Predictions for the Increase in Pressure and Water Content of Vacuum Insulation Panels (VIPs) Integrated into Building Constructions using Model Calculations

Abstract

The climatic conditions (temperature, relative humidity, and water vapor pressure) on both sides of vacuum insulation panels (VIPs) that were integrated into different building constructions are measured every hour. The influence of these conditions on the increase in air pressure and water content within the VIPs is estimated using a calculation model. The results of these model calculations are correlated with the pressure and mass measurements on VIPs, exposed to actual climate but removed for laboratory measurements. First, we find that upon use of the temperature-dependent air permeation rates for VIPs, the linear increase within the VIPs can be predicted reliably. Thus, it is sufficient to use annual average temperatures for these estimates. Second, the mass increase of VIPs due to infusion of water vapor through the barrier foil can be determined using the calculation model. The ‘driving’ force in this case is the difference in vapor pressure across the foil cover, which decreases with time, once the water vapor pressure within the VIP starts increasing. In effect, the water vapor pressure and the water content within the VIPs reach equilibrium. Depending on the climatic conditions, the maximum water content between 3 and 7 m% can be predicted.