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Moisture buffer value (MBV) is a critical parameter for assessing hygroscopic material's ability to moderate indoor humidity variation. The original MBV theory is strictly valid only for a semi-infinite (or "very thick") material. When the material is thinner than semi-infinite, the material's thickness will affect its moisture buffering ability. The existing MBV theory is inapplicable. This study proposed a new numerical method to calculate a material's MBV at different thicknesses. The proposed model is simple and efficient. The relation between a material's MBV and thickness and the optimal thickness can be obtained without extensive experimental measurement. What's more, the material's adsorption and desorption isotherms, as well as the material's hysteresis loop and scanning isotherms, are incorporated in the proposed model, making it applicable to advanced desiccant materials like Metal-Organic Frameworks (MOFs). MIL-100(Fe), one of the most promising MOF candidates for indoor humidity control, was used to validate the newly developed model. MBVs of MIL-100(Fe) samples with different thicknesses were measured, and the experimental data closely matched the simulated results. Finally, a building energy consumption simulation model was developed based on the proposed numerical model. A MOF panel with its optimal thickness was placed in the BESTEST typical office room located in Copenhagen. The results show that MOF can reduce about 30 % of the energy consumption of air conditioning in a purely passive way. • A new method to calculate the MBV of hygroscopic materials at different thicknesses. • Both the ad/desorption isotherms and hysteresis loop of the material are considered. • A building energy simulation model was developed based on the new MBV model. • The optimal thickness and energy-saving potential of a MOF panel were investigated. [ABSTRACT FROM AUTHOR]

The Nordtest method evaluates the moisture buffer value (MBV) of materials that are being exposed to indoor air. The test simulates daily variations (high RH of 75% for 8 hours, low RH of 33% for 16 hours) in MBV, which in this context refers to the moisture uptake/release in the material when it is exposed to relative humidity (RH) in a square wave. We are looking for ways to increase clay plasterâs ability to buffer moisture. Which material has simultaneously a higher ability to buffer moisture and can be added to the clay plaster mixture? The recipe for the specimen included the following: waste paper (newspaper paper), glue (methylcellulose), clay and water. Our research showed that adding paper plaster mixture to the clay plaster mixture increases the moisture buffering ability of the plaster. The bigger the amount of added paper plaster, the better the plasterâs ability to buffer moisture.

The scope of the Nordtest method is to evaluate the moisture buffer value (MBV) of materials exposed to indoor air. The test is intended to simulate daily variations with relative humidity (RH) between 75 % during 8 hours and 33 % during 16 hours. The specimens follow a recipe that consists of waste paper, glue and water. Specimens made of paper plaster were covered with different colours. The results of the experiment showed that the type of paint used and the number of layers applied affected the MBV. Natural colours have a better moisture permeability than chemical paints, but the number of natural colour layers affects the MBV. The higher the number of layers, the lower the MBV. [ABSTRACT FROM AUTHOR]

The Nordtest method evaluates the moisture buffer value (MBV) of materials that are being exposed to indoor air. The test simulates daily variations (high RH of 75% for 8 hours, low RH of 33% for 16 hours) in MBV, which in this context refers to the moisture uptake/release in the material when it is exposed to relative humidity (RH) in a square wave. We are looking for ways to increase clay plaster's ability to buffer moisture. Which material has simultaneously a higher ability to buffer moisture and can be added to the clay plaster mixture? The recipe for the specimen included the following: waste paper (newspaper paper), glue (methylcellulose), clay and water. Our research showed that adding paper plaster mixture to the clay plaster mixture increases the moisture buffering ability of the plaster. The bigger the amount of added paper plaster, the better the plaster's ability to buffer moisture. [ABSTRACT FROM AUTHOR]

The scope of the Nordtest method is to evaluate the moisture buffer value (MBV) for materials exposed to indoor air. The test is intended to simulate daily variations with relative humidity (RH) of 75% during 8 hours and 33% during 16 hours. The specimen made according to a recipe contains the following: waste paper, glue, clay plaster mixture and water. Eleven paper plaster mixtures with different percentages were used. Test results showed that a large percentage of paper in the plaster increases the MBV. An impressive result, which needs to be studied further, was that the MBV was the highest in the mixture that consisted of 80% paper. [ABSTRACT FROM AUTHOR]

