No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Study of hygrothermal behaviour of a hemp concrete building envelope under summer conditions in France
... Nowadays, the buildings sector is the largest energy-consuming sector, accounting for over one-third of final energy consumption globally and an equally important source of carbon dioxide (CO2) emissions [1]. The energy consumed by the building depends on various factors, among those we mention the buildings materials [2] [3], the housing design and the heating, ventilation and air-conditioning HVAC systems [4]. For an innovative and efficient solution, the bio-based materials appear to be promising [5].Where they have various benefits in building envelope renovation and new buildings construction [6]. ...
... The last part consist of the model validation, where an experimental facility is mounted, and described below. 2 ...
... Concerning the hygrothermal and mechanical characteristics of hemp concrete, they have already a wide range of variety. Several works carried out in order to obtain the hemp concrete properties, we can mention the works of Collet et al [15] Elfordy et al [7] Other works are performed to investigate the hygrothermal performance of hemp concrete as the works of Tran et al [16], Maalouf et al [2]. Figure. 1 (a) shows the hemp concrete sample tested in laboratory. ...
The aim of this work is to study the hygrothermal behaviour of bio-based buildings materials. In this paper, we study the coupled heat and mass transfer within porous media. First, we experimentally characterize the studied materials and evaluate their thermal properties, namely thermal conductivity and specific heat in different state (dry-wet). The hygroscopic properties, namely water vapour permeability, water vapour sorption. At second time, we present and validate the mathematical model describing heat and mass transfer within bio-based materials, by the confrontation with the experimental results. The materials properties obtained from the characterisation part are used as model's input parameters. Moreover, a test facility is mounted in the laboratory in order to compare the numerical and experimental data. The founded results show a good concordance between the simulated and measured data. According to this results the mathematical model of Philip and De Vries gives a good prediction of hygrothermal behaviour of bio-based material. This model will allow us to save money and time of the experimental part in the future.
... The results indicate that the increase of the thermal conductivity of the concrete helps to reduce the time lag. Maalouf et al. [20] investigated the transient hygrothermal behavior of a hemp concrete envelope under summer conditions in France. The authors have shown that the hemp concrete induces low thermal effusivity which means that it can store less energy and thus superheating problems in summer can occur. ...
... The time lag is the difference between the time at which the outer surface receives heat and the time at which the inner surface senses it. The time lag depends on the thermal conductivity, density, specific heat and thickness of the material [20]. According to the literature [21], the outside surface temperature of building wall can be represented by a set of sinusoidal components. ...
... It can be noted that the adding of DPF enhances the insulating performance of gypsum. A similar result was reported by Maalouf et al. [20] who have shown that incorporation of hemp fibers in concrete increases their time lag. The result above mentioned that the thermal resistance was not the unique parameter which effect the time lag, but it depends also on a complex interaction of material density, specific heat capacity, thickness and thermal conductivity. ...
The present work is a part of a large project aimed at design and development of new composite materials containing date palm fibers (DPF) primarily suitable for thermal insulation in various sectors, especially in the building sector. On one hand, porosity (P) and Young’s modulus (E) of gypsum based composites reinforced with DPF were investigated. On other hand, thermal resistance and time lag of composites were also studied. The results showed that E of DPF reinforced gypsum materials is mainly affected by the interfacial adhesion between matrix and DPF. The effect of DPF sizes and loadings is highly significant on the stiffness of gypsum. It’s noted that the adding of DPF on gypsum induces an increase of both time lag and thermal resistance of composites. This new biocomposite can be used as a raw material for reinforcement gypsum materials in order to produce a friendly biocomposite materials to use for thermal insulation in buildings.
... Here again, it is not surprising, since the two models rely on the same description of heat transfer phenomena in porous media. Furthermore, numerical and experimental curves reach the steady state after almost the same time, which was also observed in [33] for a hemp concrete wall. The longest are greater than experimental ones, which was also observed in [33]. ...
... Furthermore, numerical and experimental curves reach the steady state after almost the same time, which was also observed in [33] for a hemp concrete wall. The longest are greater than experimental ones, which was also observed in [33]. Better agreement between models and experiment was obtained at 7.5 cm and 12.5 cm depth, whereas larger difference was noticed at 3 cm depth. ...
... Validation of Mendel's model for (a) temperature and (b) relative humidity variations at 7 cm and 18 cm depths of a hemp concrete wall, based on data reported in[33]. ...
Two mathematical models describing heat and moisture transfer in porous media were used to predict the hygrothermal behavior of a new type of bio-based materials made of date palm concrete (DPC). The finite element method was used for the resolution of partial differential equations and numerical results were compared to experimental data considering similar conditions of temperature and relative humidity through the DPC wall. At first, a mesh sensitivity analysis was carried out and the optimum mesh configuration was determined. Afterwards, the hysteresis effect was implemented in the models and its influence on the variation of the relative humidity through the wall was discussed. The results revealed that the
proposed models globally provided satisfactory results for the DPC wall, with an improved accuracy when considering the hysteresis effect. Finally, a comparison in terms of thermal insulation and moisture buffering capacity between DPC and a classical building material was performed numerically. Results showed that the new bio-based wall is very promising and can contribute to mitigate temperature variation and ensure hydrothermal comfort in buildings.
... Hemp concrete is a semi-structural insulation material that can be used to bridge the gap between standard insulation panels and structural walls [75], as well as to manage thermal comfort through passive solar energy gain [31]. Anomalies in the plant materials themselves could explain the disproportionally wide range of specific heat values found in the existing body of literature for hemp concretes with comparable densities. ...
... The introduction of other measurement methods or issues with measurement procedures could have resulted in such substantial discrepancies between the same type of binder and commercial hemp shives. For densities of 300 kg/m 3 , specific heat values recorded in different publications ranged from 300 to 1700 J/kgK [75]. Thermal insulation and reaching thermal conductivity values as near to those of the shive material have been the focus of work in the previous decade. ...
A simple mixture of hemp hurd, water, and lime is used to make hemp concrete. It is indeed one of the few materials that can continue to absorb carbon after being employed in construction, storing more carbon in the atmosphere over the building's lifetime than was emitted during construction. Furthermore, hemp can be harvested in as little as 60 days. Hemp concrete is a “carbon-negative” or “better-than-zero-carbon” substance because the hemp plant absorbs more carbon from the atmosphere than it emits during its production and application on site. It is a bio-composite material that can be utilised as an alternative to concrete and standard insulation in building. Hemp concrete is also recyclable at the end of the building's lifespan. This study summarises the fast-developing body of knowledge about hemp concrete, which was recently developed.
... The theoretical model developed in the previous sections has been the subject of numerous studies on eco-friendly materials used in building sector (hemp, cork and so on). Implementation and validation details can be found in Tran Le et al. (2009) and Maalouf et al. (2014). ...
... For the hemp lime mixture, the data are based on the data of Cerezo (2005) and Collet and Pretot (2014). For the hygrothermal properties of hemp lime mixtures, the data given by Tran Le et al. (2010) and Maalouf et al. (2014) are used. For the roof formulation, the same sorption curve is used as that of wall HC mixture. ...
This article describes the results of a research project carried out at the University of Reims Champagne-Ardenne. The aim of this article is to develop a new insulating material produced by bonding hemp shives with wheat starch as a binder and to characterize its physical properties such as sorption isotherm, water vapour permeability, thermal conductivity, heat capacity and porosity. The equations of coupled heat and moisture transfer within the panels are introduced. These governing equations are applied on the room level in order to assess the hygrothermal behaviour of the panels and its impact on energy consumption and indoor comfort. Simulations are performed for Nancy (France) winter conditions with the simulation environment Simulation Problem Analysis and Research Kernel (SPARK) suited for complex problems.
... The theoretical model developed in the previous sections has been the subject of numerous studies on eco-friendly materials used in building sector (hemp, cork and so on). Implementation and validation details can be found in Tran Le et al. (2009) and Maalouf et al. (2014). ...
... For the hemp lime mixture, the data are based on the data of Cerezo (2005) and Collet and Pretot (2014). For the hygrothermal properties of hemp lime mixtures, the data given by Tran Le et al. (2010) and Maalouf et al. (2014) are used. For the roof formulation, the same sorption curve is used as that of wall HC mixture. ...
Hemp fibers are lightweight materials known for their acoustic and thermal properties. Associating these bio-fibers with mineral binder (lime or lime-pozzolan) leads to a less polluting concrete with higher insulating properties, which can reduce the energy consumption of buildings. However, the extraction process of mineral matrix contributes to the depletion of natural resources and using a vegetal matrix like starch is ecologically interesting. This paper deals with the use of a binder, wheat starch, in order to obtain a 100 % vegetal composite. Four formulations were studied with two hemp-starch ratios (H/S = 8 and 10) and different fibers proportions of 0-5 mm and 0-20 mm: 15%-85% and 30%-70%. Hygrothermal properties such as moisture buffering value and sorption isotherm are experimentally studied. Sorption isotherms are also modeled analytically using GAB and Merakeb approaches. Results show that hemp-starch composites have a high moisture buffering value, higher than that of hemp-lime mixtures. Modifying fiber size and proportion seems to have a low effect on hygric properties.
... Certains auteurs (Maalouf et al. 2014;Munaretto 2014) marquent une distinction entre l'inertie de transmission et l'inertie d'absorption. Quand on s'intéresse aux sollicitations provenant de l'extérieur vers l'intérieur (variation journalière de la température extérieure, flux solaire), on parle de transmission, le paramètre important étant alors la diffusivité des matériaux. ...
... re 38apporte des indications sur l'évolution des températures d'air intérieur avant et après rénovation. La température intérieure ne chute plus aussi rapidement lorsque les températures extérieures moyennes diminuent. Cette modification peut être interprétée comme un effet direct de l'isolation, la chaleur emmagasinée à l'intérieur restant piégée.(Maalouf et al. 2014) soulignent que la faible effusivité du matériau chaux-chanvre peut induire un risque de surchauffe estival en réduisant l'inertie d'absorption. étanchéité introduira de la chaleur dans le bâtiment, ce qui favorisera des surchauffes. Dans notre étude, le changement de menuiseries rendant le bâti plus étanche n'a été réalisé que pour le ...
Concilier patrimoine et amélioration de la performance énergétique du bâti ancien est un défi pour de nombreux centres historiques. La Communauté d’Agglomération du Grand Cahors, qui finance ce travail de thèse à travers une convention CIFRE, a souhaité s’attaquer à cette problématique en valorisant des isolants bio-sourcés. Le choix du matériau et du système d’isolation sont essentiels car ils influencent à la fois la performance hygrothermique de la paroi, la qualité de l’air intérieur, le coût et l’empreinte carbone de la rénovation. Dans cette étude, nous nous sommes focalisé sur la performance hygrothermique de la paroi afin d’assurer que la mise en place d’une isolation par l’intérieur ne soit pas source de dégradations futures de la paroi. Pour cela, nous avons confronté différents outils et méthodes tels que la caractérisation physique des matériaux, une instrumentation in-situ dans deux appartements du centre ancien de Cahors et des simulations hygrothermiques alliant différents outils numériques.
