Thermal Images of Insulated Glass Types

Mark Meshulam — Sun, 22 Nov 2009 10:00:31 +0000

As the saying goes, one picture is worth a thousand words. Here we have six pictures, so I just saved myself 6000 words of writing. Deducting the 554 words that I have written anyway, I am still coming out ahead by 5446 words! Yet another example of energy efficiency.

Jason Theios, P.E. Applications Engineer at Guardian provided these thermal infrared images of 5 types of insulated glass. These images are a result of actual testing – not calculation. The exterior temperature is held at 0 degrees F with a simulated 12 mph wind. The interior temperature is held at 72 degrees F.

Color-coding for thermal gradient

Images are provided courtesy of the Infrared Lab at Lawrence Berkeley Laboratory.

Glass type 1

Glass type 1

1″ insulated
2 lites clear non coated
krypton fill
aluminum spacer

Top edge of glass: 35°F
Bottom edge of glass: 21°F

Comment: this is the only glass type using an aluminum spacer. The foam spacer is 14-17°F warmer at the bottom, which is generally the coldest part of any insulated glass unit.

Glass type 2

Glass type 2

1″ insulated
2 lites clear non coated
krypton fill
foam spacer

Top edge of glass: 48°F
Bottom edge of glass: 35°F

Comment: Krypton is a gas with better insulating properties than dry air, which is more commonly used in glass airspaces. Argon gas is also used for the purpose of improving insulated glass.

Glass type 3

Glass type 3

1″ insulated
2 lites clear with (1) Low-E coating
krypton fill
foam spacer

Top edge of glass: 48°F
Bottom edge of glass: 36°F

Comment: Using two Low-E coatings instead of one allows for better reflecting of outside infrared while retaining roomside heat. Due to the propensity for heat energy to bounce between the coatings and build up heat in the glass, heat strengthened glass will almost certainly be required.

Glass type 4

Glass type 4

insulated – unknown thickness
4 lites clear with ( assumed 3) Low-E coatings
krypton fill
foam spacer

Top edge of glass: 41°F
Bottom edge of glass: 38°F

Comment: This can be costly from both a material and labor standpoint. 1/4″ thick glass weighs 3.2 pounds per square foot. In large sizes, 1/4″ glass will be needed. Four sheets of this glass will weigh almost 13 lbs/sf. A 4′ x 8′ unit, such as what we use in window-walls, would weigh over 400 pounds. That requires a lot of manpower and equipment to install, dramatically increasing cost.

Glass type 5

Glass type 5

insulated – unknown thickness

2 lites clear uncoated

vacuum fill

ceramic pillar spacers (dots)

unknown edge spacer

Comment:
This is the glass development I am most excited about. Reason: I believe it will potentially have the best combination of performance and cost when the technology is perfected. Glass type 4 looks great for performance, but excessive material and labor costs of a unit consisting of 4 lites of glass seems like it might be excessive, especially in large sizes. See the “Vacuum Glazing” sections of The Future of Windows, and An Interview with Guardian for more about vacuum glass.

Want to talk about energy efficient glass?

Mark Meshulam, Chicago Window Expert, thinking about glass thermal transmission

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Thermal Images of Insulated Glass Types