Windcatcher

A Badgir (Persian بادگير, " wind catchers ") is a traditional Persian architectural element, which has been used for centuries for ventilation ( ventilation) used by buildings. It is not known exactly where a Badgir has come for the first time to use, but they are still very much used in different variations. A Badgir usually has at least two vertical channels. Other wind towers like the Malqaf (Arabic ), however, usually have only one channel.

The Badgir is a massively -built tower, which ranges from the lowest rooms of a building up on the roof. It is divided, usually in four vertically guided ventilation channels that are open at the top in all four directions and can be closed to control individually. The Badgir can according to its application and integration into the building, the location and especially the current climatic situation work differently and can be combined with other institutions.

The height of the tower allows based on heat flow chimney effect, supplying fresher air and the full play of the wind. In densely built settlements to open additional freedoms, because the building orientations can be oriented independently of a main wind direction in the sun, to prevent strong irradiation in the window. Following increasingly electro-mechanical fans and air conditioners were used, enter Badgire in terms of economy and sustainability back more into focus.

Basic Functions

Prevail in the building temperatures higher than outside and no wind, affects the chimney effect. This can happen especially at night. The cold night air flowing through the building and Badgir and cools the walls acting as a heat buffer. The heated air rises and escapes in Badgir. Blowing a Wind contrast, then the flow reverses. The back pressure on the upwind side (windward ) presses the cold air through the Badgir which is cooled in the process, but does not lead to a significant heating of the air. The warm air flows according to the print conditions mostly from various openings. As soon as the air flowing out is cooler than the walls, it cools all surfaces around which flow occurs, as well as the channel in Badgir which opens on the leeward side ( Lee). In addition, at night radiate from the walls of the tower and building, especially the roof, heat.

Sinks with no wind, the ambient temperature is below the indoor temperature, the air falls down in Badgir and enters a reverse chimney effect. The air cools at night the tower cooled interior walls and ventilated the interior. Through far-reaching closing the openings, the flow can be slowed down to better utilize the " stored coolness ", ie to the tower walls do not heat up prematurely and exploit the temperature difference corresponding heat capacity by storing heat. Often it is in the building anyway still quite cool and only carbon dioxide and other substances to be discharged through the door, or other low-lying openings. If the temperature of the walls of the air temperature, the air flow is reversed and the tower acts as a fireplace with ascending flow. However, the wind comes up in this situation, the air flows against the chimney effect by ram effect and pressure difference between windward and leeward the tower down, through the opposite channel back up and out of the past to Lee opening. Via the openings to the chambers, an air exchange takes place and it is placed in the movement of air. Depending on the design and situation of air can flow out in a room or streaming in the window. Is the static pressure in the air flowing as a result of the Bernoulli effect at a natural pressure that is under natural pressure air can flow into the Badgir. It is discharged through the channel ( Lee). These operations allow the room temperature approaches the night outside air temperatures.

Use of evaporative cooling

In addition to the exchange of air in the air flow causes Badgir a circulation of the air inside of the building. This cools by Transpirationsunterstützung also the skin of the occupants and the air passing through plants. If an air flow through design of Badgir and rooms above a water surface or wet surfaces out occurs by evaporation with the evaporative cooling to cool down more. This can be done directly if the wetted cooled air into the premises or stays there, or indirectly, if this air cools the walls of the badgirs. These can absorb heat and cool it so in later situations of the then flowing in the other direction air. Often pools or fountains are located in the air flow.

The length of the channels, and thus the heat capacity and the amount of water which is available for evaporation, and cooling can be increased among others through an air duct lying in the ground. The Badgir is then with some distance from the building. The cooling effect can be enhanced by planting and watering of the soil above the Badgir, as the water evaporates in the channel. This only works when an inflow of Badgir is achieved to the building.

The Badgir can also cooperate with other systems. If the air flow out of the mouth of a bay, which represents a connection to a below- building Qanat in the Qanat crossed over the water and thus cooled air rises from the bay into the rooms. This happens because the flowing air exerts a lower static pressure than the air pressure at the natural location of the other shafts Qanats when there is no or a smaller flow so little wind takes place immediately on the ground. Other situations indicated above, may already lead to a draft of air from the qanat into the building.

The wind catcher also be used for cold rooms ( Yakhchāl ) and water reservoirs (from Anbar ) and are able to cool using the evaporative heat the stored water in the summer months to a temperature near the freezing point. At the highest point of the dome roof of this room there is an opening. There is the wind velocity in accordance with the Venturi effect is greatest, there is in accordance with the Bernoulli effect, a lower pressure. One or often four Badgire cause the cistern to air. The air passes over the water evaporates, the upper warm water layer, the latent heat of evaporation cools the water, and the moist, warm air escapes through the pressure- low- top opening.