... Par ailleurs, à noter que les travaux de Tran et Maalouf et al. (2014) abordent l'influence des revêtements sur les enveloppes en béton de chanvre à l'échelle du local. D'après leurs travaux, l'addition à l'enveloppe du béton de chanvre d'une couche de mortier engendre des effets significatifs et conduit à une surestimation de 4,23% de la consommation d'énergie de chauffage et à une sous-estimation de 8% de l'humidité relative moyenne intérieure tout en minimisant les effets d'amortissement de cette humidité relative extérieure. ...
... Le deuxième type d'inertie thermique est la capacité de la paroi à stocker de la chaleur. Elle est proportionnelle à l'effusivité thermique du matériau et intervient plutôt au confort d'été (Maalouf et al., 2014). Ainsi, pour un modèle à hystérésis, il faut effectuer des simulations pluriannuelles (quatre ou cinq années) pour que les résultats convergent vers ceux des modèles à courbe moyenne de sorption comme montré dans le chapitre II, quelle que soit l'initialisation de départ (initialisation à partir de la courbe d'adsorption ou bien de la désorption). ...
... Previous studies have shown that specific heat of hemp-lime composites can be as high as 1300 J/(kg•K) for materials with apparent density of 508-627 kg/m 3 [3,29]. Maalaouf et al. [35] reported specific heat of 1100 J/(kg•K) and sample density equal to 440 kg/m 3 . Values of 1000 J/(kg•K) and 413 kg/m 3 may be also found in the literature [36]. ...
... Previous studies have shown that specific heat of hemp-lime composites can be as high as 1300 J/(kg·K) for materials with apparent density of 508-627 kg/m 3 [3,29]. Maalaouf et al. [35] reported specific heat of 1100 J/(kg·K) and sample density equal to 440 kg/m 3 . Values of 1000 J/(kg·K) and 413 kg/m 3 may be also found in the literature [36]. ...
Different fractions of hemp shives are used in the mixtures of the hemp-lime composite. The market offers shives of different granulation. It depends on the type of industrial hemp and on the capabilities of decortication machines. The aim of the research presented in the article is to check differences in the mechanical and hygro-thermal properties of composites with different shives fractions. The research part of the paper presents the preparation method and investigation on hemp-lime composites. Apparent density, total porosity, thermal conductivity, capillary uptake, vapor permeability, specific heat, mass absorptivity, flexural and compressive strength were examined. The results confirm that the shives fraction influences the individual properties of the composites. Hemp-lime composites with fine shives are characterized by higher water absorption, thermal conductivity, mechanical strength, vapor permeability as well as lower capillary-lifting capacity and specific heat than composites with thick shives.
... In the light of their energy and environmental soundness, both bio-sourced materials as hemp-lime concrete or recycled-waste materials including recycled polyethylene terephthalate (R-PET) as insulating panels seem to be a promoting solution due to their eco-friendly advantage and their benefits on human health and environment (Maalouf et al. 2014). ...
... For the solar radiation entering through the window with the overhang, calculation was performed with Codyba software (Noël 2004) and the data was inserted in SPARK. Additional details about SPARK model validation is documented by (Maalouf et al. 2014;Tran Le et al. 2010). ...
This study reports on the performance of sustainable materials produced from natural resources as hemp-concrete or from recycled-waste non-biodegradable materials including Recycled PolyEthylene Terephthalate (R-PET). Three façades employing three different materials (Hemp-concrete, hemp-concrete with brick and R-PET) were investigated in three cities in France (Nancy and Carpentras) and Italy (Perugia) with different climate. The energy performance of each façade was assessed in terms of cooling and heating demands, electrical consumption for a constant flow rate ventilation mode, considering different orientations. The study also shows the effect of window size (10%, 25%, and 40%) on the annual energy consumption.
... Maalouf et. al [27], in turn, examined the transient hygrothermal behavior of a hemp concrete building envelope (wall of 360 mm thickness) in summer in France, taking into account different outdoor and indoor conditions. A heat-air-moisture (HAM) simulation of a room with space area of 15 m 2 with hemplime wall (thickness of 300 mm for external and 200 mm for internal wall) was also conducted, and the simulation model was used to analyze the impact of hemp concrete on indoor air humidity and air-conditioning loads [28]. ...
Thermal bridges increase heat losses in buildings and reduce the temperature of the internal envelope surface, causing moisture condensation and mould growth. This is an important issue for building materials based on organic components such as a hemp-lime composite, as they are particularly susceptible to biological degradation.The hemp-lime composite is used as a filling in timber frame construction. The increased cross-section of wooden elements together with the geometry change in the construction joints can form thermal bridges. The paper presents numerical analyses of temperature distribution in the area of construction elements connections, taking into account several variants of junctions: external walls, corners, and window placement in a wall. The thermal parameters of hemp-lime composites used in the analyses were obtained from the authors’ own research.Despite relatively good insulating properties, timber elements have a noticeable influence on the local increase of the heat transfer in hemp-lime composite structures, forming thermal bridges in the partitions themselves and in the construction nodes. However, the linear thermal transmittance coefficients in the presented joints were not very significant (in the range of 0.026 ÷ 0.092 W/(m·K) depending on the type of connection), proving the usefulness of this type of construction in energy-efficient buildings.
... During its growth hemp has taken up CO 2 through photosynthesis (Pervaiz and Sain, 2003) and lime is sequestering CO 2 by hardening through carbonation resulting in a carbon neutral or even negative final material that sequesters from 6.67 to 136.65 kg CO 2 eq./m 3 (Arrigoni et al., 2017;Ip and Miller, 2012;Pretot et al., 2014;Shea et al., 2012). The material also has good thermal insulation properties ranging between 0.05 and 0.12 W/m*K (Walker et al., 2014), exceptional moisture buffering (Maalouf et al., 2014;Rahim et al., 2015) and acoustic properties (Cérézo, 2005). Additionally, its environmental impact is lower than traditionally used building materials (Pretot et al., 2014). ...
To counter the negative environmental impact, particularly greenhouse gas emission generated by the construction industry, many low-impact materials are being produced and researched having neutral CO2 emissions and low thermal conductivity. One of these materials is lime-hemp concrete, a self-bearing bio-based insulation material with low thermal conductivity and good CO2 uptake but with weak mechanical properties. In this study alternative magnesium binders are proposed to substitute the traditionally used lime binder in hemp concrete, comparing the environmental impact of these binder composites. To make the comparison, experimental mixtures with both traditionally used and alternative binder composites were produced and their mechanical and thermal properties tested. The magnesium binders showed promising results as these composites were approximately two times stronger, having similar density and thermal conductivity. Afterwards the Life Cycle Assessment (LCA) was carried out to evaluate and compare the environmental impact of all tested composites. Lime based binder composites achieved negative CO2 emissions, varying from -46.5 to -68.6 kg CO2/m(3). Alternative binder, magnesium phosphate cement, demonstrated significantly greater environmental impact than all other binders due to its hardener, potassium phosphate, which is highly energy and resource intensive. Magnesium oxychloride cement showed promising results with bio-based filler, as their combined environmental impact was lower in most categories compared to lime-hemp concrete, and negative CO2 emissions of -37.38 kg CO2/m(3) were achieved. These negative CO2 emissions were achieved with biogenic CO2 uptake from hemp growth and low binder content, thus achieving low thermal conductivity of 0.062 W/m(2)*K at 214 kg/m(3) density.
... Concerning the thermal behavior, the measurement carried out by many authors (Collet, 2004;Cerezo, 2005;Evrard, 2008;Rahim et al., 2015) confirmed that hemp concrete has a low thermal conductivity which can reduce winter heat losses and protects from summer heat waves. On hygric point of view, hemp concrete can maintain indoor hygrothermal comfort thanks to its moisture buffering capacity (Hameury, 2005;Tran Le et al., 2010;Shea et al., 2012;Maalouf et al., 2014;Samri et al., 2014;Moujalled et al., 2018). Furthermore, regarding the emissions of bacteria and volatile organic compounds, the experimental results showed that they are negligible (Koivula et al., 2005). ...
This article develops a novel mathematical model using multi-scale homogenization approach to model the effective thermal conductivity tensors of a hemp shiv particle and lime hemp concrete (LHC). This bio-based material is an environmentally-friendly material that is used more and more in building construction. The thermal conductivity of lime hemp concrete which is generally either cast or sprayed, cannot be expressed as a scalar due to its anisotropic microstructure. The paper develops a novel model to predicting effective thermal conductivity tensor of lime-hemp concrete that takes into account the anisotropy and the size of hemp shiv, the preferred spatial distributions due to fabrication process and the imperfect particle-binding interfaces. Two probability density functions are used for modeling the particle size distributions of hemp shiv and the preferred alignment distribution of hemp particles. A good agreement is obtained between the model and experimental data provided in the literature. The presented analytical solutions offer a suitable tool for a fast optimization of the thermal conductivity of hemp concrete. Such promising future is very useful for the building design, in particular in three-dimensional (3D) simulation models.
... In the last decade, many experimental works were carried out to study their mechanical, thermal and hydric properties at material and wall scales [1][2][3]. In the same way, several models for predicting heat and mass transfers in porous building materials were developed and resolved with simulation programs such as SPARK [4], TRNSYS [5], DELPHIN [6] and Wufi. Phillip and De Vries [7] have developed a model basically for soil materials, this model took into account temperature gradients inside materials, it represents the origin of most new models, it was lately well studied and represented by Mendes et al. [8]. ...
In this work, we study the two most used mathematical models (Phillip & De Vries model and Kunzel’s model) which describe heat and moisture transfers in porous building materials. These models were implemented in COMSOL Multiphysics and solved numerically with the finite elements method. To validate the representation of the physical phenomena made by the numerical models, results were compared with data obtained by Wufi using a concrete wall. The results indicate that values estimated by both models are relatively in good agreement with those obtained by Wufi especially for temperature, while in humidity variations an underestimation by Phillip and De Vries model was Highlighted. Consequently, results confirm the suitability of these models to be used in further studies in order to predict hygrothermal behaviors of bio-based building materials and walls under various thermal and hygric conditions at different scales.
... Email: anh.dung.tran.le@u-picardie.fr and the efficiency of buildings have been numerically and experimentally demonstrated in some research (Hameury 2005;Tran Le et al. 2010;Shea, Lawrence, and Walker 2012;Maalouf et al. 2014;Samri et al. 2014). Furthermore, regarding the emissions of bacteria and VOCs (volatile organic compounds), the experimental results showed that they are negligible (Koivula et al. 2005). ...
