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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

  • LOW-E VS QUAD-GLAZING - CONTENTS: Which type of energy-efficient window glazing is better: low-E glass or quad-glazing using 2 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
  • POST a QUESTION or READ FAQs about types of Low-E window glazing
  • REFERENCES
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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.



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Comparing Energy Efficiency of Low-E Glass vs Quad Glazing

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

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

Answer: It Depends ...

High passive solar gain room (C) Daniel FriedmanThe 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.

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

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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