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The utilization of thermal insulation is one of the most effective methods to reduce the heating and cooling loss through building envelopes. However, moisture ingress driven by the pressure gradient across the insulation may lead to a variation of the effective thermal conductivity, which highly deteriorates the thermal performance of building envelopes. In order to investigate moisture transport mechanism and its impact on the heat transfer procedure, a novel simultaneous test method based on the modified guarded hot box is proposed to investigate the variations of the moisture content and the effective thermal conductivity of thermal insulation, besides, several possible visual identification methods are applied to analyze the moisture transport paths. Based on the proposed methods, both aerogel blanket and organic foam are investigated on the variations of hygrothermal properties. Results indicate that compared to the foam insulation, the moisture content has a greater impact on aerogel blankets with the thermal conductivity increase to 3 times of the initial values. Both scanning electron microscopy (SEM) combined with crystal tracer and magnetic resonance imaging (MRI) are utilized to identify the moisture transport paths of phenolic and polyisocyanurate foams. Pinholes and capillary channels are two main paths for liquid permeation into phenolic. • Propose a simultaneous test method to measure the heat and moisture transfer. • Analyze the hygrothermal performance based on the material structure. • Visualize the moisture transport paths in typical thermal insulation for the first time. • Pinholes and capillary channels are main paths for liquid water to permeate into phenolic. [ABSTRACT FROM AUTHOR]

Closed-cell thermal insulation is one typical type of thermal insulation applied in the engineering field. However, it is observed that moisture may gradually accumulate in the insulation and highly decrease the system thermal behavior. The hygrothermal behavior depends on the mesoscopic structure and moisture distribution of the closed-cell materials. In order to investigate the impact of mesoscopic structure on the hygrothermal behavior of closed-cell insulation, a multi-scale simulation study is reported in this work. An improved random reconstruction method is first proposed to describe the structure of closed-cell insulation, and then a multi-scale thermal model is proposed to study the impact of mesoscopic structure at both mesoscopic and macroscopic scales. The trend of the results derived from the proposed multi-scale model is consistent with the experimental results, and the relevant error is lower than 10% when the degree of saturation is low. Based on the proposed models, it is found that the mesoscopic structures have significant impacts on the hygrothermal behavior of closed-cell thermal insulation at multiple scales. Both the porosity related parameters and other structure parameters are considered and discussed in detail, with sensitivity analysis provided at the end. [ABSTRACT FROM AUTHOR]