thumb |An [[ab anbar (water reservoir) with windcatchers (openings near the top of the towers) in the central desert city of Yazd, Iran]]

thumb |[[Aghazadeh Mansion in Abarkooh, Iran, has an elaborate 18-m windtower with two levels of openings, plus some smaller windtowers.]]

A windcatcher, wind tower, or wind scoop () is a traditional architectural element used to create cross ventilation and passive cooling in buildings. Windcatchers come in various designs, depending on whether local prevailing winds are unidirectional, bidirectional, or multidirectional, on how they change with altitude, on the daily temperature cycle, on humidity, and on how much dust needs to be removed.

Windcatchers rely on local weather and microclimate conditions, and not all techniques will work everywhere; local factors must be taken into account in design.

Windcatchers vary dramatically in shape, including height, cross-sectional area, and internal sub-divisions and filters.). Higher air is also usually less dusty. (for an extreme example, see Tesla valve).

Other elements are often used in combination with the windcatchers to cool and ventilate: courtyards, domes, walls, and fountains, for instance, as integral parts of an overall ventilation and heat-management strategy.

Wind pressure

If a windcatcher's open side faces the prevailing wind, it can "catch" it, and bring it down into the heart of the building. Suction from the lee side of a windtower is also an important driving force, usually somewhat more constant and less gusty than the pressure on the upwind side (see Venturi effect and Bernoulli's principle).

The windtower essentially creates a pressure gradient to draw air through the building. Windtowers topped with horizontal airfoils have been built to enhance these pressure gradients. during the day.

In a windless environment, a windcatcher can still function using the stack effect. so the garden and courtyard are used as windcatchers.

Buoyancy forces are used to cause night flushing.

Night flushing (colder air)

The diurnal temperature cycle means that the night air is colder than the daytime air; in arid climates, much colder. This creates appreciable buoyancy forces. Buildings may be designed to spontaneously increase ventilation at night.

Courtyards in hot climates fill with cold air at night. This cold air then flows from the courtyard into adjacent rooms. The courtyard air will become stably stratified, the hot air floating on top of the cold air with little mixing. (it is this depth which is used for many ground-source heat pumps, often loosely referred to as "geothermal heat pumps" by laypeople). The thermal inertia of the soil evens out the daily and even annual temperature swings. In arid climates, the daily temperature swings are often extreme, with desert temperatures often dipping below freezing at night. Even the thermal inertia of thick masonry walls will keep a building warmer at night and cooler during the day; in hot-arid climates, thick walls with high thermal mass (adobe, stone, brick) are common (though thinner walls with high resistance against heat transmission are more modernly sometimes used). and for adaptation to climate change because they facilitate cooling in a warmer climate. Windcatchers can reduce temperature inside the house by in comparison to the outdoor temperature.

A window windcatcher can reduce the total energy use of a building by 23.3%.

Regional use

Africa

Egypt

In Egypt windcatchers are known as , pl. . They are generally shaped as right triangular prisms with the vertical side left open and facing directly up or down wind (one of each per building). They work best if oriented within 10 degrees of wind direction; larger angles allow the wind to escape. and only started to fall out of use in the mid-20th century. Their use is now being re-examined, as air conditioning accounts for 60% of Egypt's peak electrical power demand (and thus the need for 60% of its generating capacity).<!--Mamluk period? https://knoji.com/article/the-architecture-of-the-traditional-arab-house/-->

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Byggnadskonsten, Fornegyptiska boningshus, Nordisk familjebok.png|Dwelling house in Ancient Egypt with windcatcher. From a painting at the Pharaonic house of Neb-Ammun, Egypt, which dates from the 19th Dynasty, c. 1300 BC (British Museum). They are used in the hot, dry areas of the Central Iranian Plateau, and in the hot, humid coastal regions.

Americas

thumb|The [[Kensington Oval cricket ground in Barbados also uses a very wide aluminium windscoop. where it functions without the addition of mechanical devices in order to regulate temperature.

See also

References

Further reading

  • G.R Dehghan Kamaragi (January 2016). "https://www.badgirs.com".
  • (free fulltext)