Simple Model for the Theoretical Survey of the Green Roof Thermal Behavior

A green roof is an option for the improvement of a building thermal comfort. The objective of this work is to compare respective behaviors of a green roof and a concrete watertight roof vis-à-vis external requests in wet tropical zones. The canopy being considered as uniform, the electric analogy method was used to establish the mathematical models associated to both studied systems of roof. Based on these models, a Matlab computing code was worked out. It ensues from simulation results that in diurnal period, the green roof concrete support top face temperature is lower than that of the concrete watertight roof top face, whereas in night-period the opposite occurs. These results which highlight the energy benefit of the green roof are in agreement with the experimental measurement results obtained at the Laboratory PIMENT of the University of La Reunion. Besides, results of sensitivity analysis done with Fourier Amplitude Sensitivity Test enabled to identify a certain number of the most influential parameters of the proposed model. The above mentioned computing code also forms a help tool for the choice of plants to be experimented on the green roof

DISH STIRLING SYSTEM POTENTIAL ASSESSMENT FOR EIGHT MAIN SITES IN MADAGASCAR

International audienceSolar energy is a green and attractive renewable energy source that can be converted for power generation. The objective of this work is to evaluate the potential of dish Stirling systems if they are used in the fourth worldwide largest island of Madagascar. For that purpose, a theoretical model of the dish Stirling system based on the geometrical configuration and heat transfer was developed and coded on Matlab. Simulations were run to investigate the energy efficiency variation of the system for eight main sites in Madagascar. As results, the proposed model enables to represent the system thermal behaviour to assess its efficiency. Among the eight studied sites, those which are on the coastal zones are more propitious to the dish Stirling system. While, in the north and northwest, the sites of Diego Suarez and Majunga present high efficiencies with, respectively, 31.65(%) and 31.07(%), it is in the south in fort-dauphin that thermal efficiency rate is maximal with 32.17(%). Convincing results that suggest that the implementation of this kind of facility will solve a large part of energy supply problems in these regions

Etude théorique du séchage thermique et de la digestion anaérobie des boues des stations d’épuration – Mise au point des dispositifs pilotes de laboratoire pour la caractérisation expérimentale liée au séchage et à la méthanisation des boues

Reunion Island is a member of the Indian Ocean Commission. After having evoked the problematic and the socio-economic context related to wastewater treatments and to the elimination of sewage sludge in this island, the author did a theoretical prediction survey of the behaviour of a natural convection functioning greenhouse-dryer towards sewage sludge. Then, he did a theoretical study of a forced convection functioning solar dryer that is equipped of an electrical balance system of heating. For each of these two theoretical studies, the author worked out a Matlab code that simulates the mathematical model related to the studied drying system and did a parametric sensitivity test of that model. For that purpose, he used the screening method of Morris as well as the TMA method (Thiery Mara Analysis) that is a variant of the FAST method (Fourier Amplitude Sensitivity Test). These analyses enabled, among others, to identify parameters which are the most influential on the drying kinetics of sewage sludge. Thus, the instrumentation of the pilot laboratory dryer that this project aims to put in place was achieved by taking this information in account. The sludge drying experimentation being projected to an ulterior date, some experimentation tests with this device were done on some organic products, namely : pineapple and banana as well as cooked rice for which a model of drying kinetics was developed. The last part of this dissertation is devoted to biogas production from sludge. Two models of anaerobic digestion of fermentable wastes were presented, deepened and encoded on Matlab. The first model, that is proposed by Kiely and al., is adapted to the case of infinitely stirred digesters for pasty organic wastes. The second type of anaerobic digestion model studied here is proposed by Bernard and al. and corresponds to continuously fed digesters for liquid substrates. The analysis of parametric sensitivity of these models by means of the TMA method was also made and permitted to pinpoint their most influential parameters. That helped the author, first, on the choice of the shape of the mathematical model to be established for governing the anaerobic digestion of sewage sludge from wastewater plants, and second, on the choice of the experimental measurement devices to equip the pilot digester that he put in place for the future campaign of data collection.L’île de La Réunion fait partie des pays membres de la Commission de l’Océan Indien. Après avoir évoqué les problématiques et le contexte socio-économique liés à l’assainissement des eaux usées et à l’élimination des boues d’épuration produites dans cette île, l’auteur a effectué l’étude de prédiction théorique du comportement d’un séchoir-serre à convection naturelle vis-à-vis des boues. Puis, il a enchaîné avec l’étude théorique d’un séchoir solaire fonctionnant en convection forcée et qui est équipé d’un système d’appoint conventionnel de chauffage. Pour chacune de ces deux études théoriques, l’auteur a élaboré, sous environnement Matlab, un code de calcul simulant le modèle mathématique associé au système de séchage étudié et a mené une analyse de sensibilité paramétrique de ce modèle. Pour ce faire, il s’est servi de la méthode de screening de Morris ainsi que de la méthode TMA (Thiery Mara Analysis) qui est une variante de la méthode FAST (Fourier Amplitude Sensitivity Test). Ces analyses ont permis, entre autres, d’identifier les paramètres les plus influents sur la cinétique de séchage des boues. Ainsi, l’instrumentation du séchoir pilote de laboratoire que ce projet vise à mettre en place a été réalisée à la lumière de ces informations. L’expérimentation de séchage de boues étant projetée ultérieurement, des essais de mise en œuvre d’expérimentation avec ce dispositif ont été menés sur quelques produits organiques, à savoir: l’ananas et la banane ainsi que le riz cuit pour lequel un modèle de cinétique de séchage a été développé. La dernière partie de cette dissertation est consacrée à la méthanisation des boues. Deux modèles de digestion anaérobie de déchets fermentescibles ont été présentés, approfondis et encodés sous Matlab. Le premier modèle, qui est proposé par Kiely et al., est adapté au cas des digesteurs du type infiniment mélangé traitant des déchets organiques supposés pâteux. Le second type de modèle de digestion anaérobie étudié ici, correspond au digesteur fonctionnant en continu et traitant des substrats liquides. Il s’agit du modèle avancé par Bernard et al.. L’analyse de sensibilité paramétrique de ces modèles à l’aide de la méthode TMA a également été faite et a permis de déceler les paramètres les plus influents. Cela a aidé l’auteur sur le choix de la forme du modèle à établir pour gouverner la digestion anaérobie des boues des stations d’épuration ainsi que sur le choix des appareils de mesure expérimentale à équiper le digesteur pilote qu’il a mis en place pour la future campagne de mesure

