 | Bob Crager of Lewis Street Glass is a 26 year veteran in the glass business. Lewis Street Glass is a leading Wichita Glass company, serving the entire Wichita/Sedgwick County area since 1919. They do anything and everything having to do with glass, both residential and commercial. They also do Auto glass. They are located at 743 South Market, facing Kellogg on the South, and you can reach them by phone at (316) 263-8259. You can email Bob Crager at bcrager@lewisstreetglass.com |
Glass
2010-09-01 13:38:00
Rooms with a south and west exposure…hotter and colder?
Question: The rooms in my house that have a south and west exposure always seem a lot hotter in Summer, and colder in the Winter…what can I do to correct that?
Answer: Let’s talk about those windows in your house. If you have an older home, it’s a pretty good bet that your windows are original to the house. If they’ve been replaced or repaired, you would probably not be having the problems you’re describing to that extent. Windows, as you probably know, bring light, warmth, and beauty into buildings, whether commercial or residential. They also bring a feeling of openness and more space to our living areas. But they can also be the major sources of heat loss in the cold weather months, as well as heat gain in the hot summer months like we’ve been having here in Kansas this summer. When that daytime temperature gets up to around 100+ degrees for a number of days in a row, you will have as much as 30% of your air conditioning’s cooling efforts go right out the windows of your home or office. That’s expensive! In one recent single year, it cost the United States and its residents over $20 billion, or a quarter of all the energy used for heating and cooling our spaces in which we lived and worked that year. That’s why it’s really important to select and install proper windows in our homes or work spaces at the outset. It’s every bit as important as insulation in the walls!
Since the conservation of energy has become so important in our lives, it’s important to know some basic facts about our windows and their importance, not only to our creature comforts, but as a way to minimize our own particular footprint in the amount of energy each of us uses. By making better choices, we’ll automatically conserve our energy.
There are three major factors which contribute to the overall energy usage characteristics of our windows in use today. First, how they are framed is very important. Secondly, the type of glazing that is used to set the glass panes. And third, the type of fill that is utilized in the air space between the panes.
With absent proper sealing methodology, the window frames can be a huge source of air infiltration, and that can literally bleed the coolness and warmth right out of your home, especially with weather like we have here in Kansas. Frames are usually made out of wood, clad wood, aluminum, aluminum with a thermal break, fiberglass, insulated vinyl or vinyl, or hybrid/composite materials. The type of frame used will influence the heat flow through the window, which is measured by the window’s U factor. The lower the U factor, the better the job the window does in reducing the heat flow through the window either way. The frame generally represents about 10 to 30% of the total window area, and the material it’s made of can dramatically affect the overall window performance. Aluminum window frames tend to have higher U factors due to their high thermal conductance. Wood, hybrid/composite, fiberglass, and vinyl are usually your best choices in areas like Kansas, where heating and cooling needs are extreme during the 4 seasons.
Let’s talk about the glazing of a window, which is responsible for the majority of heat loss and solar gain. There are ways in which these factors can be modified in order to increase energy and money savings.
Glazing refers to the actual glass and coating on the window pane. In the past, single panes of clear glass were the norm, but with many advances, window glazing can provide high-performance and attractive windows. There are many types of glazing systems that control heat gain and loss through windows. These include double- and triple-pane windows with such coatings as low-emissivity (called low-e), spectrally selective, heat-absorbing (tinted), or reflective gas-filled windows, and windows incorporating combinations of these options.
Low-e glazings have special coatings that reduce heat transfer through windows and thus improve the window's U-factor. The coatings are a thin, almost-invisible metal, metal oxide or semiconductor films that are placed directly on one or more surfaces of glass or on plastic films between two or more panes. The coatings typically face air spaces within windows and reduce the heat flow between the panes of glass. Windows manufactured with low-e films typically cost about 10 to 15% more than regular windows, but they reduce energy loss by as much as 30 to 50%.
Spectrally selective coatings are designed to allow only specified ranges of radiation from the sun through the glass, reducing heat gained from the sun that’s shining into the home. These coatings filter out from 40 to 70% of the heat normally transmitted through clear glass, while allowing the full amount of light to be transmitted. Spectrally selective coatings can be applied on various types of tinted glass to produce "customized" glazing systems capable of providing the desired level of solar gain for the climate region. Computer simulations have shown that advanced glazings with spectrally selective coatings can reduce the space cooling requirements of new homes in hot climates by more than 40%.
Another technology uses heat-absorbing glazings with tinted coatings to absorb solar heat gain. Some heat continues to pass through tinted windows by conduction and re-radiation, but inner layers of clear glass or spectrally selective coatings can be applied with tinted glass to further reduce this heat transfer. Heat-absorbing glass reflects only a small percentage of light and therefore does not have the mirror-like appearance of reflective glass.
Like tinted coatings, reflective coatings greatly reduce the transmission of daylight through clear glass, thereby reducing the heat gained indoors from the sun. Although they typically block more light than heat, reflective coatings, when applied to tinted or clear glass, can also slow the transmission of heat. Reflective glazings are commonly applied in hot climates like Kansas in the summertime, in which solar control is critical. However, the benefit of reduced cooling energy demands may be offset by the need for additional electrical lighting due to less sunlight entering the home.
Gas filled windows reduce the heat conductance of the air space between multiple panes by replacing that air with either argon or krypton gas. Originally, the space between panes was filled with air before it was sealed. In a sealed insulating glass unit, air currents between the two panes of glazing, carry heat to the top of the unit and settle into cold pools at the bottom. Filling the space with a less conductive, more viscous or slow-moving gas minimizes the convection currents within the space, conduction through the gas is reduced, and the overall transfer of heat between the inside and outside is reduced. Argon is inexpensive, nontoxic, nonreactive, clear and odorless.
The amount of energy and money you save with higher efficiency windows will depend on the home or building's location, orientation, total window area and the type of glazing on the windows. Your local glass dealer can advise you on what the best course of action will be for your particular circumstances and window problems.
More next month…
