Mark Meshulam is an expert witness and consultant for windows, insulated glass, low-e glass, architectural glass and building facade.
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.
Images are provided courtesy of the Infrared Lab at Lawrence Berkeley Laboratory.
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
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
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
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
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?
Hello Mark
I have question about my home windows. Almost 11 years old double pane. When it is really cold say below freezing what I noticed. inside temperature of glass is around 48F. I am using Infrared thermometer to measure temperature. I think some is not right. It is almost everywhere in house. Near some windows I feel cold but I found it is due to loose bottom seal. I am looking for replacement windows. What is your advice?
Thanks,
Milind
Hi Milind,
If you are using double pane glass, you will achieve an R value of about 2. If you replace the windows with glass with a low-e coating and argon gas fill, you will increase the R value to almost 4. This would increase the interior temperature by an estimated 4-10 degrees.
However, as you mentioned, air infiltration could be an even bigger factor. For our clients, we use testing equipment to measure the air infiltration, then we modify the windows for better air infiltration and test again. This enables us to predict long term energy savings and can also have a dramatic effect on localized cold spots in the building.