University of Minnesota’s Center for Sustainable Building Research’s John Carmody Discusses the Latest in Efficient Window Design
RWFD: What are the primary benefits to homeowners when they install energy efficient windows in their homes?
- Reduced heating and cooling costs which provide security against rising energy costs.
- Reduced peak demand allows for smaller mechanical equipment.
- Greater comfort in summer and winter. This also means certain areas of the house can be better utilized.
- Reduced condensation/less damage from moisture.
- Reduced maintenance.
- Reduced ultraviolet radiation which causes fading of furnishings, hardwood floors and carpet.
- Improved aesthetics and view in some cases. This means that shades and blinds do not have to block views as much.
- Improved resale value.
RWFD: California utility companies have come together to inform California residents on energy efficient measures known as, ‘Energy Upgrade California’. This initiative includes a web portal for consumers on the various state and federal energy refunds available. Many other states have similar programs. How effective do you think these efforts are in reaching homeowners?
UofM: There are many programs, web sites and other information to assist homeowners in making energy efficient choices for windows. At a national level, the EWC web site provides guidance on NFRC labels, the Energy Star program, and a Window Selection Tool for your climate. You can also download RESFEN, a simple computer program for calculating energy and cost savings for windows in your home. The EWC site also provides up to date information on federal tax credits. State and local government and utility programs also provide valuable information and incentives in many cases.
RWFD: Sustainable design is intended to produce high-performance buildings that are energy-efficient, healthy, economical and use resources wisely to minimize the impact on the environment. How do today’s energy efficient windows help to achieve these goals?
UofM: Residential buildings are responsible for 21% of all energy use in the U.S. Windows play a significant role in heating and cooling which is nearly half of that total. Energy efficient windows clearly are an important contributor to reducing energy use and associated greenhouse gas emissions. Windows also provide daylight, view, and fresh air that contribute to a healthier indoor environment. The window industry is constantly striving to develop methods that reduce environmental impacts from manufacturing and depletion of natural resources. The embodied energy in manufacturing efficient windows is more than offset by energy savings over the lifetime of the window.
RWFD: Can you tell me about some of the emerging technologies in Window Materials and Assemblies?
UofM: In residential windows, achieving much greater insulating values requires triple or even quadruple glazing but they can be expensive. Various technologies are under development to provide this performance at lower costs. One potential approach is vacuum glazing where the air is removed from the space between glazing panes. For controlling solar heat gain, new low-E coatings continue to be developed. Dynamic windows are another emerging technology that permits windows to change properties at different times of the day and year. Electrochromic windows can change from a dark state where solar heat gain is very low to a clear state that allows maximum solar gain and visible light.
RWFD: We’ve all received ads in the mail from companies offering to replace our windows with "energy-efficient" windows. How much can these new energy efficient windows really save the average homeowner?
UofM: Actual savings from window replacement depends on the number and size of the windows you are replacing, the condition of the old windows, and the efficiency of the new windows. The EWC web site provides a window selection tool where you can select a major city near you and find the annual energy use for a typical house. Select “Existing Construction” and compare the energy cost for a house with your old windows and your proposed new windows. Remember this is just the heating and cooling cost, not the whole house energy cost. Results are based on a typical house (new construction: 2250 sq ft / existing construction: 2150 sq ft) with 15% window-to-floor area. Adjust the savings based on your house size and window area. To do a more accurate calculation, download RESFEN and input your specific house and window characteristics.