Lime–hemp concrete is an environmentally friendly material that is used more and more in building construction. This study develops a multi-scale homogenization approach to model the effective thermal conductivity of this bio-based material. The developed model dedicated to non-compacted and compacted hemp concrete takes into account the shape and the orientations of pores of hemp particles as well as imperfect particle-binding interfaces. Unknown properties of the solid phase of hemp particles and binding, and that of the particle-binding interface are calibrated by inverse analysis using available experimental data. The model is then used to carry out a sensitivity analysis to study the effect of the porosities of hemp particles and binding, the volume fraction of hemp particles, density and temperature on the overall thermal conductivity of hemp concrete. Analytical solution proposed can be used for a fast estimation and optimization of the thermal conductivity of hemp concrete, which is very useful for the building design.
... The porosity combine macropores of 1 mm induced by the imperfect arrangement of particles [16,22], mesopores and micropores in the binder and in major proportion of the plant aggregate [22,23]. As a result, using hemp-concrete can dampen external thermal oscillations and buffer internal moisture loads creating better indoor comfort conditions as well as contributing to better energy savings [21,24]. Consequently, hemp concrete corresponds to High Environment Quality Buildings [25]. ...
Hemp shives is a lightweight material known for its insulating properties. Associating these bio-fibers with plant-based matrix instead of a mineral binder in insulation applications is of ecological interest. This article describes the study of a low environmental impact 100% plant-based material made solely from wheat starch and hemp shives. The hemp/starch ratio (H/S) influence and hemp shive size are studied. Samples are evaluated in terms of physical properties, mechanical behaviour and hygrothermal properties through an experimental approach. Results show that increasing 0–5 mm hemp shive proportion from 15% to 30% leads to a significant enhancement of the mechanical and hygric characteristics due to the load transfer and porosity. However, when the H/S ratio increases, mechanical and hygrothermal characteristics decrease slightly. Finally, the hemp-starch agro-material with H/S equal to 8 and 30% of 0–5 mm hemp shive seems to be the optimal composition between the studied samples.
... The conclusions underlined the good tendencies but nevertheless with some lack of accuracies. In Ref. [20], experiments for similar materials under climatic variations were performed. Influence of material properties and convective coefficients were investigated to reduce the discrepancies with experimental data. ...
When comparing measurements to numerical simulations of moisture transfer through porous materials a rush of the experimental moisture front is commonly observed in several works shown in the literature, with transient models that consider only the diffusion process. Thus, to overcome the discrepancies between the experimental and the numerical models, this paper proposes to include the moisture advection transfer in the governing equation. To solve the advection-diffusion differential equation, it is first proposed two efficient numerical schemes and their efficiencies are investigated for both linear and nonlinear cases. The first scheme, Scharfetter-Gummel (SG), presents a Courant-Friedrichs-Lewy (CFL) condition but is more accurate and faster than the second scheme, the well-known Crank-Nicolson approach. Furthermore, the SG scheme has the advantages of being well-balanced and asymptotically preserved. Then, to conclude, results of the convective moisture transfer problem obtained with the SG numerical scheme are compared to experimental data from the literature. The inclusion of an advective term in the model may clearly lead to better results than purely diffusive models.
... Several numerical studies on agro-materials used in buildings were carried out using SPARK by implementing mathematical models through the finite difference method. Details and validation can be found documented by Maalouf et al. (2014); Tran Le et al. (2009Le et al. ( , 2010. ...
Energy efficiency and the reduction of greenhouse gas emissions are actual key issues in all the economic sectors and, in particular, in buildings which is acknowledged worldwide as one of the most energy-consuming.
In this context, it would be desirable to duly address those issues by searching for and assessing proper solutions and strategies: the usage of eco-friendly construction materials can be considered as one of those. This paper reports upon the performance of three façades containing sustainable products that are manufactured using natural resources and, alternatively, post-consumer waste based materials; those are: hemp-concrete; and Recycled PolyEthylene Terephthalate (R-PET), respectively. The energy performance of each façade was assessed in terms of cooling and heating demands, electrical consumptions and indoor thermal comfort including indoor temperature and relative humidity.
Additionally, a Carbon Footprint (CF) assessment was carried out considering both the estimated energy demands and the life-cycle emission factors associated with the energy mix of the countries where the façades were located, i.e. France and Italy.
Based upon the findings of the study, the R-PET façade represented the most performing solution between the three façades in all the scenarios considered and, moreover, the humidity-sensitive flow rate ventilation system came out as a solution able to reduce the electricity consumptions.
Finally, considering the Carbon Footprint results, the energy country mix emerged as a key issue, making the Italian case study the worst one, though the total electrical energy consumption were comparable with those of the other case studies.
... However, it has also been shown that during summers in France, superheating occurs in homes made of hempcrete. 9 It has been suggested that certain steps (introducing solar shadings, white roof paint etc.) be taken to regulate this superheating. 9 ...
The onset of heavy greenhouse gas (GHG) emissions from conventional construction practices has led to research on several plausible low-carbon dioxide footprint construction materials that are either carbon dioxide neutral or carbon dioxide negative. One such ‘green’ construction material is lime hemp concrete (LHC), hemp concrete or hempcrete, which are some of the many names of this novel construction material. Hemp concrete is essentially a composite made of lime and hemp shivs. This paper presents a literature review of the various studies carried out on hemp concrete to understand its properties, drawbacks and advantages in construction. The review dwells on discussion of hemp, use of lime as a binder material and the mechanical, thermal and hygric properties of LHC. The salient features of LHC with regard to mechanical, thermal and hygric properties and ecological impact are discussed in the paper. It is observed that further research on LHC is required to be able to establish mix design principles, improve the compressive and flexural strengths of LHC and its use as a load-bearing structural material for high-rise constructions and establish cradle-to-death GHG emissions, recyclability and reusability which seem to be promising propositions with hemp concrete.
... La simulation sous SPARK permet de résoudre les systèmes d'équations différentielles (Sowell and Haves 2001). Des détails sur la validation du modèle sont données par (Tran Le et al. 2009) (Maalouf et al. 2014). Dans notre étude deux cas sont présentés et comparés en termes de consommation d'énergie. ...
... They also observed that thermal mass reduced energy demand on space heating and cooling by nearly 6% and 21%, respectively. Other studies such as (Jerman et al., 2013;Dodoo, Gustavsson, & Sathre, 2012;Maalouf, Le, Umurigirwa, Lachi, & Douzane, 2014;Maref et al., 2012;Rajagopalan, Bilec, &Landis, 2010, andHill &Monsour, 2006) have evaluated hygrothermal performance of alternative exterior walls in buildings, especially those with different thermal mass, as well as various insulation thicknesses. ...
Utilizing appropriate materials and assemblies in building envelope components could lead to energy savings, increased durability, and sustainability gains. This study aims at providing an integrated assessment framework to compare three different types of exterior wall systems: wood frame, insulated concrete forms (ICFs), and pre-cast insulated concrete panel (PICP). The focus will be on building envelope performance, cost efficiency, and environmental impacts of these technologies. Such an assessment contributes to decisions on design characteristics of exterior walls as well as the selection of required materials. First, the exterior wall technologies will be compared in terms of hygrothermal performance according to ASHREA standards and other relevant literature. Then, a whole life cost analysis is conducted in order to establish the cost profile of each technology in buildings including capital costs as well as space heating costs over their service life. Finally, we will turn to assessing the environmental footprints of each technology and its components through life cycle assessment (LCA). The proposed framework incorporates multiple performance assessment criteria including well-being aspects, hygrothermal performance, life cycle assessment (LCA), and life-cycle cost (LCC). A multiple criteria decision-making framework is proposed to rank the alternative exterior wall technologies for a case study building.
... Les auteurs expliquent cet écart par l'absence de prise en compte dans le modèle d'un certain nombre de phénomènes tels que la viscoélasticité, le redressement des microfibrilles de cellulose, l'évolution du taux de cristallinité et les couplages mécano-sorptifs. [201] Maalouf et al. [202] proposent un modèle numérique permettant de simuler le comportement hygro-thermique d'un composite à matrice béton renforcée avec du chanvre. ...
Depuis la naissance d’un matériau jusqu’à sa fin de vie, la simulation numérique peut être un outil de choix pour décrire les phénomènes qui se produisent avec ou non l’influence du milieu extérieur. Complémentaires aux mesures expérimentales, les outils de modélisation apportent des réponses, mettent en évidence certains phénomènes et surtout, peuvent dans certains cas prévoir une dégradation de propriétés ou une ruine du matériau. Au travers de deux thèmes principaux, les revêtements polymères et les composites à matrice organique, l’apport de l’outil numérique a été clairement mis en évidence.
Dans le cas du pipeline, chaque étape depuis la mise en œuvre jusqu’à la mise en service a été simulée. Un suivi des contraintes a ainsi été obtenu avec des valeurs crédibles et validées parfois par un retour expérimental. Sans la modélisation, il aurait été bien difficile et laborieux d’appréhender par exemple le suivi des contraintes.
Les composites d’origine pétrochimique ont encore de belles années devant eux. Le projet proposé dans ce mémoire se place en alternative à ces matériaux lorsque cela est possible. Le composite d’origine végétale, plus respectueux de l’environnement, a des propriétés à l’état initial de bon niveau. De gros progrès ont été réalisés ces dernières années quant à l’amélioration de ces dernières, et les performances peuvent encore augmenter avec par exemple une optimisation des procédés d’extraction et de traitement des fibres. Toutefois, leur tenue mécanique est sujette à une rapide décroissance, tout particulièrement en milieu humide. Tout l’intérêt de ce projet est de bien comprendre les mécanismes mis en jeu dans cet environnement afin de trouver des solutions pour augmenter la durabilité de ces biocomposites.
... One of such materials is the limehemp concrete (LHC). It has several positive properties such as excellent thermal performance high thermal capacity and low thermal conductivity [Walker 2014], high moisture buffering capacity and moisture transfer [Maalouf 2014] [Rahim 2015], and also high sequestered CO2 amount [Ip 2012] [Shea 2012]. Weakness of the LHC is its relatively low mechanical strength, allowing its main use only with supportive load bearing frame thus making it appropriate mostly for the low rise buildings [Latif 2014]. ...