A hygrothermal characterization of new construction materials, namely unstabilized and Posidonia oceanica fiber stabilized compressed earth blocks, were studied in this work. In the first part, the sorption-desorption isotherms of unstabilized blocks were compared with others stabilized with raw and treated fibers to detect the effect of adding fibers. The results revealed an improvement in hygric properties after the addition of raw fibers. Moreover, the Guggenheim-Anderson-de Boer (GAB), the Oswin, and Brunauer, Emmet, and Teller (BET) models successfully fitted experimental sorption-desorption isotherms curves. In the second step, the moisture buffer value and water vapor permeability were evaluated under dynamic conditions. According to the classification of the NORDTEST project, the innovative and new compacted earth blocks studied in this paper seem to be excellent moisture regulators because they have an MBV greater than 2 g/ (m2. %RH). In fact, BAFBB samples (block with crushed Posidonia oceanica) achieved the best results. These formulations recorded an ideal water buffer coefficient equal to 2.66 g/ (m2.%RH) • Effect of Posidonia oceanica on the hygrothermal characterization of compacted earth blocks. • Sorption-desorption behavior, moisture buffer value, moisture diffusivity and water vapor permeability are determined. • GAB, Oswin and BET models of the sorption-desorption behavior modeling are investigated. • An innovative Posidonia oceanica fiber-reinforced CEB composite exhibit an excellent moisture performances. [ABSTRACT FROM AUTHOR]

• Hygrothermal properties of packed straw vary strongly with manufacturing process. • Conductivity is the lowest for low-density short-fiber samples with 0.0468 W/mK. • Water vapor diffusion resistance factor ranges from 3.34 to 11.20 among samples. • Moisture buffer value is higher for low-density short-fiber sample with 2.95 g/m2%RH. • Hysteresis of sorption isotherms is smaller for crushed straw particle samples. Biosourced materials are increasingly considered to replace traditional insulators to reduce environmental impacts and benefit from better hygrothermal buffering characteristics. Barley straw is cheap and abundant and can be manufactured into insulation material. However, it is necessary to understand their hygrothermal properties as a function of manufacturing to design proper assemblies. The present work aims to determine experimentally and analyze sorption–desorption curves, thermal conductivity, water vapor permeability, and moisture buffer value (MBV) of barley straw as a function of density, fiber size, and relative humidity. Expressions were developed to correlate hygrothermal properties with the characteristics of the samples. Results revealed thermal conductivity values from 0.0468 W/mK (low-density short-fiber dry samples) to 0.0799 W/mK (low-density short-fiber 90 % RH samples) and MBV from 2.12 g/(m2 %RH) for high-density long-fiber samples to 2.95 g/(m2 %RH) for low-density short-fiber samples. The water vapor diffusion resistance factors ranged from 3.34 to 11.20 depending on the method used (wet versus dry) and the sample characteristics. These results indicate that straw offers a good potential as an insulator and indoor climate regulator in buildings. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the hygrothermal and mechanical properties of innovative mortar mixtures reinforced with natural fibers. Fibers extracted from palm stems (PS) and hemp (HF) were evaluated at different percentages. Scanning electron microscope (SEM) observations showed that the PS fibers have rough surfaces and very complex microstructures. Prior to their incorporation into the mortar, the fibers were subjected to different treatments to reduce their hydrophilic character. The employed treatments showed good efficiency in reducing the water absorption of both PS and HF fiber types. Furthermore, the mortar mixtures incorporating these fibers exhibited low thermal conductivity and excellent moisture buffering capacity. Indeed, the moisture buffer value (MBV) of the investigated mixtures ranged between 2.7 [g/(%HR·m2)] and 3.1 [g/(%HR·m2)], hence providing them excellent moisture regulator character. As expected, the fiber mortar mixtures showed very high porosity and low compressive strength ranging between 0.6 and 0.9 MPa after 28 days of age. The low-environmental footprint materials developed in this study are intended for thermal insulation and building filling.

• Pore structure of bio-based materials is investigated combining WIP, MIP and X-ray CT. • X-ray CT is a promising tool for the exploration of inner porosity of plant particles. • Hygrothermal properties and compressive strength are measured on bio-based concretes. • Types of binder and aggregate impact the use performances of vegetal concretes. Bio-aggregate based building materials offer promising perspectives thanks to their low environmental impact and interesting hygrothermal behaviour. In this paper, different formulations of bio-aggregate concrete are proposed and analysed. We focus on two types of locally available bio-aggregates, namely maize and sunflower bark chips, and two types of binder matrices, based on respectively metakaolin and lime. The study specifically focuses on the pore structure of the composite material, as this quantity has a decisive impact on the insulating properties (thermal conductivity), the hygric behaviour (sorption isotherms, water vapour permeability and moisture buffer value) as well as on the mechanical performance (compressive strength). The results underline the impact of the constituents' porosity on the complex porous structure of the bio-concrete and the influence of porosity on its performance. The findings demonstrate that metakaolin and sunflower are high-potential raw materials for the design of a bio-aggregate based concrete. [ABSTRACT FROM AUTHOR]

