Three Major Ways to Save Energy
Installing window treatments in your home is a phenomenal way to reduce heat, cooling, and lighting energy needs. You can choose window treatments or coverings not only for decoration but also for saving energy. Carefully selected window treatments can reduce heat loss in the winter and heat gain in the summer. The three major ways window fashions aid in energy efficiency
- Reduce heat flow – heat loss and heat gain – through the windows.
- Controls solar heat – heat energy from the sun – by allowing heat to enter the window and home in the cool winter months and blocking hot solar energy during the hot summer.
- Enhances daylighting – the use of natural light – by diffusing and dispersing sunlight.
Winter and R-Value
R- value is the measure of a material’s resistance to conductive, convective and radiant heat flow. The higher an R-value the slower the heat transfer through the material. The walls of a home typically have an R-value of about 20, roofs about 30 and windows are anywhere from 1.0 to 3.5. A window with an R-value of 2.0 allows ten times more heat to flow through than a wall with a value of 20, therefore, the wall is 10 times more energy efficient.
Summer and Solar Heat Gain Coefficient
A product’s solar heat gain coefficient (SHGC) is a measurement of the products ability to reduce heat gain within the home from the sun. A fraction of the solar energy that strikes the window passes through and heats the room, this can be beneficial in the cold winter months but during a hot summer, window treatments are a good way to reduce heat gain and keep the home cooler. SHGC is expressed as a number between 0 (none) to 1 (all). The lower a window’s solar heat gain coefficient, the less solar energy comes through. When choosing products with louvres, slats or vanes, opt for white or light colors to further reduce heat gain. During the summer, it is important to reflect as much solar energy as possible.
Using the natural light that enters the home to illuminate a room’s interior is called daylighting.
The goals of daylighting are to diffuse incoming light deep into a room. Good daylighting not only reduces the need for electric, artificial lighting, but maximizes our visual comfort as well. Sheer or translucent fabric does an excellent job of diffusing the light and allowing it to fill a room. Another way to achieve daylighting is to redirect the sun’s rays and reflect the light into the room, blinds and shutters do this very well.
Because of the numerous openings between the slats, it’s difficult to control heat loss through interior window blinds, but the slats offer flexibility in the summer. Unlike shades, you can adjust the slats to control light and ventilation. For example, when completely closed and lowered on a sunny window, highly reflective blinds can reduce heat gain by around 45%. They can also be adjusted to block and reflect direct sunlight onto a light-colored ceiling. A light-colored ceiling will diffuse the light without much heat or glare.
Exterior roller blinds are usually made of wood, steel, aluminum, or vinyl. They’re mounted above the window, and side channels guide them as they’re lowered and raised. When you lower these blinds completely, their slats meet and provide shade. If partially raised, the blinds allow some air and daylight to enter through windows.
A drapery’s ability to reduce heat loss and gain depends on several factors, including fabric type (closed or open weave) and color. With such a wide variety of draperies available, it’s difficult to generalize about their energy performance.
During summer days, you should close draperies on windows receiving direct sunlight to prevent heat gain. Studies demonstrate that medium-colored draperies with white-plastic backings can reduce heat gains by 33%. Draperies also stay cooler in the summer than some other window treatments because their pleats and folds lose heat through convection.
When drawn during cold weather, most conventional draperies can reduce heat loss from a warm room up to 10%. Therefore, in winter, you should close all draperies at night, as well as draperies that don’t receive sunlight during the day.
To reduce heat exchange or convection, draperies should be hung as close to windows as possible. Also let them fall onto a windowsill or floor. For maximum effectiveness, you should install a cornice at the top of a drapery or place the drapery against the ceiling. Then seal the drapery at both sides and overlap it in the center. You can use Velcro or magnetic tape to attach drapes to the wall at the sides and bottom. If you do these things, you may reduce heat loss up to 25%.
Two draperies hung together will create a tighter air space than just one drapery. One advantage is that the room-side drapery will maintain around the same temperature as the interior space, adding to a room’s comfort.
When properly installed, window shades can be one of the simplest and most effective window treatments for saving energy.
Shades should be mounted as close to the glass as possible with the sides of the shade held close to the wall to establish a sealed air space. You should lower shades on sunlit windows in the summer. Shades on the south side of a house should be raised in the winter during the day, then lowered during the night.
For greater efficiency, use dual shades—highly reflective (white) on one side and heat absorbing (dark) on the other side—that can be reversed with the seasons. The reflective surface should always face the warmest side—outward during the cooling season and inward during the heating season, and they need to be drawn all day to be effective.
Quilted roller shades and some types of Roman shades feature several layers of fiber batting and sealed edges. These shades act as both insulation and air barrier, and control air infiltration more effectively than other soft window treatments.
Pleated or Cellular Shades
Several manufacturers have designed two- or three-cell pleated or cellular shades with dead air spaces, which increase their insulating value. These shades, however, provide only slight control of air infiltration.
Window shutters—both interior and exterior—can help reduce heat gain and loss in your home.
Interior shutters need a clear space to the side of the window when they’re opened. They also require hardware that is fastened to the window jams or trim. Properly designed exterior shutters may provide the best possible window insulation system. They offer several advantages:Weather protection
- Weather protection
- Added security
- No use of interior space
- No thermal shock to windows if left closed.
Exterior shutters must be integrated into your home’s architecture. Their mounting, drainage, and hinging will require special consideration, and it’s easier to address these design issues in new construction.
Most exterior shutter systems include a mechanical crank, rod, or motor to allow operation from indoors. This can help encourage daily use of the shutters, and may be required by local fire codes.
Roll-down metal exterior shutters are often used as protection against storms and/or vandalism. While metal shutters provide protection against these hazards, they don’t provide much of a barrier against air infiltration and heat.
Like window blinds, louvered shutters work best for summer shading. Movable or fixed louvers allow ventilation and natural daylight to enter a room while blocking some direct radiation. However, they won’t provide much insulation against heat loss in the winter.
Solid shutters will decrease both heat loss and summer heat gain. These insulating shutters consist of wood panels, a vapor barrier, and sometimes a decorative covering. If you fit them tightly against a window frame, they’ll provide an insulating air space between the shutter and the window.
You can combine shutters with other window treatments such as draperies for greater insulating ability.