A historic home with low-e storm windows. Image: QUANTA Technologies, Inc.
One recent addition to the arsenal of cost-effective efficiency measures is low-emissivity (low-e) storm windows. A low-e coating or glazing is a thin layer deposited directly on the surface of one or more panes of glass. The coating increases the window’s energy efficiency by reflecting radiant heat. Installing a low-e storm window over a low performing window can reduce a home’s heating and cooling costs by 10%–35%.
Between 2013 and 2015, the Pacific Northwest National Laboratory (PNNL) and its project partners worked to validate the energy savings from low-e storm windows. The Regional Technical Forum (RTF)—which serves as the advisory board to the Pacific Northwest Electric Power Planning Council and Bonneville Power Administration—reviewed the PNNL team’s research results and, in late July 2015, approved the low-e storm window measure’s savings and specifications. The RTF approval makes it easier for various energy efficiency programs to include low-e storm windows in their portfolio of energy-saving measures.
Replacing windows is expensive. Because of the high upfront cost and resulting long payback times, many homeowners and businesses keep their drafty and inefficient old windows. In the late 1990s, researchers at the Lawrence Berkeley National Laboratory (LBNL) identified a potential solution: a durable low-e glass coating on storm windows that could offer a cost-effective insulating and sealing measure for existing windows. In the following years, with support from the Building Technologies Office’s (BTO’s) Emerging Technologies Program and other U.S. Department of Energy (DOE) programs, the new technology option was researched, further developed, and field-tested—with positive results.
Regardless of their promise, new weatherization measures must overcome market barriers, such as unverified energy savings data and lack of financial incentives. To speed up market entry for low-e storm windows, BTO’s Building America initiative funded PNNL’s comprehensive market transformation effort. PNNL’s Lab Homes, a laboratory in which new building technologies can be tested in a closely monitored setting that replicates a normal home environment, conducted controlled whole-home testing to validate the windows’ technical performance and to refine technical specifications for different baseline conditions and multiple climate zones. In addition to performance validation, researchers carried out a market assessment and education and outreach on the new storm windows through different channels, such as Consortium for Energy Efficiency, the Home Performance Coalition, and Building America Solution Center.
“The energy savings demonstrated by the PNNL Lab Homes low-e storm window experiments really inspired us and gave us the confidence to pursue a technology proving project [pilot program] in our district. The validation from national lab testing has helped give this project credibility,” says Todd Blackman of the Franklin Public Utility District, describing the importance of the PNNL team’s work.
The RTF's approval is the first and essential step in integrating the low-e storm window measure into energy efficiency planning and utility programs in the Pacific Northwest. As a result of RTF approval, PNNL expects low-e storm windows will be included as a cost-effective energy savings measure in a growing number of weatherization and utility incentive programs in the Pacific Northwest and elsewhere in the country. PNNL estimates that more than 90 million homes in the United States with single-pane or low-performing double-pane windows would benefit from the technology. Low-e storm windows are suitable not only for private residences but also for small commercial buildings, historic properties, and facilities that house residents, such as nursing homes, dormitories, and in-patient facilities. Modeling shows that the technical energy savings potential from widespread adoption of low-e storm windows is up to 2 quads, equal to the amount of electricity used by 55 million homes in a year.
“You hear the word ‘storm window’ and think immediately of Grandma’s storm windows, which had to be removed seasonally and were clunky, ugly old things,” says Tom Culp of Birch Point Consulting, a member of the PNNL team. “Today’s storm window not only offers a new, modern design, it brings a tremendous opportunity to cost-effectively improve performance in windows. Low-e storm windows today cost about a quarter of what full window replacement would cost but bring similar energy savings. They’re operable, add comfort, and have a modern aesthetic.”
The Office of Energy Efficiency and Renewable Energy (EERE) success stories highlight the positive impact of its work with businesses, industry partners, universities, research labs, and other entities.