Only Online - USGlass July 2006
The Department of Energy (DOE) is actively promoting the new alternative performance-based criteria for windows destined for use in the South and South-Central climate zones (excepting California). The amendment to the qualifying criteria allowing the alternative went into effect on September 19, 2005, after months of effort to obtain an alternative to the tighter prescriptive U-value criteria released in 2003. They are based on trade-offs of higher U-factors with lower solar heat gain coefficients (SHGC), determined through analysis by Lawrence Berkeley National Laboratory (LBNL).
The table displays the trade-off numbers. U-factors and SHGC for the Northern Zone remain prescriptive, set at those required by the International Energy Conservation Code (IECC) and allows no latitude for SHGC trade-off. In the North Central Zone, the Department of Energy maintains that "the current [prescriptive U-factor and SHGC] criteria are close to optimal and therefore allow no trade-off." DOE agrees that the amendments preserve the intent of offering equal or greater energy savings than either the prescriptive criteria or applicable regional codes, providing greater flexibility and having no adverse market impacts.
In particular, it allows efficient aluminum windows to qualify for ENERGY STAR status in the indicated climate zones. While DOE admits that the still-stringent 0.43 or 0.42 U-factor required for the South Central zone poses a challenge for aluminum product designers, their opinion is that most stakeholders are confident such products can be developed.
© Copyright 2006 Key Communications Inc.
All rights reserved.