recherche & développement

S. Giroux-Julien, C. Menezo, J. Vareilles, H. Pabiou, M. Fossa, E. Leonardi. Natural convection in a nonuniformmly channel with application to photovoltaic façades, CTS 2009, Vol 1, Issue 3, p231-258

This paper investigates an active component of the building envelope: a photovoltaic-thermal double-skin facade. This element consists of a vertical open air channel bound by two parallel walls: one is made of photovoltaic panels and one is the main frame of the building. Integrating this system in a building facade is not an easy matter because the electrical output is strongly dependent on the operating temperature of the photovoltaic component. The aim of this study is to promote better cooling of the photovoltaic facade working on its typical geometrical arrangement. This consists of an alternation of photovoltaic cells (localized heat sources) and semitransparent window panes (unheated zones). Fundamentally, the flow of natural convection that develops within the vertical channel appears to be subjected to boundary-localized thermally active areas and adiabatic areas, evenly distributed throughout the height. This requires investigations of parametric variations of magnitude and space frequency of the heated areas as well as intermediate spacing. Two complementary experimental apparatuses were developed, namely, at CETHIL and at the CFD Research Laboratory UNSW in collaboration with the DIPTEM. Experiments were conducted on both. For these experiments, Grashof numbers, based on the channel width and the convective heat flux, are about 1010. The results obtained constitute an important database, which allows characterization of convective heat transfer. Some of the results concern the dynamic boundary conditions that are required for the numerical investigation. The present study compares (on a common operating range) both experimental and numerical investigations focusing on the CETHIL experiments.

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S. Giroux-Julien, C. Menezo, J. Vareilles, H. Pabiou, M. Fossa, E. Leonardi. Numerical and experimental investigation of natural convection in double façades, ICHMT 2008, Marrakech (Maroc), 11-16 May 2008, ICHMT vol 13, Issue 1, p403.

Interests of this paper concern an active component of the building envelope: a photovoltaic-thermal (PV-T) double-skin facade. This element consists of a vertical open air channel bounded by two parallel walls: one made of photovoltaic panels and one been the main frame of the building. The integration of this system in building facade remains not so obvious because electrical output is strongly dependent on the operating temperature of PV component. The aim carried out by our work is to promote a better cooling of the PV facade working on its typical geometrical arrangement. It consists of an alternation of PV cells (localized heat sources) and semi-transparent window panes (unheated zones). Fundamentally, the flow of natural convection which develops within the vertical channel appears to be subjected to boundary localized thermally active areas and adiabatic areas, periodically distributed on the height.
That requires investigations on parametric variations of magnitude and space frequency of heated areas as well as intermediate spacing. The following approach, included in a joint research program between 3 laboratories, the CFD Research Laboratory UNSW (Sydney), CETHIL (Lyon) and DIPTEM (Genoa), in both the experimental and numerical nature of the work.
Two complementary experimental apparatuses have been developed, respectively at CETHIL and at CFD Research Laboratory UNSW in collaboration with the DIPTEM. Experiments were performed on both. For these experiments Grashof numbers, based on the channel width and the convective heat flux, are about 1010. Results that have been obtained constitute an important data base which allows characterizing convective heat transfer. Some concern dynamic boundary conditions which are strongly required for the numerical investigation. First results have been presented concerning the UNSW apparatus (e.g. Ménézo et al. [2007]). The present study consists in a comparison (on a common operating range) among both experiments and numerical investigations focusing on the CETHIL experiments.


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F. Kuznik, J. Vareilles, G. Rusaouen, G. Krauss. A double-population lattice Boltzmann method with non-uniform mesh for the simulation of natural convection in a square cavity, IJHFF 2007, Vol 28, Issue 5, October 2007, Pages 862-870

In this paper, a double-population thermal Lattice Boltzmann method has been proposed to solve the problem of the heated cavity with imposed temperatures. A Taylor series expansion – and least square – based Lattice Boltzamnn method (TLLBM) has been implemented in order to use a non-uniform mesh. This allowed to investigate, at reasonable computational cost, the laminar and transitional flow fields (103 Ra 108). The numerical results, concerning the heat and mass transfers in the cases tested, are in good agreement with those from the literature. This enables the use of such method for predicting thermal flows of engineering interest.


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J. Vareilles, C. Menezo, S. Julien, E. Leonardi, Numerical simulation of natural convection in double façades. IHTC 2006, Sydney (Australie), 13 –18 aout 2006.

The aim of this paper is to investigate the physical mechanisms which drive the thermal behaviour of a double-skin photovoltaic (PV) facade, in order to be able to control the energy impact on buildings. The system consists of a channel between the PV collector and the wall of the building that ensures cooling of the PV modules and the recovery of heat to be used in the building. This permits the production of electricity and heating during cold periods (winter) and free cooling (ventilation) during hot periods (summer), whilst at the same time increasing the efficiency of the PV modules by lowering their temperature. Such natural convection systems are difficult to control and require a detailed study to be undertaken. This work focuses on the effects of alternate layering of the PV modules, which induce alternative heating zones, within the double facade. A parametric study has been performed using a RANS code to determine the best spatial configuration to improve the mixing and efficiency of the heat exchange process. The parametric analysis allows us to focus on configurations which will improve flow destabilization and therefore increase the thermal exchanges in the channel.


