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• Extended hygrothermal characterization of unstabilized rammed earth. • Low influence of density and grain size distribution on sorption isotherm. • High influence of density on thermal conductivity and vapor resistance factor. • Same linear dependency of thermal conductivity on moisture content for different soil compositions. • Vapor transfer resistance factor for a large span of relative humidity. Although hygrothermal properties of rammed earth represent great potential for improving thermal comfort during hot summers, still little knowledge is available about this topic. The literature lacks complete sets of hygrothermal characteristics of rammed earth, although they are fundamental for heat and moisture transfer modeling necessary to predict earthen building performances. The present work reports the results of a large collaboration between four academic laboratories in order to obtain an extended hygrothermal characterization of rammed earth, focusing on the material used in a modern construction in Lyon, France. The aim of the article is to provide for the same kind of soil an extend characterization on a large span of relative humidity to provide complete set of material properties for heat and moisture transfer simulation. The hygrothermal measurements cover adsorption and desorption isotherm, intermediate isotherm loop, specific heat capacity, dry thermal conductivity, moisture-dependent thermal conductivity and water vapor resistance factor for a large span of relative humidity. In addition, the capillary rise test was performed to estimate the liquid transport coefficient for suction and redistribution. The results show that variations in the density of the samples have a low impact on sorption isotherm, while they have a non-negligible impact on thermal conductivity and water vapor permeability. Surprisingly, variations in the grain size distribution do not produce a significant modification in the sorption isotherm, while hysteresis slightly reduces when bigger grains are added to the soil composition. Approximation of empirical model coefficients for the determination of moisture-dependent thermal conductivity is proposed for rammed earth materials. [ABSTRACT FROM AUTHOR]

Available throughout the world and used in construction for thousand years, earthen materials are known to improve indoor air quality while keeping the internal temperature relatively stable. In Rhône-Alpes, France, the rammed earth technic is the most spread and consists in compacting layers of earth, one by one, within a framework. Current thermal standards, which are mainly based on thermal resistance of the material, urge to insulate walls. However, due to its interaction with its environment, and its couplings between heat and moisture transfers, the observed thermal behaviour of uninsulated rammed earth can be above the expectations. The objective of the paper is to highlight the living comfort provided by non-insulated rammed earth walls, for different orientations, from in-situ measurements performed over more than two years. Winter, with low energy use for heating, and summer, with no cooling device, are studied. The study points out the important role of solar irradiance on the thermal balance of the house, and thus the importance of a good architecture. [ABSTRACT FROM AUTHOR]

Detailed modelling of air leakage paths through complex building wall assemblies is a challenging task. It requires transient modelling of diffusion and advection phenomena through fluid and solid domains, including porous materials and air channels. In this article, the development of a numerical model coupling heat air and moisture transfers (commonly called HAM transfers) is presented. The model is able to deal with non-isothermal air flow through complex 2D (two-dimensional) geometries, combining air channels and porous media, air permeable or not. A stepwise 1D validation of the model is achieved with numerical benchmarks. The model is then tested on a 2D air leakage configuration subjected to infiltration and exfiltration scenarii. [ABSTRACT FROM AUTHOR]

This study aims to check the compatibility of a selection of waste and recycled biopolymers for rammed earth applications in order to replace the more common cement-based stabilization. Five formulations of stabilized rammed earth were prepared with different biopolymers: lignin sulfonate, tannin, sheep wool fibers, citrus pomace and grape-seed flour. The microstructure of the different formulations was characterized by investigating the interactions between earth and stabilizers through mercury intrusion porosimetry (MIP), nitrogen soprtion isotherm, powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The unconfined compressive strength (UCS) was also evaluated for all stabilized specimens. Three out of five biopolymers were considered suitable as rammed earth stabilizers. The use of wool increased the UCS by 6%, probably thanks to the combined effect of the length of the fibers and the roughness of their surfaces, which gives a contribution in binding clay particles higher than citrus and grape-seed flour. Lignin sulfonate and tannin increased the UCS by 38% and 13%, respectively, suggesting the additives' ability to fill pores, coat soil grains and form aggregates; this capability is confirmed by the reduction in the specific surface area and the pore volume in the nano- and micropore zones. [ABSTRACT FROM AUTHOR]

