Comparing Energy Efficiency of Low-E Glass vs Quad Glazing
The text below is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
Readers should also see SUNGAIN, FILMS, LOW-E GLASS for details about use of Sungain film on windows and window film selection and installation, and see WINDOWS & DOORS our home page for window and door information. A wide range of energy conservation and solar energy topics is found at SOLAR ENERGY SYSTEMS. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Low-e Window Retrofit Film Products
Question: are there any low-e coated products for window retrofits?
Are there any low-e coated products available for retrofitting existing windows? - Ed Swiderski, Pawtuckett RI
Answer: Yes several low-e window films and an inside storm window
Two low-e window films and one inside storm window were available in the mid 1980's and more such products are currently provided by several manufacturers.
The add-on or "retrofit" low-e window films are applied to the inside of the window glass with a squeegee, using water as the adhesive. These "winter films" or "all-weather" films are tuned to retain winter heat and reject some outside heat gain.
They probably make the most sense as window energy improving retrofits in houses located north of the Mason-Dixon line.
Scotch-tint Plus All Season claims to reduce heat gain by 60 percent and wintertime heat loss through the window by 40 percent. it also blocks 98 percent of UV light that fades indoor furnishings. Scotch-tint is available from 3-M Co., St. Paul MN.
The second low-e retrofit window film is Gila River Products' [Chandler AZ] PWD-5 with roughly similar characteristics to the 3-M Scotch-tint film.
With a winter U-value of .85, this film ups the R-value of a single pane 1/8-inch thick window [glass] from around .90 to 1.18, a 31 percent improvement in window efficiency.
What is lost when a low-e film like these is applied to a window is some useful solar gain and light in winter, due to the film's low transmittance (0.55).
To our knowledge, the only low-e retrofit storm window is the Windo-Tite unit. It is an aluminum-framed single window that attaches to the inside of the primary window via swivel clips or sash locks. It has a tested U-value of .408 (r-2.45 for storm plus primary window). Amesbury Industries, [Amesbury MA] supplies the glazing frames and accessories to local distributors who make up the window units.
For more up to date information about the performance of films to increase solar collector efficiency, see SOLAR COLLECTOR FILMS
Q&A: Low-e Retrofit Products - Window Films - PDF version; use your browser's back button to return to this page. Original article, Solar Age Magazine, September 1986, adapted and updated for InspectAPedia.com in 2011.
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Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: email@example.com
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
3M Corporation, 3M Energy Control Products Project, Building 224-5S, St. Paul MN 55144 [1980's]
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Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
Passive Solar Handbook Volume III, the Passive Solar Handbook Programming Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v3.pdf
"Passive Solar Home Design", U.S. Department of Energy, describes using a home's windows, walls, and floors to collect and store solar energy for winter heating and also rejecting solar heat in warm weather.
"Solar Water Heaters", U.S. Department of Energy article on solar domestic water heaters to generate domestic hot water in buildings, explains how solar water heaters work. Solar heat for swimming pools is also discussed.
"Heat-Transfer Fluids for Solar Water Heating Systems", U.S. DOE, describes the types of fluids selected to transfer heat between the solar collector and the hot water in storage tanks in a building. These include air, water, water with glycol antifreeze mixtures (needed when using solar hot water systems in freezing climates), hydrocarbon oils, and refrigerants or silicones for heat transfer.
"Solar Water Heating System Freeze Protection", U.S. DOE,using antifreeze mixture in solar water heaters (or other freeze-resistant heat transfer fluids), as well as piping to permit draining the solar collector and piping system.
"Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
"Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy in the form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.
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