Building Retrofit using Vacuum Insulation Panels: Hygrothermal Performance and Durability

Doctoral thesis, 2014

Many old buildings have unsatisfactory thermal performance compared to the standards of today. One way to increase the thermal performance is to add thermal insulation to the building envelope. However, many old buildings are listed and considered to be valuable for historical and esthetic reasons. This often limits the position and thickness of the additional insulation layer. Vacuum insulation panels (VIPs) present unprecedented possibilities to reduce the required thickness of the insulation layer. The aim of this work was to investigate the possibilities, limitations and risks when using VIPs in the walls of old buildings. A special focus was on the practical experiences, durability assessment and quality assurance of the VIPs from field studies. The thesis is divided into three themes where the first theme aims to investigate the applicability of the transient plane heat source (TPS) method as a tool for quality assurance of the VIPs. The conclusion is that the method is applicable in a laboratory, but the equipment is too large to perform field measurements. In the second theme, the exterior wall of a county governor’s house was thermally insulated on the exterior with 20 mm thick VIPs. The calculated energy use for heating decreased with 24%. However, due to air and moisture diffusion into the VIPs, the energy use increases slightly during the service life. Temperature and relative humidity sensors were installed in the test wall and in a neighboring (non-retrofitted) wall as reference. It was concluded that the hygrothermal performance of the test wall was substantially better than of the reference wall. A deviation was found between the measured and numerically simulated relative humidity. Using numerical simulations, the deviation could be explained by air leakages in the wall. The third part of the thesis consists of a laboratory study where a brick wall with wooden beam ends was thermally insulated with VIPs on the interior. A parametric study was performed using hygrothermal numerical simulations to evaluate the influences by the climate, the thickness of the wall, and the properties of the brick and mortar on the moisture content in the wall. Based on these results, the wall was built and tested in a large-scale building envelope climate simulator. The wall was exposed to driving rain on the exterior surface and a temperature gradient. It was expected that the moisture content would increase in the wall with VIPs on the interior. However, the measurements showed that there was no significant difference between the cases with and without VIPs. Finally, it can be concluded that a substantial energy use reduction can be achieved when using VIPs in old buildings. With a careful design and construction process, the risk of damages to the old structure can be minimized.