Termite mound in Bangalore, India. Credit: D. Andréen
Key points:
- The unique design of termite mounds can inspire humans to create confortable buildings without air conditioning.
- The key to termites' efficient building lies in the egress complex: a lattice-like network of tunnels.
- These complex tunnels interact with wind in ways that enhance transfer of air for ventilation.
Termites are known for their ecosystem engineering. The mounds built by some, for example Amitermes, Macrotermes, and Odontotermes, reach up to 8 meters high. Over millions of years, termites have worked to improve the design of their mounds. Now, human architects and engineers are finding they may have a reason to study their ways.
In a new study published in Frontiers in Materials, researchers show how termite mounds can inspire humans to create comfortable interior climates for buildings that don’t have the carbon footprint of air conditioning.
For the study, researchers at Nottingham Trent University, studied mounds of Macrotermes michaelseni termites from Namibia. The researchers focused on the egress complex: a dense, lattice-like network of tunnels, which connects wider conduits inside with the exterior. During the rainy season, this extends over the north-facing surface directly exposed to the midday sun. Termite workers keep the egress tunnels blocked outside this season. The complex is thought to allow excess moisture to evaporate, while maintaining adequate ventilation.
First author David Andréen, a senior lecturer at Lund University, and Rupert Soar, an associate professor at Nottingham Trent University, explored how the layout of the egress complex enables oscillating flows and based their experiments on the scanned and 3D-printed copy of an egress complex fragment. They based their experiments on the scanned and 3D-printed copy of an egress complex fragment collected in February 2005 from the wild. This fragment was 4cm thick with a volume of 1.4 liters, 16% of which were tunnels.
In experiments, the team 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,” said Soar. “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.”