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Stephen's Column
Energy-Star's Solar Eclipse Ending?
Passive Solar Design is not new. You can see it in the remains of indigenous cliff communities.
The modern version was born out of the Energy Crisis of the late 70's. Modern Passive Solar Designers recognize that windows are not just a source of heat loss, but also a source of heat gain. They understand that an R-30 building with a south facing window, even an R-2 window, uses less energy than the same building without any windows. (In fact, Thermotech's windows can be more energy efficient than the walls around them for any orientation).
Passive Solar gained critical momentum through the 80's. It was simpler and cheaper than Active Solar. And it generally worked well.
Then along came Energy Star for Windows. It eclipsed the sun and Passive Solar went on life support.
When the US Energy Star Program decreed that a Northern Zone window could be energy efficient with any SHGC (Solar Heat Gain Coefficient), it was great news for the national window companies. By using a highly insulating, solar shading low e, they had a universal Energy Star patch. A patch that could be used everywhere from Alabama to Alaska.
But it was bad news for Passive Solar Designers. It made it extremely difficult to buy high solar gain windows. The Nationals standardized on a solar shading low e and didn't worry about short changing northerners.
Northerners use less energy with windows that are slightly less insulating, but have a higher solar gain than those with a solar shading low e. That means northerners with R-5.8 solar gain low e windows spend less on heating than if they had R-6.8 solar shading low e windows. Even facing north. Yes, really.
All of the primary glass companies have high solar gain low-e glass, but the structure of the Energy Star program wrecked the market for these products. Admittedly, Pilkington does push hard for high solar gain low-e. But in an industry that thinks insulating value is the single defining measure of energy efficiency, not many listen.
Only a few window manufacturers promote high solar gain low-e as the path to even lower energy bills (see columns #2 & #4). Even more heretically, we also advocate different low-e coatings on different orientations. This takes advantage of the different solar regimes on different sides of a building (see www.thermotechfiberglass.com/thermotechAdv.htm#GBO ) - that, however, is another matter…..
But now the US Energy Star program needs to raise the bar. Some Code minimums are now the same as Energy Star thresholds - making a mockery of the exemplary nature of Energy Star.
Under a spell of reason, they are considering a minimum SHGC for the Northern Zone. Interestingly, this line of thinking is getting traction with another one of the primary glass suppliers. Pilkington has understood the issue for nearly 20 years, but now ACG (formerly AFG) is publicly talking about solar gains for Northerners.
In a double-page spread in Door and Window Manufacturer (Dec. 2007 issue), ACG's ad urges the industry to stop ignoring this "elephant in the room" (click here to see the ad).
It is a relief to see a second glass manufacturer, a scant quarter century after low-e coatings became available, recognize the energy savings potential of a high solar gain low e in the Northern Zone.
This is undoubtedly a sign that eventually reason will prevail, that eventually momentum will shift away from a universal Energy Star solution, that eventually Energy Star's Solar Eclipse will end.
So the question now becomes; How much longer do you think it will take for industry forces to notice that there is a second elephant in the room - glazing by orientation???
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DEFINITION: Solar Heat Gain Coefficient
Usually abbreviated to SHGC, the Solar Heat Gain Coefficient measures the relative amount of solar energy that passes through the window or door. In other words it indicates how well a window or door collects solar energy. An opaque insulated wall has an SHGC of 0.00. A frameless, glassless 'window', would have a SHGC of 1.00.
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- Frame In? Frame Out?
- All Low e’s Are Not Created Equal
- Double Hung Inherently Flawed
- The Road Less Travelled
- The Affordable Energy Efficient House
- Green Priorities - Skin Deep Not Deep Enough
- Embodied Energy - As Important As Low Energy Design?
- Energy-Star's Solar Eclipse Ending?
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