PALO ALTO, Calif. — One key challenge regarding energy efficiency in Laundromats is dealing with window glass, which, when compared to insulated walls and ceilings, is a terrible “energy loser.” While we expect that energy-conserving walls and ceilings will dramatically insulate against heat loss and block solar radiation, knowledgeable owners and distributors anticipate far less in the way of energy conservation from even the most energy-efficient windows.
FILLING NUMEROUS ROLES
The numbers speak for themselves. Walls with an insulation performance value of R-19 are considered to be the norm. R means resistance to heat flow. The higher the number, the better the insulation performance — keeping heat in during the winter and keeping heat out during the summer.
Windows with low-emissivity-coated (Low-e) glass touting the coveted ENERGY STAR designation, and whose insulation performance tops out at R-4, are celebrated by contractors and building managers. These observers rightfully see such energy-conserving windows as a substantial improvement over conventional insulating glass whose insulation performance cannot exceed R-2.
Why do we expect our buildings to contain R-19 insulated walls and at the same time accept R-4 windows? Such an energy-conservation double standard exists because it’s easier to be a wall than a window. Walls only have to insulate well.
Windows (specifically window glass) must be transparent and colorless (viewing the interior from the outside is a key security factor), facilitating the transmission of daylight, while reflecting unwanted solar energy, decreasing ultraviolet radiation that causes fading of furnishings, reducing sound transmission and insulating against heat loss in winter and heat gain in summer. Windows must also be able to provide ventilation and egress in emergencies. Compared to walls, a window must simultaneously perform numerous functions.
If it were 1960, perhaps we could maintain one energy-conservation standard for walls and ceilings and another less-demanding standard for windows and glass. But we can no longer afford to do so.
Despite insulated walls and ceilings, and the popularity of ENERGY STAR-designated windows, 25 to 35 percent of the energy used in homes and buildings is wasted due to inefficient glass. It should be no surprise that glass is responsible for less than10 percent of the total carbon emissions in the United States annually. Inefficient windows and glass contribute to cold stores in the winter and hot stores in the summer, resulting in unhappy customers. Owners also aren’t happy when inefficiency breeds higher heating-and-cooling costs.
Glass is the heart of a window. When ordering windows, here’s what store owners need to know in terms of energy conservation:
The window story doesn’t end here. Keep in mind that recent and impending revisions to the Department of Energy’s ENERGY STAR window-performance standards will require windows possessing the ENERGY STAR designation to provide increased energy efficiency.
Glass available today that will meet the new and forthcoming ENERGY STAR window-performance standards include:
The advent of new, high-performance glass technologies for standard window and fixed-glass applications heralds the end of an energy-efficiency double standard for walls and windows.