• Bio-based composites based on rice husk (RH) and an earthen matrix are evaluated. • RH content improves thermal conductivity and contribute to hygrothermal comfort. • RH increase at least 20% the composites MBV and their ability to adsorb-desorb indoor moisture. • Pre-boiling of RH reduces biological susceptibility and improves mechanical behaviour. • Optimised composite panels can be applied in coatings systems of massive walls and ceilings. With the aim of developing economic and ecological bio-based composite panels to be used on indoor wall or ceiling coating systems, contributing to hygrothermal comfort and health, three different composite formulations were produced, differing on the content and pre-treatment of rice husk: 15% and 30%, only dried or previously boiled. Composite samples were tested for biological development and several physic-mechanical characteristics. Increasing on rice husk content decreases thermal conductivity due to bulk density decrease, decreasing ultrasound velocity, flexural strength, abrasion and fire resistance, but improving the moisture buffering capacity at least in 20%. For high rice husk-content composites, its pre-boiling decreases biological susceptibility although decreasing resistance to fire, most probably due to destruction of the cellulose wall, but significantly increases abrasion resistance and compressive strength, probably because of a better bond between the rice husk and the earthen matrix, quicker reaching a high water vapour adsorption limit. [ABSTRACT FROM AUTHOR]

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]

Highlights • Hygrothermal characterization of Date Palm Cement composites. • Adsorption-desorption curves, moisture buffer value, fictitious and dry water vapor permeability are measured. • Effect of temperature on moisture buffer value and on the penetration depth is investigated. • Hysteresis is calculated from the Adsorption-desorption curves. • Date palm cement composites exhibit an interesting hygric performances. Abstract Hygrothermal behavior of a new building material, composed of cement, sand and date palm fibers was investigated in the present work. In a first part, the sorption-desorption isotherms and the hysteresis effect were characterized under static conditions, and collected results revealed a high hydric capacity of this Date Palm Cement (DPC) mortar. In addition, the GAB model (Guggenheim-Anderson-de Boer) was successfully applied to describe the experimental sorption isotherm curve. In a second step, the moisture buffer value and the effect of temperature on successive adsorption/desorption cycles were assessed under dynamical conditions. It was found that the sorption process is highly affected by temperature. Finally, this bio-based mortar was classified as hygroscopic and breathable material with excellent moisture buffering capacity. [ABSTRACT FROM AUTHOR]

This study investigates the use of clay as binder in hemp composite and compares hemp-clay composite to hemp-lime concrete. The clay is produced from washing mud from gravels production site. Two clay drying temperature are used. The thermal properties are measured with a hot wire method and the hygric characterization is based on the measurement of Moisture Buffer Value. Performances obtained on clay blocks, hemp-clay composite and hemp-lime composite are compared. The results show that the two clay drying temperatures do not impact on the thermal conductivity nor on the moisture buffer value of clay blocks. Hygric and thermal performances of hemp-clay and hemp-lime composites with the same density are close. These materials act as excellent hygric regulators. Performances measured separately on hemp and clay underline an interesting synergetic effect in the case of hemp-clay composite leading to a higher ability to the moisture buffering. Such material can be advantageously used in buildings to moderate indoor humidity variations. [ABSTRACT FROM AUTHOR]

The use of radiant cooling systems in humid regions is limited by surface condensation. Promising advancements have been made in the field of humidity regulation through the utilization of novel high-capacity adsorption materials, known as porous metal-organic frameworks (MOF), which possess expansive surface areas. This study investigated the condensation retardation performance of MOF-based composite humidity-control materials used as surface coatings in a typical radiation cooling room. A total of 16 working conditions in summer were tested, including extreme and typical climates, open windows, and fresh air supply. The influence of two types of MOF-based coating materials and two types of ceiling constructions (with or without a desiccant interlayer) on humidity was analyzed. The results showed that the coating materials and desiccant interlayer construction significantly affected condensation retardation and indoor humidity ratio variation. The better the moisture regulation performance of the material, the lower the risk of condensation. Under extremely high-humidity conditions, the MOF-based coating delayed the critical condensation time by up to 4.5 times that under no-coating conditions. The risk of condensation decreased with improvement of ideal Moisture Buffer Value (MBV ideal) of the material, and with the addition of desiccant interlayer during ceiling construction. A coating material with a higher MBV ideal can increase the average values of the difference between the surface and dew point temperatures by as much as 181.0%, compared with an uncoated ceiling. The average difference between the surface and dew point temperatures was found to increase by up to 2.11 °C, compared with that for the desiccant-free construction. • The metal-organic frameworks (MOFs) composite materials in the radiation cooling room were tested. • A desiccant interlayer construction of radiation cooling ceiling was proposed. • MOF composite coating and desiccant interlayer construction can effectively prolong the cooling surface condensation time. [ABSTRACT FROM AUTHOR]

