Considering that Seattle’s envelope-pushing Bullitt Center mid-rise office building is designed for net-zero use of both energy and water—and over a 250-year life span—one might expect it to feature all manner of futuristic efficiency-boosting gadgetry. In fact, developer Bullitt Foundation’s sustainability-obsessed design and engineering team did consider incorporating an alphabet soup of new-wave technologies likely to play a prominent role as the quest progresses for net-zero buildings—structures that generate as much energy and harvest as much water as they consume.
ULI Case Study: Bullitt Center
Among the emerging technologies the team assessed but ultimately rejected in favor of more readily accessible systems were facade-integrated photovoltaic (PV) elements, heat-absorbing phase-change materials (PCMs) solutions, and dynamic electrochromic (EC) glazing.
But as pioneering environmentalist and Bullitt founder Denis Hayes explains, the team ultimately opted to minimize Bullitt Center’s energy and water consumption (and waste production) more through enlightened design and management approaches than new technologies. For example, exceptionally high ceilings help optimize daylighting, and lease language heavily incentivizes conservation by tenants, says Hayes, who not so coincidentally served as national coordinator of the first Earth Day back in 1970; he is also the former director of what now is known as the National Renewable Energy Laboratory. His Bullitt Foundation helps devise and fund innovative and sustainable high-risk/high-payoff solutions to complex environmental issues, particularly those facing Pacific Northwest urban areas, with an emphasis on ecosystem planning and technologies.
A key goal of the Bullitt Center project is to demonstrate that by holistically integrating a synergistic combination of performance-based design, engineering, and operating strategies, a good-sized commercial office development can achieve those zero-nets today—without heavy reliance on overly complex or highly customized systems.
Indeed, other than the exceptionally efficient new model of PV panels used in the oversized rooftop array, many of the sustainable technologies and materials incorporated into the Bullitt Center are better described as state-of-the-shelf rather than state-of-the-art, says Paul Schwer, president of PAE Consulting Engineers, the Bullitt Center’s primary mechanical/electrical engineer.
That is not to say technology does not play a prominent role in making the six-story, 52,000-square-foot (4,800 sq m) structure 83 percent more energy efficient and 80 percent more water efficient than typical office buildings in Seattle.
In addition to the striking PV panel–covered rooftop, the project—which held its grand opening on April 22, Earth Day 2013—features an efficient ground-source “geoexchange” system providing heating and cooling energy to an in-floor radiant system; a sophisticated rainwater filtering system expected to meet all the building’s water needs; a composting system that keeps human waste out of Seattle’s sewers; super-insulated curtain walls that minimize undesired air and energy leakage; and a modern automated building management system that controls numerous functions and monitors the building’s performance.
Participants in the building’s design and engineering stress that it is the performance-driven integration of so many replicable design and engineering strategies—along with truly pioneering operational mandates—that really allows the achievement of net-zero status. With the Bullitt Center’s daylight-centered architectural configuration and airtight envelope minimizing cooling and heating loads, the solar-generated juice from above and geothermal energy from below are expected to meet the structure’s diminished power needs.
Meanwhile, the foundation and several green-minded tenants have agreed to employ operational strategies aimed at dramatically cutting energy and water consumption. Convincing tenants to emphasize cloud-based internet-technology services, use laptops rather than tower-type PCs, and abandon the use of power-hogging dual monitors (among other conservation strategies) is a key component underlying the Bullitt Center’s entire net-zero energy strategy, says Chris Faul, a founding partner with the project manager—and inaugural tenant—Point32.
Accordingly, Bullitt Center visitors will not come across tenant-run data centers, but rather a small, underused basement server closet currently housing only the two machines needed due to the project’s emphasis and reliance on cloud-based services and off-site servers.
Visitors to the Bullitt Center will encounter the prominent stairway overlooking the Seattle skyline near the structure’s arguably nondescript main entrance along Madison Street. The wide, wood-heavy staircase encourages leg-powered locomotion over use of the tucked-away elevator, which actually generates electricity on its infrequent descents.
The sustainable strategies do more than boost the Bullitt Center’s impressive performance metrics, such as its remarkably low annual energy use intensity of about 16—16,000 Btu per square foot (172,000 Btu per sq m)—compared with 92 for a typical Seattle building. They also help qualify the development for eventual recognition under the ultra-green Living Building Challenge (LBC) certification program, which requires proven net-zero performance for energy and water efficiency, in addition to extraordinary materials-sourcing measures that minimize carbon emissions and nearly eliminate release of toxins.
By demonstrating that a sizable office building can achieve the absolute highest level of sustainability and still pencil out economically at competitive rental rates, the Bullitt Center may well prove nothing short of revolutionary, says Jason McLennan, founder of LBC and chief executive officer of the Seattle-based International Living Future Institute (ILFI), which administers the program.
