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| Figure 1 |
In a warm climate, reducing solar heat gain (and air leakage) through a window is even more important than a high insulating value. This is especially true for
west- and east-facing windows. Still, a window that “does it all” will save
energy year-round and can allow the entire HVAC system to be downsized
enough to offset the higher cost of high performance windows.
Insulated windows: Insulated windows have two or more layers of glass with a gap between them and are required for new construction. Inert gas fills, such as argon and krypton, have even lower conductivities than air, increasing the insulating values of the unit.Low conductance sash, frame and spacers between the glazing layers reduce heat transfer through those parts. The unit’s U-factor reflects the combined benefit.
Low-e: A Low-emittance (or Low-e") glass coating is a microscopically thin film applied to the glass. This coating hinders radiant heat flow to keep heat inside in winter and outside in summer. Choose a Low-e coating based on your climate.
Low solar gain, or southern climate, Low-e windows do a better job of blocking heat from the sun and provide the greatest energy savings in this region; they generally have an SHGC between 0.20 and 0.40.
High solar gain, or northern climate, Low-e windows are better at reducing heat loss in winter and allow more heat from the sun to enter the home; they are advantageous for south-facing glass in a passive solar home. Low-e coatings can also be added to existing windows by apply solar film to the glass.
Spectrally selective Low-e: |
| Figure 2 |