Letteratura scientifica selezionata sul tema "Dynamic hygrothermal transfer"

Coupled heat, air, and moisture transfers through building envelope have an important effect on prediction of building energy requirements. Several works were conducted in order to integrate hygrothermal transfers in dynamic buildings simulations codes. However, the incorporation of multidirectional hygrothermal transfer analysis in the envelope into building simulation tools is rarely considered. In this work, coupled heat, air, and moisture (HAM) transfer model in multilayer walls was established. Thereafter, the HAM model is coupled dynamically to a building behavior code (BES).The coupling concerns a co-simulation between COMSOL Multiphysics and TRNSYS software. Afterward, the HAM-BES co-simulation accuracy was verified. Then, HAM-BES co-simulation platform was applied to a case study with various types of climates (temperate, hot and humid, cold and humid). Three simulations cases were carried out. The first simulation case consists of the TRNSYS model without HAM transfer model. The second simulation case, 1-D HAM model for the envelope was integrated in TRNSYS code. For the third one, 1-D HAM model for the wall and 2-D HAM model for thermal bridges were coupled to the thermal building model of TRNSYS. Analysis of the results confirms the significant impact of 2-D envelope hygrothermal transfers on the indoor thermal and moisture behavior of building as well as on the energy building assessment. These conclusions are shown for different studied climates.

The aim of this work is to understand the influence of the microstructuralgeometric parameters of porous building materials on the mechanisms of coupled heat, air and moisture transfers, in order to predict behavior of the building to control and improve it in its durability. For this a multi-scale approach is implemented. It consists of mastering the dominant physical phenomena and their interactions on the microscopic scale. Followed by a dual-scale modelling, microscopic-macroscopic, of coupled heat, air and moisture transfers that takes into account the intrinsic properties and microstructural topology of the material using X-ray tomography combined with the correlation of 3D images were undertaken. In fact, the hygromorphicbehavior under hydric solicitations was considered. In this context, a model of coupled heat, air and moisture transfer in porous building materials was developed using the periodic homogenization technique. These informations were subsequently implemented in a dynamic computation simulation that model the hygrothermalbehaviourof material at the scale of the envelopes and indoor air quality of building. Results reveals that is essential to consider the local behaviors of materials, but also to be able to measure and quantify the evolution of its properties on a macroscopic scale from the youngest age of the material. In addition, comparisons between experimental and numerical temperature and relative humidity profilesin multilayers wall and in building envelopes were undertaken. Good agreements were observed.

Environmentally sound composites reinforced with natural fibers or particles interest many researchers and engineers due to their great potential to substitute the traditional composites reinforced with glass fibers. However, the sensitivity of natural fiber-reinforced composites to water has limited their applications. In this paper, wood powder-reinforced polypropylene composites (WPCs) with various wood content were prepared and subjected to water absorption tests to study the water absorption procedure and the effect of water absorbed in the specimens on the mechanical properties. Water soaking tests were carried out by immersion of composite specimens in a container of distilled water maintained at three different temperatures, 23, 60 and 80 °C. The results showed that the moisture absorption content was related to wood powder percentage and they had a positive relationship. The transfer process of water molecules in the sample was found to follow the Fickian model and the diffusion constant increased with elevated water temperature. In addition, tensile and bending tests of both dry and wet composite samples were conducted and the results indicated that water absorbed in composite specimens degraded their mechanical properties. The tensile strength and modulus of the composites reinforced with 15, 30, 45 wt % wood powder decreased by 5.79%, 17.2%, 32.06% and 25.31%, 33.6%, 47.3% respectively, compared with their corresponding dry specimens. The flexural strength and modulus of the composite samples exhibited a similar result. Furthermore, dynamic mechanical analysis (DMA) also confirmed that the detrimental effect of water molecules on the composite specimens.

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.

