Moisture Buffering Research Articles

Functional Properties of SAP-Based Humidity Control Plasters

The application of materials with high moisture storage capacity close to the interior surface presents a prospective passive method for improving indoor relative humidity conditions. In this paper, lime-cement plasters containing three different types of superabsorbent polymers (SAPs) in varying dosages are introduced and their mechanical, hygric, and thermal characteristics are analyzed in a relation to microstructure. The experimental results show a significant effect of both SAP amount and chemical composition on all functional properties of studied plasters. The incorporation of 1.5% of SAP may induce up to 2.5 better moisture buffering, thus significantly improving the passive humidity control capability. Considering overall functional parameters of SAP-modified plasters, the dosage of 1 wt.% can thus be viewed as a rational compromise between the moisture storage capability and mechanical properties. The obtained wide sets of parameters can be utilized directly as input data of computational models suitable for the assessment of the interior microclimate of residential and administrative buildings.

Ovalbumin as natural organic binder for stabilizing unfired earth bricks: Understanding vernacular techniques to inspire modern constructions

Cement and hydrated lime are usually effective for stabilizing unfired earth but they lead to a significant CO2 footprint. In the search for sustainable, efficient alternatives, old and vernacular techniques may provide ways of replacing such mineral binders. The example of the use of chicken egg white protein (ovalbumin) to improve earth construction materials is addressed in the present case study. It was used to stabilize two soils with different mineralogical compositions. Addition of 2 wt% and 4 wt% ovalbumin strongly increased both the dry and wet compressive strengths (water resistance) of the soils. For these properties, ovalbumin was a more efficient stabilizer than cement or hydrated lime. Concerning hygrothermal properties, the thermal conductivity of the soils did not change with stabilization, while the moisture buffer value decreased slightly but remained at least “good” according to the Nordtest criterion. Microstructural analysis can explain the efficiency of earth stabilization using ovalbumin by the formation of a gel that fills the microcracks in the soil and strengthens it by gluing them up.

Effect of hemp content and clay stabilization on hygric and thermal properties of hemp-clay composites

The objective of this paper is to investigate the effect of clay stabilization and hemp content on hygric and thermal performances. This experimental study is based on the measurement of sorption isotherm, moisture buffer value and thermal properties. The effect of water content on thermal conductivity is also investigated. The results show that Hemp Clay Composites (HCC) and Hemp Stabilized Clay Composites (HSCC) are hygroscopic and moisture buffering materials. The correlations between hemp content and water content are identified for sorption curves. An innovative analysis of the contribution of hemp and binder to water sorption is performed. The moisture buffer values classify the designed composites as excellent hygric regulators according to the Nordtest classification. The thermal conductivity ranges from 0.089 to 0.120 W/(m.K) at dry state, making them suitable for distributed insulation. The thermal conductivity increases linearly with density, for the two binders investigated in this study. Besides, the thermal conductivity increases linearly with water content too. Finally, this study underlines that the designed composites show high hygrothermal qualities.

Combined Effect of Superabsorbent Polymers and Cellulose Fibers on Functional Performance of Plasters

Plaster has, from ancient times, been used as a decorative material. However, the advances in materials engineering such as thermal and moisture control provide new opportunities. Superabsorbent polymers (SAPs) have been found to possess passive moisture control that may find utilization in modern buildings. However, the main drawback is associated with a limited number of applicable SAPs due to mechanical strength loss. In this regard, concurrent utilization of cellulose fibers may provide additional benefits linked with the reinforcing of plaster structure and preservation of superior hygric properties. In this regard, this study investigates the combined effect of SAP and cellulose fibers on the material properties of cement-lime plaster in terms of its mechanic, thermal, and hygric properties. To access the capability of such modified plasters to control the interior moisture fluctuations, the moisture buffering value is determined. Obtained results show the effect of both applied admixtures on material performance, whilst the synergic effect was most obvious for humidity control accessed through the moisture buffer coefficient.

