The heat transfer coefficient (Ug- value) is the amount of heat (W/m2K) passing per unit of time through 1m2 of a component at a temperature difference of 1Κ between the adjacent room and the outside air. The lower the U-value the higher the thermal insulation.

The total energy transmittance (g-value) is a quantity that can only be usefully obtained when the glass is the building material. It indicates the percentage of the solar energy that passes through the glass into the interior, including the secondary heat radiation which the glazing emits to the interior, as a result of absorbed solar energy.

The equivalent heat transfer coefficient (Ug-eq) indicates the heat quantity gained or lost through the glass on a yearly average Ug-eq= Ug-S x g (S-factor=direction).

The light transmittance (Tv) is the percentage of visible light passing through a glass relative to the brightness sensitivity of the human eye.

The light reflectance (Rv) indicates what proportion of the visible light is reflected from the glass surface.

The Psi-value (ψ) can be illustrated with the length-related heat transfer coefficient describing the thermal bridge of a component. In the window, it describes the heat transfer at the glass edge, mainly from the interaction of the window frame, the insulating glass and the spacer. The psi-value indicates the amount of heat (W/m2K) passing per unit of time through 1m of a component connection at a temperature difference of 1K between the adjacent room and the outside air.






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