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RE: Argon/Krypton Gas insulation (Follow-Up #14)

posted by: oberon on 04.04.2008 at 09:15 pm in Windows Forum

Hi kari,

Krypton is an odorless, colorless, gas that is heavier than air. Krypton is used in window IG or Insulating Glass units as an insulator. Krypton has no effect on direct sunlight thru the window glass.

Krypton is normally used in narrow airspace triple pane units. That means that there are three lites of glass in the IGU (most IG units have two lites). Krypton is very expensive and it works best in narrow spaces (approximately 1/4" give or take a little). This is why it is usually found in more expensive triple pane windows.

Argon, which is also a colorless, odorless gas, is much more commonly used as a window insulator because it is much more readily available than krypton and it is also much less expensive.

I am guessing that your friend's father has a triple pane IGU if he actually does have krypton gas. I am also guessing that if he does have a triple pane window, he has LowE2 coatings on two of the glass panes in the window system. This combination of triple pane, two LowE coatings, and krypton gas is very energy efficient, and it will do a very good job of keeping the home's heat inside in the winter and outside in the summer, but it will also do a very good job of blocking direct solar heat gain - as you describe.

In the summer, blocking direct solar heat gain is a good thing. In the winter it is nice to be able to enjoy that free heat. That leaves something of a problem for many folks. Can you have both?

Since you are in the process of designing your home, you can design to take advantage of both direct solar heat gain in winter and blocking that unwanted gain in summer.

First, LowE or Low Emissivity coatings come in two primary types hard coat or soft coat.

Second, LowE coatings come in two primary types high solar heat gain or low solar heat gain.

Hard coat or pyrolitic coating is applied during the float process (when the glass is being produced). Consisting primarily of tin oxide, hard coat LowE coatings are generally used in the north where they are an improvement over clear glass in blocking heat loss during cold weather. Most hard coat LowE coatings readily pass solar heat, but there are solar-reflective versions available as well.

The primary advantage of a pyrolitic LowE coating is its durability. It is much harder to damage than the soft coat.

Another advantage - in the right climate - is that hard coat will pass solar heat more readily than will a soft coat - this coating does an excellent job of blocking longwave infrared radiation - solar heat gain is shortwave IR. But, there is a disadvantage in that the hard coat will also pass the longwave radiation (non-solar heat) more readily than will the soft coat. What this means is that while the hardcoat lets more heat in, as direct solar heat gain, it also tends to let more heat out as well.

Hard coats also are more prone to haze and discoloration than are soft coats. Hard coats were the first on the market.

Soft or sputter coats are used in about 80-85% of LowE applications in USA.

There are two primary types of soft coat LowE coatings - high solar heat gain (HSHG) and low solar heat gain (LSHG).

Sputter coat LowE coatings are applied in a vacuum chamber. The glass is fed into the coating chamber where layers of metals and metallic oxides are applied to the glass atom by atom. The primary material for energy performance is typically silver, but titanium and stainless steel coatings are also available from various manufacturers.

High solar heat gain sputter coats have one layer of silver. This coating does an excellent job of blocking longwave infrared radiation - which is pretty much any heat that you feel other than direct solar gain - direct solar heat gain is shortwave IR. The High Solar Heat Gain coating also passes a good bit of shortwave or solar heat thru the coating, but not as much as does the hard coat.

Both the hardcoat and HSHG softcoat will pass more solar heat or shortwave IR into the home interior than will the low solar heat gain hard coat or soft coat. When the solar rays are perpendicular to the face of the window the solar rays, or IR radiation, will readily pass thru the glass and the coating and will warm the interior surfaces of the home.

The sharper the angle-of-incidence between the surface of the window and the suns rays, the less solar heat is passed into the home. In other words, when the sun is low in the sky, lots of heat can potentially be passed into a home in the form of shortwave infrared and when the sun is higher in the sky thus a sharp angle between the rays and the window surface the less shortwave IR radiation is transferred into the home. Obviously, this is an advantage in winter when the sun is lower in the sky.

In the north in winter this solar heat gain can be an advantage when using a high solar heat gain productbut with the caveat that this advantage only exists when the sun is shining directly on the window. When the sun isnt shining on the window there is no solar heat gain and there is more potential for heat loss from the home interior to the outdoors thru the window - even with the coating. But, ANY LowE coating is much better than having clear glass windows for energy efficiency.

As a general rule, the HSHG hard coat allows about 14% more solar gain than the HSHG soft coat. But, the HSHG soft coat has about 14% more insulating ability than the hardcoat.

Enough for now...this is long enough.

Questions are welcome.


clipped on: 07.25.2009 at 09:29 pm    last updated on: 07.25.2009 at 09:29 pm