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Recently, atmospheric water harvesting (AWH) based on hygroscopic salt on an inorganic or organic carrier has attracted great attention because of its significant potential applications in the environment. The major technical challenges for practical applications are how to prevent the leakage of hygroscopic salt while achieving a high capacity for sorption of atmospheric water and a high sorption rate. Additionally, techniques for converting sorbed water (in the form of a lithium chloride (LiCl) solution) into clean water need to be developed. Here, a novel method for continuous atmospheric water harvesting, leveraging LiCl@PHEA hydrogels is introduced. Synthesized via one‐step UV polymerization in saturated LiCl solutions, these hydrogels exhibit remarkable air distension ability (>60 times), achieving high water sorption efficiency (11.18 gg−1 at 90% relative humidity in 30 min) with over 90 wt.% salt content and no leakage. This water collection system integrates a porous evaporator and a 3D‐printed silica substrate, ensuring an extraordinarily high evaporation rate (>11 kgm−2 h−1 under sunlight) and efficient water transmission. A prototype based on this achieves a record‐breaking collection rate of over 5 kgm−2 h−1, enabling large‐scale efficient atmospheric water harvesting. Additionally, continuous hydrogen production through electrolysis using the collected water (< 5 ppm of salts) is demonstrated. [ABSTRACT FROM AUTHOR]

Passive actuation is the production of movement or deformation without external power sources or control systems. This phenomenon has been gaining significant attention in the engineering community due to its potential use in energy‐efficient systems, in which part of the functionality is programmed in the material composition to reduce overall cost and complexity. Biological organisms, formed through millennia of evolution in a paradigm of limited resources and energy and at a multiscale equilibrium with their environment, have developed a myriad of outstanding materials and strategies for integrating complex functionalities into their multiscale structural design. In this study, the arthropod exoskeleton's chitinous composition and manufacturing strategies are used to reproduce its complex relations with external forces and water‐driven molecular rearrangement and use them to produce electricity and actuate a mechanical hand. The proposed technology is unique in combining the generation of strong forces and the integration of the principles and materials of biological organisms, leading to significant advances in the design and performance of passive solutions integrated into biological systems for a wide range of applications, such as biorobotics, medical devices, and energy harvesting. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) could be used in envelopes to moderate indoor temperature while hygroscopic materials could be used in envelopes to moderate indoor humidity. However, it remains unsolved whether these two materials are mixed to generate a better effect than single materials. Therefore, a transient model for coupled heat and moisture transfer through hygroscopic PCMs (HPCMs) was presented. The numerical cases of periodic boundary conditions and realistic weather conditions were conducted to investigate the heat and moisture transfer characteristics of three gypsum-based HPCMs containing different mass ratios of microencapsulated PCMs. Quantitative analyses were conducted to capture the effects of hygrothermal properties on heat and moisture transfer characteristics of HPCMs. The numerical results show that the mixing of PCMs and hygroscopic materials could generate a better temperature-humidity controlling effect than pure hygroscopic material, and the condensation risks inside the envelopes could also be reduced. Both the studied cases indicate that the HPCMs could be applied in building envelopes to passively moderate the indoor temperature and humidity simultaneously, reducing the building energy consumption and condensation risks inside the envelopes. The effects of hygroscopic and moisture transfer properties on temperature-control performance of HPCMs are relatively small, while the thermal properties play an important role in the improvement of temperature-humidity controlling performance of HPCMs with the increase of PCM concentration. [ABSTRACT FROM AUTHOR]

This paper aligns with the rising interest in improving indoor comfort and health of occupants by moisture buffering with hygroscopic materials and the use of bio-based materials with low embodied emissions. The study focuses on literature on light timber frame walls (LTFW) with bio-based insulation and hempcrete walls, both without a vapor barrier. The aim is to highlight the consequences of omitting the vapor barriers in such wall assemblies and to ensure their durability. This review examines two main questions. Firstly, is there a risk of mold growth in LTFW with bio-based insulation and no vapor barrier? Secondly, are there possible links between these building envelopes and the indoor climate and its potential effects on occupants? The findings show that the risk of mold growth in vapor-open walls depends on the external climate, user behavior and applied materials. It is influenced by several factors such as vapor pressure difference, water vapor resistance ratio, exterior finishing, presence of a ventilated cavity, and the hygroscopic properties of insulation materials. Vapor-open walls exhibit a higher risk of mold growth between insulation and exterior lining compared to walls with vapor barriers. Additionally, there is a lack of field studies that visually examine mold growth in vapor-open buildings. While simulations suggest that vapor-open buildings with hygroscopic insulation can buffer interior relative humidity fluctuations, supporting field studies are limited. Further research and field studies are needed to improve the understanding of vapor-open or permeable building and its implications on mold growth as well as on the indoor climate and effects on occupants. [ABSTRACT FROM AUTHOR]

Soluble silica content and the concentration of hydrogen peroxide were used to achieve porous geopolymers with nano, meso and milliporosity. The use of rice husk ash as a partial replacement for metakaolin allows to maintain the SiO2/Al2O3 ratio between 1.93 and 2.71 and achieve layered bulks with the desired moisture buffering capacity. Stereo Optical Microscopy, Environmental Ecanning Electron Microscopy, Mercury Intrusion Porosimetry, and Microtomography were used with the aim of correlating the intrinsic characteristics of the porous network to the moisture buffering capacity. A detailed analysis of the results permitted to link the moisture buffering capacity to the SiO2/Al2O3 ratio and the gel pores/large pores ratio. The saturation regime of these layered porous systems was found between 20 and 27%, while the daily moisture buffering capacity varied from 0.37 to 4.82% considering cycles of desorption and absorption. It was revealed that specimens with a high volume of gel pores (nano and meso) and optimal aeration with millipores are ideal matrices for hygroscopic applications. The porous matrices were found promising for the design of building systems with passive thermal comfort. [ABSTRACT FROM AUTHOR]

