Windcatcher
A windcatcher, wind tower, or wind scoop (
Neglected by modern architects in the latter half of the 20th century, the early 21st century saw them used again to increase
Windcatchers rely on local weather and microclimate conditions, and not all techniques will work everywhere; local factors must be taken into account in design.[5] Windcatchers of varying designs are widely used in North Africa, West Asia, and India.[12][2] A simple, widespread idea, there is evidence that windcatchers have been in use for many millennia, and no clear evidence that they were not used into prehistory.[3][2][12] The "place of invention" of windcatchers is nonetheless intensely disputed; Egypt, Iran, and the United Arab Emirates all claim it.[12][13]
Windcatchers vary dramatically in shape, including height, cross-sectional area, and internal sub-divisions and filters.[2]
Windcatching has gained some ground in Western architecture, and there are several commercial products using the name windcatcher. Some modern windcatchers use sensor-controlled moving parts or even solar-powered fans to make semi-passive ventilation and semi-passive cooling systems.[2]
Windscoops have long been used on ships, for example in the form of a
Location
The construction of a windcatcher depends on the
Windcatchers in areas with stronger winds will have smaller total cross-sections,[15] and areas with very hot wind may have many smaller shafts in order to cool the incoming air.[14]: Ch. 5 Windtowers with square horizontal cross-sections are more efficient than round ones, as the sharp angles make the flow less laminar, encouraging flow separation;[2] suitable shaping increases suction.[14]: Ch. 5
Taller windcatchers catch higher winds. Higher winds blow stronger and cooler[16] (and in a different direction[17]). Higher air is also usually less dusty.[16]
If the wind is dusty or polluted, or there are insect-borne illnesses such as malaria and dengue fever, then air filtering may be necessary.[2] Some dust can be dumped at the bottom of the windcatcher as the air slows (see diagram below), and more can be filtered out by suitable plantings or insect mesh.[16] Physical filters generally reduce throughflow, unless the flow is very gusty.[2] It may also be possible to fully or partially close the windcatcher off.[15]
The short, wide right-triangle-prism malqaf are usually bidirectional, set in symmetrical pairs, and are often used with a salsabil (evaporative cooling unit)[2] and a shuksheika (roof lantern vent).[16] Wide malqafs are more often used in damper climates, where high-volume air flow is more important compared to evaporative cooling. In hotter climates, they are narrower, and air is cooled on its way in.[14]: Ch. 5 They are more commonly used in Africa.[2] Baudgir, on the other hand, are multisided (usually 4-sided), and they are typically tall towers (up to 34 meters tall) which can be closed in winter. They are more common in the Persian Gulf region[2] and in areas with dust storms.[15] Taller windcatchers also have a stronger stack effect.[14]: Ch. 5
Cooling methods
Night-flushing cools the house by increasing ventilation at night, when the outdoor air is cooler; windtowers can assist night flushing.[16]
A windcatcher can also cool air by drawing it over cool objects. In
Windcatchers that cool by drawing air over water use the water as a heat reservoir, but if the air is dry, they are also cooling the air with
Simply moving the air also has a cooling effect. Humans cool themselves using evaporative cooling when they
Airflow forces
The windcatcher can function in two ways: directing airflow using the pressure of wind blowing into the windcatcher, or directing airflow using
Airflow speed is also important, especially for evaporative cooling (since it only works on dry air, and humidifies the air). It is possible for a windtower-ventilated building to have very high flow rates; 30 air changes per hour were measured in one experiment.[5] Uniform, stable flow with no stagnant corners is important. Turbulent flow should therefore be avoided; laminar flow is more effective at maintaining human comfort[4] (for an extreme example, see Tesla valve).
Other elements are often used in combination with the windcatchers to cool and ventilate:
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).[14]: Ch. 5
Routing the wind through the building cools the people in the building interior. The air flows through the house, and leaves from the other side, creating a through-draft; the rate of airflow itself can provide a cooling effect.[citation needed] Windcatchers have been employed in this manner for thousands of years.[14]
The windtower essentially creates a pressure gradient to draw air through the building[18] . Windtowers topped with horizontal airfoils have been built to enhance these pressure gradients.[2] The shape of the traditional shuksheika roof also creates suction as wind blows over it.[14]: Ch. 5
Convection
Buoyancy is usually not the main effect driving windcatcher air circulation[2] during the day.
