Energy Efficient Windows
A number of articles have appeared lately announcing large stimulus grants distributed by the Department of Energy to research and produce more energy efficient windows. These research projects propose to find more efficient ways to produce high performance windows. Here are a few of the announcements:
Southwall Awarded $1.4 Million from Department of Energy to Make Homes and Buildings More Energy Efficient (via MarketWatch)
Traco to get $1.3M DOE stimulus grant (via Pittsburgh Tribune)
DOE Aims to Make 'Low E' Windows a Must-Have for Home Construction (via New York Times)
Selecting high performance windows and glazing is critical to energy saving and interior comfort. Here are some basics about how energy efficient windows work.
As shown in the diagram above, a typical window looses energy in 4 ways: conduction, radiation, air leakage and convection.
In terms of residential construction, Fine Homebuilding has a nice article here explaining the science of energy efficient windows:
Windows are thermal holes. An average home may lose 30% of its heat or air-conditioning energy through its windows. Energy-efficient windows save money each and every month. There are even some cases where new windows can be net energy gainers. The payback period for selecting energy-efficient units ranges from two years to ten years.
The Window as a complete assembly
To avoid confusion, the National Fenestration Rating Council (NFRC) offers a window rating system based on the complete window assembly. These ratings take into account the resistance to heat-flow (U-factor), the heat admitted as radiant energy (solar heat gain coefficient) and the visible transmittance (VT).
The Glass
Firstly, an efficient window should be comprised of insulating glass (double-glazed or triple-glazed), not a single-glazed glass. Next, a low-e coating can be applied to reduce the flow of radiant heat. Check out the previous post on curtain walls mentioning briefly where these coatings are applied. Also, The Efficient Windows Collaborative has a concise explanation of low-e coatings on this page. Beyond coatings the air space between the the glass surfaces can be evaluated. Some units simply contain a sealed air space between the two layers, but improved performance can be realized by filling the gap with a less conductive gas that minimizes the transfer of heat. An explanation of how Argon and Krypton have been used for this purpose can be found here. There is some concern and discussion about the long term leakage of the gas from within this air space. If you're evaluating different technologies and manufacturers, seek out answers on the likelihood and consequences of such leakage occurring.
The Frame
The frame plays a significant role in the overall window performance. This surface can be the source of substantial heat transfer between the interior and exterior environments.
- Metal Frames
- Aluminum extrusions make for highly durable frames, but are also highly conductive. To address this problem, a thermal break should be utilized to seperate the interior and exterior frame components. The thermal break is a less conductive material inserted between frame extrusions.
- Non-Metal frames
- Wood framed windows have long been used for their appearance in residential applications. Thermally, wood performs fairly well, but it's not the most durable material in outdoor conditions.
- Wood-clad frames are available that provide a vinyl or aluminum wrapper around wood construction to create a durable surface.
- High performance hybrid frames are also available consisting of vinyl, fiberglass and engineered thermoplastics.
6 Comments
Reader Comments (6)
Energy efficient windows should be installed in everybody's homes to save lots of energy. We are now in a state of energy depression. Energy is mindlessly wasted and now is the time to reverse that.
If you have traditional windows installed in your home such as single glazed timber windows or upvc double glazed windows then an energy rated window may be the ideal choice for providing an energy saving solution that could pay off over the coming years.
If you want to boost your home’s energy efficiency the windows are the best place to start. It’s not necessary to invest in replacement windows to boost performance. With some inexpensive materials and a day or two of work you can significantly cut your heating and cooling costs.
The most efficient windows nowadays is defending on the number of glass panes it have. The good thing about this article is providing information that is very vital in improving house and help to save money.
Double Glazed windows are an ideal asset to have to your home. Double glazing has long been associated with health benefits, as well as heat retention which are very popular with people in the United Kingdom. The draught prevention and noise reduction double glazing presents has contributed to the magnified popularity of double glazing in the home. Additionally, double glazing can also offer a greater sense of security with it's framework and installation sturdiness via it's lock-in systems.
I appreciate you very nice post,It really informed me a lot and i will look forward for more post later.I would say that without industrial materials we will not able to build it.outdoors curtain