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.
A wind tower is an architectural device used for many centuries to create
natural ventilation in buildings.
The function of a wind tower tower is to catch cooler breeze that prevail
at a higher level above the ground and to direct it into the interior of
the buildings. It is not known who first invented the wind tower, although
some claim it originated in Iran and it can be seen in. wind towers come
in various designs, such as the uni-directional, bi-directional, and
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 combi- nation 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 cur-
rents. 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
First, a wind tower is capped and has several directional ports at
the top (traditionally four). By closing all but the one facing away
from the incoming wind, air is drawn upwards using the Coanda effect,
similar to how opening one facing the wind would push air down the
shaft. This generates significant cooling ventilation within the
structure below, but is not enough to bring the temperature below
ambient alone - it would simply draw hot air in through any cracks or
windows in the structure below.
Therefore, the key to generating frigid temperatures seems to be
that there are very few cracks at the base of the thick structure
below, but there is a significant air gap above the qanat (a water
management system used to provide a reliable supply of water to human
settlements or for irrigation in hot, arid and semi-arid climates). A
qanat has quite a lot of water inside, because there are frequent
well-like reservoirs along its path. Completely shaded from the sun, a
qanat also aggregates the cold, sinking air of the night, which is
then trapped within, unable to rise up to the less dense surface air.
A wind tower, however, can create a pressure gradient which sucks at
least a small amount of air upwards through a house. This cool, dry
night air, being pulled over a long passage of water, evaporates some
of it and is cooled down further.
Finally, in a windless environment or waterless house, a wind tower
functions as a Solar or thermal chimney that uses convection of air
heated by passive solar energy. It creates a pressure gradient which
allows less dense hot air to travel upwards and escape out the top.
This is also compounded significantly by the day-night cycle mentioned
above, trapping cool air below. The temperature in such an environment
can't drop below the nightly low temperature. These last two functions
have gained some ground in Western architecture, and there are several
commercial products using the name wind tower.
When coupled with thick mud brick, the wind tower is able to chill
lower-level spaces in mosques and houses in the middle of the day to
So effective has been the wind tower in Persian architecture that it has
also been routinely used as a refrigerating device.
Many traditional water reservoirs, or ab anbars, are built with wind
towers that are capable of storing water at near freezing temperatures for
months in summer. High humidity environments destroy the evaporative
cooling effect enjoyed in the dry conditions seen on the Iranian plateau;
hence the ubiquitous use of these devices in drier areas such as Yazd,
Kashan, Nain, and Bam.
Modern wind towers may incorporate the use of water near the top of
the tower to enhance their effectiveness as water has a much higher
heat capacity than air and this is much more efficient in removing heat
air and delivering cool.
Wind towers use gravity to move cool air without any fans, although
fans may be used to reduce the size of the towers. The most common wind
towers do this by having a wet pad medium in the top of the tower. Since
cool air is heavier than warm air, it will fall, creating its own airflow.
Wind while not required, greatly improves the airflow.
Basic modern wind tower design Not really very effective and the tall tower means high cost.
This tower requires a very long drop and the resulting cost of a tall
tower could be better spent on a more advanced design system.
The tower would have to be wider in diameter to support it's height.
This system operates only on the Buoyancy Principle described above
and does not require wind to operate.
If you live in an area with no wind, then this is the tower for you.
Generally wind towers without fans are from 6 to 9 metres tall and between
2 and 3 m2. Typically wind towers of this size will perform
better with the addition of a fan of 10 to 150 watts, and will cool
a small house. Airflow for these wind towers will range from 70 to 225 m3
Passive ventilation systems rely on the movement of air through buildings
to equalize pressure. The pressure difference can be caused by wind or the
buoyancy effect created by stratified warm air. In either case, the amount
of ventilation will depend critically on the size and placement of
openings in the building.
Buoyancy ventilation is more commonly referred to as temperature-induced
or stack ventilation. Buoyancy results from differences in air density.
