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Greenhouse floor slab insulation retrofit (C) Daniel Friedman Steven Bliss Benefits of Low-E Window Glazing

vs. Quad-Glazing using Sungain Film

Which type of energy-efficient window glazing is better: low-E glass or quad-glazing using two layers of Sungain film for sunspace or greenhouse windows?

Matching type of energy efficient window glazing to room type and use.

Optimizing window glass for comfort vs. solar gain.

Optimizing window glazing for heat producing sunspace - solar heating. Specifications of low-e glass. Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices.

Page top photo: a rooftop solar greenhouse in Poughkeepsie, New York.

This article compares the benefits and differing applications for low-e window glazing versus Sungain type window film coatings and explains different applications in which each type of product is likely to be more satisfactory.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Comparing Energy Efficiency of Low-E Glass vs Quad Glazing

High passive solar gain room (C) Daniel FriedmanThe question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss. Photos: D. Friedman.

PVC Vinyl Window Warping Q&A

Question: What are the facts about the occurrence of shrinkage and warping in PVC or Solid Vinyl Windows?

A window salesperson suggested to me that triple glazing with low-emissivity (low-e) glass would be better than quad glazing (two layers of 3M Sungain film) for sunspace (or greenhouse) windows.

He maintained that the low-e window units would make the room feel warmer because it would reflect the long-wave radiation (heat) back into the room.

Which window glazing product, low-E glass or 3M Sungain films, would be better for this application? - Roger Saunders, Hollis NH

Our photo above-left shows a very high-gain passive solar home in San Miguel de Allende, Mexico.

Answer: It Depends ...

The answer to the question of which window glazing approach will perform better depends on the type of room and its intended use, according to H. J. Koester of Weather Shield, a company that makes both types of window glazing.

Choosing Window Glazing for Optimum Comfort

If the sunspace is a direct extension of the living area and comfortable sitting conditions are of greater importance than solar gain, he suggests that the low-e glass would be a better value due to its higher R-value and lower cost.

This could have been an installation where comfort weighed more heavily than the need for optimizing for solar heat.

Choosing Window Glazing for Optimum Solar Gain - Solar Heating

For a heat-producing sunspace, he says that the quad glazing approach with Sungain film would be a better approach, because of its higher solar transmittance and small sacrifice in R-value.

Efficient Window Glazing Specifications

As we discuss in more detail at SUNGAIN, FILMS, LOW-E GLASS, here is a quick comparison of window types and their efficiencies:

Comparison of Window Type Energy Efficiencies1
Window Type U-Value2
Single-glazed standard glass 1.13
Double-glazed, 1/2" air space 0.56
Triple-glazed, 2 1/2" air spaces 0.34
Low-E, double glazed, 1/2" air space 0.33
Heat Mirror, double glazed, 1/2" air space 0.23

Notes to the table above

1. Popular Science Magazine in 1982

2. U-value is the measurement of heat transmission through a material - it's the reciprocal of R-value. R-value is a material's resistance to heat transfer.

This article is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Original article


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Citations & References

In addition to any citations in the article above, a full list is available on request.

  • Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
  • 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: info@buildingadvisor.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]
  • 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.
  • In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested

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