By Kara Wahlgren
When homeowners think of solar technology, they may envision a roof lined with bulky (and expensive) solar panels. But the growing trend of passive solar design allows homeowners to harness the sun's energy without spending a fortune or cluttering their property with solar-energy collectors. Instead, the key to a successful passive solar design is a strategic approach to installing windows.
The right window, when installed properly, can keep a home warm in winter and cool in summer -- and add enough natural light to reduce electricity usage. Whether you're building a new home or replacing windows at an existing property, here's how to choose windows that help conserve.
1. Pick the right placement.
Passive solar design experts use the sun's path through the sky to determine where windows should be installed in a home. Ideally, the majority of windows should be placed on the south side of the home and shaded by a small roof overhang.
"The fundamental principle is that in winter, the sun is low in the sky, and in the summer, it's high in the sky," says Andy Lemann, an energy efficiency expert with Energetechs, a green building team in Missoula, MT. "The low sun in the winter will come in beneath the overhang and warm the building, and in the summer, the overhang will keep the [high] sun out of the building."
At any time of year, the hottest sun often comes from a blazing sunset, so limit the amount of glass on a west-facing wall -- it might be pleasantly toasty in the winter, but it can create a steamy solarium in the summer.
2. Choose the right type.
Some homeowners might be surprised to learn that window options go way beyond "White or wood?" Although aesthetics play a role, it's also important to consider a window's functionality and efficiency. New windows are designed with energy savings in mind, and manufacturers readily boast their insulating properties. For maximum passive solar benefits, keep these factors in mind when selecting windows:
- U-value/R-value. The U-value measures how much heat a window allows to pass through; its inverse, the R-value, measures how well a window insulates. Always look for a window with a low U-value and a corresponding high R-value.
- Solar Heat Gain Coefficient (SHGC). The SHGC measures how much solar heat comes through the window. Lemann recommends a high SHGC on south-facing windows; they'll let heat in during winter months and proper shading will keep the sun out during summer months. On all other walls, opt for a low SHGC. "It's difficult to shade windows on the west side because the sun comes in so low -- so that's when you want a window that doesn't let too much heat through," Lemann explains.
- Operation. As a rule, small or fixed windows are more efficient than oversized or operational windows. But few homeowners would choose a tiny porthole over a sprawling picture window, so the key is to install operational windows in a location where they'll capitalize on the benefits of ventilation -- by allowing a cool sea breeze to blow through the house, for example.
3. Add the right accessories.
Once you've installed energy efficient windows in their optimal location, window coverings can boost the money-saving benefits. Awnings can shade a window from overhead summer sun, but Lemann cautions that awnings can be expensive, vulnerable to wind damage and inconvenient to operate.
An affordable alternative is to install blinds on every window, which can be closed in warm months to keep sunlight from streaming in. However, Lemann says, "The problem is that once the sun hits the blind, [the heat] has already come in through the window." So although blinds are an excellent energy-saving supplement, they're no substitute for choosing the most efficient window a homeowner can afford.
THE BOTTOM LINE: It's nearly impossible to install every window in its ideal location -- if a homeowner has a sweeping mountain view to the west, you'll be hard-pressed to discourage them from installing a huge picture window, no matter how eco-conscious they may be. As Lemann notes, "The thing with windows is that it's a whole series of juggling acts. No one thing is ever perfect, but hopefully the whole balance is perfect." By installing energy efficient windows with a close eye on the principles of passive solar design, you can help a homeowner reduce energy costs for years to come.
For more expert tips and advice on energy-saving windows, see "Energy Efficient Windows" on HGTVPro.com.
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