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A louver (
American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. English is the most widely spoken language in the United States and in most circumstances ...
) or louvre (
British English British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, "English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in England, or, more broadl ...
; see spelling differences) is a window blind or shutter with horizontal slats that are angled to admit light and air, but to keep out rain and direct sunshine. The angle of the slats may be adjustable, usually in blinds and windows, or fixed.


History

Louvers originated in the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
as lantern-like constructions in wood that were fitted on top of roof holes in large kitchens to allow ventilation while keeping out rain and snow. They were originally rather crude constructions consisting merely of a barrel. Later they evolved into more elaborate designs made of pottery, taking the shape of faces where the smoke and steam from cooking would pour out through the eyes and mouth, or into constructions that were more like modern louvers, with slats that could be opened or closed by pulling on a string.


Construction

Modern louvers are often made of aluminum, metal, wood, or glass. They may be opened and closed with a metal lever, pulleys, or through motorized operators. The Standard specifies requirements for the construction of buildings using louver in bushfire-prone areas in order to improve their resistance to bushfire attack from burning embers, radiant heat, flame contact and combinations of the three attack forms. The revised building standard details various construction methods and materials that must be used depending on the homes level of bushfire risk. This includes changes to the window and glazing requirements for homes located in a Bushfire Attack Level category greater BAL-Low.


Jalousies

Often used interchangeably by mistake, the key difference between louvers and jalousies is that louvers are fixed position. Jalousies are installed within a movable adjustable mechanism which positions all jalousies into any parallel position with respect to each other.


Use


In architecture

Louvers are rarely seen as primary design elements in the language of
modern architecture Modern architecture, or modernist architecture, was an architectural movement or architectural style based upon new and innovative technologies of construction, particularly the use of glass, steel, and reinforced concrete; the idea that for ...
, but rather simply a technical device. Louvers are part of the design of
Demerara window Demerara windows were built primarily into 18th- and 19th-century Colonial architecture-styled buildings to cool homes in hot climates, such as Guyana, before the invention of air conditioning. Demerara is a historical region of Guyana. The wind ...
s to help keep 18th and 19th century buildings cool in hot climates and block direct sunlight. Some modern louver systems serve to improve indoor daylighting. Fixed
mirror A mirror or looking glass is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the im ...
ed louver systems can limit glare and of redirect diffuse light. Such louvers may be integrated in between two panes of double glazing. In industrial facilities such as steel foundries and
power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many ...
s, louvers are very common. They are utilized for natural ventilation and temperature control. Louvers are frequently found in bell towers, where they are utilised to let out as much sound as possible, while having the bells remain unexposed to the weather. There are examples of architects who use louvers as part of the overall aesthetic effect of their buildings. The most well-known example is Finnish modernist architect Alvar Aalto who would create aesthetic effects in the facades of his buildings through the combination of different types and sizes of louvers, some fixed some moveable, and made mostly from wood (e.g., the various buildings of the Helsinki University of Technology). A second example, taking influence from Aalto, is the second-generation modernist architect Juha Leiviskä.


In infrastructure

Louvers may be used as a type of flood opening, usually covered by one or more moving flaps. They are designed to allow
flood A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
waters to enter and leave the building, equalizing
hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body " fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an i ...
on the walls and mitigating structural damage due to flooding. Louver windows are a staple in the design of homes and perfect to withstand the pressures of future cyclonic conditions. Cyclone homes have always been synonymous with louver windows, louver blades have been tested for ‘debris type B’ for cyclonic regions.


In transportation

Rear window louvers are also available as an accessory for some automobiles. They have also been used over the years in hoods, trunk lids, and other various body panels; typically hot rods, but by no means exclusive to that period. Their purpose in this regard is both as a functional means of ventilation, but also as a styling modification. Louvers are used as semi-passive means of thermal control on airplanes and
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...
as well. "The system devised for Rosetta employs several new techniques, including the installation of louvres over the radiators, to keep spacecraft hardware at proper operating temperatures" Louvers may also be used on traffic light lenses to prevent traffic from seeing the wrong traffic signal.


See also

*
Air conditioning Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
* Jalousie window * Window shutter


References

;Notes ;Bibliography *Henisch, Bridget Ann ''Fast and Feast: Food in Medieval Society''. The Pennsylvania State Press, University Park. 1976. *"Foundation Flood Vents". National Association of Home Builders (NAHB) Research Center. 2001. https://web.archive.org/web/20130116013400/http://toolbase.org/about.aspx. {{Use dmy dates, date=April 2017 Windows Ventilation Architectural elements Shading (Architecture)