A traditional method commonly used in building façade energy evaluation is to consider the energy performance of a designed glazed area compared to the same area glazed with 3mm clear soda lime glass. It is referred to as an indicator of the “Shading” performance of the glass design with respect to that of a 3mm glazing.
The value is calculated by dividing the Total Energy Transmittance by 0.87 and is specified using a value ranging from 1.00 to 0.00.