Windcatcher

An ab anbar with double domes and windcatchers in the central desert city of Naeen, near Yazd, Iran

A windcatcher (Persian: بادگیر‎ bâdgir; bâd "wind" + gir "catcher", Arabic: ملقف Malqaf or بارجيل "Barjeel" in Eastern Arabia) is a traditional Persian architectural elemement used for many centuries to create natural ventilation in buildings. It is not known who first invented the windcatcher, but it still can be seen in many countries today. Windcatchers come in various designs: uni-directional, bi-directional, and multi-directional. Examples of windcatchers can be found in traditional Persian-influenced architecture throughout the Middle East, Pakistan and Afghanistan.

Background

Central Iran has a very large day-night temperature difference, ranging from very cold to extremely hot, and the air tends to be very dry all day long. Most buildings are constructed of very thick ceramics with extremely high insulation values. Furthermore, towns centered on desert oases tend to be packed very closely together with high walls and ceilings relative to Western architecture, maximizing shade at ground level. The heat of direct sunlight is minimized with small windows that do not face the sun.

Function

A windcatcher or malqaf used in traditional Persian / Arabic architecture

The windcatcher can function by several methods:

One of the most common uses of the badgir is as an architectural feature to cool the inside of the dwelling, and is often used in combination with courtyards and domes as an overall ventilation / heat management strategy. The malqaf is essentially a tall, capped tower with one face open at the top. This open side faces the prevailing wind, thus 'catching' it, and bringing it down the tower into the heart of the building to maintain air flow, thus cooling the interior of the building. This is the most direct way of drawing air into the building, but importantly it does not necessarily cool the air, but relies on a rate of air flow to provide a cooling effect. This use of the malqaf or windcatcher has been employed in this manner for thousands of years, as detailed by contemporary Egyptian architect Hassan Fathy.

A windcatcher and qanat used for cooling

The second usage is in combination with a qanat, or underground canal. In this method, the open side of the tower faces away from the direction of the prevailing wind. (This can be adjusted by having directional ports at the top). By closing all but the one facing away from the incoming wind, air is drawn upwards using the Coandă effect, similar to how opening the one facing towards the wind would pull air down into the shaft.

As there is now a pressure differential on one side of the building, air is drawn down into the passage on the other side. This hot air is brought down into the qanat tunnel, and is cooled by the combination of coming into contact with the cold earth (as it is several meters below ground, the earth stays continuously cool) as well as the cold water running through the qanat. The air is therefore cooled significantly, and is then drawn up through the windcatcher by the same Coandă effect. This brings cool air up through the building, cooling the structure overall, with the water vapour from the qanat having an added cooling effect.

Finally, in a windless environment or waterless house, a windcatcher functions as a solar chimney. It creates a pressure gradient which allows less dense hot air to travel upwards and escape out the top. This is also compounded significantly by the day-night cycle mentioned above, trapping cool air below. The temperature in such an environment cannot drop below the nightly low temperature. These last two functions have gained some ground in Western architecture, and there are several commercial products using the name windcatcher.

When coupled with thick adobe that exhibits high heat transmission resistance qualities, the windcatcher is able to chill lower level spaces in mosques and houses (e.g. shabestan) in the middle of the day to frigid temperatures.

So effective has been the windcatcher in Persian architecture that it has been routinely used as a refrigerating device (yakhchal) for ages. Many traditional water reservoirs (ab anbars) are built with windcatchers that are capable of storing water at near freezing temperatures for months in summer. The evaporative cooling effect is strongest in the driest climates, such as on the Iranian plateau, hence the ubiquitous use of these devices in drier areas such as Yazd, Kerman, Kashan, Sirjan, Nain, and Bam. This is especially visible in ab anbars that use windcatchers.

A small windcatcher (badgir) is called a "shish-khan" in traditional Persian architecture. Shish-khans can still be seen on top of ab anbars in Qazvin, and other northern cities in Iran. These seem to be more designed as a pure ventilating device, as opposed to temperature regulators as are their larger cousins in the central deserts of Iran.

Gallery

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  The windcatcher of "Dowlat-abad" in Yazd, Iran — one of the tallest extant windcatchers

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  Borujerdi ha House, in central Iran. Built in 1857, it is an excellent example of ancient Persian desert architecture. The two tall windcatchers cool the andaruni section of the house.

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  The tower on this Barasti made (Palm Fronds) house catches the wind in the same way as a normal wind tower and cools the interior.

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  Wind towers in Dubai

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  Windtower of Isa bin Ali House, in Muharraq, Bahrain

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  Golestan palace, Tehran

Structure and architecture

Windcatchers are made with one, four, or eight openings. In the city of Yazd all the windcatchers are made four or eight sided. The construction of a windcatcher depends on the air flow direction in that specific site: if in some place the wind always blows from just one side, the windcatchers are built with just one downwind opening. An example of this is the city of Meybod, 50 kilometers from Yazd: all the windcatchers are short and have a single opening. To keep buildings free of dust and sand blown in from the desert, builders made windcatchers facing away from the wind.

See also

• Yakhchal
• Solar chimney
• Solar updraft tower
• Qanat

External links

• Hassan Fathy: "Natural Energy and Vernacular Architecture"
• Bahadori, Mehdi N. (February 1978). "Passive Cooling Systems in Iranian Architecture". Scientific American 238 (2): 144–154. doi:10.1038/scientificamerican0278-144. http://paccs.fugadeideas.org/disclaimer/fairuse.php?file=cooling_syst_iran.html&title=Passive%20Cooling%20Systems%20in%20Iranian%20Architecture. Retrieved 2007-07-17. 
• Bahadori, Mehdi N. (August 1994). "Viability of wind towers in achieving summer comfort in the hot arid regions of the middle east". Renewable Energy 5 (5–8): 879–892. doi:10.1016/0960-1481(94)90108-2. 
• A. A'zami. "Badgir in traditional Iranian architecture" (PDF). http://www.inive.org/members_area/medias/pdf/Inive%5Cpalenc%5C2005%5CAzami2.pdf. Retrieved 2007-07-17. 
• Yazd, the city of windcatchers. (broken link)
• The famous Dowlat-abad windcatcher in Yazd
• Windcatchers are incorporated into the architectural expression of traditional Persian buildings. Notice this sample, with 6 symmetrical badgirs, in Yazd.
• ventilation cowl on a ship