ABSTRACTThis work explores responsive hydrophilic polymers for convergent functions of climate control with architectural material systems. In buildings, the transition across exterior and interior space occurs through the envelope, which is an enclosure system that mediates heat, light, air and moisture transfer functions. Conventional building envelopes are typically constructed to form a barrier that insulates and hermetically separates outdoor and indoor conditions. The dynamic environmental responses of superporous intelligent hydrogels are shown to be beneficial at the interior layer of a double-skin glazing system for building envelope applications. If the hydrogels are integral to the building envelope system, then various environmental functions (such as natural daylighting, heat transfer, airflow and moisture control) can be achieved through integrated actuators to result in improved building energy performance.The composite embodiments emulate bio-analytical functions when embedded microbore-tube water channels serve as actuators for swelling and deswelling kinetics respectively. Each prototype is conceived in response to hot-arid climate contexts. The prototype presented here is a lightweight ventilation cooling and daylighting system. Initial prototypes are inserted into an environmental test-bed that is consequently divided into two chambers to represent an outdoor and indoor condition. The input chamber includes controllable heat and light elements that affect the dynamics of the hydrogel system. The output chamber on the opposite side of the prototype division includes temperature, humidity and photo sensors that are connected to an Arduino board for data collection. Dependent upon the environmental conditions of chamber two, a control program actuates small hydro-pump to saturate the gels with water.The initial results provide correlations between mechanical (elasticity) and thermal (conductivity) properties. Current work in progress includes documentation of average rates for sorption-desorption kinetics and correlations between saturation loading and visible transmittance. The physical test data will also be integrated into building-scale energy performance simulations and hygrothermal transfer numerical analysis for building envelope compositions. The embedded material logic of the hydrogel is exploited in an architectural configuration for a convergence of prior building mechanical system and building envelope functions. The current work demonstrates a highly promising application of soft-skin membranes for much needed reductions in energy consumption within the building sector.

Numerical models of heat and moisture transfer for performance forecast of lightweight insulating assemblies require many inputs. These include exterior climate data (i.e. temperature, relative humidity, solar radiation), interior climate data or standard models, transfer coefficients, correct initial conditions, etc. Most importantly, one needs reliable material models. A material model includes porosity, density, heat capacity, but also non-constant properties, such as thermal conductivity, vapor/liquid water diffusivity, sorption curves. These are, in general, difficult to determine, and material database entries often are incomplete, or simply non-existent. However, if one performs long-term monitoring of temperature and relative humidity dynamics within building envelopes, there is a way to determine hygrothermal curves and properties of the underlying materials. This can be done by performing simulations and finding the set of optimal hygrothermal curves and coefficients such that the experimental data is matched sufficiently well. Despite the appeal, this best-fit model approach is fraught with perils due to many unknowns and must be used carefully. In this article, we demonstrate the application of this method to insulating assemblies for which 6+ years' worth of experimental data is available, and showcase our results obtained using WUFI Pro 6.3 and the derived and verified material models.

This study focuses on the hygrothermal performance of Moso bamboo. The knowledge in this aspect is remarkable important for the research of building energy saving and the low carbon building design. However, the detailed hygrothermal properties of Moso bamboo are fairly rare. To obtain these data, a series of experimental works have been done for measurement of density, porosity, thermal conductivity, specific heat capacity, water vapour permeability, hygrothermal expansion and sorption isotherm of Moso bamboo. To obtain further understanding on the hygrothermal performance of Moso bamboo, a number of dynamic heat and moisture transfer experiments were conducted. These experiments simulated two extreme outdoor environments and one indoor environment. The temperature and RH responses of Moso bamboo panels were monitored. Then a coupled transient heat and moisture transfer numerical simulation at the material level was conducted to predict and validate the hygrothermal performance of Moso bamboo. A sensitivity study of the hygrothermal properties of bamboo was also presented to indentify the influence of each hygrothermal property of Moso bamboo. Major findings include the following aspects. Both experiment and simulation results appear to be consistent with the results of measurements of the basic hygrothermal parameters. The parametric study found that density can be regarded as the most sensible parameter to influence the temperature simulation results at the transient state, while the thermal conductivity dominated the temperature variation at the steady state. The water vapour diffusion resistance factor can be regarded as the most critical parameter to influence the RH simulation results. The influence of liquid water diffusivity is negligible in this study. The parametric study results indicated that the simulation with moisture is more accurate than the simulation without moisture in both equilibrium and transient state. The results also imply that the existence of moisture could increase the heat capacity and reduce the thermal conductivity. The results of this study recommend that the external part of the bamboo culm wall can be utilised to minimise the RH variation of the panel while the internal part of the bamboo culm wall is suitable to increase the thermal insulation performance of the panel. To avoid hygroexpansion, the implementation of external part of bamboo culm wall needs to be minimised.

