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Termite mounds reveal the secret to creating “living and breathing” buildings that could save energy.

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Amitermes, Macrotermes, Nasutitermes, and Odontotermes termites build mounds that can reach up to eight meters high, which makes them some of the largest biological structures in the world. These mounds have been refined over tens of millions of years by natural selection. Could architects and engineers learn from the ways of termites if they were to study them? Indeed, a new study in Frontiers in Materials shows how scientists can use termite mounds to make buildings comfortable without the carbon footprint of air conditioning.

Dr David Andréen, a senior lecturer at the bioDigital Matter research group of Lund University, said,

“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.”

Andréen and co-author Dr. Rupert Soar, an associate professor at the School of Architecture, Design, and the Built Environment at Nottingham Trent University, conducted research on mounds of Macrotermes michaelseni termites in Namibia. Colonies of this species can contain over a million individuals. The symbiotic fungus gardens, which are farmed by the termites for food, are at the core of the mounds.

The researchers studied the egress complex, which is a network of tunnels that looks like a dense lattice. These tunnels are between 3mm and 5mm wide and connect larger conduits inside the structure with the outside environment. During the rainy season (November through April), the egress complex can be seen over the north-facing surface of the termite mound, which is exposed to the midday sun. The termite workers block the egress tunnels during other seasons. It is believed that the complex design allows excess moisture to evaporate while maintaining proper ventilation. But how does this process work?

Andréen and Soar investigated how the egress complex layout facilitates oscillating or pulse-like flows. They conducted their experiments using a scanned and 3D-printed copy of a fragment of an egress complex that was gathered from the wild in February 2005.

The researchers used a speaker to create wind by causing vibrations in a CO2-air mixture. Then they measured the mass transfer with a sensor. The results showed that the most air flow occurred at oscillation frequencies between 30Hz and 40 Hz, moderate air flow at frequencies between 10Hz and 20 Hz, and the least airflow at frequencies between 50Hz and 120 Hz.

The researchers found that tunnels in the termite complex interact with the wind blowing on the mound in ways that improve air ventilation. Wind oscillations at specific frequencies create turbulence inside, which helps remove respiratory gases and excess moisture from the center of the mound.

“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.”

The authors next simulated the egress complex with a series of 2D models of increasing complexity, from straight tunnels to a lattice. An electromotor was used to drive an oscillating body of water (made visible with a dye) through the tunnels, and the mass flow was filmed. Surprisingly, the motor only needed to move air back and forth a few millimeters (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.

“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.”

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.”

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