Reducing energy consumption for future buildings using bio-based insulation materials is currently one of the most attractive research pursuits. The specific purpose of this research was to optimize thermo-pressing conditions for new low-environmental-impact bio-insulation fiberboards from bamboo fibers and protein-based bone glues. The microstructure, thermal insulation, water sensitivity, and mechanical properties of these fiberboards were investigated in this study. As illustrated by the results, protein-based bone glue acts as a good internal binder for bamboo fiberboards when 30% (w/w) of glue was added and elaborated under specific thermo-pressing conditions (150 kgf/cm 2 , 160 °C) during 15 min. Indeed, this board presents the best mechanical properties and water resistance due to the effective adhesion of the proteins. The thermal conductivity of all the fiberboards is in a low range, between 0.0582 and 0.0812 (W.m −1 K −1 ) at 57% RH and 25 °C, and it changes according to relative humidity levels and moisture content variation. The bamboo fibers have great potential for buildings thermal insulation with a thermal conductivity below 0.082 Wm −1 K −1 . [ABSTRACT FROM AUTHOR]

Innovative and efficient ways to perform numerical simulations are worth investigations to reduce the computational complexity of building models and permit to solve complex problems. This paper proposes a Proper Generalised Decomposition (PGD) model reduction technique for heat and moisture multizone modelling. First, the transient multizone problem is written using PGD formalism and solved in a non-incremental way to assess hygrothermal fields. The computational complexity and accuracy of results of the reduced-order model and the large original model are compared, highlighting that the fields are precisely represented with the PGD resolution. The complexity of the reduced-order model is lower, offering interesting numerical savings, particularly when the number of the building zones increases. The second advantage of the method is for solving parametric problems. Two illustrations are proposed. The first considers a climate and ventilation flow rates parametric multizone problem. The PGD model analyse the behaviour of building zones as a function of these two extra-parameters. For the second, an initial condition and source-term PGD parametric solution is computed. It is then coupled with a wall model to perform whole-building hygrothermal simulation. For both studies, the model represents accurately the hygrothermal fields in the different zones with important computational savings. [ABSTRACT FROM AUTHOR]

[Display omitted] • The moisture diffusivity of rammed earth is studied by modifying the X-ray method. • A confinement eliminates disturbances by material evolution during the test. • The Boltzmann transformation is corrected for the presence of a wick and paper. • This is done via their hydraulically equivalent height in the capillary absorption. • Taking this equivalent height into account is indispensable for the studied cases. The determination of the moisture diffusivity in the capillary range is studied for rammed earth building materials, using the X-ray method. To prevent liquefaction and expansion of these materials during the capillary absorption test, a brick wick and paper are added as lower sample parts and a confining sealing is utilised. Since the wick and paper bring about a composite case, the compatibility with the Boltzmann transformation must be redeveloped. It is found that the solution lies in adjusting the Boltzmann transformation through the equivalent height capturing the hydraulic impact of the wick and paper on the capillary absorption process. [ABSTRACT FROM AUTHOR]

This paper describes the effect of inorganic adsorbents on the hygrothermal performance of insulating materials. The addition of the inorganic adsorbents leads to significant effect to the microstructure and mechanical properties of these materials. The thermal conductivity rang of the materials containing adsorbents from 0.095 to 0.116 (W/m−1 K−1) is lower than that of those without adsorbents (0.121 (W.m−1 K−1)), resulting in reducing the heat consumption of these insulation materials. The kinetics and isotherms water vapor adsorption confirm an increase in moisture uptake capacity at low relative humidity (33%) and small variation of moisture adsorption capacity at high relative humidity (75%) in the presence of the adsorbents. The moisture buffering of the boards containing different adsorbent contents is improved with an excellent moisture buffer value up to 2.7 g/(m2.%RH). [ABSTRACT FROM AUTHOR]