Development of methods to measure the potential of a plaster to regulate indoor humidity

Moisture buffering utilises hygroscopic construction materials as a more sustainable approach to passively moderate indoor humidity. This study seeks to develop a reproducible test method to obtain a moisture buffering value of common building materials under conditions that reflect typical indoor environmental conditions. Temperature and humidity variations in sinusoidal profiles for two different materials, typically used to finish internal surfaces, have been studied to identify their potential moisture regulation behaviour. Outcomes were then combined and ranked indicating the potential of materials to passively regulate the indoor humidity and the need for robust methods of investigation. Practical application: In response to current practice and materials’ testing procedures, a reproducible test method is considered to enable comprehensive understanding of a hydroscopic materials’ behaviour, where subsequent interpretation of their performance can be quantified. The practicality to consider the use of passive regulation using hygroscopic materials can then be justified to bring indoor RH closer to the optimal range without heavy reliance on mechanical solutions, achieving a more effective passive indoor climate monitoring. It is expected that the outcome of this investigation can potentially form the basis of further improvement on a standardised test method to obtain moisture buffering value of hygroscopic non-structural elements for pragmatic application during design integration process.

Impact of Temperature on the Moisture Buffering Performance of Palm and Sunflower Concretes

The use of bio-based materials (BBM) in buildings is an interesting solution as they are eco-friendly materials and have low embodied energy. This article aims to investigate the hygric performance of two bio-based materials: palm and sunflower concretes. The moisture buffering value (MBV) characterizes the ability of a material or multilayer component to moderate the variation in the indoor relative humidity (RH). In the literature, the moisture buffer values of bio-based concretes were measured at a constant temperature of 23 °C. However, in reality, the indoor temperature of the buildings is variable. The originality of this article is found in studying the influence of the temperature on the moisture buffer performance of BBM. A study at wall scale on its impact on the indoor RH at room level will be carried out. First, the physical models are presented. Second, the numerical models are implemented in the Simulation Problem Analysis and Research Kernel (SPARK) suited to complex problems. Then, the numerical model validated with the experimental results found in the literature is used to investigate the moisture buffering capacity of BBM as a function of the temperature and its application in buildings. The results show that the temperature has a significant impact on the moisture buffering capacity of bio-based building materials and its capacity to dampen indoor RH variation. Using the numerical model presented in this paper can predict and optimize the hygric performance of BBM designed for building application.

Determination of specific heat capacity of bio-fibre earth mortars stabilised at different relative humidities using Differential Scanning Calorimetry

Understanding the relationship that earth-based mortars have with both water and temperature is imperative to optimise moisture buffering properties. Specific Heat Capacity (Cp) is a key factor to understand the benefits in terms of thermal mass and latent heat. This paper presents the results of bio-based earth mortars (with fibres consisting of two varieties of sheep wool: Wool 1 (W1), Wool 2(W2) and Saw Mill Residue (SMR)) stabilised at 53% and 75% Relative Humidity (RH). Differential Scanning Calorimetry (DSC) according to ISO 11357–4 was used to calculate Cp of the aforementioned mortars. The temperature range of this experiment was that of 0–50 °C with a particular focus on values at 20 °C as this best represented a suitable indoor temperature. From these experiments, the results demonstrate that when stabilised at different RH, the difference in Cp was bio-fibre dependant and had a range between 0.71– 1.01 kJ/kg.K at 53% RH and 0.85–1.14 kJ/kg.K at 75% RH. These differences could potentially be attributed to the materials ability to readily accept water molecules. This emphasised that incorporating bio-fibres to a plain mixture (PL) can increase the Cp by up to 60%; significantly improving the thermal inertia of the building material. By reducing this temperature differential, it will reduce the heating requirements of a building which as consequential carbon reduction and thermal comfort benefits. Overall, SMR has the largest Cp for 75% at 20 °C was 1.141 kJ/kg.K, therefore specifically, this fibre would be the most effective to implement within a building. It also demonstrates the differences of the samples adsorption and absorption of water in differing hygrothermal environments.