The article presents the results of experimental study for types of loose soils are easily subject to dusting. In connection with this problem, the task is the study and study of the causes and structure of the formation of dustiness in the roadside zone of roads with common types of coatings or without coatings. The experimental study aims to determine the drying time of chemical dust prevention solutions under the influence of solar radiation and the norm of their distribution. The object of the research is dust generated on roads with low transport and operational performance (temporary roads in places of road repair work, roads to quarries, etc.), and materials used for dedusting road surfaces. The problem to be solved is to reduce the emission of a large amount of dust on roads without pavements or with inferior types of pavements, which adversely affects the human body. The results obtained are the identification of a way to combat dust on road surfaces, ensuring a decrease in wear when vehicles move on roads without pavements. At the same time, the classification of dust according to their sources of formation is expected at the output result. Due to their features and characteristics, these results allowed the author to solve this problem - effective ways to combat dust on road surfaces are: treating them with dust-removing materials that reduce wear; maintaining the original evenness; reduction of air pollution; improvement of traffic conditions for cars and the sanitary and hygienic condition of roads near settlements. For experimental tests, traditional salt solutions of various concentrations (NaCl, MgCl2, CaCl2, MgCl26H2O, etc.) and solutions of foreign-made stabilizing additives Durasoil and Soiltac from SOILWORKS were taken. [ABSTRACT FROM AUTHOR]

• Moisture and latent heat transfer occurs during HFM measurements of wet samples. • Reaching steady state can take up to 150 h for wet samples. • Development of abacus to evaluate equilibrium time for different class of materials. • Up to 40% of uncertainty on thermal conductivity if steady state is not reached. • 7% uncertainty in energy loss for internally insulated walls due to measurement errors. Knowing the value of a material's thermal conductivity as a function of temperature and water content is useful for fine-tuning the prediction of building energy performance or hygrothermal comfort. When performing thermal conductivity measurements on moist insulating materials using steady-state methods, moisture is transferred from the warm to the cold side of the sample. This results in the release of latent heat, which has the potential to impact the accuracy of the measurements. The aim of this study is to examine the impact of these moisture transfers in various moist hygroscopic insulating materials during thermal conductivity measurements using heat flow meter method. The materials tested are aerated concrete, biobased composites, cellulose wadding and wood fiber insulation. The results are examined to predict the test duration leading to hygrothermal equilibrium within the sample, to assess the experimental moisture dependence of thermal conductivity, to quantify the errors made in case of premature interruption of the test, and finally to test methods proposed in the standards EN 12664 or ISO 10051 for reducing the number of tests. Last, hygrothermal simulations of an internally insulated wall are performed to evaluate the required precision on thermal conductivity to predict relative humidity at insulation masonry interface and heat flow at the inner side of the wall. [ABSTRACT FROM AUTHOR]

Plastic materials can absorb moisture from the atmosphere even after drying. This absorbed moisture can cause many defects in the molding process. Conventionally, a dryer is used to reduce the moisture content. However, the use of a drying unit involves huge daily power consumption and is also time-consuming. Therefore, this study proposed a new method to reduce the impact of moisture on molded product part quality through the optimization of plasticization parameters while reducing drying time. Two plastic materials, polyurethane (TPU) and polycarbonate (PC), were used for the experimental verification. Key plasticization parameters, including back pressure, screw rotation speed, and barrel temperature were chosen; their influence was investigated by the design of experiments (DOE). Moisture-induced defects, such as air bubble area, part surface gloss, and appearance were measured and correlated with the plasticization parameters. It was found, after optimization via a three-level DOE and factorial design multivariate statistical analysis using TPU, that the gloss (GU) of the PC part without drying was very close to that (98.4 GU) of the fully dried PC. The proposed methodology may help molders to improve production efficiency and achieve cost savings. [ABSTRACT FROM AUTHOR]

Plastic materials can absorb moisture from the atmosphere even after drying. This absorbed moisture can cause many defects in the molding process. Conventionally, a dryer is used to reduce the moisture content. However, the use of a drying unit involves huge daily power consumption and is also time-consuming. Therefore, this study proposed a new method to reduce the impact of moisture on molded product part quality through the optimization of plasticization parameters while reducing drying time. Two plastic materials, polyurethane (TPU) and polycarbonate (PC), were used for the experimental verification. Key plasticization parameters, including back pressure, screw rotation speed, and barrel temperature were chosen; their influence was investigated by the design of experiments (DOE). Moisture-induced defects, such as air bubble area, part surface gloss, and appearance were measured and correlated with the plasticization parameters. It was found, after optimization via a three-level DOE and factorial design multivariate statistical analysis using TPU, that the gloss (GU) of the PC part without drying was very close to that (98.4 GU) of the fully dried PC. The proposed methodology may help molders to improve production efficiency and achieve cost savings.

