In 1991, Old Mutual Properties wished to construct a 55,000 square metres shopping centre in Harare. They reached out to Mick Pearce, a Zimbabwean architect with a unique demand that the centre should use passive and natural cooling methods. They wanted to save the cost of long-term air-conditioning systems along with conserving energy consumption. Pearce and ARUP Engineers collaborated for the Eastgate Centre, the largest commercial building in the nation. Pearce became heavily invested in the project, working manually at the site.
The Termite Model
The termite mounds built using soil, saliva and excretions of termites inspired Pearce. Mounds could be metres high or of varying shapes such as mounds, domes, cones, wedge-shaped or pillar-like.
Martin Luscher, a Swiss entomologist, published an article in Scientific American, 1961 about termite mounds. He proposed that termite mounds act as air conditioners and regulate the environment from top to bottom through a convective flow.
The mounds sustain thousands of termites and fungus, the food for termites. Termites constantly maintain 87 F° for the fungus while the temperature during the day remains at 104 F° and at 35 F° during the night. They control the cooling and heating vents, taking in air from lower sections through the height and dissipating the heat from the top. Pearce worked on concrete and steel using the mounds design.
Bio-mimicry at Eastgate
Built of concrete, the building absorbs heat during daytime and releases it during the night. Fans are installed in the lower floors facilitating cooling, which enters through the base of further floors. The warm air is sucked up by the exhausts from the vaulted ceilings connected to the vertical ducts. There are forty-eight such ducts across seven floors of offices. Pearce classified his design as biomimetic, which regulated the temperature itself.
The complex showcases two types of architectural approaches. The older design is utilised in the glass roof, suspension bridges made up of glass and steel, lattice steel work and hanging lift cars. The newer designs include the large overhangs above windows, reducing the heat that can enter from the windows. It is more of a regional and traditional stone architecture style.
All-round savings
The owners saved $3.5 million from the construction costs as the air conditioning system was not installed in the building structure. The centre utilises less than 10% energy in comparison to the conventional complexes of the same size. Very low energy usage saves more than 90% energy compared to the energy consumption of traditional buildings.
Along with its eco-friendly nature, the centre also saves around 20% rental charges for the tenants of this complex, considering the local market rates. The temperature trends published by ARUP Engineers show that the air inside remains 3°C cooler. Rare events of cloudy nights followed by a cloudy day reduce the heat radiation capacity of the centre, which keeps the inside temperature elevated but still below 26°C.
The twist in the procedure
An American scientist, Scott Turner,r researched the South African termite mounds. He found that the carbon dioxide and oxygen were not exactly regulated, contrary to what was believed earlier. He found the gaseous exchange took place through mixing of air due to external atmospheric pressure. Like the alveoli of human lungs, the air would permeate into the porous surface into the interiors of the mound.
The centre functions smoothly irrespective of the understanding of the mounds. The success can be credited to the convergence of Pearce’s skills, the network of ducts and chimneys, the mound’s permeable surface and the thermal heating mechanism.
The larger significance of biomimicry
Termites, like other small insects, build intricate homes and are born with innate knowledge. They sharpen their skilful behaviour with successive generations, according to John Wenzel, an entomologist at Carnegie Museum of Natural History in Pennsylvania.
Japanese bullet trains move rapidly without any noise as they use aerodynamic shells. The beaks of diving birds were the inspiration for the shells. The swimsuits have a drag-reducing texture similar to sharkskin; this facilitates smooth swimming.
Biomimicry today is more of a human tendency to draw associations with other living beings. 3D printers can improve the biological mimicking, helping preserve natural building designs.
ARUP Engineers also built a self-sufficient greenhouse inthe Sahara Desert, drawing inspiration from a beetle’s exoskeleton, which condenses the humidity from the air into water for survival. After three decades, ARUP’s construction at Eastgate remains a symbol of sustainability and a low carbon footprint.
References:
- IMechE
- Amusement Logic
- Nautilus
- Inhabitat