Simulation and validation of indoor temperatures and relative humidity in multi-zone buildings under occupancy conditions using multi-objective calibration

Buildings are expected to be energy efficient but also to provide a comfortable environment to their occupants as well as to be durable. Indoor relative humidity influences the energy consumption, structure and the occupants’ comfort and health. Therefore, it is necessary to control and predict indoor environmental conditions. This work aims to simulate indoor temperatures and relative humidity in a multi-zone building model under realistic conditions, such as occupancy and moisture gains, operation of windows and doors and mechanical ventilation. The combined multi-zone air flow model is developed with TRNSYS and TRNFLOW and it is applied to a phase of the Twin Houses extended experiment of the international energy agency, energy in buildings and communities (IEA EBC) Annex 71. The main novelty of this work is to determine the masses of surface and deep moisture buffer storage by performing a multi-objective calibration of indoor temperatures and relative humidity. Results prove that building energy simulations need to model the moisture buffering of internal materials to accurately predict indoor humidity. The error in simulating relative humidity is reduced by 69% in the house with moisture gains after calibration of the masses of buffering materials. Moreover, the calibrated multi-zone building model shows a great agreement between simulated and measured data with an average root mean square error (RMSE) among thermal zones of 0.51 °C and 0.48 °C in indoor temperatures and 3.58% and 2.21% in relative humidity for the two houses in the validation period.

Determining the Impact of High Residential Density on Indoor Environment, Energy Use, and Moisture Loads in Swedish Apartments-and Measures for Mitigation

Recently, there has been an increase in apartments with a large number of inhabitants, i.e., high residential density. This is partly due to a housing shortage in general but also increased migration, particularly in suburbs of major cities. This paper specifies issues that might be caused by high residential density by investigating the technical parameters influenced in Swedish apartments that are likely to have high residential density. Interviews with 11 employees at housing companies were conducted to identify issues that might be caused by high residential density. Furthermore, simulations were conducted based on extreme conditions described in the interviews to determine the impact on the energy use, indoor environmental quality, and moisture loads. In addition, the impact of measures to mitigate the identified issues was determined. Measures such as demand-controlled ventilation, increase of a constant ventilation rate, and moisture buffering are shown to reduce the risk for thermal discomfort, mold growth, and diminished indoor air quality; while still achieving a lower energy use than in a normally occupied apartment. The results of this study can be used by authorities to formulate incentives and/or recommendations for housing owners to implement measures to ensure good indoor environmental quality for all, irrespective of residential density conditions.

Indoor storage time affects the quality and quantity of volatile monoterpenes emitted from softwood timber

Abstract Wood as a construction material affects indoor environmental quality by moisture buffering, good acoustic properties and by the wood specific volatile organic compounds (VOC). The most abundant VOCs of soft wood are volatile monoterpenes (VM) giving the typical odor of wood. In the present study, long-term VM emissions of wood of two northern coniferous tree species, Scots pine and Norway spruce were observed regularly during one year in storage. Fresh and dried 20 cm long wood blocks were placed in a test chamber; VMs were collected with the solid phase micro extraction fiber and analyzed by gas chromatography-mass spectrometer. Average emission of nine different VMs, α- and β-pinene, 3-carene, limonene, terpinolene, myrcene, camphene, ortho-cymene and ƴ-terpinene, decreased 68–87% during one-year long storage. Moisture content (MC), knots, tree species and tree individual affected the VM emissions from wood. When a certain level of MC (12%) was reached, the VM levels decreased, but the method of drying (industrial or dried in storage) did not affect the amount of released VMs. Rehydration and dehydration increased and decreased VM emissions, respectively. Moreover, two of the eight Scots pine heartwood planks contained almost no 3-carene while being the most abundant monoterpene in the others.

