Retrofitting an inefficient home often requires replacing the windows and doors and adding thermal mass to interior walls, but low-cost alternatives like solar screens and solar films on the windows offer a significant bang for the energy efficiency buck without the need for major construction. East-, west- and south-facing windows each offer a pathway for solar radiation to enter the home as heat and light. The heat gain accounts for as much as one-third of the cooling costs in a building, according to the Buildings Energy Data Book, an annual publication of the U.S. Department of Energy 1.
Energy use in the home is determined, in part, by the number and orientation of the openings. Windows and doors create a breach in an otherwise well-insulated wall. Combating the effects of that breach without walling yourself off inside your home is a challenge you can meet with low-cost options such as window coverings and films 3. Many of the newer, more energy efficient windows are built with savings in mind. They come with multiple layers of pre-coated glass and inert gasses between panes to maximize efficiency, but retrofitting an entire home with such windows can be daunting and expensive.
Using inexpensive films or solar screens, you can upgrade the efficiency of your existing windows at a fraction of the cost and trouble. Solar window film comes in a variety of colors and opacities that excel at different applications, while the choice for solar screens is a little simpler 4. Screens block unwanted heat gain while attempting to limit the obstruction to the view as much as possible, and they are rated according to their “openness factor,” a measure of the degree of obstruction to the view.
Solar screens are made from a variety of plastics, generally gray to black in color, and they are woven into a mesh that blocks a portion of the sun’s radiant energy while allowing a limited view of the outside world. Films are made from a blend of polyester and metalized components. Highly reflective films contain more metal than colored or smokey tints.
Solar screens necessarily alter your view of the great outdoors, an inconvenience magnified by the permanently mounted exterior varieties. Interior screens operate like a roller shade, giving you the option in different seasons to either block the sun’s energy or allow it into the house to reduce heating costs, but they only block radiant energy after it has entered the building. At that point, some of the absorbed heat is reradiated into the room rather than back to the outside.
All window films block 95 to 99 percent of ultraviolet light, but that portion of the spectrum does not contribute to the amount of heat radiated into the building, according to Darrell Smith, executive director of the International Window Film Association. Metalized films that block the greatest portion of solar heat gain also block high levels of visible light, which can defeat the effect of reduced cooling costs if they necessitate more interior lighting. More translucent films, tinted in smoke, green or blue, allow more visible light to pass through, but they are less efficient blockers of solar heat. Films are permanent, so in the winter months in moderate climates, when extra heat from the sun is desired, they could offset the balance of the summer savings with increased heating needs.
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