Développement d'un modèle de Boltzmann sur gaz réseau pour l'étude du changement de phase en présence de convection naturelle et de rayonnement

La réduction des émissions de gaz à effet de serre (GES) passe par la réduction des consommations d énergie. Le stockage de la chaleur dans les parois des bâtiments permet de réduire la consommation d'énergie. Parmi les techniques de stockage, le stockage latent a la capacité de stocker une quantité d énergie par unité de volume plus importante qu un système sensible. Le projet INERTRANS a proposé le développement d une façade associant une isolation translucide et le stockage latent avec un matériau à changement de phase (MCP). La fusion du MCP s accompagne de la convection naturelle et l absorption ou transmission du rayonnement. Le couplage de l ensemble de ces phénomènes n a pas été étudié dans la littérature. Dans cette thèse un modèle numérique 2D pour l étude du changement de phase a été développé. Ce modèle utilise la méthode de Boltzmann sur réseau (LB) à temps de relaxation multiple (MRT), pour la résolution du champ de vitesse et la méthode des différences finies, pour la résolution du champ de températures. Le changement de phase a été traité par la formulation enthalpique. L originalité est l application de ce modèle au problème de changement de phase avec convection naturelle, d une part, et au changement de phase avec convection naturelle et rayonnement, d autre part. Pour vérifier notre modèle sans rayonnement, un cas de référence de la littérature a été simulé. Il s agit de la fusion des deux MCP, l étain et l octadécane, à faible et fort nombre de Prandtl, respectivement. La simulation de l étain a confirmé un écoulement multicellulaire. La simulation de l octadécane a montré une forte influence de la convection avec un front de fusion qui se déforme sur toute la cavité. Le nombre de Nusselt pour l octadécane avec convection est plus de trois fois le Nusselt sans convection. La simulation de l acide gras de la brique INERTRANS a montré que la convection ne doit pas être négligée, car le flux prédit avec convection peut être jusqu à trois fois plus grand que le flux prédit sans convection. La fraction fondue est près du double qu en conduction seule. La méthode LB appliquée aux transferts radiatifs a été étudiée. Il se trouve, qu à l état actuel cette méthode n est pas compétitive par rapport à une méthode classique des ordonnées discrètes (MOD). Enfin, nous avons couplé la MOD pour le calcul du flux radiatif avec la méthode LB pour le calcul du champ de vitesses et des différences finies pour l équation de l énergie. Le rayonnement grande longueur d onde n a pas d influence notable sur les transferts thermiques. Le rayonnement courte longueur d onde augmente les transferts thermiques, pourtant, cet effet n est pas aussi important que l augmentation due à la convection pour le matériau choisi. Puisqu aucune solution de référence n existe dans la bibliographie, nos résultats peuvent désormais servir d éléments de comparaison pour de futurs travaux. Une validation expérimentale constituerait une perspective nécessaire.Reduction of greenhouse gas emissions requires reduction of energy consumption. Energy storage on building walls allows reduction in energy consumption. Among storage techniques, latent heat storage offers higher energy storage density than sensible heat storage. INERTRANS project has proposed the development of an innovative facade, coupling transparent insulation and energy storage with a fatty acid phase change materials (PCM). Melting of PCM comprises different phenomena, namely, natural convection in the liquid phase and radiation absorption or transmission. The coupling of all this phenomena is not still studied in scientific literature. In this thesis, a 2D numerical model for studying phase change has been developed. This model uses the lattice Boltzmann method (LBM) with multiple relaxation time (MRT) to resolve velocity field, and finite differences for the temperature field. Phase change is treated with the enthalpy formulation. The original contribution is application of this hybrid approach to the phase change with natural convection, on the one hand, and to the phase change with natural convection and radiation, on the other hand. To verify the model without radiation, a test case taken from literature has been simulated. It concerns the melting of two PCM with a low and high Prandtl number, the tin and octadecane, respectively. Tin melting simulation confirms multiple cells flow, starting with four rolls which merges in three then two rolls. Octadecane simulation shows high convection effect, with a melting front deforming all along the cavity height. Nusselt number plot for octadecane melting with convection is more than three times with conduction only. INERTRANS fatty acid simulation shows that convection shall not be neglected, because predicted heat flux with convection may be up to three times that predicted with conduction only. Melted fraction is almost twice than with conduction only. The lattice Boltzmann method applied to radiative heat transfer has also been explored. It turns out that in its current state, this method is not competitive compared to a conventional discrete ordinates method (DOM). Finally, we coupled the DOM for radiation heat flux, with the LBM for velocity field calculation and finite differences for the energy equation to solve the coupling between phase change, convection and radiation. Long wavelength radiation has no noticeable effect on heat transfer. Short wavelength radiation increases heat transfer, however, this increase is not as important as that produced by convection for this kind of material. Since no reference solution exists in the literature, our results can now serve as a basis for future work. An experimental validation would be a necessary perspective.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Event-Driven User-Centric Middleware for Energy Efficient Buildings and Public Spaces

