CEN - EN 673
Glass in building - Determination of thermal transmittance (U value) - Calculation method
|Publication Date:||1 February 2011|
|ICS Code (Glass in building):||81.040.20|
This European Standard specifies a calculation method to determine the thermal transmittance of glazing with flat and parallel surfaces.
This European Standard applies to uncoated glass (including glass with structured surfaces, e.g. patterned glass), coated glass and materials not transparent in the far infrared which is the case for soda lime glass products, borosilicate glass and glass ceramic. It applies also to multiple glazing comprising such glasses and/or materials. It does not apply to multiple glazing which include in the gas space sheets or foils that are far infrared transparent. The procedure specified in this European Standard determines the U value1) (thermal transmittance) in the central area of glazing.
The edge effects due to the thermal bridge through the spacer of a sealed glazing unit or through the window frame are not included. Furthermore, energy transfer due to solar radiation is not taken into account. The effects of Georgian and other bars are excluded from the scope of this European Standard.
The Standard for the calculation of the overall U value of windows, doors and shutters (see A.1) gives normative reference to the U value calculated for the glazing components according to this standard.
For the purpose of product comparison, a vertical position of the glazing is specified. In addition, U values are calculated using the same procedure for other purposes, in particular for predicting:
- heat loss through glazing;
- conduction heat gains in summer;
- condensation on glazing surfaces;
- the effect of the absorbed solar radiation in determining the solar factor (see Clause 2).
Reference should be made to ,  and  or other European Standards dealing with heat loss calculations for the application of glazing U values determined by this standard.
A procedure for the determination of emissivity is given in EN 12898.
The rules have been made as simple as possible consistent with accuracy.
1) In some countries the symbol k has been used hitherto.