The major CO2 emitting countries have concluded an agreement aimed at reducing the CO2 emissions at the Paris Climate Conference 2015. However, the emission levels are still on the rise. As the building material industry is one of the largest producers of CO2, it should find solutions to limit these emissions, such as development of new materials with negative CO2 balance and low thermal conductivity for energy saving during lifespan. The lime-hemp concrete (LHC) could be one of the solutions as it has negative CO2 emissions balance (up to 80 kg/m 2) and low thermal conductivity (0,07-0,09 W/m*K). Even though, the LHC has been gaining popularity and recognition over the past years, it is still not used enough to contribute significantly to lowering the global CO2 emissions. One of the reasons is the low mechanical strength of this material that can be mostly used only with supportive load bearing frame appropriate for the low rise buildings. It could be improved by enhancing the binder strength either through supplementing or substituting it with the magnesium based binders. Made of calcined MgO with possible additions of magnesium salts or other hardeners, the early and overall compressive strength shown by these binders is greater compared to hydraulic lime binders used in the LHC. The magnesium based binders also remain unaffected by the organic water soluble constituents that react with calcium ions in hydraulic lime, thus delaying or preventing hydration process. Various MgO binders are tested in this research, focusing mainly on mechanical strength and thermal conductivity, in order to understand the effect that adding the magnesium binders has on important LHC properties. The obtained results suggest that the MgO binders are viable alternative to hydraulic lime as their superior compressive strength allow for lower amount of binder to be added thus enhancing thermal conductivity or giving material wider possible use due to this strength increase.
... In parallel, vegetal fiber materials have undergone notable evolution in construction field thanks to their interesting thermal and hydric properties and ability to absorb air carbon dioxide (D'Alessandro et al., 2014), namely hemp concrete (Moussa et al., 2018). Plentiful researches, devoted on hemp concrete material, have been conducted on wall scale (Amziane and Arnaud, 2013), (Colinart et al., 2013), (Maalouf et al., 2014). They succeeded to validate its hygrothermal behavior when subjected to different climatic conditions. ...
... They validated that the model can be useful to compare other walls with a typical wall made of concrete. Maalouf et al. [24] performed a numerical study of a hemp concrete envelope under several French climatic conditions. The hygrothermal transfer within the walls was simulated with a 1D model. ...
This study experimentally and numerically investigates the hygrothermal behavior of a wall made of washing fines hemp composite under typical French and Tunisian summer climates. Actually, insulating bio-based building materials are designed in order to reduce energy and non-renewable resources consumptions. Once their multiphysical properties are characterized at material scale, it is necessary to investigate their behavior at wall scale. Washing fines hemp composite shows low thermal conductivity and high moisture buffer ability. The test wall is implemented as separating wall of a bi-climatic device, which allows simulating indoor and outdoor climates. The numerical simulations are performed with WUFI Pro 6.5 Software. The results are analyzed from the temperature, relative humidity and vapor pressure kinetics and profiles and from heat and moisture transfer and storage. The thermal conductive resistance calculated at the end of the stabilization phase is consistent with the theoretical one. The hygric resistance is consistent for simulation up to steady state. The dynamic phase under daily cyclic variation shows that for such cycles two thirds of the thickness of the wall on the exterior side are active. It also highlights sorption-desorption phenomena in the wall.
... On the other hand, several studies have shown that the hygrothermal properties of hemp concrete allow it to reduce the daily changes in relative humidity, limit energy consumption [25] and maintain hygrothermal comfort in buildings [26]. Many experimental and numerical investigations have been reported on hemp concrete [17,22,24,[27][28][29][30][31]. The results show a good thermal inertia for hemp concrete walls [28] and emphasised the ability of hemp concrete to dampen external weather conditions by showing good results for indoor temperature and relative humidity [32]. ...
The aim of this paper is to analyse the impact of hemp concrete on the overall hygrothermal behaviour of the building when it used as an infill layer in the envelope of wood-frame structures. Three wall configurations were considered in different climates. Then, a hygrothermal co-simulation approach was used to integrate the model of coupled heat and moisture transfer through multilayered walls in a dynamic thermal simulation tool for the building. The material properties which constitute the input parameters for the model were determined experimentally, according to the hygrothermal state of the material. The results showed that hemp concrete significantly reduces the energy consumption of the building and has better insulation properties than the two conventional building materials: brick and aerated concrete. This is justified by the good hygrothermal properties of this bio-based material, especially its high thermal resistance of 3.08 K.m²/W compared to 0.88 K.m²/W of brick and 2.28 K.m²/W of aerated concrete. In addition, for the three climates considered, the thermal comfort of the hemp concrete envelope is significantly improved. This material also allows stabilisation of relative humidity levels in the ambient air by naturally regulating the hygrometry, to ensure better ambience. The study shows that hemp concrete has interesting hygrothermal properties. Thus, this material can be used massively in the construction field in order to meet the requirements of the current standards which aim to reduce the energy and environmental impacts of dwelling and office building.
... Several studies have confirmed the impact of moisture by adsorption and desorption between building material and indoor air on the energy efficiency of buildings. Mendes et al. showed that whole-building energy simulation models that ignore moisture transfer in the building envelope may overestimate conduction peak loads up to 210% and underestimate the yearly integrated heat flux by up to 59%, which can lead to oversized heating, ventilation, and air conditioning equipment (particularly in dry climates) and underestimate energy consumption (primarily in humid climates) [2,14,15]. Liu et al. reported that the energy consumption of an air conditioning system for a pine-board house can be decreased by approximately 40%, and the air-conditioning operation time can be decreased owing to the moisture effect [16]. Overall, the accurate calculation of building energy consumption should consider moisture transfer together with heat transfer through building envelopes as well as between the building envelope and the indoor environment [12,13]. ...
To more accurately evaluate the indoor hygrothermal environment of a building, control the indoor temperature and humidity, evaluate the thermal comfort of occupants, and select the capacity of the heating, ventilation, and air conditioning (HVAC) system, moisture transfer from and into architectural materials should be considered. However, the most widely used commercialized software ignores the moisture effect from envelopes or adopts a simplified model based on the difference in humidity ratios between hygroscopic materials and interior zone air. In this study, the effects of the driving forces of hygrothermal models were identified and quantified. The calculated results show that the indoor humidity changes differed when the moisture effect by moisture adsorption and desorption was considered in the models. Because the simplified effective moisture penetration depth (EMPD) model uses differences in the humidity ratio as a driving force, the calculated results of the indoor humidity ratio exhibit relatively constant tendencies. However, the thermodynamic chemical potential model corresponds to a detailed heat, air, and moisture transfer (HAM) model that uses the water potential as a driving force; this model can consider the moisture effect based on temperature and humidity changes. Therefore, the humidity ratios calculated using the detailed thermodynamic HAM model show differences of 0.01%–38.78%, and the difference in relative humidity between building materials and indoor air becomes smaller; these results are comparable to those of the simplified model. Finally, the adoption of a simplified model can result in differences in the sensible heat load of 4.4%–13.8% and latent heat load of 16.1%–51.2%. Thus, this study confirmed that a coupled HAM model, which uses the water potential as a driving force, can be employed to accurately simulate the hygrothermal behavior of building envelopes.
... Recent carbon emissions have forced human to make efforts against disastrous manifestations of climate change. Thus, application of natural materials can be considered safe for human health and environment (Benfratello et al. 2013;Maalouf et al. 2014). Natural material can be obtained from animals or plants for example from hemp, flax, kenaf, wood, and bamboo is available in the market and can be used for several purposes. ...
Rising human population has increased the utilization of available resources for food, clothes, medicine, and living space, thus menacing natural environment and mounting the gap between available resources, and the skills to meet human desires is necessary. Humans are satisfying their desires by depleting available natural resources. Therefore, multifunctional plants can contribute towards the livelihoods of people, to execute their life requirements without degrading natural resources. Thus, research on multipurpose industrial crops should be of high interest among scientists. Hemp, or industrial hemp, is gaining research interest because of its fastest growth and utilization in commercial products including textile, paper, medicine, food, animal feed, paint, biofuel, biodegradable plastic, and construction material. High biomass production and ability to grow under versatile conditions make hemp, a good candidate species for remediation of polluted soils also. Present review highlights the morphology, adaptability, nutritional constituents, textile use, and medicinal significance of industrial hemp. Moreover, its usage in environmental conservation, building material, and biofuel production has also been discussed.
... Hence, the modelling of hygrothermal behaviour is crucial to predict the behaviour of the material when different constructive strategies are applied, e.g. application of hygroscopic plaster, external or internal insulating layer [18][19][20]. ...
In the framework of Circular Economy policies aimed at reducing the consumption of raw materials, shives, an agricultural by-product of hemp cultivation, have gained a renovated life in the construction sector; new building materials, suitable for various executive techniques, have been developed exploiting the excellent thermal insulating properties of shives. When this vegetal material is mixed with a mineral binder such as lime or cement, the mixture is usually referred to as hemp-lime. In Italy, the use of hemp-lime blocks and the development of new production chains dates back only to about the last decade, while other European countries have more long-lasting experiences. In order to assess the potential benefits of hemp-lime blocks in the construction sector, it is necessary to evaluate the performance of these materials in situ, i.e. on the construction site, to obtain fundamental data to ensure that consumers and designers receive trustworthy and relevant information on products and their durability.
This research work aims to be a solid base for the development of future guidelines and/or regulations at national and international level, in order to guarantee the maximum diffusion of this type of product. Then, a study plan has been carried out regarding the functionality of hemp-lime blocks in masonry, layered with finishing plaster made of fine hemp shives, to evaluate the in situ thermo-hygrometric building performance. In particular, experimental methods were developed and measurements were carried out on two structures, one in northern Italy and one in southern Italy, and precisely in Sicily, focusing the study on the performances of the walls subjected to warm Mediterranean climates.
... Thermal performance materials significantly increase the energetic efficiency of buildings. The manufacture of bio-composites with local lost natural fibers participates to reducing another part of energy consumption and GHG emission [3]. Natural fibers are usually agricultural residue or lost natural plants present several advantages such as low density, high porosity, low cost. ...
The growing need for the reduction of energy consumption in the building has prompted scientist and engineers to find materials with low cost and low energy consumption for their production, and during their service. Therefore, a large number of materials based on natural fibers and various matrices (polymers, cement, soil…) are utilized for different applications. This work present a focus on the development of natural fiber mortar with the aim to exploit abundant plant wastes in mountainous regions in Algeria. In this context, we choose to investigate on the laboratory, the effect of the addition of xerophytic fibers of two plants: Doum (dwarf palm) (Chamaeropshumilis) and Diss (dis grass) (Ampelodesmosmauritanicus) on the thermal properties of Portland cement mortars prepared with different fiber-binder ratio. Thermal conductivity measurement is performed after curing period of 28 days for different degree of saturation using hot wire method. Thermogravimetric (TG) analyzer coupled with differential scanning calorimetry (DSC) was used to study the thermal degradation and combustion characteristics of the materials. The results show a significant effect of the fibers addition on thermal conductivity of the composites. Therefore, increasing the content of vegetable fibers in mortars resulted in an increase of their weight loss at high temperatures. Similarly, the addition of the fiber promotes the absorption of heat by the composite and affects its combustion process.
