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Heliostat Spreads Light Into Darkest City Corners

posted 12 Mar 2014, 05:21 by Mpelembe   [ updated 12 Mar 2014, 05:21 ]

Architects in SydneyAustralia have found a way to light up a part of the city that was once perpetually dark, hidden from the sun by tall buildings. They've done it by capturing the sunshine, and bouncing it between buildings with an architectural device called a heliostat.

SYDNEY, NSW, AUSTRALIA  (REUTERS) -  As the sun rises over Sydney, Australia, its rays will be captured in a very unusual way. A new building on the skyline features a dramatic horizontal platform which houses a collection of mirrors known as a heliostat. It redirects the light of the sun and channels it to an area of the city that receives no sunshine.

Jason Langer from the Robert Bird Group was the lead structural engineer on the project.

"Generally speaking on projects, you use the sun, you use the sun to actually deliver you your light. This project essentially was the architect saying the sun is not in the right spot for us, so we're going to create a new sun in the sky where we want it," he said.

The heliostat involves an array of mirrors sitting across two buildings in a residential apartment complex known as One Central Park. The sunlight first strikes mirrors on the roof of the lower building, and is reflected upward to the heliostat on the higher building. The light then deflects downward to illuminate a plaza and a new public park in what was formerly an industrial area. It also shines through the glass roof of a building below the heliostat to fill an indoor shopping centre with natural light.

"When we did research on heliostats that had been used on buildings in the past, we found a few that relied on light being reflected once, but nobody had ever tried to reflect light off two buildings into a final space. So this was beyond anything anyone had tried before," said Langer.

While the upper mirrors are fixed, the lower mirrors are all motorised. A computer tracks the position of the sun and continually adjusts the angle that each mirror tilts to keep the sunlight directed at the mirrors above. Tim Phillip's company, Kennovations, designed the mirror arrays.

"This is the largest architectural installation of heliostats anywhere in the world, and it's unique in that we're dispersing sunlight instead of concentrating it," he said.

The One Central Park building was designed by French architect Jean Nouvel. The detailed plans were prepared by Australian firm PTW, and its architect Matt Dobbs.

"So the concept for the light, the heliostat, wasn't for a beam of light to hit the ground. The idea is that it is a dapple light, so if you can imagine walking under a canopy of trees," Dobbs said.

When the sun has gone down, the heliostat's 2800 LED lights come alive to perform a light show in the night sky. It's inspired by reflections on water.

Residents of the building can walk onto the cantilever platform that supports the heliostat. It features a garden area and spa pool, all suspended at a giddying height above the ground. It presented many engineering challenges.

"With normal towers that are built straight up, because you can build one floor above the other. This tower gets to 35 stories up, and then goes the equivalent of 12 stories sideways," said Langer.

The heliostat weighs over 100 tonnes. Supporting it high above the city tested the engineers' abilities. They knew that standard building techniques would not work.

"Once we'd worked out what we needed the structure to do, that's when we had to think to ourselves, how on earth are we going to build this? And that's when we actually decided that bridge construction techniques were the answer," said Langer.

To support the heliostat, the engineers decided to use trusses. Steel frames arranged in triangular patterns to create strength. It's the same technique used to build steel bridges. The trusses can be seen travelling all the way through to the back of the building where they are anchored.

But these symbols of strength are contrasted with things delicate. A vertical garden is beginning to grow, and when it takes hold, most of the buildings walls will be covered in plants.

"It gives what is typically a very masculine tower typology a very soft feel. It just brings this element of green into the city," said Dobbs.

While the former industrial landscape is turning green, this previously dark area of the city will now be bright, thanks to its new sun in the sky.