ÖNORM EN 673

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 silicate glass products (called hereafter soda l h e glass), borosilicate glass and glass ceramic. It applies also to multiple glazing cornprising such glasses andlor materials. It does not apply to muttiple giazing which include in the gas space sheets or foils that are far infrared transparent. The procedure specified in this European Standard determines the U valuel) (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. Furthemore 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 C.1) gives normative reference to the U value calculated for the glazing components according to this standard. For the purpose of product cornparison, a vertical position of the glazing is specified. In addition U values are calculated using the same procedure for other purpoces, in particular for predict ing: 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 C.2). Reference should be made to C.4 and C.5 or other European Standards dealing with heat loss calculations for the application of glazing U values deterrnined by this standard. A procedure for the determination of emissivity is also given. The rules have been made as simple as possible consistent with accuracy