Analytical Model for Computing Thermal Bridge Effects in Thermally Highly Performing Building Panels

Although vacuum insulation panels (VIPs) have widely been used in refrigerators and transport containers for a long time, they have only recently been discovered by the building sector. A vacuum insulation panel is a thermal insulator consisting of an open-celled core material, which is after evacuation tightly sealed into a high barrier laminate to maintain the state of vacuum. In this state of vacuum, the ideal or centre-of-panel thermal conductivity of a VIP is as low as about 0.004 W/m/K. As a consequence, vacuum insulation panels combine high thermal performance with limited construction thickness. Integrated into building panels, however, a thermal bridge effect occurs at the panel's edge due to the combined effect of the high barrier laminate around the VIP and the (structural) edge profile along the circumference of the component. Especially the latter effect reduces the overall thermal performance significantly, the amount of which depending on the thermal conductivity and thickness of the core, the thermal conductivity and thickness of the face sheets and the width and thermal performance of the edge configuration. Until now, numerical calculation tools are used for estimating the overall thermal performance of building panels. This procedure however is time-consuming and does not give insight into the relations between relevant parameters. This paper therefore presents and numerically validates an analytical model for calculating this thermal edge effect, especially for thermally highly performing building components with vacuum insulation panels as core. The model however is generally valid for thermal shunting effects due to the edge of building panels. Based upon a comparison of analytical results and numerical data, it is shown that the inaccuracy of the analytical model compared to numerical data is less than about 10% within limitations specified. Based upon this analytical procedure, manufacturers, building scientists and architects can optimise the thermal performance of building constructions, thus contributing to the required energy reduction of buildings in their occupational phase and the desired well-being of building occupants.