Replicating the project’s ultra-high performance elsewhere will “just get easier,” says McLennan, who expects the Bullitt Center to show that LBC certification is viable in virtually any climate zone. He helped Hayes and his associates assemble the Bullitt Center’s design and engineering team and also consulted on various sustainability matters.
But a net-zero development with a 250-year life span gives a whole new meaning to penciling out. Hayes estimates that the Bullitt Center’s numerous sustainability-facilitating features added 20 percent to its $18.5 million in hard construction costs—admittedly beyond the green premium seen with many environmentally friendly institutional development projects. But long-term operating cost efficiencies and other benefits more than justify the extra upfront expenditures, Hayes and others emphasize.
As Schwer points out, the investment in on-site energy generation acts as an insurance policy, essentially prepaying electric bills for 30 years or more. “Knowing what we know today [about energy cost dynamics], do you think we would have liked to lock in 40 years of electricity costs in 1970?” Schwer asks. “You pay now and keep reaping all those savings.”
Similarly, it might take 15 years for heating and cooling energy savings to cover the higher first costs of installing Bullitt’s geoexchange system—a considerably longer payback period than for-profit real estate investors tend to target, Schwer acknowledges. “But those savings are going to be there for the next 100 years.”
The higher soft costs related to the project’s additional design and engineering efforts likewise portend significant societal benefits, Hayes says. Participants in the building’s development are happy to share the considerable knowledge gained through design and construction efforts with other development teams, along with the Bullitt Center’s real-world operations and performance experiences.
“We see [the higher soft costs] as a programmatic expense rather than a building expense,” Hayes explains. “The next time around, those additional costs will be far less.” In fact, when asked how much higher the Bullitt Center’s architectural and engineering bills ended up being compared with a typical multitenant office development’s, Hayes said he had not even felt compelled to do the math. Faul subsequently estimated that the additional architecture and engineering costs probably amounted to no more than 2 percent.
Predictably, the design and engineering team employed no shortage of mathematics and related disciplines in devising net-zero strategies for energy and water use for the infill site in a neighborhood just east of Seattle’s central business district known as Capitol Hill. (Capitol Hill was named generations ago by the area’s developer either in an attempt to attract the state government from Olympia or as a reference to a district in his wife’s hometown of Denver.) The fundamental challenge entailed designing a building that would consume no more electricity than optimally performing on-site renewable energy systems would generate over the course of a typical year.
As Schwer notes, a logical step was to explore how tapping the site’s ever-present geothermal energy might help meet the heating and cooling components of the building’s electricity load. As work on the building’s basic configuration and systems progressed, it became clear that a ground-source geoexchange system—tapping into 26 individual 400-foot (122 m) tube-filled boreholes below the building—would team effectively with a modern, in-floor hydronic radiant heating-and-cooling network.
The efficient radiant-slab system provides excellent mechanical control of heating and cooling at little cost, Schwer says. Such radiant systems heat and cool space by circulating heated or chilled water as needed via pipes in floors, in or below ceilings, or even in walls in some cases—a far more efficient heating/cooling method than circulating air through ventilation ducts.
Helping keep the Bullitt Center’s expected space-conditioning electricity needs to just 5 percent of the overall load was tapping the geoexchange system as both a heat source and heat sink. Pumping water through the bore holes allows the constant temperature of the earth to either absorb the excess heat from above when needed for cooling or provide geothermal heat for heating. Though upfront costs are higher than those for conventional heating, ventilation, and air-conditioning (HVAC) systems, ongoing operating costs are much lower. In typical office buildings in Seattle, space conditioning accounts for 35 percent or more of the overall electricity load.
Whereas energy-intensive information technology equipment tends to make cooling the primary HVAC challenge at modern office properties, even in colder climates, in Seattle’s temperate climate, the reduced tenant-driven electricity load instead makes the Bullitt Center’s HVAC equipment a heating-dominated system, Schwer notes.
Factoring in the energy supplied by the geoexchange system, along with the substantial benefits of the daylight-intensive configuration and stringent policies regarding plug loads—equipment plugged into outlets—the team’s most aggressive calculations for the Bullitt Center’s annual electricity consumption came to roughly 230,000 kilowatt-hours, recalls Brian Court, the Miller Hull Partnership associate who acted as principal architect.
Accordingly, the team needed to pin down a roof size and configuration that could best accommodate a solar PV array powerful enough to approach that target’s corresponding average daily load, Court says. (The Bullitt Center’s PV panels tend to transmit more electricity to the grid than the building buys on sunny days, and less when clouds limit energy generation.)
After exploring more than 50 combinations of size, shape, and pitch, the designers conceded that the roof would need to extend to the curbs surrounding the building in order to generate enough energy to meet overall likely consumption over the course of a typical year, even with the best PV panel technology available. This conclusion factored in the U.S.-developed SunPower PV system’s impressive sunlight-to-electricity conversion efficiency of 20 percent—a bit beyond all other top performers available today from producers around the world, Hayes says.
