Eastgate Centre, Harare

The pink-hued Eastgate Centre, with its distinctive chimneys

Schematic of the natural ventilation of the building

Passively cooled buildings, inspired by the remarkable climate control mechanisms of termite mounds, represent a groundbreaking concept in architectural design. This innovative approach to climate control has the potential to revolutionize energy-efficient and sustainable building solutions.

Applications

The principles of passively cooled buildings are applicable to various structures, including commercial and residential buildings.

UN Sustainable Development Goals Addressed

This concept aligns with Goal 11: Sustainable Cities & Communities by promoting sustainable urban development and more energy-efficient building solutions.

The challenge

Many regions require year-round cooling for buildings, resulting in substantial expenses for traditional air-conditioning systems. The challenge was to develop self-regulating ventilation systems that maintain comfortable indoor temperatures while reducing both immediate and long-term costs.

Innovation Details

Passively cooled buildings rely on innovative architectural and design strategies that eliminate the need for traditional fuel-based air conditioning. These structures employ construction materials with high thermal capacity, enabling them to store and release heat from the surrounding environment. Fans and natural ventilation cycles help enhance heat storage during the day and heat release at night. Internal heat generated by occupants and appliances facilitates airflow within the building, reducing temperature fluctuations. Openings throughout the building promote passive internal airflow driven by outside winds. These design features not only maintain a stable internal climate but also result in cost savings by eliminating the need for conventional air-conditioning systems, leading to reduced energy costs and more affordable rents.

Biological Model

Inspired by the remarkable climate control abilities of termite mounds, passively cooled buildings aimed to replicate the stable internal climates found within these natural structures. Although subsequent research altered our understanding of termite mounds' function, the concept of passively cooled buildings continues to harness cost-effective and energy-efficient mechanisms for internal climate control, inspired by the ingenuity of nature.

This innovative architectural concept represents a sustainable and energy-efficient approach to building design, reducing the environmental impact and operational costs associated with traditional climate control systems. The inspiration drawn from nature's remarkable structures has the potential to transform the way we design and construct buildings to create more sustainable and comfortable environments.

Passive cooling

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.

Modern use of traditional solutions

To work well, the building must be very carefully designed. After computer simulation and analysis, the engineering firm Ove Arup, gave Pearce a set of rules.

They said that no direct sunlight must fall on the external walls at all and the north façade [direction of summer sun] window-to-wall area must not exceed 25%. They asked for a balance between artificial and external light to minimise energy consumption and heat gain. They said all windows must be sealed because of noise pollution and unpredictable wind pressures and temperatures, relying on ducted ventilation. Above all, windows must be light filters, controlling glare, noise and security.

To help with this last, the windows have adjustable blinds, but Pearce also used deep overhangs to keep direct sun off windows and walls. Deep eaves are a traditional solution in Africa, shading the walls completely from the high summer sun, while allowing the lower winter sun to warm the building in the morning.

Further, passive cooling systems are particularly appropriate for this part of Africa because, long before humans thought of it, passive cooling was being used by the local termites. Termite mounds include flues which vent through the top and sides, and the mound itself is designed to catch the breeze. As the wind blows, hot air from the main chambers below ground is drawn out of the structure, helped by termites opening or blocking tunnels to control air flow.

Example: Eastgate Centre in Zimbabwe

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.

See also

• Biomimetics
• Energy conservation
• Passive solar
• Solar chimney
• Architecture of Africa

Sources

• Fu, S. & Zhong, Xiaoling & Zhang, Y. & Lai, Tsz Wai & Chan, Oscar K.C. & Lee, K.Y. & Chao, Christopher. (2020). Bio-inspired cooling technologies and the applications in buildings. Energy and Buildings. 225. 110313. 10.1016/j.enbuild.2020.110313.
• Abdullah, Amatalraof & Said, Ismail & Ossen, Dilshan. (2018). Cooling strategies in the biological systems and termite mound: The potential of emulating them to sustainable architecture and bionic engineering. Journal of Engineering and Applied Sciences. 13. 8127-8141.
• Turner, Scott. (2008). Beyond biomimicry: What termites can tell us about realizing the living building. Proceedings of 1st International Conference on Industrialized, Intelligent Construction.
• Baird, George (2001). The Architectural Expression of Environmental Control Systems. Spon Press. ISBN 0-419-24430-1
• Gissen, David (2003). "Big and Green: Toward Sustainable Architecture in the 21st Century. Princeton Architectural Press. ISBN 1-56898-361-1