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Moisture buffering is the capacity of hygroscopic building materials or adsorbents to mitigate the humidity fluctuations in the indoor environment through the adsorption/desorption phenomenon. NORDTEST proposed the moisture buffer value to quantitively characterize the moisture buffering capacity of porous materials. Materials with high moisture buffer values have a higher ability to passively control indoor humidity conditions and thus reduce building energy consumption and improve indoor thermal comfort. However, the ideal moisture buffer value theory is based on the assumption that the thickness of the studied materials should exceed the penetration depth of that material. This assumption significantly limits the application of moisture buffer value theory to thin-layer materials, such as textiles, desiccant coating, wallpaper, wood wall panels, etc, which represent a large proportion of moisture buffering in the built environment. In this study, we developed a new numerical model to calculate moisture buffer values for hygroscopic materials with different thicknesses. Experimental measurements were also carried out to validate the solutions. The moisture buffer value of a new kind of desiccant (metal-organic frameworks) under different thicknesses were measured by climatic chamber tests. Simulated results showed agreement with both the measurements and theory. The results indicate that the new moisture buffer value model can be used to find the optimal thickness of desiccant coating or hygroscopic materials for autonomous indoor humidity control.

Volatile organic compounds (VOCs) are the major indoor air pollutants that affect human health, comfort, and working performance. Sorbent material and adsorption technology are considered to be one of the most effective and economical ways to remove VOCs from indoor air. Among many sorbent materials, metal-organic frameworks (MOFs) have received more and more attention because of their superior performance in capturing a variety of compounds. In this work, the adsorption characteristic of a newly synthesized pyrazole-based metal-organic framework (Al-pda) for different VOCs was investigated. First, the single-pass VOC adsorption rates of Al-pda and activated carbon were tested under different low-concentration VOCs mixture, which is in line with the practical application in the indoor environment. The results showed that Al-pda had an especially high adsorption ability for formaldehyde. The single-pass efficiency of formaldehyde adsorption was up to 89% at the beginning of the test and gradually stabilized at 66%. Compared with activated carbon, Al-pda had significantly higher selectivity and adsorption efficiency for the capture of formaldehyde. Then the effect of relative humidity on formaldehyde adsorption was investigated. After increasing the relative humidity from 15% to 65%, Al-pda's formaldehyde single-pass adsorption rate almost remained at a similar level. Preliminary research showed that Al-pda is a promising material for the selective adsorption of indoor formaldehyde under humid conditions. More work is needed to probe this new MOF's adsorption mechanism and application method.

Functional materials with large hygrothermal inertia can passively mitigate indoor temperature and humidity variations, thus improving indoor environmental quality and reducing energy demand for heating, ventilation, and air-conditioning (HVAC) systems. In this study, a novel functional phase-change humidity control material (PCHCM) was developed based on the integration of microencapsulated phase-change material (MicPCM) and novel moisture adsorbent: Metal-Organic Frameworks (MOFs). The novel MOF-based PCHCM is a dual-functional composite material. It can simultaneously uptake/release heat and humidity from indoor air and control the hygrothermal environment passively. The materials characterizations show that the new MOF-based PCHCM has better thermal and moisture buffering ability than most conventional building materials. The effect of the new material on building energy conservation was calculated by a newly developed HAMT-enthalpy model. The simulation results show that MOF-based PCHCM can effectively moderate the fluctuations of temperature and relative humidity and reduce building energy consumption in most climates worldwide. The maximum energy-saving potential could reach up to 35% in hot-dry climates. The paper will guide the application and further development of dual-functional PCHCM composites under different climates.