Thermal and hygroscopic study of hemp concrete in real ambient conditions

Most building materials, and more particularly bio-based materials, are subject to hygrothermal transfers in the environment in which they are disposed. These transfers depend on their thermophysical characteristics as well as the ambient humidity and temperature conditions. In such environment, and despite these variations, the material must be able to ensure in a sustainable manner, the functions for which it was implemented (thermal, mechanical, acoustic …). Among these materials, hemp concrete, which is a bio-based material, is widely considered in building construction for its superior thermal and hygroscopic performance. The hygrothermal modelling of such materials in real conditions is essential for a better understanding of buildings’ energy performances. Several works targeted the numerical hygrothermal modelling of hemp concrete; however most of them are done in controlled laboratory conditions, which may be different from the real buildings scenarios. In this paper, heat and mass transfer are investigated both numerically and experimentally in real conditions. The hygrothermal properties of hemp concrete were first determined through laboratory experiments; then, an experimental wall segment made of hemp concrete was instrumented in real ambient conditions in order to validate the Philip and De Vries model describing heat and mass transfer. The comparison of the numerical results to the experimental data leads to interesting results regarding local temperature and relative humidity variations. Moreover, numerical investigation of the moisture buffer values of hemp concrete was performed and the results were validated by bibliographic data. The hemp concrete was found to be a very interesting potential hygrothermal regulation material in terms of thermal conductivity, decrement factor, time lag, and humidity regulation.

Simple and effective route to tailor the thermal, acoustic and hygrothermal properties of cork-containing waste derived inorganic polymer composites

Future generation building materials produced using sustainable precursors and exhibiting multifunctional properties are in huge demand, as they might be a key tool to tackle the carbon dioxide emissions from the building sector. This study provides new insights regarding the impact of the cork particle size on the hardened-state properties of inorganic polymer composites derived from fly ash waste. The composites were characterised regarding their mechanical, thermal, acoustic and hygrothermal properties. The use of smaller sized particles favours the specimens' sound insulation and moisture regulation capacity, while larger granules enhance the specimens’ mechanical performance. The best performing composite containing 80 vol% of small size cork granules shows an excellent moisture buffer value (2.22 g/m2 Δ%RH), low thermal conductivity (79 mW/m K) coupled with high sound insulation ability. In addition, the cork-composites show sound absorption frequency selectivity according to the thickness of the samples or the size of the cork granules used in their production, and this allows tuning the specimens according to the frequency of the sound pollution source. This study reduces the knowledge gap regarding the production cork-containing inorganic polymers which might foster the technology deployment.

Hygrothermal performance of temperature-humidity controlling materials with different compositions

In this paper, gypsum, zeolite, expanded vermiculite, and shell powder were used as substrates respectively, and phase change microcapsules were mixed into different substrates at a certain mass ratio to prepare phase change microcapsule composites with different substrates. Through the moisture absorption and desorption performance experiments, water vapor permeability coefficient experiments, and isothermal equilibrium moisture content experiments, the moisture buffering properties of composite phase change materials with different substrates were compared. Differential scanning method, specific surface area and pore analysis, and scanning electron microscope were used to study their thermal performance, apparent morphology, and pore distribution characteristics. The moisture buffering performance index of zeolite-based phase change microcapsule composites is 1.5 times that of pure zeolite materials and 2 to 10 times that of other materials. The zeolite-based composites with good stability, large phase latent heat, and the best humidity controlling performance in all substrates have the phase transition temperature range (20 ~ 25℃) closed to the ideal room temperature, which are the most suitable for use as temperature-humidity controlling building materials.

Impact of humidity on formaldehyde and moisture buffering capacity of porous building material

The aim of this article is to present a validated model to study the influence of humidity on formaldehyde sorption of building material and the effect of formaldehyde and moisture buffering capacity of hygroscopic porous material on indoor air environment. New empirical formulas proposed to describe the diffusion and partition coefficients as functions of humidity based on previous experimental data are incorporated in a coupled moisture and pollutants transport simulation model. The numerical model that takes into account the effect of RH (or moisture) in building materials on VOC diffusion can be used to simulate VOC emissions/sorption from building materials. The developed model is implemented in the environment SPARK (Simulation Problem Analysis and Research Kernel) using finite difference technique. The model is then applied to study the hygric and formaldehyde (FOR, a water soluble VOC) behavior of calcium silicate (CS) subjected to different dynamic conditions of RH and formaldehyde. The results obtained in this paper help to emphasize the importance of moisture and formaldehyde buffering capacity as a new key parameter when selecting clean and hygroscopic building materials in building design because they can contribute to dampen indoor RH and formaldehyde variations. In addition, the impact of RH variation is significant and needed to be taken into account in the simulation to correctly predict the indoor formaldehyde concentration. The model developed in this paper can also be used to optimize the hygric performance and IAQ in building.

