- Model NO.: Low Emissivity Glass
- Color: Lowe or Tinted
- Trademark: GLOBALSTAR
- HS Code: 7007190090
- Certification: ISO 9001, CE
- Thickness: 4-19mm
- Origin: China
When heat or light energy is absorbed by glass, it is either shifted away by moving air or re-radiated by the glass surface. The ability of a material to radiate energy is known as emissivity. In general, highly reflective materials have a low emissivity and dull darker colored materials have a high emissivity. All materials, including windows, radiate heat in the form of long-wave, infrared energy depending on the emissivity and temperature of their surfaces. Radiant energy is one of the important ways heat transfer occurs with windows. Reducing the emissivity of one or more of the window glass surfaces improves a window's insulating properties.
This is where low emissivity (or low-e glass) coatings come into play. Low-e glass has a microscopically thin, transparent coating-it is much thinner than a human hair-that reflects long-wave infrared energy (or heat). Some low-e's also reflect significant amounts of short-wave solar infrared energy. When the interior heat energy tries to escape to the colder outside during the winter, the low-e coating reflects the heat back to the inside, reducing the radiant heat loss through the glass. The reverse happens during the summer. To use a simple analogy, low-e glass works the same way as a thermos. A thermos has a silver lining, which reflects the temperature of the drink it contains. The temperature is maintained because of the constant reflection that occurs, as well as the insulating benefits that the air space provides between the inner and outer shells of the thermos, similar to an insulating glass unit. Since low-e glass is comprised of extremely thin layers of silver or other low emissivity materials, the same theory applies. The silver low-e coating reflects the interior temperatures back inside, keeping the room warm or cold
Low-e coatings are applied to the various surfaces of insulating glass units. In a standard double panel IG there are four potential coating surfaces to which they can be applied: the first (#1) surface faces outdoors, the second (#2) and third (#3) surfaces face each other inside the insulating glass unit and are separated by an airspace and an insulating spacer, while the fourth (#4) surface faces directly indoors.
Whether a low-e coating is considered passive or solar control, they offer improvements in performance numbers. The following are used to measure the effectiveness of glass with low-e coatings:
-U-Value is the rating given to a window based on how much heat loss it allows.
-Visible Light Transmittance is a measure of how much light passes through a window.
-Solar Heat Gain Coefficient is the fraction of incident solar radiation admitted through a window, both directly transmitted and that is absorbed and re-radiated inward. The lower a window's solar heat gain coefficient, the less solar heat it transmits.
-Light to Solar Gain is the ratio between the window's Solar Heat Gain Coefficient (SHGC) and its visible light transmittance (VLT) rating.
here are performing data for clear on-line LowE glass
|thickness||Light Trans%||Light Refl.%||SHGC||SC||U-value|