Highlights • Thermal conductivity decreases with the addition of plant aggregates. • Earth material is highly water vapour permeable. • Sorption–desorption isotherms are assessed with DVS and saturated salt solution methods. • MBV of earth-based materials is excellent. Abstract Earth is a material presenting good hygric properties, which is an important point as comfort and indoor air quality have become major issues. Nowadays, the energy efficiency of a construction is also crucial, but the thermal insulation provided by an earth brick is quite low. Therefore, some plant aggregates were added to lighten the material, thus decreasing its thermal conductivity. The hygrothermal properties of seven formulations made of earth with 0, 3 or 6% by weight content of barley straw, hemp shiv or corn cob were assessed. The properties determined were thermal conductivity, specific heat capacity, water vapour permeability, and sorption–desorption isotherms measured with the saturated salt solution and DVS methods. The theoretical MBV was also calculated. The study showed a large decrease in thermal conductivity when a large volume of plant aggregates was added while plant aggregates incorporation conversely affected the thermal inertia parameters. Concerning water vapour permeability, as earth is a very permeable material, the addition of plant aggregates did not improve this property. The sorption capacity of bio-based earth materials was slightly increased in comparison with earth alone. Finally, the calculated MBV showed the excellent buffering capacity of this kind of material, with and without plant aggregates. [ABSTRACT FROM AUTHOR]

Construction and demolition debris, mainly concrete and masonry rubble, represent a significant share of municipal waste. Recycling crushed concrete aggregates and using them as substitutes for natural ones might therefore be determinant in reducing landfilling and mineral resource depletion. An innovative way to give new value to Recycled Concrete Aggregates (RCAs) is to ram them in layers to form load-bearing walls for stabilised Rammed Earth (RE) applications. However, the success of those few existing RE projects using RCA is mainly due to the knowledge and experience of the contractors rather than official standards or guidelines or scientific literature. The objective of this study was to further the knowledge of this building technique by determining the effect of different RCA replacements on the material’s mechanical resistance, sustainability and hygroscopic properties: indicative of the structure’s structural, environmental and hygrothermal performance. Mechanical resistance was assessed by means of the Unconfined Compressive Strength (UCS, commonly used for rammed earth-like materials), hygroscopic properties via Moisture Buffer Value (MBV) and sorption isotherms while the sustainability was assessed via consequential Life Cycle Assessment (LCA). Microstructural investigations via mercury intrusion porosimetry, nitrogen adsorption-desorption isotherms, scanning electron microscopy and X-ray diffraction were performed to understand and explain material mechanical and hygroscopic behaviour. The building technique, already proven to be durable, was demonstrated to be resistant (from 4 to 12 MPa at 28 days depending on the RCA replacement and cement content), sustainable (down to 25 kg CO 2 -eq. of embodied carbon per square meter of load-bearing wall) and to have good moisture buffering abilities (0.88 g/(m2%RH) for mixtures containing only RCA). Strength appeared to be more related to the particle size distribution of the mix rather than to the percentage of RCA added. The amount and type of stabiliser added to the mix and the distance covered by the RCA during its lifetime strongly affected the environmental sustainability of the mixture; to maximise the potential of this building technique, reducing the amount of cement in the mixture by using alternative stabilisers should be the main priority. [ABSTRACT FROM AUTHOR]

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 European ISOBIO project aims to develop new bio-based building insulating materials which contribute to reduce environmental impacts of buildings. The developed materials shall have low embodied energy and low carbon footprint and shall contribute to reduce energy needs of buildings and to ensure high hygrothermal comfort of users. This study investigates the valuation of agro resources as bio-based aggregates and as binding material to produce wholly bio-based composites. The developed composites are made of hemp shiv glued with wheat straw. After a feasibility study which investigates several ways to use wheat straw as a gluing material and several hemp to wheat straw ratio, three hemp-straw composites are selected. Specimens are produced to characterize thermal and hygric properties of developed composites. They show interesting thermal and hygric properties as they have low thermal conductivity (0.071 to 0.076 W/(m.K)) and they are excellent hygric regulators (MBV > 2 W/(m².%RH)). [ABSTRACT FROM AUTHOR]

This work test the feasibility and characterize the thermohygric properties of composite materials, realized with eco-friendly raw materials and designed to make suspended ceilings or interior partition walls. Several raw materials are considered: recycled paper (granules or cellulose wadding) and wood fibers. Aggregates or fibers are bonded with organic or mineral binder. One of the binder considered is starch, due to its availability in Ivory Coast (cassava flour). The calcium sulfate hemihydrate is also used for comparison. The density of the produced composites ranges from 400 to 1200 kg/m 3 depending on formulation. The thermal conductivity increases proportionally with the density and ranges from 0.09 to 0.5 W/(m.K). The characterization of hygric behavior is based on the measurement of moisture buffer value (MBV) [1]. The hydric performances of the composites made of mineral binder goes from moderate (MBV around 1 g/(m².%RH)) to excellent (MBV > 2 g/(m².%RH)). The moisture buffer value of the paper granules -starch composite is also excellent (MBV > 2 g/(m².%RH)) [ABSTRACT FROM AUTHOR]