Water utilization is accompanied with the development of human beings, whereas gaseous moisture is usually regarded as an underexploited resource. The advances of highly efficient hygroscopic materials endow atmospheric water harvesting as an intriguing solution to convert moisture into clean water. The discovery of hygroelectricity, which refers to the charge buildup at a material surface dependent on humidity, and the following moisture-enabled electric generation (MEG) realizes energy conversion and directly outputs electricity. Much progress has been made since then to optimize MEG performance, pushing forward the applications of MEG into a practical level. Herein, the evolvement and development of MEG are systematically summarized in a chronological order. The optimization strategies of MEG are discussed and comprehensively evaluated. Then, the latest applications of MEG are presented, including high-performance powering units and self-powered devices. In the end, a perspective on the future development of MEG is given for inspiring more researchers into this promising area., (© 2023 Wiley‐VCH GmbH.)

The effective management of atmospheric water will create huge value for mankind. Diversified and sustainable biopolymers that are derived from organisms provide rich building blocks for various hygroscopic materials. Here, a comprehensive review of recent advances in developing biopolymers for hygroscopic materials is provided. It is begun with a brief introduction of species diversity and the processes of obtaining various biopolymer materials from organisms. The fabrication of hygroscopic materials is then illustrated, with a specific focus on the use of biopolymer-derived materials as substrates to produce composites and the use of biopolymers as building blocks to fabricate composite gels. Next, the representative applications of biopolymer-derived hygroscopic materials for dehumidification, atmospheric water harvesting, and power generation are systematically presented. An outlook on future challenges and key issues worthy of attention are finally provided., (© 2023 Wiley‐VCH GmbH.)

As water scarcity becomes a pending global issue, hygroscopic materials prove a significant solution. Thus, there is a good cause following the structure-performance relationship to review the recent development of hygroscopic materials and provide inspirational insight into creative materials. Herein, traditional hygroscopic materials, crystalline frameworks, polymers, and composite materials are reviewed. The similarity in working conditions of water harvesting and carbon capture makes simultaneously addressing water shortages and reduction of greenhouse effects possible. Concurrent water harvesting and carbon capture is likely to become a future challenge. Therefore, an emphasis is laid on metal-organic frameworks (MOFs) for their excellent performance in water and CO 2  adsorption, and representative role of micro- and mesoporous materials. Herein, the water adsorption mechanisms of MOFs are summarized, followed by a review of MOF's water stability, with a highlight on the emerging machine learning (ML) technique to predict MOF water stability and water uptake. Recent advances in the mechanistic elaboration of moisture's effects on CO 2  adsorption are reviewed. This review summarizes recent advances in water-harvesting porous materials with special attention on MOFs and expects to direct researchers' attention into the topic of concurrent water harvesting and carbon capture as a future challenge., (© 2023 Wiley‐VCH GmbH.)

The global energy crisis caused by the overconsumption of nonrenewable fuels has prompted researchers to develop alternative strategies for producing electrical energy. In this review, a fascinating strategy that simply utilizes water, an abundant natural substance throughout the globe and even in air as moisture, as a power source is introduced. The concept of the hydrovoltaic electricity generator (HEG) proposed herein involves generating an electrical potential gradient by exposing the two ends of the HEG device to dissimilar physicochemical environments, which leads to the production of an electrical current through the active material. HEGs, with a large variety of viable active materials, have much potential for expansion toward diverse applications including permanent and/or emergency power sources. In this review, representative HEGs that generate electricity by the mechanisms of diffusion, streaming, and capacitance as case studies for building a fundamental understanding of the electricity generation process are discussed. In particular, by comparing the use and absence of hygroscopic materials, HEG mechanism studies to establish active material design principles are meticulously elucidated. The review with future perspectives on electrode design using conducting nanomaterials, considerations for high performance device construction, and potential impacts of the HEG technology in improving the livelihoods are reviewed., (© 2023 Wiley‐VCH GmbH.)

Soft robots are composed of compliant materials that facilitate high degrees of freedom, shape-change adaptability, and safer interaction with humans. An attractive choice of material for soft robotics is crosslinked networks of liquid crystal polymers (LCNs), as they are responsive to a wide variety of external stimuli and capable of undergoing fast, programmable, complex shape morphing, which allows for their use in a wide range of soft robotic applications. However, unlike hydrogels, another popular material in soft robotics, LCNs have limited applicability in flooded or aquatic environments. This can be attributed not only to the poor efficiency of common LCN actuation methods underwater but also to the complicated relationship between LCNs and water. In this review, the relationship between water and LCNs is elaborated and the existing body of literature is surveyed where LCNs, both hygroscopic and non-hygroscopic, are utilized in aquatic soft robotic applications. Then the challenges LCNs face in widespread adaptation to aquatic soft robotic applications are discussed and, finally, possible paths forward for their successful use in aquatic environments are envisaged., (© 2023 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

The abstraction and implementation of plant movement principles into biomimetic compliant systems are of increasing interest for technical applications, e.g., in architecture, medicine, and soft robotics. Within the respective research and development approaches, advanced methods such as 4D printing or 3D-braiding pultrusion are typically used to generate proof-of-concept demonstrators at the laboratory or demonstrator scale. However, such techniques are generally time-consuming, complicated, and cost-intensive, which often impede the rapid realization of a sufficient number of demonstrators for testing or teaching. Therefore, we have produced comparable simple handcrafted compliant systems based on paper, wood, plastic foil, and/or glue as construction materials. A variety of complex plant movement principles have been transferred into these low-cost physical demonstrators, which are self-actuated by shrinking processes induced by the anisotropic hygroscopic properties of wood or paper. The developed systems have a high potential for fast, precise, and low-cost abstraction and transfer processes in biomimetic approaches and for the “hands-on understanding” of plant movements in applied university and school courses.