Moisture buffering effect of hygroscopic materials under wall moisture transfer

Hygroscopic material can moderate the indoor humidity variation due to its moisture buffering effect. This effect would change when used as interior finish mainly due to air exchange and wall moisture transfer. The author focused on clarifying the extent of the wall'’s influence on indoor moisture buffering and building humidity environment. A room model was established and the situation of no wall moisture transfer was simulated by adding a vapour barrier between the interior finish and the wall. Comparing this result with wall moisture transfer, the moisture buffering effect of the wall can be quantitatively analysed. The results verify that the buffering effect and the humidity environment, especially the seasonal buffering, change with the wall moisture transfer. The wall has great impacts on buffering in the cases of thin interior finish, high moisture production and low ventilation. Because the layer under the hygroscopic material also has buffering capacity, the difference of using various thicknesses of material is not obvious. Frequent ventilation reduces the buffering effect but improves the RH optimality.

Characterization of Responsive Plasters for Passive Moisture and Temperature Control

Ambient comfort maintenance accompanied by excessive energy consumption is hugely criticized concerning the limited sustainability of the building sector in the long-term. In this sense, the energy reduction strategies based on the employment of passive air-control techniques are viewed as a prospective solution for improved energy performance. In order to contribute to this significant issue, this paper is aimed at the design and material characterization of novel plaster with an improved thermal and humidity control performance. For this purpose, a form-stable diatomite/dodecanol-based phase change material together with superabsorbent polymer are used as admixtures for the passive moderation of indoor air quality by newly designed modified plasters. The experimental assessment of the functional properties by means of mechanical strength, thermal conductivity, and hygric properties is performed. Considering the goal of the paper, particular attention is paid to the characterization of water vapor storage and moisture buffering according to the Nordtest method. Differential scanning calorimetry is employed for the description of phase change intervals as well as the specific enthalpy of phase change. The obtained results point to significant improvements in the hygroscopic performance and increased thermal energy storage that can be used for passive moderation of the indoor temperature and reduction of the relative humidity swings.

Earth stabilisation via carbonate precipitation by plant-derived urease for building applications

Raw (unfired) earth represents a sustainable and efficient alternative to traditional construction materials but its dissemination into building practice has been hindered by a relatively high vulnerability to water erosion. Enzyme induced carbonate precipitation (EICP) can improve the durability of earth materials without using traditional chemical binders such as cement and lime. EICP utilises the urease enzyme to catalyse the hydrolysis of urea, which produces carbonate ions that react with the calcium ions dissolved in the pore water, thus resulting in the precipitation of calcium carbonate. The calcium carbonate fills the soil voids and binds particles together, which reduces water permeability and increases material strength. The urease enzyme is a hexameric protein that is found in the tissues of many common plants. This work proposes a low-cost and simple stabilisation technology that makes use of crude urease enzyme extracted from soybeans. This technology is applied to the stabilisation of compacted earth, whose properties are then assessed via unconfined compression, moisture buffering and durability tests. The findings suggest a noticeable improvement of material strength and durability, though further investigation is necessary to increase the competitiveness of EICP stabilisation against standard techniques using cement and lime.

The Effect of Willow (Salix sp.) on Soil Moisture and Matric Suction at a Slope Scale

