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Close to downtown Seattle, Washington, USA, the Bullitt Center has been called the “greenest commercial building” in the world. It produces its own energy via photovoltaics. It collects and reuses its water. Its toilet waste is composted in the basement. Geothermal energy provides heat to a solar-powered hydronic radiant floor heating system. A vegetated roof cleans graywater. Oodles of daylight filter through triple-pane, argon-filled, low-e windows, including a glazed-wall staircase with views of Puget Sound. There’s no parking garage, no fossil fuels and there are no hazardous building materials. Every worker has access to fresh air and daylight, and it’s in an urban area, and much more.
This building, perhaps more than any other urban green building to date, shows us what’s possible to help our global cities become resilient. It also opens questions: can this be achieved on a massive scale? Could older buildings be retrofitted with similar systems to also achieve net zero energy and water? Can the world afford such buildings? Can the world afford to not construct such buildings? Is this building a “magic bullet” for urban sustainability?
Denis Hayes, president and CEO, of the Bullitt Foundation, and initiator of the Bullitt Center, has been quoted as saying, “The era of cheap abundant energy, plentiful fresh water and localized impacts of human activities is over.” Setting his sights on a real-world solution, and as a chief changemaker, he chose the greenest building program in the world to use as a framework for the Foundation’s new headquarters within the Bullitt Center.
Following the stringent performance goals but flexible design options of the Living Building Challenge, Hayes set out to erect a building “that is influential and begins to change the way that architects, engineers, contractors, developers and financial institutions shape the built environment.” Reviewing the Bullitt Center in The New York Times, Bryn Nelson called it “an unparalleled – and very public – experiment in sustainability.”
Designed by Miller Hull Architects of Seattle, the Bullitt Center is purported to be the most energy-efficient commercial office building in the world (as of July 2014). This 50,000 square foot, six-story office building sits at the edge of Seattle’s Capitol Hill district. It boasts a mortarboard of photovoltaic cells on the roof and geothermal wells in the basement, and the building is a net-positive electricity consumer – which means its systems generate more power than the building itself uses. In its first year, the Center used less than 20 percent as much energy per square foot as the average building built under Seattle’s stringent energy code. To facilitate its energy efficiency, the building envelope is high performance with triple-glazed windows and external shades that automatically raise, lower, and tilt based on glare and heat.
The project team calculated that roughly 14,000 square feet of low-slope PV panels could fit on the building. This translated to a maximum energy production of ~240,000 kilowatt hours (kWh) on average per year, which equated to an EUI (Energy Use Intensity) requirement of about 16 kBtu/ft²/yr.
According to project consultant Rob Pena of the University of Washington, the low-slope array at the Bullitt Center follows the ground slope of ~5 degrees and the site orientation which is west of south by about 58 degrees, conforming to the zoning height and allowable building envelope. Despite this sub-optimal orientation, the efficiency penalty is small. Since Seattle gets most of its solar energy during four mid-summer months, the array is positioned to focus on summer energy collection when there are long days of mostly overhead sun at Seattle’s latitude (almost 48 degrees). Therefore, there is a net energy outflow into the grid in the summer months, and in the winter months the building will pull energy off the grid to reach the goal of an overall net zero sum over the course of a year. In its first year, the Center was a net energy exporter for eight months and a net importer the other four months. It exported 142,800 kWh, and it purchased 37,500 kWh back.
Although the panels are operating at less than optimum output because of their low angle relative to the sun, Pena says that more of the highly efficient modules are able to fit within the available area and so the maximum amount of energy possible for the site can be produced.
Pena futher explains that if a panel is tilted to a higher angle, structural issues arise because the angle increases both structural loads and wind loads. Fewer panels can be installed in a given area because of row to row shading, where one panel shades another behind it, so the spacing must be increased between rows of panels, or a larger plane of panels requires more substantial structure. Also, the loss from reducing the tilt of the panels from their optimum angle of ~32.5 degrees is surprisingly small, at only about 11.5%. In Seattle, the same array at a 90 degree tilt would operate at about 65% efficiency; at 0 degree tilt the efficiency would be ~86%, with the panel tilt at the Bullitt Center of 5 degrees, facing WSW (azimuth 238 degrees) the efficiency is ~88.5% of optimum, with the added benefit of greater production area available than would be possible at a higher tilt.
There are 575 425-watts-per-panel PV panels on the roof of the Bullitt Center, manufactured by Sunpower Corporation of San Jose, California. The solar collection area is 13,400 square feet and the photovoltaic array’s DC (direct current) rating is 244.38kW. There are 19 string inverters located under the array in the designated mechanical area, along with an AC Combining Panel Board, a Utility Required Disconnect, and the other required building fire safety systems. The roof surface under the solar array is white, which in itself reduces the cooling load by about 15% not counting the solar PV shading. The fact that the panels are shading the roof itself doubles the lifespan of the roof.
Water and Graywater Systems
The basement is outfitted with a 56,000-gallon cistern that collects rainwater and composters that collect toilet waste from six stories to make the building a net-zero water user. Space-age restrooms dispense foam into the toilet bowls, replacing the whooshing sound of flushing with a sort of hum. To maintain this net-zero water-use facility, the Bullitt Center’s maintenance super attended training that was akin to that for running a city water system. The building is also designed to gather and treat water for drinking, pending eventual approval by King County and the state Department of Health. The building will connect to the municipal supply only for fire prevention.