In this paper, a series of experiments assessing the moisture buffer value (MBV) of four internal wall assembly samples made from hygroscopic materials was performed. A modified Nordtest protocol was used. Moisture buffer values of all the investigated wall assemblies, with varying moisture loads in the range of 50% to 80%, showed a moderate moisture buffer value (MBV: 0.5–1.0 (g·m−2·%RH−1)). The results showed that in a wall assembly where the MBV of the whole assembly is lower than the MBV of the outer layers, the moisture-buffering capacity of the inner layer is untapped. Outer layers affect inner layers by changing their moisture-buffering capacity, which in turn changes the overall performance of the whole assembly. In addition, it was observed that if the penetration depth value of the outer layer is greater than its thickness, vapour reaches into the deeper layer and wall assemblies made of layers with materials characterized by a lower value of penetration depth reach steady state more slowly. The WUFI Pro tool was used to compare the simulated and experimental results. Despite the discrepancies between these results, it offers a simplified method, helping designers make decisions about which materials to choose to improve the moisture-buffering effect. [ABSTRACT FROM AUTHOR]

The importance of humidity control is spreading through a broad spectrum of applications, from food and pharmaceutical industries to biomedical and chemical fields. During the last decades, the growing interest in fiber Bragg gratings (FBG) led to new approaches and applications for the humidity measurement by means of the deposition of hygroscopic materials on gratings. The influence of the coating material and its features such us coating thickness (tk) and concentration (wt%) on static and dynamic metrological properties have been investigated in this paper. In this paper, four agar-coated FBG sensors for humidity measurements have been fabricated, and the influence of tk and wt% on the sensors’ sensitivity and response time has been experimentally assessed. Sensitivity increases with tk and wt%: for instance, at 1 wt% it was $0.0024\,\,\text {nm}\cdot {\%}^{\mathrm {-1}}$ and $0.0052\,\,\text {nm}\cdot {\%}^{\mathrm {-1}}$ for $\text {tk}=87\,\,\mu \text{m}$ and $\text {tk} = 212\,\,\mu \text{m}$ , respectively. Results showed that also the response time increased with tk and wt%: for instance, at 1 wt% it was 56.7 s and 107.6 s for $\text {tk} = 87\,\,\mu \text{m}$ and $\text {tk}=212\,\,\mu \text{m}$ , respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A visual relative humidity (RH) sensor based on a bioinspired and hygroscopic seed-like robot (I-SeedPel) is reported. • The RH sensor is powered solely by the RH variation itself. • The RH sensor is composed of biodegradable polymers that does not need to be retrieved after its function and working period. • The RH sensor works in a wide range of humidity (30–90%), with an accuracy of 97–98%, and a resolution of 0.17–0.52% of RH. Visual sensors for relative humidity (RH) are of interest for distributed and autonomous environmental monitoring. Most of the visual humidity sensors are based on colorimetric sensing through the employment of hygroscopic inorganic pigments or photonic crystals (PCs). However, the toxicity of some inorganic pigments poses a risk to the environment especially if dispersed during in-situ measurements. On the other hand, the angle-dependent structural colours reading of the PCs, make these devices non suitable for autonomous and in-situ environmental monitoring. Here, we report the first visual humidity sensor using an artificial and hygroscopic seed-like robot (I-SeedPel) recently (2023) developed by our group for hygro-driven environmental exploration (https://doi.org/10.1002/advs.202205146). The I-SeedPel design is bioinspired to the hygroscopic and layered tissues of the Pelargonium appendiculatum seed and fabricated through additive manufacturing techniques using biodegradable polymers. The hygro-mechanical response of the I-SeedPel generates a reversible change of the geometrical features in the artificial seed structure (i.e., awn's angular displacement and diameter variation) related to the RH. The variation of the geometric properties can be quantified and correlated to RH in a wide range (30–90 %), with an accuracy of 97–98 %, with a resolution of 0.17–0.52 % of RH and a good reproducibility (average RSD = 14.7 %). [ABSTRACT FROM AUTHOR]

The standard methods to determine the vapour permeability and the moisture sorption curve may lack of accuracy since discrepancies are observed when comparing numerical predictions to experimental data. Moreover, these properties are determined in steady state conditions while the numerical predictions are carried in transient regime. Thus, this paper presents an experimental design to estimate these properties using dynamic measurements and identification method. The experimental facility is presented, enabling to measure at the same time the relative humidity within the material and the total moisture content. The performance of the facility and protocol in terms of reproducibility, uncertainty and direction of heat and moisture transfers are checked, confirming the abilities of the set-up. Then, experimental results are used to determine the hygrothermal material properties using a trust-region algorithm. Investigations are done to analyse important issues as the choice of the observation: relative humidity and/or mass measurements, to solve the parameter estimation problem. The estimated properties are finally validated by comparing the numerical predictions with experimental data for other boundary conditions. [ABSTRACT FROM AUTHOR]

Validated by a large-scale experimental investigation on moisture buffering (MB) effect, a whole building Heat, Air and Moisture (HAM) simulation tool, BSim, is applied to evaluate the impact of a number of parameters on the moisture buffering potential of a full-scale test room finished with hygroscopic materials. The Maximum Accumulated Moisture Buffering Value (MAMBV), developed from the moisture balance analyses in the experimental study, is used in the BSim simulation result analyses to evaluate the impact of various parameters. The parameters investigated include ventilation rates (0.5–5 ACH), types of materials (uncoated gypsum board, wood paneling, orientated strand board, aerated cellular concrete, and telephone book paper), humidity conditions of supply air, volume rates, and steady-state outdoor conditions. It is found that all these parameters have a significant impact on the moisture buffering potential except for the steady-state outdoor conditions. Two material properties, the moisture capacity and vapor permeability, determine the moisture buffering capacities of materials under different moisture generation regimes.