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J. Vareilles, S. Giroux-Julien, C. Menezo. Simulation numérique des écoulements de convection naturelle sous perturbations thermiques périodiques : Application aux double-peaux photovoltaïques (PV). SFT 2006, Ile de Ré, 16 – 19 mai 2006.

Ce travail porte sur les écoulements de convection naturelle dans un canal vertical soumis à des perturbations thermiques périodiques réparties de façon alternée sur les deux parois du canal. L’étude paramétrique, réalisée à l’aide d’un code RANS, présente l’influence de la taille et de la position des sollicitations thermiques sur l’écoulement fluide dans le canal. Ceci permet de faire ressortir les configurations qui favorisent le mélange et les transferts de chaleur à l’interface fluide/paroi. L’influence du rayonnement sera prise en compte.


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J. Vareilles, C. Muresan, S. Julien and C. Menezo. Etude numérique des transferts de chaleur et de masse en convection naturelle dans un canal vertical soumis à des perturbations thermiques périodiquement reparties sur ses parois. JITH 2005, Tanger (Maroc), 15 – 17 novembre 2005.

L’étude des écoulements de convection naturelle en canal vertical différentiellement chauffé trouve de nombreuses applications aussi bien dans l’industrie informatique pour le refroidissement des composants électroniques, que dans le bâtiment pour l’optimisation des façades double-peau.
Nous nous intéressons au cas particulier des doubles-peaux photovoltaïques-thermiques (PV-T). Le but recherché est de refroidir au maximum les cellules PV dont la perte de rendement est liée à leur augmentation de température lors de la production d’électricité. L’idée émise est d’arriver à déstabiliser l’écoulement dans le canal en le perturbant thermiquement et d’atteindre ainsi un régime d’écoulement turbulent. L’intérêt d’avoir un écoulement turbulent est que celui-ci s’accompagne d’une augmentation des échanges convectifs. Cette perturbation est réalisée en jouant sur une alternance de zones opaques qui sont des sources de chaleur (panneaux PV) et de zones « froides » transparentes (verre) sur les parois de la double peau .
L’objet de cette étude est donc de présenter l’influence de la répartition des sources de chaleur sur l’écoulement fluide dans le canal. L’approche proposée est numérique et s’appuie sur le code FLUENT. L’objectif à court terme est de compléter cette étude par une approche expérimentale, ainsi que par une étude paramétrique sur le rapport de forme du canal.


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C. Muresan, R. Bennacer, C. Menezo, J. Vareilles and S. Julien. Effect of humidity on the natural convection in a vertical channel. ICCHMT ICCHMT 2005, Paris-Cachan (France), p493, May 17-20

In this paper, a numerical investigation of turbulent convective flows transporting humidity in a vertical heated channel is carried out. The governing equations associated to k-ε low Reynolds models (Jones & Launder and Rodi), are solved in a two-dimensional domain using a control volume method and the SIMPLER algorithm for the velocity pressure coupling is employed. Special emphasis is given in the analysis of the inlet humidity on the transversal profiles of the velocity. The variations in the local Nusselt number depending on the inlet humidity are investigated.


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C. Muresan, J. Vareilles, C. Menezo, S. Julien and R. Bennacer. Numerical predictions of the fluid flow in a photovoltaic double skin. PLEA 2004, Eindhoven (Pays Bas), 19 – 22 sept.

This paper presents a theoretical study of turbulent natural convection flow in a vertical channel with discrete heaters. The influence of the arrangement of the heaters symmetrically or alternated is investigated via global scaled relations. The model used is a k- low Reynolds number model. The background of this theoretical study is related to the integration of a combined photovoltaic-thermal collector as a component of the building’s facades. The heaters modelise the silicon cells which assumed opaque to the solar radiation. The comparison of scaling relations shown that the alternate heating allow a better cooling of photovoltaic facades.


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J. Vareilles, C. Muresan, C. Menezo, S. Julien et R. Bennacer. Convection naturelle dans une double-peau photovoltaïque. IBPSA France 2004, Toulouse (France), 8 – 9 oct.

Ce papier présente une étude théorique de la convection naturelle en régime turbulent dans le cas d’un canal vertical chauffé de manière discontinue sur ses parois. L’influence de la repartition des zones chauffées, symétrique ou anti-symétrique, est étudiée par l’intermédiaire de corrélations. Le modèle utilisé est un modèle k-ε à bas nombre de Reynolds. Cette étude numérique s’inscrit dans le cadre de l’intégration de capteurs photovoltaïques-thermiques comme éléments de façade des bâtiments.
Les zones chauffées représentent les cellules de silicium qui sont supposées être opaques au rayonnement solaire. La comparaison des corrélations montre que l’alternance des zones chauffées permet d’avoir un meilleur refroidissement des façades photovoltaïques.


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