Inside Beijing's Big Box of Blue Bubbles

A multidisciplinary design team employed an innovative digital process to produce a surprising, highly integrated envelope-and-structure combination.
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From Architectural Record
Joann Gonchar, AIA

The ETFE cavity wall and roof also provide thermal efficiency. The double skin is designed to capture solar energy to heat the swimming pools and the building and light the interior spaces. The building collects 20 percent of the solar energy that lands on it, equivalent to covering the 340,000-square-foot roof with photovoltaics, according to Arup. The firm estimates that the Water Cube saves 30 percent of the energy typically devoted to lighting and half of the energy that would be required to heat a well-detailed and well-insulated metal-clad box.

The Water Cube relies on the thermal mass provided by the pool water and surrounding concrete to retain heat during the day and release it at night. The double skin allows the venting of excess heat in the summer but permits its containment during the winter, when solar gain is most beneficial. The concept was realized almost unchanged from the design team's original competition entry scheme.

One of the few features of the envelope implemented differently in the built Water Cube is the solar control strategy. The team originally imagined the inner ETFE cladding as an operable and variable surface, providing the facility's managers with the ability to turn shading on or off, depending on the desire to admit sunlight and control glare within the Water Cube's various spaces. But in the end, the designers opted for a fixed aluminized frit pattern that blocks between 10 to 95 percent of visible light. The frit is most dense on areas of building skin that enclose areas where direct sun is least desirable and glare would be most distracting. For example, the roof over the competition pool admits only 5 percent of visible daylight due to strict broadcast-industry lighting-control requirements.

The building's on-site welded space frame consists of 22,000 steel tubes connected at spherical nodes (top). Workers encapsulated the Water Cube's structural frame in 4,000 ETFE pillows, installing up to 30,000 square feet of the material each day (below).

Photo courtesy Vector Foiltec


Though much of the building's heating needs are satisfied through passive means, some spaces within the Water Cube do require mechanical cooling, setting up a challenge for designers. In the competition pool area, "it was tricky to keep the swimmers warm and wet and the spectators cool and dry," says Carfrae. In order to cope with the differing requirements of the building's various types of occupants, the engineers relied on the displacement ventilation principle, supplying cool air through an underseat supply system, conditioning only the zones occupied by spectators.

Software that Arup developed helped designers optimize and size these components (above) and generate a 3D model as well as traditional 2D construction documents (below).

1. Base of space frame
2. Steel plate
3.Steel angle
4.Concrete slab

Drawings courtesy Arup

 

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Originally published in Architectural Record
Originally published in July 2008

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