In this paper, a series of experiments assessing the moisture buffer value (MBV) of four internal wall assembly samples made from hygroscopic materials was performed. A modified Nordtest protocol was used. Moisture buffer values of all the investigated wall assemblies, with varying moisture loads in the range of 50% to 80%, showed a moderate moisture buffer value (MBV: 0.5−1.0 (g·m−2·%RH−1)). The results showed that in a wall assembly where the MBV of the whole assembly is lower than the MBV of the outer layers, the moisture-buffering capacity of the inner layer is untapped. Outer layers affect inner layers by changing their moisture-buffering capacity, which in turn changes the overall performance of the whole assembly. In addition, it was observed that if the penetration depth value of the outer layer is greater than its thickness, vapour reaches into the deeper layer and wall assemblies made of layers with materials characterized by a lower value of penetration depth reach steady state more slowly. The WUFI Pro tool was used to compare the simulated and experimental results. Despite the discrepancies between these results, it offers a simplified method, helping designers make decisions about which materials to choose to improve the moisture-buffering effect.

The energy demand for the air-conditioning of buildings has shown a very significant growth trend in the last two decades. In this paper three alternative hygroscopic materials for desiccant wheels are compared considering the operation of the air handling unit they are installed in. The analyses are performed by means of the TRNSYS 17® software, simulating the plant with the desiccant wheel made of: silica-gel, i.e., the filling actually used in the experimental plant desiccant wheel of the University of Sannio Laboratory; MIL101@GO-6 (MILGO), a composite material, consisting of graphite oxide dispersed in a MIL101 metal organic framework structure; Campanian Ignimbrite, a naturally occurring tuff, rich in phillipsite and chabazite zeolites, widespread in the Campania region, in Southern Italy. The air-conditioning system analyzed serves a university classroom located in Benevento, and it is activated by the thermal energy of a solar field for which three surfaces are considered: about 20, 27 and 34 m2. The results demonstrate that a primary energy saving of about 20%, 29%, 15% can be reached with silica-gel, MILGO and zeolite-rich tuff desiccant wheel based air handling units, respectively.

When comparing measurements to numerical simulations of moisture transfer through porous materials a rush of the experimental moisture front is commonly observed in several works shown in the literature, with transient models that consider only the diffusion process. Thus, to overcome the discrepancies between the experimental and the numerical results, this paper proposes to include the moisture advection transfer in the governing equation. To solve the advection-diffusion or the so-called convection differential equation, it is first proposed two efficient numerical schemes whose efficiencies are investigated for both linear and nonlinear cases. The first scheme, Scharfetter – Gummel , presents a Courant-Friedrichs-Lewy (CFL) condition but it is more accurate and faster than the second one, the well-known Crank – Nicolson approach. Furthermore, the Scharfetter – Gummel scheme has the advantages of being well-balanced and asymptotically preserved. Then, to conclude, results of the convective moisture transfer problem obtained by means of the Scharfetter – Gummel numerical scheme are compared to experimental data from the literature. The inclusion of an advective term in the model may clearly lead to better results than purely diffusive models. [ABSTRACT FROM AUTHOR]

Wood as hygroscopic material has the capacity to absorb moisture and thus to moderate the indoor relative humidity (RH) in a building, resulting in lower ventilation demand. In addition, when moisture migrates in hygroscopic structures energy is released through latent heat phenomena. The diurnal variation of moisture content in wood hold a potential for contributing in the buildings energy balance. This study presents the theoretical energy savings in low energy buildings with interior wooden surfaces under different moisture protocols indoors. The requirements of the Norwegian Building Regulations (TEK10) are followed regarding the U-values of the envelope components. A hygrothermal simulation tool is employed to estimate the potential diurnal variations of moisture content in the wood structure. The latent heat released and absorbed is mathematically calculated for a reference building. The results show the potential of hygroscopic structures to save thermal energy by means of heat of sorption and to reduce the conductive heat losses through opaque building elements. The limitations of the phenomena are also discussed. [ABSTRACT FROM AUTHOR]

Sorption-based atmospheric water harvesting (AWH) is a promising approach for mitigating worldwide water scarcity. However, reliable water supply driven by sustainable energy regardless of diurnal variation and weather remains a long-standing challenge. To address this issue, a polyelectrolyte hydrogel sorbent with an optimal hybrid-desorption multicyclic-operation strategy is proposed, achieving all-day AWH and a significant increase in daily water production. The polyelectrolyte hydrogel possesses a large interior osmotic pressure of 659 atm, which refreshes sorption sites by continuously migrating the sorbed water within its interior, and thus enhancing sorption kinetics. The charged polymeric chains coordinate with hygroscopic salt ions, anchoring the salts and preventing agglomeration and leakage, thereby enhancing cyclic stability. The hybrid desorption mode, which couples solar energy and simulated waste heat, introduces a uniform and adjustable sorbent temperature for achieving all-day ultrafast water release. With rapid sorption-desorption kinetics, an optimization model suggests that eight moisture capture-release cycles are capable of achieving high water yield of 2410 mL water kg sorbent -1 day -1 , up to 3.5 times that of single-cyclic non-hybrid modes. The polyelectrolyte hydrogel sorbent and the coupling with sustainable energy driven desorption mode pave the way for the next-generation AWH systems, significantly bringing freshwater on a multi-kilogram scale closer., (© 2023 Wiley-VCH GmbH.)

