Glazing
Glazing is the generic term for the transparent, or sometimes translucent, material in a window. The most common glazing material used in today's windows is glass.
When multiple glass panes are assembled into units, they are commonly referred to as glazed units.
The modern windows usually consist of a separately manufactured glazed unit which is sealed to prevent air and moisture from entering the air space. The seal also keeps dirt from getting on the interior surfaces of the glazing. If the seal is broken, the only cure is to replace the sealed glazed unit.
Windows are always characterized as being either single,double or triple glazed which is a reference to the number of panes of glass in the window. A single-glazed window consist of just one pane of glass. A double-glazed window consist of two panes of glass separated by one spacer, in a triple-glazed window three panes of glass separated by two spacers.
A single glazed window will allow the most light and energy from the sun to pass through. A double glazed window, compared to single glazed window, reduces solar gain by about 10%; A triple-glazed window - by 20%.
Low-E coating also can reduce solar gain for double glazed windows by 10% to 40%, depending on the coating.
Low-E Coating
A Low-E, or low-emissivity, coating is a thin transparent metallic layer, only several atoms thick, applied directly to the glazing surface. In a typical double glazed window, it will be applied to a surface between the two panes of glazing.
The low-E coating allows solar energy to pass through into interior and reflects the radiant heat emitted by object in a room back into the room, significantly reducing heat loss. A double-glazed window with low-E has about the same insulating value as an uncoated triple-glazed unit. The low-E coating alone improves the R-value from R-2 to R-3. There are different types of low-E coating with different characteristics. A window
with a good low-E lowers your
energy bill because in the summer it reflects sunlight; and in
the winter, it allows the room to be warmed by direct sunshine.
Spacers
Between the window glasses in a conventional double-glazed window, a spacer is used to maintain a uniform separation between the panes of glass. Spacers are sometimes made of hollow aluminum that conducts heat easily and can be a significant source of heat loss. One of the many advances that has been made in window technology is the development of low conductivity or "warm edge" spacers. The best insulating spacers made from metal-reinforced butyl, rubber or insulated silicone foam and conduct less heat energy. The result is a more energy efficient window, reduced heat loss and reduced condensation at the edges of the glazing because the glass temperature is higher.
All windows in Canada should be at least double glazed, with Low-E and gas filled to achieve the level of energy efficiency and performance required to be effective in our changing climate.
Gas Fills
New window technology offers improved insulating value. In standard glazed unit space between the panes of glass filled with air. In a gas fill glazed unit, an inert gas is pumped into the sealed unit replacing the air. The gas fill increase the insulating performance by reducing conduction heat loss because the gas fill has a lower conductivity than air.
Argon is commonly used in insulated glazing. Krypton is more expensive, used to produce very thin double-glazing units or relatively thin, extremely high performance triple-glazed units. These gases are non-toxic, clear, odorless, chemically inert and totally safe.
Frame construction
One-third of the overall window is the frame and sash.
Up to 25% percent of window’s heat loss occurs through conduction in the sash and frame parts. Frames can also have significant impact on solar gain. It is important to make sure that the frame has sufficient thermal breaks to minimize heat loss.
Wood frames provide insulation that is much better than aluminum but require painting or other maintenance.
Vinyl frames, in turn, provide a very good thermal barrier and therefore good insulation. A top-quality vinyl window system comes with many internal cavities. The more the better since each cavity provides heat transfer barrier, reduces distortion in changing temperatures, adds strength during welding, allows internal pressure to equalize preventing leaking and even improves sound insulation.
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