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Renovation Relies on Innovative Processes to Achieve Net Zero Energy

By Kevin Wilcox

The American Geophysical Union is renovating its headquarters, in Washington, D.C., to be a good neighbor and a model to others.

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The large solar photovoltaic array atop the building is designed to be evocative of an architectural element. © Hickok Cole Architects

January 24, 2017—Sustainability is a guiding principle for the American Geophysical Union (AGU) and its more than 60,000 members in 137 countries. So when the group's headquarters building, in Washington, D.C., was due for a renovation, the leadership established an ambitious goal for the project: net zero energy. The building, in other words, was to generate as much, if not more, energy than it would consume.

This goal is achieved through a combination of strategies that generate energy and dramatically reduce the building's energy demand. It is certainly consistent with the AGU's mission "to promote discovery in Earth and space science for the benefit of humanity." It also proved to be a challenge for the team of architects and engineers given the task of carrying out a net zero energy renovation that would be able to serve as a model for other building owners in the nation's capital and, indeed, in the country as a whole.

"When the project is complete, if any [building] could be close to a physical … embodiment of the mission and passion and values of the organization, that's what [this] building is going to be," says Chris McEntee, the AGU's executive director and chief executive officer. "So, we set goals for the renovation, one of which was the lowest environmental imprint we could have in terms of energy, water, waste, and reuse." The AGU also wanted the building to be a healthy, productive workplace, as well as a community amenity that would offer exhibition and meeting spaces.

The AGU headquarters building is near Dupont Circle at the intersection of 20 th Street and Florida Avenue. It was completed in 1994, and its robust steel structure is in good condition. The mechanical, electrical, and plumbing systems, however, are nearing the end of their service lives. The architect for the renovation is Hickok Cole Architects, a Washington, D.C., firm. Yolanda Cole, FAIA, LEED AP, a senior principal and owner of the firm, served as principal in charge on the project.

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Ensuring that the renovation worked well within the DuPont Circle neighborhood was important to an array of stakeholders. © Hickok Cole Architects

Cole says one of the key challenges was homing in on the correct combination of sustainable strategies from the more than 40 that the team examined. "It took us a while to settle in on the set of strategies—our bundle—that was going to get us to net zero," Cole says. In the end, no fewer than 27 different strategies are employed, working together as a system to achieve the goal. These strategies can be grouped into four categories: generation, absorption, reduction, and reclamation.

The team examined the feasibility of vertical wind turbines and solar concentrators before selecting a large solar photovoltaic array as the key generation strategy. The Washington, D.C., office of Interface Engineering, which is headquartered in Portland, Oregon, provided the mechanical, electrical, and plumbing engineering on the project.

The array, which covers most of the roof, comprises a total of 717 high-performance photovoltaic panels, 693 of them mounted on a canopy and the other 24 attached to vertical elements. Each panel is roughly 3.5 by 5 ft. The array is elevated 12 ft above the roof and cantilevers beyond the building's envelope. Tadjer-Cohen-Edelson Associates, Inc., headquartered in Silver Spring, Maryland, was the structural engineer when the building was constructed and is handling the renovation.

The array is supported by a series of steel tube columns connected by wide-flange steel beams with in-plane bracing. The columns transfer loads to the building's structural steel columns and beams via connections made by cutting openings through the concrete on the steel deck roof, according to Pete Hults, P.E., S.E., M.ASCE, an engineer at Tadjer-Cohen-Edelson. Hults explains that the team developed an insulated connection to reduce heat transfer between exterior columns and the supporting roof framing.

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The team opened the ground level with more glass so the building, with its exhibition and conference spaces, is more inviting. © Hickok Cole Architects

The additional weight of the array and any added wind loads were examined carefully by the engineering team. "The roof was already designed for snow loads.… It's a little bit larger area, but the solar panels aren't that heavy themselves," Hults says.

Because Tadjer-Cohen-Edelson performed the original structural engineering, the firm had access to structural drawings and institutional memory about the project. But since many of the structural steel connections weren't detailed in the drawings, its staff opened some areas of the building and "counted the number of bolts, the size, the whole works," Hults says.

Because the array is visible from the street, the designers needed to develop a support system that would be aesthetically acceptable as well as functional. Guil Almeida, LEED GA is an associate at Hickok Cole Architects and served as the project designer. He notes that incorporating the array into the design was an even greater challenge because the building is already beloved in the neighborhood, which has a number of historically important structures.

