Whither the Windcatcher?

Old-world cooling system makes a comeback in modern green buildings

An ancient form of air conditioning is getting a second look in an age of global warming and rising energy costs. Windcatchers—towers or specially designed roof vents that pull fresh air into a building—have been the main indoor cooling strategy in hot, arid regions such as the Persian Gulf for the past three millennia. Air circulation is induced simply by the difference between inside and outside pressure and temperature.

Traditional windcatcher towers are open on the side facing the predominant wind direction to “catch” the wind and direct the breeze down into the structure. Air circulation even works without wind: a building’s masonry walls will remain cold from low nighttime temperatures, so warm air entering the tower will cool, sink, and flow into the building. In some setups, a pool of water puts an extra chill into the air through evaporative cooling.

Despite the effectiveness of this zero-carbon air conditioning, windcatchers have taken a back seat to modern, energy-intensive cooling systems. Recently, however, a new generation of “green” architects is experimenting with new twists on the old technology to slash a building’s energy costs.

For example, the Council House 2 in Melbourne, Australia, uses five three-story-tall “shower towers” made of lightweight fabric to cool the interior. A shower head at the top of each sleeve trickles water onto the fabric, which pulls in hot air. Evaporation from the surrounding cloth cools the air, and the resulting downdraft drives it into the ground floor lobby, shops, and arcade.

Other high-tech tweaks make windcatchers practical in different climates. The U.K.-based company Monodraught manufactures small rooftop ventilation systems that capture wind blowing in any direction. Some also work in tandem with solar-powered fans to boost circulation on especially hot or windless days. A hybrid system in the U.K.’s Bluewater Shopping Centre toggles between 39 customized Monodraught windcatchers and a mechanical ventilation system based on temperature, precipitation, relative humidity, and wind speed and direction—all recorded on a connected weather station.

With heating, cooling, and ventilation accounting for more than 60 percent of a building’s total energy consumption, windcatchers could be the smartest way to clear the hot air. (1) ❧

—Lindsey Doermann

1. Saadatian et al. 2012. Renewable and Sustainable Energy Reviews doi:10.1016/j.rser.2011.11.037.

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