Dans le cadre de la rénovation énergétique durable du bâti ancien et afin d'améliorer l'efficacité énergétique des parois soumises aux remontées capillaires, une nouvelle technologie de rupture consiste à incorporer un système de ventilation d'un espace tampon situé entre l'isolation thermique et l'ossature porteuse humide. Cette technologie est considérée comme l'une des solutions efficaces et peu onéreuses pour lutter contre les remontées capillaires, tout en assurant la durabilité de l'isolation et la pérennité structurelle de l'ossature.Physiquement, le dispositif aéraulique est basé sur la génération d'un flux laminaire de convection forcée d'air neuf dans un canal vertical en contact avec la surface interne de la paroi humide. Cette technologie crée alors un front d'évaporation à la surface interne de la paroi, où par conséquence, un échange hygrothermique simultané se produit entre la paroi et la lame d'air ventilé et entre la paroi et l'environnement extérieur. La modélisation numérique de ces phénomènes physiques couplés est complexe. Nous avons alors suivi une démarche scientifique explicite qui consiste, dans un premier temps en une simplification du modèle grâce à l'approche de Darcy simple dans le milieu poreux et aux équations de la convection forcée. Notre objectif est de mettre en exergue les transferts hygrothermiques entre le mur humide et le canal d'air ventilé, en supposant que la face externe de la paroi est en conditions adiabatiques et que le milieu poreux est saturé en eau. Dans un second temps, le modèle est étendu vers un modèle généralisé basé sur l'approche de Luikov qui assimile la paroi à milieu poreux partiellement saturé sous conditions diabatiques. Ces équations de transferts hygrothermiques sont résolues par une méthode hybride combinant la méthode de Lattice - Boltzmann, la méthode des volumes finis, et la méthode itérative de sur-relaxation ponctuelle.Un jeu de données "matériaux" est identifié par le truchement d'une campagne expérimentales de caractéristiques physiques, hygrothermiques et mécanique afin de constituer des paramètres d'entrée des modèles numériques. Les techniques traditionnelles de construction dans le Nord de la France sont ciblées, au travers de parois humides en briques de terre cuite anciennes. À l'aune de ces résultats, le modèle est validé analytiquement, grâce à une démarche proche et simplifiée et expérimentalement, via un dispositif expérimental conçu au sein du laboratoire. Enfin, une étude de sensibilité du modèle aux paramètres d'entrée du modèle est proposée, suivie de l'analyse de l'influence des conditions de soufflage d'air neuf (hygrothermie dynamique) et des conditions environnementales extérieures sur la performance du canal ventilé adossé à une paroi partiellement saturée en conditions diabatiques. Les résultats sont présentés en termes de distributions de température et de teneur en eau pour la paroi, de champs d'isothermes et d'iso-concentration de vapeur d'eau, et de nombres adimensionnés locaux pour identifier la nature des échanges à l'interface entre la paroi humide et l'espace tampon ventilé. De nombreuses perspectives de recherche peuvent se dégager de notre étude, notamment au travers du transfert de cette technologie sur le marché de la rénovation énergétique du patrimoine humide. Outre l'optimisation du fonctionnement du dispositif aéraulique et son automatisation face aux conditions environnementales, un retour d'expérience en site réel occupé est actuellement en cours d'élaboration
As part of the sustainable energy renovation of old buildings and in order to improve the energy efficiency of walls subjected to capillary rise, a new breakthrough technology consists of incorporating a ventilation system of a buffer space located between the thermal insulation and the wet load-bearing framework. This technology is one of the effective and inexpensive solutions to fight against capillary rise, while ensuring the durability of the insulation and the structural durability of the framework.Physically, the aeraulic device based on the generation of a laminar flow of forced convection of fresh air in a vertical channel in contact with the internal surface of the wet wall. This technology then creates an evaporation front at the internal surface of the wall, where as a result, simultaneous hygrothermal exchange occurs between the wall and the ventilated air space and between the wall and the external environment.Numerical modeling of these coupled physical phenomena is complex. We then followed an explicit scientific approach, which firstly consists in a simplification of the model thanks to the simple Darcy approach in the porous medium and to the forced convection equations. Our objective is to highlight the hygrothermal transfers between the humid wall and the ventilated air channel, assuming that the external face of the wall is in adiabatic conditions and that water saturated the porous medium. Secondly, the model extends to a generalized model based on the Luikov approach, which assimilates the wall with a partially saturated porous medium under diabetic conditions. A hybrid method, combining the Lattice - Boltzmann method, the finite volume method, and the iterative succesive over-relaxation method, solves these hygrothermal transfer equations.A "materials" data set identified by means of an experimental campaign of physical, hygrothermal and mechanical characteristics in order to constitute input parameters for the numerical models. Traditional construction techniques in the North of France targeted, through damp walls made of old terracotta bricks. In the light of these results, we can validate the model analytically, thanks to a similar and simplified approach, and experimentally, via an experimental device designed in the laboratory.Finally, a study of the sensitivity of the model to the input parameters of the model proposed, followed by the analysis of the influence of the fresh air blowing conditions (dynamic hygrothermal energy) and of the external environmental conditions on the performance of the ventilated duct leaned against a partially saturated wall in diabatic conditions. The results are presented in terms of temperature and water content distributions for the wall, isothermal fields and iso-concentration of water vapor and local dimensional numbers to identify the nature of the exchanges at the interface between the wet wall and the ventilated buffer space.Many research perspectives can emerge from our study, in particular through the transfer of this technology to the energy renovation market for wet properties. In addition to optimizing the operation of the aeraulic system and its automation in the face of environmental conditions, feedback on a real occupied site is currently being prepared

