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Termite mounds could inspire “living and breathing” buildings

Among the approximately 2,000 species of termites, many are extraordinary ecosystem engineers. For instance, mounds built by some of the genera – including Amitermes, MacrotermesNasutitermes, and Odontotermes – are some of the world’s largest biological structures, reaching up to eight meters in height. 

Now, researchers from Lund University in Sweden and Nottingham Trent University in the UK have found that the design of termite mounds could have major applications in architecture, helping us develop comfortable interior climates for our buildings that do not have the carbon footprint of air conditioning.

“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,” explained lead author David Andréen, a senior lecturer in Architecture at Lund.

Together with his co-author Rupert Soar, an associate professor in Sustainable Technologies at Nottingham, Andréen examined mounds built by Macrotermes michaelseni termites from Namibia. At the heart of these mounds – which can shelter over a million inhabitants – lie symbiotic fungus gardens, farmed by termites for food. 

The experts focused on the egress complex, a dense, lattice-like network of tunnels three to five millimeters wide that connects wider conduits inside with the exterior. While during the rainy season (when the mound is growing), the egress complex extends over the mound’s north-facing surface to be exposed to the midday sun, outside this season, termites keep the egress tunnels blocked. Such methods are thought to allow evaporation of excess moisture, while maintaining adequate ventilation.

To clarify how this structure works, the researchers explored how the layout of the egress complex enables oscillating or pulse-like flows. When simulating wind with a speaker that drove oscillations of a CO2-air mixture through a fragment of a complex collected from the wild, they discovered 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.

These findings suggest that tunnels in the complex interact with the wind blowing on the mound in a way that increases mass transfer of air for ventilation. At the same time, wind oscillations at certain frequencies generate turbulences inside the mound, and 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,” Soar said.

Subsequently, the researchers replicated the egress system by employing a sequence of 2D models. These models progressively evolved from simple straight tunnels to a more intricate lattice structure. To observe the movement of water within the tunnels, they utilized an electromotor to generate oscillations, allowing the dyed water to become visible on camera. 

To their astonishment, they discovered that the motor only required slight back-and-forth movements, equivalent to gentle wind oscillations spanning a few millimeters, for the ebb and flow to permeate throughout the entire complex. Crucially, the necessary turbulence emerged solely when 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,” Andréen said.

“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,” Soar concluded.

The study is published in the journal Frontiers in Materials.

More about termite mounds

Termite mounds, also known as termite hills, are large, complex structures made by a certain species of termites. They are a prime example of insect architecture, and they vary in design depending on the species of termite, the type of soil, and the climate.

Most termite mounds are built by subterranean termites, which live underground. These mounds can range in size from a few inches to over 30 feet tall. The mound is not the actual colony but a structure that provides an optimal environment for the colony which is located below the ground.

The construction of a termite mound is a marvel of natural engineering. Termites mix dirt, saliva, and feces to form a strong, cement-like substance. This is then used to build a complex network of tunnels and chambers. The outer wall of the mound is particularly hard and resistant to predators.

Inside the mound, there are various chambers serving different functions such as nurseries, fungal gardens, and royal chambers. The royal chamber, deep within the mound, houses the queen and king termites, responsible for the growth and survival of the colony.

A termite mound is not just a place for termites to live; it’s also an incredibly efficient system for climate control. The mound’s structure aids in regulating temperature and humidity, which is crucial for the survival of the termites as they are sensitive to environmental conditions. 

Many mounds feature a complex system of vents and conduits which facilitate air circulation, thus maintaining a stable internal environment regardless of external conditions.

Despite being known as pests due to their wood-eating habits, termites play a crucial role in ecosystems, especially in nutrient recycling, soil formation, and influencing plant community structure.

By Andrei Ionescu, Staff Writer

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