Models for the prediction of heat and mass transfers in building porous materials have been developed since the 90's with simulation programs such as MATCH, UMIDUS, DELPHIN and Wufi. These models are used to analyze the physical phenomena occurring and particularly the impact of moisture on buildings' energy performance and durability. With this goal in mind, it is important to validate the representation of the physical phenomena made by the numerical models. This article reviews recent studies comparing the results obtained with numerical models and experimental data. An overall trend can be observed for most of these studies, highlighting that the experimental front always rushes faster than the simulation results. Therefore, this study analyses theses comparisons to explain these discrepancies based on the effects of (i) the type of materials, (ii) the boundary conditions, (iii) the scale of the design facility, (iv) the model used to describe the physical phenomena and (v) the influence of the model input parameter. The general trend shows that discrepancies are observed most particularly for highly hygroscopic or bio-based materials. These discrepancies are also greater for time dynamic boundary conditions, particularly at the scale of the wall. Moreover, some of the assumptions on the properties of the materials used as input in the models are questioned. Indeed, the models considering the hysteresis effects and temperature dependency of the moisture storage capacity show better agreement with experimental data. Finally, the physical phenomena used in the models only consider diffusive transport while it appears that the advective of moisture through the porous material may play an important role. [ABSTRACT FROM AUTHOR]

Graphical abstract Thermal conductivity measurement. Highlights • The hygrothermal properties of bamboo particles are studied. • Novel binders from natural resources are used for building bio-insulation materials. • Influence of high relative humidity on durability of bamboo particles is investigated. • Thermal insulation of bio-materials is evaluated under different humidity conditions. Abstract Bio-insulating materials are well known to reduce the environmental impact of constructions and are able to regulate the indoor temperature and humidity of buildings. This study investigates the influence of high-absorbing bio-glues based on a protein and lignin compound on moisture transfer and storage as well as on thermal performance of bamboo particleboards. The investigations are based on the moisture buffer value, vapor permeability, isothermal vapor sorption and thermal conductivity. Simultaneously, the mechanical properties and mold growth of these materials, manufactured for the study, are also investigated. The results demonstrate excellent moisture buffer capacity, from 2.13 to 3.26 g/(m2·%RH). The vapor sorption isotherm results exhibit the materials’ high moisture storage, and the vapor permeability behaves like commercial bio-insulating materials. The thermal conductivity of particleboards shows a low value, in accordance with their density and variation in moisture content. In addition, the results indicate mold appearance on the surfaces of specimens after 14 days exposure to 84% relative humidity. Moreover, a comparison of the hygrothermal characterizations between bamboo particleboards and fiberboards (Nguyen et al., 2017) is carefully made to highlight the exceptional features of those bio-boards. [ABSTRACT FROM AUTHOR]

The impact of air infiltration on the hygro-thermal performance of a wall is closely linked to the air dispersion inside it, but there is a lack of experimental studies and methods for the air path investigation within light-weight wall assemblies. A new technique has therefore been developed, consisting in an innovative use of fluorescein micro-particles as tracer inside the insulation material. It is a destructive method but it has the great advantage of not being intrusive unlike the use of any type of sensor. The experimental protocol is detailed in this paper. This technique was tested on a number of preliminary tests which showed consistent results and a good repeatability of the measurement. A fluorescein transport model was developed to facilitate the comparison between the experimental fluorescein concentration mappings and the numerical velocity fields. This method was then applied to a specific configuration: an air channel in contact with porous media. A simple analysis of the resulting fluorescein concentration mappings enabled to draw conclusions on the impact of parameters such as the flow velocity or the insulation material on the air infiltration. It has also given evidences of phenomena such as the appearance of thin air gaps between the components of the wall assembly. The results were compared to a numerical study with the fluorescein transport model coupled to a CFD model. [ABSTRACT FROM AUTHOR]

