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February 27, 2014

Old warehouse now a super-efficient office building

  • Portland’s Vestas headquarters uses 70 percent less energy than a conventional office building thanks to a thrifty HVAC system and other strategies.


    To the passerby, the Vestas North American headquarters in Portland’s Pearl District, looks like a simple, modern commercial building converted from a historic block building. Hidden beneath the surface, it is in fact one of the highest-performing office buildings in the country.

    Renovated from the old Meier & Frank warehouse into Class A office space in 2012, the Vestas headquarters is a leader in energy savings. While the average office tenant in the Pacific Northwest pays around $1.60 per square foot in annual energy costs, the cost of energy at Vestas is less than $0.50 per square foot. In 2013 alone, annual energy costs are just $0.45 per square foot, helping the owner improve its bottom line.

    After nearly two years of operation, Vestas is consuming approximately 70 percent less energy than a conventional office building in the Pacific Northwest and is on track for an Energy Star score of 100, making it one of the most efficient large office buildings in the entire country.

    The building achieves these benchmarks mostly from a dual-path HVAC system, efficient lighting design, a rooftop solar electric system and a building performance dashboard.

    Dual-path HVAC

    The HVAC system is responsible for 40 percent of the energy savings. Fresh air is supplied through an underfloor air-distribution system, with individual control at each desk.

    Photo by Jeremy Bitterman [enlarge]
    The atrium draws natural light into the building.

    A supplemental system maintains thermal comfort in each local area using a variable refrigerant flow system. The HVAC system uses less than half the energy of a conventional variable air-volume system used in most office buildings across the country.

    This HVAC system is a variation of a dual-path system and is becoming a common approach for low-energy-use buildings. A dual-path system separates control of outside air for ventilation from a local thermal comfort system that maintains occupant comfort. As a result, the building only uses energy to maintain comfort when and where it is occupied.

    Dual-path systems have been used at Seattle’s Experience Music Project and at several Portland buildings, including the Mercy Corps headquarters, the Edith Green-Wendell Wyatt Federal Building and two buildings on the Portland Community College Cascade Campus. All of these projects represent the newest standard in achieving low energy use in Pacific Northwest office buildings.

    Lighting design

    The lighting design accounted for 15 percent of the energy savings. The design focused on providing enough ambient light for the space, but with local task lights at the desks that allow staff to adjust light levels to their individual needs.

    Typically, offices provide lighting for all needs in all areas all the time, which results in excess power consumption. In this case, daylight dimming controls were integrated into the ambient lighting system as well, using artificial lighting as a supplement to natural light from outside.

    Perimeter windows maximize natural light and the atrium draws light into the core of the building. As a result, the total lighting energy consumed is approximately 75 percent less than a conventional office building.

    Solar panels

    A 125-kilowatt solar array provides 10 percent of building energy use each year.

    The system occupies approximately 16,000 square feet of the roof outside the fifth-floor penthouse. Occupants can see the renewable energy system outside their windows, and energy production is visible via the building performance dashboard.

    Photo courtesy of Glumac [enlarge]
    This 16,000-square-foot solar array provides 10 percent of the building’s energy each year.

    Performance dashboard

    The utility dashboard has been a key part of attaining actual energy savings. The system, provided by Deck Monitoring, helps building staff better understand electricity, gas and water consumption in the building.

    After six months, the building was on track to perform as expected with an “energy use intensity” (EUI) of 29 kilo-British thermal units per square foot. Using the data, Glumac worked with building staff to understand operations and where further savings could be achieved. This resulted in an EUI of 23 kilo-British thermal units per square foot, an additional energy savings of 20 percent in an already high-performance building, and almost $30,000 annual savings in operating costs.

    As the commercial real estate market begins to renovate aging, historic buildings across the Pacific Northwest, following the Vestas systems blueprint can be a successful strategy for building owners.

    The infrastructure is smaller, thereby maximizing usable square footage. The integrated daylight dimming controls create more inviting work spaces while upholding a commitment to sustainability. Finally, the robust monitoring helps to maximize savings and ensure that they continue over time.

    This design approach helps create the modern office space that is in high demand in the current real estate market while repurposing the existing built environment.

    Mitch Dec is an associate principal at Glumac, a full-service consulting engineering firm.

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