Keeping cool: the use of evaporative cooling in vernacular Moroccan architecture.

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In dry and hot climates it is crucial to keep your body cooled and hydrated. There is of course lots of methods in doing this. If we look at strategies in vernacular architecture for keeping an interior environment cool and humidified we find a vast world of knowledge and intricate systems for using small amounts of resources with great effect.

 

botijo-de-madridPorous jars: This is a ceramic water cooling jar that probably originated from the Indus Valley Civilization. It is known in the Spanish part of the world as Botijo but existists in several cultures around the Mediterranean Sea and in Mexico. When the jar is filled with water it is placed outside in the shade. Because of the jars porosity, a small amount of water filters through the clay and evaporates when it comes in contact with the dry environment. Since the evaporation requires thermal energy, it extracts this from the water inside the jar, creating a cooling effect.

 

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Mashrabiyas: the Mashrabiya is a multifunctional element in vernacular Arabic architecture. It controls the passage of light and flow of air, reducing the inner temperature of the air and increasing the humidity. It also gives the dwellers privacy. It is usually a projected part of the wall, made out of wooden lattice, which extrudes from the second floor or higher up in the building. The lattice is watered, either manually or by the constantly seeping water from a porous water jar, that sits on the Mashrabiya.  The name is derived from the word ´drink´ in Arabic, because it used to be the place where the drinking water was cooled.

It uses evaporative cooling an efficient way. The lattice has a lot of small cavities where the water can be absorbed by the wooden lattice, retained and then released in the air flow, which creates the cooling effect.

 

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Malkaf  or Wind catchers and Salsabil or Courtyard fountain system: both wind catchers and courtyards in vernacular Arabic architecture use evaporative cooling to create a comfortable interior climate. The water element is usually a fountain or a small pool, that gets its water from a local source or man-made system of wells, called qanats.

The Salsabil is a system of fountains and open channels that, in combination with natural ventilation, creates a cooling effect. Trees are commonly planted in the courtyard to enhance shading and evaporative cooling effects. The water system is reliant on the proportions of the courtyard. It cannot be to wide, otherwise the cool air from the water will evaporate into the sky.

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Principles for evaporative cooling: When water is evaporated, energy is lost from the air, reducing the temperature. So it is not that the water cools through a lower temperature, it is through enegy movement. Two temperatures are important when dealing with evaporative cooling systems.

Dry bulb temperature; is the temperature that we usually think of as air temperature, measured by a regular thermometer exposed to the air stream.

Wet Bulb Temperature; is the lowest temperature that can be reached by the evaporation of water only.

 

Contemporary examples:

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In  Microclimates, design duo Postler and Fergusson has created a sculpture that mimics the evaporative charactaristics of both the porous jar and the Mashrabiya. In the designers’ own words: “Using custom software, our Microclimates project is a way of building. It’s based on a three-dimensional interpretation of the masharabiya built from arabic clay. The complex structure has a large internal surface area that efficiently conditions air passing through it by evaporative cooling. Each cooling tower is made from 3D-printed sand using technology developed by D-Shape.”

 

 

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The design team behind Emerging Objects has in their project Cool Brick used evaporative cooling in a similar way but with another function. Designers description: “Comprised of 3D printed porous ceramic bricks set in mortar, each brick absorbs water like a sponge and is designed as a three dimensional lattice that allows air to pass through the wall. As air moves through the 3D printed brick, the water that is held in the micro-pores of the ceramic evaporates, bringing cool air into an interior environment, lowering the temperature using the principle of evaporative cooling.”

Summery:

 

References:

Elawa, Sami. Housing Design in Extreme Hot Arid Zones with Special Reference to Thermal Performance. Lund, Sweden: Dept. of Building Science, LTH, U of Lund, 1981. Print.

http://archive.aramcoworld.com/issue/199503/keeping.cool.htm, accessed

http://archive.aramcoworld.com/issue/197404/the.magic.of.the.mashrabiyas.htm

http://www.solaripedia.com/files/488.pdf

Cool Brick

http://www.postlerferguson.com/design/microclimates

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