ÖNORM EN 674

This European Standard specifies a measurement method to determine the thermal transmittance of glazing with flat and parallel surfaces. Structured surfaces, e.g. patterned glass, can be considered to be flat. This European Standard applies to multiple glazing with outer panes which are not transparent to far infrared radiation, which is the case for soda lime silicate glass prducts (called hereafter soda lime glass), borosilicate glass and glass ceramics. Interna1 elements may 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 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 document for the calculation of the overall U value of windows, doors and shutters (see A.l) gives normative reference to the U value evaluated for the glazing components according to this standard. A vertical position of the glazing is specified. U values evaluated according to the present standard are used for product cornparison 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 or other European Standards dealing with heat loss calculations for the application of glazing Uvalues determined by this standard. The determination of the thermal transmittance is performed for conditions which correspond to the average situation for glazing in practice.