... The vapor diffusion coefficients were determined according to Zeknoun et al. [30], and Maalouf et al. [31]. The transport coefficients associated with moisture gradient are related to the water vapor permeability δ 0 and the specific hygric capacity ξ, which is the slope of sorption curve: ...
Many new insulation materials are being developed and thermally tested aiming at understanding and improving their insulation characteristics in order to improve the energy performance of new and existing buildings. Bio-sourced materials appear among the new insulation solutions presenting the advantage of being able to save energy on one hand and having a low environmental impact on the other. The wood fiber material is one of the most successful natural insulation materials being recently used in building constructions. It presents many advantages besides its insulation performance; due to its density, it stores moisture thereby improving the indoor air quality; it is also an excellent acoustic insulator because it has a natural tendency to absorb and reduce sounds. In order to evaluate its effectiveness in building applications, this study analyzes the hygrothermal modelling and performance of the wood fiber insulation in building applications by adopting two approaches: A numerical approach using a mathematical model that describes heat and mass transfer within the wood fiber material being considered as porous media. The hygrothermal characteristics of the wood fiber material are first determined experimentally for this purpose, namely the thermal conductivity, the heat capacity, and the isotherms of sorption and desorption. An experimental approach is carried out in controlled and uncontrolled ambiance conditions in order to validate the numerical model. A 50 cm × 50 cm wood fiber sample having an 8 cm thickness is tested for this purpose. A very high accordance is observed between the measured and modelled results for both the temperature and the relative humidity evolutions within the sample at x = 2 cm and x = 4 cm with a mean difference ΔT¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{\Delta \mathrm{T}} $$\end{document} of 0,21 °C at x = 4 cm and 1 °C at x = 2 cm. The maximum recorded differences for the relative humidity are: 5,5% and 4,5% at x = 2 cm and 4 cm respectively. The ability to predict the thermal and the hygric behavior of the wood fiber insulation will thus allow a better understanding of the efficiency of natural insulation materials.
... These latter differ mainly due to the choice of transfer potentials: temperature and water content, or capillary pressure or vapour pressure. The aim was to better predict the hygrothermal behaviour of different building materials, including hemp concrete Colinart et al. 2016;Maalouf et al. 2014;Tran-Le et al. 2010). Other studies have focused on the application of real weather conditions (Costantine et al. 2018) for modelling the transient hygrothermal response of hemp concrete walls, or the use of special methods at two temperatures (23 °C and 40 °C) for determining sorption isotherm curves from dry state to 85% relative humidity, or partial relative humidity cycles between 23 and 85% (Fabbri and McGregor 2017). ...
Bio-based materials, such as hemp concrete, have been widely recommended to reduce carbon emissions and energy consumption of buildings as a means of addressing current environmental problems. These materials may possess very interesting hygrothermal and acoustic performance. Hemp concrete is composed of hemp particles embedded in a binder that forms a very heterogeneous and porous component. The aim of this paper is to examine the influence of hemp concrete heterogeneity on the mechanisms of heat and mass transfer. The originality of this paper is to consider the real 3D structure of hemp concrete for modelling coupled heat and moisture transfers within the material. These 3D microstructures were obtained using 3D X-ray tomography reconstruction with a voxel size of 31.8 μm. Then, a specific finite element mesh was generated from the real, heterogeneous geometry of hemp shives, binder and interparticle air. A mesoscopic model was developed to simulate coupled heat and mass transfer phenomena within the material. The 3D temperature and relative humidity fields showed high heterogeneity and complex distributions that are governed by the hemp concrete morphology. In addition, the anisotropy of the material led to different effective thermal conductivities in each transfer direction. Numerical comparison with simulations performed on the fictive elementary representative volume of hemp concrete showed that consideration of the real geometry allows a better understanding of coupled heat and moisture transfer phenomena modelling.
... Additionally, natural and bio-based construction materials represent a promising solution for optimizing buildings' environmental sustainability Ingrao et al., 2019). Over the years, they have been documented as causing any release in the environment of toxic substances affecting both the quality of the environment and the health and safety of humans (Benfratello et al., 2013;Maalouf et al., 2014;Ingrao et al., 2015). ...
Construction is considered as one of the most relevant sectors in terms of environmental impacts, due to the significant use of raw materials, fossil energy consumption and the consequent Greenhouse Gases emissions. The use of unconventional and environmentally-friendly materials and technologies is worldwide recognised as a key factor to enable the decrease of material and energy consumption in buildings. Between natural/sustainable materials, those using hemp products and by-products (fibres and hurds) have rapidly widened their field of application in the building industry, mainly because of their good hygrothermal and acoustic insulation properties. Moreover, the usage of these materials allows high carbon storage due to the CO2 sequestration during the agricultural phase.
This study represents an energy and environmental assessment of hemp crop cultivation in France, carried out through a Life Cycle Assessment approach, showing positive and negative contribution related to the different life cycle phases. The total CF evaluated through the IPCC, 2013 GWP 100 method (IPCC, 2013) is equal to 0.975 kgCO2eq, in view of a CO2 uptake of −1.29 kgCO2eq. So, it is understood that the total CF results therefore lower than the CO2 uptake due to the biogenic carbon captured and stored during hemp growth. The total Energy Footprint, instead, was calculated in 17.945 MJ. The Upstream phase came out as the main contributor to the impacts. A sensitivity analysis was performed to explore changes in results related to main inputs assumptions and, in particular, the environmental benefits associated with the replacement of conventional fertilisers (ammonium sulphate) with organic matter were highlighted.
... Locally produced organic materials and by-products were used as filler material -hemp shives, wood sanding dust and wood fiber. Hemp shives is an industrial by-product from hemp fiber production, which is used to produce lime-hemp concrete (LHC), a new type of building insulation material that is being used more widely in recent years due to its low thermal conductivity and high thermal capacity [6], high moisture transfer and moisture buffering capacity [7] [8] and good sound insulation capabilities [9]. Woodbased fillers have also been used for insulation materials as there is constant search for use of shavings and dust from wood product [10] and also have shown good thermal insulation capabilities [11] [12]. ...
The aim of this paper is to study possibilities to obtain composite materials using organic rich lake sediments (further-sapropel) and lime as binders and hemp shives, wood fibre, and wood sanding dust as fillers. The mechanical and thermal properties of the obtained composite materials are investigated and compared to similar composites, such as lime-hemp concrete (LHC) and magnesium oxychloride hemp composite (MHC). Because of the high amount of organic content these materials are prone to biodegradation, therefore the materials were coated with ALINA LIFE TM organoclay additive that helps to extend product lifetime , reducing rate of biodegradation. The effect of the coating on the resistance against fungi Alternaria alternata and Cladosporium herbarum was investigated in two conditions: before and after experimental accelerated ageing of materials in climate camera. Results indicated that the composites made of sapropel and lime have similar mechanical properties as LHC and MHC: compressive strength of 0.77 MPa for sapropel-lime binder compared to 0.90 MPa for LHC and 1.12 MPa for MHC. As organoclay additive provided higher resistance to biodegradation, sapropel-lime composites have shown sufficient amount of positive properties to be considered for application in construction material industry and as an object for further research.
... Moisture transport and heat transfer in porous materials are inseparable (Min et al., 2017), and many HAM (Heat and Moisture) models that take into account different forms of mass transport (liquid or vapor phase) were developed and tested on hemp concrete walls (Evrard and De Herde, 2010;Maalouf et al., 2014;Rahim et al., 2017;Samri, 2008). ...
In the context of global warming associated with the excess of energy consumption, energy saving and environmental sustainability in buildings have become significant issues at both national and European levels. Therefore, the adoption of energy-efficiency measures in new and renovated dwellings will increase the demand for thermal insulation, which is crucial to improve the housing comfort by reducing the heat loss through the building envelope. Over the past two decades, several bio-based materials have been used in building thermal insulation, such as hemp concrete. Promoting the use of hemp concrete in new constructions and restoration of existing buildings first requires a validation of its hygrothermal behavior at both wall and building scales. For this, several models dealing with various physical aspects of hemp concrete were developed to understand their impact on the prediction of changes in temperature and relative humidity. These physical phenomena include hemp concrete hygroscopic hysteresis and thermal dependency of sorption curves. The preliminary results show that hysteresis has a significant influence on the numerical prediction in the short-term, while temperature dependency has less influence at the wall scale. The next part of this article is devoted to the study of these phenomena at the room scale by monitoring the internal conditions and energy consumption of a virtual hemp concrete office. The results highlight the fact that hysteresis and thermal dependency have low impact on indoor conditions, which could probably be related to the other parameters at the room scale.
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.
In this thesis work, the hygrothermal transfer in date palm concrete (DPC) has been studied numerically at wall scale. In the first part, the phenomena of heat and mass transfer are modeled. Then, the effect of mesh on the precision of the numerical results was studied for the developed models. In the second part, the developed models have been validated with experimental data for the case of a DPC wall. The results show that the studied models give good predictions of the temperature and relative humidity profiles. In addition, taking into account a hysteresis model improves the results of moisture transfer. The validation study was followed by a comparative numerical investigation of the hygrothermal performance of a DPC wall compared to a conventional insulation material. DPC was found to perform better in terms of thermal insulation and thermal inertia. In the last part of this work, a sensitivity analysis was carried out to assess the effect of the different parameters and conditions on the hygrothermal model outcome. The obtained results highlighted the possible sources of errors in the resulting
numerical profiles. Heat transfer is influenced by errors in heat capacity and density, while the parameters that influence moisture transfer are the sorption isotherm and the vapor diffusion resistance factors. Furthermore, it was noted that moisture transfer is very sensitive to any errors in initial conditions or sensors position. In addition, the neglect of liquid water diffusion in the model led to significant underestimates in the relative humidity profiles during the adsorption phase.
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 (CO2), 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.
New energy-efficient materials are increasingly used in architecture and civil engineering today. Many of these are based on the reuse of plants and plant residues from industry and agriculture for the production of bio-sustainable insulation materials, and as aggregates in concretes. This paper presents the results of our study of research into hemp concrete, an emerging material in the green building sector, since it first appeared about twenty-five years ago to the present day. The study centres on a growing bibliography over this period, emphasizing some fundamental parameters of hemp raw materials and related building materials, the binders used in the production of hemp aggregate concretes and assessments of different aspects of their performance. The most important properties of hemp concrete vary according to the quality of the plant aggregates, the choice of binders (typically aerial or hydraulic lime), the proportions of the raw materials and the application techniques. Organic aggregates are less stable than inorganic aggregates and are therefore more difficult to use in a concrete mix with both inorganic and organic binders. Among other reasons, this is due to the disproportionate amount of water required in the mixing of plant-based concretes and to the release of organic compounds, which can have serious effects on the hardening process. This problem was identified in scientific studies on the use of hemp concrete in sustainable, bioclimatic construction, whether applied as a semi-liquid mass or as a precast element. This new biomaterial offers excellent results in terms of its application on site and has important physical properties, such as high durability and easy conservation. This study seeks to provide a useful tool for future research into sustainable building materials, better use of available energy and plant-based resources and more efficient recycling of the waste produced by human activities.
