Look to the Termites
Back in 1992, a designer’s biggest challenge was figuring out how to optimise Zimbabwe’s 10°C diurnal swing on either side of comfort level (say 20°C in a mid-altitude (1400 Mts ASL), subtropical climate) to eliminate the need for refrigerant cooling systems and associated costs and energy consumption.
It was one evening during this time when I saw David Attenborough’s BBC Life series showcase the inside of a termite nest in Nigeria. I was greatly moved by the thought that these animals (which are even more sensitive to environmental conditions in the spaces they occupy than humans) were able to make an architecture that performed in such extreme climates without a power connection to the mains for either water or electricity.
Termites are so sensitive to temperature and humidity that when they move outside on the surface of the ground, they have to make tunnels of mud and spit to move in. They do this by arching, which follows the column of pheromone gas that runs in the path they must follow. This tunnel presumably ensures they are protected from direct sunlight and humidity is maintained at the optimum level for their survival.
The mounds, which rise up above ground atop their nests, are breathing devices. They do not live in these mounds: they live in the ground below. The mounds are built from the excavated material produced from forming the voids. Some of the mounds are open at the top and look like chimneys (if you put your hand over the opening, you can feel hot air coming out!). Others (different species) are closed, and breathing occurs through the surface membrane of the mound by gas diffusion.
Simply put, the mounds are lungs, and what lies below is the body with a stomach where fungi digests food (biomass material) through symbiotic processes just like bacteria does the same in our stomachs. So, what we are looking at is a body (about the size of a goat) with one million termites transferring the energy like blood circulating in veins. It is a complex living system. Scott Turner describes this in physiological terms in his book by explaining the house they live in is an extension to the organism, and he applies this theme to many other examples of animal architecture.
In 1992, I was trying to make human architecture, but without the benefit of Scott’s insights. Recently, however, during a long conference call between Scott Turner, Rupert Soar, and myself, Scott said, ‘It was only when I began to see the thing as a process like an earth fountain and not an object that I began to understand how it worked. It is all physiology.’ This was also a turning point for me about 15 years later. We should try to see things in nature not as objects frozen in time and copy their form, but as processes and systems.
So going back to Harare in the early 1990s, I saw the open-at-the-top termite mounds, and I thought and read that they worked rather like chimneys. Stack effect driven by temperature differentials particularly at night when the nest temperature below ground remains more or less the same as ground temperature due to the thermal mass of the soil, while the air and surface temperatures dropped dramatically due to back radiation to space at night. The bigger the differential the greater the buoyancy and the faster the air exchange. Exhaust hot CO2 rich air is replaced by colder O2 rich air. The hot air goes up the flute and the cold air enters through smaller ports at the bottom of the mound. But Scott and Rupert have since proved this to be incorrect. It is much more complicated — see Scott’s books. Their studies were with the closed type and the process is similar to the mammalian lung gas diffusion through membranes.
That said, the important thing for me was, and still is, that looking at animal architecture holds important clues for creating buildings that follow nature’s processes, cycles, and systems. This is particularly true at a time when we must reduce energy and water consumption. Therefore, by copying the termite we were inspired to design a building that responds to the climate and can function with very little added power. We began to call this ‘designing for solar-powered passive systems’ (chimneys), and added power active systems electric powered fans. The trick here is to coordinate the weather outside the building with the controlled internal environment, taking lag times into account. Almost like tuning an organ in a church. And so Eastgate Centre — a mixed-use office and shopping complex — was born in Harare, Zimbabwe.
Sustainable architecture must satisfy the needs of present users without diminishing the prospects of future generations. It must also be embedded in its natural and social environment. Eastgate is an expression of two architectures: the new order of brick and reconstructed stone and the old order of steel and glass. The new order moves away from the international glamour of the pristine glass tower archetype towards a regionalised style that responds to the biosphere, to the ancient traditional stone architecture of Great Zimbabwe, and to local human resources.
In the new order, massive protruding, hooded stone elements not only protect the small windows from the sun, but also increase the external surface area of the building to improve heat loss to space at night and minimise heat gain by day. These are made of precast concrete, brushed to expose the granite aggregate that matches the lichen-covered rocks in Zimbabwe’s wild landscape. The horizontal protruding ledges are interrupted by columns of steel rings supporting green vines to bring nature back into the city.
The old order comprises the lattice steel work, the hanging lift cars, the glass and steel suspension bridges, and the glass roof. It is the architectural expression of the technology brought to Zimbabwe by the mineral-hungry settlers in the late nineteenth century.
With a bio-inspired passive heating and cooling system modelled after the termite mound, the building’s architectural expression can be likened to a prickly desert cactus. A bristled form will shield itself more efficiently in direct sunlight and disperse heat more efficiently at night during multidirectional back radiation. Similarly, Eastgate’s form copies a natural process, where the diurnal shift of 10 degrees is exploited to disperse excessive solar heat. Furthermore, variations in wall thickness, light coloured paints, external shading, a specially designed basement, and a labyrinth of circulation pipes and ventilation chimneys regulate the interior temperature.
Along the ridge of the red-tiled roof are 48 brick funnels topping internal stacks, which pull the exhaust air out of the seven floors of offices below. Under the office floors is a mezzanine plant room behind the cross chevron screen where 32 banks of low and high-volume fans draw air from the atrium through filters. This air is pushed up through the supply section of vertical ducts in the central spine core of each office wing. From the duct the air is fed through the hollow floors to low level grilles under the windows. As it is warmed by human activity, it rises to the vaulted ceiling where it is sucked out via the exhaust ports at the end of each vault through a system of masonry ducts to the exhaust sections of the central vertical stacks. In the office space, uplighters use the concrete vaulted ceiling to reflect light downwards and to absorb their heat.
The sandwich of the vaulted ceiling and the voided floor above acts as a heat exchanger. The cold night air passing through the void festooned with concrete teeth removes the heat of the previous day, and on the following day warm external air is cooled about 3°C by the same teeth before entering the room. Normally the high-volume fans run at night to give ten air changes per hour, and low volume fans run during the day, giving two air changes per hour. By timing the changeover from low to high air velocities, the optimum use of the diurnal swing of the biosphere can be utilised.
The engineers, Ove Arup & Partners, installed a data logger which continuously records air temperature at five critical positions.
Eastgate uses 35% less total energy than the average consumption of six other conventional buildings with full HVAC in Harare. The saving on capital cost compared with full HVAC was 10% of total building cost. During the frequent shut downs of mains power, or of HVAC due to poor maintenance in the other buildings, Eastgate continues to operate within acceptable comfort levels with its system running by natural convection.
There are countless other outstanding structural traits of termite mounds that can be utilised through biomimicry for the human race. With the help of these small insects, we could build taller sturdier and even more efficient buildings using designs already in place in nature.