A windtower (wind catcher) (Persian: بادگیر bâdgir: bâd “wind” + gir “catcher”) is a traditional Persian architectural element to create natural ventilation in buildings. Windcatchers come in various designs: uni-directional, bi-directional, and multi-directional. The devices were used in ancient Egyptian architecture. Windcatchers remain present in Iran and can also be found in traditional Persian-influenced architecture throughout the Middle East, including in the Arab states of the Persian Gulf (mostly Bahrain and the United Arab Emirates), Pakistan, and Afghanistan.
The central region of Iran is desert, which, due to the lack of moisture in the air, generates large temperature differences between day and night. Thus the air goes from fresh to extremely hot in summer and with very low relative humidity all day. Most buildings are constructed of very thick adobe or brick walls, which provide thermal insulation and thermal mass. With this passive design strategy, it is possible to absorb the great variation between day and night until making it imperceptible by looking for an average temperature close to hygrothermal comfort. On the other hand, the great thickness of the walls allows to accumulate the diurnal heat to move the heat wave towards the night when the outside temperature falls below the comfort level.
The cities are located near or around desert oases in order to ensure the provision of water. They are also very closed plot: narrow streets, high walls and whitewashed with lime to minimize the absorption of solar heat. The buildings and houses have deep patios and terraces where the inhabitants sleep on hot summer nights. During the day the people are grouped in the interior shade.
The heat of sunlight is reduced to a minimum with the use of small windows protected by thick wooden lattices that serve as sun protection.
Central Iran shows large diurnal temperature variation with an arid climate. Most buildings are constructed from thick ceramic with high insulation values. Towns centered on desert oases tend to be packed very closely together with high walls and ceilings, maximizing shade at ground level. The heat of direct sunlight is minimized with small windows that face away from the sun.
The windcatcher’s effectiveness had led to its routine use as a refrigerating device in Persian architecture. Many traditional water reservoirs (ab anbars) are built with windcatchers that are capable of storing water at near freezing temperatures during summer months. The evaporative cooling effect is strongest in the driest climates, such as on the Iranian plateau, leading to the ubiquitous use of windcatchers in drier areas such as Yazd, Kerman, Kashan, Sirjan, Nain, and Bam.
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.
Windcatchers in Egypt
Windcatchers were used in traditional ancient Egyptian architecture. A painting depicting such a device has been found at the Pharaonic house of Neb-Ammun, Egypt, which dates from the 19th Dynasty, c. 1300 BC (British Museum). In Egypt the windcatchers are known as malqaf pl. malaaqef.
Structure and architecture
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 downwind opening. This is the style most commonly seen in Meybod, 50 kilometers from Yazd: the windcatchers are short and have a single opening.
Types of attachments
The individual wind turbines facing the prevailing wind are usually built within the same thickness of the wall and are usually no more than 50 cm x 20 cm in diameter. The bottom ends with an opening that does not exceed one meter above the floor. Its upper openings cover a rectangular or curved ramp with a semicircular arch topped by a cylindrical vault. (Lokoc, 1978)
Exhaust air vents of the prevailing wind are used to pull hot air out of the compartments into the outside air, which replaces wet air coming from the yard.
The wall air intake depends on the effect of wind pressure on the large surfaces of the walls of the rooms. They appear from the outside in the form of horizontal hollow slats located in the middle of the outer wall height and at the bottom of the alcove there is a shutter to control the opening or closing of the interior. The high-pressure air passing through the outer wall of the room facing the wind gathers inside the loops and pushes inside through the openings, causing air movement inside.
The upper half of the blade is made up of two overlapping surfaces, the front or outer surface of which is the lower half of the drum. It is built of bricks or compact clay. The upper half is flipped back, leaving a gap for the passage of the air and works in the way of the wall hangers.
Ventilation towers, is a square tower divided from inside to four ventilation wells anchored by two perpendicular walls and parallel to the outer walls. The air enters two wind-proof wells while the hot air exits through the other two wells.