The density of air depends on temperature and humidity. Cool air is
heavier than warm air at the same humidity. Thus, airflow is generated by
the dropping of heavier air, forcing lighter air to exhaust. Tower height,
or the distance from the air intake (top of tower) to the air outlet
(bottom of tower), will determine the velocity or pressure of the air. The
greater this distance the more air pressure created, similar to a water
column. The tower uses a column of cool moist air (compared to the hot dry
air outside) to create this pressure.
Wind causes a positive pressure on the windward side and a negative
pressure on the leeward side of buildings. To equalize pressure, fresh air
will enter any windward opening and be exhausted from any leeward opening.
Cooler pads sit at the top of a tower with a pump re-circulating water
over them. As hot air passes through the pads it is cooled by the
evaporation of the water. Cool moist air is heavier than hot dry air
and drops down the tower and into your house. In order for the cool air to
flow in, hot air must be exhausted.
Design Of Your Tower
Your tower should be a minimum of 2m X 2m. square and about 8m
in height, most are about about 9m tall. Your tower should be
insulated with at least an R-10 Factor, but R-19 or higher would be
Where prevailing breezes are not dependable enough to rely on wind-induced
ventilation and where keeping indoor temperature sufficiently lower than
outdoor temperature to induce buoyant flow is a problem, then a solar
chimney may be an effective solution. The chimney is isolated from the
occupied space and can be heated as much as possible by the sun or other
means. Hot air is simply exhausted out the top of the chimney creating a
suction at the bottom which is used to extract indoor air.
A large solar chimney can be used to exhaust the air from your home, but a
downwind swiveling exhaust scoop is a better alternative. The more
exhaust scoops you have the better. These enhancements will increase the
air flow; using upwind and downwind scoops that swivel to orient the wind
is the best choice.
Most common modern wind tower design As wind blows through the wet pads, the water evaporates and cools
Placing pads at the top of the tower usually requires
appropriately 6.5 to 7.5 m2 of pads.
With evaporative coolers you must leave an exit for the air to escape
from your house.
In normal water coolers a blower circulates the air, in this design
wind and buoyancy will do the job for you.
Standard cooler pads will work, but there are better, more efficient
pads available that have less wind resistance .
Of course these higher quality pads will cost more.
Water must flow down the pads and air must pass through them in order
to have the evaporation needed to cool the air.
Vents must have a larger opening than those used with a forced air
system because there is no pressurized fan blower in this
This tower is 2 x 2 x 9 m .
If using wind, your cooler pads will be at the top or inside of the tower,
depending on the design. Just below the cooler pads you should have a tank
containing 55 to 110 litres of water with a float valve assembly to keep
the tank full. Locate outside the tank a small 12 Volt pump. It is best to
use a non submergible pump.
Evaporating water is what creates the cooling and makes evaporative
coolers and wind towers work. Rain water is the perfect source for the
water used in wind towers because it does not have dissolved salts or
minerals. Well water can contain dissolved minerals. As the water
evaporates from the cooler pads, whatever minerals it contains are left
behind. This buildup can eventually clog the pads and block air flow
Advanced modern wind tower design To create a larger air flow down the cool tower, install one
large upwind swivel scoop above the pads in the tower.
Your air scoops should have a venturi system (tail) to keep the scoop
oriented into the wind.
Instead of one large exhaust vent for the hot air, install smaller
openings in the roof with down wind swivel scoops to remove the heat.
Your exhaust vents should also swivel with a venturi system to keep
the exhaust openings oriented away from the wind.
With this system the wind can blow from any direction and your cool
tower will continue to function.
This is a more efficient design than using a solar chimney.
The intake air scoop should be made out of light aluminum or designed
with an aluminum frame with canvas stretched over it.
The canvas scoop is recommended because it is lighter and generates
almost no noise.
In this design the pads are just below the scoop inside the tower with
ducting to direct the air flow into and through the pads .
This reduces the size and area of the cooler pads, thus reducing the
This design requires about 2m2 of 100mm. thick pads.
Cooler pads that are inside the tower and below the scoop are
protected from direct sun light and last longer due to lack of UV
damage caused by the sun.
The tower itself is 2m X 2m and 9m. in height.
The air scoop occupies the top 1.25m.
Two pads about 0.25m2 by 100mm thick are located just below
the air scoop with this design you can also add removable doors to
close off top of tower in case of a wind storm