Heat transmission coefficient
The heat transfer coefficient (U-value) is the unit of measurement for determining the heat loss of a component. The U-value indicates the amount of heat that passes through 1 m² of a component per unit of time at a temperature difference of 1K. The lower the U-value, the lower the heat losses to the outside and the correspondingly lower energy consumption. For insulating glass, the U-value (designated Ug according to the test standard SN EN 674) is probably the most important parameter. In practice, the Ug value can be precisely determined for each individual insulating glass structure using certified calculation methods. It should be noted that the Ug value applies to the so-called undisturbed area, i.e. without influence of the edge area (in which the heat flow is considerably greater). The edge seal is therefore irrelevant for the Ug value. Only when determining the U-value for the entire window (glass incl. window frame), the Uw-value (w = window) is included.
Thanks to highly efficient thermal insulation coatings, SILVERSTAR insulating glass achieves Ug values of up to 0.4 W/m²K. This corresponds to the insulation of a wooden wall at least 25 cm thick.
Energy or heat transport in insulating glass takes place in three different ways
- Through the individual glass and through the gas or air fillings in the spaces between the panes.
- Convection, by flow of gas or air fillings in the gaps between the panes.
- Radiation, by heat radiation (long-wave infrared radiation) of the glass surfaces.
The heat radiation contributes by far the largest part (approx. 2/3) to the heat loss. With wafer-thin, practically invisible thermal insulation coatings, it is possible to improve the thermal insulation capacity decisively.