Replacement Windows in Virginia by
The Window Replacement Company
Window Technologies: Low-E
Coatings
Low-emittance (Low-E) coating are microscopically thin, virtually invisible,
metal or metallic oxide layers deposited on a window or skylight glazing surface
primarily to reduce the U-factor by suppressing radiative heat flow. The
principal mechanism of heat transfer in multilayer glazing is thermal radiation
from a warm pane of glass to a cooler pane. Coating a glass surface with a low-emittance
material and facing that coating into the gap between the glass layers blocks a
significant amount of this radiant heat transfer, thus lowering the total heat
flow through the window. Low-E coatings are transparent to visible light.
Different types of Low-E coatings have been designed to allow for high solar
gain, moderate solar gain, or low solar gain.
Double-Glazed with High-Solar-Gain Low-E Glass
This figure illustrates the characteristics of a typical double-glazed window
with a high-transmission, Low-E glass and argon gas fill. These Low-E glass
products are often referred to as pyrolitic or hard coat Low-E glass, due to the
glass coating process. The properties presented here are typical of a Low-E
glass product designed to reduce heat loss but admit solar gain. High solar gain
Low-E glass products are best suited for buildings located in heating-dominated
climates. This Low-E glass type is also the product of choice for passive solar
design projects due to the performance attributes relative to other Low-E glass
products which have been developed to reduce solar gain.
In heating-dominated climates with a modest amount of cooling or climates
where both heating and cooling are required, Low-E coatings with high, moderate
or low solar gains may result in similar annual energy costs depending on the
house design and operation. While the high solar gain glazing performs better in
winter, the low solar gain performs better in summer. Low solar gain Low-E
glazings are ideal for buildings located in cooling-dominated climates. Look at
the energy use comparisons under Window Selection to see how different glazings
perform in particular locations.
Double-Glazed with Moderate-Solar-Gain Low-E Glass
This figure illustrates the characteristics of a typical double-glazed window
with a moderate solar gain Low-E glass and argon gas fill. These Low-E glass
products are often referred to as sputtered (or soft-coat products) due to the
glass coating process. (Note: Low solar gain Low-E products are also called
sputtered coatings.) Such coatings reduce heat loss and let in a reasonable
amount of solar gain and are suitable for climates with both heating and cooling
concerns. In heating-dominated climates with a modest amount of cooling or
climates where both heating and cooling are required, Low-E coatings with high,
moderate or low solar gains may result in similar annual energy costs depending
on the house design and operation. Look at the energy use comparisons under
Window Selection to see how different glazings perform in particular locations.
Double-Glazed with Low-Solar-Gain Low-E Glass (Spectrally Selective)
This figure illustrates the characteristics of a typical double-glazed window
with a low solar gain Low-E glass and argon gas fill. These Low-E products are
often referred to as sputtered (or soft-coat) due to the glass coating process.
(Note: Moderate solar gain Low-E products are also called sputtered coatings.)
This type of Low-E product, sometimes called spectrally selective Low-E glass,
reduces heat loss in winter but also reduces heat gain in summer. Compared to
most tinted and reflective glazings, this Low-E glass provides a higher level of
visible light transmission for a given amount of solar heat reduction.
Low solar gain Low-E glazings are ideal for buildings located in
cooling-dominated climates. In heating-dominated climates with a modest amount
of cooling or climates where both heating and cooling are required, Low-E
coatings with high, moderate or low solar gains may result in similar annual
energy costs depending on the house design. While the high solar gain glazing
performs better in winter, the low solar gain performs better in summer. Look at
the energy use comparisons under Window Selection to see how different glazings
perform in particular locations.
Variants on low solar gain Low-E coatings have also been developed which lower
solar gains even further. However this further decrease in solar gains is
achieved by reducing the visible transmittance as well - such coatings, which
may appear slightly tinted, are best suited for applications where cooling is
the dominant factor and where a slightly tinted effect is desired.