Two researchers at Lund University and Nottingham Trent University have studied mounds of Macrotermes michaelseni termites from Namibia, to find out what architects can learn from them in order to design more energy-efficient buildings.
This species of termite forms colonies of more than a million individuals, building large mounds to house them. At the heart of the mounds lie the symbiotic fungus gardens, farmed by the termites for food.
The team focused on the egress complex: a dense, lattice-like network of tunnels, between 3mm and 5mm wide, which connects wider conduits inside with the exterior. The complex is significant because it is able to allow adapt itself to different temperatures, by allowing the evaporation of excess moisture, while still maintaining adequate ventilation.
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.
In a recent study, the researchers showed how termite mounds can teach architects to create comfortable interior climates for our buildings that don't have the carbon footprint of air conditioning.
"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 Dr David Andréen, a senior lecturer at Lund University.
The two researchers explored how the layout of the egress complex enables oscillating or pulse-like flows.
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 per cent of which were tunnels.
The researchers then simulated wind with a speaker and measured 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.
From this study, the team concluded that the 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 Dr Rupert Soar, an associate professor 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."
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 through the tunnels, and filmed the mass flow. They found that the motor needed to move air back and forth only a few millimetres 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.
"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 said.
The researchers' findings have been published in the journal Frontiers in Materials.
