Iranian report on ancient natural cooling with windtower ventilation

International Conference “Passive and Low Energy Cooling 71
for the Built Environment”, May 2005, Santorini, Greece
Wind tower a natural cooling system in Iranian traditional architecture
P.S. Ghaemmaghami
Iran University of Science and Technology
M. Mahmoudi
Qazwin Islamic Azad University
ABSTRACT
This paper is a synopsis of the results of a research
on form of wind towers. Wind tower is
an architectural element in traditional architecture
of Iran. It can be seen in cities with hot-dry
and hot-humid climates. This analysis demonstrates
wind towers' characteristics with emphasis
on their morphology.
1. INTRODUCTION
Wind tower is a key element in traditional architecture
of Iran. It is seen in settlements in hot,
hot-dry and hot-humid climates. They look like
big chimneys in the sky line of ancient cities of
Iran. They are vertical shafts with vents on top
to lead desired wind to the interior spaces and
provide thermal comfort. This architectural
element shows the compatibility of architectural
design with natural environment. It conserves
energy and functions on the basis of sustainability
principles.
The result of this research shows that traditional
architecture can give ideas to enrich modern
architecture. In traditional architecture of
Iran, climate, local materials and renewable energy
resources have been used. Wind tower
shows the harmony of human built environment
with nature. Traditional building techniques
were normally well adapted to the climate.
However, the modern way of life and imported
western technologies have often replaced the
established traditions in the design of the buildings.
There examples which reflect the way
people organize their environment in various
forms. This paper shows different forms of wind
towers adopted by people in different situations.
Wind towers are described in terms of their
function, structure, details, components, ornaments
and form.
2. HISTORY AND DEFINITION OF WIND
TOWER
Wind is one of the important elements for
studying the climate. One of its important users
is the provision of comfort in hot region. This is
because the wind current creates a difference in
pressure on the exterior walls that has an effect
on the natural ventilation and interior air temperature
of a building. For architects, the wind
is an important factor in the design of a building.
They consider the wind's effect on the
thermal comfort through convection or ventilation
and the penetration of air in interior spaces.
Wind has been given much attention in urban
design, and in particular in cities with hot
weather such as Yazd, it is to be seen clearly
from the images of the city. The effect of the
wind on building forms is recognized through
the use of formal features such as wind towerwhich
provides for the best use of the wind for
the comfort of the occupant. Thus, along the
northern shores of the Persian Gulf and the sea
of Oman, architects have known how to make
effective use of the sea breeze. They have
achieved this by designing the wind towerwith
an opening towards the breeze for the maximum
use of natural ventilation.
Wind towers as their name implies, are
ventilation tools used for obtaining natural
cooling. They have been used for centuries in
countries with hot-arid climates, particularly in
Iran. Wind towers in the central cities of Iran are
known as "badgir" which literary means wind
72 International Conference “Passive and Low Energy Cooling
for the Built Environment”, May 2005, Santorini, Greece
catcher. Wind towers not only appear on top of
ordinary houses but also can be seen on top of
water cisterns, mosques. The first historical evidence
of wind towers dates back to the fourth
millennium BC. An example of a simple wind
tower was found in Iran by a Japanese expedition
in a house from the site of Tappeh chackmaq
some eight kilometres north of Shahrood
and the southern slopes of Alborz Mountains in
north eastern Iran. Wind tower comprises a
tower with one end in summer living quarter of
the house and the other end rising from the roof.
Wind tower is divided into several vertical
air passages by internal partitions or shafts. The
shafts on top terminate in to opening on the
sides of the tower head. The flow in side the
wind tower is in two directions, up and down.
Namely, when the wind blows from one direction
the windward opening will be the inlets and
the leeward opening will be the outlet and vice
versa.
3. ORIENTATION AND FUNCTION OF
WIND TOWER
The orientation of wind tower generally means
the positions of the wind tower flank based on
the four main geographical directions. It is determined
in view of function, use of wind power
and the desired direction in which the wind
blows. There are one-directional wind towers in
Meibod, they are facing to the desired wind and
in some cases one directional wind towers act as
air suctioning and the air flow turned its back to
the wind to locate itself in a negative pressure
region to cause warm air in interior to blow out
of the house. The desired wind currents in Yazd
blow from the north-west. The long sides of
wind towers are, therefore, oriented towards the
north-west for maximum usage of the wind to
provide cooling for buildings. In coastal regions
like Bandar Lengeh, buildings have an east-west
orientation. Sea breeze that blows during both
days and nights but the most desirable wind
blows from the east to the west.
