Eastgate Centre in Harare, Zimbabwe – Best Example of Biomimetic Architecture case study
Most offices and shopping centers around the world look the same- glass facades with steel framework. These designs use an elaborate HVAC arrangement that is expensive to construct and maintain. They keep recycling air, leading to high levels of air pollution within the premises. While this is true everywhere in the world, a country like Zimbabwe encounters additional problems. Problems like import of the system, spare parts, and squandering of foreign exchange reserves. Hence, when asked to design an office in Harare, Mike Pearce, the architect decided to tread the road not taken. Despite being in the tropics, Harare has a temperate climate that oscillates between 10 to 14°C, making it suitable for mechanical or passive cooling systems. The office and shopping complex, therefore, plays away from the average glass fortress and operates at a level of vernacular architecture that responds to its environment.
The mid-rise building has 5,600 m² of retail space, 26,000 m² of office space, and parking for 450 cars. Its style defines “old meets new”, where the traditional stone architecture of Zimbabwe is combined with modern brick and glass construction. It employs the 19th-century modernist technology of lattice steelwork; glass suspension bridges and glass roof, along with localized stone masonry techniques. It is made up of two buildings linked through a glass roof. The atrium in-between is composed of steel bridges and lifts, which are suspended on cables from the steel lattice beams that run across it.
The lifts are associated with a suspended glass skywalk that spans the atrium at level 2. In succession, the middle portion of the skywalk is hitched to the street level by escalators, where the street leads to the city.
Both buildings have a gable roof, with a series of 48 brick chimneys to funnel out the exhaust air from the offices below. There is a mezzanine plant room under the office floors. It is present behind the cross-chevron screen along with 32 low and high-volume fans. Which draws air from the atrium through filters.
SHADING STRATEGIES in Eastgate Centre
After computer simulation and analysis, the engineering firm Ove Arup gave Pearce a set of rules. One of the major requirements was to provide shading against direct sunlight. Additionally, the windows needed to be sealed to protect against noise pollution and unpredictable wind pressures and temperatures. They needed to act as light and noise filters, control glare, and offer security to the tenants. Pearce came up with a comprehensive solution to solve them, all the while permitting the low winter sun rays to mellow the insides.
The windows are furnished with adjustable binds and deep precast concrete overhangs to regulate sunlight in the interiors. The protruding stone elements (overhangs) also increase the external surface area for increased heat loss at night and minimize heat gain during the daytime. The precast concrete is cleaned to expose the granite aggregate underneath to match the lichen-covered rocks of the wild landscape of the region. The horizontal projecting ledges that interrupts by steel columns that support green vines.
WHY IS PASSIVE COOLING BEFITTING OF AFRICA?
In a hot country like Zimbabwe, cooling a building using artificial means is costly and impractical. Moreover, the termites of Africa are the supposed masterminds behind the passive cooling strategies we use today. The tall mounds include conducts which release air from the top and sides. While the mound itself is a design to capture the breeze. As the wind blows, hot air from the dominant chambers underground is carried out of the edifice, supported by termites modulating the tunnels to control airflow. Ergo, it is only appropriate to use the knowledge gained from the termites to the benefit of humans.
PASSIVE COOLING POLICY in Eastgate Centre
It is a perfect example of biomimicry in architecture where the passive cooling system has been inspired by the ‘self-cooling termite mounds’ found in the continent. Simply put, “Passive cooling works by storing heat in the day and discharging it throughout the night”.
At the beginning of the day, the temperature of the building remains cool. As the day proceeds, the fabric of the building absorbs the heat generated from the sun, machines, and people. The temperature inside does not rise significantly as the materials have a high heat capacity. As the temperature begins to drop outside, the warm internal air rises and is let out through chimneys on the roof by means of fans. As a result, cool air is brought via the bottom of the building. This activity extends throughout the night until an ideal temperature reaches.
CHALLENGE AHEAD for Best Example of Biomimetic Architecture
The system, though imperfect is continuously monitoring and refining by a logger set up. They have identified two areas of improvement namely-
- Firstly, Fresh control systems that take advantage of the uncertain air temperatures prevailing outside.
- Secondly, Promote further research into the designing of concrete floor slabs that optimize heat transfer.
“This was an attempt to design a building based on the metaphor of a living system more like a termitary. An ecosystem, not a machine for living in”.Mike Pearce
The chart above demonstrates that the Eastergate Centre consumes less than 50% of the energy used in regular air-conditioned buildings. Further, the control system in the building has deducted that Eastgate uses 35% less energy than the average consumption of six regular complexes in the area. Numbers aside, Eastgate’s true success is its ability to continue operations even when other buildings couldn’t due to reasons such as power shut down or poor maintenance of HVAC systems. The naturally cooled building provides comfortable internal environs for about 52 weeks a year. Such passive cooling through natural convection systems has enabled a 10% ($3.5million) saving of the total cost of the building. This, in turn, leads to 20% lower rents than the surrounding buildings. Therefore, Eastgate Centre in Harare, Zimbabwe – Best Example of Biomimetic Architecture is better for both the mother earth and the people in it.