No A/C? No problem, if buildings copy networked tunnels of termite mounds

The hills so sure types of termites Building above their nests has long been thought of as a form of built-in natural climate control — an approach that has intrigued architects and engineers wanting to design greener, more energy-efficient buildings that emulate these principles. There has been decades of research dedicated to modeling how these nests work. A new paper The study, published in the journal Frontiers in Materials, offers new evidence for an integrated systems model, where the mound, nest and its tunnels work together in a manner similar to a lung.

Perhaps the most famous example of the influence of termite mounds on architecture is the Eastgate Building in Harare, Zimbabwe. It’s the country’s largest commercial and retail complex, yet uses less than 10 percent of the energy that a conventional building of this size uses, as there is no central air conditioning and only a minimal heating system. Architect Mick Pearce As is well known, his design in the 1990s was based on the cooling and heating principles of the region’s termite mounds, which serve as mushroom farms for the termites. Mushrooms are their main food source.

For the fungus to thrive, the conditions need to be just right. Therefore, the termites must maintain a constant temperature of 30°C in an environment where outside temperatures range from 1°C at night to 30°C during the day. Biologists have long proposed doing this by building a series of heating and cooling vents in their mounds that 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 air vents and solar panels.

There are different types of termite mounds depending on the species, which makes identifying universal principles somewhat difficult. For example, in 2019Scientists at Imperial College London studied the mounds of another species of African termite found in Senegal and Guinea. This species does not grow fungi, so its mounds lack the distinctive chimneys and window-like openings of Zimbabwe’s termite mounds that inspired Pearce’s design for the Eastgate Building. No openings are visible at all. Instead there are pores, the natural result of how the mounds are made: by stacking sand beads mixed with termite spear and soil. It is these pores that help the structure to “breathe” and dry out faster even after heavy rains.

In the case of termite mounds in Zimbabwe, the exact mechanism has long been a matter of debate. Is it a form of induced flow (aka “chimney effect“), the fact that the heat of the residents of the colony drives the air up and out through the vents of the hill (thermosiphon flow) or a combination? Or maybe another model is needed.

SUNY-Syracuse physiologist Scott Turner and Rupert Soar of Nottingham Trent University are co-authors a work from 2008 on the grounds that Pearce had relied on incorrect assumptions when designing the Eastgate building. In particular, there is no solid evidence that termites regulate the temperature of their nests. Pearce’s design was a success nonetheless, but Turner and Soar envisioned “buildings that are not simply inspired by life—biomimetic buildings—but that are, in a sense, as alive as their occupants and the living nature in which they are embedded are.”

This latest paper by Soar and David Andréen of Lund University in Sweden examines an alternative hypothesis first proposed by Turner in 2001. In this scenario, the termite mound is one component in a larger integrated system that includes the subterranean nest and the complex lattice-like network of excavated tunnels known as the “exit complex” that could serve as a driver for selective airflows. Turner envisioned this system as a functional analogue of a lung, letting oxygen in and carbon dioxide out. In practical terms, it is a multi-phase gas exchanger.

The termites can also achieve faster evaporation of the excess water after rainfall by transporting the water around the exit tunnels and depositing them there. These tunnels are most ventilated by the wind, speeding up evaporation without disturbing the oxygen/CO2 balance in the nest.

Soar and Andréen wanted to show that the exit complex could be used to promote air, heat and moisture flows in architectural design. “When you ventilate a building, you want to maintain the delicate balance of temperature and humidity inside without impeding the movement of stale air out and fresh air in.” said Soar. “Most HVAC systems struggle with this. Here we have a structured interface that allows for the exchange of respiratory gases, driven simply by differences in concentration between one side and the other. The conditions inside remain the same.”