Cooling Systems In Traditional Iranian Architecture
By: Pedram Izadpanah and Hussein Zareie
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 is similar 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.
As 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 streets must
have lofty walls. In addition to sun radiation 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
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. Meanwhile the compacted nature of the
buildings prevent the very high temperature of sun radiation to penetrate into
1.4 RESIDENTIAL QUARTERS BUILT IN THE DIRECTION OF SUN RADIATION AND
FACING THE BLOWING WIND
residential buildings are exactly according to the climatic design. In other
words the residential quarters are such that the winter sun deposits its maximum
heat over 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
2. BUILDING MATERIAL
Every building material in desert town is composed of mud and its
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 July 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 the conditions
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 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
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 sit and 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 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:
Exclusively operated air traps.
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 and due 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 has accumulated 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 velocity and 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 and in summer the dome-like roof of the
water reservoir and the upper layer of the water grows warm. Therefore the upper
layer of water evaporates and exits from the reservoir with the air flowing in
the air trap. Naturally in order to prevent dust and insects from penetrating
the reservoirs the reservoirs are not equipped with ventilators. Since the water
is stagnant in the reservoir, it is not suitable for drinking purpose. Despite
the fact that the main and popular material in desert regions is unbaked brick,
due to nearness of the water reservoir to the flowing water (qanats) their walls
are coated by bricks to resist the destructive effect of water and this brick is
known as water reservoir brick. At various occasions too beside brick and mortar
the architect employs stones too for the water reservoir the majority of which
are lime combinations. For example lime mortar which is composed of mud and
lime, is applied at the back of the reservoir wall and another mortar made of
dust, sand and lime is applied to the facing bricks. The covering of the surface
of the water reservoir was the most difficult part of the operation because to
cover openings of 15 to 16 m width needed a lot of experience, but this was done
by resorting to bends and the elliptical arches which prevent the expelling
force. Meanwhile by digging a well the polluted water was extracted from the
reservoir and led into a dry qanat.
3.3 ICE BUILDERS
regions the temperature at winter nights is just a few degrees above zero point.
By using traditional ice-builders the ice was produced at winters and stored for
consumption at winter. The system mostly depended on the transfer of temperature
in the form of radiation from the water surface to the clean and chilly sky at
cold winter nights.
The ice builder was a big pit 10 to 15 m deep in which one or several shallow
rectangular water lagoons were built. These lagoons had a width of 10 to 20 from
north to the south and a length of several hundred meters from east towards
west. A tall mud wall south of the lagoon and other shorter mud (unbaked brick)
walls were set at eastern and western sides of the lagoon to prevent the sun
from radiating on the lagoon at sunrise and sunset when the water was converted
into ice. Under such conditions with the loss of temperature from radiation,
necessary conditions were developed for freezing was developed. The thickness of
the frozen water differed according to the climate. On the following day the ice
was broken and transferred to the store. The heat flowing from earth into the
ice inside the lagoons helped the ice to break and be transferred to the store.
Nowadays the water in reservoirs or the ice produced through traditional systems
can be used for various purposes other than drinking.
In conclusion we must say that all of us Iranians are bound to protect our
historical and cultural relics and monuments which is the fruit of centuries of
ancestors' labor, otherwise one cannot be sure if such buildings can survive in
the coming years. These are buildings which must live for centuries in order to
exhibit the cultural values of this ancient land to the futurity.
A 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