NBN EN 675:2011

This European Standard specifies a measurement procedure to determine the thermal transmittance of glazing with flat and parallel surfaces. For the purpose of this Standard, structured surfaces may be considered to be flat..
This European Standard applies to multiple glazing with outer panes which are not transparent to far infrared radiation (in the wavelength range 5 to 50µm), which is the case for soda lime silicate glass products, borosilicate glass and glass ceramics. Internal elements can be far infrared transparent.
The procedure specified in this European Standard determines the U value (thermal transmittance) in the central area of glazing. The edge effects due to the thermal bridge through the spacer of an insulating glass unit or through the window frame are not included.
The edge effects due to the thermal bridge through the spacer of an insulating glass unit or through the window frame are excluded. Energy transfer due to solar radiation is also excluded.
The procedure specified in this European Standard should be considered only when the thermal transmittance of the glazing cannot be calculated in accordance with EN 673.
The determination of the thermal transmittance is performed for conditions which correspond to the average situation for glazing in practice.
NOTE Patterned glass is an example of a glass with a structured surface;

For the purposes of product comparison, a vertical position of the glazing is specified (see Clause 10).
U values evaluated according to the present standard are used for product comparison as well as for other purposes, in particular for predicting:
- heat loss through glazing;
- conduction heat gains in summer;
- condensation on glazing surfaces;
- the effects of the absorbed solar radiation in determining the solar factor (see A.2).
Reference should be made to A.3, A.4, A.5 or other European Standards dealing with heat loss calculations for the application of glazing U values determined by this Standard.
The determination of the thermal transmittance is performed for conditions which correspond to the average situation for glazing in practice.
NOTE Patterned glass is an example of a glass with a structured surface;