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U.S. Department of Energy Energy Efficiency and Renewable Energy

For Builders

In order for the volume purchase to succeed, the participation of national builders is a must. Specifically, the DOE Building Technologies Office (BTO) is requesting input on the types, sizes, and quantities of high performance windows of interest along with permissible price premiums and warranties. Most importantly, BTO is requesting the commitment of national builders to purchase high performance windows in volume if prescribed performance and cost specifications are achieved.

Cutaway drawing of a room with a man standing in the middle. The left wall consists largely of a window. On the floor under the window is a box (heater) with arrows radiating in all directions into the room. Curvy arrows move upwards along the inside of the window and along the ceiling, showing Perimeter Radiation.

A lower U-Factor in highly insulated windows may render perimeter heating near windows unnecessary.

Cutaway drawing of a room with a man standing in the middle. The left wall consists largely of a window. The outside temperature is 0 degrees F. Above the man it is 70 degrees F. The right side of the room is 65 degrees F. Wavy arrows emanate from the man both to the left and to the right.

Radiation from a warmer body to the colder glass causes discomfort because the two sides of the body have very different rates of radiant heat loss

Wisdom Way Solar Village

One successful example is Wisdom Way Solar Village, a small residential development comprised of 10 duplexes in western Massachusetts. These homes were designed and built to showcase energy-efficient building performance at affordable price points. Duplexes of this project range in size from 2-bedroom units at 1,137ft² to 4-bedroom units totaling 1,773ft². Successful use of triple-pane R-5 windows in concert with an improved overall building envelope allowed for the scale-down from a conventionally sized heating system to a 12,000 Btu natural gas unit. This heating unit reduction represented a $4,500 savings in the total cost of the system. Additionally, due to the superior insulating properties of the windows and overall envelope, occupants can expect to save over $1,000 annually on energy. Despite a $7,000 incremental cost for an enhanced building envelope—$3,500 of which was spent on window upgrades—achieving building performance that allows for a more compact heating system can offset much of this incremental cost and significantly reduce the payback period.


More Advantages for Builders

In cold and mixed climates, builders can reduce capital costs through the use of high performance windows which may permit elimination or redesign of perimeter duct heating systems, and installation of smaller heating, ventilating, and air conditioning (HVAC) units.

Horizontal bar chart comparing typical winter window heat loss in Btu/ft2/hr for 3 window types in 4 U.S. cities. The top bar represents a conventional 2-pane window; the middle bar represents a typical ENERGY STAR window, and the bottom one represents an high performance window. In Boston, MA, the top bar is > 40, the middle >30, and the bottom < 20; in Cleveland, OH, the top bar is > 35, the middle > 25, and the bottom > 15; in Minneapolis, MN, the top bar is nearly 50, the middle > 35, and the bottom > 20; in Spokane, WA, the top bar is > 45, the middle is about 35, and the bottom > 20.

The rate of heat loss determines the window surface temperature and the need for perimeter heating.

Highly insulating windows also allow builders to pitch market differentiation and a green edge. Home and business owners can cost-effectively lower lifetime energy costs, while improving temperature uniformity and room comfort, and potentially acoustic characteristics. Depending upon their structure, three pane high performance windows can moderately to significantly lower noise levels compared to standard two pane windows.

In the Future

BTO will be providing additional support to help successfully transform the market for high performance windows. This support will include a follow on manufacturer production engineering solicitation to further improve performance and drive down costs, addition of commercial-grade high performance windows, a Phase II volume purchase, and visibility and recognition mechanisms for builders who routinely install high performance windows.