Wind towers are therefore, built with a fourdirectional
orientation in order to use all of the
desirable winds from north to south and from
east to west (Figs. 1 and 2). Orientations of
wind towers are different according to the blow
of main desired wind.
A Wind tower is a formal structural element
in Iranian architecture that is used to convey the
wind current to the interior spaces of buildings
in order to provide living comfort for occupants.
In Iranian architecture a wind tower is a combination
of inlet and outlet openings.
The tunnel provides cool air for the building
while serving as a conduit through which the
stuffiness within the building is conveyed
through its shaft. There were wind towers in
Bam which were destroyed by earthquakes; they
weren't directly connected to the living hall.
They were built away from the house. An additional
underground tunnel links the base of the
wind tower to the basement.
In most wind towers, especially the four
sided types, the tower is divided by partitions.
One of the shafts operates all the time to receive
the breeze and the other three shafts work as
outlet air passages. They convey the stuffiness
out of the living space through the “flue”
(chimney) effect. The chimney effect is based
on the principle that the air density increases
with the increase in temperature. The difference
in temperature between the interior and exterior
parts of a building and between different regions
creates different pressures and result in air currents.
The average relative humidity in moisture in
hot and dry regions is low and it is necessary
more humidity there for wind towers are used to
provide living comfort through the use of the air
current and evaporation. Through the wind
tower, the air current first passes over a stone
pond and fountain after entering a building,
thereby bringing humidity to the other spaces in
the building (Fig. 4).
In some places, mats or thorns are placed
within the wind tower, and users pour water on
them in order to increase the humidity and the
coolness of the air flow. The hot weather in
Yazd has the potential effect of causing water to
evaporate easily to develop cooling in the living
spaces and relative humidity in the air, thereby
reducing the heat and dryness.
It is clear that there is usually high humidity
in hot and humid regions because of their being
in vicinity of the sea. In these regions, wind
towers reduce the temperature of the weather
only through the movement of the air they facilitate,
not through increased humidity (Fig. 3).
The level of humidity in this region is already
high and an increase in the humidity would
make living conditions troublesome.
A wind tower in a hot and dry region brings
about comfort by evaporation and air motion but
a wind tower in a hot humid region only moves
the air and conveys the wind into spaces. Different
function and shapes were designed for
different climates (Figs. 5 & 6).
4. CATEGORIES BASED ON FUNCTIONS
The tower head may have vents on one, two or
four sides that face the predominant wind direction
to accommodate wind in suitable directions.
Wind towers are often described by the number
of directions in which they face; such as one
directional (yek-tarafe), two directional (dotarafe),
four directional (char-tarafe), and eight
directional (hash-tarafe).
4.1 The one directional towers (yek- tarafeh)
These towers generally face north-west or north.
They have a sloping roof and one or two vents
only. Otherwise they are commonly described
by the direction in which they face such as
“shomali” or north facing. The survey of wind
towers Roaf (1988) reveals that 3% of the wind
towers were unidirectional in Yazd.
4.2 The two directional towers (do- tarafe)
The tower, in a simple example, is divided in to
two shafts by a vertical brick partition. It has
only two vents. They are often called by direction,
such as north-south towers. Roaf’s survey
indicates that 17% of the towers are in this kind
and all are made on the ordinary houses.
4.3 The four directional towers (chahar- tarafe)
Studies indicate that this is the most popular
wind tower. They have four main vertical shafts
divided by partitions. More than half of the
wind towers in hot and dry region have been of
this kind, as reported. They are so common locally
called Yazdi. All of wind tower in hot humid
region are four sided type.
4.4 The eight directional towers (hasht- tarafe)
According to the Roaf survey (1988) only 2% of
the wind towers of Yazd are in this kind. They
are most common on water cistern. The greatest
Figure 3: Function of tower in hot and humid.
Figure 4: Function of tower in Yazd.
Figure 5: Wind tower in
Abarghoo.
Figure 6: A wind tower in
Yazd.