In a windless environment, a windcatcher can still function using the stack effect.[16] The hot air, which is less dense, tends to travel upwards and escape out the top of the house via the windtower.[2]
Heating of the windtower itself can heat the air inside (making it a solar chimney), so that it rises and pulls air out of the top of the house, creating a draft. This effect can be enhanced with a heat source at the bottom of the windtower (such as humans, ~80 Watts each[citation needed]), but this heats the house and makes it less comfortable.[2] A more practical technique is to cool the air as it flows down and in, using heat reservoirs and/or evaporative cooling.[5]
A
Buoyancy forces are used to cause night flushing.
Night flushing (colder air)
The
Courtyards in hot climates fill with cold air at night. This cold air then flows from the courtyard into adjacent rooms.
Subterranean cooling
A windcatcher can also cool air by bringing it into contact with cool thermal masses. These are often found underground.
Below approximately 6m of depth, soil and
Windcatchers are also often used to ventilate lower-level indoor spaces (e.g. shabestans), which maintain frigid temperatures in the middle of the day even without windcatchers. Ice houses are traditionally used to store water frozen overnight in desert areas, or over winter in temperate areas. They may use windcatchers to circulate air into an underground or semi-underground chamber, evaporatively cooling the ice so that it melts only slowly and stays fairly dry (see lede image). At night, the windcatchers may even bring sub-freezing night air underground, helping to freeze ice.
Evaporative cooling
In dry climates, the
Windcatchers are used for evaporative cooling in combination with a
A salasabil is a type of fountain with a thin sheet of flowing water, shaped to maximize surface area and thus evaporative cooling.[16][14]: Ch. 7 Windcatchers are often used with salasabils may be used to maximize the flow of unsaturated air over the water surface and carry the cooled air to where it is needed in the building.[4]
Wetted matting can also be hung inside the windcatcher to cool incoming air.[16] This can reduce flow, especially in weak winds. However, it can also produce a downdraft of cool air in windless conditions.[2] The evaporative cooling within a windtower causes the air in the tower to sink, driving circulation. This is called passive downdraught evaporative cooling (PDEC). It may also be generated using spray nozzles (which have a tendency to get blocked if the water is hard) or cold-water cooling coils (like hydronic underfloor heating in reverse).[5]
Windcatchers and climate change
Windcatchers can be used for
A window windcatcher can reduce the total energy use of a building by 23.3%.[27]
Regional use
The examples and perspective in this may not represent a worldwide view of the subject. (August 2020) |
Africa
Egypt
In Egypt windcatchers are known as malqaf, pl. malaaqef.
Windcatchers in Egypt are often used in conjunction with other passive cooling elements.[16]
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Ancient Egyptian House miniature showing windcatchers, dating fromEarly Dynastic Period of Egypt, found in Abou Rawsh near Cairo. Now in Louvre.
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Model of an Ancient Egyptian house with windcatcher, Roemer- und Pelizaeus-Museum Hildesheim
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Windcatchers in Khartoum, Sudan
Middle East and Asia
Windcatchers are common feature across many Middle Eastern countries influenced by the spread of culture under Islamic rule.
Iran
In Iran, a windcatcher is called a bâdgir, bâd "wind" + gir "catcher" (Persian: بادگیر). The devices were used in Achaemenid architecture.[15] They are used in the hot, dry areas of the Central Iranian Plateau, and in the hot, humid coastal regions.[15]
Central
The windcatcher's effectiveness had led to its routine use as a refrigerating device in Iran. Many traditional water reservoirs (.
Windcatchers tend to have one, four, or eight openings. In the city of Yazd, all windcatchers are four- or eight-sided. The construction of a windcatcher depends on the direction of airflow at that specific location: if the wind tends to blow from only one side, it is built with only one
Windcatchers in Iran may be quite elaborate, due to their use as status symbols.[15]
A small windcatcher 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 function more as ventilators than as the temperature regulators seen in the central deserts of Iran.
