A windcatcher, wind tower, or wind scoop ( ; ) is a traditional architectural element used to create cross ventilation and passive cooling in buildings. Windcatchers come in various designs: unidirectional, bidirectional, and multidirectional. Windcatchers are widely used in North Africa and West Asia. Iran, especially in the south of Fars province and Hormozgan province, and other countries around the Persian Gulf have used windcatchers for the past three thousand years. Neglected by modern architects in the latter half of the 20th century, the early 21st century saw them used again, to increase ventilation and cut power demand for air-conditioning. Generally, the cost of construction for a windcatcher-ventilated building is less than that of a similar building with conventional heating, ventilation, and air conditioning (HVAC) systems. The maintenance costs are also lower. Unlike powered air-conditioning and fans, windcatchers are silent and continue to function when the electrical grid power fails (a particular concern in places where grid power is unreliable and expensive). Windcatchers rely on local weather and microclimate conditions, and not all techniques will work everywhere; local factors must be taken into account in design. Structure and function Windcatchers vary dramatically in shape, including height, cross-sectional area, and internal sub-divisions and filters. Windcatching has gained some ground in Western architecture, and there are several commercial products using the name windcatcher. Some modern windcatchers use sensor-controlled moving parts or even solar-powered fans to make semi-passive ventilation and semi-passive cooling systems. Windscoops have long been used on ships, in the form of a dorade box. Windcatchers have also been used experimentally to cool outdoor areas in cities, with mixed results; traditional methods include narrow, walled spaces, parks and winding streets, which act as cold-air reservoirs, and takhtabush-like arrangements (see sections on night flushing and convection, below). Prevailing wind conditions The construction of a windcatcher depends on the prevailing wind direction at that specific location: if the wind tends to blow from only one side, it may have only one opening, and no internal partitions. In areas with more variable wind directions, there may also be radial internal walls, which divide the windtower into vertical sections. These sections are like parallel chimneys, but with openings to the side, pointing in multiple directions. More sections reduce the flow rate, but increase the efficiency at suboptimal wind angles. If the wind hits the opening square-on, it will go in, but if it hits it