Thermal Bridges in Vacuum-insulated Building Façades

In architecture, the outstandingly low thermal conductivity of vacuum insulation panels (VIPs) of 4 103 W/(m K) allows to realize thin thermal insulation layers. Typical U-values are 0.2 W/(m2 K) for a 2 cm-thick VIP. On the other hand, with vacuum-insulated faç ades the relative effect of thermal bridges is much stronger than that for conventionally insulated buildings. In this work, different thermal bridges are investigated. Especially with VIPs with laminated Al foils (here the aluminum foil is 8 mm thick and laminated on both sides with plastic foils of 15 mm PET and 50 mm PE), strong thermal bridges around the perimeter of the VIPs occur. Also the mounting system can have a strong negative effect on the thermal performance of VIP-insulated walls. As our calculations show, the effect of the thermal bridge depends strongly on the thermal contact of the VIPs with the wall. Therefore, it is necessary to optimize every vacuum-insulated construction in order to make the best use of the low thermal conductivity of VIPs. As an example, we describe how VIPs were effectively integrated into a renovated gable faç ade and into a new ultra-low energy timber building.