Effective thermal conductivity of a staggered double layer of vacuum insulation panels

The use of vacuum insulation panels in buildings has gradually increased in the past few years and developments in their production have occurred in parallel. This has mainly lead to an optimization of different hygro-thermal properties of both the core material as well as the envelope. The issue of thermal bridges caused by the 300 nm thin metallic layers of the barrier envelope and by the joints between two adjacent panels remains. The present study investigates the influence of these thermal bridges on the effective thermal conductivity of a staggered double-layer of vacuum insulation panels. For this purpose a series of guarded hot plate measurements on single- and double-layers of vacuum insulation panels was carried out. The variety of the existing thermal bridge situations was accounted for by different panel size compositions. The results hereof were compared to those of a simplified numerical model. The target is to determine the effective thermal conductivity by a minimum number of required tests and the simplest numerical model. This will enable the determination of additional heat loss induced by the mentioned thermal bridges for a specific envelope laminate type without knowing the details of its composition especially the metallic layers.