Search

This paper deals with the experimental investigation of hygrothermal behavior of wooden-frame building envelope. The experiment was based on in-situ monitoring of a full size experimental monozone house built at the University of Lorraine. Variations in temperature and relative humidity inside and outside the envelope were logged simultaneously with local meteorological data. Results showed the high coupling between temperature and relative humidity variations within the envelope materials. An overall hygrothermal response of the wall highlighted an interesting hygrothermal dynamic behavior of the envelope which may contribute to mitigate variations of relative humidity inside the building. Nevertheless, relative humidity evolves within a range of values ​​that can lead to mold growth at a certain position which may alter wooden envelope life.

Hydrogen generation through electrolyzers has gained a growing interest from researchers and industries to decarbonize transportation and electricity production. The performance of electrolyzers is strongly dependent on their operating conditions, such as the supply current, temperature, and pressure. To meet near-zero emissions, the electrolyzer must be supplied by low-carbon energy sources. Therefore, renewable energy sources must be considered. However, these sources are strongly linked with the weather conditions, so they have a high dynamic behavior. Therefore, this article is focused on the investigation of the effects of these dynamic solicitations on the electrical and thermal performance of electrolyzers. In this study, a proton exchange membrane (PEM) has been chosen to carry out this investigation. Experimental tests have been performed, emphasizing the relationship between the electrical and thermal performance of the PEM electrolyzer. The purpose of this work is to provide an optimal scenario of the operation of the electrolyzer under dynamic solicitations and consequently, to decrease the degradation of the electrolyzer.

In this study, the Lattice Boltzmann Method (LBM) is employed in order to examine the fluid flow and forced convection heat transfer inside a two-dimensional horizontal channel with and without obstacles. In order to enhance the heat and thermal energy transfer within the channel, different obstacle arrangements are posed to the flow field and heat transfer with the purpose of studying their sensitivity to these changes. The results indicate that, when the value of the Reynolds number is maximum, the maximum average Nusselt numbers happens on the lower wall (Case 4). The paper extends the topic to the use of nanofluids to introduce a possibility to enhancement of the heat transfer in the channel with an array of the obstacles with forced convection. For this purpose, the AgMgO/water micropolar hybrid nanofluid is used, and the volume fraction of the nanoparticle (50% Ag and 50% MgO by volume) is set between 0 and 0.02. The results showed that, when the hybrid nanofluid is used instead of a typical nanofluid, the rate of the heat transfer inside the channel increases, especially for the high values of the Reynolds number, and the volume fraction of the nanoparticles. Increasing the volume fraction of the nanoparticles increase the local Nusselt number ( 1.17-fold). It is shown that the type of obstacle arrangement and the specific nanofluid can exerts significant effects on the characteristics of the flow field and heat transfer in the channel. This study provides a platform for using the LBM to examine fluid flow through discrete obstacles in offset positions.

The Comoros is an archipelago in the Indian Ocean located in the Mozambique Channel between the African continent and Madagascar. Geographically Comoros is composed of four islands: Grande Comores, Anjouan, Moheli and Mayotte (under French administration). Apart from Mayotte, the others three independent islands commonly known as the Union of the Comoros are suffering from energy stress since their independence year 1975 until nowadays. The energy supplied and distributed by the national electricity company, SONELEC produced by diesel engines, is not stable with so much load shedding all the time. This instability energy leads to a lack of a phone network in some telecommunications towers connected to grid. The majority of telecommunications towers are located in rural areas not connected to grid and running on diesel generators, which once again leads to a problem with the telecommunications network when diesel engines fail. The two competing companies which operate in the field of telecommunications in the Comoros, namely Comores Telecom, a national public company and Telma, the private one, are still unable to ensure the provision of the telecommunications network on a regular basis. This is why we propose in the present work, a sizing of hybrid system composed essentially of a diesel generator, a wind turbine and a photovoltaic solar system with storage in batteries for supplying telecommunications towers in order to permanently ensure the provision of the telecommunications network for the well-being of the population. Our future energy must be based on non-polluting energies with significant resources. Renewable energies are the best candidates but with intermittent production especially in rural areas not connected to the national electricity grid whose energy demand is more important to meet the needs of the population. The aim of this work is the sizing of a hybrid system composed of a diesel generator, a wind turbine and a photovoltaic solar system with storage in batteries for supplying telecommunications towers located in rural areas in the Comoros. In fact, to verify the performance of the hybrid system, a numerical study has been carried out with the HOMER 2.68 Beta software using meteorological data from the Comoros. The results obtained show that this hybrid combination is more profitable in the margin of economic cost and environmental assessments with a less expensive investment. These results also show a better optimization of Wind/PV/Battery of the hybrid system used, satisfying the demand and contributing to the preservation of the environment to fight against climate change with a low cost of energy.

Bio-based materials have strong hygrothermal behavior and phase change materials (PCMs) have high thermal inertia, but they have usually been studied separately in most research. In this paper, the hygrothermal behavior of a multilayer building envelope integrating hemp lime concrete (HLC) and PCM was investigated at experimental level. The envelope was flanked by a climate chamber and the laboratory ambient to imitate the outdoor and indoor environments, respectively. Four envelope configurations comprising a reference (without PCM) and three configurations with PCM (PCM placed on the outdoor and indoor side, in the middle of the envelope) were considered in order to study the effect of PCM and its position on the hygrothermal behavior of the envelope. The results showed that the PCM had a significant effect on the hygrothermal behavior of HLC, based on the high coupling between temperature and relative humidity. The characteristic time was considered to quantitatively evaluate temperature and relative humidity trends, and their value was increased with the participation of PCM. Moreover, PCM increased the heat store/release capacity linearly with its position. The closer the PCM was to the outdoor, the higher the heat store/release capacity and the lower the heating/cooling load from the envelope to the indoor environment. These phenomena were closely related to the PCM's temperature distribution and its corresponding specific heat capacity. Therefore, due to the envelope's thermal and hygric inertia on the indoor environment and the building's energy saving potential, it was recommended that the PCM be placed close to the outdoor side.

