Project DescriptionIF THINGS GO ACCORDING TO PLAN, it won't be long before Masdar City in Abu Dhabi is the undisputed pacesetter for sustainable design practices. The desert city—with its highly publicized master plan by Foster + Partners of London—broke ground on Feb. 9. Developed by the Masdar Initiative, a government program for “energy security, climate change and truly sustainable human development,” the project boasts a $22 billion budget and the goal of being zero-carbon, zero-waste, and zero-energy.
Near the city center, the Masdar Initiative plans to build itself a headquarters that will be the world's first large-scale, mixed-use, “positive-energy” building. In other words, the 1.5-million-square-foot complex will aim to produce more energy than it consumes. The schematic design emerged from a two-stage international competition conducted at breakneck speed (about six weeks from start to finish) and won by Adrian Smith + Gordon Gill Architecture (AS+GG)—a Chicago architecture firm launched just 19 months ago by seasoned SOM alumni Smith, Gill, and partner Robert Forest.
The project brief laid out square footage requirements, a mix of office and residential uses, and an ambitious sustainability mandate. Beyond that, the competitors were given a height limitation of eight stories, an outline of infrastructure and mass transit concepts, and a site plan indicating where surrounding open space is planned. Gill maintains that the headquarters will change the way buildings are designed, constructed, and inhabited. “Philosophically,” he says, “we are seeking to absorb the environment and use it to its best advantage.”
ELEVEN TOWERING, glass-enclosed wind cones perform many critical functions. At the top, they provide the structural support for the building's curvilinear roof. At the ground plane, they delineate courtyards that serve as entrances, orientation points, and giant intakes to bring ground-source cool air into the building. In between, they siphon warm air up and out of the building and allow diffused daylight from the rooftop into the office floors below.
To aid pedestrian movement, the cones are placed at strategic locations connecting with paths penetrating the site. Some cones serve as entries or gardens on the grand plaza to the west. Others are cut into the building, forming negative space on the east façade. Interior courtyards vary— some are landscaped, some have water features, others have suspended artwork or pedestrian bridges overhead. “We want to make each one memorable, to not be confusing or disorienting as one moves through,” says Gill. The overall layout is regularized to move people efficiently through the building.
While the exact number of cones may vary in the final design, the choice of 11 during the competition phase was based on pragmatic concerns, such as spacing, structure, and projected volume of air movement. The geometry resembles that of a nuclear plant cooling tower, promoting wind movement while preventing sunlight from shining directly on the interior glass surfaces below the narrow neck of the cone. Cones are organized in the core to optimize the penetration of diffused daylight into the office interiors. Workers adjacent to a cone will enjoy views into the courtyard, and operable windows would allow for cross-ventilation.
The design team is exploring the use of operable louvers at the top of the cones to close off the neck during dust storms. Caps on the top of the cones could also help in balancing horizontal air movement through the office space, says Gill, because one cone could be closed off and the next one opened to shift the pattern of air flow. Engineers tested different orientations and forms for the tops of the cones, settling on a chamfered top with the high point facing toward the prevailing wind. This resulted in the most negative pressure at the top of the cone, promoting the greatest draw.
roof and garden
AS+GG COLLABORATED CLOSELY with its consulting engineers from the early stages of the competition. Gill says the fundamental idea of wind cones supporting a broad roof was no more than “a simple little section drawn on a piece of paper about three inches square” before the M/E/P and structural engineers were brought in to react. “With the idea of the cones and the roof, the structural engineers were important,” says Gill. “And that curve in the roof provides structural integrity.”
Gill likens the project to an oasis—a fragile microclimate in which a pool of water provides nourishment to palm trees, which in turn shade the water and keep it from evaporating too quickly. “So you end up with a canopy structure there that's protecting the very source that allows the canopy to exist in the first place,” he muses. “It's totally symbiotic—they coexist in this kind of equilibrium.”