Water and biodegradable soap used in the taps and showers drain into a 500-gallon storage tank in the basement of the building. From here, 500 gallons per day can be pumped up to the third-floor constructed wetland. The constructed wetland is a green roof that has been filled with layers of porous gravels and soils. The gravel harbors beneficial microorganisms that devour any pathogens that pass through the system. Horsetails, or equisetum, are used as the primary plant for their hardiness, love of water, and ability to thrive in Seattle’s climate. The water is pumped through a series of perforated pipes so that the plants can absorb the nutrients. It is then collected and pumped through the system several more times until the nutrients have been absorbed and it is safe to release into the bio-swales along the western edge of the site. In the bio-swales, the water filters down through 20 feet of gravel before it is deposited into the water table. Functioning similar to the local Douglas fir forests, this catch and slow release of water allows the Bullitt Center to restore 61% of the water to the ecosystem either through ground infiltration or evaporation, and mitigate storm water during and after rain events.
The building components emit no unhealthy vapors. In all, more than three hundred potentially harmful chemicals and materials commonly used in buildings have been avoided, including cadmium, lead, mercury, PVC plastics, or hormone-mimicking substances. The core and essential structures have been built with materials selected to last a minimum of 250 years – and the design is flexible enough to allow for changes in the building’s skin, fenestration, and equipment as technologies and uses evolve. Straightforward, exposed materials such as concrete, glass and wood are integral to the structure, eliminating the need for pricey “finishes.” To minimize shipping and carbon emissions, the large triple-pane windows were arranged to be manufactured in Washington State, even though they are a German product. A stairway is bathed in natural daylight with views of Seattle with the thinking that it will encourage climbing stairs to save electricity and promote fitness of workers. Heat exchangers provide ample fresh air in all seasons, and the building has operable windows in all perimeter spaces.
The Bullitt Center site was chosen for its high visibility and accessibility, and the development was designed with Puget Sound, site sustainability and non-point source pollution in mind. The location is pedestrian, bicycle, bus, shared-car, lightrail and trolley friendly. It has clear southern exposure, with a zoning height limit of 30 feet to the south, which means its investment in solar photovoltaics will be protected through the anticipated 250-year life of the building. On Madison Street, a planting strip improves the character of the street and sidewalk for pedestrians. Understory plantings within the sidewalk zones do not compete with the mature tree canopy that stretches over 15th Avenue. Low to medium height sidewalk plantings establish a physical separation between the pedestrian and vehicle zones, without restricting views to and from these zones.
The project site also offers commercial development opportunity in a neighborhood that is largely residential and striving for economic development, as identified in the neighborhood plan that includes such desirable attributes as improved walkability, economic development that takes advantage of the strategic positioning of Madison Street as a neighborhood zone connector, sensitive infill development, and the creation of interesting urban spaces.
In addition, McGilvra Place Park is a half-acre public space adjacent to the Bullitt Center that underwent a transformation into an activated, enlivened pocket park. The park’s renovation includes protection and celebration of eleven century-old London Plane trees on the site, conversion of an adjacent street to a public plaza, replacement of turf with native vegetation, installing park furniture made of reclaimed timber as well as a concrete ping pong table, and providing improved accessibility to the site. It also is the first project in the world to pursue the Living Building Challenge for the Infrastructure + Landscape Typology.
Does It Cost More? Yes, but….
The Bullitt Foundation estimates that it paid a premium of about 25 percent for the building’s green features, over and above the cost of constructing conventional Class A office space in Seattle. Others point out that, beyond higher construction costs, the first-of-a-kind building’s architectural, engineering, legal, accounting, and other consulting costs were very high. Hayes responds, “That’s inherent in the term ‘first of a kind.’ We tried myriad approaches to solving tough problems, and we kept trying until we found solutions that worked.” Even with Foundation funds, loans, tax credits, and eventually rent-paying tenants, did anyone ever doubt the building would be expensive? This is a groundbreaking building, pun intended.
For such a small foundation (Bullitt has five employees in addition to Hayes), this is a gigantic leap into resiliency and sustainability. A prototype is always more expensive than its followers, and presumably the operating expenses will be less than a conventional building.
The Bullitt Foundation is to be commended for dipping its toes into the stream of veritable improbability by creating an urban building that manages to capture and use all its own water, and capture and use all its own energy, and treat all its own waste, and avoid use of toxic materials. Its leader, Denis Hayes, is not a stranger to whipping up excitement as a trailblazer and champion for the environment. He was the national organizer of the first Earth Day in 1970 and is said to be musing about the 50th Earth Day in 2020. Maybe this building is the magic “Bullitt” we’ve been seeking to rethink how we build buildings.
BULLITT CENTER BY THE NUMBERS
Code Green Article OCT 2013 (478 kb)
Bullitt Center Irresistable Stairs (215 kb)
Bullitt Center Daylighting (327 kb)
Bullitt Center Code Innovation (376 kb)