In the last years people has become aware of energy saving and thermal comfort requirements for home buildings in hot and cold seasons. In the present study, hybrid multifunctional constructive components made of a reinforced mortar channel filled with cement-soil-sawdust (CL2MSCAL) were evaluated to experimentally determine their thermal performance (thermal conductivity, thermal time lag and decrement factor). The experimental analysis performed in this study was based on dynamic climatology. Measurements of components surface temperature were conducted to determine temperature damping and temperature wave lag. Monthly average temperature and direct solar radiation data of the site was considered. Measurements of real scale constructive components were conducted on a fully equipped thermal conductive system and thermal chambers (test cells) built for this purpose. Results are compared to concrete components (CCL) that account for approximately 71.6% of the houses built in Mexico and 43.2% in Oaxaca and reinforced mortar (CML) used as prefabricated housing systems. Best results were found for component CL2MSCAL that has a thermal conductivity of 0.81W/m K, a thermal damping of 81.5% (decrement factor of 0.166) and time lag of 7:37 hours compared to CCL that present a time lag of one hour and decrement factor of 0.9. Thus it is concluded that CL2MSCAL roofing channel components are an alternative for energy saving and thermal comfort.
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.
The main objective of this study is devoted to the development of new insulating and ignifuged miscanthus fibers (Mf)/recycled textile fibers (RTf) reinforced biocomposites (BCs) using chitosan as polysaccharide‐based binder and aluminum trihydroxide (ATH) fillers while focusing on the fire behavior. To achieve this goal, a preliminary study was carried out on flame retarded chitosan‐based films with various ATH‐filler ratios (20, 33, 50, and 60 wt %). ATG and pyrolysis‐combustion flow calorimeter analysis showed significant improvement of chitosan thermal behavior with the addition of 33 wt % and above of ATH. Mechanical properties of films were, however, degraded. Thereafter, different ratios of miscanthus/RTf reinforced BCs (fibers content up to 89.5–90 wt %) were elaborated through thermocompression process using neat chitosan and chitosan/ATH (67/33 wt %) as a binder. Mechanical, thermal, and fire behavior were evaluated. Higher mechanical properties were found for hybrid materials containing the association of both RTf and Mf in comparison to those containing only RTf or Mf. Fireproof BCs (E rating: according to the NF EN ISO 11925‐2), with thermal conductivity values between 0.07 and 0.09 W m−1 K−1 and density range between 270 and 299 kg m−3 were successfully elaborated. The results of this study show a promising use of the chitosan/ATH system as flame retardant for biobased insulating building materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 136, 47306.
Thermal insulations have begun to play an increasing important role in realizing building energy saving in the past years. Thermal insulations made of biomasses like agro-residues, forest residues, etc., are developing very fast recently, although their research and development history is relatively short. In order to help researchers to achieve a global viewpoint of the research on this topic and to improve the research and application progress, a systematic review is presented in this study. After review and screening, 144 original research journal papers were selected as samples and analyzed to investigate the following topics: Historical development of bio-insulations from 1974 up to April 2016, from viewpoint of number of papers published and corresponding journals; Geographical distribution of researchers, according to country and continent categories; Kinds of biomasses under research including agro-residues, forestry residues, economic plants, etc.; Analysis methodologies and research scale of bio-insulations; Common types, manufacturing methods and properties of bio-insulation; Experimental equipment, software, and corresponding standards. Moreover, the shortcomings of the current research are discussed in details. Finally, some suggestions are presented, including: a scientific plan on bio-insulation research; selection of suitable types; traditional and innovative treatments for improving specific properties; the required properties testing order; scientific presentation of research results. This study can help to achieve a more precise comprehension about bio-insulations research status, find suitable experimental equipment for effectively testing various properties, adopt innovative ways to improve specific properties, avoid making mistakes during the research and provide a better expression of the research results. Furthermore, this study can stimulate the research and application of bio-insulations to get a great-leap-forward development in the near future, especially in the fabricated building field. 1. Background and introduction Nowadays, industry, transportation and buildings are the three major social energy consumers. In particular, with the increasing demand of indoor thermal comfort, more and more energy is consumed in the building sector by the energy systems providing heating, ventilation, and air conditioning services. The improvement of the thermal insulatio n of buildings is one of the most effective ways to get energy savings, through the reduction of heat or cold losses through envelopes. However, many traditional construction materials do not have good thermal insulation properties. So, many kinds of extra thermal insulation materials, like solid boards (panels), solid bucks, particles, sandwiches, coils are being used in many parts of the buildings, such as in the exterior walls, roofs, floors and exterior doors. These materials can be applied not only in traditional buildings but also in fabricated buildings. The common insulations can be classified into four categories depending on the raw material: (1) from rocks and slags, such as rock-wool, glass-wool, expanded perlite, glass beads, vermiculite, cinder, ceramic products, etc.; (2) from petrochemical and coal chemical intermediate products, such as Polystyrene, Polyurethane, Polyethylene, etc.; (3) from plants, including agricultural waste, forestry waste and industrial plants fiber waste, such as straws, rice husk, waste papers, wood shavings, cotton, corn crops, etc.; (4) from metals, such as metal reflection film, hard metal visor, radiation plate, etc., the applications of which are still limited because they can only be applied in roofs and they are much more expensive than other thermal insulation materials. Jelle [1] summarized the state of traditional thermal building insula-http://dx.
This chapter gives the state of the art of previous studies on hygric and thermal properties of bio-aggregate based building materials. Firstly, hygric characteristics such as sorption isotherms, water vapor permeability and moisture diffusivity are given. The ability of bio-aggregate based building materials to moderate ambient relative humidity may be valued using moisture buffer value. Then thermal properties (thermal conductivity, thermal diffusivity conductivity and specific heat capacity) are reported. Finally, concluding remarks on hygrothermal behavior with simultaneous heat and mass transfer are provided, they underline that considering only thermal conductivity and specific heat capacity is not sufficient to evaluate the energy performance of bio-aggregate based building materials. The results found in bibliography mainly concern wood-based and hemp-based materials.
Global warming, the scarcity of natural resources, the polluting emission is a major concern for the human community. The construction sector especially has a significant impact on the environment and has therefore a role to play in the development of innovative sustainable solutions. Bio-based materials are known to be an interesting solution to address energy and environmental issues. In particular, hemp, fast growing renewable raw vegetal, has the qualities to be a serious alternative to modern insulation solutions. Hemp wool using the fibres and hemp concrete using the shivs of the plant have interesting hygrothermal properties and a good thermal insulation level. Their porous, hygroscopic and permeable structure gives them high moisture transfer and storage capacities, improving the hygrothermal comfort felt by the inhabitants.
Bio-based building materials are composites of vegetal particles embedded in an organic or mineral matrix. Their multi-scale porous structure confers to them interesting thermal, hygroscopic and acoustic properties. These performance properties have spurred research on these materials as alternative building materials with low embodied energy. This review contains a comprehensive critical analysis of mechanical, thermal, and acoustic properties of bio-based building materials with a particular focus on the interactions of various constituents and manufacturing parameters. Alkali-activated binders are reviewed for their potential use in high strength bio-based composites. A detailed physico-chemical characterisation of the aggregates and compatibility analysis allow a comprehensive understanding of fundamental phenomena affecting mechanical, thermal, and acoustic properties of bio-based building materials. A wide range of biomass materials is available for building composites, and hemp shives remain the most prevalent bio-aggregate. In the context of England, the farming of industrial hemp remains limited, due in part to the long, costly licencing process and the abandonment of processing subsidy as part of the EU common agricultural policy in 2013. On the other hand, Miscanthus (elephant grass) is a perennial, low-energy, and well-established crop in the England which is gaining interest from farmers in the South West region. Its development aligns with actual agricultural, land management and environmental policies with potential to fuel innovative industrial applications. This review performs a critical assessment of the performance of bio-based materials in an attempt to identify potential frameworks and opportunities to develop building insulating materials from miscanthus.
In the present paper, we study with both experimental and numerical aspect the heat and moisture transfer properties of a wall based on concrete filled with the natural fibers. The wall was placed in climatic chamber and temperature and relative humidity were monitored at different depths. A developed model describing heat and moisture transfers in porous building materials was implemented in COMSOL
Multiphysics and solved with the finite element method. The obtained results are compared with experimental data. A relatively good
greement was obtained for both temperature and relative humidity
variation at different depths. Finally, the developed model gives almost a good prediction despite the classical difficulties encountered at the experiment, which is very promising for the prediction of the hygrothermal behavior of bio-based building materials at different conditions.
Alternative products such as green materials are either back or newly implemented in the construction field. The low environmental impact of hemp concrete and its thermo-hydric behaviour show the possibilities of healthier construction and let obtain a better comfort of users. In contrast with usual concrete, the hemp concrete has huge hygroscopic buffer capacity. The aim of this work is to study the hempcrete with prompt natural cement, which is a concrete block made of a mixture of hemp shivs and "Prompt natural cement". For that, its behaviour in energy consumption and comfort at a wall and building size level are analysed thanks to simulation and experimental measurements, which are conducted in parallel. Experimental tests have been run at wall scale in two PAS SYS test facilities. Test walls are subject to weather solicitations outside and hydrothermal regulation inside. For numerical study, a 2D coupled heat and moisture transport model is defined. Numerical analysis gives results in the same trends as experimental data.
The aim of this paper is to compare hemp shiv and sunflower pith properties when they are used as plant aggregates incorporated into a pozzolanic matrix. Scanning electron microscope observation of these aggregates showed distinct microstructures, which could be responsible for the differences in mechanical and thermal behaviour observed between composites including these two types of plant aggregates. The long-term behaviour of composites revealed the mineralization of plant aggregates, in particular hemp shiv, by calcium compounds.
Lime-hemp concrete (LHC) is a sustainable building material that combines hemp shiv and building limes. Moisture fixation and thermal properties of LHC were determined so as to gain knowledge about the material's behaviour in a cold, wet climate. Sorption isotherms were produced over the whole moisture range for two LHC mixes by means of glass jar tests and a pressure plate apparatus. Thermal properties were determined for the mixes at different relative humidities using a transient plane source method. The results showed relatively low thermal conductivity and a steep sorption isotherm in the interval between 95% and 100% RH.
