How do Low Emissivity Coatings make vinyl windows more energy efficient?
Low Emissivity Coatings Retard Heat Transfer
A dual pane insulated unit with one LoE Glass panel and one regular panel performs equally as well as a triple pane insulated unit. In fact, a LoE unit blocks 85% to 90% of radiant heat, and improves the overall performance of a standard dual pane unit by as much as 55%! There are two processes that deposit the coating on the glass. Sprayed-on Soft Coat (Sputter Coating) has a higher effectiveness on blocking radiant heat (up to 90%), and Fused-on Hard Coat (Pyrolytic Coating) has a 5% lower effect on radiant heat (85%).
Visible light in a dual pane insulated unit, is only reduced 5 to 6% over a single pane unit. There is no visible loss in visibility. Solar Heat gain results from direct sunlight on the interior surfaces of the room which heats them up. In the winter, with the lower angle of the sun, direct sunlight falls on the interior surfaces for maximum heat gain (over 55%). And, because the LoE glass keeps the heat in (no loss of reradiated heat) the retained solar heat gain is greater than with the regular glass.
Summer Efficiency In the summer, the sun (which is directional in it's wave emissions) has a higher angle of incidence which prevents much of the direct sunlight from entering the home. Shade from trees, and the way in which the house faces, can substantially reduce the amount of direct sunlight entering the home that would heat-up the interior. The real problem in the summer is the super-heated driveways, exterior bricks, etc. that radiate multi-directional heat waves that would enter the home through the windows, even long after the sun has set. LoE prevents the passage of this reradiated heat into the home, keeping it cooler.
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