Air or Argon gap
How is double glazing made?
A double glazing window comprises two panes of glass, separated by a spacer bar and seals to create a hermetically-sealed environment. The cavity width between the two panes, air or another gas filling used and the type of spacer bar, are all key factors in the unit’s final energy, solar and acoustic insulation properties.
The cavity is filled under vacuum conditions with either dehydrated air or an inert gas to improve insulation and prevent condensation within the unit. Depending on the gas filling used and the type of window, the cavity width for a double glazing window is generally between 4 to 20 mm.
The recommended cavity width for Low E energy saving double glazing window when filled with dehydrated air is 16mm – and 14mm when the cavity is filled with argon gas.
The cavity width requirements for acoustic insulation glazing depend very much on the specific insulation requirements and need to be advised on a case by case basis.
Less heat transmission with double glazing window.
The physical properties of the dehydrated air used in the cavity, means that it transmits (ie loses) less heat by convection or conduction than normal air. This is because the molecules of dehydrated air are relatively immobile, and therefore have a ‘lower thermal conductivity’. The same physical properties of dehydrated air also give it lower acoustic conductivity, for improved sound insulation.
But window energy efficiency can be further increased by substituting dehydrated air with an inert gas, such as argon, xenon or krypton within the unit.
Energy rating of thermal insulation glass improved.
Double glazing window energy efficiency can be further increased by substituting dehydrated air with an inert gas, such as argon, xenon or krypton within the unit. Argon, which has 34% lower thermal conductivity than air, is the most commonly used. Although argon-filled units cost around 5% more than air-filled units, they can improve a double glazing window’s U value or energy rating by over 30%. Argon fillings should last the lifetime of a double glazing window and over a period of 25 years should not lose more than 5%.
Krypton and Xenon are even more energy efficient than Argon but are seldom used in double glazing window as they are more expensive.
It would be interesting to provide the ratio of gas costs between Argon, Krypton and Xenon. Also it is important to note that sometimes you do have to use Krypton/Xenon limited width is available. I.e.: in old buildings for example.