This paper presents the research status of hygroscopic materials, points out the weak links as targets for major breakthroughs, and introduces humidifying mechanisms and their categories. In this paper, we simulated a single-monomer Shenyang office building with different envelopes of inner-surface hygroscopic materials for indoor humidity conditions, energy consumption, and economy, which are three aspects of energy consumption analysis in EnergyPlus software. To obtain the best moisture buffering performance from hygroscopic materials, we also simulated different cases including the laying area, ventilation strategy, thickness, and initial moisture content of different hygroscopic materials. The humidity fluctuation, with changes in the style of hygroscopic materials and usage conditions, of a room in a building can be analyzed by numerical simulation. This allows the determination of the best moisture buffering performance of the building structure. The results show that hygroscopic materials have great advantages in three energy saving aspects of building assessment. Hygroscopic materials can regulate indoor air humidity and reduce energy consumption. In addition, the entire life-cycle cost can be minimized. Lower rates of air exchange and larger usable areas can help enhance the level of performance of hygroscopic materials. The thickness and initial moisture content of hygroscopic materials have little impact on the moisture buffering value. This study strived to provide a theoretical basis and technical guidance for the production and installation of hygroscopic materials. It also promoted the passive materials market and the building’s energy savings. The best moisture buffering performance, evaluated at room level in this paper, can be obtained through real-world environmental simulation.

Thermal conductivity is one of the most important parameters of building insulation materials. This parameter is dependent on the temperature, and on the moisture content for hygroscopic materials. When measured by steady-state methods (with the HFM device and the guarded hot plates), moisture will migrate from the hot side to the cold, influencing the measured heat flux and, thus, the measured thermal conductivity. This study aims to analyze the effects of moisture transfer on the thermal conductivity measurement of wet hygroscopic light building insulation material (namely wood fiber insulation). Several experiments are performed on instrumented samples to evaluate the influence of parameters like the thickness, the mean moisture content, the mean temperature, or the temperature gradient on the measured heat flux, on the temperature and relative humidity distributions and on the time to reach hygrothermal equilibrium. Particularly, the measurement errors made when shortening the experiment are discussed and the moisture dependence of true thermal conductivity is evaluated experimentally by considering the notions of apparent and diffusive thermal conductivities. Last, by using a validated heat and moisture transfer model, this dependency is compared to the one predicted by the methods proposed in the standards EN 12664 or ISO 10051. • Thermal conductivity of moist insulation is measured with HFM apparatus. • Influence of mean moisture content and temperature, and thickness is investigated. • Moisture dependence of true thermal conductivity is evaluated. • Shorten the experiment overestimates thermal conductivity of moist sample. • Methods proposed in the standards EN 12664, or ISO 10051 are limited. [ABSTRACT FROM AUTHOR]

The phase change of water from liquid to vapor is one of the most energy-intensive physical processes in nature, giving it immense potential for cooling. Diverse evaporative cooling strategies have resulted worldwide, including roof ponds and sprinklers, courtyard fountains, wind catchers with qanats, irrigated green roofs, and fan-assisted evaporative coolers. These methods all require water in bulk liquid form. The evaporation of moisture that has been sorbed from the atmosphere by hygroscopic materials is equally energy-intensive, however, yet has not been examined for its cooling potential. In arid and semi-arid climates, hygroscopic earth buildings occur widely and are known to maintain comfortable indoor temperatures, but evaporation of moisture from their walls and roofs has been regarded as unimportant since water scarcity limits irrigation and rainfall; instead, their cool interiors are attributed to well-established mass effects in delaying the transmission of sensible gains. Here, we investigate the cooling accomplished by daily cycles of moisture sorption and evaporation which, requiring only ambient humidity, we designate as "intrinsic" evaporative cooling. Connecting recent soil science to heat and moisture transport studies in building materials, we use soils, adobe, cob, unfired earth bricks, rammed earth, and limestone to reveal the effects of numerous parameters (temperature and relative humidity, material orientation, thickness, moisture retention properties, vapor diffusion resistance, and liquid transport properties) on the magnitude of intrinsic evaporative cooling and the stabilization of indoor relative humidity. We further synthesize these effects into concrete design guidance. Together, these results show that earth buildings in diverse climates have significant potential to cool themselves evaporatively through sorption of moisture from humid night air and evaporation during the following day's heat. This finding challenges the perception of limited evaporative cooling resources in arid climates and greatly expands the applicability of evaporative cooling in contemporary buildings to water-stressed regions. [ABSTRACT FROM AUTHOR]

This study aims to investigate the hygrothermal environment by estimating the room air conditioner (RAC) heat load in a room with hygroscopic materials. The sensible and latent heat capacity and the water retention quantity in the RAC indoor unit are tested in cooling and dehumidification operation modes. Then, a model is developed to predict their values and investigate room temperature and humidity. The RAC model numerical analysis estimates the heat load by taking into account indoor hygroscopicity. In particular, the water is retained from several hundred grams to approximately 1 kg in the indoor unit. The RAC model is implemented considering the heat exchanger temperature distribution. In the weak cooling dehumidification mode, the room relative humidity is maintained between larger than 5% and 8% of the target value with and without hygroscopicity, respectively. Hygroscopicity does not affect the heat load in the bedroom during night time. [ABSTRACT FROM AUTHOR]

