Federal Center South Building 1202: Seattle, WA
Shaped to Perform
Echoing the ever-changing waterway that passes the Seattle district headquarters of the U.S. Army Corps of Engineers, the “oxbow” shape of the USACE’s new building represents the transformation from a “silo” office culture to an integrated community. In the Corps’ previous home — a former 1930s Ford Motor warehouse that was later converted to offices — tall cubicle walls and limited access to daylight or exterior views did little to encourage interaction. Now, employees meet members of other departments when they take the open stairs. A variety of conference rooms, hybrid spaces and informal collaboration areas that are centralized in the daylit atrium support project teams as they grow and shrink. Nearly every space provides daylight and views of the restored 4.6 acre former brownfield site, including the Duwamish Waterway.
While the $72 million project provides a beautiful, collaborative workplace, its exceptional energy performance places it among the most elite class of high performance buildings in the U.S. It is the result of a guaranteed performance-oriented contract — a first for the U.S. General Services Administration and an emerging industry trend — which withheld a portion of the contract funds until the first year energy use was verified.
The project was shaped by government programs designed to spur innovative high performance design for federal buildings and stimulate the economy via the release of stimulus funds from the American Recovery and Reinvestment Act (ARRA) as quickly as possible. The GSA used the tight time line demanded by the stimulus dollars and the competitive bidding market in 2009 to experiment with a design-build competition.
A design-build contract meant that the money could be budgeted immediately, and the rapid three-year project time line allocated final funding two to three times faster than traditional design-bid-build contracts.
Three teams participated in the three-month design competition in which proposals were developed to a schematic design level to express design intent, but also assess cost, schedule and performance criteria. In the midst of a struggling economic climate at the end of 2009, these three firms participated in an unfunded competition, each taking a substantial risk to secure a rare, fully funded project at that time.
As part of its Design Excellence program, the GSA specified a set of holistic sustainable performance criteria, required LEED Gold certification and encouraged the reuse of materials from the USACE’s existing on-site warehouse building.
The guaranteed energy performance target required the building team to meet an energy goal 30% better than the ASHRAE/IESNA Standard 90.1-2007 baseline model, or an effective EUI of 27 kBtu/ft2·yr, with 0.5% of the overall contract award retained until the first year of performance was verified through a measurement and verification (M&V) process.
The central atrium “commons” forms the social heart of the building and houses all shared resources, including conference rooms, kitchenettes, the library and informal seating areas to encourage interaction and create a sense of community.
Performance Oriented Design
Peak Load Reduction and Form Optimization. It was a challenge in the three-month competition phase to develop a schematic design proposal that could meet the guaranteed budget and energy performance criteria, while developing compelling media renderings to adequately express the complexity and unique user experience of the building. One essential design challenge was the need to balance views of the Duwamish Waterway to the west of the site and the solar gain inherent to a western exposure.
The team discovered that an approximately 60 ft wide office floor plate would provide the optimal combination of workplace flexibility and daylight availability. An orientation energy model was developed, and this idealized office bar was rotated at 22.5 degree increments to isolate the effect of orientation on performance.
While there was some effect on annual energy use, the exercise underscored the disproportionate effect on peak cooling loads, an important factor since mechanical system selection sizing would have significant impact on the guaranteed maximum project first cost. The final building form, a closed oxbow, creates long orientations facing northwest, east and south while minimizing surface area. This efficient ratio of surface area to volume also limits thermal loads, with the building’s rounded form enclosing a centralized commons and atrium.
The western edge doesn’t have the same rounded efficiency, but limits open office space on the toughest orientation and features flexible program space and community gathering areas. Extensive shading protects the west-facing windows, which provide a direct connection to rehabilitated landscape adjacent to the Duwamish Waterway.
Integrated Systems and Collaborative Workplace
The atrium and centralized commons pool conference rooms and other specialized and shared functions into the center of the building. Through sharing, the number of meeting rooms for the headquarters ’ 19 departments was reduced, while promoting connection and collaboration through more encounters among staff in this dynamic space.
High Performance Office. The structure wrapping the commons, in turn, is optimized for open office space. A narrow 60 ft width from exterior to the toplit atrium provides extensive daylight, connectivity and flexibility as the three-story steel structure wraps continuously around the commons.