The aim of this study is to provide new knowledge on the effect of willow on hillslope hydrology at a slope scale. Soil moisture and matric suction were monitored in situ under willow-vegetated and fallow ground covers on a small-scale hillslope in Northeast Scotland for 21 months. The retrieved time series were analysed statistically to evaluate whether the dynamics of soil moisture and matric suction changed with the hillslope zone (i.e., toe, middle, and crest) under the two ground covers. The effect of air temperature and rainfall on the dynamics of soil moisture and matric suction, as well as the relationship between the two soil-water variables, under both ground covers, were also investigated by analysing the cross-correlation between time series. The results of 21 months of monitoring showed that willow contributed substantially to reduce soil moisture and to increase matric suction with respect to fallow soil. Additionally, willow-vegetated soil exhibited higher water retention and moisture buffering capacity than fallow soil. The effect of willow was highest at the hillslope toe due to a denser vegetation cover present within this zone. Both air temperature and rainfall had a strong effect on soil moisture and matric suction. However, the effect of air temperature was more consistent and easier to interpret than that of rainfall. Soil moisture and matric suction were shown to have a complex relationship and the soil water characteristic curve for vegetated soil requires further research. This study provides novel, field-based information supporting the positive effect of willow on hillslope hydrology. The results gathered herein will undoubtedly enhance the confidence of using woody vegetation in Nature-based Solutions (NBS) against geo-climatic hazards.

Structure and Functions of Cocoons Constructed by Eri Silkworm.

Eri silkworm cocoons (E cocoons) are natural composite biopolymers formed by continuous twin silk filaments (fibroin) bonded by sericin. As a kind of wild species, E cocoons have characteristics different from those of Bombyx mori cocoons (B cocoons). E cocoons have an obvious multilayer (5–9 layers) structure with an eclosion hole at one end and several air gaps between the layers, which can be classified into three categories—cocoon coat, cocoon layer, and cocoon lining—with varying performance indexes. There is a significant secondary fracture phenomenon during the tensile process, which is attributed to the high modulus of the cocoon lining and its dense structure. Air gaps provide cocoons with distinct multistage moisture transmission processes, which form a good moisture buffer effect. Temperature change inside cocoons is evidently slower than that outside, which indicates that cocoons also have an obvious temperature damping capability. The eclosion hole does not have much effect on heat preservation of E cocoons. The high sericin content of the cocoon coat, as well as the excellent ultraviolet absorption and antimicrobial abilities of sericin, allows E cocoons to effectively prevent ultraviolet rays and microorganisms from invading pupae. The ultraviolet protection factor (UPF) of the E cocoon before and after degumming were found to be 17.8% and 9.7%, respectively, which were higher than those of the B cocoon (15.3% and 4.4%, respectively), indicating that sericin has a great impact on anti-UV performance. In the cocoon structure, the outer layer of the cocoon has 50% higher content than the inner layer, and the E cocoon shows stronger protection ability than the B cocoon. Understanding the relationship between the structure, property, and function of E cocoons will provide bioinspiration and methods for designing new composites.

Modeling the similarity and the potential of toluene and moisture buffering capacities of hemp concrete on IAQ and thermal comfort

Controlling and understanding indoor humidity and pollutants can help reduce the risk of health concerns. The experimental results suggested that there is a similarity relationship between water vapor and Volatile Organic Compounds (VOC) in diffusion through porous media. In this paper, the similarity between the moisture and pollutant transport and storage coefficients of porous building materials has been clearly established and explained. In addition, two similarity coefficients have been defined for VOC storage and diffusion to estimate the VOC properties from the moisture properties of the same material. A coupled hygric-pollutant (VOC) model which can be used to simulate VOC and hygric behavior of building materials under dynamic conditions is presented. The model which is implemented in the environment SPARK (Simulation Problem Analysis and Research Kernel) suited to complex problems using finite difference technique with an implicit scheme, has been validated with the experimental data. It is then applied to study the effect of toluene and moisture buffering capacities of a hemp concrete wall on indoor toluene concentration and relative humidity (RH). Hemp concrete was chosen in this study because it is an environmentally-friendly material that is used more and more in building construction. The toluene (TOL, selected VOC for this study) transport and storage properties obtained from hygrique properties of hemp concrete based on the assumption of the similarity between toluene and moisture transport have been modelled and investigated. At the room level, the results obtained show that taking into account the sorption capacity toward moisture and toluene has a significant effect on indoor RH and IAQ because hemp concrete contributes to dampen indoor RH and toluene variations. The numerical model presented is very useful for the building design optimization and can be used for a fast estimation of indoor pollution and hygrothermal conditions in building.