This paper presents the Umidus program which has been developed to model coupled heat and moisture transfer within porous media, in order to analyze higrothemal performance of building elements when subjected to any kind of climate conditions. Both diffusion and capillary regimes are taken into account, that is the transfer of water in the vapor and liquid phases through the material can be analyzed. The model predicts moisture and temperature profiles within multi-layer walls and low-slope roofs for any time step and calculates heat and mass transfer. Umidus has been built in an OOP language to be a fast and precise easy-to-use software.
Hemp concrete is a sustainable lightweight concrete that became popular in the field of building construction because of its thermal and environmental properties. However; available experimental data on its hygrothermal behavior are rather scarce in the literature. This paper describes the design of a large-scale experiment developed to investigate the hygrothermal behavior of hemp concrete cast around a timber frame through a spraying process; and then coated with lime-based plaster. The equipment is composed of two climatic chambers surrounding the tested wall. The experiment consists of maintaining the indoor climate at constant values and applying incremental steps of temperature; relative humidity or vapor pressure in the outdoor chamber. Temperature and relative humidity of the room air and on various depths inside the wall are continuously registered during the experiments and evaporation phenomena are observed. The influence of the plaster on the hygrothermal behavior of hemp concrete is investigated. Moreover; a comparison of experimental temperatures with numerical results obtained from a purely conductive thermal model is proposed. Comparing the model with the measured data gave satisfactory agreement.
This paper presents the results of a research that looks for to identify the effects of moisture transfer on thermal inertia and for different materials through the case of a simple layer wall under internal periodical conditions. To study moisture transfer in materials, we used a coupled heat and moisture transfer model in which moisture transport is made through liquid and vapour phases. The liquid phase is supposed to move by capillarity whereas the vapour phase diffuses under vapour partial pressure gradient. For the numerical approach, a simulation model was developed and implemented in the program oriented object SPARK. Simulations were used to study the effect of moisture transfer on heat energy storage in simple layer walls and mainly for hemp concrete which is a green material with low environmental impact. Sensitivity analysis identifies the most important parameters.
In building design, thermal inertia is an important
passive parameter that affects occupants’ thermal comfort. The
purpose of this paper is to study the effect of moisture transfer on
material thermal inertia for different materials by studying the
behaviour of a simple wall under variating outdoor conditions and
mainly to study transient hygrothermal behaviour of a vegetal fibre
material made of a mixture of lime and hemp fibres. To study
moisture transfer in materials, we used a coupled heat and moisture
transfer model in which moisture transport is made through liquid and
vapour phases. The liquid phase is supposed to move by capillarity
whereas the vapour phase diffuses under vapour partial pressure
gradient. For the numerical approach, a simulation model was
developed and implemented in the program oriented object SPARK.
Simulations were used to study the effect of moisture transfer on the
damping effect, time lag and heat conduction loads through simple
layer walls.
The objective of this work is to study the effect of taking into account interface contact resistance on the prediction of moisture distribution through multilayered building envelope. Therefore, two mathematical models to describe coupled heat and mass transfer in double-layered porous materials have been investigated: one that considers imperfect contact between layers and another that ignores this phenomenon. Both models are one-dimensional and were implemented using finite difference technique with an implicit scheme. Numerical results are presented in terms of moisture distribution for a double-layered wall and compared with the experimental data available in the current literature. The comparison has shown that the model that disregards interface contact resistance between layers cannot predict correctly one-dimensional heat and moisture transfer within double-layered porous materials. The sensitivity analysis of the simulation parameters and the impact of contact resistances at the whole building level are presented in detail and their effect on the whole building level was analysed. Our results suggest that the thermal contact resistance is the most influent parameter on the moisture flux across the hydraulic contact interface. On the whole building level, simulations indicate that taking into account contact resistances had a slight effect on the indoor relative humidity but a noticeable effect on heating input energy. A decrease of 10% in energy consumption is obtained when contact resistances are considered.
Les matériaux de construction sont des matériaux poreux, et donc très sensibles à leau. Du fait de conditions thermique et hygrométrique ambiantes variables, ils sont le siège de plusieurs phénomènes : migrations de vapeur deau, changements de phase, humidification, séchage. Le couplage de tous ces phénomènes conditionnent ses propriétés thermiques et sa durabilité. A titre dexemple, pour un béton de chanvre de type « mur » soumis à une hygrométrie de 75%, sa conductivité thermique augmente de 30% (forte conduction de leau). La mise en place dune cellule déchange a donc pour but de caractériser les performances hygrothermiques de trois matériaux de construction : le béton cellulaire autoclavé, le béton de chanvre et la brique à perforations verticales, en fonction des conditions ambiantes. Létude sappuie tout dabord sur une approche expérimentale. Lobjectif est de créer des gradients de T et HR en fonction du temps et ainsi mesurer la distribution en température et humidité relative dans la paroi ainsi que la reprise en eau du matériau lorsque celui-ci est soumis, sur la face en contact avec lenceinte climatique, à des sollicitations statique et cyclique en T et HR. Ensuite, létape suivante consiste à modéliser le comportement des matériaux comme enveloppe grâce à un modèle de conduction thermique pure tout dabord. Les grandeurs thermiques des matériaux (?, ?, c, hs et a) sont alors déterminées. Enfin, pour les bétons de chanvre, on doit procéder à une modélisation numérique des transferts couplés de chaleur et dhumidité afin danalyser plus précisément linfluence des transferts de masse sur le comportement thermique.
Using plant material as raw materials for construction is a relatively recent and original topic of research. This book presents an overview of the current knowledge on the material properties and environmental impact of construction materials made from plant particles, which are renewable, recyclable and easily available. It focuses on particles and as well on fibers issued from hemp plant, as well as discussing hemp concretes. The book begins by setting the environmental, economic and social context of agro-concretes, before discussing the nature of plant-based aggregates and binders. The formulation, implementation and mechanical behavior of such building materials are the subject of the following chapters. The focus is then put upon the hygrothermal behavior and acoustical properties of hempcrete, followed by the use of plant-based concretes in structures. The book concludes with the study of life-cycle analysis (LCA) of the environmental characteristics of a banked hempcrete wall on a wooden skeleton. Contents 1. Environmental, Economic and Social Context of Agro-Concretes, Vincent Nozahic and Sofiane Amziane. 2. Characterization of Plant-Based Aggregates. Vincent Picandet. 3. Binders, Gilles Escadeillas, Camille Magniont, Sofiane Amziane and Vincent Nozahic. 4. Formulation and Implementation, Christophe Lanos, Florence Collet, Gérard Lenain and Yves Hustache. 5. Mechanical Behavior, Laurent Arnaud, Sofiane Amziane, Vincent Nozahic and Etienne Gourlay. 6. Hygrothermal Behavior of Hempcrete, Laurent Arnaud, Driss Samri and étienne Gourlay. 7. Acoustical Properties of Hemp Concretes, Philippe Glé, Emmanuel Gourdon and Laurent Arnaud. 8. Plant-Based Concretes in Structures: Structural Aspect - Addition of a Wooden Support to Absorb the Strain, Philippe Munoz and Didier Pipet. 9. Examination of the Environmental Characteristics of a Banked Hempcrete Wall on a Wooden Skeleton, by Lifecycle Analysis: Feedback on the LCA Experiment from 2005, Marie-Pierre Boutin and Cyril Flamin.
A theory of moisture movement in porous, materials under temperature gradients is developed which explains apparently discordant experimental information, including (a) the large value of the apparent vapor transfer, (b) effect of moisture content on net moisture transfer, and (c) the transfer of latent heat by distillation. The previous simple theory of water vapor diffusion in porous media under temperature gradients neglected the interaction of vapor, liquid and solid phases, and the difference between average temperature gradient in the air‐filled pores and in the soil as a whole. With these factors taken into account, an (admittedly approximate) analysis is developed which predicts orders of magnitude and general behavior in satisfactory agreement with the experimental facts. An important implication of the present approach is that experimental methods used to distinguish between liquid and vapor transfer have not done so, since what has been supposed to be vapor transfer has actually been series‐parallel flow through liquid ‘islands’ located in a vapor continuum. Equations describing moisture and heat transfer in porous materials under combined moisture and temperature gradients are developed. Four moisture‐dependent diffusivities arising in this connection are discussed briefly.
The need to reduce greenhouse gases emission produced by the building sector leads to the research of renewable and less impacting materials that can replace traditional ones. This subject has encouraged new researches on biocomposite concretes with the aim to exploit renewable resources like vegetal fibres intended as materials whose production processes are generally characterized by low costs and energy demand. This biocomposite is obviously much lighter than concrete and, therefore, can be suitably used in such cases where a structure cannot be overloaded, for instance in the realization of a green covering on top of a preexistent building. In this work, a first analysis of the thermal and structural behaviour of a biocomposite concrete, constituted by a mineral matrix (lime) with the addition of vegetal fibres (hemp), has been carried out, with particular attention to the amount of fibres and its granulometry in the mixture. The drying process contemplate a permanence of the material in a thermostatic chamber. The analysis carried out shows that hemp can be used both for the realization of insulation panel (hemp fibres alone) and as a construction material (hemp bast and concrete mix). This biocomposite has shown good insulation properties and some mechanical resistance. However, the results show that further analyses should be carried out on the drying process of the material, as it can greatly influences thermal and mechanical properties.
In a context of sustainable development and energy sparing, a life cycle assessment (LCA) may be useful to make good choices. Thus, this study concerns the LCA of an environmentally friendly material used for building construction, hemp concrete. The functional unit is first defined per square such that the wall may provide the function of bearing wall meter and its thermal performance is described by a thermal resistance of 2.78 m².K/W. The results then showed that the production phase of raw materials is mainly responsible for the environmental impact of the wall, mostly due to the binder production. It was also shown that, compared to traditional construction materials, hemp concrete has a low impact on environment. Moreover, hemp concrete contributes to reduce climate change as photosynthesis-mediated carbon sequestration and carbonation serve to reduce atmospheric carbon dioxide. A sensitivity analysis is performed on three criteria: wall thickness, renewal of coatings and compounds of the indoor coating. Our results show that environmental indicators evolve with wall thickness, except for the climate change indicator. It improves with thickness due to carbon sequestration and carbonation. Moreover the increase in the wall's thermal resistance with wall thickness is not taken into account in such an LCA performed at the material level. The renewal of coating slightly impacts the environmental indicator for small numbers of renewals but it leads to negative effects if they are too numerous. It appears that hemp-lime coating has a greater impact than sand-lime coating as it embeds more binder.
Hemp concrete is a multifunctional ecological material used in buildings. Due to its high porosity (about 80% in volume), it presents an “atypical” mechanical behavior and its thermal and acoustic properties are particularly interesting. It is today possible to design this material according to the required use. This paper focuses on the mechanical properties of hemp concrete. It is shown that extreme curing conditions (30%, 75% and 98% RH) are prejudicial to the mechanical setting of the hydraulic binders whereas only high relative humidity disrupts the one of the air lime-based binder. It is also established that the binder content hugely influences the setting and hardening of the material. Finally, according to the hemp particle size, it appears that small particles (about 3 mm in length) lead to reduce the porosity and consequently the setting process of hemp concrete as compared to concrete manufactured with large particles (about 9 mm).
