Architects: Miller Hull
Year Built: April 22, 2013
Size: 52,000 SF, 6 Stories
Structural Engineer: DCI Engineers
Engineers: PAE Engineers
Certifications: Living Building Challenge v2 (2015)
The Bullitt Center is a six-story commercial office building in Seattle, Washington, USA. Designed by The Miller Hull Partnership and built to house the new headquarters of the Bullitt Foundation. The Bullitt Center is considered one of the world's greenest commercial buildings and achieved Living Building Challenge certification in April 2015.
The Living Building Challenge is a stringent set of standards for buildings designed to maximize positive social and ecological impact while minimizing adverse effects on people and the planet. To earn the certification, the Bullitt Center had to demonstrate that it could produce more electricity than it uses in a year, deal with on-site human waste disposal, capture and filter rainwater for drinking, and eliminate toxic chemicals from the building process. All of this requires extensive regulatory challenges. Here are some ways the building is considered one of the greenest in the world and how it achieved Living Building Challenge certification.
Energy: A solar-powered net-zero building
Seattle isn't exactly known for its sunny skies, but the Bullitt Center is proof that buildings can achieve net-zero energy consumption even in a cloudy, rainy city. 575 solar panels generate more energy than the building uses in a year. It was estimated that the panels would produce 230,000 kWh per year. However, during its first year of actual data, the building's solar panels generated 252,560 kWh of clean, renewable energy from the solar panels on its roof, far exceeding the initial estimates.
Solar panels are usually installed facing south, at an angle that allows them to receive solar radiation throughout the year. Realizing that the sun's low angle during the cloudy winter months would generate very little energy, the designers optimized the panels for the summer sun, with excess energy sent back to the electrical grid.
To achieve its net zero energy status, the Bullit Center sells surplus electricity to the grid during the summer months and purchases power from the grid in winter, essentially utilizing the grid as a virtual energy storage system.
A typical office building would generally operate at 92 EUI (Energy Use Intensity), requiring a vastly more extensive solar panel array than the 14,000 square feet array installed on the Bullitt Center. Several other sustainable methods are implemented into the building's design so the Bullitt Center can achieve a EUI of 16. These design features include passive ventilation, a ground-source heat pump, natural daylighting, and tenant energy budgets.
Energy: Closed-loop Geothermal System and Heat Recovery Ventilation
Five ground-source heat pumps convert 53°F (12°C) water from underground tubes to 95°F (35°C) for heating the building through a series of radiant tubes placed throughout the building's concrete floors. The ground source heat loop runs 400 ft below the Bullitt Center. This efficiently heats the building during the winter and can run reverse during summer to help cool the building. This is a highly efficient heating and cooling system and only requires energy to run the pumps and compressors.
In addition, the ventilation system can recover heat from the stale air being exhausted from the building and heat the incoming fresh air from outside the building. Using this technology, the ventilation system can recover 65% of the heat from the exiting air.
Water: Rainwater Harvesting and Greywater Reclamation
Seattle gets about 50 inches of rain annually, making it one of the wettest major cities in America. The Bullitt Center captures this rainwater to provide 100% of the building's water requirements, including drinking water for its occupants. The Bullitt Center published a white paper on how they achieved a net-positive water system while conforming to highly regulated drinking water laws. This can be a useful starting point for architects and designers implementing such a system. Greywater from the building is treated and re-used in the vacuum-flush toilet system, with any excess greywater returned to the soil to help recharge the aquifer.
Composting Toilets vs. Vacuum Toilets
From 2013 until 2021, the Bullitt Center used composting toilets to deal with human waste. The system was removed in 2021 and replaced with vacuum toilets. A white paper was issued with the rationale for replacing the composting toilets and lessons learned to help other architects and designers. Vacuum toilets use approximately 70% less water than standard toilets. The vacuum toilets use reclaimed greywater from the building sinks, showers, and dishwashers for flushing.
Water: Integrated Wetlands
For greywater diverted to the constructed wetland, it passes through layers of porous gravels and soils. Horsetails, or equisetum, are used as the primary plant for their hardiness and ability to thrive in Seattle’s climate. The water is pumped through a series of drip lines so the plants can absorb the nutrients. It is then collected and pumped through the system several times until the nutrients have been absorbed and it is safe to release in the bio-swales along the site's western edge.
Any excess greywater from the building is diverted to a constructed wetland on the third floor. The water is pumped through a series of driplines. The wetland is planted with native plants that absorb nutrients from the water until it is safe to be released into bio-swales on the ground level. In the bio-swale, the water filters through 20 feet of gravel before it returns to the aquifers below the building.
Winds and Shades
Triple glazed operable windows with a deployable external shading system help keep the building cool in the summer and warm in the winter. Interior operable blinds enable occupants to control the amount of daylight to reduce glare on workspaces. The operable windows also provide additional cross ventilation and cooling.
With a concrete base, much of the buildings above ground structure is built with mass timber—glulam beams and columns. Mass timber has the added benefit of sequestering carbon into the building, with 545 metric tons of carbon locked away in the Bullitt Center for the next 250 years. Mass timber also reduces embodied carbon by reducing the amount of high embodied energy materials such as concrete and steel typically used as structural elements. 100% of the wood used in the building is Forest Stewardship Council (FSC) certified.
Built to Last
The Bullitt Center was designed for a minimum lifespan of 250 years.
Building Management System
The Bullit Center has a Building Management System (BMS) that monitors and controls all aspects of the building's climate. It opens and closes windows to allow fresh air circulation during hot summer days, adjusts the external shading, and controls the heating system, cooling system, passive and active ventilation systems, daylight control, and grey water systems. The BMS operates to achieve maximum efficiency in the central control room in the core of the building.