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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]

Highlights • Provide a mesoscopic model to study the heat transfer in soil-like materials. • Perform thermal probe tests to study the fractal quartz sand in mesoscopic scale. • Clarify the impacts of mesoscopic structural parameters in dry and moist materials. • Verify that the randomness of the porous structure does have considerable impact. Abstract The ground heat exchanger (GHE) is a key component in the ground coupled heat pump (GCHP) system. The design of GHE significantly depends on the effective thermal conductivity of the ambient soil, which is derived from thermal response tests in the field. However, the test results normally indicate large differences in value, even at the same location. Such variations might be caused by the mesoscopic structure of soil. In order to clarify the impacts of the mesoscopic structural parameters on the effective thermal conductivity of soil-like materials, this paper presents and analyzes the findings from thermal probe tests and a modified random fractal model. It is found that porosity and degree of saturation are still the dominant factors, while the impacts of fractal dimension and size ratio are minor. The randomness of the porous structure in the soil-like materials does have considerable impact on the effective thermal conductivity. [ABSTRACT FROM AUTHOR]