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most likely solutions for your “hot
SourceS oF heAT gAiN
window” problems.
If you want to compare products
“by the numbers,” look for the Shad-
Walls & Doors
ing Coefficient (SC) or the more recent
Solar Heat Gain Coefficient (SHGC)
19%
ratings. When comparing items,
use only one of these rating systems
though, because their scales aren’t
compatible.
The benchmark rating is 1/8”
People &
Windows
clear glass, with a 1.0 Shading Coef-
Activities
48% ficient. Standard dual-pane windows
have a 0.87 SC. Smaller numbers are
14%
better. For example, if you’re compar-
ing a solar screen rated at 0.25 SC
with a window tint rated at 0.50 SC,
you can see that the sun screen is
Infiltration
going to do a better job of minimizing
13%
heat gain.
Ceiling
It is important to look at product
6%
samples held in front of your own
windows or store displays with full
window coverage. Some people prefer
the softer, diffused lighting provided
for our Arizona climate, look for prod- heat gain, except in rare cases where
by window tinting, and are willing to
ucts with a Light-to-Solar-Gain (LSG) the materials used are insulative, and
sacrifice a little efficiency for en-
ratio greater than 1.0. Higher numbers the window treatment is constructed
hanced aesthetics. Either way, you’ll
are better, but will not likely exceed to actually trap or reflect the heat.
limit the heat gain and preserve your
1.3 LSG. Some products use metal-
view.
lic coatings to reflect heat (which
How to compare different
sometimes have a metallic sheen on
types of products David Wells is a partner in OneSolar,
the outside surface), while others use
It’s hard to come up with realistic a community-minded, Green Energy
ceramic coatings to selectively admit
numbers on how efficiently some of Systems consultancy, helping Phoenix-
some bands of light, but not others. At
these items – such as palo verde trees area homeowners sensibly reduce
OneSolar.org, we prefer the appear-
and interior roman blinds – actually their energy needs and move towards
ance and performance of ceramic
perform, because there hasn’t been energy independence. OneSolar can
over metallic window films, but that’s
a lot of research into those specific help you with awnings, solar screens
largely a matter of taste.
shade devices. Solar screens and and window tinting, or any other
If you’re considering window
window tinting are more of an apples- home energy-reduction projects. Go
tinting, be aware that in some cases,
to-apples comparison, have the most Green at www.OneSolar.org, or call
applying tint films can void your
research behind them, and are the 623-535-0744.
original window glass warranty, due
to increased heat retention in the glass
itself. It also costs more than solar
screens.
interior window coverings
This includes shutters, blinds, curtains
and roll-down shades – anything that
keeps the light out, and traps some
of the heat. Unfortunately, they work
best when they’re completely closed,
which plunges you back into dark-
ness, makes you use more electric
lighting and eliminates your view. This
is the least effective way to reduce
Pr i n t e d o n re c y c l e d Pa P e r t o Pr o t e c t t h e en v i r o n m e n t
August 2009 39
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