Development of a simplified model for phase change in presence of natural convection and radiation : application to a novel heat storage translucent superinsulated wall

Cette thèse vise à étudier l'exploitation du rayonnement solaire grâce à un nouveau concept de mur capteur passif. Dans ce contexte, le comportement thermique d’un mur solaire semi-transparent a été étudié. Le mur fournit un éclairage naturel et est composé d’une couche d’aérogel de silice assurant une isolation thermique et acoustique, et d’un MCP. Ce dernier est contenu dans des briques de verre assurant l’absorption, le stockage et la restitution de chaleur. Ce mur a été caractérisé expérimentalement au centre PERSEE à Sophia. Il a été remarqué que la performance thermique du mur est élevée en hiver, tandis qu’une surchauffe estivale a été rencontrée. Un modèle numérique simplifié a été développé pour modéliser la convection naturelle et le rayonnement pendant la fusion du MCP. Ce modèle est validé à l’aide d’un modèle CFD, et des résultats de Benchmark. Pour optimiser la performance du mur en été, un modèle numérique du transfert de chaleur à travers le mur a été développé sous MATLAB. Ce modèle a été couplé à TRNSYS afin d’évaluer la performance thermique de l'ensemble du bâtiment. Le modèle couplé a été validé expérimentalement. Le comportement thermique du mur est testé dans des différents climats, et des solutions passives sont proposées pour assurer le confort thermique. Enfin, ce modèle a permis d'étudier le comportement thermique annuel d’un bâtiment intégrant un mur MCP- aérogel dans son enveloppe et une étude économique a été réalisée. Ces études ont confirmé l'intérêt du mur vis-à-vis de l'amélioration des performances énergétiques du bâtiment. La faisabilité économique de l'application du mur dépend du climat, du coût d’énergie, et du coût d'investissement.This thesis aims to study the exploitation of solar radiation thanks to a new concept of passive sensor wall. In this context, the thermal behavior of a novel semi-transparent solar wall has been studied. The wall is composed of glazing, silica aerogel (TIM) and glass bricks filled with fatty acids (PCM). This wall provides storage and restitution of heat, thermal-acoustic insulation and daylighting. The thermal performance of the TIM-PCM wall is tested in a full-sized test cell located in Sophia, PERSEE center. In winter, particularly in sunny cold days, the PCM absorbs solar radiation, melts, and then releases the stored heat to the building at night. During summer, overheating is encountered, the PCM remains in its liquid state and is unable to release the stored heat. A simplified model for PCM melting in presence of natural convection and radiation is developed and validated using a CFD model, and benchmark solutions. Then, a numerical model describing the heat transfer mechanisms through the wall is developed. This model is linked to TRNSYS to assess the thermal performance of the whole building. The MATLAB-TRNSYS model is then validated experimentally. The thermal behavior of the wall is tested under different climates, and passive solutions are proposed to ensure thermal comfort in summer. Finally, the validated model is used to study the annual thermal behavior of a building integrating TIM-PCM wall and an economic study is conducted. These studies confirm the interest of the wall vis-à-vis the improvement of energy performance of the building. The economic feasibility of applying the TIM-PCM wall depends mainly on climate, energy costs, and investment cost

Modèle simplifié de changement de phase en présence de convection et rayonnement : application à un mur translucide associant superisolation et stockage d'énergie thermiques

