Termites are constantly refining the “designs” of their mounds. Some of them can reach heights of up to eight meters and are among the largest biological structures in the world. According to experts, research on mounds could help create ‘living and breathing’ buildings that use less energy.
There are about 2,000 species of termites in the world. Mounds built by some genera, for example Amitermes, Macrotermes, nasutitermes and Odontothermes, reach a height of up to eight meters and are among the largest biological structures in the world. According to the researchers, research on mounds could help create ‘living and breathing’ buildings that use less energy.
Dr. David Andréen of Lund University in Sweden and Dr. Rupert Soar of Nottingham Trent University in the UK studied termite mounds Macrotermes michaelseni from Namibia to see how they manage to maintain optimal conditions without carbon footprint air conditioning in their mounds. In the center of the mounds, which are inhabited by up to millions of individuals, there are “gardens” with symbiotic fungi grown by termites for food. Researchers focused on the ‘exit complex’: a dense network of tunnels, 3 to 5 millimeters wide, that connects the wider inner and outer channels. During the rainy season (November to April), when the mound is expanded, the complex extends over its northern face, directly exposed to the midday sun. Out of season, termites block the exit tunnels. It is believed that the complex allows excess moisture to evaporate while maintaining adequate ventilation. The researchers’ conclusions were published in the journal “Frontiers in Materials”. Andréen and Soar investigated how the layout of the complex allows oscillating or pulsating flows. They based their experiments on a scanned and 3D printed copy of a piece of the complex collected from nature in February 2005. ‘We show that the ‘exit complex’, the intricate network of interconnected tunnels found in termite mounds, can be used in a novel way to improve the flow of air, heat and moisture in human architecture,’ said Dr Andréen. The researchers simulated wind with a loudspeaker that drove the carbon dioxide/air mixture to oscillate, while tracking mass transfer with a sensor. As it turned out, the airflow was greatest at oscillation frequencies between 30 and 40 Hertz, moderate between 10 Hz and 20 Hz, and lowest at frequencies between 50 Hz and 120 Hz. The researchers concluded that the tunnels in the complex interact with the wind in a way that increases air mass flow, providing ventilation. Wind oscillations at certain frequencies generate turbulence within the mound, which has the effect of carrying breathing gases and excess moisture away from the center of the mound. – When ventilating a building, you want to maintain a delicate balance between the temperature and humidity created inside, without hindering the movement of stale air to the outside and fresh air to the inside. Most air conditioning systems have a problem with this. Here we have an organized complex that allows the exchange of respiratory gases, simply driven by differences in concentration from one side to the other. In this way, optimal conditions inside are maintained, explained Soar. Scientists simulated the output complex with a series of models of increasing complexity. They used an electric motor to drive an aqueous dye solution to oscillate through the tunnels and filmed the flow. Surprisingly, the motor only had to move the solution back and forth a few millimeters (corresponding to a weak wind oscillation) for the ebb and flow to penetrate the entire complex. The necessary turbulence appeared only with the right arrangement of tunnels.
The authors of the paper concluded that the outlet complex could enable wind-driven ventilation of termite mounds in light winds. ‘We imagine that the walls of the buildings of the future, made with new technologies such as 3D printers, will contain networks similar to the output complex,’ said Andréen. – Construction-scale 3D printing will only be possible if we can design structures as complex as they are in nature. The exit complex is an example of a complex design that can solve many problems at once: maintaining comfort in our homes while regulating the flow of respiratory gases and moisture through the building envelope, concluded Soar.
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