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Borujerdi House, in Kashan, central Iran. Built in 1857, it is an excellent example of ancient Persian desert architecture. The two tall windcatchers cool the andaruni (courtyard) of the house.
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Golestan Palace, in Tehran, Iran
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A windtower from below, inside, showing that it is partly closed-off
Australia
Council House 2 in Melbourne, Australia, has 3-story-tall "shower towers", made of cloth kept wet by a showerhead trickling at the top of each one. Evaporative cooling chills the air, which then descends into the building.[19]
Europe
The
The
Americas
A windcatcher has been used in the visitor center at Zion National Park, Utah,[35] where it functions without the addition of mechanical devices in order to regulate temperature.[33]
See also
- Ridge vent – Vent installed at the peak of a sloped roof
- Passive cooling – Building design that reduces inside temperatures without air conditioning
- Qanat – Water management system using underground channels
- Salsabil (fountain) – Thin-sheet fountain for evaporatively cooling buildings or water
- Solar updraft tower – Thermal convection power plant
- Vernacular architecture – Architecture based on local needs, materials, traditions
- Yakhchal– Ancient Persian ice-house
References
- ^ Malone, Alanna. "The Windcatcher House". Architectural Record: Building for Social Change. McGraw-Hill. Retrieved July 27, 2023.
- ^ .
- ^ a b c d e Attia, Shady (June 22–24, 2009). Designing the Malqaf for summer cooling in low-rise housing, an experimental study (PDF). PLEA2009 – 26th Conference on Passive and Low Energy Architecture. Quebec City, Canada.
- ^ a b c d Niktash, Amirreza; Huynh, B. Phuoc (July 2–4, 2014). "Simulation and Analysis of Ventilation Flow Through a Room Caused by a Two-sided Windcatcher Using a LES Method" (PDF). Proceedings of the World Congress on Engineering.
- ^ .
- ^ Plumer, Brad (February 16, 2021). "A Glimpse of America's Future: Climate Change Means Trouble for Power Grids". The New York Times. Retrieved July 29, 2023.
- ^ "U.S. power and natgas prices spike in Texas and California heatwaves". Reuters. June 16, 2021. Retrieved July 29, 2023.
- ^ Singh, Maanvi (February 19, 2021). "'California and Texas are warnings': blackouts show US deeply unprepared for the climate crisis". The Guardian. Retrieved July 29, 2023.
- ^ "A Tale of Two Grids: Texas and California". www.nrdc.org. March 2, 2021.
- ^ "Power grid struggles in Texas similar to those in California". ABC7 Los Angeles. February 18, 2021. Retrieved July 29, 2023.
- ^ unreliability of American grids[6][7][8][9][10]
- ^ a b c Abdolhamidi, Shervin (September 27, 2018). "An ancient engineering feat that harnessed the wind". www.bbc.com. Retrieved July 29, 2023.
- ^ "Arab States Obstructing Registration Of Iranian Windcatcher At UNESCO". ifpnews.com. June 16, 2019. Retrieved July 29, 2023.
- ^ a b c d e f g h i j k l m Hassan Fathy (1986). "The wind factor in air movement". Natural Energy and Vernacular Architecture. Retrieved July 29, 2023.
- ^ a b c d e f g h i A. A'zami (May 2005). "Badgir in traditional Iranian architecture" (PDF). International Conference "Passive and Low Energy Cooling 1021 for the Built Environment", May 2005, Santorini, Greece. Retrieved March 21, 2012. (the English is hard to understancd)
- ^ a b c d e f g h i j k l m n o p Mohamed, Mady A. A. (2010). S. Lehmann; H.A. Waer; J. Al-Qawasmi (eds.). Traditional Ways of Dealing with Climate in Egypt. The Seventh International Conference of Sustainable Architecture and Urban Development (SAUD 2010). Amman, Jordan: The Center for the Study of Architecture in Arab Region (CSAAR Press). pp. 247–266.
{{cite book}}
:|work=
ignored (help)low-res bw version - ISBN 0-521-01122-1.
