Cooling without air conditioning: the termite mound myth

Can a building really cool itself without air conditioning? Yes, to our mind, and with no technical feat: through a plan the air can cross from side to side, and a mass you discharge at night so it soaks up the day’s heat. That is the real engine. And to understand it, let us take one of biomimicry’s most famous examples, the termite mound, and see what is genuinely interesting about it, and what belongs to myth.

A mound of the genus Macrotermes in southern Africa, or Odontotermes obesus in India, does not hold its nest at a steady temperature like a thermostat. It exchanges gases: it flushes out the carbon dioxide of millions of workers and their fungus, and draws in oxygen. Its engine is not a metabolic chimney but the swing of heat between day and night, and the wind pushing air out. Work by Hunter King, Samuel Ocko and Lakshminarayanan Mahadevan at Harvard showed this in 2015; the physiologist J. Scott Turner had sensed it before them. The mound does not cool. It breathes.

So where does the legend come from? From a fine building: the Eastgate Centre in Harare, Zimbabwe, designed by the architect Mick Pearce with the engineers of Ove Arup and completed in 1996. It is said everywhere to copy the termite mound. In truth it owes its comfort to a sound engineering principle far older than biomimicry: heavy thermal mass cooled at night by a sweep of air, with fans to help. Its designers and the press have claimed it uses a small fraction of the energy of a comparable air-conditioned block; the building makes that claim, but, to our knowledge, no independent measurement has confirmed it, and the distinction matters. Eastgate is a good building. Its origin story is a false legend, but a legend that inspires innovative architecture.

What travels from one climate to another, then, is not the exotic object but the physics. Three levers, all as old as shelter itself. Cross-ventilation: two opposite façades that open, and the air sweeps the volume instead of stagnating. Stack effect: warm air, being lighter, rises and escapes high up, as in a chimney. And night cooling, the most effective under our climates: you open wide at night to chill the heavy walls and floors, which then soak up the day’s heat. In a temperate climate, with heavy construction and a good night sweep, studies put the peak gain at 3.6 to 4.3°C during a heatwave. That is real, and it is honest to state its limits too: in a city centre that stays warm after dark, on nights that are already tropical, the method runs out of breath, and it will not do everything in the summers ahead.

The rest belongs to its place, and does not transplant. The badgir, the wind tower of Yazd in Iran, assumes a desert: very dry air, a wide gap between day and night, a steady wind, and often a coupling to the cool water of underground cisterns. None of that under our humid skies (and water is precisely the subject of the companion article). The mashrabiya, for its part, does ventilate a little, but its real strength lies elsewhere: it is a light filter, a shade machine. To copy the tower or the screen for its silhouette would be to keep the folklore and forget the lesson. The lesson is the physics of moving air.

In practice, here, it comes down to three moves, from the safest to the most committing. First, from the very first sketch, seek a through-plan, so no room is blind on a single side: in a house this is often a matter of drawing; in collective housing it has to be negotiated, as the building’s depth and the layout of the units come into play, and it is precisely at sketch stage that this negotiation is won. Then provide high and low operable openings over a mass left accessible to the air, to discharge it at night: low-tech, robust, nothing to unplug. Lastly, if the project deserves it, a draught chimney on the roof, the badgir reimagined as an extract duct, to be sized with an engineer. Nothing revolutionary in any of that, and so much the better: French regulation now values summer comfort, and these moves do not break down and add nothing to the energy bill. One question remains, the only one that counts on site: before ordering air conditioning, what if we first looked at how the air wants to cross the house?