Ocean Thermal Energy Conversion (OTEC) is considered as a non-intermittent base energy resource. It consists in using the difference of temperature between the hot surface seawater in tropical seas and the cold deep seawater to produce electricity by mean of a thermodynamic motor cycle. The Organic Rankine Cycle (ORC) is adapted for this kind of application. In the literature, performances of such a system are often studied under steady state conditions, mainly because the temperature of the sources do not present intermittency. However, the study of the transient behavior of an OTEC power plant could be of major interest for piloting purposes. With this aim, a dynamic model of heat exchanger is presented with the use of a Moving Boundary Model (MBM) in order to distinguish the monophasic and diphasic parts of the transfer. Moreover, experiments have been carried out on an onshore OTEC prototype located in Reunion Island and compared to simulations. The case being studied is an increase of 1 °C of the hot water during 3 minutes leading to a good agreement between simulation and measurement.

 Development of a general model for the choice of the working fluid using Entropic 12 Mean Temperature Difference. 13  Comparison of 26 working fluids over 107 according to four criteria: technicity of the 14 installation, security, environmental impacts and thermodynamic performances.

Un modele dynamique d'un Cycle Organique de Rankine (ORC) applique a l'Energie Thermique des Mers a ete developpe en utilisant un modele a frontieres mobiles pour les echangeurs de chaleur. La simulation de la reponse a un echelon descendant en debit de fluide de travail a alors ete realisee avec comme parametres d'entrees les caracteristiques d'un Prototype A Terre (PAT ETM) a La Reunion. Les resultats montrent que le temps de reponse d'un tel systeme est relativement court (inferieur a 2 minutes) et qu'une utilisation de l'ETM non seulement comme moyen de production de base mais aussi comme outil pour reguler les instabilites sur un reseau electrique est envisageable. Nomenclature A section de passage, m 2 cp capacite calorifique massique, J/kg/K Cv coefficient de debit,-h enthalpie specifique, J/kg L longueur, m m debit massique, kg/s S surface d'echange, m 2 P pression, Pa Q puissance thermique, W q puissance thermique lineique, W/m T temperature, K t temps, s z abscisse le long d'un echangeur, m Symboles grecs  coefficient d'echange, W/m 2 /K  titre en vapeur moyen,- rendement,-  masse volumique, kg/m 3  frequence de rotation, Hz Indices et exposants e entree s sortie p paroi is isentropique turb turbine sat saturation

Climate change is the greatest challenge of our time for development. Adaptation to this change combined with the reduction of greenhouse gas emissions can help to boost the economic transformation which stimulates growth, fills the energy gap and reduces poverty. This paper focuses on the potential of renewable energy sources (RES) for electricity generation in Madagascar which is a lower-income country. A large accessibility to electricity could be a driving force for the economic development of this fourth worldwide Island. The Electricity mix is currently heavily dependent to fossil fuel imports. Indeed, most of the electric demands are fulfilled by diesel power plants. An overview of the power situation and renewable energy potential of Madagascar is first presented, then different scenarios for the evolution its electricity mix are proposed.

A general model of an ORC (Organic Rankine Cycle) that is applicable to various technologies of heat exchangers has been carried out. It has been done considering the entropic mean temperature difference between the heat source and the working fluid as a parameter for heat exchangers. This model allows to compare pure fluids and mixtures in similar operating conditions. Simulations were conducted in the case of OTEC (Ocean Thermal Energy Conversion), for which the inputs are based on experimental measurements on an onshore prototype in Reunion Island. 26 fluids have been compared, considering thermodynamic performances (thermal efficiency and volumic work), technicity, security and environmental impacts. In the end, NH3, R507a and R1234yf appears to be the most suitable ones. In order to have a better understanding of the model and to determine its validity in the whole domain of variation of the parameters for OTEC, a parametric sensitivity analysis has been carried out by ANOVA (ANalysis Of VAriance) associated to polynomial chaos expansion method. The most sensible parameters are heat source temperature, heat exchangers entropic mean temperature difference and turbine isentropic efficiency. The ranking given for the fluids is still valid in the whole range of the parameters for OTEC.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Modélisation et expérimentation d’échangeurs d’un cycle de Rankine pour l’énergie thermique des mers Frantz Sinama, Alexandre Dijoux, Bertrand Clauzade, Olivier Marc, Jean Castaing-Lasvignottes