"Our first goal was to ensure that we were not only respecting the building but designing something that would tie into the historic context. That's a pretty big challenge when you're talking about … a large photovoltaic array hovering … above the roof," Almeida says. The team treated the array and the supports as if they were an architectural embellishment, reminiscent of a traditional cornice when viewed from the street below.

This elegant approach helped greatly as the project moved through a design review process that began with community and neighborhood organizations and culminated with the city's Historic Preservation Review Board. The project also required a zoning ordinance exception, according to Holly Lennihan, LEED AP, an associate at Hickok Cole Architects, who served as the project manager. Extensive community outreach garnered strong support, and that made this review process much smoother.

"I think we've learned that it's really, really important not to surprise your neighbors, your community, and your stakeholders," McEntee says. "We tried to make it a very inclusive and collaborative approach—with the community, those in D.C. who make approvals …, and finally with the members."

Although the generation strategy for the project is the most dramatic and visible, the absorption strategy also is quite unusual. Absorption strategies are based on the concept of finding streams of energy that move around the building and tapping into them to draw energy into the building, explains Roger Frechette, P.E., LEED AP, M.ASCE, a managing principal at Interface Engineering.

In this case, one of those streams of energy is 30 ft below the street—a combined storm and sanitary sewer line owned by the District of Columbia Water and Sewer Authority. The project team was granted permission to penetrate this egg-shaped brick vault with an extraction system. The system will pump fluid out of the sewer and convey it to an approximately 35 ft deep wet well on the site. A screening system within the well will remove solids and return them to the sewer. The remaining fluid will then flow through a heat exchanger.

Fluid temperatures in the sewer system vary seasonally and with storm events but average 55°F. The heat exchanger acts as a conventional chiller, Frechette explains. The sewer fluid flows through one side of the exchanger, and water from the building's radiant cooling system flows through the other. Energy is transferred through the walls of the exchanger.

"For much of the year—whenever the water temperatures in the sewer are, say, 55 degrees and lower—we can use that water to cool the building without having to run chillers," Frechette says. "In the winter, it works similar to a conventional geothermal system. We have the ability to extract both heat and cooling."

The project is much more than an impressive collection of energy strategies, however. The AGU placed a high priority on making the interior a healthy, collaborative space for its employees. The team worked within the existing steel frame structure to cut a series of large, open staircases through the concrete-on-metal deck to provide a sense of connection to colleagues and discourage trips on the elevators. The stair landings are hung from the floor above, and the stair stringers connect to the existing steel framing at each floor, Hults explains.

Employees will work in modular office spaces that will enable more daylight to penetrate farther into the building. They will be able to reserve quiet spaces for more focused work, avail themselves of conference rooms for team efforts, or find a large stuffed chair in a working lounge.

Light-emitting diodes that use direct current from the photovoltaic panels will illuminate work spaces. Radiant ceiling panels filled with circulating water will provide heating and cooling. Circulating air will be cleaned with a hydroponic phytoremediation installation. Air will pass through the leaves and roots of plants growing in modular trays of water arranged on interior walls. This will minimize the need to draw outside air into the building and then heat or cool it.

The AGU also placed a premium on opening the building to the neighborhood. The team removed nonstructural columns at the ground level and replaced them with high-tech glass to give passersby a view of the conference spaces, which are available for rent, and of the exhibit spaces. The AGU also plans to give tours of the building, and it hopes that the project will serve as an example of what can be done on a budget of less than $42 million.

"One of the biggest challenges we gave [the team] was to make sure that, when we do this, we are doing it in a way [and] at an expense price point that others will say, 'We are willing to put in that price point.' We really wanted others to see that it could be done at what would be a reasonable price point. I think that's critical," McEntee says.

In keeping with that guidance, Frechette notes that although some of the technologies in the building are uncommon in the United States, "none of them are inventions. They are all systems you can find someplace in the world." Thus, the building can serve as an example of what kind of performance can be achieved on a budget for a renovation at a site with little space to spare.

Frechette says that the bundle of strategies that worked for the AGU building might not work for another project. For instance, the site lends itself to the use solar energy but not wind. In some instances, the reverse might be true. However, many of the strategies that reduce a building's energy consumption would work in nearly any building.

"There is no silver bullet to be able to get net zero energy," Frechette says. "When you are trying to do something unique, it takes a little bit of extra effort … to push through the finish line."


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