Analytical Models for Calculating Thermal Bridge Effects Caused by Thin High Barrier Envelopes around Vacuum Insulation Panels

Abstract

Although vacuum insulation panels (VIPs) are thermal insulators with very low center-of-panel thermal conductivity, their effective thermal conductivity is raised significantly due to large edge heat fluxes caused by a continuously enveloping high barrier laminate, especially if metal based foils are applied. This study therefore presents and validates two analytical approximating models for calculating this thermal edge effect for thin high barrier laminates around VIPs. A comparison of these models with numerical simulations shows that they can be applied with an inaccuracy of <5% for idealized barrier laminates, considering the limitations specified. These models also demonstrate that the linear thermal transmittance, representing this edge effect, amongst others depends on envelope thickness and thermal conductivity, panel thickness, and center-of-panel thermal conductivity. Moreover, this study shows that these models are able to estimate the linear thermal transmittance resulting from more realistic VIPs with seams near their edges, as well. For these realistic panels, deviations between numerical data and prediction model maximally amount to about 9%. Using the presented models then, enables VIP designers, architects, and building engineers to estimate the overall thermal performance of a VIP.