Un modele de Cycle Organique de Rankine (ORC) permettant de comparer les performances de fluides de travail aux proprietes tres differentes dans des conditions de fonctionnement similaires proches des conditions reelles avec un nombre reduit d'hypotheses a ete developpe, en introduisant la difference de temperature entropique moyenne dans les echangeurs. Une application a l'ETM (Energie Thermique des Mers) a ete realisee, avec une approche multicritere. Une analyse de sensibilite globale du modele basee sur la determination des indices de Sobol a ensuite ete menee. Les resultats montrent que la difference de temperature entropique est un indicateur des performances globales de l'echangeur.

Un modele a ete elabore pour comparer une grande quantite de fluides de travail aux proprietes diverses, notamment des fluides purs et des melanges, dans des conditions similaires de fonctionnement pour un Cycle Organique de Rankine (ORC) a basse temperature de source chaude. Ce modele repose sur l'utilisation de la difference de temperature entropique moyenne dans les echangeurs. Une application a ensuite ete realisee sur l'Energie Thermique des Mers (ETM), en utilisant des donnees experimentales d'un prototype a La Reunion. Il en resulte que l'ammoniac, le R1234yf et le R507a paraissent etre de bons fluides pour l'ETM. Une analyse de sensibilite basee sur la determination des indices de Sobol a ensuite ete menee en considerant 10 parametres d'entree du modele. Celle-ci montre que la sensibilite du modele est peu influencee par le fluide choisi et que les parametres les plus influents sont la temperature de source chaude, les differences de temperatures entropiques moyennes dans les echangeurs et le rendement isentropique de la turbine.

L'ile de La Reunion, situee dans l'Ocean Indien, est confrontee a un contexte energetique complexe. L'utilisation de L'Energie Thermique des Mers (ETM) offre une alternative interessante aux energies renouvelables classiques. En effet, en utilisant la difference de temperature presente entre l'eau de surface (entre 23 et 28 °C selon la saison) et l'eau en profondeur (environ 5°C a 1000 m), il est possible de produire de l'electricite grâce a un cycle organique de Rankine (ORC). Cette technologie entre dans le plan d'autonomie electrique de la Region Reunion prevu pour 2030. Cet article presente l'installation experimentale appelee PAT ETM (Prototype A Terre Energie Thermique des Mers). L'ammoniac est le fluide de travail utilise et le niveau de puissance echangee dans le condenseur ou l'evaporateur est d'environ 500 kW pour une production d'electricite de l'ordre de 15 kW. La qualite des resultats et de l'analyse etant tres dependante des moyens de mesure, un effort particulier a ete realise en la matiere ainsi qu'au niveau du controle/commande sur ce prototype et fait l'objet d'une presentation detaillee. Un seul point experimental est presente et analyse en termes de temperature, de pression, de debit, de puissance et de bilan energetique. Du fait d'un ecart de temperature entre sources assez faible, le rendement thermique est lui aussi faible (2,5 %) mais neanmoins superieur aux valeurs obtenues sur d'autres prototypes. Nomenclature P pression, Pa h enthalpie specifique, J.kg-1 s entropie specifique, J.kg-1 .K-1  W puissance mecanique, W  Q puissance echangee, W  m debit massique, kg.s-1 T temperature, K Indices et exposants R Reel V Virtuel pompe Pompe

Un modele permettant de comparer plusieurs fluides de travail pour un cycle organique de Rankine (ORC) applique a l'energie thermique des mers (ETM) est ici propose en considerant une approche generale qui permet de s'affranchir de la description detaillee des differents composants du cycle. La notion de temperature entropique moyenne est utilisee afin de pouvoir comparer des fluides azeotropiques ou non dans des conditions similaires. Vingt-sept fluides de travail ont ete evalues selon trois criteres : les performances thermodynamiques, la securite et les impacts environnementaux. Trois fluides presentent de bons compromis : le R1234yf, l'ammoniac et le R507a.

