Technical Envelope PUSHING THE EN

In the drive to reduce buildings’ energy consumption and environmental impact, designers and engineers are jettisoning tried-and-tested facade materials to experiment with innovations inspired by nature. The practice of biomimicry or bioinspiration, whereby designers try to refl ect the structure or function of a biological entity, is centuries old, but only recently has it progressed into adaptive technological systems. Recent cutting edge examples include Bioskin, developed in Japan, whereby water evaporates from the surface of leaves to create a cooling effect. Meanwhile, in Germany, engineers have grown algae inside the walls of a residential block. And in the Netherlands, a cladding made entirely out of plant-based bioresin and hemp fi bre has been designed for a future when oil-based construction materials become diffi cult and expensive to produce. Stephen Cousins reports on a whole new world of “natural” construction.

Tokyo’s pipe dream

THE WORLD’S FIRST evaporative cooling facade, installed on Sony’s 25-storey Osaki Home Entertainment HQ in Tokyo, is proving so effective it is being adapted for use on two new Japanese buildings and other possible projects in Southeast Asia. Bioskin comprises a network of porous

ceramic pipes, similar to horizontal railings, arranged across the east elevation of the Osaki building, through which rain water, collected from the roof, is circulated and which heats up under sunlight. The system was invented by Japanese architectural practice Nikken Sekkei, which collaborated with its in- house engineering team. The water penetrates the ceramic and

evaporates from the pipe surface, cooling the surface of the envelope by up to 12.6o 2-3o

C and the surrounding air by around C. Its main purpose is to reduce

the “heat island” effect, seen in cities like Tokyo, by cooling the environment around the building. It is designed to work

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best in high temperature, high humidity climates, although Nikken Sekkei says the technology could be adapted for other climates. The system is based on the phenomenon of transpiration, whereby water moves through a plant and is evaporated from the leaves, stem and fl owers, as well as the Japanese concept of “Uchimizu” — the sprinkling of water on gardens and streets to lower ambient temperatures and keep dust at bay. “Using this fundamental physical phenomenon as the base, and adding the latest design technology using computer simulations, the Bioskin was born,” explains Tomohiko Yamanashi, principal executive offi cer at architect Nikken Sekkei, who invented the system with three architect colleagues, and developed it in collaboration with an in-house engineering team. “Conventional facade suppliers were unable to manufacture the system because it is based on plumbing and ceramics, so we asked the leading toilet bowl manufacturer, Toto, to realise our

“Conventional suppliers were unable to manufacture the system, so we asked a leading toilet bowl manufacturer to realise our idea.” Tomohiko Yamanashi, Nikken Sekkei

idea,” he adds. This decision proved key as Toto’s

ceramic incorporates photocatalyst technology, developed to keep the surface of toilet bowls clean, and prevents moss and fungi from forming without the need for chemicals. The photocatalyst also breaks down nitrogen oxides in the air, equivalent to the effect of 1,300 poplar trees.

Rainfall collection Rainwater pumped through the Bioskin is taken from a 30-tonne capacity storage tank installed in the building’s basement between footing beams, which is roughly equivalent to 50% of the capacity needed to run the system at full capacity during the summer. Sourcing water isn’t a problem as Japan has some of the highest rainfall in the world, but the system is also designed to be topped up with tap water, which is very cheap in Tokyo, although so far this hasn’t been necessary. The cost of running the system is negligible compared to the Osaki Building’s total energy usage, says

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