The difference between the amount of heat gain and heat loss through glazing. Also known as the "Effective U-Value".
Emissivity is a surface characteristic of a material. It is the relative ability of a surface to absorb and emit energy in the form of radiation. Low-emissivity (Low E) coatings reduce the surface emissivity of the glass. The coatings are mainly transparent over the visible wave.
Energy Absorptance (A)
The percentage of solar radiant heat energy absorbed and re-emitted externally and internally by the glass.
Energy Reflectance (RE)
The percentage of solar radiant heat energy reflected by glazing.
Energy Transmittance (T)
Percentage of solar energy flow transmitted directly through the glass.