Today glazing units are the best way to obtain glazing satisfying the requirements of modern buildings. When designing a glazing unit, we need to take into account the basic and additional functions it is supposed to fulfil. By applying two or more glass panes, additionally furnished with coating providing them with additional function, we can obtain the required technical parameters. Nowadays one of the most important parameters that need to be satisfied by a glazing unit is thermal insulation. A parameter that determines thermal insulation of a partition in construction industry is the U value – thermal transmittance.

In practice, U value determines the amount of heat expressed in Watt, transmitted through 1 m² of a partition at the temperature difference on both sides of the partition equalling 1°K.

The higher U value, the better thermal insulation performance the window pane offers, and in practice so does a glazing unit consisting of several glass panes. In case of glazing units, nowadays all types of energy losses are taken into account and improved in order to obtain an improvement of thermal insulation: conductivity, convection, and radiation.

Low-emissivity coatings are applied on window panes, and the best coating available on the market today is a vacuum applied and laser hardened coating ECLAZ. Low-e coatings improve insulation by reducing the phenomenon of radiation. Thanks to them thermal radiation gets reflected into the room, thus reducing heat losses. Heat transmittance in the processes of conductivity and convection is limited by means of replacing air in the space between the panes with a gas with a lower thermal conductivity, usually with argon. Additionally, warm edge spacers are applied in glazing units and their U value is better and better as they are manufactured from materials with the lower and lower thermal conductivity coefficient. By using the glass ECLAZ with a low-e coating and argon in the space between the panes in double glazing units it is currently possible to obtain Ug = 0.5 W/m2K.

Glass panes also allow to obtain additional heat gains as a result of obtaining energy from solar radiation shining directly on the window. The coefficient which describes what share of this energy will be obtained by the glazing unit is g. By applying the best low-e coatings it is possible to create a glazing unit with very low heat losses and high energy gains. By applying ECLAZ in a double glazing unit it is possible to obtain simultaneously Ug = 0,5 W/m2K and g of 60%, i.e. 0.60.

When designing complicated glazing units one needs to remember that lower heat losses are associated with the use of a bigger number of glass panes and a more complicated system making use of low-e coatings. The effect of such a system is always higher losses in terms of the amount of light which will be transmitted inside through a glazing unit. The amount of light transmitted inside a glazing unit is described by the TI coefficient and expressed in %. Advanced triple glazing units usually transmit ca. 73% of light, which means that their TI is 0.73, but thanks to the application of window panes with ECLAZ coatings it is possible to obtain light transmittance of even 79%, and 77% is a standard value. This result corresponds to eliminating one additional glass pane from the system.