Glazing for Passive Houses

Physical properties for window glazing of interest for planning Passive Houses are total solar energy transmittance and U-value, predominantly.
NFRC 100 and 200 are the standards used in the United States and some other countries, while in Europe and some other parts of the world EN 410 and EN 673 standards are used to assess these values.
Using NFRC standards will result in U and g-values that differ significantly from those derived from the relevant European standards.
Certification criteria for Passive Houses require the use of EN 410 ( g-value) and EN 673 ( U-value) as assessment standards, and PHPP results may be inaccurate, when NFRC values are used instead.
Total solar energy transmittance ( g-value, Europe) or solar heat gain coefficient (SHGC, USA) give the proportion of solar energy that passes through the glazing.
Ug for glazing U-value gives the thermal transmittance of the glazing, in other words: the amount of heating energy that can escape through a square meter of this glazing unit. This is however determined at the centre of glass; with multi-pane units the influence of the material of the edge spacer can significantly add to the heat loss for the glazing unit.

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