How Nature Does It
Openings at bottom of this termite mound in Tanzania provide ventilation and air flow through the structure. This keeps the temperature constant through the hot days.
The Eastgate Centre, in Harare, Zimbabwe, mimics the vertical ventilation structures of the termite mound. In this way, the air flowing through the building is cooled or heated using passive techniques.
Consider this: Buildings use 40% of all energy consumed by people. How is it that in nature, species such as termites create remarkable temperature-control systems to keep themselves cool, without fans, air blowers, or air conditioners?
Imagine for a moment a termite mound on the African savanna, where temperatures swing between 40°C (104°F) during the day and 1°C (34°F) at night. Termites survive, though, only if their environment has a constant temperature of 30°C (86°F). That’s the temperature needed to grow the fungus that is their food. So how do the termites keep a mound at a consistent temperature?
First, let’s take a look at how the mounds are built. Termite mounds are tall, often reaching up to 7.6 m (25 ft) high and rooting 3 m (10 ft) underground. The mounds are built with a long tube at the top that looks like a small chimney or smokestack. They are sturdy, too. When termite mounds are found to be in the way of building projects, dynamite is often needed to remove them.
Termites create small openings in the wet mud at the bottom of the mounds. These tunnels act as breeze catchers, lowering the temperature of the air as it moves through the tunnels of wet mud. This process is called evaporative cooling. When dry air passes over water, the air absorbs some of that water. This occurs as the vapor pressure and the temperature of the air and the water try to become equal. The heat moves from the higher air temperature to the lower water temperature, thus cooling the air. Other examples of evaporative cooling include animals that sweat to regulate temperature, and clay roofs in tropical climates (see the Cool Clay experiment).
The termite mound also makes use of natural air currents. Because warm air rises, the convection currents draw air from the tunnels at the bottom up and out through the opening, or flue, at the top of the mound. To regulate the heat and humidity in the mound, the termites work constantly to change the position of the tunnels, opening up new tunnels and blocking others.
Applying Lessons from Termites
Architect Michael Pearce based his design of the Eastgate Centre in Harare, Zimbabwe, on the design of termite mounds. Spanning half a city block in Harare’s business center, Eastgate combines an office complex with a shopping mall.
Like the termite mound, Eastgate is ventilated, cooled, and heated entirely through natural means. The building has four heavy masonry walls on the outside, with a seven-story-high atrium on the inside. Outside air is pulled in through multiple vents and is either warmed or cooled by the building mass depending on which is hotter, the concrete of the structure or the air.
Eastgate’s ventilation costs one-tenth of that of a standard air-conditioned building and uses 35% less energy than six conventional buildings. As the owners of Eastgate found out, an energy-efficient building can also be good for the pocketbook. In the building’s first five years, its unique design saved its owners $3.5 million in energy costs.
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