Posted in Efficiency, Author: Peter L Pfeiffer
Don't Build An Energy Dud
All too often, architects and homeowners will ignore the simple solution in favor of a new technology that promises the world. This is especially true when looking to reduce the monthly energy consumption of a new home.
For example, spending top dollar on a state-of-the-art HVAC system can dramatically reduce energy use when the system is running. On the other hand, an architect can achieve the same energy savings by designing a home that better withstands the summer heat so that the HVAC system has to cycle on much less often. Typically, these design improvements won’t have a significant impact on the time or cost of construction.
Using “passive solar” strategies in your architectural designs can achieve predictable, verifiable energy savings. The key is to defend the two primary entry points where solar heat can invade the home. The first is the windows.
Minimizing the number of west-facing windows – especially in the South and Southwest areas of the U.S. – will substantially reduce the amount of heat energy from the sun that can enter the home. Consider using non-living space such as a laundry room, garage, or walk-in closet along the western exterior wall to avoid the need for windows. If windows are necessary, simply shade them with eaves or other design elements.
The other source of solar heat is the roof. Blocking the sun (with tall trees, for example) would be effective but is almost universally impractical throughout the U.S. Instead, consider a radiant barrier that will block up to 97% of heat energy.
A radiant barrier is relatively simple technology where a standard roof decking material is laminated on one side with an aluminum foil. The building material is then installed with the foil facing down and exposed to the attic air. Although aluminum easily gains or loses heat through direct contact with another material (conduction), it emits amazingly little heat energy through the air (radiation) no matter how hot it gets.
By the numbers, a radiant barrier such as LP® TechShield® Radiant Barrier will radiate about 3% of the heat energy absorbed by the aluminum foil. Compare that to un-laminated roof decking materials, which radiate 80%-90% of the heat they absorb. The installation is the same either way, so a radiant barrier takes no more labor time or training on the job site. The difference in the cost of materials is negligible for an average-sized house.
According to an independent study by Oak Ridge National Laboratories, a radiant barrier can lower the temperature in attics up to 30 degrees and save homeowners up to 17% on air conditioning bills. Installing a radiant barrier during construction costs far less than other more expensive energy-saving measures. Plus, radiant barriers require no maintenance and come with up to 20-year warranties.
When selecting a brand-name radiant barrier, an important factor to look for is incising—which is a pattern of small slits in the aluminum that allows water vapor to escape. Without incising, moisture in the wood can become trapped beneath the lamination. Trapped moisture may also pool between the wood and aluminum, creating “blisters.” If these blisters pop, they create a pathway for radiant heat to enter the attic space.
Blocking solar heat from entering a home not only limits the stress on the HVAC system, but also reduces the need to run it. Homeowners can go longer in the spring without turning on the air conditioning and stop using it earlier in the fall. Also, turning on a ceiling fan or opening the windows becomes a more effective (and comfortable) means of keeping the home cool when the sun’s effects on the interior are kept to a minimum.
These strategies are referred to as “passive” because the homeowner doesn’t have to do anything in order to enjoy the benefits. Once construction of the home is complete, they can essentially be forgotten and still produce energy savings.
Additional energy-smart options to consider include:
- high-quality fluorescent lighting
- air-tight ductwork (20% of air leaks out of ducts in a typical home)
- a front-loading laundry machine
- low-flow shower heads
Based on simplicity and cost, these strategies are “low-hanging fruit” that should be included among the first steps towards designing an energy-efficient home. Once the easy solutions are in place, an architect or builder can take proper advantage of more advanced technologies for energy savings.
Peter Pfeiffer, FAIA, is a principal at Barley & Pfeiffer Architects in Austin, Texas. He can be reached at firstname.lastname@example.org.
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