_wind catchers_, the cooling systems in traditional iranian architecture _ c

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IRANIAN ARCHITECTURE

"Wind Catchers"

The Cooling Systems In Traditional Iranian

Architecture

By: Pedram Izadpanah and Hussein Zareie

Abst ract: The buildings in the

Iranian desert regions are

constructed according to the

specific climatic conditions and

differ with those built in other

climates. The desert buildings are

equipped with air traps, arched

roofed, water reservoirs with

arched domes and ice stores for

the preservation of ice. The

operation of modern coolers issimilar to the old Iranian air traps

which were built at the entrance

of the house over underground

water reservoirs or ponds built inside the house.

Lofty walls, narrow and dry streets, highly elevated air traps, big water

reservoirs and arched roofed chambers, are the outstanding features of

desert towns in Iran. The ever shining scorching sun of the desert has

rendered life very difficult for its hardy and warm-blooded inhabitants and

has compelled them to resort to facilities that can moderate the

unbearable heat. In the following article subjects relating to the building

materials of desert towns and the method of operation of the traditional

cooling systems in the cities with warm and arid climates are described.

1. STRUCTUREAs a whole all warm and dry towns enjoy the following general

specifications:

A dense web and closely interconnected buildings.

Fully enclosed city environment.

Narrow and irregular streets.

Residential quarters towards the direction of sunrise and

winds.

1.1 VERY COMPACTED WEB AND INTERCONNECTED BUILDINGS

The reason for such a

compressed building to

prevent the radius of the

sun ray to penetrate the

streets and since the air

moisture is meager, the

slight current in the

streets is enough to cool

the air. Therefore, these

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streets must have lofty

walls. In addition to sunradiation another reason

for the very high walls is

the interior configuration

of the buildings in which the surface floors a little below the street level

and the first floor is sitting with an elevation of 3 or 4 meters over the

ground floor and serves as a hall living quarter, which not only prevents

exposure to sun but causes the height of walls at the two sides of the

streets to rise to even 6 meters.

1.2 CITY ENVIRONMENT IS FULLY ENCLOSED

As a whole the city structure resembles a battlement fully enclosed from

all directions which prevents the invasion of enemies from any side. In

fact it is for the defense purpose and prevents high velocity winds and

sand storms to penetrate into the town. For that reason the inside of the

city is wholly different from outside facing and the inside air is more static

than the outside air.

1.3 NARROW AND IRREGULAR STREETS

The main streets in the town are facing the direction of the wind. Of

course the streets are more narrow than streets built for other purposes

(in other regions). Surely if the streets were not narrow more wind would

have flown into the streets and the moving sands of the desert and

ferocious winds would have penetrated into the city districts. Meanwhilethe compacted nature of the buildings prevent the very high temperature

of sun radiation to penetrate into the town.

1.4 RESIDENTIAL QUARTERS BUILT IN THE DIRECTION OF SUN

RADIATION AND FACING THE BLOWING WIND

The residential buildings are

exactly according to the

climatic design. In other words

the residential quarters are

such that the winter sun

deposits its maximum heatover the building and in

summer a pleasant wind blows

and ravishes the residents. Of course other factors are involved in such

compacted web including the construction of the towns over water

reservoirs. In other words the qanats feed many water reservoirs in their

route and houses and other buildings such as mosques, bazaars, public

baths and caravansaries were built in the past near the qanats.

2. BUILDING MATERIAL

Every building material in desert town is composed of mud and its


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derivatives. In fact nothing but mud and mortar can be used in such

regions because there are no other building material in the region. Here

one must refer to the question of self-sufficiency in desert regions

because all the earth excavated during housing construction is used as

building material in the form of mud. In such regions one cannot find any

other building material except unbaked bricks and mud which strongly

resist the incessant sun rays in the very warm months of J uly and

August. In the meantime in cold seasons the chambers are warmed with

very little heat and even the unbaked brick walls turn into massive and

intact blocks after drying and are fully resistant and hardy.

