Experimental evaluation of passive cooling using phase change materials (PCM) for reducing overheating in public building

Indoor Environmental Quality (IEQ) is essential for the health and productivity of building users. The risk of overheating in buildings is increasing due to increased density of occupancy of people and heat emitting equipment, increase in ambient temperature due to manifestation of climate change or changes in urban micro-climate. One of the solutions to building overheating is to inject some exposed thermal mass into the interior of the building. There are many different types of thermal storage materials which typically includes sensible heat storage materials such as concrete, bricks, rocks etc. It is very difficult to increase the thermal mass of existing buildings using these sensible heat storage materials. Alternative to these, there are latent heat storage materials called Phase Change Materials (PCM), which have high thermal storage capacity per unit volume of materials making them easy to implement within retrofit project. The use of Passive Cooling Thermal Energy Storage (TES) systems in the form of PCM PlusICE Solutions has been investigated in occupied spaces to improve indoor environmental quality. The work has been carried out using experimental set-up in existing spaces and monitored through the summer the months. The rooms have been monitored using wireless temperature and humidity sensors. There appears to be significant improvement in indoor temperature of up to 5°K in the room with the PCM compared to the monitored control spaces. The success of PCM for passive cooling is strongly dependent on the ventilation strategy employed in the spaces. The use of night time cooling to purge the stored thermal energy is essential for improved efficacy of the systems to reduce overheating in the spaces. The investigation is carried within the EU funded RESEEPEE project

Latent Thermal Energy Storage Technologies and Applications: A Review

The achievement of European climate energy objectives which are contained in the European Union's (EU) “20-20-20” targets and in the European Commission's (EC) Energy Roadmap 2050 is possible, among other things, through the use of energy storage technologies. The use of thermal energy storage (TES) in the energy system allows to conserving energy, increase the overall efficiency of the systems by eliminating differences between supply and demand for energy. The article presents different methods of thermal energy storage including sensible heat storage, latent heat storage and thermochemical energy storage, focusing mainly on phase change materials (PCMs) as a form of suitable solution for energy utilisation to fill the gap between demand and supply to improve the energy efficiency of a system . PCMs allow the storage of latent thermal energy during phase change at almost stable temperature. The article presents a classification of PCMs according to their chemical nature as organic, inorganic and eutectic and by the phase transition with their advantages and disadvantages. In addition, different methods of improving the effectiveness of the PCM materials such as employing cascaded latent heat thermal energy storage system, encapsulation of PCMs and shape-stabilisation are presented in the paper. Furthermore, the use of PCM materials in buildings, power generation, food industry and automotive applications are presented and the modelling tools for analysing the functionality of PCMs materials are compared and classified

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

International audienc

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

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

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

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