Tribute to the termites

The Eastgate complex in central Harare owes its unique design to termites

The Eastgate building in central Harare uses the same heating and cooling principles as the termite mound (see the diagram). Inside the termite mound, insects farm fungus for consumption. This fungus must be kept at an optimum temperature. By carefully adjusted convection currents air is sucked in at the lower part of the mound, down into enclosures with muddy walls and up through a channel to the peak of the termite mound. The termites constantly dig new vents and plug old ones to regulate the temperature. So, if the air from outside the termite mound is warmer it should warm up the inside of the termite mound. On the other hand if the air is cooler it cools the termite mound. That way, the fungus in the mound should be kept at an optimum temperature and the insects in the mound will not starve.

The Eastgate complex has a ventilation system which operates in a similar way. This is made possible by the fact that the building is largely made up of concrete. Air drawn from outside is either warmed or cooled by the building mass depending on which is hotter, the building concrete mass or the air. It is then vented into the offices to regulate the temperature there before leaving the building through chimneys at the top. The complex consists of two buildings side by side that are separated by an open space which is covered by glass and open to the breezes. Air is drawn from the open space by fans on the first floor. It is pushed up vertical supply sections of ducts that are located in the central spine of each building. At each floor level it enters a horizontal duct which lies between the ceiling concrete slab of one office and the floor slab of the office above. When the air leaves the horizontal ducts it enters the office above through low level grilles. This fresh air replaces stale air which rises and exits through exhaust ports in the ceiling. It then enters the exhaust section of the vertical ducts before it is flushed out of the building through the chimneys.

Where does Mathematics come in?

Studies have shown that the ventilation system does most work in the horizontal ducts that are sandwiched by floor and ceiling slabs. These are referred to as ventilated floor slabs. If the system has to be controlled in such a way that people in the building do not complain (for example, about very hot offices in October), then the engineers should be able to predict temperatures in the ventilated floor slabs. This is where we consult Mathematics, the Queen of the Sciences. The journey does not end there. Mathematics can also predict the best input parameters, like fan speed to use so that people in the building live comfortably.

The heat transfer in the ventilated floor slab is governed by a system of coupled partial differential equations with the appropriate boundary and initial conditions. The system is driven by an input temperature obtained from measured data, hence a solution is obtained by numerical techniques - for example, using the finite element method. On optimizing design and operational parameters, the theory of genetic algorithms and artificial neural networks can be consulted. This is part of my doctoral studies in mathematical modelling in the Department of Mathematics at the University of Zimbabwe.

Last words

Engineers and architects who designed and built the building, lawyers, sales people, and everyone else working in the Eastgate complex, owe it to Mother Nature. Eastgate is a classic example of ``putting nature into technology."

- Gerald Marewo.

File translated from TEX by TTH, version 2.78.
On 17 Jul 2001, 09:14.