74 International Conference “Passive and Low Energy Cooling
for the Built Environment”, May 2005, Santorini, Greece
wind tower on top of bagh-e dolatabad has an
octagonal plan.
5. CATEGORIES BASED ON FORMS OF
PLANS
Forms of the plan were reported square, rectangular
and octagonal. The square form is the type
used in the four directional wind towers in
Yazd. (Fig. 9) The rectangular forms consist of
one, two, four directional wind towers. Eight
directional wind towers are those with an octagonal
plan. There are enormous range of size
and dimension from 0.40 x 0.80 m to 5 x 5 m. in
plan and the ratio between widths to length is
1:2 of which, is reported.
Partitions are component in wind towers to
divide it in to several shafts. They are built of
mud brick. These partitions form a plane grid of
vents ending to a heavy masonry roof on top of
the tower. Partitions can be classified in to
group: main partition and secondary partitions.
Main partitions continue to the center of the
tower, forming a separate shaft behind the vents.
These partitions often start between 1.5-2.5 m
above the ground floor level. The patterns of the
partitions vary from tower to tower, but the
most commons are in forms of I, H and diagonal.
Secondary partitions remain as wide as the
external wall, about 20-25 cm. A shaft can be
subdivided by a number additional partitions
performing either structural or thermal role.
These can separate the tower, respectively in
two or four shafts. Wind towers could be categorized
according to forms of the plan and patterns
of the partitions (Table 1).
Partitions divide tower to small shafts to increase
air motion according to “Bernoly effect”.
It express that air rate will be increased when air
pass from narrow section. Such an arrangement
provides more surfaces in contact with the flowing
air, so that the air can interact thermally
with the heat stored in the mass of these partitions.
They act climatically in spite of aesthetic
aspects. They work as fins of cooler window or
fins of radiator because mud brick partitions
give back stored heat during night and they are
prepare to absorb heat. Warm wind contact with
mud brick partitions there for its heat transfer to
partitions after that wind with less heat enter to
space.
6. MATERIAL, COLOUR, TEXTURE AND
HEIGHT
The construction materials used for wind towers
depend on climate. The choice of materials is
made to ensure that the wind tower operates effectively
as a passive cooling system. Wind
towers in hot dry are built either of mud brick or
more commonly of baked brick covered with
mud plaster. Mud brick (adobe) passes heat at
long time, because soil has got uncompressed
volume and mud makes from water and soil.
After evaporating, there is made empty pit. It
causes that heat and cool can not arrive in molecules
of soil and mud brick or adobe. Mud plaster
(kah_gel) is mixture of wet earth with fine or
chopped coarse straw. These construction materials
give the wind tower a coarse texture. The
mud plaster covering the facade of a wind tower
has a light colour and there for reflects rays
well.
Wind towers in hot humid are covered with
(gach) plaster and (sarooj) this type of covering
Figure 7: Typical plan of one directional wind towers.
Figure 8: Typical plan of two directional wind towers.
Figure 9: Typical plan of four directional wind towers.
Table 1: Categories of wind towers based on plan.
International Conference “Passive and Low Energy Cooling 75
for the Built Environment”, May 2005, Santorini, Greece
resists moisture. Vapor in the air in this region
sits on the surface with temperature less that
dew point in the environment. If there are high
penetration on walls and surfaces of building,
these drops penetrate in wall for the osmosis
pressure or absorption of materials. It causes
demolition of surfaces. It pushes salts of materials
out of surfaces. The texture of wind towers
is polished with a white colour, which also ensures
that the wind towers do not absorb rays. It
provides more operation in climatic function.
Wind towers trap the desired wind currents
and transport these to interior spaces. To fulfil
this purpose, a wind tower is designed to raise
above roof the building. To enable its serve its
function effectively through the appropriate
utilization of wind currents, the ratio of its
length and its width to height is important.