The ocean thermal energy conversion (OTEC) process uses the difference in temperature between the warm seawater on the ocean surface and the deep cold seawater to operate a Rankine cycle system for producing electrical power without consuming fossil fuel. This thermodynamic cycle uses a very low temperature gradient that limits its efficiency at 3-5%. Consequently every consumptions and losses of the system have to be optimized to increase the cost-effectiveness of this technology. This paper presents a thermodynamic analysis of a closed OTEC Rankine cycle. The model used in this paper is based on the work of Martins, using the concept of equivalent Gibbs systems. In an equivalent system, mass, energy and entropy are linked through the Gibbs equation, and the entropy production can easily be expressed in terms of fluxes and their related forces. Assuming linear phenomenological laws, the phenomenological coefficients are assessed from technical data. This method permits the study or design of a lot of process engineering. Moreover, a reliable analysis of the second principle can be realized, in order to compare several processes. This method will be used to analyze the cycle, to determine which components need to be optimized. Based on these results, sensitivity analysis are made on these components and the generic optimization program GenOpt is used to determine the optimized parameters of a 10 MW OTEC plant that could be installed on Reunion Island. (C) 2015 Elsevier Ltd. All rights reserved.

During the last twenty years, the comfort and cooling requirements of office buildings and occupants have evolved significantly in Reunion Island, particularly during the summer period. This intensive use of air conditioning has resulted in a significant increase in electricity consumption such as traditional cooling technologies (mechanical vapor compression systems). In this context, solar cooling systems are one of the more interesting alternatives to conventional air conditioning systems. Thus in 2008, the PIMENT laboratory in Reunion Island proposed to set up an experimental platform called RAFSOL, on the University Institute of Technology of Saint-Pierre, to study the absorption solar cooling technology for a University building. Experimental and numerical investigations of RAFSOL allowed to identify several research topics to improve global performances of the installation. One of them concerns the incorporation of a new thermal storage into the solar cooling system. Indeed, the addition of thermal storage (hot and/or cold) give the following advantages: (i) sufficient cooling power to cover the entire building’s needs, (ii) intelligent use the weekend energy potential, (iii) prevents overheating of the solar loop because of lower cooling needs. This thermal storage would also improve the system performance since it brings the temperatures of the hot and cold sources closer to their nominal values and thus optimizes the running time of the absorption chiller. In this work we decided to study only the incorporation of a hot thermal storage composed of a phase change material, and to investigate the influence of this storage on the solar cooling system performances. Three different phase change temperatures are investigated according to the state of art of this echnology: 79, 84 and 90°C. Simulation results are then analyzed and discussed to identify the optimal configuration of the thermal storage. In this first approach, the results show that the most interesting melting temperature, to improve most of performance indicators is 79°C.

This paper presents a dynamic modeling of a single-effect absorption chiller working with LiBr–H2O solution used in a solar cooling installation operating without any backup systems (hot or cold). In this case, the absorption machine is powered only by a solar collector field. Given the highly variable nature of solar radiation and the building loads, the range of the three source temperatures of the chiller can vary widely since there is no backup system. These fluctuating source temperatures mean that the chiller does not operate in steady state phase during the day. The dynamic modeling of the absorption chiller is therefore very important to predict its performance, taking into account both the transient and steady state phases. The numerical model presented in this paper is based on the mass and energy balances of each component, equations of state and equations of heat transfers. In the first part, this article presents the dynamic modeling of a LiBr/H2O absorption chiller. Then, experimental validation elements are proposed to validate pressures and temperatures of the chiller. Finally, a method is presented to optimize the thermal COP according to different levels of refrigerating capacities.

Because of their low cost, small air conditioning systems (AC) like split air conditioning systems are often installed without a proper study of building envelope performance. Furthermore, these systems are sometimes installed by tradesmen who neglect to comply with the appropriate rules and regulations. Finally, when routine maintenance is not rigorously carried out (as so often happens), the energetic performance of the system is compromised over time. This article presents a practical, global approach to diagnose the performance of existing small air-conditioning installations in buildings applied in Reunion Island. This tropical Island aspires to become electricity self-sufficient. This approach relies on a numerical tool and dynamic simulations of buildings equipped with AC. The simulations, which take account of the building envelope, a description of the system as well as the practices of the users, are based on the kernel calculation EnergyPlus. They also take into account the climatic conditions and provide an estimate of the annual electricity consumption related to the cooling of the zone. This global analysis helps to qualify the entire system by assigning an energy label. In addition to the tool, a diagnostic procedure is proposed, helping an auditor defining guidance to improve the building envelope and to install and maintain the system.

