Eastgate Centre

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.

These five images were taken of the same termite breathing tower to show how the form changes in real time responding to external threats and seasons.

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.

Architecture of Heatflow

Membrane Air Mixing Process

The and as a heat

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.

The western façade louvres close in a Mexican wave pattern. These panels were made from recycled Australian hardwood timber cut from structural beams and columns from old wool processing sheds. The vertical slats are bolted onto galvanised steel frames, which turn via hydraulic rams powered by solar PV panels.

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.

Melbourne City Council House 2 (CH2)

I was the principal design architect for Melbourne City Council House 2 — which is even more efficient and economical than Eastgate. At 12,500 m², it consumes 80% less energy and 70% less water than the average building its size.

Similar to the termite biomimicry principles employed at Eastgate, CH2 effectively uses natural convection, ventilation stacks, thermal mass, phase change material, and water for cooling. Another strategy taken from nature is the skin system on the façade.