U.S. commercial building owners could save substantially on annualheating and cooling energy costs by improving airtightness of theirbuildings' envelope, according to a recent National Institute ofStandards and Technology (NIST) study. The research used simulationsoftware to evaluate the energy impact of improved air barriers inthree typical non-residential buildings in five cities, each in adifferent climate zone. The results predicted potential annual heatingand cooling energy cost savings as high as 37 percent.
With baseline energy, climate and building data from each city, theresearchers simulated conditions of a typical, two-story officebuilding; a one-story retail building; and a four-story apartmentbuilding in Bismarck, N.D.; Minneapolis, Minn.; St. Louis, Mo.; Miami,Fla.; and Phoenix, Ariz. Each building was modeled with wood frame andmasonry construction. Methods for increasing air tightness includedbuilding wraps or coatings for masonry blocks. The study focused onchanges in energy expenditures as a result of increased airtightness,not on the methods themselves, so it does not single out a "best"airtightness method.
For the frame construction, the combined annual gas-electriccost savings of improved airtightness would be 33 percent for thehypothetical office building, 21 percent for the retail building, and31 percent for the apartment in Bismarck. In Minneapolis, the predictedsavings would be 37 percent, 26 percent and 33 percent, respectively.In St. Louis, the numbers would be 37 percent, 24 percent and 31percent.
Improved air tightness in the warmer climates would produce smallersavings but could still be significant in the long run. In Phoenix, theestimated cost-savings are 10 percent, 16 percent and 3 percent for theoffice, retail and apartment, respectively; and in Miami, the estimatesare 9 percent, 14 percent and 9 percent.
Predicted savings for the masonry buildings were similar to theframe construction. Although not evaluated in this report, improvingbuilding envelope airtightness also reduces the potential for problemscaused by air leakage such as poor indoor air quality, thermal comfortand degradation of building materials due to moisture damage. (Likemost commercial buildings, the buildings in the study used mechanicalventilation systems to maintain good indoor air quality.)
The NIST findings are expected to be useful to the AmericanSociety of Heating, Refrigerating and Air-Conditioning Engineers(ASHRAE), which is currently considering updating building air leakagerequirements in its non-residential building energy standard 90.1.
Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use (NISTIR 7238) is available at http://fire.nist.gov/bfrlpubs/build05/art007.html.
The research was sponsored by the U.S. Department of Energy Office of Building Technology.
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