- S2CID 55886961.
- ^ a b c "Whither the Windcatcher?". Conservation. May 23, 2012.
- ^ "Groundwater temperature's measurement and significance". National Groundwater Association. August 23, 2015. Archived from the original on August 23, 2015.
- ^ "Mean Annual Air Temperature". www.icax.co.uk.
- ^ "Ground Temperatures as a Function of Location, Season, and Depth". builditsolar.com.
- ISSN 0276-1084. Archived from the original (PDF) on February 17, 2012. Retrieved March 21, 2009. The author issued an updated versionof this article in February 2001.
- . Retrieved August 28, 2023.
- S2CID 244435768. Retrieved August 28, 2023.
- ^ Hambling, David (July 13, 2023). "Ancient windcatchers in Iran give architects cooling inspiration". The Guardian. Retrieved August 28, 2023.
- hdl:10919/113078.
- ^ Ahmed Abdel Wahab Ahmed Rizk; Mohamed Abdel Mawgoud Abdel Ghaffar; Mohamed Hefnawy (April 11, 2007). "The effect of wind-catchers (el-Malaqef) on the internal natural ventilation in hot climates with special reference to Egypt: A study on small physical models". www.aun.edu.eg (in English and Arabic). Asyut: Assiut University. p. 1. Archived from the original (Microsoft Word document (.doc)) on September 23, 2015. Retrieved September 21, 2016.
EL-MALAQEF
- ^ "Industrial architecture in Egypt in the 19th and 20th centuries, Arsenal in the Citadel of Cairo: workshop hall with timber roof construction and wind catcher (malqaf)". Dainst.org. Archived from the original on May 13, 2013. Retrieved April 22, 2013.
- ^ Shady Attia (June 22–24, 2009). "Designing the Malqaf for summer cooling in low-rise housing, an experimental study" (PDF). 26th Conference on Passive and Low Energy Architecture (PLEA2009). Archived from the original (PDF) on May 3, 2013. Retrieved April 22, 2013.
- ^ "Air-conditioning avoidance" (PDF). Archived from the original (PDF) on October 23, 2007.
- ^ "Air-conditioning avoidance" (PDF). Archived from the original (PDF) on October 23, 2007.
- ^ a b c d "How Ancient Persian Architecture Captured Wind Energy Underground to Green Buildings". This Big City.net. March 20, 2012. Retrieved March 20, 2012.
- ^ "Queen's Building, DeMontfort University" (PDF).
- ^ "Zion Canyon Visitor Center". National Park Service. Retrieved October 29, 2018.
Further reading
- Bahadori, Mehdi N. (1978). "Passive Cooling Systems in Iranian Architecture". Scientific American. 238 (2). Springer Science and Business Media LLC: 144–154. S2CID 119819386.
- Bahadori, Mehdi N. (1994). "Viability of wind towers in achieving summer comfort in the hot arid regions of the middle east". Renewable Energy. 5 (5–8). Elsevier BV: 879–892. ISSN 0960-1481.
- Kassir, Radwan M (September 4, 2015). "Passive downdraught evaporative cooling wind-towers: A case study using simulation with field-corroborated results". Building Services Engineering Research and Technology. 37 (1). SAGE Publications: 103–120. S2CID 111048250.
- Montazeri, H.; Azizian, R. (2008). "Experimental study on natural ventilation performance of one-sided wind catcher". Building and Environment. 43 (12). Elsevier BV: 2193–2202. ISSN 0360-1323.
- Sangdeh, Parham Kheirkhah; Nasrollahi, Nazanin (2022). "Windcatchers and their applications in contemporary architecture". Energy and Built Environment. 3 (1). Elsevier BV: 56–72. ISSN 2666-1233.
External links
- G.R Dehghan Kamaragi (January 2016). "Badgirs, Persian Gulf".
- Fathy, Hassan. "The wind factor in air movement". Natural Energy and Vernacular Architecture. (free fulltext)
- Roaf, S. (1988). "Bādgīr". Encyclopaedia Iranica. Vol. III. pp. 368–370.