This study focuses on manufacturing by thermo-pressing new low-environmental-impact bio-insulation fiberboards from bamboo fibers and bone glue, modified with sodium lignosulfonate. The aims are to measure moisture buffer value, water vapor permeability, bending properties, thermal conductivity and vapor sorption isotherms of these materials. The moisture buffer values of these materials belong to the “excellent” category, ranging from 2.5 to 3.9 g/(m 2 .%RH), higher than the value for bamboo fiberboard without glue (1.7 g/(m 2 .%RH). The water vapor diffusion resistance factor ranges from 8 to 17, which is similar with other fiber insulation materials. The bending properties show a significant improvement when 30% (w/w) glue is used, the glue being a mixture between bone and sodium lignosulfonate glues. Moreover, the variation in thermal conductivity of the fiberboards with relative humidity and moisture content is investigated to evaluate the hygrothermal performance of the fiberboards. The results are promising for both thermal insulation and moisture buffering, thus these fiberboards could be used for passive control of indoor environment. [ABSTRACT FROM AUTHOR]

This study focuses on manufacturing by thermo-pressing new low-environmental-impact bio-insulation fiberboards from bamboo fibers and bone glue, modified with sodium lignosulfonate. The aims are to measure moisture buffer value, water vapor permeability, bending properties, thermal conductivity and vapor sorption isotherms of these materials. The moisture buffer values of these materials belong to the “excellent” category, ranging from 2.5 to 3.9 g/(m 2 .%RH), higher than the value for bamboo fiberboard without glue (1.7 g/(m 2 .%RH). The water vapor diffusion resistance factor ranges from 8 to 17, which is similar with other fiber insulation materials. The bending properties show a significant improvement when 30% (w/w) glue is used, the glue being a mixture between bone and sodium lignosulfonate glues. Moreover, the variation in thermal conductivity of the fiberboards with relative humidity and moisture content is investigated to evaluate the hygrothermal performance of the fiberboards. The results are promising for both thermal insulation and moisture buffering, thus these fiberboards could be used for passive control of indoor environment. [ABSTRACT FROM AUTHOR]

Poor airtightness in buildings can lead to an over-consumption of energy and to many issues such as moisture damage and poor indoor climate. The timber frame constructions are particularly subject to air leakages, and further knowledge in this field is needed to meet the regulation requirements tightened by the development of low-energy and passive houses. This article focuses on a three-scale experimental study carried out in laboratories to quantify the impact of a number of construction details on timber frame wall airtightness. For this purpose, we built two original experimental setups and to complement an existing large-scale facility. Each setup enables to carry out pressurization tests at a different scale. The results put all together give quantitative information for more accurate simulations of building performance. Some specific construction details were investigated. It has been found in particular that the density of the insulation material is significant since a soft glass wool can have an air permeability three times higher than a rigid one with the same thermal performances. Moreover, it has been pointed out that the bond between the gypsum board and the insulation has a significant impact on the resulting pressure–flow law, and to ensure that there is no air gap the whole interface should be glued. The air flow directions also influence the flow values for high-pressure differences. Finally, at wall scale we have found that the sealing of the gypsum boards and the vapor barrier against the bottom wall plate is not very significant as long as the exterior side is sealed correctly. On the other hand, a proper sealing on both sides of a window is required because of the air gaps along it. [ABSTRACT FROM AUTHOR]

The goal of this paper is to identify the effects of in-pore transport of liquid water and water vapor as well as phase changes on the hygrothermal behavior of earthen buildings. Indeed, one of the main assets used to promote these constructions is their role in moisture buffering hence temperature and relative-humidity quality controlling. However, there is no clear consensus yet concerning the impact of these phenomena on the global energy performance of the buildings. A coupled model is therefore proposed in this paper, based on heat and mass balances inside the earthen walls, in order to clarify this question. This model considers separately the kinematics of each phase (e.g. liquid water, vapor, dry air and solid matrix), in interaction with each other. It also takes into account the impact of pore water confinement on the liquid-to-vapor phase change, in particular on the resulting latent heat released or absorbed. The model is successfully compared to experimental results on instrumented full-scale rammed earth wall subjected to temperature cycles. It eventually allows identifying the singular hygrothermal behavior of earth material by testing the range of applicability of the simplifying assumptions which are commonly made in function of the permeability of the tested material. [ABSTRACT FROM AUTHOR]