An efficient structural system, known as a diagrid, wraps the exterior of the building and is prominently expressed at the ends of the oxbow. It is essentially an oversized truss comprised of diagonal column and bracing that resists lateral and gravity loads while addressing progressive collapse.
The steel and concrete deck, like most systems, is exposed, limiting fit-out costs while providing thermal mass. A raised floor system provides the necessary space for electrical and IT distribution, as well as space for ventilation air supply, which is decoupled from the in-zone heating and cooling systems.
Passive chilled beams provide cooling, taking advantage of high temperature chilled water, a particularly effective strategy in Seattle’s mild climate.
Extensive integrated modeling optimized perimeter systems in concert with the exterior façade. The resulting efficient envelope, with high performance, low-e insulated glass, meets the project budget while enabling energy-efficient systems. An orientation-specific shading system, with vertical fins and a variable number of horizontal louvers depending on orientation, limits solar loading, reducing annual energy consumption and first cost through decreasing the required number of chilled beams and plant size.
Energy modeling, which was embedded in the design process, determined that triple glazing alone would not be sufficient to provide comfort for all occupied hours. So, perimeter fin tubes are used provide the required heating.
Collaborative Commons. The atrium commons functions as the social and cultural heart of the project. Timber provides the primary structure and enclosure of this space, reclaiming approximately 200,000 board feet of structural timbers and tongue-and-groove decking from the existing warehouse on the site.
To make the structure work with the limited amount of timber, the team’s structural engineers developed the first application of a composite beam. Lag bolts in the top of structural timbers engage the concrete topping slab, providing additional effective depth for the beam, reducing the number of beams by providing greater spanning capacity.
In the conference rooms, hydronic variable air volume terminal boxes triggered by CO2 sensors provide the capacity and control to manage thermal comfort and ventilation associated with intermittent occupancy.
In addition to its role as collaborative commons, the atrium is integral to the building’s high performance strategies. Return air from the office is collected by the atrium; buoyancy drives the air, as 70% efficient flat plate heat exchangers arranged at the top of the atrium precondition incoming ventilation air.
The atrium also daylights half of the office’s 60 ft floor plate, in addition to the conference rooms and circulation space. Plants and landscaping within the space, in concert with exposed wood, changing daylight conditions, and views to the river, reinforce a biophilic design approach that emphasizes a connection to nature.
Office Daylighting Strategies. The climate of the Pacific Northwest presents challenges to using daylight as the primary illumination source. Cloudy skies are the predominant sky condition, but clear sunny days occur sporadically in winter, and are most frequent during the summer, when peak cooling conditions occur.
A balance had to be struck between opening up to the cloud skydome and protecting from the direct beam condition. Exterior windows optimize their daylight contribution by maximizing window head height and using orientation-specific shading.
The shading system reduces heat gain and assists with visual comfort. Internal venetian blinds at all exterior windows offer additional glare control, allowing occupants to adjust to their comfort.
Daylight is also provided to inboard occupants by the atrium, where a variable frit pattern, ranging to a maximum density of 66%, is strategically deployed on the atrium skylights, based on individual work spaces’ exposure.
Light colored interior surfaces as well as 42 in. tall partitions topped with 8 in. glazed strips help facilitate daylighting. The partition walls are oriented parallel to the façade with the taller furniture running perpendicular to the façade.
Electric lighting is provided via high efficiency, direct/indirect fluorescent fixtures, which are used throughout the office spaces. Fixtures are controlled through a combination of zoned daylight sensors, occupancy sensors and the building management software.
The 66% frit was not dense enough to protect occupants on the atrium side of the northern office plate, and roller shades were retrofitted to protect them from direct beam and the associated glare. Due to peer pressure from those deeper in the plate, perimeter office workers are encouraged to raise the shades so views to the atrium are preserved once the discomfort has subsided.
Central Systems. The hydronic system allowed for the efficient integration of ground source heat and the inclusion of a phase change material (PCM) tank for thermal storage. Polyethelene tubing was run into 135 hollow structural steel piles that were driven an average of 160 ft deep through the sandy riverbank soil to find bedrock.
