Public Power - September 2008 - (Page 37)

Low-e glass now makes up 56 percent of the market for windows and glass. As states adopt Energy Star requirements as the basis of their energy codes, the utilization rate is expected to reach 70 percent in the near future. While this proliferation of low-e glass is an energy conservation success story, Energy Star mandates the use of windows with less than R-3 insulation performance, compared with the R-19 insulating performance that is typically achieved by the walls surrounding those windows. With window insulating performance at its current levels, improving window per- more energy-efficient window technologies, in fact glass with insulating performance far surpassing Energy Star’s existing performance standards has been available for several years. To appreciate the energy saving capability of currently available alternatives to generic low-e glass, it is necessary to understand a bit about the use of glass in the modern era. For most of U.S. history, single-pane glass was the norm, providing protection from weather more than insulating against heat loss in winter and heat gain in summer. Though patented in 1865, insulating glass — two panes of glass separated by a sealed percent heavier than standard insulating glass, imposing size constraints and requiring stronger window framing, which often means increased costs. Suspending a low emissivity and solar reflective coated polyester film mounted inside of an insulating glass unit is often a superior alternative. Without the weight disadvantages of a third pane of glass, film can create two, three or even four insulating cavities that maximize light transmission and provide conservation performance ranging from R-6 to R-20 to meet the unique requirements of both commercial and residential new construction and reno- If enthusiastically promoted by electric utilities and better appreciated by electricity users as a high-priority conservation option, more efficient windows could significantly save energy, impede global warming and help obtain independence from foreign oil. formance represents a significant opportunity for tremendous energy savings. However, there is still a dramatic performance gap between what low-e glass provides and what optimum energy conservation promises. If enthusiastically promoted by electric utilities and better appreciated by electricity users as a high-priority conservation option, more efficient windows could significantly save energy, impede global warming and help obtain independence from foreign oil. Recognizing the opportunity for further savings through improved window performance, DOE is implementing changes to the Energy Star program that will require windows to exceed current performance requirements. Realizing that generic low-e insulating glass no longer provides a level of energy efficiency required to “transform the market,” DOE’s revisions to the Energy Star window performance standards will be phased in beginning next April. DOE is expected to require tougher window performance standards again in 2012 and 2015. The department’s stated goal is for R10 windows to be commercially available by 2020. While it may appear as if DOE is focused on stimulating the development of www.APPAnet.org air space—was not widely adopted until the mid-20th century. In post-World War II America, insulating glass came to be considered the energy-efficient alternative to single-pane glass and became the choice for heating-intensive climates. In the early 1980s, low-e coatings were introduced to the market. Windows with low-e glass have supplanted traditional, dual-pane windows to become the energy-efficient standard for residential construction. Just as the introduction of single-cavity insulated glass provided a breakthrough in performance beyond single-pane glass, the introduction of multi-cavity constructions, consisting of two or even three insulating cavities, is providing the next performance breakthrough for insulating glass. Two alternatives to single-cavity low-e insulating glass are available, meeting or exceeding the new Energy Star glass performance standards. One is triple-pane glass, consisting of three panes of glass and two low-e coatings. By using a third pane of glass to create a second insulating cavity, triple-pane low-e glass improves generic low-e insulating glass performance by about 50 percent from R-4 to R-9. Unfortunately, triple-pane glass is 50 vation projects. Nevertheless, internally mounted, low-e coated films do not replace low-e glass. Rather, they leverage the benefits of filmbased coatings and glass-based coatings to create a lightweight, multi-cavity insulating glass that offers a new level of performance. Most units incorporating film utilize low-e coated glass to minimize solar heat gain, while using coated film technology to maximize insulation performance. A variety of inert gases are used to fill the internal air space and further impede heat transfer. Performance at the edge of the insulating glass unit, traditionally where insulation is least effective, compared to the center of the glass, is improved by using thermally insulated spacer materials to separate the glass, often referred to as “warm edge” con- SEPTEMBER 2008 37 http://www.APPAnet.org

Table of Contents Feed for the Digital Edition of Public Power - September 2008

Public Power - September 2008 Contents Perspective 10 Questions What’s Good About RTOs? Capturing Coal’s Carbon Carbon Safety Valves Greater Glass, Greater Savings Getting Customers to Embrace Compact Fluorescent Lights LEEDing Green Kansas City Shows How to Build Green For Governing Boards Safety Community Broadband Hometown Connections Parting Shot

Public Power - September 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.