Environmental and natural phenomena play a very significant role in laying the region’s interrelated cultural, economic and social infrastructures.
The buildings in the Iranian desert regions are constructed according to the specific climatic conditions and differ with those built in other climates. 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.
In the past, without modern facilities, it was only the intelligent architecture of the buildings that enabled people to tolerate the hot summer. The ventilation structures called Badgirs were the most important means by which the interior was cooled. The wind-catcher operates according to the condition of the wind and sun radiation in the region. In ancient times and in traditional buildings in arid and dry regions the air trap functioned like the present modern air conditioning system.
Wind-catcher is like a chimney whose end is in the underground and the top is set over a specific height on the roof and were built at the entrance of the house over underground water reservoirs or ponds built inside the house.
The dry and warm wind will pass over a pond with a fountain gets cool and wet through evaporation. The Badgir’s material again plays another role. Due to high fluctuation of temperature differences between day and night in this climate and night time coldness, Badgir which is made with mud-brick, gets cool by radiation and convection.
The system works, when there is no wind, but when wind is blowing this system does not have problems. Because during the day, if there is wind, then cool air flows faster and at night, with wind, it may absorb the heat of the walls, because the night wind is cool enough.
The wind-catcher has been used in Iran since early times, it is one to the special masterpieces of Iran’s architecture and it is also the signs of predecessors’ intelligence in agreement with the climate, you can consider it the most specific examples of clean energy. The most number of wind-catchers are in Iran; these wind-catchers are made in two areas: the hot and humid area in south (such as Lenghe Port) and the hot and dry area of central plateau (such as Yazd) wind-catcher is a device with real/noble form and constant structure in Iran architecture, it leads the suitable wind through the inner part of the building and it is the most effective function in making comfort. There are actually two kinds of main functions about wind-catchers:
1. The function according to the principle of traction of opening facing the wind and the suction of openings back against the wind.
“The way a wind-catcher works is mainly based on taking the fresh air into the building and sending the hot and polluted air out or” the suction functions” perhaps it is not so necessary to explain that when the wind hits against the walls of internal blades of the wind-catcher it necessarily falls down, but it is necessary to refer to this point that the other holes of the indcatcher turning back to the wind direction, gives the hot and polluted air into the wind and so works like a ventilation and a sucked machine (Pyrnia, 1981).
The function of this kind of a wind-catcher is actually performed according to this fact that when the wind hits an obstacle, and since the density of the air is thick on the side of the wind direction, so in this direction there is a positive pressure, but a negative pressure on the other side. Therefore, when the ventilation is open on the sided of the wind there will be a positive pressure to a negative pressure. In the wind-chatchers, according to this principal, the opening facing the wind takes the e air into the porch and the air in the porch with its negative pressure on the opening back of the wind is drawn out (Fig. 1). Sometimes according to the superficial evaporation the wind-catcher supplies the necessary moisture by conveying the wind over the weather and the cold-storage.
2. The function according to temperature difference. But it seems that there is a little attention of technicians about the function of a wind-catcher regarding the temperature difference. In fact when there is not a windy blast sensibly, the wind-catcher acts according to this action.
During the day, since the sun hits on the southern face of the wind catcher, the air heats in the southern face of the wind catcher, and goes up. This air taken above through the inner air of the porch is compensated and in fact it makes a kind of proportional vacuum inside the porch, and takes the cool air of the inner court into itself, so the existing air in the northern opening is pulled down too (Fig. 2).
During the night it becomes cold outside, and the cold air moves down. This air is saved by the heat and becomes warm on parapets and then goes up. This circle continues till the temperature of the walls and outside temperature become equal. But before it usually arrives at this situation the night ends and once again the wind-catcher acts its function as mentioned above. In general, in most time, wind-catcher does as we explained it, in order to the traction, suction, and the effect of temperature difference.
We suggest you to visit Bagh-e Dolat Abad Yazd as one of the best sample of Badgir (wind-catcher).
KINDS OF WIND-CATCHERS
Wind-catchers are usually small towers in the form of quadrilateral and regular polygons, triangular forms are not seen at all among them.
Wind-catchers can be divided into one-sided, two-sided, three-sided, four sided, hexahedral, and octahedral both of the shaping and regional point of view.
1. One Sided Wind-Catcher
One sided wind-catcher is related to the areas in which there is “black wind” and it is near the Kavir. Cities like Meybod, Ardakan, Mahan and Bam.
2. Two-sided wind-catcher
The water-reservoir in Yazd has a two sided wind-catcher.
3. Three-sided wind-catcher
This kind of wind-catcher is not so usual, but types of wind-catchers like the wind-catcher in Tabas are being made with this form.
4. Four-sided wind-catcher
Four-sided wind-catchers are the most current wind-catchers in Yazd. This kind of wind-catchers is made of both squaral and rectangular plans. The rectangular forms are usually made specially the big face is towards the appropriate wind.
The hexahedral and octahedral wind-catcher can be found in the water-reservoirs of Yazd Shrine, and the octahedral one can be found in the water- reservoirs of Khanom-Jan in Ezz-Abad Village.
These kinds of wind-catchers are very limited and the best known of them is the windcatcher of Dowlat-Abad Garden in Yazd with 33 meters and the wind-catchers of the water-reservoirs of six wind-catchers. These wind-catchers are higher than any other wind-chatchers, and they have been designed in the form of octagon, because in this case the form of the wind-catcher has more flexibility against the wind, and also the wind. Lateral forces decreases against the wind-catcher frame. The six wind-catchers of water-reservoir in this region from the viewpoint of climatic conditions and wind blast direction are in the octahedral forms.
Of course, it is necessary to say that wind-chatchers are different structures from each other according to their functional similarities. Regional differences of hot and dry climates and some social and economic factors, and various functions of buildings are affective in this regard. In regions like Yazd, the wind-catchers according to their functions are divided into two general groups: merely functioning and symbol functioning.
The first one is most seen in ordinary houses in the form of one-sided wind-catcher. The second one not only has a special function but also shows the distinction of the land lord. Here, the wind-catcher dimensions have been more from a three-door room.
Each elements of a wind-catcher form is effective in its final formation. A wind-catcher in order from down to upward is formed of following parts: 1) chimney, 2) stalk, 3) catgut and chain, 4) shelf.
1 . Chimney
The chimney part of the wind-catcher is usually an incomplete pyramid form. The different proportions of upper part of the wind-catcher are arranged with this part. In some samples, its height is as high as a person’s height and in some other it is some meters high.
That part of the wind-catcher which is located between shelf and the room is called the “stalk”; the higher is the wind-catcher the higher is its stalk too. The higher of the stalk in Yazd indcatchers according to the climatic reasons and the height of the wind-catcher is for taking suitable wind which blows in heights, the beauty of this part is mostly dependent on the brick working decoration.
3. Catgut and chain
The catgut and chain is located between the stalk and the shelf. This element would be made and the shelf, this element would be made in different shapes.
The head of the wind-catcher is the shelf which includes the blades, the channel of air passing. The common types of geometric figure of the shelf include: a lengthened, vertical rectangle, horizontal and a square. Shelves are usually front open or front closed. And this feature would be changed according to the wind blast, on the other hand two shelves would be usually considered for each ways of air channel towards the room.
Iran’s traditional architecture is caused by the climate and conditions in which it has been grown and developed, so climate as the most effective factor has been affecting in architectural element structure, specially the wind-catcher, which has climatic function. The wind-catcher is the most intelligent arrangement that proceeds of exploitation from the wind natural energy, and at last it makes possible the coldness comfort ability in hot regions.