Hygroscopic building materials have the ability to moderate the relative humidity variation without the need for active systems. The moisture buffer phenomenon can be assessed by way of the Moisture Buffer Value (MBV). Some authors have pointed out that the MBV is sensitive to several parameters, however, there is no model that involves all them. The aim of the developed PC-tool is to take into account all these variables to calculate the MBV of hygroscopic building materials. The material hygroscopic properties will be needed to solve the moisture storage and transport inside the porous materials and consequently to predict its MBV. [ABSTRACT FROM AUTHOR]

One of the acknowledged qualities of rammed earth (RE) is its moisture buffering capacity. Recently, stabilisation of RE has become a common practice to improve the mechanical resistance but very little is known about the effect that stabilisation has on hygroscopic properties. The present study aims to fill this gap by understanding the role that stabilisation plays in the buffering and sorption capacity of RE. The use of alternative stabilisers such as fly ash and calcium carbide residue and a comparison with traditional unstabilised RE (URE) have also been investigated. Moreover, the effect of weathering, simulated by cyclic wetting-drying, on hygroscopic performance has been analysed. Moisture Buffer Value (MBV) testing, moisture and nitrogen adsorption-desorption isotherms and mercury intrusion porosimetry were performed on stabilised samples to examine microstructural phenomena responsible for behavioural changes. URE was confirmed to be a good-to-excellent passive air conditioner according to the MBV scale but its performance seemed to be highly influenced by the soil particle size distribution and mineralogy. Based on the experimental outcomes of the mixtures investigated, stabilisation had a detrimental effect on the moisture buffer capacity of rammed earth, likely due to the inhibition of the physico-chemical interactivity between moisture and clays. Weathering had a variable effect on the buffering capacity, depending on the availability of unreacted particles in the matrix. [ABSTRACT FROM AUTHOR]

This paper presents a study of eco-aggregates produced by a new Accelerated Carbonation Technology (ACT) in a sustainable approach. These eco-aggregates, obtained by mixing industrial by-products or wastes such as ashes with carbon dioxide (CO 2 ), have some characteristics which make them useful in the field of construction materials such as natural aggregates replacement in concrete or mortar. Hygric and thermal characterizations were performed on carbonated aggregates with adapted methods. The results have been compared to that obtained with two reference aggregates: natural gravel and expanded clay. Then thermal and hygric behaviors of concretes-based on carbonated aggregates were analyzed and discussed in the field of construction. These results proved that carbonated aggregates can be valorized through the manufacturing of concrete building blocks with several advantages: mechanical strength, thermal and hygric inertias. Experimental properties allowed a numerical/digital simulation in dynamic conditions for a simple and multilayered wall using the SPARK object-oriented simulation environment that is adapted to complex problems. Their performances were compared to those of concretes based on two reference aggregates in order to highlight the feasibility of manufacturing building blocks. [ABSTRACT FROM AUTHOR]

The absorption or release of heat and moisture by interior surface layers of building envelopes under specific conditions can set effective limits to the extreme levels of indoor air parameters. Moderation of interior climate achieved in this way can contribute to a reduction of energy demands for building conditioning and overall operation cost using a straightforward material solution. In this paper, lime-cement plasters modified by two types of PCM based admixtures are designed specifically for the moderation of relative humidity and temperature fluctuations of the interior environment. The plasters are subjected to a detailed characterization procedure including the assessment of a complex set of basic physical, hygric, thermal and mechanical properties. Experimental results show that the application of small encapsulated PCM particles leads to an up to 10% increase of open porosity, as compared with the reference plaster. Contrary to this fact, the water vapor transport is slightly decelerated, what is attributed to the encapsulating polymer shell which creates impermeable barrier for water vapor transmission. Two contradictory factors affect the liquid water transport, namely the higher porosity of PCM modified plasters and increasing content of not-wettable polymer shells. The moisture storage capacity increases with the increasing amount of PCM in the mix. The moisture buffer value is improved due to the utilization of both PCM admixtures, the developed plasters can be classified as good moisture buffering materials. The thermal conductivity of modified plasters is greatly improved, as well as the heat storage capacity, the additional phase change enthalpy being up to 13 J/g. Although the inclusion of PCM into the lime-cement matrix decreases the mechanical strength, the achieved values of tested mechanical parameters are still satisfactory for the application of the designed plasters in building practice. In summary, PCM modified plasters can be considered a prospective solution for the moderation of interior climate in contemporary buildings. [ABSTRACT FROM AUTHOR]