Bio-based and earth materials are growingly used for the building envelopes because of their numerous benefits such as slight environmental impact, great hygrothermal performances, effective regulation of the perceived indoor air quality and human comfort. In such materials, the phenomenon of mass transfer is complex and has a great impact on the performance of building envelope. Therefore, it is important to identify and understand the hygrothermal phenomena to be able to simulate accurately the envelope behavior. Nevertheless, the classical models that depict hygric transport within building materials seem not accurate enough for bio-based materials as they are simplified on several points of view. The correlation that exists between water content and relative humidity is mostly simplified and is modeled by a single curve, the hygric storage capacity is often overstated and the hysteresis is neglected. This paper deals with numerical study of hygric transfer within hemp-earth building material by using WUFI® Pro 6.5, a commercial software, and TMC code developed at the LGCGM (Moissette and Bart, 2009) . This code was validated regarding EN 15026 standard (Moissette and Bart, 2009) and has evolved over the years by integrating the hysteresis phenomena (Aït-Oumeziane et al., 2015). Thus, a significant enhancement of the numerical simulations on desorption phase was shown. This study investigates the simulation of MBV test performed on a hemp-earth material for which only the adsorption curve is known as input. Missing parameters (water vapor permeability and desorption curve) are fitted considering the first cycle of MBV test with TMC code. Then, MBV test is simulated with WUFI® Pro 6.5 and TMC code without and with hysteresis. The results highlight the need to include hysteresis to accurately simulate dynamic hygric phenomena, and show that it is possible to find missing parameters by fitting dynamic solicitations.