The iconic images of the Wright brothers’ first powered flight in the sands of Kitty Hawk’s footprint and Neil Armstrong on the moon represent years of research and study aimed at finding the safest and most feasible path not only to these achievements , but also others that would build. about its success.
It is therefore fitting that the nearly completed renovation of the Smithsonian Institution’s National Air and Space Museum in Washington, DC, is the result of a similar effort to determine the most effective and practical modernization strategy for ensure the long-term protection of thousands of prized artifacts. while enriching the experience for millions of visitors each year.
What was originally conceived as an HVAC repair and replacement project soon revealed a much more complex set of problems and, at times, conflicting considerations for the team led by architect Quinn Evans of Washington, selected by the Smithsonian in 2013 to conduct a comprehensive condition assessment of the entire building.
The museum’s existing structural frame required additional steel reinforcement for the larger exterior cladding and curtain wall components.
Credit: Smithsonian photo by Jim Preston
Along with the expected results of the weather and the elements, some problems were rooted in the rapid 1970s design and construction of the building. The design, large pavilions separated by atriums with 60-foot-high curtain walls and topped with 125-by-155-foot acrylic domed skylights, was intended to provide the sky as a backdrop for aviation artifacts.
In reality, says Quinn Evans project manager Colin MacKillop, the vaulted spaces were overexposing artifacts to harmful unfiltered light and creating “solar heat gain hot boxes” that complicated the capacity of the aging HVAC infrastructure. maintain adequate temperature and humidity control.
Also problematic was the exterior cladding of the Tennessee pink marble exterior panels—”a beautiful stone, but weaker when cut to expose the veins,” MacKillop says, making them susceptible to cracking and warping. Backed by only minimal moisture-trapping urethane foam insulation, he adds, the 1-1/4-inch-thick panels accelerated the thermal hysteresis effects of Washington’s climate.
Quinn Evans project manager Leora Mirvish notes that with a return air plenum located directly behind the stone and insulation, “there was no way to get the stone out of the building without killing the air conditioning”.
As problematic as these elements were, the museum’s appearance had become synonymous with the varied architecture of Smithsonian museums along the National Mall, including listing on the National Register of Historic Places. At the same time, any modernization strategy should conform to the Smithsonian’s commitment to sustainability, minimize life-cycle costs, and allow as much of the museum as possible during construction.
Extensive daylighting studies led to new glazing and lighting controls that will significantly reduce artifact light exposure.
Credit: Smithsonian photo by Jim Preston
Putting science to work
Quinn Evans’ team would use a variety of technically intensive studies, ranging from daylight modeling and solar angle studies to computational fluid dynamics and material analyses, to assess and weigh alternatives
The solution to the envelope was to replace the original siding with 2-inch thick Colonial Rose granite panels supported by a 4-inch metal rain screen system and a lightweight, thermally broken aluminum stud system. Addressing the myriad interior challenges was aided by extensive consultations with curators and a timely Smithsonian symposium on some long-held assumptions about temperature and humidity.
Mirvish explains that many museums tend to be “energy hogs” to maintain a standard of 70 degrees with 50 percent humidity.
“We learned that they originated in an obscure British museum built in the 1800s without heating or air conditioning, and later became the accepted standard when really they were arbitrary levels,” he says. “Optimal indoor conditions depend on the type of collection you have, whether it’s paper or industrial artifacts.”
For the Air and Space Museum, it was found that only allowing for normal seasonal variations in temperature and humidity was most beneficial for the majority of the collection, with the added benefit of saving up to 20% in energy costs.
Other elements of the solution included the installation of daylight sensors and the installation of atriums with graduated fried glass that is darker at the top and gradually brightens to preserve transparency at street level . Retractable blinds that adjust to the team’s seasonal solar angles were also installed, and the team evaluated 14 different custom fabrics to find the right balance between visible light transmission and reflectivity.
The new cladding panels for the museum’s exterior addressed several considerations such as thermal hysteresis and preservation of the building’s landmark status on the National Mall.
Credit: Smithsonian photo by Jim Preston
As a result, Mirvish says, the atrium feels bright, but is actually much darker than before. He adds that the lighting analysis data also helps curators locate particularly sensitive artifacts around the renovated museum.
Identifying the best power source for the museum also required careful evaluation of multiple options. After examining museum visitor data and assessing the interaction of crowds with indoor conditions, the team opted for a building-specific heating system and cooling plants, with the possibility of take advantage of an existing chilled water circuit that serves the shopping center for peak summer loads. In addition, two large cisterns capture rainwater from the roof to meet Washington’s stringent stormwater requirements and provide water for cooling tower ventilation, irrigation and toilet flushing.
MacKillop and Mirvish credit the Smithsonian with the latitude to conduct such extensive research, which they say provided a learning experience for themselves and potentially other museums with entirely different types of collections.
“Meeting all these requirements and doing everything sustainably is very important,” says MacKillop.
Mirvish adds that the approach was appropriate for an installation that celebrates the spirit of exploration.
“Because the Smithsonian allowed us to go down this path, we came up with a much better project than if it had been just repair and replacement of HVAC,” he says. “They saw it as an opportunity to transform the museum, even change the program to one of ‘revitalization’. It was great to be a part of that process.”
