Termites may be highly destructive for building structures but two researchers from Sweden and the United Kingdom are studying the termite mound to create buildings that have comfortable interiors using very little energy.
In a new study published in Frontiers in Materials, the researchers revealed how the ‘egress complex’, an intricate network of interconnected tunnels found in termite mounds, could be replicated to create a pleasant interior climate within buildings – without the carbon footprint of air conditioning. According to the researchers, the layout of this lattice-like network of tunnels can intercept wind around the termite mound to create turbulence inside, which can power ventilation and control the interior climate.
There are approximately 2,000 known species of termites, and mounds built by some genera, for example, Amitermes, Macrotermes, Nasutitermes, and Odontotermes, can reach up to eight metres high, making them some of the world’s largest biological structures. What could human architects and engineers learn from the termite ecosystem?
“Here we show that the ‘egress complex’ can be used to promote flows of air, heat, and moisture in novel ways in human architecture,” said Dr David Andréen, a senior lecturer at the bioDigital Matter research group of Lund University, and the study’s first author.
Andréen and co-author Dr Rupert Soar, an associate professor at the School of Architecture, Design and the Built Environment at Nottingham Trent University, studied mounds of Macrotermes michaelseni termites from Namibia. Colonies of this species can consist of more than a million individuals.
The egress complex consists of a dense, lattice-like network of tunnels, between 3mm and 5mm wide, which connects wider conduits inside with the exterior. During the rainy season (November through April) when the mound is growing, this 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.
Andréen and Soar explored how the layout of the egress complex enables oscillating or pulse-like flows. Using a 3D-printed copy of a 4cm thick egress complex fragment collected in February 2005 from the wild, 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 40 Hz; moderate at frequencies between 10Hz and 20 Hz; and least at frequencies between 50Hz and 120 Hz.
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. 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,” explained Soar.
The authors 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. They found, to their surprise, 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 at weak winds.
“We imagine that building walls in the future, made with emerging technologies like 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.
Soar concluded: “Construction-scale 3D printing will only be possible when we can design structures as complex as in nature. 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.”
Image source: @FrontiersIn
