Natural cross-ventilation of buildings, an experimental study

International audienceNatural cross ventilation can be a promising passive solution for summer thermal comfort in buildings. It takes advantage of the night temperature of the air to cool the walls of the building. Although this technique is well-known in hot climate, its use in new buildings requires being able to predict the quantity of heat that can be dissipated. There is indeed a lack of experimental data either to build design rules for engineers or to validate numerical code dedicated to the design. In this study, experimental research is carried out on a full-scale dwelling and a small-scale model, and evidence is given on the relevance of such a comparison. The flow has been estimated with spatially discrete local sensors in both systems, and flow visualizations have been additionally performed in the small-scale controlled model. For windy periods, the indoor airflow is found to be driven by the wind, as expected. For calm periods which are critical for summer comfort, the flows look much more complex with the observation of unsteady flow reversals

Convection naturelle dans un canal vertical en eau avec chauffage pariétal : influence de la stratification

Pour des applications liées à l'intégration de l'énergie solaire sur les bâtiments, nous étudions la convection naturelle qui se développe dans un canal vertical ouvert en haut et en bas avec un chauffage pariétal. Le fluide est de l'eau pour s'affranchir des problèmes de rayonnement entre parois. Nous présentons des mesures expérimentales de température, de flux de chaleur et de vitesse dans le canal. Outre des corrélations globales à l'échelle du canal, nous présentons des résultats issus de mesures en deux points très proches de température et de vitesse

Etude d'une paroi ventilée multifonctionnelle adaptée à la rénovation énergétique des bâtiments par l'intérieur

Le secteur tertiaire représente une source potentielle d'économie incontournable pour parvenir à réduire la dépendance énergétique de la France. Le taux de renouvellement du parc immobilier Français étant relativement faible, un effort doit être porté sur l'existant. Dans ces travaux, nous étudions un procédé innovant de rénovation par l'intérieur, dont l'élément principal est une paroi ventilée multifonctionnelle, assurant l'isolation, l'émission de chaleur basse température ainsi que la finition des surfaces murales. Les premiers travaux sur cette paroi ventilée furent menés sur un prototype dimensionné _a l'aide d'un modèle numérique simplifié. Deux séries d'expériences menées dans une cellule climatique nous ont permis de quantifier les flux de chaleur à travers le système. Le bon fonctionnement de la paroi ventilée repose sur les mécanismes de convection naturelle dans un canal vertical. Les résultats issus du prototype ont montré la présence de phénomènes complexes intervenant au sein de l'écoulement. Nous avons donc choisi d'étudier plus en détails les phénomènes thermoconvectifs dans un système du type source chaude/cheminée avant de poursuivre l'étude sur le système global. Une étude théorique et une expérience ont été menées sur un cas académique du problème. A l'issue des résultats expérimentaux, nous avons observé plusieurs régimes d'écoulements, dépendants du rapport de forme du canal et du nombre de Richardson en sortie. Enfin, nous proposons un modèle analytique de la paroi ventilée comprenant l'ensemble des variables géométriques influentes. Ce modèle a été implémenté dans l'environnement de simulation Trnsys, dans la perspective d'effectuer des simulations annuelles à l'échelle du bâtiment.In France, energy consumption due to buildings heating is an important part of the global primary energy consumption. The tertiary sector represents an unavoidable source of economy in order to reduce energy dependency of France. The turnover of French real estate being relatively low, an effort must be focused on the existing. In this work, we investigate on an innovative process of internal thermal renovation, whose main element is a multifunctional ventilated wall, providing insulation, low temperature heat emission and the wall surfaces finishing. The first works on this ventilated wall were conducted on a prototype designed using a simplified numerical model. Two series of experiments conducted in a climatic cell allowed us to quantify the heat flow through the system. The smooth functioning of the ventilated wall is based on the natural convection in a vertical channel and the results from the prototype showed the presence of complex phenomena within the flow. We therefore chose to study in detail the thermoconvective phenomena in a chimney-like system before continuing the study of the overall component. A theoretical study and PIV experiment were conducted on an academic case of the problem. At the end of the experimental results, we observed several flow regimes, depending on the channel aspect ratio and the outlet Richardson number. Finally, we propose an analytical model of the ventilated wall including all influential geometrical variables. This model has been implemented in the simulation environment Trnsys with the perspective to make annual simulations on a building scale.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Design processes and multi-regulation of biomimetic building skins: A comparative analysis