Hemp concrete is a bio-based building material the main qualities of which are its low environmental impact and its hygrothermal behaviour. Even for one kind of application (for example: wall), several compositions and manufacturing methods are encountered in the market. This study compares the hygroscopic behaviour of three hemp concretes used for building walls to identify whether composition and manufacturing have an impact on hygric properties. The investigations are based on the measurement of the sorption curve, of the water vapour permeability versus humidity and of the moisture buffer value. Moisture diffusivity is calculated from the sorption curve and from the water vapour permeability. The results underline the high transfer and storage capacities of these materials; they are classified as excellent (or nearly excellent) hygric regulators. A slight effect of porosity, connected with composition and manufacturing method, is observed.
The effects of moisture on sensible and latent conduction loads are shown by using a heat and mass transfer model with variable material properties, under varying boundary conditions. This model was then simplified to reduce calculation time and used to predict conduction peak load and yearly integrated wall conduction heat flux in three different cities: Singapore (hot/humid), Seattle (cold/humid) and Phoenix (hot/dry). The room air temperature and relative humidity were calculated with the building energy simulation program DOE-2.1E. The materials studied were aerated cellular concrete, brick, lime mortar and wood. It is shown that the effects of moisture can be very significant and that simplified mathematical models can reduce the calculation time with varying effects on accuracy.
Lime—Hemp (LH) composites are innovative building materials. They can be used in renovated or thermally upgraded as well as new buildings. This article reviews hygrothermal properties of LH wall assemblies and compares their transient performance to five traditional assemblies using WUFI ® simulation. While the annual quantity of energy was similar, LH assemblies showed a strong ability to improve indoor comfort.
Wall time varying conduction heat transfer investigations are very important for the prediction of heating and cooling loads in air conditioning practice and absolutely essential to the passive solar heating design. The walls store heat, absorb and dissipate a fraction of it and transmit the rest into the conditioned space at a later time, which depends on the wall thermal inertia. The present work aims at the description of a developed numerical model, which is validated successfully against analytical results from the literature and allows the prediction of transient and quasi-steady-state thermal behaviour of two basic structural wall design groups of a growing thermal inertia. The model allows the calculation of the time varying conduction heat flux for a wide range of progressively heavier wall designs, under the effect of time varying meteorological conditions, something which allows their design evaluation for a specific application. A drastic reduction of the daily fluctuation of the quasi-steady-state heat flux would be possible by using a broad range of heavier walls, something which can be quantified by the introduction of a dimensionless quantity defined as wall damping-out efficiency. This is attributed to the thermal inertia of a specific wall design, which is also responsible for phasing-out of the maximum heat flux. Both phenomena, which are comparatively investigated for the two groups of specified walls, are desirable particularly for the development of peak load control strategies.
In this study, the effects of thermophysical properties and thickness of a wall of a building on time lag and decrement factor have been investigated. For this purpose, one dimensional transient heat conduction equation was solved using Crank-Nicolson scheme under convection boundary conditions. To the outer surface of the wall, periodic boundary conditions were applied. A very general code which can take care of composite walls under any kind of boundary condition was developed. Single and combined effects of the thickness and thermophysical properties on the time lag and decrement factor were investigated. It was found that thermophysical properties have a very profound effect on the time lag and decrement factor. The computations were repeated for different building materials and the results are discussed.
A new model is presented for predicting the dynamic thermal response of indoor spaces to indoor heat pulses. The model is based on the concept of the “indoor surface thermal capacitance”, Cs, which characterizes the thermal inertia of an indoor space and expresses the heat stored within indoor air and surface layers of walls and furnishings, per degree of mean temperature difference between indoor air and building envelope. Extensive comparisons with measurements and rigorous finite-difference solutions show that the accuracy of the proposed model is satisfactory for a wide range of practical applications. Comparison with other indoor space simulations of the same class, characterized as “simplified approaches”, show that the present one may provide considerably increased accuracy.
To fulfil the requirements in the Danish building regulations for new buildings it is necessary to have a limited heating demand. The heating demand is calculated on the basis of a number of energy related parameters. One of these is the heat capacity of the building. In the present study three different methods for determination of the heat capacity of the building have been assessed: Tabulated values in connection with the Danish calculation method, a simplified CEN method and the active heat capacity. To estimate the active heat capacity an analysis has been made where surfaces with different materials are exposed to a diurnal variation of the room temperature. The heat which is transmitted into the surface during a 12 hour period with positive heat flux, and stored in the material, is called the ability to store heat. Examples are shown of how it is possible to calculate the heat capacity for different materials. It is demonstrated how the heat capacity for the single surfaces can be added in order to calculate the heat capacity of a whole building. The result expressed as the heat capacity per m² heated floor area, is used as one of the input values in the Danish calculation programme for assessment of the energy demand of buildings. This study indicates that it can normally not be expected that a detailed calculation will provide a larger heat capacity than when the Danish tabulated values are used. This is the case for both lightweight and solid buildings. There might be a need for assessment of the Danish tabulated values to check whether the level the heat capacity is appropriate.
Enclosures divided by multiple vertical diffusive partitions have high insulating qualities and may provide tangible benefits as a construction material. In this study, we have developed one-dimensional analytical model of coupled heat transfer (conduction, convection, radiation) in such enclosures. This model is numerically and experimentally validated for an important number of configurations and size of alveolus. The variation of the thermal resistance versus the number of partitions has been experimentally validated. The model is then used to find the partitions number that maximizes the thermal resistance of a partitioned enclosure. Effects of thermal and geometrical parameters on the maximal thermal resistance of the partitioned enclosure have been also investigated. We have shown that the thermal resistance could be improved by decreasing the thermal conductivity of walls; decreasing the emissivity of the partitions faces; or using very thin partitions. The use of relatively thick exterior vertical walls marginally degrades the optimal thermal resistance while at the same time increases the thermal inertia. The combination of the different parameters gives a set of solutions when one desires to obtain precise characteristics for an insulating envelope. The presented model can help to determine the most suitable combination of parameters allowing to get the desired maximal thermal resistance.
Concrete blocks, made of a mixture of lime and hemp shives (also called “hemp hurds”), have been manufactured by a recently developed projection process. Lime carbonatation kinetics is determined by X-ray diffraction. Density measurements are made within blocks, and thermal and mechanical properties are measured (flexural strength, compression strength and hardness). The main observations are moderate density variations within a given block, and an influence of the projection distance on density. Both thermal conductivity and mechanical properties increase with the mortar density, which is well described by existing theoretical models. Compression tests induce a compaction, or densification, of the material.
This paper deals with an adsorption/desorption model in order to predict evolutions of boundary conditions during the mass
transfer process versus time in timber elements. This model is derived from a thermodynamic balance between the free water
and its saturated vapor pressure, and is generalized for the bound water phase. It allows describing a realistic adsorption
and desorption phenomena characterized by a moisture content hysteresis induced by cyclic variations of the relative humidity
and the temperature. The sorption isotherm explains the equilibrium between the bound water phase in wood and the vapor pressure
in the environment. The model includes different latent heats for the adsorption and desorption process. An analytic explanation
allows to model partial variations in terms of relative humidity domain.
The efficiencies of methods employed in solution of building simulation models are considered and compared by means of benchmark testing. Direct comparisons between the Simulation Problem Analysis and Research Kernel (SPARK) and the HVACSIM+ programs are presented, as are results for SPARK versus conventional and sparse matrix methods. An indirect comparison between SPARK and the IDA program is carried out by solving one of the benchmark test suite problems using the sparse methods employed in that program. The test suite consisted of two problems chosen to span the range of expected performance advantage. SPARK execution times versus problem size are compared to those obtained with conventional and sparse matrix implementations of these problems. Then, to see if the results of these limiting cases extend to actual problems in building simulation, a detailed control system for a heating, ventilating and air conditioning (HVAC) system is simulated with and without the use of SPARK cut set reduction. Execution times for the reduced and non-reduced SPARK models are compared with those for an HVACSIM+ model of the same system. Results show that the graph-theoretic techniques employed in SPARK offer significant speed advantages over the other methods for significantly reducible problems and that by using sparse methods in combination with graph-theoretic methods even problem portions with little reduction potential can be solved efficiently.
Existing methods available for practising designers and architects to calculate moisture transfer through building constructions are reviewed and a transient model on combined heat and moisture transfer in composite constructions is introduced. Results using the transient model on a particular case are compared with those obtained using the traditional methods. The consideration of hygroscopic inertia by the transient model significantly alters the prediction of how moisture migrates within and through a building construction.
The sustainable world's economic growth and people's life improvement greatly depend on the use of alternative products in the architecture and construction, such as industrial wastes conventionally called green materials. For this purpose, hemp concrete is more and more recommended by the eco-builders because hemp is a renewable plant, recyclable and does not degrade within time. It corresponds perfectly to the requirements of high environmental quality buildings. The objective of this article is to study transient hygrothermal behaviour of hemp concrete at whole building level. The physical model is one-dimensional and was implemented into the object-oriented simulation environment SPARK, using the finite difference technique with an implicit scheme. The numerical result showed that the use of hemp concrete wall in buildings can ensure good indoor air quality and energy savings in winter. Besides, the combined effect of moisture buffering with the adequate ventilation strategies increases hemp concrete building performance. Our results also suggest that taking into account the hygrothermal transfer at whole building level with heat and moisture production sources has significant effects on predictions.
It has been found in many countries with arid climates that massively walled buildings provide steady, comfortable inside temperatures even though the outside temperature fluctuations may be sizeable. The adobe houses of the American South-West, and the rondavels of southern Africa are particular examples. This phenomena is often termed the thermal flywheel effect. One explanation is that the temperature at the inside of a massive wall lags approximately out of phase with the outside, and so it partly offsets the direct, in phase, infiltration losses into the building. Thus the room temperature is kept approximately constant. In this paper the question of designing a non-homogeneous wall to optimize this effect is considered.
Simultaneous Heat and Moisture Transport in Building Compo-nents, Fraunhofer Institute of Building Physics
- M Kunzel
M. Kunzel, Simultaneous Heat and Moisture Transport in Building Compo-nents, Fraunhofer Institute of Building Physics, Germany, 1995, available on: http://www.wufi.de/index e.html
Simultaneous Heat and Moisture Transport in Building Components
- M Kunzel
M. Kunzel, Simultaneous Heat and Moisture Transport in Building Components, Fraunhofer Institute of Building Physics, Germany, 1995, available on:
http://www.wufi.de/index e.html