Reunion Island is heavily dependent on fossil fuels, but seeks to become energy self-sufficient by 2025. ocean thermal energy conversion provides a means of producing electricity that harnesses the available energy of the ocean by using the temperature gradient between its deep and its upper layers. This paper presents the projected experimental facility which is to be installed at the University of St. Pierre on Reunion Island. A dynamic model of the installation has been developed (on a Delphi interface) by using the concept of equivalent Gibbs systems. In such equivalent system, mass, energy, and entropy are linked through the Gibbs equation, and the entropy production can easily be expressed in terms of fluxes and their related forces. Assuming linear phenomenological laws, the phenomenological coefficients are assessed from technical data. Using a digital tool (Genopt), an optimization study has been conducted in order to determine the best operating parameters according to the temperature of the sea water. This model allows us to anticipate the potential of this technology on Reunion Island. Once validated on the facility, the model will serve as a tool to assist design of the future 10MW pilot plant planned for 2014. Copyright (c) 2012 John Wiley & Sons, Ltd.

Ce travail presente un modele dynamique de machine a absorption simple effet, fonctionnant avec le melange binaire bromure de lithium (absorbant) / eau (fluide frigorigene). Ce type de machine est de plus en plus utilise dans les installations de rafraichissement solaire appliquees aux bâtiments. Du fait de la grande variabilite de la ressource et du besoin, un modele dynamique semble necessaire pour evaluer precisement les performances de la machine en particulier lorsque l’installation fonctionne sans appoint de chaleur. Dans une premiere partie, le modele dynamique de la machine est presente. Les resultats de simulation sont ensuite confrontes aux donnees experimentales extraites de notre installation et les erreurs sont calculees et analysees. Cette analyse nous permet de conclure que notre modele prend bien en compte a la fois les regimes permanents et transitoires de la machine a absorption.

For the last two decades, economic development in Reunion Island has led to major structural changes. The latter have been characterized by an increase in energy demand per person. This demand is mostly related to a high population growth (1.55% per year). Reunion currently has 833,000 inhabitants. The population will rise to 1 million in 2030. Like most ultraperipheral regions of the European Union, Reunion is heavily dependent on imported fossil fuels for its energy production. The total primary energy consumption amounted to 1352ktep in 2009 and 87.1% is imported energy. The development of various renewable energies such as solar energy, biomass, ocean energy, etc. is thus of priority concern to aim to achieve energetic independence. Just like other French overseas territories, Reunion policies have widely invested in Renewable Energy Sources (RES) since 2000. This paper aims at presenting the current status, the major achievements of policies and the future objectives in the deployment of renewable energy programmes. The perspective of a net zero energy island versus the pressure of the population is analysed. The barriers to penetration of RES in a small-scale territory are also discussed.

In the last recent years, research in thermal comfort during summer has induced a significant increase in electricity consumption in buildings due to the notable use of mechanical vapor compression air conditioners. Solar cooling systems are an attractive alternative to overcome this problem. The development of these systems requires a fundamental approach with the development of numerical models to predict the behavior of the whole installation. The ultimate goal is to estimate the comfort, the refrigerating power, the power consumption and the overall performance of the facility based on external factors (solar radiation, outside temperature, occupancy in the building). For this, we chose the EnergyPlus environment that is proving to become a reference tool in the field of building simulation. This simulation tool facilitates the coupling of energy systems to the building with a wide range of models (solar thermal collectors, absorption chiller, stratified storage tanks, cooling tower). In this paper, we present the modeling of the solar cooling installation “RAFSOL” within the EnergyPlus environment at the Technology University Institute (IUT) of Saint Pierre in La Reunion. The simulations are then discussed and compared with data extracted from our experimental platform. Then, the model is used to propose a solution to improve the seasonal performances of the installation.