One little known method of cooling (and night time warming) a building that requires no electricity, no freon, and no gas, is that of the "wind tower." wind tower This ancient Middle-Eastern technology relies solely on the natural principles of convection and thermodynamics to create a natural "air conditioner". air conditioning

The basic principles behind a traditional Middle-Eastern wind tower are ridiculously simple. (Implementation in a modern building, however, is not.) The tower sticks up above the top of the building some 12′ (twelve feet) or more and is open on anywhere from two to eight different sides. The average in the Middle-East is four sides. Two sides face the wind; two face away from the wind. Inside, the tower is divided into fourths in an X pattern. (An eight sided tower would be divided into eighths, and so on.)

Madinat Jumeirah and the Burj al Arab Hotel, United Arab Emirates (The wind towers are the structures sticking up from the top of the building)

The two sides facing the wind "catch" it. During the day, the hot air is cooled by the thick masonry walls of the tower as it moves downward, into the building. Since cool air is heavier than warm air, the cooled air sinks to the lowest point in the building, forcing the hot air, which is higher up, out the down wind side of the tower. The ventilation and air movement is further facilitated by the pressure differential of the tower itself. Like an airplane wing, the down wind side literally "pulls" the hot air out of the building.

At night, the process reverses. The wind tower, having warmed from removing heat from the outside air all day, is now warmer than the cool night air. As the warm air is pushed into the building on the windward side of the tower, being warmed by the thermal mass of the tower, the cooler air is pulled out of the building by the leeward side of the tower.

This method of heating and cooling buildings heating and cooling buildings, HVAC, heating, cooling is so efficient that the technology is still in use today, even in large hotels like the Madinat Jumeirah and Burj al Arab shown above.

Traditional wind tower atop a home in Dubai (As the buildings are made of clay brick, the wooden poles work like rebar in concrete, providing sheer strength to the tower.)

A study performed by the University of Arizona showed an 18° temperature difference between the inside of a modeled building and the outside temperature during the heat of the day using only the natural convection natural convection currents of a wind tower. Though, in the University of Arizona model study, their building used a solar stack solar stack to vent the hot air, rather than partitioning the wind tower in the traditional manner.

That said, other tests — both computer models and tests performed on functioning buildings with wind towers — show similar results with a traditional single, partitioned tower. Further, those results can be improved by adding other methods of cooling such as a courtyard with a fountain, shading the building during the heat of the day, and underground venting.

With this last technique, pipes are placed underground where the temperature is relatively constant. If properly placed, the ground will change temperature at pipe depth no more than about ±2° from the heat of the day to the cool of the early morning. The pipes are then vented to the outside, some distance away from the building. The wind tower can then draw air cooled by the underground pipes into the building during the day. At night, as the outside air temperature falls below that of the underground pipe, the warmer underground air is drawn into the building, adding to the warmth provided by the thermal mass of the wind tower itself.

Commercial successes like the Mithun Offices/Pier 56 in Seattle and the Hood River Public Library in Hood River Oregon show some of the possible permutations this ancient technology offers us here in the Pacific Northwest. Other modern buildings are, and have been, built using wind tower concepts around the world, further expanding the pool of engineering knowledge about this ancient technology. (See Sustainability Goes Mainstream (Sun, Wind & Veils), by Guy Battle.)

For the home builder, the downside of the wind tower concept is primarily initial cost. Traditional homes around the Middle-East middle-east followed known designs to ensure the success of the heating/cooling wind tower system. Given the harsh conditions, it was, quite literally, a matter of life and death. Experimentation on what worked was not often encouraged. Today, modern homes are individualized. Each one offers a unique set of challenges and possibilites. Because natural convection currents are at the heart of the wind tower system, engineering and modeling is virtually a necessity to make sure that the system will work as designed, meeting the building’s needs.

But given the rising costs of utilities, it could very well be money well spent over the lifetime of the home.

Share This

Technorati Tags: wind tower, air conditioning, heating and cooling buildings, HVAC, heating, cooling, natural convection, solar stack, middle-east

This entry was posted on Sunday, April 29th, 2007 at 5:35 pm and is filed under Building Systems & Methods. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.