According to the American Institute of Architects (AIA), the use of glass in the average home expressed as a percentage of the total home living space has grown from seven percent in the 1930s to more than 15 percent today. The volume of glass used in home construction also has grown as homes have become larger. The average modest home has grown in size from about 1,100 square feet to 1,400 square feet of living space over the same period.
While the increased use of glass as a building material meets today's open-air lifestyle, it also brings with it its own distinctive baggage: increased energy costs, glaring sun and the dramatic fading of home furnishings, fabrics, carpets, fine woods, antiques and artwork. It is not surprising therefore that treating glass is increasingly looked at as a means of reducing energy bills. A recent study by the Arizona Commerce Department shows that some 40 percent of a home's heat use is the result of its window space, and approximately half of a home's utility bill can be attributed to heat gain and loss through glass. Cooling the home in summer with air conditioning to combat solar heat gain and heating it in winter to keep the home warm are the primary energy uses for most homes.
Window film is fast becoming the technique of choice for containing home energy bills. It is no longer principally a method for controlling glare and reducing fading. The proven effectiveness of window film in energy savings is recognized by the many local utilities that recommend window film.
How It Works
What exactly is window film? It is a carefully crafted laminate composed of a number of layers of materials. It generally includes a scratch-resistant coating, polyester film, laminate adhesive, metalized layer, another layer of adhesive, another layer of polyester film and a final adhesive for placement on the room-side glazing surface. In refining this complex mix of layers, window film also has become more durable. Better clear, distortion-free adhesives and scratch-resistant coatings have dramatically increased the endurance of window films to the point that top-quality films today carry a life-time warranty for residential use.
How does window film save on energy costs? The sun radiates enormous amounts of energy, a tiny portion of which reaches the earth in the form of electromagnetic radiation. The solar electromagnetic energy spectrum is divided into three parts by wavelength: infrared, visible light and ultraviolet. Window film is designed to deal with individual wavelengths of the sun's energy in such a manner as to curb heat passing through the glass (infrared), control light transmission and virtually eliminate ultraviolet radiation, the main cause of fading.
Infrared heat represents more than half the sun's energy that reaches earth. Window films either reflect solar energy back to the environment, absorb it or transmit it to the interior of a building. External and internal solar energy are reflected away from the glass and kept in their respective environs. In summer, this helps the air-conditioning system maintain a cool temperature. In winter, the reflected near infrared light and heat contribute to heating savings.
Shading coefficient, a window film standard, is a measure of the efficiency of a window system's solar control capacity. It is expressed as the ratio of the solar heat gain through any given window system to the solar heat gain that would occur under the same conditions if the window were made with clear, unshaded double-strength window glass. The lower the shading coefficient the greater the capacity of the window to control solar energy. Shading coefficients are calculated using standardized procedures that ensure comparable benchmarks.
Other industry-wide criteria related to heat loss are U-value and emissivity. U-value is a measure of the amount of heat passing through one square foot of glass in one hour for every one degree of Fahrenheit temperature difference. The lower the U-value, the greater the heat loss reduction. Emissivity accounts for the ability of a surface to absorb heat and to reflect it. The lower the emissivity, the less room heat is absorbed, thus more heat is reflected back into the room.
Window film is installed as a retrofit item on the interiors of windows. However, the proper installation of window film is critically important to its performance, aesthetics and longevity. It is best handled by highly trained specially selected dealers who are responsible for installation -- dealers who also are technologically trained to help the home owner select the most appropriate film to meet his or her requirements. When properly done, professional installation is quick, without mess or the need to interrupt normal day-to-day activities.
Modern manufacturing techniques and evolving technology have led to the introduction of new and sophisticated spectrally selective window films tailored to precise consumer needs. These state-of-the-art solar control films strike an ideal balance between light transmission, heat rejection and fade control. Too much light and heat entering an interior creates unacceptable fading and eye discomfort, while a substantial reduction of light will create a dismal environment. One of the window films that meets this challenge is Vista SpectraSelect[TM] from Courtauld's Performance Films. It allows 58 percent of the light to pass through windows while reducing heat by more than half and rejecting virtually all ultraviolet light (99 percent).
The installaton of a new counter-balanced film in sun-filled interiors will help keep homes cooler in summer heat and will insulate interior heat in winter by as much as 15 percent. A nearly invisible, virtually colorless film will not change the appearance of the glass, unlike highly reflective films that can create a mirror-like surface externally in daylight and internally at night. Objects viewed through glass fitted with this film usually appear to be more sharply focused than through untreated glass.
More and more home owners are turning to window film for energy conservation and protection from fading while using a combination of draperies or blinds for privacy. This trend is likely to accelerate as the public becomes more aware of what is available and seeks installation of this high-tech energy saving home protector.
Virginia L. Kubler is the director of sales and marketing for Courtaulds Performance Films, Inc., Martinsville, VA, (800) 345-6088; Web site: http://www.vista-films.com.