A coupled heat and moisture transfer 1D-model is developed to simulate the hygrothermal behavior of a coated hemp concrete wall. The hysteretic behavior of each layer (hemp concrete and plasters) is included in the modeling whereas a perfect hygrothermal contact is assumed between each layer. The numerical results are first compared to experimental ones obtained on a facility specially designed to measure mass variations as well as temperature and relative humidity fields within a coated sample. The comparison gives satisfactory results and underlines the influence of the hygrothermal properties, but also of plaster's thickness. Furthermore, it is observed experimentally that coating layers reduce moisture transfer and, thus, moisture buffer value of multilayered materials. A second comparison is performed with experimental data measured on a multilayer wall subjected to climatic variations. It was found that including the hysteresis in the modeling improve the prediction of the relative humidity field within a wall subjected to isothermal and non-isothermal conditions. However, it requires knowing the hygrothermal history of the wall in order to set initial moisture content of each layer. [ABSTRACT FROM AUTHOR]

Hemp-lime mortars are generally used as indoor insulating plasters of building envelopes. They can be applied in thick coat to allow high enough hygrothermal performances to be reached in retrofit case. This study investigates hygric and thermal properties of two hemp-lime plasters. These plasters are made with the same lime-based binder and differ from their kind of hemp shiv. The two kinds of hemp shiv are defibered but one is smaller than the other. This experimental study is based on the measurement of sorption isotherm, water vapour permeability, moisture buffer value and thermal properties (conductivity and diffusivity). The effect of temperature on moisture buffer value and on thermal properties is also investigated. It is shown that hemp-lime plasters are hygroscopic and breathable materials. They are good hygric regulators according to the Nordtest classification and their moisture buffering ability is slightly impacted by temperature in the range from 11° to 23 °C. The hemp-lime plaster with the smallest hemp shiv is a better hygric regulator than the one with the biggest hemp shiv. Hemp-lime plasters show a quite low thermal conductivity, around 0.2 W/(m.K). The hemp-lime plaster with the smallest hemp shiv is slightly more conductive than the one with the biggest hemp shiv. The temperature does not impact thermal conductivity at dry state. At wet state, for a given relative humidity, when the temperature increases the thermal conductivity decreases simultaneously with water content. This study underlines that hemp-lime plasters show high hygrothermal qualities. [ABSTRACT FROM AUTHOR]

• Elaboration and characterization of SCBA‐lime binders. • λ of SCBA‐lime binders is 0.8 to 2.2 times lower than cement‐based or lime‐based mortar materials of the literature. • Ability of SCBA‐lime binders to regulate relative humidity 2 to 10 times better than concrete materials. The aim of this study is to produce Sugar Cane Bagasse Ash (SCBA) with an improved pozzolanic reactivity. Inert particles and impurities present in the initial SCBA were removed by sieving. Resulting sieved SCBA was mixed with hydrated lime to obtain SCBA-lime binders. These prepared alternative SCBA-lime binders were physically, chemically and mechanically characterized. Their thermal conductivity and moisture buffer values were compared to cement, concrete and other metakaolin-lime binders ones. Selection of SCBA particle size leads to (1) an increase of 50 % of pozzolanic reaction kinetics between ash and lime compared to un-sieved SCBA, to (2) an increase of 30 % of SCBA-lime binder compressive strength and to (3) a decrease of alkalinity of the interstitial solution present in SCBA-lime binders. Indeed, their alkalinity is around 3 % lower than the cement binder interstitial solution one after 10 days of hydration at 55 °C. Thermal conductivity λ of studied SCBA-lime binders is 0.8 to 2.2 times lower than cement-based or lime-based mortar materials of the literature. More, the ability of SCBA-lime binders to regulate relative humidity is excellent, that is to say 2 to 10 times better than concrete materials, which present negligible to moderate capacity to regulate. [ABSTRACT FROM AUTHOR]

Experiments were carried out according to the Nordtest protocol to study the moisture buffer potential of hemp-lime walls with a range of different internal linings and surface treatments. It was observed that the moisture buffer value was ‘Excellent’ when the inner surface of hemp-lime was exposed. ‘Excellent’ moisture buffer values were also obtained for hemp-lime with lime plaster. All other assemblies demonstrated ‘Good’ moisture buffer value. Moisture buffer values of the assemblies, after application of paint on the upper surfaces, were also determined. It was observed that application of synthetic pigment based trade paint could reduce the moisture buffer performance of the assembly consisting of hemp-lime and lime-plaster from ‘Excellent’ to ‘Good’ while between 61 and 69% reduction of moisture buffer value was observed for the other assemblies. However, the reduced buffer values of the assemblies are still comparable with other moisture buffering building materials. It was further observed that moisture buffer performance was improved when clay based organic paint was used instead of trade paint. [ABSTRACT FROM AUTHOR]

To investigate the influence of plastering on the moisture buffering behavior of hemp concrete, experiments are performed on two samples, one uncoated and one coated with less hygroscopic lime-based plasters. Global mass variations were monitored and results indicate in this case that coating reduces the MBV of hemp concrete. In addition, local temperatures and relative humidities are also measured at several depths within the samples in the view of validating a heat and mass transfer model. Results show that including the hysteretic behavior of each layer (hemp concrete and plasters) leads to a better agreement between numerical and experimental results, but also plays a significant role in the prediction of stored energy. [ABSTRACT FROM AUTHOR]