Likewise, Masdar's floating roof literally translates that idea by shading the building and creating a cool environment beneath, reducing the demand for air conditioning. Plans call for the roof to be covered with a 290,000-square-foot photovoltaic array that will harvest the intense solar energy in the Abu Dhabi desert and convert it to power for the building. Beneath the curving roof, which articulates and promotes the pattern of air movement, is a vast garden space—what Gill refers to as “a displaced ground plane.” Residential units with human-scale massing are organized around the perimeter of the garden. Residents will enjoy views of the shaded courtyard or the city, which is limited to a height of six stories (two less than the Masdar headquarters). “It gives one a very unique perspective,” Gill says.
In keeping with its desire to build humane environments, AS+GG has already asked the client to consider the possibility of building the roof and cones first, which would allow the photovoltaics to provide energy for constructing the rest of the building while at the same time shading the construction site so that the workers aren't toiling in the hot sun. The proposal's practicality is still being evaluated.
sustainable systems and materials
THE BIG IDEAS AT WORK in the building won't succeed without a nexus of sustainable systems and materials. “It's a tightly woven relationship between environmental systems, building performance, and usability,” says Gill. If properly implemented, the latent systems and new technologies should produce 3 percent more energy than the building will use. And because of Masdar's central political control, excess energy can be transferred to the grid.
In addition to generating its own power with photovoltaics—envisioned now as polycrystalline cells on the roof surface— the building uses solar vacuum tubes for air conditioning. Plus a geothermal system is being explored for additional cooling.
The architects also are proposing the use of wind turbines for power generation, a technology they used in a Chicago high-rise. Gill says the inclusion of wind turbines is conjectural at this point, awaiting further analysis of economic feasibility. But if the turbines become a demonstration project, they may be justifiable simply for data collection, he adds.
As the project moves forward, a key area for research and development will be the exterior wall, a critical component in minimizing the building's thermal load. “During the competition, we were thinking in terms of a masonry wall, eight stories tall and solid, with maybe 30 percent open,” Gill recalls. The ultimate goal is to thermally shield the building while allowing controlled daylight in to reduce the lighting load, and the design team is working with a manufacturer to develop a high-performance wall system.
Building materials will be evaluated with respect to what Gill calls “global environmental contextualism”—a phrase he uses to describe how a building should relate to its local environmental context while respecting its global context in terms of developing and available technologies. “What we are finding in terms of the sustainable performance of buildings is there can be a much greater global influence on the building,” he asserts. “It can be winds. It can be solar patterns. But, especially in today's market, it can also be materials. One can look at a bigger pattern of access to material or at sustainable processes and bring those to the project in order to increase performance.” In the case of Masdar, the client is demanding cradle-to-cradle office interiors. But Gill says that seemingly simple performance standard raises a host of other questions. Where do the products and raw materials come from? What manufacturing processes are involved? And how do those factors impact zero-carbon and zero-waste goals?
toolboxdesign and presentation
Adrian Smith + Gordon Gill Architecture designed the Masdar headquarters using AutoCAD, 3DS Max, and Rhino 3D. This software combination allowed the architects to analyze the building in three dimensions. In the competition process, AS+GG also created 3-D fly-through simulations for the jury to consider. Most of the modeling was done in-house before being turned over to an outside consultant for material-specific rendering. Gordon Gill explains: “The final product is out-of-house; the process is in-house.” Renderings are available for viewing on AS+GG's website, smithgill.com.
Once the basic design was in place, the architects uploaded the information into Ecotect (squ1 .com/products/ecotect), a building-design and environmental-analysis tool developed by Square One Research. Gill recalls that this particular program was very useful in planning the energy-generation tactics that will make the Masdar headquarters a positive-energy building. “We use Ecotect to run radiosity performance diagrams,” he says. “In other words, you could run a solar study on it, which allows you to see where the greatest heat is occurring on your wall surfaces. You can begin to see where it protects it and where it does not.”
The architects used other types of models, such as CFD or computational fluid dynamic models, to analyze the effect and performance of the wind cones. The engineers also used these models in more directed and specific tests on the wind cones. “They ran wind speeds of 3.5 meters per second to see what kind of negative draw they were getting on the cone vertically,” Gill says. “So they knew what kind of wind they were creating.”