In this work, the design of an event-driven user-centric middleware for monitoring and managing energy consumption in public buildings and spaces is presented. The main purpose is to increase the energy efficiency, reducing consumption, in buildings and public spaces. To achieve this, the proposed service-oriented middleware has been designed to be event based, also exploiting the user behaviours patterns of the people who live and work into the building. Furthermore, it allows an easy integration of heterogeneous technologies in order to enable a hardware independent interoperability between them. Moreover, a Heating Ventilation and Air Conditioning (HVAC) control strategy has been developed and the whole infrastructure has been deployed in a real-world case study consisting of a historical building. Finally the results will be presented and discusse

Vers une méthode de conception HYGRO-thermique des BATiments performants : démarche du projet HYGRO-BAT

Cet article présente la démarche mise en oeuvre dans le projet collaboratif ANR Hygrobat, qui vise à donner des outils pour quantifier de manière fiable l'impact des transferts de masse sur les transferts de chaleur dans les parois de bâtiments comprenant des matériaux fortement hygroscopiques. Les matériaux sélectionnés dans ce projets (fibre de bois, bois massif, OSB) ont été soigneusement caractérisés. Leurs propriétés hygrothermiques ont été mesurées en laboratoire, puis ils ont été mis en oeuvre dans des parois, soumises à des conditions aux limites de variées. L'originalité de l'étude réside dans : (i) la démarche "pas à pas" de complexité croissante, partant des caractérisations d'un seul matériau en conditions stationnaires, jusqu'aux mesures sur une paroi multicouche en climat réel ; (ii) les vérifications croisées de mesures expérimentales, qui sont effectuées dans deux des laboratoires partenaires du projet, parfois sur des dispositifs différents ; (iii) association des benchmarks expérimentaux et numérique

Contribution à la qualification des systèmes de ventilation des bâtiments

Aujourd'hui l'homme passe plus de 90% de son temps dans des ambiances artificielles : bureaux, habitats, transports. La qualité de ces ambiances constitue donc un enjeu important pour garantir la santé et le confort des occupants. Les systèmes de ventilation contibuent fortement à la qualité de ces ambiances intèrieures. Les travaux présentés dans ce mémoire étudient la qualité des ambiances intérieures de bâtiments au travers de deux critères : l'efficacité de la ventilation et le confort thermique. Il s'agit d'un travail essentiellement expérimental mis en oeuvre sur une cellule d'essai en grandeur réelle. Divers systèmes de chauffage, dits "éléments perturbants", sont intégrés afin d'observer leur influence sur l'efficacité du système de ventilation en place et le confort thermique pour un occupant. Le confort thermique est abordé à l'aide des indices PMV et PPD. Des essais monozones et bizones ont été effectués. Les champs de températures d'air, de vitesses d'air et de concentrations en gaz traceur sont établis et étudiés. A partir des mesures réalisées, nous déterminons l'efficacité d'extraction des polluants et les indices PMV et PPD. Par ailleurs, une étude numérique est menée afin de comparer un cas expérimental avec des résultats issus d'une simulation numérique avec un code CFD (FLUENT).VILLEURBANNE-DOC'INSA LYON (692662301) / SudocLA ROCHELLE-BU (173002101) / SudocSudocFranceF

2D Conduction Simulation of a PCM Storage Coupled with a Heat Pump in a Ventilation System

