Thermal insulation function of low e coating
In the mid-1970s, it was discovered that most of the heat transfer of double glazing was caused by infrared radiation exchange from one layer of glass to another. Therefore, as long as the emissivity of any one of the double glazing is reduced, the heat transfer can be greatly reduced. This is the reason for LOW-E glass.
There is data showing that the clear float glass has an emissivity of 0.84 and the low e coated glass with an emissivity of 0.2 reduces the radiation exchange rate by 3/4, so the U value also decreases. When the glass thickness is 4mm and the air thickness is 12mm, U value is about 2.8W/(m2*k). If the LOW-E is applied, the glass U value is reduced to 1.8 W/(m2*k). ).
The advantages of LOW-E are obvious. Since the coating is very thin, it is transparent to the short-wave radiation, allowing ultraviolet rays and visible light to pass substantially, and is opaque to long-wave infrared radiation. In winter, the indoor heat energy is kept, making it difficult to radiate outward, and in the summer, a large amount of heat radiation emitted from the outdoor high temperature is reflected back, making it difficult to enter the room, so that “warm winter and cool summer”.
LOW-E is divided into online LOW E and offline LOW E. Generally speaking, the quality of online LOW-E is relatively stable, and it is not as easy to oxidize and fail as offline. LOW E The shortcoming is that the U value is not as good as offline. If you want to improve the heat insulation effect by improving coating thickness, the glass color will be Rapidly deepen, the light transmittance is greatly reduced. Offline LOW-E has good thermal insulation and must be used in double glazed units(insulated glass).The offline low e is easily oxidized, resulting in a decrease in transparency. Both online and offline have their own advantages and disadvantages.
The high quality LOW-E can last for more than 10 years, but it is too short compared to the decades of construction. Especially the offline LOW-E, which is easy to oxidize, because whether it is to change the glass or replace the glass frame will bring great trouble to the daily use of the building. So double glazed units(insulated glass) quality is quite important when making glass purchasing decision.
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