Life Cycle Analysis of Green Roof Implemented in a Global South Low-Income Country

International audienceEnvironmental protection becomes a global challenge currently. Green roof is one of the innovativeconcepts to face this battle. An increase in its use is noticed in urban areas worldwide. But a question arises: what are the environmental consequences of the green roofs’ life cycle? In this paper, the environmental performance of two complete systems of lighter and heavier green roofs implemented in a global south low-income country are analyzed and compared in order to determine the potential impacts of both types of green roof systems. For proposing solutions aiming at reducing environmental loads of green roofs, Life-Cycle Assessment (LCA) approach was used in the present study. For this purpose, the approach consists of the following phases: definition of the objective, life cycle inventory, characterization of impacts, and interpretation of results. LCA calculations were done with the help of OpenLCA software. Results show that, non treated materials and / or imported ones are more environmentally impactful. Hence, it is profitable to reduce the use of cement, gravel, virgin plastics, and soil as well as imported materials whose transport is done by plane. In addition, use of natural fertilizer for amending the growth substrate and water from well for watering the green roof, is also recommended

Dynamic Simulation of the Green Roofs Impact on Building Energy Performance, Case Study of Antananarivo, Madagascar

Green roofs improve building energy performance and constitute an alternative to sustainable buildings. A green roof model is dynamically coupled with a building thermal model to assess its energy performance that takes into account the indoor air temperature dynamic changes. Under the climate conditions in Antananarivo, we compared green and conventional roofs. The present study shows that green roofs protect the roof structure under extreme temperature and large temperature fluctuations. For the case of Antananarivo, the amplitude of the temperature fluctuations at the top face of the support is reduced by 28 °C when using green roof. The impact of the green roof on indoor air temperature and energy demand is investigated. The vegetation decreases the maximum indoor air temperature and improves the building thermal comfort during summer days. It has no effect on the minimum indoor air temperature, but additional soil thickness can increase it. In addition, a global sensitivity analysis, which is carried out on the proposed model without considering any specific weather data, allows us to identify the most influential parameters on the energy demand. It has been found that green roofs have almost insignificant thermal impact in insulated buildings; however, their potential prevails over the building envelope and weather characteristics in the case of non-insulated building

Techno-Economic Investigation of a Thermal Cure Center Excess Heat Recovery System for Producing Hot Water for a Hotel in Antsirabe Madagascar

Energy saving is a significant feature to take in account in the choice of renewable energy technologies to use. This paper techno-economically investigates an excess heat recovery system that is proposed to be installed in a thermal cure center geothermal source for producing domestic hot water to be conveyed through piping to a nearby three star hotel located in Antsirabe Madagascar. For that purpose, the hotel hot water needs were determined by using an available online free code, called Solo, and the effectiveness-NTU method was used to size the plate heat exchanger to be used to recover the geothermal heat. The proposed hybrid geothermal solution performance was compared with that of hybrid solar energy water-heaters in terms of electricity consumption related to water temperature adjustment. It follows from comparison results that the proposed hybrid geothermal solution is more profitable and allows about 73.2 (%) of electric energy saving while it is 54.9 (%) for hybrid solar option. Besides, economic evaluation confirmed that the geothermal installation allows a shorter return on investment more favorably

Sensitivity Analysis to Optimize a Solar Absorption Cooling System

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Modélisation et analyse de sensibilité globale d’un toit vert en zone tropicale humide

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Numerical investigation of green roof performance

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