This thesis aims to study the exploitation of solar radiation thanks to a new concept of passive sensor wall. In this context, the thermal behavior of a novel semi-transparent solar wall has been studied. The wall is composed of glazing, silica aerogel (TIM) and glass bricks filled with fatty acids (PCM). This wall provides storage and restitution of heat, thermal-acoustic insulation and daylighting. The thermal performance of the TIM-PCM wall is tested in a full-sized test cell located in Sophia, PERSEE center. In winter, particularly in sunny cold days, the PCM absorbs solar radiation, melts, and then releases the stored heat to the building at night. During summer, overheating is encountered, the PCM remains in its liquid state and is unable to release the stored heat. A simplified model for PCM melting in presence of natural convection and radiation is developed and validated using a CFD model, and benchmark solutions. Then, a numerical model describing the heat transfer mechanisms through the wall is developed. This model is linked to TRNSYS to assess the thermal performance of the whole building. The MATLAB-TRNSYS model is then validated experimentally. The thermal behavior of the wall is tested under different climates, and passive solutions are proposed to ensure thermal comfort in summer. Finally, the validated model is used to study the annual thermal behavior of a building integrating TIM-PCM wall and an economic study is conducted. These studies confirm the interest of the wall vis-à-vis the improvement of energy performance of the building. The economic feasibility of applying the TIM-PCM wall depends mainly on climate, energy costs, and investment cost.Cette thèse vise à étudier l'exploitation du rayonnement solaire grâce à un nouveau concept de mur capteur passif. Dans ce contexte, le comportement thermique d’un mur solaire semi-transparent a été étudié. Le mur fournit un éclairage naturel et est composé d’une couche d’aérogel de silice assurant une isolation thermique et acoustique, et d’un MCP. Ce dernier est contenu dans des briques de verre assurant l’absorption, le stockage et la restitution de chaleur. Ce mur a été caractérisé expérimentalement au centre PERSEE à Sophia. Il a été remarqué que la performance thermique du mur est élevée en hiver, tandis qu’une surchauffe estivale a été rencontrée. Un modèle numérique simplifié a été développé pour modéliser la convection naturelle et le rayonnement pendant la fusion du MCP. Ce modèle est validé à l’aide d’un modèle CFD, et des résultats de Benchmark. Pour optimiser la performance du mur en été, un modèle numérique du transfert de chaleur à travers le mur a été développé sous MATLAB. Ce modèle a été couplé à TRNSYS afin d’évaluer la performance thermique de l'ensemble du bâtiment. Le modèle couplé a été validé expérimentalement. Le comportement thermique du mur est testé dans des différents climats, et des solutions passives sont proposées pour assurer le confort thermique. Enfin, ce modèle a permis d'étudier le comportement thermique annuel d’un bâtiment intégrant un mur MCP- aérogel dans son enveloppe et une étude économique a été réalisée. Ces études ont confirmé l'intérêt du mur vis-à-vis de l'amélioration des performances énergétiques du bâtiment. La faisabilité économique de l'application du mur dépend du climat, du coût d’énergie, et du coût d'investissement

Melting of a phase change material in presence of natural convection and radiation: A simplified model for engineering applications

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Melting of a phase change material in presence of natural convection and radiation: A simplified model

International audienceIn this article, a simplified model for melting of a phase change material (PCM) in presence of natural convection and radiation is presented. A modified enthalpy method is adopted to solve the phase change problem, the natural convection occurring in the liquid PCM is accounted for using the enhanced thermal conductivity approach coupled with the scaling theory, and the absorbed shortwave radiation flux is added into the energy equation as a source term using a simplified solution algorithm. Two dimensional implicit finite volume method is used to solve the energy equation. First, the simplified model for melting with natural convection is validated using a CFD model, in addition to experimental and numerical benchmark solutions for a test case. Then, the simplified model for melting with combined natural convection and radiation is applied to the melting of a fatty acid eutectic filled in glass bricks, which will be used later to model the annual thermal behavior of a special translucent façade. This complete model is validated against the lattice Boltzmann-discrete ordinate method LBM-DOM. It was shown that (1) the proposed simplified model is simple to implement and its simulations run significantly faster than those of CFD models and LBM-DOM model. Consequently, it can be easily integrated into an energy simulation tool for yearly performance evaluation, (2) during PCM melting process, natural convection has a noteworthy role as it enhances the average fraction of liquid and the position of the melting front, (3) shortwave radiation enhances the average liquid fraction

Matériaux à changements de phase (MCP) pour le confort d'été

International audienceContexte - Problématiques et Objectifs - Méthodes et Résultats principaux - Travaux futur

Modèle simplifié pour la prise en compte de la convection naturelle dans la modélisation du changement de phase solide-liquide

