scope:

This International Standard applies to glass, coated glass and materials opaque in the far infrared wavelengths. It gives the fundamental rules for calculating the thermal transmittance, U ^I), in the glazing central area, The combined edge effects due to the thermal bridge of a glazing unit spacer and of the window frame are not included.

These rules are intended to enable the heat loss through glazing in a building to be estimated from the glazing U values and, together with heat losses through the opaque elements of the building, are used to determine the capacity of the heating or cooling plant.

In addition, U values for other purposes can be calculated using the same procedure, in particular for predicting:

a) conduction gains in summer;

b) condensation on glazing surfaces;

c) seasonal heat loss through glazing in determining overall energy use in buildings;

d) contribution of absorbed heat in determining the solar factor.

The rules have been made as simple as possible consistent with accuracy.