Approved through Seattle’s permitting process usually applied to sky bridges, the portion of the roof extension beyond the typical four-foot (1.2 m) allowance for balconies, awnings, and the like entails an annual fee paid to the city for occupying right-of-way airspace. The 242,000-kilowatt array ended up covering 14,300 square feet (1,300 sq m) of roof space—about one-third the area likely needed for a system supplying the net electricity needs of a building of comparable size built to Seattle’s energy code.
Aiming to mitigate their impact, the designers chose a light color for the roof extensions and built in some translucency that might emulate a forest canopy from viewpoints below, Court notes.
As critical to the net-zero cause as on-site energy production was the effort to design a building that would allow occupants to work smoothly and comfortably while consuming minimal amounts of electricity and water. To address this, the designers tinkered extensively with the building’s dimensions, configuration, and orientation to maximize both natural light and thermal performance.
One critical solution the team devised is the oversized ceiling heights—11 feet (3.4 m) on some floors, 13 feet (4 m) on others—compared with the typical nine feet (2.7 m) for a mid-rise building. Extra glazing on the oversized curtain walls helps allow daylighting of more than 80 percent of the usable floor space, qualifying the Bullitt Center for the additional ten feet (3 m) of height beyond the zoned maximum allowed through Seattle’s Living Building pilot program.
“Officials from multiple city agencies have made efforts to consider code [restrictions] with fresh eyes in the interests of getting better buildings,” Court says.
To optimize the effects of the tall floors and glazing-heavy curtain walls, the designers aimed to maximize the amount of floor space lying within 25 feet (7.6 m) of the perimeters, Court adds. The strategy proved effective: the Bullitt Center’s lighting power density in its office spaces is just 0.4 watt per square foot (4.3 W per sq m)—less than half the 0.9 watt per square foot (9.7 W per sq m) allowed under the Seattle code.
A larger atrium might have generated enough solar heat gain to forgo the ground-source heating and cooling system, but the economics of such a plan did not pencil out because it would have eliminated too much revenue-generating floor area, Court says. “Once we took the bigger atrium plan off the table, the ground-source system seemed to be the best solution that could meet LBC guidelines.”
A critical technology minimizing the Bullitt Center’s artificial lighting load is its system of dimmable ballasts automated in conjunction with daylight sensors, adds Faul. Building management works closely with tenants in selecting and arranging the most efficient task-lighting systems, he adds. “We show them the pathway, but let them choose.”
In addition to maximizing natural light, the Bullitt Center’s curtain walls are a key factor diminishing the HVAC load. Schwer terms the super-insulated envelope featuring triple-glazed, ten-by-four-foot (3 by 1.2 m) windows “exceptionally tight” with respect to air flow and thermal retention.
Many windows open automatically to provide natural ventilation when desired and release unwanted heat at night. Because the oversized windows open as a unit by extending about six inches (15.2 cm) horizontally rather than swinging from side hinges, they can remain open even while automated exterior shades are deployed to block direct sunlight. During cold months, the exhaust air is routed through a heat-recovery mechanical ventilator.
The Bullitt Center’s occupants will play a critical role in minimizing electricity and water consumption. Because the design team projects that tenant plug loads will account for half of the energy consumed in the building, lease language incentivizes conservation by refunding 100 percent of a tenant’s submetered electricity bill as long as the tenant meets its agreed-on energy allowance.
Building managers cannot control the distribution of computers, phones, and other equipment within individual suites, Faul notes, but they can help tenants monitor consumption with smart plug strips—either purchased by tenants or supplied as part of tenant improvement allowances—that provide granular data on consumption through individual outlets.
“We’re relying on tenants to make cognizant efforts” to manage power consumption with frugality in mind, Faul says. It is computing-related consumption that appears to be the biggest factor differentiating electricity use among individual tenants, he notes.
These factors help explain why the tenant roster is made up mostly of businesses and organizations heavily committed to sustainability, including several that were involved in designing and developing the property. The Bullitt Foundation shares the top floor with Portland-based PAE’s local office, and Point32 shares the fourth floor with a shared-workspace facility. ILFI and sister organization Cascadia Green Building Council (CGBC) share the ground floor with the University of Washington’s Integrated Design Lab, which served as a lighting consultant and leases part of the second floor. ILFI/CGBC as a charter tenant is achieving its energy and water conservation goals during the first several months of the Bullitt Center’s operations, McLennan confirms.
Schwer points out that by locating at the Bullitt Center, shifting to cloud-based services, and using laptops rather than PCs, PAE’s new Seattle office is likely cutting its electricity consumption by 75 percent or more relative to alternative locations. “It’s not often you get to design a building that changes how you run your business.”