The preservation of artworks is profoundly influenced by fluctuations in temperature and, especially, relative humidity. Thus, it is crucial for hygrothermal conditions in museums to be stabilized, particularly inside display cases. Today there are advanced hygrothermal simulation models available that enable us to quantify the temperature and relative humidity fluctuations of the air inside the museum display cases, provided that we know the climate in the exhibition rooms, the degree of ventilation of the display case and the constitution of its surroundings. However, the placement of hygroscopic materials inside display cases also influences the fluctuation of interior relative humidity. This paper presents the results of an experimental study conducted in a flow chamber, showing the enormous potential of hygroscopic materials in stabilizing relative humidity inside of display cases. In addition, it presents a numerical simulation study conducted in display cases evaluating how the insertion of hygroscopic finishing materials in the base of the display case, under varying ventilation conditions influences stabilization of interior relative humidity. [ABSTRACT FROM AUTHOR]

To assist with the correct design of buildings, many computational models have been developed to assess the transient heat, air, and moisture (HAM) transfer within building walls. Validation of these computational models is essential to gain confidence in the codes. This paper provides datasets for validating 1-D heat and mass transfer models step by step, gradually increasing the complexity of a multilayer wall with hygroscopic components. The experiments were performed using a double climatic chamber. The climatic conditions on either side of the wall progress from the simplest boundary conditions (isothermal) to more complex ones with oscillations that mimic the mid-season period. To assess the hygrothermal response of the tested walls under such climatic conditions, the conditions of ambient air and the temperature and humidity profiles within the wall thickness are monitored during the test. This paper gives some detailed information on the chamber design, the instrumentation, the materials, and the climatic conditions so that other researchers can use the collected data for validation of their models or to build future test facilities. The results obtained with the test facility highlight the coupling that exists between heat and mass transfers across multilayer walls using hygroscopic components. The heat release by moisture adsorption is observed in the temperatures profiles. During the mid-season period, the results show the differences of the phase shift and the amplitude attenuation of the temperature and the water vapour pressure across the wall thickness. [ABSTRACT FROM AUTHOR]

The phase change of water from liquid to vapor is one of the most energy-intensive physical processes in nature, giving it immense potential for cooling. Diverse evaporative cooling strategies have resulted worldwide, including roof ponds and sprinklers, courtyard fountains, wind catchers with qanats, irrigated green roofs, and fan-assisted evaporative coolers. These methods all require water in bulk liquid form. The evaporation of moisture that has been sorbed from the atmosphere by hygroscopic materials is equally energy-intensive, however, yet has not been examined for its cooling potential. In arid and semi-arid climates, hygroscopic earth buildings occur widely and are known to maintain comfortable indoor temperatures, but evaporation of moisture from their walls and roofs has been regarded as unimportant since water scarcity limits irrigation and rainfall; instead, their cool interiors are attributed to well-established mass effects in delaying the transmission of sensible gains. Here, we investigate the cooling accomplished by daily cycles of moisture sorption and evaporation which, requiring only ambient humidity, we designate as “intrinsic” evaporative cooling. Connecting recent soil science to heat and moisture transport studies in building materials, we use soils, adobe, cob, unfired earth bricks, rammed earth, and limestone to reveal the effects of numerous parameters (temperature and relative humidity, material orientation, thickness, moisture retention properties, vapor diffusion resistance, and liquid transport properties) on the magnitude of intrinsic evaporative cooling and the stabilization of indoor relative humidity. We further synthesize these effects into concrete design guidance. Together, these results show that earth buildings in diverse climates have significant potential to cool themselves evaporatively through sorption of moisture from humid night air and evaporation during the following day’s heat. This finding challenges the perception of limited evaporative cooling resources in arid climates and greatly expands the applicability of evaporative cooling in contemporary buildings to water-stressed regions.

The moisture buffering potential is defined as the capacity of hygroscopic materials to absorb and release moisture under cyclic moisture loads. In a large-scale experimental investigation, the authors found a significant difference in the moisture buffering potential and the moisture residual between wood paneling and gypsum board when subjected to different moisture load profiles. This difference is attributed to the different moisture capacity and vapor permeability of these two finishing materials. A further study, motivated by these observations, was carried out by the authors to investigate the impact of different moisture load profiles and the effect of moisture history on the moisture buffering potential through hygrothermal simulations. Ten hygroscopic materials are categorized into three groups based on their moisture capacity and vapor permeability. The moisture buffering potential of these three material groups were investigated under different moisture load profiles. The moisture residual in the first daily moisture load cycle was studied as well. The simulation results verify that the different response of these materials to the moisture load was determined by the materials' moisture capacity and vapor permeability, i.e. moisture effusivity, and material thickness. In addition, the moisture residual phenomenon is related to the penetration depth of materials. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of a series of novel wood fibre, sepiolite and expanded perlite (WSE)-based mortars that have been developed by Hunan University. The evaluation investigated the influence of morphology structure and the effect of different hot-humid environments on hygroscopic properties of WSE-based mortar to form breathable wall which can provide a moderation of moisture, indoor air quality and thermal insulation of building. The microstructure, thermal conductivity, mechanical properties and hygroscopic properties of WSE-based mortar specimens were assessed to characterize the relationship between performances of the material. WSE is an inorganic porous fibre-aggregate mixture. The hygroscopic properties of the mortars can be greatly improved by adding the WSE fibres-aggregates, especially under high temperature (40℃) and high relative humidity (98%) during summer. The addition of admixture can improve the properties of WSE-based mortar to meet requirements of special performances (such as compressive strength) without affecting the hygroscopic properties. The WSE-based breathable wall is a good moisture buffering controller that could improve indoor air quality. The evaluation presented in this paper should provide the design fundamental for development of breathable wall for future built environment, to allow optimizing the boundary conditions for energy saving and control of indoor humidity environment by incorporating the mortars as finishing materials. [ABSTRACT FROM AUTHOR]