The PCM tank, a large cylindrical tank filled with stacked containers of eutectic salts that change phase at 55°F, acts as a direct source of chilled water for the chilled beams and as a source of heat for the heat recovery chillers to deliver 120°F heating hot water. The PCM tank, in theory, operates similarly to a ground source system, but with a daily, rather than a seasonal, cycle.
The PCM system was designed to address typical Seattle days where morning warm-up and afternoon cooling are required. It also helps store cooling generated from economizer cycles that run during the cool summer nights.
During the commissioning process, it was discovered that the capacity of the PCM tank was less than promised by the manufacturer. This was mitigated by changes in controls and greater reliance on the energy piles, which were recharging more rapidly than expected, most likely due to the adjacency to the Duwamish Waterway. The systems are meeting 90% of the building’s heating load with heat recovery chillers sourcing heat from the ground loop, the PCM tank or simultaneous 24/7 cooling loads. The remainder of loads are met with a traditional boiler and the heat recovery chiller acting as a traditional chiller.
Water Systems. This 4.6 acre site, transformed from 100% impervious to 50% pervious, is surrounded with infiltration and evaporation swales that manage and cleanse storm water flows prior to discharge into Duwamish Waterway. The storm water system eliminates the need to connect to the already overtaxed municipal sewer system.
Native and adaptive plantings reduce irrigation demand and provide habitat opportunities along the industrial waterway and complement ongoing efforts to restore ecosystems as the Duwamish enters the Puget Sound.
High efficiency fixtures and a rainwater harvesting system help reduce potable water demand. Rainwater is collected from the roof and is reused for toilet flushing, irrigation and cooling tower makeup water. The rainwater system, which offsets 400,000 gallons of potable water use annually, is highlighted for occupants and visitors via a truth window facing the atrium.
Large rocks within the atrium serve as water features, inspired by the tributaries of the Duwamish Waterway. During rain events, storm water flows through stream channels chiseled in the stones, providing a direct tie to the climate and surrounding environment.
The building’s diagrid structure angles outward at one end of the oxbow where a conference room has sweeping views of the Duwamish Waterway.
Measuring the performance of the building started in January 2013, less than three months after substantial completion of the project. The first few months of M &V required coordination between the designers, builders, controls contractor and building operator — the M&V team — to ensure that the building was being properly measured and that the measured data could provide information on how the building was running and how it could be improved.
During the first quarter of operation, the M&V team tuned the building’s HVAC systems, which were running outside of building operating hours, improved thermal comfort in select spaces, improved acoustics and identified glare issues. The team also identified opportunities for the USACE to reduce plug loads by shutting computers off at night, and controlling the server’s 24/7 loads.
After one year of operation, the building was tuned from operating at 10% over the target in the first quarter, to 12% below the target in the fourth quarter. The final first year EUI is 25.7 kBtu/ft2 (adjusted for plug loads and operation outside of the hours of operation agreed upon during the design); the project’s metered EUI (without adjustment) in 2013 was 33 kBtu/ft2.
The adjustments to the building operation from M&V save the GSA and the USACE up to $40,000 per year in energy costs and have dramatically improved comfort. Meeting the energy performance target allowed the design build team to receive the 0.5% of the construction contract retained for proof of performance — nearly $400,000.
Renewable Energy Evaluation
The integrated design was developed to meet energy goals without the need for on-site renewable generation. Initial life-cycle cost analysis of a solar domestic hot water system and supplemental photovoltaic system were outside the range of acceptable return. The roof is designed to allow the installation of a photovoltaic array in the future should the life-cycle cost benefits improve.
Even with its low operating energy, its integrated systems, and attractive interior spaces, arguably the most noteworthy aspect of this project relates to its performance-oriented design delivery. The GSA’s use of a guaranteed energy performance contract coupled with the Design Excellence Program pushed the team to deliver not only a beautiful building, but also one that performs as promised.
This project demonstrates the success of performance-oriented contracting, an emerging industry trend, as well as the value of M&V. The substantial amount of money at risk incentivized the team to create a thorough approach, and for a project of this scale, the effort proved to be quite cost effective at a building operations level. •