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Describes the fraction of total incident energy which passes through a glazed area of a building when compared with the incident energy upon it. The components considered for this calculation are the “Direct Solar Energy” transmittance and the indirect “Thermal Energy” heat transfer values.

The calculation sums the fractions of Incident Direct Solar Energy and the ambient thermal energy which passes through the glazed area under specific environmental conditions. The calculation takes account of the following factors, specified by regional international standards:

- The angle of the sun with respect to the façade.
- Ambient air temperature differential across the glazed assembly.
- Surface heat exchange coefficients for both internal and external surfaces.

ASTM E971-11, EN 410, and ISO 9050 are the most commonly applied standards for energy performance calculation for glazed areas.

These calculations provide standardized values of the heating energy arriving inside a building and is expressed as a number between 0.00 and 1.00. A lower Total Solar Energy number means less heat penetration inside and a reduction in air-conditioning operating cost.

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.

� 2015