The Eastgate Centre is a shopping centre and office block in central Harare, Zimbabwe, designed by Mick Pearce. Designed to be ventilated and cooled by entirely natural means, it was probably the first building in the world to use natural cooling to this level of sophistication. It opened in 1996 on Robert Mugabe Avenue and Second Street, and provides 5,600 m² of retail space, 26,000 m² of office space and parking for 450 cars.
The Eastgate Centre’s design is a deliberate move away from the “big glass block”. Glass office blocks are typically expensive to maintain at a comfortable temperature, needing substantial heating in the winter and cooling in the summer. They tend to recycle air, in an attempt to keep the expensively conditioned atmosphere inside, leading to high levels of air pollution in the building. Artificial air-conditioning systems are high-maintenance, and Zimbabwe has the additional problem that the original system and most spare parts have to be imported, squandering foreign exchange reserves.
Mick Pearce, the architect, therefore took an alternative approach. Because of its altitude, Harare has a temperate climate despite being in the tropics, and the typical daily temperature swing is 10 to 14°C. This makes a mechanical or passive cooling system a viable alternative to artificial air-conditioning. Passive cooling works by storing heat in the day and venting it at night as temperatures drop.
Start of day: the building is cool.
During day: machines and people generate heat, and the sun shines. Heat is absorbed by the fabric of the building, which has a high heat capacity, so that the temperature inside increases but not greatly.
Evening: temperatures outside drop. The warm internal air is vented through chimneys, assisted by fans but also rising naturally because it is less dense, and drawing in denser cool air at the bottom of the building.
Night: this process continues, cold air flowing through cavities in the floor slabs until the building’s fabric has reached the ideal temperature to start the next day.
Passively cooled, Eastgate uses only 10% of the energy needed by a similar conventionally cooled building. When actively cooled, the Centre consumes 35% less energy to maintain the same temperature as a conventionally cooled building.
Eastgate is emulated by London’s Portcullis House (2001), opposite the Palace of Westminster. The distinctive giant chimneys on which the system relies are clearly visible.
