Previous studies show that a large part of the net energy demands of an office building is related to window heat loss and cooling demands induced by solar irradiance. Windows with improved thermal transmittance (U-value) and solar heat gain coefficient (SHGC or g-value) are important for reducing the related energy demands.
There is a scarcity of available scientific work addressing multilayer window technologies. Hence, in this study, simulations with the aim of identifying the parameters that play a key role in improving thermal performance of multilayer glazing units have been carried out. A state-of-the-art review is presented, alongside an overview of promising new products and future perspectives and improvement possibilities for multilayer glazing technologies.
It has been found that increasing the number of glass panes in the insulating glazing units (IGU) yields U-value reductions that decrease for each added glass pane. Cavity thicknesses between 8 and 16 mm were found to be optimal for IGUs with four or more panes. Reducing cavity gas thermal conductivity was found to impact IGU U-value. Improving low-emissivity surface coatings beyond the best-available technology has minor effect on U-value reductions.
In addition to the thermal performance of the glazing units, optical properties, aesthetics, ageing properties and robustness should be further studied before the use of such multilayer IGUs may be recommended. Preliminary numerical simulations have demonstrated that thermal stresses to the glazing units due to high cavity temperatures can pose a problem for the robustness and lifetime of such units.