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The
windows you choose can have a dramatic affect on your home's overall
appearance.
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Homeowners
love windows – the light they bring, the views they frame, the feel they
give to homes. Energy experts hate windows – the heat they bring, the
heat they drain, the added energy consumption they cause. The race is
on to develop the technology that will allow builders to incorporate windows
and homeowners to place them wherever they want without fear of skyrocketing
energy costs.
Low-e Coatings
Windows have continued to improve over the years, first with insulated
glass units that provided a buffer zone of air between two panes of glass
to reduce the heat loss incurred by single pane units during cold weather.
Improvements continued with the advent of low-e or low emissivity coatings.
These microthin metallic coatings reflect heat, sending it back where
it came from. Low-e coatings significantly improve the thermal quality
of insulated glass units, helping homes to stay warmer in the winter and
cooler in the summer. Adding argon or krypton gas fill between these coated
panes adds to the insulative properties of the window unit.
At the high end of available window technology
is spectrally selective coatings. The coatings are applied to the panes
of glass to reduce heat gain by blocking selected rays from entering the
home. This enhancement to low-e coated glass helps further reduce heat
loss from inside and heat gain from outside. It also serves to protect
furniture and fabrics within from sun bleaching. With gas-filled, spectrally
selective coated glass in a well-constructed insulated glass unit, the
R-value of a window can approach that of a well-insulated wall. Still,
short of drawing the shades or awnings, beating sun challenges all windows
and causes solar heat gain that can compromise any energy budget.
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New
Window Technology
Companies are now researching technologies that will allow maximum visible
light to enter the home while blocking the rays that cause heat buildup
within the home. Enter switchable windows that respond with a flick of
the switch to darken, lighten, or almost completely block the sun from
entering living space. Technology already exists to bring switchable privacy
glass (SPG) to homes, but these windows don't block heat gain or ultra
violet (UV) light penetration. SPG changes from clear to milky white when
switched, which allows light to enter the interior space while the view
is blocked from outside. Marvin Windows brought this technology to the
residential market, but was forced to abandon it due to failures. "The
quality of the glass and reject rate became frustrating for both our supplier
and us and were hurting sales," says Anthony Head, Regulatory Product
Planner for Marvin. With Marvin's longstanding commitment to quality,
durability, and a 20-year warranty, they had no choice but to discontinue
the line. "There's still quite a bit of it operational in the field,"
Head says. "We continue to monitor this technology today in our advanced
research area. The most promising technology seems to be glass that isn't
a privacy glass, but is a variable tint type of glass."
The prize will be to discover a switchable tinted window that responds
to light and heat gain by absorbing rays while allowing light to penetrate.
The only problem is that any such technology must clear a number of hurdles
before making it to the marketplace. There are many companies in competition
to develop an electrochromic or chemical window solution that can darken
and lighten windows at the flick of a switch or by automatic sensor. "Much
of this development is heavily cloaked in secrecy as patents are sought
and technology continues to develop," explains Head.
Building a Better Window
The key stumbling blocks are threefold: durability, thermal stability,
and reliability with regard to switching. Gentex Corporation, a Zeeland,
Michigan company, known for its electrochromic automobile mirrors that
automatically darken and lighten to eliminate glare, is undergoing its
own tests for electrochromic windows. "We've made increases in durability,
fairly significant ones," says Tom Guar, Vice President of Chemical
Research for Gentex. Still, the goal has to be to produce a window that
can stand up for 20 years. "When you think about it, it's a pretty
tough environment," Guar says of the stresses a window designed to
absorb heat must endure. "If you think about your glass pane absorbing
great amounts of light and heat, it will get very hot, maybe even crack
the glass," he says. Add to that susceptibility to water penetration,
which is a problem for all insulated glass units (IGUs), and oxygen penetration,
and there's a lot to overcome. Marvin struggled with making sure the film
adhered to the glass and the seal remained undisturbed. Any future product
will need to address the same issues.
Faribault, Minnesota's Sage Electrochromics, makers of SageGlass, has
developed an electrochromic window technology that has passed all four
levels of testing by the Department of Energy. To get DOE approval, Sage
must demonstrate that their product is durable as well as efficient. "There
are three key reasons why this approval is so critical," says Mike
Myser of Sage. "The first is durability. In order for a window company
to sell our product they need to know it's durable, and will withstand
the thermal stress and UV degradation of the sun." Sage is the first
to receive DOE approval for durability. With this approval in hand, Sage
can partner with glass and window manufacturers to create a product that
will be available to consumers for home use.
Making Window Efficiency Affordable
"I think their technology is very good," admits Guar. Still,
as he sees it, the key will be to produce a window that is affordable,
reliable, and durable. The manufacturing implications are huge, he says.
"Handling large sheets of glass is non-trivial," Guar says.
Covering that glass with a chemical film is even harder. "It's not
an easy thing to accomplish," Guar says. Still, the right partnership
would make the glass available to window companies who feel they could
provide a dependable seal for this technology. The fact that Sage is partnering
with Honeywell to provide the switching capability gives a great boost
to their product.
Granted, there are technologies available
that use advanced chemical solutions to address energy efficiency. Heat
Mirror is an excellent product that was developed to insulate glass from
heat loss and heat gain. Heat Mirror windows have an insulative reflective
barrier that is suspended between the panes of glass. It is spectrally
selective and allows visible light to enter while blocking near infrared
rays that cause heat buildup. It functions like a third layer of insulation
and greatly increases the R-value of walls with windows. But, while the
R-value with Heat Mirror windows is exceptional, the cost for insulating
windows of this caliber is very high. And they're not switchable. The
key to winning the high efficiency window race, most experts agree, is
to produce an affordable technology that can be mass produced and last
for the lifetime of a standard window warranty.
Changing the Way We Work With
Windows
SageGlass plans to offer an affordable technology that is durable, reliable,
and ripe for the market. "We're trying to change an industry,"
explains Myser. Consumers want more glass, but they demand efficiency
and control. Bringing electrochromic device technology to the window industry
will allow homeowners to control the amount of light and heat that enters
the building. "People want skylights, they want windows in their
homes, the light it brings, but what do they do about the heat? We've
solved that. Switchable control means controlling both the light and the
heat," Myser says. Since the SageGlass coating is applied to only
one of the panes of glass, their hope is that they can provide affordable
switchable technology to the window industry and its customers.
"People understand this technology
and want to buy it," Myser says. For homeowners it could revolutionize
window placement and home design. It would mean windows where you want
them, not just where heat gain can be reasonably avoided. This technology
may even allow designers to place windows on west-facing facades without
sustaining the incredible burden a beating western sun places on the air
conditioning system. It may also mean designing for the glorious morning
sun that so many homes currently avoid. Better yet, since this technology
is device-controlled, it can even be programmed to darken or lighten automatically
so that indoor climates can be effectively controlled even when the homeowner
is absent.
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