GANA Energy Division Takes Notice of Air Leakage Criteria
October 18, 2011
The meeting of the Glass Association of North America's (GANA) Energy Division concluded yesterday with a discussion of one topic--the brand new division has not previously touched: air leakage.
In a presentation on "Air Leakage in Buildings Mitigation and Code Issues," Stanley Yee, building enclosure consultant of the Facade Group in Portland, Ore., acknowledged that the topic is one his audience "may have heard of in the periphery but may not have made the connection to energy." According to a 2005 NIST study, Yee said, air infiltration (or leakage, which he defined as uncontrolled air infiltration/exfiltration) is responsible for 33 percent of the total heating energy use. Sources of air leakage include the mechanical systems; the building enclosure by stack effect; and the building enclosure by wind effect. Seeing as how fenestration is an integral part of two of those causes, he said, this should be a topic of notice.
In particular, Yee said, a change noted by one of the groups that has set air leakage criteria should be of particular concern.
A number of organizations, ranging from the International Energy Conservation Code to the General Services Administration (GSA), have set air leakage criteria at 0.40 cubic feet per minute (CFM)/square foot. That criteria, he noted, has not necessarily been enforced to date.
The National Institute of Standards and Technology had surveyed a sample of building stock and found that building air infiltration is more typically 3.5 times than allowance, Yee said. With that in mind, the U.S. Army Corps of Engineers earlier this year set a requirement that all new buildings and major retrofits need to be 0.25 CFM/square foot. "I can tell you now that there will be many to follow suit in that number, ASHRAE being one, GSA being next ... it's just a matter of time before we start seeing this number as the norm," Yee said.
The Corps expects total energy costs savings to range from 5 percent to 25 percent by this improved air infiltration and, as such, is expected to enforce the new number more stringently than in the past, Yee said.
Yee also went over how to test for air leakage, explaining the process for the ASTM E779 air blower test. However, he pointed out, that test is used on a finished building and if the building does not then meet the criteria, it cannot get occupancy. In addition to using AAMA 502 and 503 for pressure testing along the way, he mentioned thermography as one way to diagnose air leakage. The tool shows heat differences in a building, revealing where the hot air used in the blower test is escaping.
One listener pointed out how striking it was to see the thermographic image of a relatively "young" building - two years old - showing dramatic air leakage through the fenestration. What does this say for the life cycle of the building, he commented, if the fenestration isn't keeping air and energy effectively inside at the beginning.
Yee said that among the ways to prevent air leakage and improve infiltration and exfiltration is attention to how glazing system design, assembly and installation can contain and prevent air from moving inside the building, and ensuring a connection between door and window frames and the air barrier.
Fenestration has an important role to play in improving air infiltration and improving energy, Yee concluded, but it must do so in conjunction with other trades and in the context of the whole building.
The GANA Fall Conference continues through October 19 in Kansas City, Mo. Stay tuned to USGNN.com for more updates from the conference.
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