How Do Termite Mounds Regulate Temperature? – ASME

Posted: February 4, 2021 at 10:51 am

We humans like to congratulate ourselves for our ingenuity. Yet natures passive designs often outperform our expensive, energy-hungry technologies. And while engineers and architects can improve their designs by mimicking the natural world, nature always has another lesson to teach. That has certainly been the case for termites and air conditioning.The story begins in 1992, when Zimbabwean architect Mick Pearce received a commission to build Eastgate Centre, a two-building office complex and shopping mall, in the countrys capital city of Harare. Pearce, however, wanted to do more than just build a new building. He wanted to eliminate the huge heating and cooling plants a 340,000 square feet development typically needed.Pearce already had a solution in mind. He began to formulate it while watching BBCs natural history series, Life, on TV one evening.I saw David Attenborough climbing inside the chimney of a termite nest in Nigeria, he said, and he realized that evolution had already solved the problem.Pearce had grown up in Zimbabwe and was familiar with such chimneys. They rose six to 30 feet above termite nests and were strong enough for elephants to use to scratch their flanks.Below the chimneys, the termites farmed fungi for food. While the termites relied on soils thermal storage capacity to help keep temperatures stable, Pearce realized that the termites also had to breathe.It was an elegant design. The hot air generated by the nest and its fungus farm, which had higher concentrations of carbon dioxide and methane, exited through the chimney through convention. As the hot air left, it pulled in fresh air from the surface through moist foraging tunnels, which added water vapor to the stream. The chimney, warmed by the sun, heated the air exiting through it, adding an extra push to the convection cycle.The termite nest was warmer than the outside, particularly at night, Pearce said in an interview. You get air rising out the chimney, and that pulls air in from the holes they go out to forage. Thats how they breathe.If termites could do it, Pearce thought, why not humans?EastgatePearce had one thing going for him: Although Zimbabwe is semitropical, Harares 4800 ft. elevation keeps it cool and provides an average temperature swing of about 10 degrees Celsius each day. Pearce figured he could pull in night air to cool concrete and masonry structures. They would act like the soil in a termite nest to store cooling. He could then chill incoming air by running it over those structures during the day.In the building that Pearce and multidisciplinary engineering firm Arup Group designed, each floor had air ducts running underneath it. These ducts contained concrete blocks with protruding teeth, whose high surface area enabled them to cool down and heat up efficiently.Banks of fans drove the cool air through the shopping area and seven floors of offices. As the air warmed, it rose and exited through a central atrium connecting the two towers and 48 brick chimneys that ran along their roofs.Pearces designed also used several other tricks inspired by nature. Office windows, for example, are shaded by overhangs and plants to keep sunlight from heating the building too quickly. The exterior features jagged gabbles and facades that act like cactus spikes, whose high surface areas disperse heat rapidly at night.On many levels, worked spectacularly well. Eastgate cost 10 percent less to build than a similarly sized building with air conditioning. The building also used 35 percent energy when comparable buildings in Harare and saved $3.5 million in energy costs during its first five years.Further Reading: Storing Heat from Nuclear Power Plants Could Improve Output

Of course, office temperatures are not as tightly controlled as conventional buildings. Most of the time, they hover in the mid-70s degrees Fahrenheit range, but they may reach 80-82 degrees at the end of the day for several weeks each year. This led Pearce and Ove Arup to improve the control system.The trick is to coordinate the weather outside with the controlled internal environment, taking into account lag times, he said. Its like tuning an instrument, like an organ in a church.Pearce was a pioneer of biomimicry, which draws inspiration from the natural world for human design. He went on to apply his approach to a more efficient office block in Melbourne, Australia, and build a tower and dining hall in China.I was convinced that by looking at animal architecture, there are important clues for an architecture which inspires the design team to make buildings that follow natural processes, cycles, and systems, he said.Yet despite his successes, Pearce did not learn everything termites had to teach him.

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Eastgate Centre was built on a wrong conception of how termites regulate the temperature of their nests, Singhs co-author, Guy Theraulaz of the University of Toulouse, said. Still, Eastgate works.It is appropriate to speak of [Eastgate] as termite-inspired design, Turner, a biologist at the SUNY College of Environmental Science and Forestry, added. The architect, Mick Pearce, drew more on inspiration rather than knowledge of how these mounds worked.In the end, he created a successful building design because he approached the engineering challengea building in semi-tropical climate without an air conditioning plantin an imaginative way.What made this design successful was several termite-inspired ideas, like tall stacks, porous walls, and a large central atrium that could draw air passively through the building. What is often not mentioned is the clever use of large heat storage blocks that could damp temperatures through the hot day, while using high-powered fans to empty those heat stores during the cool night. Termites do not have the latter. Termites do not use this to maintain temperature.So if the Eastgate model isnt quite right, what is?

This ought to work in buildings once we recognize that differential heating of the center and the periphery suffice to drive flow, he said.Unfortunately, what ought to work in theory does not always pan out in the real world.Instead, the mechanism that you find at the scale of the termites has to be adapted, Theraulaz said. So we have to discover new principles to design the architecture to get the same kind of properties. When we understand what happens at the microscale, we can build models and try to see what kind of architecture we can build.New technologies, such as Mahadevans sensors and simulations, promise that easier.We now have a set of techniques by which we are able to analyze nest architectures, Theraulaz said. In the past 10 years, we have scanned more than one hundred termite nests, so we have a huge basis [for analyzing their] architecture.We can apply the same [simulation] techniques to achieve a broader understanding of how these structures play a role in thermoregulation. For the moment, we dont have a clear idea. Perhaps there are multiple ways to achieve the same kind of thing. Its something we are beginning to explore.The most interesting thing is that we can apply the same tools we use to analyze the nest architecture to human architecture, to analyze the diffusion of gases, how temperature behaves inside. And by simulation we can try to find the parameters in the architecture that will optimize it, Theraulaz said.Ultimately, the successful adaptation of natural climate control methods to human structures means saving energy and reducing carbon emissions. But it also means creating buildings that are more in tune with the Earths natural rhythms. It is, indeed, beyond biomimicry.I think we are just at the beginning of an interesting story, Theraulaz said.Mark Wolverton is a science writer living near Philadelphia.

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How Do Termite Mounds Regulate Temperature? - ASME

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