Biomimetics is an opportunity for the development of energy efficient building systems. Several biomimetic building skins (Bio-BS) have been built over the past decade, however few addressed multi-regulation although the biological systems they are inspired by have multi-functional properties. Recent studies have suggested that despite numerous tools and methods described in the literature for the development of biomimetic systems, their use for designing Bio-BS is scarce. To assess the main challenges of biomimetic design processes and their influence on the final design, this paper presents a comparative analysis of several existing Bio-BS. The analyses were carried out with univariable and multivariate descriptive tools in order to highlight the main trends, similarities and differences between the projects. The authors evaluated the design process of thirty existing Bio-BS, including a focus on the steps related to the understanding of the biological models. Data was collected throughout interviews. The univariate analysis revealed that very little Bio-BS followed a biomimetic design framework (5%). None of the Bio-BS was as multi-functional as their biological model(s) of inspiration. A further conclusion drawn that Bio-BS are mostly inspired by single biological organisms (82%), which mostly belong to the kingdom of animals (53%) and plants (37%). The multivariate analysis outlined that the Bio-BS were distributed into two main groups: (1) academic projects which present a strong correlation with the inputs in biology in their design processes and resulted in radical innovation; (2) public building projects which used conventional design and construction methods for incremental innovation by improving existing building systems. These projects did not involve biologists neither a thorough understanding of biological models during their design process. Since some biomimetic tools are available and Bio-BS have shown limitations in terms of multifunctionality, there is a need to promote the use of multidisciplinary tools in the design process of Bio-BS, and address the needs of the designers to enhance the application of multi-regulation capabilities for improved performances

Hybrid III-V on silicon lasers for photonic integrated circuits on silicon

This paper summarizes recent advances of integrated hybrid InP/SOI lasers and transmitters based on wafer bonding. At first the integration process of III-V materials on silicon is described. Then the paper reports on the results of single wavelength distributed Bragg reflector lasers with Bragg gratings etched on silicon waveguides. We then demonstrate that, thanks to the high-quality silicon bend waveguides, hybrid III-V/Si lasers with two integrated intra-cavity ring resonators can achieve a wide thermal tuning range, exceeding the C band, with a side mode suppression ratio higher than 40 dB. Moreover, a compact array waveguide grating on silicon is integrated with a hybrid III-V/Si gain section, creating a wavelength-selectable laser source with 5 wavelength channels spaced by 400 GHz. We further demonstrate an integrated transmitter with combined silicon modulators and tunable hybrid III-V/Si lasers. The integrated transmitter exhibits 9 nm wavelength tunability by heating an intra-cavity ring resonator, high extinction ratio from 6 to 10 dB, and excellent bit-error-rate performance at 10 Gb/s

Développement expérimental et simulation d un capteur solaire hybride photovoltaïque-thermique

