As a seaport community situated off the Pacific Ocean, Seattle is known for its rainy weather. The metropolitan area experiences an average of 152 rainy days a year, defined as a day that sees rain or melted snow or ice accumulations of at least 0.01 inch, according to weather.com. So, how is one building overcoming overcast skies to produce net-positive energy?
Integrated Design
The Bullitt Center, located at Madison Street and 15th Avenue, opened on Earth Day 2013 and in its first decade of operation generated almost 30% more energy than it used from solar panels affixed to the roof. The integrated design elements include a long building life cycle, net zero water and net zero energy operation, and occupant buy-in of the sustainable living standards.
Building Something Notable
The Bullitt Foundation owns the Center, which is a 52,000-square-foot, market-rate, Class-A commercial office building with 90% of the space leased to commercial enterprises. The heavy timber, concrete and steel structure has a projected 250-year lifespan and is surrounded by a high-performance envelope with a 50-year skin and an active photovoltaic installation with a 25-year lifespan.
It generated 2,475,021 kWh—a net-positive energy production of 551,481 kWh—which could power 41 homes in Seattle for a year. The average house uses 13,376 kWh annually, according to a Bullitt Center press release.
But that success wasn’t just happenstance. It took a concerted effort by the owners, architects, engineers and general contractors to design and construct a net zero commercial building. Denis Hayes, CEO of the Bullitt Foundation, said that for about a year prior to breaking ground, the stakeholders in the integrated design process had a weekly meeting to inspire everyone involved to take pride in the craftsmanship.
“We surveyed multiple vendors and ground-truthed technologies to ensure that other buildings had had good experiences with them,” Hayes said. “And we held training sessions with all the sub-contractors to make sure they knew that the Center was designed to tight standards to achieve something notable.”
PAE Consulting Engineers developed a performance benchmark to measure energy performance—the Energy Use Index (EUI). The average Seattle office building reports an EUI of 72 kBTU/sf per year and the Center’s target EUI was16.1 kBTU/sf. The Center’s actual performance was later measured at 9.4 kBTU/sf per year. That’s 41% better than predicted and 77% better than the 2009 Seattle Code minimum building.
For a comprehensive product list for the Bullitt Center, visit tinyurl.com/BullittProducts.
Net Zero Energy
Unfortunately, the project team could not think of a way to boost the sunshine, but they knew they could maximize the area covered by solar arrays and install the most efficient panels commercially available. The Bullitt Center’s 242 kW photovoltaic solar array extends beyond the roofline, cantilevering them over the surrounding sidewalk. The city owns the air rights above the sidewalk, so the Bullitt Foundation leases this area. The Sunpower panels installed were 20% more efficient than the competition in 2010, Hayes said. Over the first 10 years, the solar panels generated on average 247,502 kWh annually. The grid functions as the battery.
The panels are just one of many features that make the Bullitt Center a living system that pioneered sustainable, multi-story design in the Seattle area.
Biomimicry components include natural ventilation with night flush and operable windows and blinds that open and close to regulate heat inside the building. Nature’s ability to shed heat like the stomata in plants and pores in our skin regulates internal temperatures, much in the same way the windows and blinds do for the center. The Venetian blinds rise when maximum light is required and lower when shade is needed, Hayes explained. The blinds also tilt upward to allow light to illuminate inside without causing unwanted glare on electronic devices. The large windows also provide adequate natural lighting so electric lamps are rarely needed.
The windows also pop out 8 inches to allow air circulation overnight. The warm air exits out the top of the window as cooler night air circulates through the bottom.
“It cools off the concrete floor, which acts like a thermal flywheel, keeping the rooms cool well into the following day,” he said. “It functions much like a cold-blooded animal, which regulates its body temperature by taking advantage of sunshine and shadows.”
Mechanically, the ground source heat exchange allows for radiant heating and cooling through the air system.
Net Zero Water
And remember those 152 rainy days? The team devised methods to take advantage of that moisture as well. Most of Seattle’s commercial power comes from hydropower reservoirs, according to the city. The rainwater collection reservoirs fill up during the winter, creating a need to spill water and ideally generate energy. The reservoirs slowly drop throughout the summer, requiring users to stretch water use farther. The Center’s water collection is 100% demand met on-site with a 50,000-gallon cistern, so it feeds the excess water into the grid that wants it over the summer. Winter power generation is less than consumption and takes back power created by the hydropower dams.
There is a greywater treatment system that uses evapotranspiration and infiltration as well as waste compost.
Considered one of the world’s greenest commercial buildings, it achieved Living Building Challenge certification in April 2015, which attempts to raise the bar as stewards and co-creators of a living future. The challenge consists of seven performance categories: place, water, energy, health and happiness, materials, equity and beauty.
Occupant Buy-in
All that success is not without buy-in from tenants to maintain the sustainability standards that make it a beacon of hope for future construction. Tenants are asked to watch water usage, use the stairs and choose furnishings that don’t off-gas to aid the operations of the lights, heat pumps, fans and appliances that were the most efficient 10 years ago.
“If every tenant were to have the same electricity usage as the average office worker in Seattle (where electricity is much cheaper than in most of America), our plug loads would be too high to be met by on-site production,” Hayes said.
To keep the living building performing at its best, the building engineer keeps systems operating well by cleaning the PV arrays and windows annually. Power output increases nearly 10% after dust and pollen are removed from the solar panels, Hayes said. The manager monitors tenant’s plug loads and helps when they are near energy budget limits. Unused energy can be transferred.
The Bullitt Center is at the cusp of the green architecture movement in Seattle and with a projected lifespan of 250 years, its track record points to net positive.