A double climatic chamber based on the guarded hot box method was designed to study the hygrothermal behaviour of different compositions of timber walls. Equipment installed allows to reproduce in the climatic chamber hygrothermal conditions close to real climatic conditions and to assess the evolution of temperature and humidity profiles of the tested wails. This paper deals with the hygrothermal behaviour of a timber-framed wall including hygroscopic materials. The results showed that the ability of the experimental device to reproduce desired conditions made it possible to measure wall thermal properties during steady-state (thermal resistance) and transient conditions (decrement factor and time lag). The hygroscopic behaviour of tested materials was also observed during the tests. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents experimental data measured in a bed of gypsum boards in the transient moisture transfer (TMT) facility at the University of Saskatchewan. The relative humidity and temperature were measured at two depths in a gypsum bed and the moisture accumulation was measured for the entire bed. Experiments were conducted for both coated (acrylic and latex paint) and uncoated gypsum. These experimental data are compared to simulated data from eight different numerical models. The agreement between the experimental and numerical data is good and often within the experimental uncertainty bounds. A sensitivity analysis was performed to show the influence of material properties such as sorption, vapour permeability and the transfer coefficients on the simulated results. One model examines hysteresis of the sorption isotherm. [Copyright &y& Elsevier]

Abstract: As numerical models of heat and moisture transfer in porous building materials advance and numerical investigations increase in the literature, there remains a need for simple accurate and well-documented experimental data for model validation. The aim of this two part paper is to provide such experimental data for two hygroscopic building materials (cellulose insulation and spruce plywood) exposed to 1-D and transient boundary conditions. Part I of this paper describes the transient moisture transfer (TMT) facility used to generate the experimental data as well as the uncertainty and repeatability of the measured data. The measured material properties are also presented to fully document the experimental data set and permit its use by other researchers. [Copyright &y& Elsevier]

As simultaneous heat and mass transfer between building envelopes and indoor air is complicated and expensive to measure in laboratory and field experiments, a numerical model is important in understanding and extrapolating experimental results. In this paper a numerical model that solves simultaneous heat and mass transfer between building envelopes and indoor air is verified using the field measurements presented in Part I of this paper. The verification results show that the model is able to predict the transfer of water vapor, CO2, and SF6 between the building envelope and air. The model is then applied to investigate the humidity, comfort, and air quality in a bedroom of a wooden building located in four European countries (Finland, Belgium, Germany, and Italy). The numerical results show that moisture transfer between indoor air and the hygroscopic structure significantly reduces the peak indoor humidity (up to 35% RH), percent dissatisfied with warm respiratory comfort (up to 10%) and the percent dissatisfied with indoor air quality (up to 25%). [ABSTRACT FROM AUTHOR]

In this paper, measurements are presented which quantify the mass transfer of tracer gases and water vapor between indoor air and a permeable and hygroscopic building envelope. The transfer of tracer gases through the envelope requires the entire envelope to be permeable, while the transfer of moisture requires sufficient hygroscopic mass to be in contact with the indoor air. The results show that mass transfer can improve the indoor air quality and climate. The diffusion of gases through the building envelope significantly increases the effective ventilation rate for poorly ventilated rooms, but only moderately increases the effective ventilation for well-ventilated rooms. Moisture transfer, on the other hand, has a significant influence on the indoor humidity for both poorly and well-ventilated rooms. [ABSTRACT FROM AUTHOR]

Donning of personal protective equipment (PPE) in the healthcare sector has been intensified by the on-going COVID-19 pandemic around the globe. While extensive PPE provides protection, it typically limits moisture permeability and severely hinders the sweat evaporation process, resulting in greater heat stress on the personnel. Herein, a zinc-poly(vinyl alcohol) (Zn-PVA) composite film is fabricated by embedding a super-hygroscopic zinc-ethanolamine complex (Zn-complex) in the PVA matrix. By attaching the Zn-PVA composite film, the relative humidity (RH) inside the protective suit decreases from 91.0% to 48.2%. The reduced RH level, in turn, enhances evaporative cooling, hence bringing down the heat index from 64.6 to 40.0 °C at an air temperature of 35 °C, remarkably lowering the likelihood of heat stroke. The American Society for Testing and Materials tests conducted on a sweating manikin have also proven that the Zn-PVA composite films can significantly reduce the evaporative resistance of the protective suit by 90%. The low material cost, facile fabrication process, and reusability allow the Zn-PVA composition films to be readily available for healthcare workers worldwide. This application can be further extended to other occupations that are facing severe thermal discomfort and heat stress., (© 2022 Wiley-VCH GmbH.)

High-temperature-induced fire is an extremely serious safety risk in energy storage devices; which can be avoided by replacing their components with nonflammable materials. However; these devices are still destroyed by the high-temperature decomposition; lacking reliability. Here, a fire-tolerant supercapacitor is further demonstrated that recovers after burning with a self-healable "solute-in-air" electrolyte. Using fire-tolerant electrodes and separator with a semiopen device configuration; hygroscopic CaCl 2 in the air ("CaCl 2 -in-air") is designed as a self-healable electrolyte; which loses its water solvent at high temperatures but spontaneously absorbs water from the air to recover by itself at low temperatures. The supercapacitor is disenabled at 500 °C; while it recovers after cooling in the air. Especially; it even recovers after burning at around 647 °C with enhanced performance. The study offers a self-healing strategy to design high-safety; high-reliability; and fire-tolerant supercapacitors; which inspires a promising way to deal with general fire-related risks., (© 2022 Wiley-VCH GmbH.)