L intérêt grandissant pour les bâtiments à haute efficacité énergétique nécessite le développement de nouveaux types d enveloppe active et multifonctionnelle pouvant couvrir une partie des besoins énergétiques du bâtiment. Les travaux présentés dans cette thèse concernent le développement de capteurs hybrides solaires photovoltaïques thermique pour la production simultanée d eau chaude sanitaire et d électricité au sein d un unique capteur. L objectif de cette thèse a été dans un premier temps d analyser la faisabilité et la complexité du concept de capteur hybrides PV-T. Puis, à partir d un modèle numérique développé spécifiquement pour appuyer la phase de conception du capteur PV-T les raisons expliquant la limitation des performances de tels capteurs ont été analysées, pour enfin proposer différentes solutions innovantes, tant au niveau des cellules solaires que des matériaux du modules PV et du design du capteur final afin d en augmenter les performances. L approche développée est par conséquent multi-échelle allant de la prise en compte des phénomènes physiques pris isolément, des propriétés locales des matériaux jusqu à la mise en œuvre d un composant et à l analyse énergétique et exergétique de ses performances dans un environnement numérique dédié au bâtiment.In the context of greenhouse gas emissions and fossil and fissile resources depletion, solar energy is one of the most promising sources of power. The building sector is one of the biggest energy consumers after the transport and industrial sectors. Therefore, making use of a building s envelope (façades and roofs) as solar collecting surfaces is a big challenge facing local building needs, specifically in regard to heat, electricity and cooling. However, available surfaces of a building with suitable orientation are always limited, and in many cases a conflict occurs between their use for either heat or electricity production. This is one of the reasons why the concept of a hybrid photovoltaic-thermal (PV-T) collector seems promising. PV-T collectors are multi-energy components that convert solar energy into both electricity and heat. In fact, PV-T collectors make possible the use of the large amount of solar radiation wasted in PV modules as usable heat in a conventional thermal system. Therefore, PV-T collectors represent in principle one of the most efficient ways to use solar energy (co-generation effect). However, such a concept still faces various barriers due to the multidisciplinary knowledge requirements (material, semi-conductors, thermal) and to the complexity of the multiple physical phenomena implied in such concepts.The objective of this PhD work is to carry out a study based on a multi-scale approach that combines both numerical and experimental investigations regarding the feasibility of the concept of hybrid solar collector. The performance of such components is estimated through an appropriate design analysis, and innovative solutions to design an efficient PV-T collector are presented. Based on improved processing methods and improved material properties, an efficient covered PV-T collector has been designed and tested. This collector was made of PV cells connected to the surface of an optimized flat heat exchanger by an improved lamination process and covered on the front side by a static air layer and AR-coated glass pane and on the back side by thermal insulation material. The results showed a significant improvement of both thermal and electrical efficiency in comparison to all previous works on PV-T concepts found in the literature. System simulations were carried out for a hot water system with the software TRNSYS in order to get a clearer statement on the performance of PV-T collectors. The results show that the integration of PV-T collectors can be more advantageous than standard solar components in regard to thermodynamic considerations (energy and exergy) and environmental considerations (CO2 and primary energy saving).VILLEURBANNE-DOC'INSA LYON (692662301) / SudocVILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Étude des transferts de chaleur dans un canal vertical differentiellement chauffé (application aux enveloppes photovoltaïques thermiques)

Ce travail traite de l intégration des modules photovoltaïques (PV) au bâti. Leur rendement est fortement dépendant du niveau de température d où une intégration par adjonction d une lame d air permettant un rafraîchissement passif. La configuration étudiée est une double-peau photovoltaïque-thermique où l écoulement de convection naturelle se développe sous l effet d une répartition périodique des sollicitations thermiques imposées en flux sur les deux parois du canal. La réalisation d une cellule expérimentale permet d étudier l effet d un chauffage alterné sur les transferts de chaleur. Les mesures de température pariétale et l évaluation des échanges convectifs montrent que la périodicité des sources permet de réduire leur échauffement par rapport à une intégration continue. Ces résultats, confirmés par l étude numérique menée à l aide d un code RANS, conduisent à des tendances intéressantes mais restant à approfondir sur la disposition de composants PV en façade des double-peauxThis work involves the integration of photovoltaic modules within the building frame. The efficiency of PV panels is strongly dependent on their temperature level, which leads to an integration by addition of an air blade allowing their passive cooling. The line-up of the study is a double skin photovoltaic-thermics, where the natural convection develops in the air blade under periodic thermal disturbance imposed on both sides of the channel. The experimental cell made allowing the observation of the effects of an alternate (or continuous) heating on heat transfers. The temperature measurements on the wall and the evaluation of the heat transfer coefficients show that the periodic sources distribution makes it possible to reduce their temperature level compared to the case of a continuous distribution. These results, which are confirmed by a numerical study carried out using a RANS code, lead to interesting tendencies for the integration of PV components that remain to be deepenedLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Unsteady behaviour of natural convection flow in a vertical channel inside a cavity

