1: Passive Solar Cooling | 2: Natural Ventilation | 3: Air Cooling
Natural Ventilation
Wind towers function as both air inlet and air exit devices, and are of course driven by the positive and negative air pressures created by the wind. The term wind-catcher is used here to refer to an air inlet device open on the windward side and designed to "capture" breezes and drive air into a building using positive air pressure. The term wind-escape is used to refer to an air outlet device open on the leeward side and designed to draw air out of a building using negative air pressure.
Traditional wind towers or badghir found in Iran and other areas of the Middle East consist of a four-sided capped tower extending several metres above a building, each side of the tower having a port or window at the top. When all ports except that one facing away from an incoming wind are closed, air is drawn upwards out of the building using the coanda effect. The use of horizontal slats in the tower as devices for speeding up the flow of air is also reported. Another traditional variation of the wind tower is the malqaf or wind-catcher which is oriented into prevailing winds. Again, such devices are aerodynamically designed to increase air flow velocities. Used in conjunction with evaporative cooling methods described below, wind towers form part of highly effective traditional cooling systems capable of reducing air and water temperatures to near freezing levels. In windless environments, wind towers can enhance the natural stack effect to remove hot air.
The solar chimney or thermal chimney uses the convection of air heated by passive solar energy to enhance natural stack ventilation through a building. The simplest form of solar chimney consists of a black-painted chimney extending several metres above a building. During the day, solar energy heats the chimney and the air within it, creating an updraft of air in the chimney. The suction created at the chimney's base can be used to ventilate the building below. Several design variations exist, including glazed solar chimneys built vertically against an exterior wall oriented towards the sun, and the Trombe wall in its summer operation mode.
Wind-driven devices are usually more effective generators of ventilating draughts, but solar chimneys can provide a degree of ventilation in windless environments. Also, solar chimneys can only function during daylight hours, whereas wind-driven devices can function whenever sufficient wind is available.
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