No air conditioning? No problem, if the buildings copy the network tunnels of termite mounds

Enlarge / Part of the reticulated tunnel system (exit complex) of a Macrotermes michaelseni termite mound from Namibia. D.Andréen

The mounds that some species of termites build over their nests have long been considered a kind of built-in natural climate control, an approach that has intrigued architects and engineers wanting to design more ecological and more energy-consuming. efficient buildings emulating these principles. Decades of research have gone into modeling how these mounds work. A new paper published in the journal Frontiers in Materials offers new evidence for an integrated system model in which the mound, nest and its tunnels work together like a lung.

Perhaps the most famous example of the influence of termite mounds on architecture is the Eastgate Building in Harare, Zimbabwe. It is the largest retail and commercial complex in the country, and yet it uses less than 10% of the energy consumed by a conventional building of its size because there is no central air conditioning and only a minimal heating system . Architect Mick Pearce based his design in the 1990s on the cooling and heating principles used in the area's termite mounds, which serve as mushroom farms for termites. Mushrooms are their main source of food.

The conditions must be ideal for the fungus to grow. Thus, termites must maintain a constant temperature of 87°F in an environment where outdoor temperatures range from 35°F at night to 104°F during the day. Biologists have long suggested doing this by building a series of heating and cooling vents in their mounds, which can be opened and closed during the day to keep the temperature inside constant. The Eastgate Building relies on a similar system of well-placed ventilation and solar panels.

Enlarge / The passive cooling design of the Eastgate Center in Zimbabwe, with its distinctive chimneys, was inspired by termite mounds. David Brazier/CC BY-SA 3.0

There are different types of termite mounds, depending on the species, which makes identifying universal principles a bit tricky. For example, in 2019, scientists from Imperial College London studied the mounds of another type of common African termite in Senegal and Guinea. This species does not grow mushrooms, so their mounds lack the distinctive chimneys and window-like openings of termite mounds in Zimbabwe that inspired Pearce's design for the Eastgate Building. There are no visible openings. Instead, there are pores, the natural result of how the mounds are made: by piling up pellets of sand mixed with termite spit and dirt. It is these pores that help the structure "breathe" and dry out faster after heavy rains.

In the case of termite mounds in Zimbabwe, the precise mechanism has long been debated. Is it some form of induced flow (aka "the chimney effect"), the fact that heat from the inhabitants of the colony causes air to rise and exit through vents in the mound (thermosyphon flow), or some combination ? Or by...