Innovative and efficient ways to carry out numerical simulations are worth of investigation to reduce the computational complexity of building models and make it possible to solve complex problems. This paper presents a reduced order model, based on Proper Generalised Decomposition (PGD), to assess 2-dimensional heat and moisture transfer in walls. This model is associated with the multizone model Domus using an indirect coupling method. Both models are co-simulated to perform whole-building hygrothermal simulation, considering 2D transfer in walls. The whole-building model is first validated with data from the IEA Annex 41. Then, a case study is considered taking into account a 2-zones building with an intermediary shared wall modelled in 2 dimensions to illustrate the importance of the technique to analyse the hygrothermal behaviour of the wall. It has been highlighted that the whole model enables to perform more precisely analyses such as mould growth on the internal surface. In addition, important theoretical numerical savings (90%) are observed when compared to the large original model. However, the effective numerical savings are not so important (40%) due to the limitations of the co-simulation method. [ABSTRACT FROM AUTHOR]

• Optimal retrofit plans for building stocks are generated using genetic algorithm. • The phasing of retrofit actions is integrated in the optimisation search space. • Results show that proposed optimal strategies are different when phasing is integrated. Decision making for the energy retrofit of building stock is key to improve the energy efficiency and comfort in buildings. This article present a methodology developed in order to help the building stock or real estate manager to improve the efficiency of his buildings. The methodology is based on the multi-objective optimization of the retrofit, and specifically of the walls and windows of the buildings. The paper presents the integration of a temporal dimension with the phasing of the construction work in the retrofit strategies on multiple buildings in order to get closer to real world practice in the construction sites. The case study is carried out on a small building stock with the NSGA-II genetic algorithm. The search space of the optimization are vertical and horizontal walls and windows of each building; objective functions are heating demand, price of the proposed retrofit and an overheating indicator based on adaptive comfort. Overheating and heating demand are evaluated using EnergyPlus simulations. Phasing is implemented directly into the optimization formalisation with a separated chromosome describing temporality. As a result, different retrofit strategies were obtained by integrating phasing than with a standard optimisation with no temporal planning of operations. The main difference lies into the which building is selected to be retrofitted first, and in the improved performance of each retrofit material proposed: it led to an increase of performance of 10% in the overheating while thermal performance decreased for 2% in the retrofit strategies possible in reality when including the phasing. These results highlight the importance of formulating the optimization problem as close as possible to the real world constraints in construction in order to have accurate retrofit strategies. [ABSTRACT FROM AUTHOR]

• The capillary absorption of rammed earth is studied using modified methodologies. • The wick and paper eliminate liquefaction disturbances during capillary absorption. • Their hydraulic impact can be corrected by a relatively limited equivalent height. • The material stability when confined enables a standard hygric characterisation. • Evolution in the unconfined test induces distortions in the absorption properties. The capillary absorption test is redeveloped for rammed earth building materials. Since these materials liquefy and expand upon contact with water, the standard method must be modified to tackle this material evolution during the test. Firstly, a thin permeable wick and paper are applied as lower sample parts, to counter the liquefaction. It is shown that their influence on the resulting absorption properties is limited. In addition, a confining sealing is utilised against the expansion. It is shown that this confined way of testing offers crucial advantages as a result of the material remaining stable throughout the test. [ABSTRACT FROM AUTHOR]

Clay-based materials are the most traditional components of buildings. To improve their performance in a sustainable way, agents can be mixed to fired clay acting as a pore-forming factor. However, firing temperatures highly influence their microstructure which is closely linked to a material's final performance as a ceramic block. To highlight the influence of the firing temperature on microstructure, and more specifically on the pore size distribution of clay-based materials, three innovative porous materials were manufactured. These materials were produced by mixing clay and pore-forming agents. They were characterized by optical and scanning electronic microscopy, x-ray diffraction, mercury intrusion and nitrogen adsorption. These techniques allow the phase identification of materials, show sample microstructure and quantify the pore size distribution at different scales. Furthermore, geometric parameters of sample microstructure such as grain diameter and roundness are estimated by using computer software. To conclude, results provide an enlightenment about the influence of material microstructure on the pore size distribution at two firing temperatures. These results can be useful to allow the tune of porous characteristics and, therefore, contribute to the production of more sustainable construction materials. [ABSTRACT FROM AUTHOR]