International audienc

Early-stage natural convection in a vertical channel

International audienceThis work deals with transient natural convection in a vertical channel with wall heating, the channel being located inside a cavity. This experimental work is focused on the first hours after the onset of the heating. The aim of this study is to investigate the link between the heat transfer in the channel with respect to the flow outside the channel. A thermal model of the fluid above the channel is performed and the result fits well with the experimental data. Moreover, the model leads to an expression for the ascending mass flow rate in the channel by using temperature measurements which is an important result because direct measurements remain a tricky problem. This study confirms the approach developed by the same team in a previous wor

Etude des transferts thermiques rayonnement spectral - conduction - convection naturelle dans des systèmes photovoltaïques hybrides en vue de leur intégration au bâti

Ce travail s'attache à l'étude de composants hybrides PhotoVoltaïques/Thermiques en phase d'intégration au bâti. Partant de la problématique liée aux composants PhotoVoltaïques de type cristallin(s) (échauffement diminuant leur efficacité énergétique), le modèle développé vise l'évaluation de leur champ de température interne. Une modélisation du comportement radiatif de composants multicouches de milieux semi-transparents non diffusants est réalisés. La propagation d'un flux collimaté et celle d'un flux diffus sont traitées de manières séparées. La composante collimatée est traitée suivant une approche de type lancer de rayons. La méthode des Ordonnées Discrétes associée à la méthode des volumes finis est employée pour la solution numérique de l'Equation du transfert Radiatif en composante diffuse dans le cas d'une géométrie plane monodimensionnelle. Les quadratures directionnelles sont établis de manière adaptative par couche et pour chaque fréquence spectrale. Les directions discrètes d'une des couches correspondent à celles réfractées de la couche voisine. Le couplage de ce modèle RANS à bas Nombre de Reynolds est ensuite réalisé afin d'étudié les transferts convectifs pour des configurations d'intégration de type double façade. Les perspectives de cette étape consistent à analyser l'influence des paramètres favorisant le rafraîchissement naturel des modules (épaisseur, hauteur lame d'air, distribution spatiale des conditions aux limites thermiques,...). Enfin, le phénomène de conversion électrique, complétant le bilan énergétique d'une cellule PV, est brièvement abordé en adéquation avec le niveau de modélisation des transferts thermiques couplés.This work deals with the study of PhotoVoltaic/Themal hybrid components in building frame integration configuration. Starting from the basis of thermal problems related to the Photovoltaic components of crystalline type (heating decreases their energy effectiveness), the developed model aims at the prediction of their internal temperature field. A modelling of the radiation in a multi-layer component of non diffusing semi-transparent media is carried out. The propagation of a collimated flux and of a diffuse flow are separately treated. The collimated part is treated according to an approach of ray emission model. The Method of the Discrete Ordinates associated the method of finite volumes is employed for the numerical solution of the diffuse radiation in the case of a monodimensional plane geometry. Directional quadratures are established in an adaptative way for each spectral frequency. The discrete directions of one of the layers correspond to those refracted of the close layer. The coupling of this model to a model RANS with low Reynolds number is then carried out in order to study the convective transfers for a double façade configuration of building integration. The prospects for this step consist in analysing the influence of the parameters supporting the natural cooling of the modules (thickness, height of air gap, spatial distribution of the thermal boundary conditions, ). Lastly, the electric phenomenon of conversion, supplementing the energy balance of a cell statement, is briefly approached in adequacy with the level of modelling of the coupled thermal transfers.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF