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Engineering Nature: Termite Mounds
As we continue the current series that examines biomimetic innovations in engineering, we will analyze the various thermodynamic flows that allow an African termite mound to stay at an ever-constant temperature of 87 degrees while the outside temperature varies from the low 30s at night to well over 100 degrees during the day. Termite nests must be meticulously regulated because their main food source, a fungus that grows in the mound, only grows at a specific temperature. Termite mounds are among the tallest non man-made structures in the world, standing at several meters tall. They are built slowly by termites carrying various sediments in their mouths and using saliva to “glue” it together. The material produced is so strong and resistant to water many of the locals use it in their own construction. By examining the interesting, but simple, properties that allow a termite mound to regulate its temperature, structural engineers and architects are developing ways to apply the technology to new buildings and structures to improve their energy efficiency and environmental impact.
Engineering Mechanics Behind It
From the outside a termite structure may not seem impressive, appearing only as a large rock. However, what is unseen from the outside is the constant state of flux that the mound undergoes. The inner workings of a termite mound are very similar to the inner workings of a lung, as opposed to the common notion that they work in a basic convective scheme. To start the process the mound captures light gusts of wind, similar to taking in a breath. This begins to oscillate the static air that is already inside the mound and mixes with the wind-refreshed air. Little parts of the air then vent into small tunneled capillaries which begin to resonate and hum.i This humming allows for gas exchange through the semi permeable mud of the mound which not only supplies the termites with oxygen when they are subterranean, but also works as an active ventilation system to keep the temperature regulated. When this is coupled with the natural barrier of thickness provided by the walls of the mound, the temperature inside is perfectly controlled. Termites are the only known animals on Earth that harness this kind of engineering with respect to natural and renewable energy. ii
Applications and Innovations
A building recently constructed in Zimbabwe, known as the Eastgate Centre, utilizes a very basic understanding of the termite mound properties. The building has no air conditioning system whatsoever, but instead regulates temperature using vents at the base of the structure and on the roof. During the heat of the day the vents are closed, but at night when the temperature drops the vents are opened to allow the cool air to enter through the bottom vents and forces the hot air out of the top.iii This system allows the building to use about 10% of the energy a conventional building its size would, as well as saving 3.5 million USD at the beginning of the project by not investing in a traditional air conditioning system.iv While this isn’t the exact technology that would be exhibited through biomimicry it utilizes the basic concepts of a termite mound. A group out of Loughborough University recently started the TERMES project which aims to map the three dimensional design of a termite mound and then use computational fluid dynamic simulations to understand how the tunnels and air conduits are able to easily exchange gases, maintain temperature, and regulate humidity better than any man-made structure. Currently the largest challenge in using a complete biomimetic recreation of the termite mound is developing the small capillaries to create a resonance that works with the building materials of the structure. If engineers were to eliminate the resonance aspect of the structure, a semi-permeable building material that could selectively diffuse would be required.
While many aspects of nature may be simple compared to our technological advances, in other areas nature out paces us. If we are able to develop the correct materials to consistently apply the technology behind a termite mound to modern architecture we will make great improvements in energy preservation.