Down Under, A Highly Sustainable High-Rise

Down Under, A Highly Sustainable High-Rise

Double-wall façade is first for an Australian high-rise, providing optimum daylight and solar control, and is twice as efficient as standard best practice facades. Photo courtesy of H.H. Esch, Hennef.

1 Bligh Street, a new 27-story high-rise office building in Sydney, Australia, is a striking addition to the city’s skyline. It stands out against most other structures because they are sheathed in dark, reflective glass that has all the transparency of Darth Vader’s mask. In contrast, this tower’s crystalline, low-iron glass façade is practically clear.

What the average observer doesn’t see are the innovations that put 1 Bligh in the forefront of a new era of smarter buildings, highlighted by its elliptical form, dual glass skin, and best-available technology that reduces its reliance on artificial lighting and mechanical cooling and heating.

Dexus Property Group, Sydney, the building’s developer and one of its owners, asked Ingenhoven Architects, Dusseldorf, Germany, and Architectus, a Sydney-based Australian architecture firm, to design 1 Bligh to Australia’s highest environmental standards. These firms were assisted by Arup’s Sydney office, which designed the complex double-wall façade that protects the building, as well as engineering its mechanical, electrical, and fire-protection systems.

Tony Gulliver, head of development for Dexus says his company feels the effort to make the building a resource-conserving one will pay dividends. Its prime location in the center of the main business district already commands high prices. But tenants demand cutting-edge design and technology to justify paying high-cost leases. Gulliver is betting 1 Bligh's combination of design and systems technology will sustain demand for many years. “We will hold this building in our portfolio for decades,” he says. 

Extensive fluid dynamic modeling proved ventilation scheme, which maximized inlet and outlet air flow by floor.

Extensive computational fluid dynamics modeling proved ventilation scheme, which maximized inlet and outlet air flow by floor.

Beyond Green

In Australia, buildings are evaluated using National Australian Built Environment Rating System (NABORS). It is similar to the U.S. Green Building Council’s LEED rating system. The owners’ commitment and designers’ success can be measured by the fact that the building received the first six-star NABORS rating ever given.

The building features a full-height, naturally ventilated atrium, and a hybrid natural gas-fueled tri-generation plant for combined heat, cooling, and power. The office spaces are conditioned using chilled beams at the building’s perimeter zone, and a variable-air volume system in the interior. There are a little over 1,600 sq m of leasable office space per floor.

In addition, a state-of-the-art treatment plant processes black water harvested from Sydney’s sewers. Every day the system provides 90,000 liters of nonpotable water for cooling towers and toilet flushing.

Louvers are fitted to each floor, allowing air to enter between twin layers of glass and blind.

Louvers are fitted to each floor slab, allowing air to ventilate the cavity between twin layers of glass.

The building's floor plans are oval, with the long axis running southwest to northeast. This orientation places the office spaces on the northwest, and gives the upper floors spectacular views of Sydney Harbor. The concrete floor slabs are cantilevered up to 6 meters so that columns don’t interrupt either the view or the seamless appearance of the façade from the outside.

Northern Exposure

However, this orientation also leaves office windows exposed to the sun on the north, northwest, and west. The architects and engineers used a mechanically shaded, passively ventilated, double-wall façade to alleviate much of the solar load.

The double-wall façade starts on the building’s second floor and runs to the bottom of the 27th floor, broken only by louvers fastened at the edge of each floor slab (the 27th floor is a roof terrace, used for special occasions). The floor-to-floor height is 3,850 mm.

The façade has inner and outer glass units about 600 mm apart. The outer glass is a single sheet whose primary purpose is to protect the automatic, mechanically operated venetian blinds from the wind. The building management system tracks the sun and raises and lowers the blinds as needed. That system is overridden when high winds or cloudy conditions are detected.

Atrium is naturally ventilated, with air entering from ground levels moving up and out.

Atrium is naturally ventilated, with air entering from ground levels moving up and out.

The blinds, in turn, hang immediately in front of the inner, insulated high-performance double-glazed unit (DGU). According to Arup façade engineer Kerryn Coker, “When the sun shades are lowered, the overall facade system achieves a shading coefficient (SC) of 0.15. The inner DGU’s SC without the shades is 0.32.”

The visible light transmission (VLT) of the inner double-glazed unit is 60%. The VLTs of windows in Sydney’s Darth Vader-like commercial buildings are typically much lower, only 35-40%.

Although the blinds block most of the visible sunlight striking the DGUs, without some form of ventilation, heat would still build up inside the façade cavity. To prevent this, louvers break the facade at each floor slab. They allow exterior air to enter at the bottom of each cavity, and vent it out the top.

The multifinned airfoil-shaped louvers were computer-modeled using computational fluid dynamics, then physically mocked up for wind-tunnel tests. This was done to verify light breezes would not disturb the blinds, and that hot air exiting the top of one facade cavity would not be drawn into the cavity above it.

Breezes are nearly always present in downtown Sydney, and air moving around the building improves the louvers’ performance. “The temperature inside the cavity is generally close to the temperature outside the building,” says Coker.

Louvers used in double-wall façades in cold climates are often designed to open and close mechanically, so air heated in the cavities can be drawn into the interior of the building on cold sunny days. Sydney’s climate is mild, however, and the louvers cannot be closed.

The interior of the double-wall facade is accessible in several locations on each floor, so the glass and blinds can be cleaned and serviced. At the present time, the interior glass panels on all 26 floors are fixed. However, if future tenants wish, the interior glass can be retrofitted with hardware that would allow them to be opened so fresh air can enter.

Charles Linn is an independent writer.

A state-of-the-art treatment system processes black water harvested from Sydney’s sewers.


December 2011

by Charles Linn,