Efforts to simulate heat transfer in a PCM (Phase Change Material) storage device are generally led by considerations of Biot number and material thickness, of 2D versus 1D representation, and of possible hysteresis effects arising from the characterisation of the PCM using differential scanning calorimetry (DSC). In this paper we present a numerical treatment of heat conduction in a paraffin-based storage brick, based on experimental data for a full scale, heat storage component studied under laboratory conditions. The PCM was modelled adopting equivalent thermophysical properties during the phase change. An equivalent heat capacity and thermal conductivity were provided for an appropriate description of energy release and storage in the process of solidification and melting. The geometry of the metal container induces 2D effects that are generally neglected in numerical modelling. The thickness of the plates (about 2 cm) is sufficiently large to require the modelling of conduction in the PCM, but can also induce convection that has been neglected in this study. Experimental results are presented and compared for both a 1D and 2D model of the PCM device. It was concluded that a 2D representation is essential for configurations; like the case study and geometry we had; with a large difference in thermal conductivity between PCM and metal casing. Two curves of equivalent heat capacity (measured via DSC) were introduced for heating and cooling phases. Comparisons to experimental results indicated significant errors in the models during melting and solidification of the PCM, which could be reduced by instead adopting the mean of the two heat capacity curves. The rate of temperature change during the experiments and for the DSC characterisation was analysed and found to explain well the observations. In particular, as novelty, two peaks of equivalent heat capacity have been observed with DSC when the rate is very low instead of only one peak using current rate: and that explains the real behaviour in the experiments

Modeling of an active facade containing Phase Change Materials

International audienceToday there are several technologies to improve energy efficiency in buildings. One of the most used methods is to intervene at the thermal envelope insulation, which reduces heat losses in winter or gains in summer. A more advanced technique is to design an active envelop (coupled to the ventilation system) to make the best solar gains.The Trombe wall is a well-known technology to exploit solar radiation storing thermal energy in the building envelope and restitute it during night for the winter application. This system can so reduce the energy requirements of the building ensuring a level of comfort to the occupants. For the thermal energy storing of this structure it is possible to introduce phase change materials (PCM), which allows an increase of the the wall’s performance, by reducing the thickness, which is also a benefit to the architectural level. This paper presents a numerical code for simulating the behavior of a Trombe wall incorporating one or two layers of PCM. For this, we started with an existing model under TRNSYS environment (Type36) representing a classical Trombe wall and we changed it to allow the introduction of phase change materials. Parametric studies are then presented and analyzed.The results show that, compared to conventional Trombe wall, phase change materials present several assets and ensure a reduction in heat loss increasing the thermal performance of the façade

Experimental assessment of a phase change material for wall building use

The thermal performances of a PCM copolymer composite wallboard has been experimentally investigated in a full scale test room. The test cell is totally controlled so that a typical day can be repeated (temperature and solar radiative flux). Effects of the PCM are investigated comparing the results obtained with and without composite wallboards for three cases: a summer day, a winter day and a mid-season day. The results show that: (1) for all the cases tested, the decrement factor varies between 0.73 and 0.78 which is quite interesting for use in buildings and particularly for renovation; (2) the air temperature in the room with PCM lowers up to , the comfort enhancement is more important if the surface temperatures are also considered; (3) the PCM wallboards enhance the natural convection in the room and then there is no thermal stratification contrary to the room without composite; (4) the numerical experiments are fully described and can then be used to evaluate PCM numerical modeling.Phase change material Wallboard Energy storage Experimental investigation Temperature fluctuation

Multi-source energy systems analysis using a multi-criteria decision aid methodology

International audienceIn this article, an original multi-criteria approach is applied to multi-source systems used for the design and the choice of the optimal alternative. The high number of alternatives and potential solutions when dealing with multi-source systems require a decision support method to be implemented and easy to use. Information data on the economic variables, energy performance and impact on the environment of the systems are presently data which analysis and quantification is difficult. To deal with this high level of complexity and uncertainty, an evaluation approach is needed. The multi-criteria decision support methodology concept is described (ELECTRE III) and then applied for a case study. The decision support algorithm has its bases on the developed models and makes the outranking of possible solutions. It is also shown that multi-criteria analysis can provide a technical-scientific decision-making support that is capable to justify the clearly rank of the alternatives in the renewable energy sector. The use of multi-criteria decision aid for assessing the multi-source systems showed encouraging results and interesting insights

Space heating control of an individual dwelling by a fuzzy controller acting on the flowrate of a heating floor

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