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Gas Filled Window Units

Glass


Double Glazed Unit Thickness

The thickness of the glass will depend on the size of the window or rebate size. In houses, the most common high performance windows, have an air gap width of 16mm. With a glass thickness of 4mm on both sides, the double glazed unit make-up is therefore measured by giving the thickness size, 4-16-4, giving a total double glazed unit thickness of 24mm (or 1 inch). This size

Newer double glazing is now more commonly using 4-20-4 (28mm overall). Other make-ups of glass units in double, triple or quadruple glazing may use different thicknesses and air gaps i.e. 4-10-6-20-4

Pane Separation in Double and Triple Glazing

Double and triple glazed units for house windows are generally available with air gaps from 6mm to 20mm. In frames with narrow air gaps, the closeness of the panes can cause heat to pass from the inner pane to the outer pane more quickly.

Where the air gap is wider, a larger volume of air holds more heat and causes air currents to set up within the air gap. Also, the wider the air gap, the better the sound insulation or acoustic performance, especially when used in conjunction with specilised acoustic glass.

Air or Noble Gas Cavity - Argon/Krypton/Xenon

The two panes of glass separated by a spacer bar are sealed to create a hermetically-sealed environment. The cavity width between the two panes, the filled air or noble gas insert 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 noble gas to improve insulation and prevent condensation within the unit.

The physical properties of the dehydrated air used in the cavity, means that it transmits 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.

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 energy efficiency of glazed units 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 help an old buildings overall efficiency. The compounded effect of every sealed unit that is cavity filled with noble gas, will 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 is important to note that sometimes Krypton and Xenon are a manditory component within the sealed unit when being installed in.

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