The 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
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. Meanwhile the 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 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 qanats.
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
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
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
In desert 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 article.