Laboratory assessment of the hygrothermal performance of an external vacuum-insulation composite system

Abstract

In this paper, a novel laboratory test campaign to assess the hygrothermal performance of an external vacuum-insulation composite system is proposed and carried out on a large-scale specimen placed in a climatic chamber. The experimental procedure includes standard ageing cycles such as heat/rain, freeze/thaw and a new approach to simulate solar radiation conditions, allowing the study of the effect of using different finishing coat colours. Additionally, numerical modelling based in 2D transient heat transfer simulations was carried out and results were compared with those obtained experimentally. Temperatures and heat fluxes were recorded at areas around the centre of the vacuum panels and at areas near the joints between panels. Heat fluxes at the joint area were around four times higher than those measured at the centre of panel. The external vacuum-insulation system was considered to be resistant to hygrothermal cycles, since no blistering, cracking, detachment or loss of vacuum was detected. However, solar radiation cycles were found to be sensitive to the finishing colour and to potentiate anomalies that were not observed with the standard test methods, namely microcracking of the finishing coat layer. Also, the VIP thermal conductivity practically doubled after one month of accelerated ageing cycles.