International audienceUn modèle simplifié basé sur l'approche de la conductivité efficace ainsi que sur la théorie d'échelle est présenté dans ce travail pour modéliser la convection naturelle pendant le processus de fusion d'un matériau à changement de phase. Le modèle mathématique est codé sous MATLAB en utilisant la méthode des volumes finis en deux dimensions. Les résultats du modèle simplifié sont ensuite comparés à ceux d'un modèle CFD complet créé dans COMSOL, et aux résultats numériques des benchmarks trouvés dans la littérature. En particulier, une corrélation du nombre de Nusselt correspondant à notre cas d'étude est trouvée, sur la base du modèle CFD, et est ensuite implémentée dans le modèle simplifié. Les résultats montrent que, pour un temps de calcul largement plus court que celui de la CFD, les valeurs de fraction liquide moyenne et de la position du front de fusion sont acceptables. De plus, Les résultats du modèle de conductivité efficace proposé ont montré un très bon accord avec les résultats numériques des benchmarks

Thermal behavior of a translucent superinsulated latent heat energy storage wall in summertime

International audienceThis paper investigates the thermal performance of a translucent solar wall providing, concurrently, storage and restitution of heat, super thermal-acoustic insulation and daylighting to the interior environment. The wall is composed of glazing, silica aerogel used as a transparent insulation material (TIM) and glass bricks filled with fatty acid, an eutectic phase change material (PCM). To assess the TIM–PCM wall thermal behavior, experimentations were conducted in-situ in a full-sized test cell located in Sophia Antipolis, southern France. Experimental data shows that the tested wall is more effective in winter and might cause overheating during the summer mainly due to solar gains and un-cycling behavior of PCM which remains in liquid state. To enhance the energy performance of the wall in summertime, a numerical model describing the heat transfer mechanisms occurring in the PCM layer in combination with the other transparent wall layers is developed. Then, the model of the wall is linked to TRNSYS software to assess the thermal performance of the whole building. The numerical model is validated experimentally and a good agreement is shown comparing the simulated values with the measured data for seven consecutive days in summer and winter. The importance of considering the natural convection effect in the liquid PCM is also demonstrated. Moreover, it was shown that shading devices can effectively reduce overheating while natural night ventilation decreases the indoor temperature without affecting the PCM performance since the outdoor temperature is always higher than the phase change temperature. The use of a glass with selective solar reflection properties depending on the season instead of the ordinary glazing is shown also to be very effective way to overcome the overheating problem. Finally, the TIM-PCM wall is tested under different climate conditions and passive solutions are given to ensure thermal comfort in summer season

Simplified Model Taking into Account the Natural Convection during Melting of PCM

International audienceOutline : Introduction – Objectives - Physical phenomena - Case study - Numerical procedure – Results - Conclusion and perspectiv

Phase Change Materials (PCM) for cooling applications in buildings: A review

International audienceCooling demand in the building sector is growing rapidly; thermal energy storage systems using phase change materials (PCM) can be a very useful way to improve the building thermal performance. The right use of PCM in the envelope can minimize peak cooling loads, allow the use of smaller HVAC technical equipment for cooling, and has the capability to keep the indoor temperature within the comfort range due to smaller indoor temperature fluctuations. This article presents an overview of different PCM applications in buildings for reducing cooling loads under different climate conditions, and the factors affecting the successful and the effective use of the PCM. Many drawbacks have been found in PCM applications, mainly the intense impact of summer weather conditions over the PCM performance, which prohibits its complete solidification during night, and thus, limiting its effectiveness during the day. Proposed solutions are reviewed in this article. Finally, a topology diagram is presented to summarize the steps leading to an effective use of PCM in building applications

Convection and Radiation During Melting of a Phase Change Material: A Simplified Model for Engineering Applications

International audienceA simplified model for combined natural convection and radiation during melting process of a phase change material (PCM) is presented. First, the simplified model for natural convection during melting is validated using a CFD model, in addition to experimental and numerical benchmark solutions for a test case. Then, the simplified model for both natural convection and radiation is applied to the melting of a fatty acid eutectic filled in glass bricks and validated against lattice Boltzmann-discrete ordinate method (LBM-DOM). Finally, the complete model is applied to study the thermal behavior of a translucent wall; then validated experimentally using a full-scale building located in southern France