Materials with high moisture exchange capacity may have a strong impact on indoor climate conditions as well as building energy performance. Crop-based materials, characterized by their high porosity and hygroscopicity, belong to this category. Modeling their hygrothermal behavior accurately is thus particularly relevant for appropriate building design. A COMSOL Multiphysics transient heat air and moisture model is developed in this article to simulate moisture exchange between a lime–hemp concrete block and surrounding air during a Moisture Buffer Value evaluation test. Results are then compared with the validated heat air and moisture software using performance criteria showing a slight preference for both moisture exchanges and latent heat effect characterization. It offers yet additional advantages in terms of flexibility and transparency as well as further evolution potential. [ABSTRACT FROM PUBLISHER]

This paper presents an inverse modelling approach for parameter estimation of a model dedicated to the description of moisture mass transfer in porous hygroscopic building materials. The hygric behaviour of unfired clay-based masonry samples is specifically studied here and the Moisture Buffer Value (MBV) protocol is proposed as a data source from which it is possible to estimate several parameters at once. Those include materials properties and experimental parameters. For this purpose, the mass of two clay samples with different compositions is continuously monitored during several consecutive humidity cycles in isothermal conditions. Independently of these dynamic experimental tests, their moisture storage and transport parameters are measured with standard steady-state methods. A simple moisture transfer model developed in COMSOL Multiphysics is used to predict the moisture uptake/release behaviour during the MBV tests. The set of model parameters values that minimizes the difference between simulated and experimental results is then automatically estimated using an inverse modelling algorithm based on Bayesian techniques. For materials properties, the optimized parameters values are compared to values that were experimentally measured in steady state. And because a precise understanding of parameters is needed to assess the confidence in the inverse modelling results, a sensitivity analysis of the model is also provided. [ABSTRACT FROM AUTHOR]

Moisture transfer in hygroscopic building materials affects the indoor air quality by exchanging moisture and buffering the ambient relative humidity variations. The paper deals with experimental and numerical study on hysteretic sorption behaviour of the hemp concrete sorption process. Experimental intermediate scanning curves of hemp concrete are measured and used to compare two hysteresis models, Huang's model and Carmeliet's model. An original method is achieved to fit the numerical results on the experimental ones leading to the identification of the main desorption curve. The most relevant model, Huang's model, is implemented in a heat and moisture transfer model based on Künzel formalism. The transient hydric response of hemp concrete submitted to cyclic hydric loadings is investigated and compared to experimental results issued from the literature. These investigations show the relevance to consider the hysteresis phenomenon into the model. Then, the influence of initial conditions is discussed. The results point out that transient response of hemp concrete strongly depends on the initial hydric state (initial moisture content as well as initial relative humidity). [ABSTRACT FROM AUTHOR]

• Sunflower-based concrete is highly hygroscopic and has self-insulating properties. • Glycerol carbonate limits shrinkage of earth plasters. • Clay-rich earth plaster exhibits higher sorption and moisture buffer capacity. • A coupled heat and moisture transfer model satisfactorily estimates MBV. The hygrothermal behaviour of bio- and geo-based bilayer wall assemblies is investigated. The highly hygroscopic nature and thermal insulating properties of a sunflower-based concrete make it a promising building material. However, vegetal concretes are usually coated to satisfy aesthetic requirements. Therefore, the finishing layer is taken into consideration when investigating the hygrothermal behaviour of a wall. To improve the heat and mass storage and transport properties, without jeopardizing the general behaviour of plasters, an organically admixed mortar formulation was developed and the hygrothermal properties of each layer (sunflower concrete and plaster) were determined experimentally. The data were included in a coupled heat and moisture transfer 1D-model, which was applied to simulate the hygrothermal behaviour of the sunflower concrete specimen coated with earth plaster. The comparison of numerical moisture buffer values with experimental data for the wall assembly gave satisfactory results in spite of the heterogeneity of the materials and the experimental uncertainty. As expected, the numerical results show that the bilayer structure with the optimised plaster exhibits higher moisture buffer capacities than one with the reference formulation. [ABSTRACT FROM AUTHOR]

Highlights: [•] This study compares the hygric behaviour of three hemp concretes. [•] The materials differ from their formulations and manufacturing methods. [•] Sorption curve, water vapour permeability and moisture buffer value are measured. [•] Hygric diffusivity is calculated from sorption and water vapour permeability. [•] The results show slight differences between the three materials. [Copyright &y& Elsevier]

