Designing the World’s Greenest Office Building
Amory Lovins, physicist and chief scientist at the Rocky Mountain Institute, says that “we don’t care about dirty black rocks (coal) and sticky black liquid (oil); we care about mobility, cold beer and blaring stereos.” We want the services that our modern buildings, machines and devices provide, but we don’t really care about what powers them as long as it’s not too expensive.
Oil, coal and natural gas are the dominant fuels that power modern societies worldwide, but we’ve learned over the past few decades that the carbon left behind in the atmosphere when we burn these fuels is causing global temperatures to rise, oceans to acidify, and ice sheets to melt. Since nearly half of this energy flows through buildings, architecture is central to both the problem and the solution to the climate crisis.
If we could get the services that support our good lives and modern lifestyles without burning fossil fuels, at the same price, we’d all switch service providers in a heartbeat. That’s what this building is setting out to prove we can do.
“Quality, cost, schedule: pick two” is the old adage of building construction. In the case of the Bullitt Center, it was quality, cost and performance, and the design and construction team were told to achieve all three. In this case, quality and performance includes not only the standards of beauty and comfort expected in a Class A commercial office building, but also all seven “petals” of the Living Building Challenge (LBC). The most challenging and arguably the most important LBC criteria is that “one hundred percent of the project’s energy needs must be supplied by on-site renewable energy on a net annual basis.” This was the most influential challenge for the design team.
To meet this challenge the architects from the Miller | Hull Partnership and engineers from PAE had to design an ultra-efficient building, one whose predicted energy use was set by the quantity of solar electricity that can be produced by PV panels on the building. Every building project has a cost budget, but few have an energy budget as absolute as this project’s. That number, the building’s energy use intensity or EUI, was initially set at 20 (kBTU/sf • yr), the whole-building energy use performance number similar to a car’s “miles-per-gallon.” To place this in context, a typical commercial office in Seattle operates at a EUI of about 75 kBTU/sf • yr, nearly four times the budget allowed for this building.
The conceptual design that emerged from the first design charrette was a six-story mass extending to the boundaries of the zoning envelope with a rectangular slice taken from the center to form an atrium to bring light and air to the building’s core. This concept was capped by planar PV array following the slope of the site and extending over the sidewalks, along with a vertical south-facing array with additional panels integrated into the building’s southeast façade punctuated by openings for daylight, and revealing the central design challenge: the competition for light.
As the building’s form developed in the weeks after this charrette, Miller|Hull explored dozens of variations on the configuration of the PV arrays in order to maximize the solar energy production while allowing as much daylight into the building as possible to reduce the need for electric lighting. From the daylighting analysis performed by the Integrated Design Lab (IDL) and the energy analysis by PAE, several influential observations emerged. The first was that the atrium provided very little useful daylight to the building’s core, the proportion of the atrium was just too narrow and the size of the roof aperture was too small. Second, with windows extending to the ceiling plane to maximize daylight penetration into the building, raising the floor-to-ceiling height from about 11 feet to 13.5 feet, increases the daylight penetration by nearly 6 feet, extending the floor area that’s daylit most of the year to nearly 30 feet from the building’s perimeter. Finding the “sweet spot” of window area and distribution to maximize daylight and minimize heat loss involved a back-and-forth between the daylight analysis and the energy model.
What emerged from these simultaneous and integrated investigations of the PV arrays, windows, height and the shape of floor plates, and organization of the building’s façade, is the form and organization of the building that is now nearing completion. The atrium was eliminated and the upper four floors were stepped back approximately 15 feet from the perimeter to create narrower floors that are more fully daylit. The south-facing vertical PV array was also eliminated in favor of a slightly larger “hat,” an orientation for PV panels in Seattle that collects more energy over the course of the year. And the building became 10 feet taller, which was allowed under a provision of the Living Building Ordinance, to promote greater energy efficiency. At the end of this process, the new energy budget for the building was reduced to 16 kBTU/sf • yr, the predicted energy the PV array will produce during a year.
Performance-based integrated design aims to satisfy as much of the heating, cooling, ventilation and lighting demands by architectural rather than mechanical means. So with the building form optimized for sun, light and efficiency, the mechanical systems have a smaller and simpler job to perform. But while the mechanical systems are mostly “state-of-the-shelf” technology, they were mostly selected from the “top shelf” since their performance must be first-rate. For heating, twenty-six 400 feet deep wells were drilled underneath the building to tap-in to the steady 50°F thermal energy of the ground. Heat pumps convert this “geothermal” energy into hot water which is circulated through tubing embedded in the building’s concrete floor decks, using only 3% of the energy budget for space heating, compared to about 30% in comparable buildings. When outdoor temperatures are comfortable, large windows automatically open to provide building occupants fresh air. At other times, a demand-controlled ventilation system provides fresh air that recovers about 85% of the heat in the air exhausted from the building. When it’s warm and sunny, louvered blinds outside the windows automatically deploy to intercept direct sunlight and scatter this daylight into the building. When it’s cool or cloudy, they retract to maximize daylight and solar heating.
The resulting building is predicted to use no more energy than it produces in a year, collects and purifies all the water it uses and returns the remainder to the hydrosphere in an undiminished condition, and offsets all the energy embodied in its construction by planting and preserving carbon sequestering forests in the region. So it may satisfy the performance and quality criteria, but what about its cost? While a full analysis of the project costs is yet to happen, as the building nears completion it appears that the construction costs will be about 18% higher than a comparable Class A commercial office building in Seattle. Not bad for a building where tenants should never have a utility bill. And because this building is meant to last 250 years and is backed by more patient money than a typical commercial real estate venture is, lease rates are competitive with other commercial office spaces in the City.
The next ultra-high performance building will be less expensive, as will the next, and the hundredth won’t cost any more at all. Then, we’ll all be changing providers for the services we’ve come to expect in our modern buildings.
“One building off by itself has zero impact on the world’s climate but a building that is influential and begins to change the way that architects, engineers, contractors, developers and financial institutions shape the built environment, that’s a building that was worth building.” - Denis Hayes, President of the Bullitt Foundation
Written by Rob Peña