Due to very hot temperature the building materials first absorb the heat

and then rapidly repel it. In other words this heat and energy is preserved

in the walls about 8 hours and the other parts of the covering and

gradually is transferred to inner compartments. Such a quality provides

leads to two alternatives in cold and warm seasons:

- In cold seasons the absorbed temperature serves as an isolation barrier

which protects the inside air from being affected by the chilly winter

desert climate specially at nights because during daytime the temperature

is absorbed by the walls and the building and although the air is cold

outside, the inside of the house remains warm.

- During hot seasons the absorbed temperature causes problems and theconditions inside the building prevent comfort for residents. As a result

during nights and during sleep the people prefer to sleep on the roofs so

that because of loss of temperature attracted by the roof they can feel

cooler. At daytime too, the concept of using the summer quarter with the

air traps which is a distinguished element for that purpose is observed,

because the summer quarter is backing the sun and is to some extent

immune from sun radiation. Meanwhile the air trap too operates as a

ventilator and air cooler at the summer quarter of the house and plays an

important role in cooling the apartment during day time.

3. COOLING SYSTEM

3.1 AIR TRAP

Due to lack of access to

modern heating and

cooling equipment in

ancient times the

architects were obliged to

rely on natural energies

to render the inside

condition of the buildings

pleasant. For example

use of arched towers

became popular 3000

years before the birth of

Christ.

Since in arid and dry climates the daytime in summer is very warm and at

nights cold, traditional Iranian architects benefitted from this vast

difference of temperature to cool the house. One of these skills was using

very thick muddy and unbaked brick walls which has been described

above. Other systems for cooling consisted of an air trap, duct (ventilator)

and water reservoir.

Air trap was the specific feature of architecture in the majority of warm

regions. Only when the region is placed at the bottom of hills and the

town is relatively cool or is attacked by storm and warm winds air trap is

not used. Air traps were normally in a suitable location in the house


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according to the size of the building, the number of air traps that was

necessary to cool the summer apartment. In cities where suitable wind is

blowing from a specific direction the air trap is open at one direction and

closed from the other three directions.

In ancient times and in traditional buildings in arid and dry regions the air

trap functioned like the present modern air conditioning system. Air trap is

like a chimney whose end is in the underground and the top is set over a

specific height on the roof. At the upper outlet many small openers or

ducts are set. At the end of the air trap at the bottom of the door often a

pool is set whose water was provided by qanats (aqueducts). In the

vicinity of this pool or reservoir a place was designed for residents to sitand preserve their easily decaying foodstuff in summers. The height of

the surface of the cross sections, the number of openers and the location

of the air traps versus the building differed in different buildings.

The air trap operates with the change of air temperature and the

difference of weight of inside and outside the trap. The difference of

weight of the air impels a suction process which causes the air to flow

either to the bottom or to the top. Air circulation in various points in the

building is adjusted by opening or closing the various openers or ducts at

the bottom of the air trap.

The air trap operates according

to the condition of the wind

and sun radiation in the region.The inside and outside walls

absorb a lot of temperature

during daytime. As a result

they cause a balance of

temperature at night and

bestow the attracted warmth to

the cold night air. The

thickness of the air trap walls

and the dimension of the holes

inside it was designed in a manner to allow enough heat. The light warm

air inside the air trap ascends and is sucked by upper elevations. As a

result cool air flows from windows and doors into the house and continues

all the night.

If wind blows at night, the air will circulates on the opposite direction in

the air trap. In other words the cold air is sucked by the air trap into the

house. Of course in such a condition the cold air flowing from the air trap

duct which has been heated during the day time will warm the inlet air a

little. Nevertheless air circulation again refreshes the inside temperature.

During daytime the air trap acts contrary to a chimney. In other words the

upper parts of the air trap has been cooled the night before and upon

contacting the walls of the air trap the warm air cools down and moves

towards the bottom and eventually circulates into the house and exits

from doors and windows. The flow of air at daytime accelerates the

ventilation process.

