California Academy of Sciences
Verdant Laboratory: A multi-faceted institution sheltered by an undulating green roof takes a holistic approach to sustainable design
Sustainable buildings don’t always look green, but the California Academy of Sciences, in San Francisco’s Golden Gate Park, is one that does. Covering the 400,000-square-foot building, which replaces a complex damaged beyond repair by the 1989 Loma Prieta earthquake, is an undulating 2.5-acre living roof dotted with porthole-like skylights. This rolling landscape was conceived as a swath cut from the park and elevated 36 feet to the height of the old buildings, according to Renzo Piano, the Genoa, Italy-based architect of the academy’s new home.
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The green roof—designed to reduce stormwater runoff, provide insulation, and create habitat for birds and insects—is the most conspicuous manifestation of the academy’s mission “to explore, explain, and protect the natural world.” Or, as Greg Farrington, the museum and research institution’s executive director explains, the academy’s activities are focused on pressing questions such as “How did we get here?” and “How we are going to stay?”
However, the rolly polly planted roof is just one of a whole array of coordinated strategies that helped the $488-million building earn Platinum LEED certification soon after its opening in late September. For example, contractors recycled 90 percent of demolition debris from the old academy; much of the new building, including open office areas and the main exhibition space, is naturally ventilated; almost all of its public spaces have access to daylight and views; and, the structure is surrounded by a glass-and-steel trellis that incorporates 60,000 photovoltaic (PV) cells, expected to generate 220 kWh of electricity annually.
According to data provided by the project team and interpreted by GreenSource, the new building will use 12 percent less energy than one designed to comply with ASHRAE 90.1-1999. The number is lower than the roughly 30 percent savings shown in the project’s LEED documentation partly because it is based on projected energy use rather than on energy cost. But more significantly, it assumes no savings in plug and process loads. Such loads are significant at the Academy, where energy-intensive equipment is required to support features like an aquarium, a planetarium, a man-made rain forest, and research laboratories, and to maintain the temperature and humidity levels necessary for preserving a vast collection of scientific specimens.
This programmatic complexity is packed into an envelope that (except for its bulbous roof) is remarkably straightforward. The building’s main floor plan is a simple rectangle, defined by four poured-in-place concrete structures at each corner. One contains the gift shop and café, two are devoted to research and administrative areas, and one houses a recreated exhibit from the original building devoted to Africa’s ecosystem.
Separating the individual shoe-box-like structures is floor-to-ceiling low-iron glazing that opens the building to the park and a 36,000-square-foot cruciform-shaped exhibition area. The space has a central skylit and largely open-to-the-air “piazza” flanked by two 90-foot-diameter steel-framed spheres. One sphere is glass-clad and encloses a multi-level rain-forest exhibit, while the other is aluminum-clad and houses the planetarium.
These domed elements are responsible for the roof’s primary protrusions: They “push” the height of exhibition hall from 36 feet at its lowest point to 70 feet as the steel structure and the living roof above rise to accommodate them. The aquarium occupies the level below, with large open tanks extending up to the main floor and defining the edges of the piazza.
The planetarium and rain forest each deploy their own climate control strategies. The planetarium relies on displacement ventilation, with cool air supplied through floor grilles. The system is quieter than those that provide forced air from above and is more efficient since it conditions only the occupied space rather than the planetarium’s entire volume, explains Kang Kiang, AIA, a senior associate with Mark Cavagnero Associates and formerly project manager for the academy’s executive architect, Stantec (originally Gordon Chong Partners Architecture).
The environment inside the rain forest is kept appropriately warm and humid. Light necessary for the tropical plants to grow is provided through the circular skylights and by supplemental electrical lighting. Misting ensures that temperatures do not rise above the design criteria of 79 to 84 degrees with 50 to 70 percent humidity, and a stream of high-velocity air prevents condensation from forming on the inner pane of its terrarium-like enclosure.
