Scientists studying termite mounds in Namibia have suggested that elements of the mounds’ design could be copied by architects to create a comfortable climate in human buildings with little energy.
The scientists investigated the ‘egress complex’ of Macrotermes michaelseni termites, which appears to promote moisture regulation and gas exchange. They showed that the layout of this lattice-like network of tunnels, which are between three and five millimetres wide and connect wider conduits inside with the exterior,can intercept wind around the termite mound to create turbulence inside, which in turn, can power ventilation and control the interior climate.
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‘Here we show that the egress complex, an intricate network of interconnected tunnels found in termite mounds, can be used to promote flows of air, heat and moisture in novel ways in human architecture,’ said David Andréen, a senior lecturer at the bioDigital Matter research group of Lund University.
Colonies of the termite species can consist of more than a million individuals. Their mounds contain symbiotic fungus gardens that are farmed by the termites for food.
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During the rainy season (November–April), when the mound is growing, the egress complex extends over its north-facing surface, directly exposed to the midday sun. Outside this season, termite workers keep the egress tunnels blocked. The complex is thought to allow evaporation of excess moisture, while maintaining adequate ventilation. But how does it work?
The researchers explored how the layout of the egress complex enables oscillating or pulse-like flows. They based their experiments on a scanned and 3D-printed copy of an egress complex fragment collected from the wild. This four-centimetre-thick fragment had a volume of 1.4 litres, 16 per cent of which was made up of tunnels.
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They simulated wind with a speaker that drove oscillations of a CO2-air mixture through the fragment, while tracking the mass transfer with a sensor. They found that air flow was greatest at oscillation frequencies between 30Hz and 40Hz; moderate at frequencies between 10Hz and 20Hz; and least at frequencies between 50Hz and 120Hz.
The researchers concluded that tunnels in the complex interact with wind blowing on the mound in ways that enhance mass transfer of air for ventilation. Wind oscillations at certain frequencies generate turbulence inside, whose effect is to carry respiratory gases and excess moisture away from the mound’s heart.
‘When ventilating a building, you want to preserve the delicate balance of temperature and humidity created inside, without impeding the movement of stale air outwards and fresh air inwards,’ explained Rupert Soar, an associate professor at the School of Architecture, Design and the Built Environment at Nottingham Trent University. ‘Most HVAC systems struggle with this. Here we have a structured interface that allows the exchange of respiratory gasses, simply driven by differences in concentration between one side and the other. Conditions inside are thus maintained.’
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The scientists then simulated the egress complex with a series of 2D models, which increased in complexity from straight tunnels to a lattice. They used an electromotor to drive an oscillating body of water (made visible with a dye) through the tunnels and filmed the mass flow. To their surprise, they found that the motor needed to move air back and forth only a few millimetres (corresponding to weak wind oscillations) for the ebb and flow to penetrate the entire complex. Importantly, the necessary turbulence only arose if the layout was sufficiently lattice-like.
The authors concluded that the egress complex can enable wind-powered ventilation of termite mounds in weak winds. ‘We imagine that building walls in the future, made with emerging technologies such as powder bed printers, will contain networks similar to the egress complex. These will make it possible to move air around, through embedded sensors and actuators that require only tiny amounts of energy,’ said Andréen.
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‘Construction-scale 3D printing will only be possible when we can design structures as complex as in nature,’ Soar concluded. ‘The egress complex is an example of a complicated structure that could solve multiple problems simultaneously – keeping comfort inside our homes while regulating the flow of respiratory gasses and moisture through the building envelope. We are on the brink of the transition towards nature-like construction; for the first time, it may be possible to design a true living, breathing building.’
The research has been published in Frontiers in Materials.