Compound aerators, sets of ventilators co-create a combined ventilation tower, serving a number of chambers and is commonly used in humid, humid areas.
Ice pieces are placed in places of the Badenhang to increase cooling or the charcoal is ignited in some of the heating angle.
Development on the air intake
In studies at the University of Arizona, air intake consists of building towers (mud or other materials) with dimensions and heights that correspond to the areas to be cooled. The openings have upper openings on four sides. These openings are mounted on cellulose or hay cells that are constantly moistened with water by a small pump. The excess water goes down to the channel under the net and returns to the pump tank again. The air is cooled inside the tower and descends down and enters the building, instead replacing the dry and hot outside air and thus producing an air current. (Degelis, 2003).
But widespread use of this old technique on a large scale, would greatly reduce the energy consumption of buildings. We learned the Syrians thousands of years ago, but we, as usual, did not learn the lesson…
In History and Literature
The invention of Al-Maftaf is one of the important inventions that facilitated life in the Middle Ages and paved the way for modern air conditioning. A number of people, such as Ibn Battuta, Judge Al-Fadil, and poet Muhyad Al-Dailami, sang a series of books in this field. Burhanuddin Qirati, a poet from the Mamluk era, pointed out to Al-Badhang, saying:
O goodness, the breath of the Badhenge is still in the air of our souls
A mugger attracts the wind from its horizons and it has a wind magnet
He said in the Badhang Shahabuddin bin Abi Hijla :
And the magic you see As a branch, he is in a trance
Shake at gifts For he is resting
The windcatcher can function in three ways: directing airflow downward using direct wind entry, directing airflow upwards using a wind-assisted temperature gradient, or directing airflow upwards using a solar-assisted temperature gradient.
Downward airflow due to direct wind entry
One of the most common uses of the windcatcher is to cool the inside of the dwelling; it is often used in combination with courtyards and domes as an overall ventilation and heat-management strategy. It is essentially a tall, capped tower with one face open at the top. This open side faces the prevailing wind, thus “catching” it, and brings it down the tower into the heart of the building to maintain air flow, thus cooling the building interior. It does not necessarily cool the air itself, but rather relies on the rate of airflow to provide a cooling effect. Windcatchers have been employed in this manner for thousands of years.
Upward airflow due to temperature gradient
Wind-assisted temperature gradient
Windcatchers are also used 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 (the tower’s orientation can be adjusted by directional ports at the top). By keeping only this tower open, air is drawn upwards using the Coandă effect.
The pressure differential on one side of the building causes air to be drawn down into the passage on the other side. The hot air is brought down into the qanat tunnel and is cooled by coming into contact with the cool earth[Note 1] and cold water running through the qanat. The cooled air is drawn up through the windcatcher, again by the Coandă effect. On the whole, the cool air flows through the building, decreasing the structure’s overall temperature. The effect is magnified by the water vapour from the qanat.[clarification needed]
Solar-produced temperature gradient
In a windless environment or waterless house, a windcatcher functions as a solar chimney. It creates a pressure gradient which allows hot air, which is less dense, to travel upwards and escape out the top. This is also compounded significantly by the diurnal cycle, trapping cool air below. The temperature in such an environment cannot drop below the nightly low temperature.
When coupled with thick adobe that exhibits good resistance against heat transmission, the windcatcher is able to chill lower-level spaces in mosques and houses (e.g. shabestans) in the middle of the day to frigid temperatures.
Directing airflow upwards using wind-assisted or solar-produced temperature gradients has gained some ground in Western architecture, and there are several commercial products using the name windcatcher.
The windcatcher approach has recently been utilized in Western architecture, such as in the visitor center at Zion National Park, Utah, where it functions without the addition of mechanical devices in order to regulate temperature.
Using aluminum for the windcatcher provides a more efficient capturing system, allowing for wind capture from multiple directions. The Kensington Oval cricket ground in Barbados and the Saint-Étienne Métropole’s Zénith both use this method.
Source From Wikipedia