The thermal insulation performance required of building envelopes is rising all the time. This is especially true in the context of the more stringent thermal insulation standards demanded by the German Energy Saving Ordinance. There is still room for improvement here, particularly in the area of windows.

The thermal-insulation properties of glazing have indeed improved considerably in the last thirty years: the best example of this is the current development of vacuum-insulated glass, where a vacuum in the cavity between the panes leads to a heat transfer coefficient for the glazing unit of 0.5 W/m²K. Nonetheless, windows still represent a weak point in terms of the energy performance of building envelopes. One reason for this is the type of frames currently available.

The thermal insulation values of conventional window frames are still significantly above the heat transfer coefficients of the best glazing. Even passive-house windows with very good thermal insulation provided by the frames and the triple glazing rarely achieve Uw values below 0.8 W/m²K. The downside here is that these are inelegant systems with larger profiles and fittings and with increased installation depths. All in all, window frames that are highly insulating and are nonetheless sleek and light are well overdue.

The goal of the “Highly Insulating Window and Facade Systems” research project is the development of frame designs which fulfil these requirements. The participating researchers have the task of developing these frames for use as standard windows in new residential buildings and in the refurbishment of older structures, while also incorporating modern glazing such as vacuum-insulated glass. In all, two research institutes and seven medium-sized companies are participating in this research project which is supported by funds from the German Federal Ministry of Economics and Technology (BMWi).