For the open exhibit hall surrounding the spheres, engineers took advantage of San Francisco’s mild climate, developing a natural ventilation scheme. Fresh air enters the exhibit hall through high and low level openings in the glazed facades, and warm air is vented, via the stack effect, through the porthole-shaped operable skylights on the roof. But ensuring that air would evenly penetrate, without creating dead zones or overly breezy spots, was no easy feat, because of the hall’s plus-sign-shaped plan, the undulating roof, and the two spherical obstructions.
“The unusual shape meant we couldn’t rely on rules of thumb to develop the natural ventilation scheme,” says Karl Lyndon, project mechanical engineer and an associate director in the London office of Arup. The San Francisco office, where Lyndon was previously based, provided multiple services on the project, including LEED consulting and mechanical and structural engineering.
In order to better understand how to naturally ventilate the exhibit hall, engineers analyzed the space using computational fluid dynamics (CFD) starting with schematic design. They refined these analyses as the design progressed and validated the results against the performance of physical scale models that they subjected to wind tunnel tests. Sensors measured factors such as pressure on the facades, wind speed, and direction.
The tests not only focused on visitors’ thermal comfort, but also on ensuring that indoor air was free of contaminants. For example, one study helped the design team optimally locate exhaust from boilers and mechanically ventilated spaces to keep foul air out of the path of exhibit hall vents and a rooftop observation deck. A particular concern was the placement of the roof stack from the penguin exhibit. “Penguins have bad body odor,” says Lyndon.
Ultimately the design team used the data garnered from the CFD analysis and wind tunnel tests to create a control sequence for the building automation system (BAS). The BAS, which monitors interior conditions through a series of sensors, and exterior conditions via a roof-mounted weather station, directs operation of the windows and roof vents, and other building systems, such as a radiant floor that provides supplemental heating and cooling, external roller blinds for sun shading, and daylight dimming.
Designers emphasize that these systems are tightly integrated with each other. “The academy’s natural ventilation can’t be thought about in isolation,” says Kiang. Other features, like the geometry of the living roof, and the insulation it provides, also help make natural ventilation a viable interior climate control strategy, he points out.
The roof provides other performance benefits as well, including absorbing almost all of the rainwater that falls on it. On the rare occasions when the its saturation point is exceeded, runoff drains into an underground recharge chamber and slowly percolates into the surrounding soil, explains Larry Reed, a principal in the Sausalito, California office of SWA, the project’s landscape architect. Reed estimates that annually only two percent of the runoff will reach San Francisco’s often overloaded combined sewer and stormwater system.
SWA worked with the museum’s own botanists and ecologist Paul Kephart of Carmel Valley, California-based Rana Creek Living Architecture to select the roof’s plant material. They evaluated species on the basis of their capacity to attract birds and pollinating insects, and for their ability to thrive in shallow soil and bluff-like conditions. The group eventually settled on a scheme of sedum, self-heal, sea thrift, and beach strawberry.
Because Piano wanted an alternative to the typical plastic trays used in most modular green roof systems, Kephart developed the BioTray, a 17-inch-square biodegradable container for growing medium and plants made of natural latex and coconut coir—a rapidly renewable product derived from coconut husks.
The 50,000 trays arrived at the site pre-planted and were installed on the roof within a 24-foot grid of gabions. The rock-filled cages prevent the trays from sliding down the roof’s hills and provide an infrastructure for drainage and irrigation, as well as a walkway for maintenance workers, says Reed.
Such innovative solutions for the roof, and the building as a whole, would not have been possible without the involvement of a mutli-disciplinary team starting with the earliest design phases. “This project embraced the concept of integrated delivery long before the term was a buzz word, ” says Matt Rossi, project director for general contractor Webcor Builders, San Mateo, California.Sometimes as many as 25 people, including the owner’s representatives, the architects, the contractor, and consultants were in the same room trying to resolve questions surrounding constructability, budget, and schedule, according to Jean Rogers, an Arup environmental engineer and principal. “The burden of solving such problems fell to the whole team.”
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