 | 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
2006-10-01 10:54:00
Low E window glass, money saver?
QUESTION: Low E Window Glass…Can It Save Me Heating Dollars?
ANSWER: We spend millions of dollars every year to heat our homes and businesses. That is why it is so important to understand the role that windows play in how buildings use energy. One of the best ways to measure the effect of windows on building energy use is known as a U-factor rating. Windows are not like walls and insulation. The high prices for natural gas, electricity, and home heating fuel that followed the first oil embargo in the early 1970s made energy a high profile, pocketbook issue. Many consumers became aware of R-values, which is a measurement of a product’s resistance to heat loss. They learned that materials with higher R-values (floors, walls, and roofs) are more energy efficient. R-values are still used by many building material companies , especially insulation. As we said earlier, windows are very different from insulation in walls and ceilings. Windows let the light in and allow people to see out, and they interact with their environment in ways that insulation does not. They react to outside air temperatures, sunlight, and wind, as well as indoor air temperatures and occupant usage. Windows are strongly affected by solar radiation and the airflow around them. R-value does not accurately reflect this interaction. Therefore, the window industry measures the energy efficiency of their products in terms of thermal transmission, or U-factor. U-factor measures the rate of heat transfer through a product. Therefore, the lower the U-factor, the lower the amount of heat loss, and the better a product is at insulating a building. The biggest difference between U-factor and R-value is that U-factor measures the rate of heat transfer (or loss) while R-value measures the resistance to heat loss. R-value is a measure of conductivity.
A product with high conductivity will transfer heat quickly, like a hot pan on the stove or a single pane of glass on a cold day. U-factor, on the other hand, takes into account more than conductivity. It also is affected by the airflow around the window and the emissivity of the glass. Emissivity is the ability of a product to absorb certain types of energy, specifically infrared and radiate that energy through itself and out of a room. A product with high emissivity, such as one pane of clear glass, will transfer over 84 percent of the infrared energy from a warm room outside to the cold air. The lower the conductivity and emissivity of the glass, the lower the rate of heat loss and the lower the U-factor. There have been significant technological developments over the last 10 years involving low emissivity (low-e) coatings on the glass. There are now many glass products available with these low-e coatings, which are typically used in dual pane windows and insulating glass units. Let's button it up for Winter! More next month…