In their recent paper in Building Simulation (Trabelsi et al. (2012), Building Simulation, 5: 107-115), 'Assessment of temperature gradient effects on moisture transfer through thermogradient coefficient', Trabelsi et al. introduce their assertions on 'the occurrence of significant thermal diffusion'. In this comment, the premises and outcomes of their analysis are challenged, based on my own recent paper on that same topic (Janssen (2011), 'Thermal diffusion of water vapour in porous materials: Fact or fiction?' International Journal of Heat and Mass Transfer, 54: 1548-1562). Firstly Trabelsi et al.'s physical model and measurement methodology are critiqued, partially based on their own measured results. Reinterpretation of their data indicates that no consistent nor significant thermal diffusion can be found, confirming vapour pressure as sole significant transport potential for diffusion. This suggests that their physical model, built upon vapour density and temperature, is physically confusing and needlessly complicated. The model additionally requires a thermogradient coefficient, the measurement of which is complex and unreliable. A physical model for vapour diffusion based on vapour pressure, making use of the easy to measure vapour permeability, is thus pragmatically and fundamentally preferable. The comment finally ends by disputing Trabelsi et al.'s findings on the impact of thermal diffusion on moisture buffering: it is argued that they are practically and fundamentally faulty. [ABSTRACT FROM AUTHOR]

Abstract: This study deals with dynamic characterization of hydric behaviour of sprayed hemp concrete. The measurement of moisture buffer value (MBV) is held according to the NORDTEST protocol (Rode, 2005). Specimen are exposed to daily cyclic variation of relative humidity: 8h at 75%RH and 16h at 33%RH the test is held under isothermal conditions (23°C). The experimental set-up is validated by comparison of moisture buffer value measured on cellular concrete with values given in the NORDTEST project for the same kind of material. Results show that sprayed hemp concrete has an excellent moisture buffer capacity (MBV=2.15g/(m2 %RH)). So, it is an excellent hydric regulator that improves hygrothermal comfort and reduces energy needs. Moisture effusivity is then calculated from sorption and water vapour permeability value and from dynamic test of MBV. The results (respectively 5.8×10−07 and 4.8×10−07 kg/(m2 Pas1/2) show a slight discrepancy between values obtained from steady-state and from dynamic conditions. Finally, the penetration depth for daily cyclic variation is estimated about 5.8cm for sprayed hemp concrete. Also, the experimental data set can be used for benchmarking buffering models. [Copyright &y& Elsevier]

Abstract: One of the variables that have a greater influence on the determination of the moisture buffering capacity of a material to be used as inner surface layer of an enclosure is the value of the vapour resistance of the surface film layer. In this paper, the influence of such a surface resistance on the moisture buffering value (MBV) is studied by means of a small experimental equipment where the tests were developed according to the NordTest protocol, but modifying the air speed over the samples, in order to take in count its influence. The tested material is an autoclaved ceramic made from the shells of the molluscs grown in Brazil, with the aim of using it as indoor surface layer of the enclosures in museums and buildings used to keep archives and documents, and where it is required to control the conditions of the indoor air by means of passive systems based on the moisture buffering capacity of the materials. The theoretical MBV is determined too based on the effusivity of the material which is obtained from its basic hygroscopic characterization. [Copyright &y& Elsevier]

Indoor air quality, occupant’s comfort, durability of building parts, and energy consumption are highly related to the variations in indoor relative humidity. Since interior finishes and objects assist in dampening the peaks in relative humidity, the knowledge of the moisture buffer potential of room enclosures is necessary to include its effect in whole-building simulations. In this article, a method for the in situ determination of the moisture buffer potential of room enclosures is presented. During a period of some days, a humidifier is placed in a room and a moisture production scheme is implemented. Based on the measured RH-increase and decrease during loading and unloading steps, the ventilation rate and moisture buffer potential of the room are determined inversely by solving the moisture balance of the room using the effective capacitance and effective moisture penetration depth models. The methodology is validated by well controlled experiments in a large climatic chamber with known hygric inertia, and afterwards applied to real room enclosures. Main advantage of the proposed method is that a simple and fast experiment allows obtaining a comprehensive characterization of the hygric inertia of the whole building enclosure — including all interior finishes and multidimensional interior objects such as furniture, carpets, drapes, books, etc. [ABSTRACT FROM PUBLISHER]

Abstract: This paper reports the results of an extensive experimental characterization of the sorption isotherms, vapour permeability and Moisture Buffer Value (MBV) of finishing solutions that are commonly applied on buildings interior surfaces. The experimental and analytical procedures followed either international standards or well-established methodologies, supporting an innovative analysis of coated renders moisture behaviour. The results support the discussion on the relevance of finishing materials contribution to a room’s hygroscopic inertia, and the influence of finishing coatings on that contribution. A renewed interest on the influence of hygroscopic inertia in the moderation of relative humidity variation was the main motivation for this study. [ABSTRACT FROM AUTHOR]