on a building in Yazd, Iran via Wikimedia Commons by Diego Delso with usage type - Creative Commons License. September 21, 2016
via Wikimedia Commons by Strassberger, B. with usage type - Public Domain. 1878
Windcatchers on the Souq Waqif, Doha, Qatar via Wikimedia Commons by Diego Delso with usage type - Creative Commons License. August 6, 2013
Windcatchers on the Qatar University Campus via Wikimedia Commons by Sky2105 with usage type - Creative Commons License. July 5, 2011
Tall Windcatcher structure on the Pavillon du jardin Dolat Abad, Yazd, Iran via Wikimedia Commons by Bernard Gagnon with usage type - GNU Free. October 23, 2016