In September, the Bullitt Center was about 80 percent leased at annual rates of $28 to $30 per square foot ($301 to $323 per sq m), comparable to rates for the local Class A competition.
The design and engineering team was also challenged to obtain sustainable and healthy building materials, as required by the LBC program. As illustrated by choices as fundamental as the specification of the Bullitt Center’s structural framing material, decision makers sometimes have to weigh conflicting goals such as favoring local sourcing versus improving thermal performance.
Whereas a fully concrete frame would have provided superior thermal capacity—absorbing heat and delaying the impact of peak air temperatures by several hours—using native Douglas fir would better employ local resources, not to mention provide aesthetic benefits. The compromise solution is a two-story concrete podium with an exposed heavy-timber frame comprising the upper-floor beams and columns, with some steel framing providing additional seismic support.
The plan also features three-inch concrete topping slabs embedded with tubes that carry the in-floor radiant fluid. The slabs are laid atop rows of fir two-by-sixes—supported by wood or concrete columns and beams, depending on the floor—creating attractive ceilings for the office levels below.
Use of the slab floors makes up for about half of the thermal capacity lost by opting for the wood framing on the upper floors rather than all concrete, Court estimates. It is a fairly effective if not perfect compromise that features beautiful regional wood obtained with minimal carbon emissions while tapping the superior thermal storage capacity of concrete, he says. “And it gives us a better shot at lasting 250 years.”
Also, in order to adhere to LBC’s so-called Red List of prohibited toxins, the team assessed more than 1,000 products for possible use in constructing and operating the Bullitt Center. It was a challenge to put together a plan avoiding use of more than 360 banned substances, including lead-tainted brass plumbing fixtures, formaldehyde-tainted composite materials, or even PVC piping.
In the quest for net-zero water use, a tricky set of challenges was entailed in retaining and treating rainwater to potable status sufficient to meet the Bullitt Center’s estimated overall daily demand of 500 gallons (1,900 liters). Not only do local, state, and federal regulations hinder the use of rainwater for drinking water, but the standard practice of using chlorine for purification would violate Red List material guidelines, Schwer notes.
LBC program administrators ultimately approved an activated charcoal system that filters out all the chlorine at faucets. The rest of the multiphased filtration and purification processes take place in a basement space the size of a walk-in closet adjacent to a 950-square-foot (90 sq m) space housing the 56,000-gallon (212,000 liter) collection cistern.
Nearly 70 percent of the rainwater hitting the roof is reused in faucets, showers, low-flow urinals, and toilets—and eventually returned to the earth through an on-site bioswale and the constructed wetland atop a lower-floor roof extension. As is the case with plug loads, tenants are reimbursed entirely for water expenditures if they stay within allocated limits.
The team is still waiting for approval of an independent water district for the Bullitt Center that would permit the filtration of rainwater into potable water. Even when that happens, however, the building will not be entirely independent of the water utility because the building code requires that the fire sprinkler system be fed by the utility’s water pressure.
Prospects for composting toilet waste likewise generated no shortage of discussion among team members—and others. Because the site offers little room for the requisite wetlands-based filtration, it ultimately made more sense to go with waste composting for the blackwater rather than trying to combine it with the on-site graywater treatment, Faul explains.
Though system descriptions might conjure visions of campground pit–type facilities, Schwer notes that waste gets flushed—albeit with less than a cup of water per use—from standard-looking toilets into ten composters also located in the basement.
“It’s not often you get to design a building that changes how you run your business.” —Paul Schwer
The compost and nutrient-rich leachate is being drained from the machines and contributed to a large city composting facility where it becomes fertilizer—and does not further tax the sewer system. “Talk about a living building serving a living community,” Schwer comments. The liquid leachate, which flows to separate tanks from the excreta, had been drained once so far as of late August and taken to the city composting facility, and will be drained again fairly soon. The principals are not exactly sure how often the composting excreta/solid waste will need to be removed from the composters; some think it could be two years before necessary and all say at least one year.
These efficiencies will be gained over a protracted life cycle. The quarter-millennium strategy for the building entails relatively easy planned upgrades of key building systems that are bound to become obsolete or simply not last as long, including the solar array, curtain-wall materials, shading devices, and filtration systems. But as Hayes explains, the PV system will likely be in place for at least 25 to 30 years, and curtain-wall materials should be good for 50. And the core structural components are designed to endure for centuries. “Once you get past 100 years, who knows how long they might last—150 or maybe 400 years,” Hayes says.
Hayes would be thrilled if overhanging solar-equipped roofs become something of a design standard for developments pursuing net-zero-energy and net-positive-energy status. “Why not design buildings to maximize harvesting of this free and infinitely renewable source of energy?”
Brad Berton is a Portland, Oregon–based freelance writer specializing in real estate and development topics.
