Prediction of moisture transfer within material using a classic diffusive model may lack accuracy, since numerical simulations underestimate the adsorption process when a sample is submitted to ...variations of moisture level. Model equations are always established with assumptions. Consequently, some phenomena are neglected. This paper therefore investigates the impact of improving traditional diffusive models by taking into account additional phenomena that could occur in moisture transport within hygroscopic fibrous materials such as wood-based products. Two phenomena in the porous material are investigated: (1) non-equilibrium behaviour between water vapour and bound water, and (2) transport by air convection. The equations of each model are established by starting from averaging conservation equations for the different species considered within material (water vapour, bound water and air). In addition, the validity of assumptions currently used in the models is verified. Then the three models are compared with experimental data to highlight their capacity to predict both the vapour pressure and the mass of adsorbed water. This comparison tends to show a slight improvement in predictions with the new models. To increase our understanding of these models, the influence of the main parameters characterising phenomena (sorption coefficient, intrinsic permeability,
Péclet
number and
Fourier
number) is studied using local sensitivity analysis. The shape of the sensitivity coefficients shows that the first kinetics period is only impacted a little by the non-equilibrium. In other periods, the influence of the diffusion phenomenon represented by the
Fourier
number is much greater than that of the two other phenomena: advection and sorption. Nevertheless, the sensitivity study shows that these two phenomena have some influence on vapour pressure.
This study aims to check the compatibility of a selection of waste and recycled biopolymers for rammed earth applications in order to replace the more common cement-based stabilization. Five ...formulations of stabilized rammed earth were prepared with different biopolymers: lignin sulfonate, tannin, sheep wool fibers, citrus pomace and grape-seed flour. The microstructure of the different formulations was characterized by investigating the interactions between earth and stabilizers through mercury intrusion porosimetry (MIP), nitrogen soprtion isotherm, powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The unconfined compressive strength (UCS) was also evaluated for all stabilized specimens. Three out of five biopolymers were considered suitable as rammed earth stabilizers. The use of wool increased the UCS by 6%, probably thanks to the combined effect of the length of the fibers and the roughness of their surfaces, which gives a contribution in binding clay particles higher than citrus and grape-seed flour. Lignin sulfonate and tannin increased the UCS by 38% and 13%, respectively, suggesting the additives' ability to fill pores, coat soil grains and form aggregates; this capability is confirmed by the reduction in the specific surface area and the pore volume in the nano- and micropore zones.
In the coming years, heat waves will be more and more frequent and severe. New buildings must ensure thermal comfort to the occupants despite hot summer conditions, using passive elements, such as ...solar shadings, night ventilation, limitations of heat gains. The real performance of such systems is very sensitive to occupants’ actions in the case of un-automated systems. In order to better understand and quantify the influence of different occupants’ actions (window opening, solar shading closing, etc) on the building thermal response, novel cooling indicators are proposed based on building energy simulation and global temporal sensitivity analyses. Partial signed variances are used to quantify the impact of each action in terms of intensity and duration. In the present work two indicators are proposed and discussed: cooling indicator and global cooling indicator. They are applied on a case study of an energy efficient detached house constructed in France. 1000 simulations are run, with random selection of actions’ parameters. Maximal temperatures in the main bedroom reach values between 27 and 33°C and are strongly impacted by night ventilation. The proposed cooling indicators aggregate the vast amount of information provided by the simulations and temporal sensitivity analyses and facilitate detailed investigations and comparative studies.
Clay-based materials are the most traditional components of buildings. To improve their performance in a sustainable way, agents can be mixed to fired clay acting as a pore-forming factor. However, ...firing temperatures highly influence their microstructure which is closely linked to a material's final performance as a ceramic block. To highlight the influence of the firing temperature on microstructure, and more specifically on the pore size distribution of clay-based materials, three innovative porous materials were manufactured. These materials were produced by mixing clay and pore-forming agents. They were characterized by optical and scanning electronic microscopy, x-ray diffraction, mercury intrusion and nitrogen adsorption. These techniques allow the phase identification of materials, show sample microstructure and quantify the pore size distribution at different scales. Furthermore, geometric parameters of sample microstructure such as grain diameter and roundness are estimated by using computer software. To conclude, results provide an enlightenment about the influence of material microstructure on the pore size distribution at two firing temperatures. These results can be useful to allow the tune of porous characteristics and, therefore, contribute to the production of more sustainable construction materials.