Height of Wind tower in hot dry and hot humid
is different. Height of wind towers in hot dry
regions is more than hot humid regions. When
the air current is closer to the land surface, it is
warm because of the effect of the sunshine on
the ground. Thus in a hot and dry region, because
of the low temperature and a higher wind
velocity at greater heights, wind towers are built
higher to enable them to trap such currents. The
residential regions in hot humid are built near to
the beach. In the hot and humid regions, the
temperature on the land surface is low and desired
wind and breeze or current is at a lower
level thus wind towers in such areas do not rise
very high at their highest, they rise only one
level above the roof. Since building levels in
central plateau of Iran are also below the ground
level, wind towers are designed to service two
interior spaces in different levels: the basement
space and the reception hall on the ground floor
used in summer. Water surface in Bandar
Lengeh is higher because of the proximity of the
sea. Thus there are no basements in the buildings
in this region. (Fig. 11) Here the transportation
of wind currents at their minimum temperature
is an important design objective for wind
towers.
Survey shows that over 60% of all wind towers
are less than 3 meters high above the roof
parapet level and only 15% rise above 5 meters
high. The higher towers carry the potential for
structural failure, particularly in the head of the
towers, which are weakened by a number of
vents.
Shafts of wind tower in hot dry regions are
longer than shafts in hot and humid regions.
Firstly, because wind towers in hot dry areas
serve to basement floor, and this service is not
needed in hot humid regions. Secondly, the
height of wind from the earth has also a role in
determining the height of wind towers. If desired
wind current is in low levels, wind towers
must receive it in low height. Longer shaft also
increases wind speed during the shaft.
7. STRUCTURE AND ORNAMENT
Body of wind towers soar to receive winds in
the height. Open vents reduce resistance in front
of horizontal forces there for it is clear importance
of structural elements. Mud brick and
timbers are used in the construction of wind
towers (Fig. 13). Since a wind tower rises above
a building, it needs elements to support it. The
wind towers are built of mud brick or more
commonly of baked brick and timbers. The
main structure of a typical wind tower consists
of a tower, several vents and partitions (Fig. 14).
Timber beams are used to support partitions
at various levels and to fasten the structure together
in order to increase the shear resistance
of the tower. The beams are left to project out of
Figure 10: Typical plan of eight directional wind towers.
Figure 11: Section of a house in Bandar Length.
Figure 12: Section of a house in Yazd.
76 International Conference “Passive and Low Energy Cooling
for the Built Environment”, May 2005, Santorini, Greece
the structure to provide a ladder and scaffolding
for building the tower and for use during subsequent
maintenance. Main and subordinate partitions
are accounted as an element to support
wind towers more.
There are two kinds of ornamental features in
wind towers, which may be considered notable
among Iranian ornamental architecture. The first
comprises ornamental elements that are added
to the body of the wind tower for aesthetic reasons.
The second consists of ornamental elements
that serve as functional elements. Features
of the wind towers of Yazd that may be
referred to as ornamental elements include the
gach feature placed at the end of the fins in different
shapes in a variety of arches. Each architect
used a different type of arch according to
his personal preference; it can thus be said that
this type of ornamentation was his signature
(Fig. 15). Such features are just for decoration
and serve no other function. For example, brick
rows are sometimes placed on the top and bottom
part of the head of a wind tower, thereby
probably creating a shadow effect on the body
of the wind tower. These differences in ornamental
elements are in now way connected with
the climatic conditions and functional problems
existing in these areas, but are rather a reflection
of cultural features and effects.
8. CONCLUSION
In respect to the growing need for environmentally
responsive architecture from one side, and
from another side, the shortcoming in provision
of electricity in many small cities and villages in
Iran, the use of traditional wind towers are recommended.
In large cities, in low and medium
rise buildings, with new mechanism and some
skills, the natural cooling systems can be renewed.
REFERENCES
Battle McCarthy Consulting Engineers, 2002. Wind towers,
Ahmadinezhad (translator), page 29.
Ghiabaklou, Z., 1996. Passive cooling system, Ph.D. thesis,
New South Wales University, 1996, p. 1, quoted
from Rapaport, 1969.
Ghobadian, V., 1995. Climatic analysis of the traditional
Iranian buildings, Tehran, Tehran University press,
p13.
Kasmaee, M., 1999. Climate and architecture, page 344,
400.
Mahyari, A., 1997. Wind catchers, Ph.D thesis, Sydney
University, page 58-62.
Zomorshidy, H., 1999. Iranian architecture, Tehran Amir
Kabir, page15.
Figure 13: Wind tower in Yazd.
Figure 14: Structures of wind towers.
Figure 15: Examples of vent head details (Roaf, 1988).