Meanwhile it must be added that against each opener facing the wind, an

opener or duct is set opposite the wind. Air trap acts in two ways. Some

air traps only change the air temperature and others cause conditions

which not only change the air temperature but the air moisture too. For

example the water reservoir set at the bottom of the air trap is the coolest

place in the building and is normally set in the underground. Not only

these pools emit cold around themselves they blow moisture and cold

against the inside walls and the inside of the air trap and render the air

cool and moist, because part of the air sucked by the trap cools after

passing the inside of the air trap and then enters the house. This change

of temperature in the air trap impels the moisture to move in the trap and


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prevents the moisture from remaining static at a single location. Of course

part of the wind directly blows into the water reservoir which cools the

reservoir and shakes the water and prevents the water from stagnation

and pollution. Thus when transferred to the halls and the other sections of

the summer quarter the dry desert winds practically pass from cold and

moist canals.

From another angle air traps can be divided into two general groups:

1. Exclusively operated air traps.

2. Symbolic air traps.

Exclusively operated air traps exist in the majority of houses. The

symbolic air trap is available at few houses and beside its normal they

represent the personality of the house owner and at times the air trap is

larger than a room with three doors. In certain desert regions where the

elevation of wind differs, we can see air traps which have two outlets at

two different elevations.

Sometimes besides using air traps to cool the house the people benefit

from the flow of underground waters. When the air flows from the air trap

into the underground, due to narrowness of the canal the wind velocity is

increased and its pressure is decreased. As a result the air is sucked

from the mouth of underground outlet towards the upper elevation anddue to coolness of underground waters the ascending air is also cooled

and causes a pleasant ventilation process in the building.

One of the problems with the air traps is that insects, birds and dust

penetrate into the house. Of course by covering the trap by net one can

prevent the penetration of birds. Another method of preventing the dust is

to increase the elevation of the air trap which will involve a lot of cost.

Another method to prevent the dust from entering the building is to make

the bottom cross session larger compared to the upper cross section

which can reduce the speed of air circulation and let dust to settle at

certain spots set for that purpose in the canal. At times architects build

arched roof for the air traps. Because of its elevated blocks, the arched

roof always generates wind. This reduces the heat which the roof hasaccumulated due to severe sun radiation. As mentioned earlier at nights

too the temperature, repelled by the roof, is quickly emitted. In the

construction of public buildings where traffic is tense, two layers of arches

are set and the space between the two layers act like an isolation tunnel

help the inner layer to remain colder than the outer layer. From

geometrical point of view the size of a semi-arched building is nearly

three times its base. Therefore the velocity of warm sun radiation over the

round roof is reduced and the lower part of the circular dome attracts less

temperature and incites a breeze. Thus the arched roofs are less affected

by sun radiation. The circular dome is also suitable for air radiation and

cooling at night because the heat expelled by the building at nights is

better emitted by the arched dome. Occasionally a duct is placed at the

top of the circular or cylindrical dome which because of higher velocityand lower pressure helps the warm air to be emitted from the duct on top

of the cylinder dome or circular dome. This duct is covered by a

protecting cover too.

3.2 WATER RESERVOIR

The water reservoir is dug to a depth of 10 to 20 m on the ground and is

covered by a dome-like roof and equipped with several ducts. The water

is collected from qanats and is kept cool in the reservoir at the warm

summer days. In the design of water reservoirs the architect benefits from

change of seasonal temperature in desert regions and the isolated nature

of the ground. During the winter the water is accumulated in the reservoir


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4.4 COMMENDATIONA great part of this article was extracted from a project covering the

adjustment of environmental conditions by five students from the College

of Architecture of Tehran Azad University which was the fruit of their

several days trip to the Yazd Province. Therefore, the writers of this

article would like to thank Farbod Eskandar Khalaj, Samanzadeh

Koochak, Tahmoores Zandi, Masood Sherafati and Ali Salehi Rad who

sincerely cooperated in the compilation of the article.

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