This paper describes the effect of inorganic adsorbents on the hygrothermal performance of insulating materials. The addition of the inorganic adsorbents leads to significant effect to the ...microstructure and mechanical properties of these materials. The thermal conductivity rang of the materials containing adsorbents from 0.095 to 0.116 (W/m
−1
K
−1
) is lower than that of those without adsorbents (0.121 (W.m
−1
K
−1
)), resulting in reducing the heat consumption of these insulation materials. The kinetics and isotherms water vapor adsorption confirm an increase in moisture uptake capacity at low relative humidity (33%) and small variation of moisture adsorption capacity at high relative humidity (75%) in the presence of the adsorbents. The moisture buffering of the boards containing different adsorbent contents is improved with an excellent moisture buffer value up to 2.7 g/(m
2
.%RH).
Graphical abstract
The thermal conductivity measurement in RH-Boxes.
A Demand-controlled ventilation (DCV) has been recognized as a promising solution for decreasing energy consumption while ensuring good Indoor Air Quality (IAQ) in buildings. However, its application ...in the residential sector has increased first recently. Implementation of DCV systems brings the problem related to assessing their performance, not only in the view of energy savings but also in the ability to ensure IAQ. The objectives of this paper were to introduce a multicriteria performance-based approach for the evaluation of residential ventilation systems with CONTAM airflows simulations; illustrate its applicability to three DCV strategies in the context of renovated apartment buildings in Denmark and challenge the minimal background airflow requirements anchored in the Danish building code.
Our performance-based approach allows assessing ventilation performance regarding IAQ (CO
2
, humidity, PM
2.5
, and formaldehyde-based indicators), energy consumption, and ventilation heat loss.
Our results show that DCV strategies can improve IAQ while decreasing airflows. For example, application of DCV reduced the cumulative indicator of occupant exposure to formaldehyde, IHCHO by 6 to 28 %, compared to the constant-airflow system. For humidity controlled mechanical exhaust ventilation, the heat loss can be reduced up 51%.
Rammed earth construction is built by compacting humid soil into formworks layer by layer, using clay fraction as only binder between the grains, without firing procedure. At this stage, the material ...is unsaturated, and capillary forces thus act to add cohesion between particles. Indeed, a peculiarity of this material is its high hygroscopic capacity, which allows water vapor to be absorbed and desorbed into the clay matrix. The variation of hydric state in the material leads to a variety of mechanical and thermal properties. Consequently, the complexity in studying this material is due to the strong dependence of many parameters on the moisture content and still few data are available in the literature on this subject for rammed earth materials. A soil used for an existing rammed earth building in Lyon is here characterized in order to determine its hygrothermal properties. Earth conductivity was firstly characterized in a reference dry state, then the influence of humidity variations was investigated. Sorption and desorption isotherms were determined to investigate the ability of the material to store and release humidity. Thermal conductivities were measured at different relative humidity, to put into evidence the influence of environmental conditions.
The building materials used indoors constantly interact with the environment in which the occupants live. Recent studies have shown that natural materials, such as wood, can improve human well-being. ...In addition, the building materials facing the indoor air are able to adsorb and desorb water vapour from their surface and exchange it with the surrounding air. This mass exchange comes along with heat exchange, modifying their surface temperature, and thus the indoor environment. Therefore, in this article, we are investigating whether moisture buffering has an impact on comfort. For this purpose, room-scale numerical simulations have been carried out with WUFI Plus, comparing two types of interior cladding materials: painted plasterboards and a raw spruce panelling. The results show a slightly lower surface temperature and air temperature during the summer period when using spruce. A higher hygroscopicity of the spruce than the gypsum can explain this difference in behaviour between the two studied materials. Thus, spruce exchanges more latent heat with the surrounding air. However, only this thermal difference cannot explain the difference in comfort perception between the gypsum and the wood.
Rammed earth hygric properties and evolution Indekeu, Margaux L.; Feng, Chi; Janssen, Hans ...
MATEC Web of Conferences,
2019, Volume:
282
Journal Article, Conference Proceeding
Peer reviewed
Open access
The hygric characterisation of authentic rammed earth materials is presented. Since these materials expand and liquefy upon contact with moisture, currently available methods are adapted to deal with ...this material evolution during the tests. In particular a thin permeable wick is introduced in the capillary absorption test. Moreover, confined and unconfined ways of testing are addressed. The results show that both the material origin and the material evolution can significantly impact the hygric properties.
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