VIP service life assessment: Interactions between barrier laminates and core material, and significance of silica core ageing

Abstract

a b s t r a c tAs a result of temperature and humidity vacuum insulation panels (VIP) age: their thermal resistance decreases due to the combined effect of internal pressure and solid conduction increase. For given conditions this depends on the duration of the exposure and on the permeance of the envelope, as well as on the hygric and thermal behaviour of the core material. This paper begins by assessing the severity of the various building applications with regard to the VIP. It then presents the main behaviours and models needed and explains the life evaluation approach under stationary conditions. Furthermore particular attention is paid to the ageing of silica core material. It concludes that for a realistic estimation of the service life one needs to take into account both the thermal and hygric behaviour of the core material, the permeance of air and water vapour through the envelope, the temperature and humidity service conditions, and the thickness of the panel.

Permeation of water vapor through high performance laminates for VIPs and physical characterization of sorption and diffusion phenomena

“…-the model of proportionality between the permeation/diffusion coefficients of a polymer film and those of the same film metalized, governed by the equivalent surface fraction of defect  [6,7] and expressed by Eq. (17), is compatible with the presented results. This does not exclude other influences like the geometrical one, which is equivalent to consider not the real size of the defect but an equivalent size, taking into account the diffusion into the polymer in front of the defect.…”

“…These values are calculated on the basis of the severities of these applications described in another paper [17]. Table 3 Comparison of the sensitivities of the experimental methods regarding the measured flux as well as the sensitivity of the permeance calculated with different water vapor partial pressures.…”

“…The relation of Eq. (17) corresponds also to the one written by Langowski, replacing 1/Â by what he calls the barrier improvement factor (BIF) [9].…”

“…Second this allows to use with confidence the activation energies to evaluate both the severity of the different applications or conditions, and the acceleration factor of accelerated aging tests [17]. Indeed: -The two methods used for the diffusion measurement agree on non metalized films, and match with the literature data, therefore the method based on the transient stage of the permeation test is relevant; -This last method, based on the exploitation of the transient regime of permeation tests, is the only relevant one for metalized films and laminates because of the single flux imposed through all the layers; -The activation energy Q (26 kJ mol −1 ) is based on a large number of tests made with the VIPs.…”

“…(8)) at 40 • C and 40% RH: 0.8 × 10 −13 < 1−met < 1.8 × 10 −13 kg m −2 s −1 Pa −1 ); -with one to three metalized layers; -tested between 23 and 70 • C and from 40 to 90% RH. The model used for the influence of temperature and humidity is given by the following equation [17]:…”