Home ventilation design has changed a lot over the years – from no ventilation 100 years ago, to the new smart ventilation systems being developed today.
Smart ventilation is the continual adjusting of ventilation systems to maximize efficiency. The most obvious use of smart ventilation is reducing the ventilation if a building is unoccupied. A smart system could also be used to sense the indoor air quality and adjust the ventilation if poor air quality is detected. Smart ventilation systems adjust the ventilation during periods when it’s cooler outside for ventilated cooling.
What Can Termites Teach Us?
A termite’s nest self regulates both CO2 levels and the internal temperature using the structure of the nest and the properties of the building materials. Some termite nests grow fungus inside the nest as a food source. This fungus produces CO2 that needs to be eliminated from the nest. This is mainly done in fungus growing nests through tiny openings in the outer wall of the nest that the termites open and close as needed. This is essentially the equivalent of physically opening and closing your windows.
In nests that are not growing fungus, the method of ventilation isn’t as clear. There are no tiny openings in the outer wall like in the fungus nests. What mechanisms do they use to ventilate their nest? A study published in the March 2019 issue of Science Advances looked to answer that by studying two African non-fungus growing nests using multiscale X-ray imaging with three-dimensional flow field simulations.
The Walls Have Holes
In both nests large microscale pores were seen in the walls. In one of the nests, the walls had both large and small pores. In previous studies, these pores were thought to be disconnected. The small pores could be interparticle pores in soil pellets formed by the termites. The larger pores are thought to be pores formed during construction of the wall when the soil pellets were fused together like bricks. In the other nest, only the large pores were found. This is thought to be due to nest being built primarily using clay – clay doesn’t form many interparticle pores.
Researchers tested if these large pores could form from random construction methods, like a random sand pack. They found that the large pores are not formed if the construction method is random. This implies the termites build the nests in the way they do for a specific purpose; however, researchers acknowledge this could simply be a consequence of geometry of the pellets and the way they fit together.
What Does This Mean for Human Buildings?
Both nests were found to have a high percentage of connectivity of the pore space. Between 92% and 98% of the pores were part of a connected system. The interconnected large pores increased the porosity of the walls – reducing the exchange of internal and atmospheric air and, thereby, increasing the thermal insulation inside the nest. The larger pores also play an active role in the diffusion and advection of CO2.
Breathable, porous walls are currently being studied and designed. Using the studies published in Science Advances and what termites have taught us, we can design better breathable walls. Combining these termite-based, breathable walls with smart ventilation techniques would better enable heat exchange and decentralized ventilation in buildings.
Building envelope with porous material optimized to exchange heat to the incoming air (sucked in by a fan or a chimney) with minimal conduction losses. A water circuit integrated at the interior surface of the panel controls the temperature. Weatherproofing and wind-buffering can be done by an external rain-screen. https://www.sciencedirect.com/science/article/pii/S0378778817300476