A modelling approach based on the Substitutive Coefficients Network (SCN) is developed to predict the thermal behavior of a system in the dynamic state-space, without requiring knowledge of the thermal mass. The method can apply either to large- (building, combined solar systems, geothermal energy, and thermodynamic installations) or to small-scale systems (heat exchangers, electronic devices cooling systems, and Li-ion batteries). This current method is based on a dimensionless formulation of the simplified dynamic thermal balance model, using relaxation time as a key parameter to establish the model. The introduction of relaxation time reduces the parameters set as guidance coefficients. The parameters are finally expressed by a combination of global heat transfer coefficients related to each layer and/or sub-layer of the system. Advantages of the method are reliability, “non-destructibility”, i.e., it allows a reliable prediction of the thermal behavior which experimentally is inaccessible, and reducibility of the parameters size estimate. Additionally, the method is inexpensive in terms of computation memory. It is also easy to implement in practical numerical schemes. In this paper, the method leads to a simplified mathematical model that predicts the thermal behavior of a mono-zone eco-cottage building installed at Lorraine University (in Longwy, France) as a case study. Thermal performance of the building is estimated under the hourly weather conditions onsite, as obtained from the Meteonorm software. The thermal dynamics within hourly Typical Meteorological Year 2 (TMY2) Meteonorm data disturbances and the internal heating input state in the winter period were simulated with a simplified numerical discretization method. Results provide a general dynamic state of the different sub-components of the system, with limited design of the model parameters.

Refrigeration by absorption is gaining more and more importance, especially in applications, where the source of energy used in the generator is renewable. Our work aimed at providing a cooling system adequate to the weather conditions in Tunisia as well as other Euro-Mediterranean regions. Furthermore, this cooling system is at the same time environment-friendly and economical. Heat wastes and solar energy were used as the source of energy in the generator. In this context, we were interested in the thermodynamic analysis of the single-effect absorption refrigeration machine operating with the pair ammonia/water. The modeling and simulation of this machine were carried out by the software Engineering Equation Solver (EES) in order to look for the optimal conditions for the work of this machine and study the effect of various operating parameters on the system efficiency.

The present work proposes a continuous solar adsorption refrigerator for a positive cold storage room of 231 m3 used for fruits and vegetables preservation and installed in the south of Tunisia. After the estimation of the storage room cooling load which is equal to 13 kW, a parametric study, aims to improve the performance of the chiller is done in order to achieve the storage room need and to estimate the required heat in the refrigerator generator. A theoretical model, based on the thermodynamics of the adsorption process, heat and mass transfer within the porous medium and energy balance in the system components, is developed and a simulation with Matlab/Simulink, is carried out. The model was established and validated with the literature experimental data.A maximum coefficient of performance of 0.52 and cooling load of 22 kW are reached at cycle time of 800 seconds. The inlet temperatures of heating, cooling and chilled water are 85°C, 22°C and 15°C, respectively.

International audience

Building-based active envelopes play an important role to reduce active heating supplies. Several techniques are developed to enhance the energy performances of active building envelopes; meanwhile, numerous numerical and mathematical models are also developed to conduct the performance analysis of these techniques. In this paper, we propose a state-space model for solar active wall-based Phase Change Materials (PCM). The advantage of this method remains in its simplicity to provide details of internal nodes and input/output parameters. The low-cost calculation is a supplementary advantage versus a heavy numerical method. The proposed numerical model is applied for a multi-layer wall with PCM Wallboards (PCMW) embedded between indoor and outdoor environments. The results show the ability of the state-space model to estimate the thermal behavior of the system, as well as the thermal characteristics of embedding PCM in the internal face of the wall. It significantly contributes to stabilize the indoor temperature and to ensure the thermal comfort.

The present paper investigates numerically the effect of an external magnetic field on heat transfer and entropy generation of Ag–MgO (50:50 vol%)/water hybrid nanofluid flow in a partially heated irregular ventilated cavity. A finite-volume FORTRAN code has been written to solve the governing partial differential equations. New empirical correlations specifically dedicated to predict the dynamic viscosity and the thermal conductivity of the considered hybrid nanofluid were employed. After validation of model, the analysis has been done for a wide range of Reynolds number (10 ≼ Re ≼ 600), Hartmann number (0 ≼ Ha ≼ 80) and total nanoparticle volume fraction (0 ≼ φ ≼ 0.02). The results are presented in terms of streamlines, isotherms and isentropic lines as well as the average Nusselt number (Num), the average entropy generation (Sgen,m) and the Bejan number (Beavg). The criterion ξ = Sgen,m/Num is adopted to discuss the thermal performances of the system. The results reveal that the intensification of the magnetic field tends to attenuate the heat transfer convection and to reduce the thickness of the thermal boundary layer, close to the active walls. Globally, adding nanoparticles to the base fluid improves the heat transfer but increases the total entropy generation.

The aim of the proposed work is to study the solidification process within a rectangular enclosure provided with three internal rectangular fins attached to the left vertical wall cavity. This latest is filled with a phase change material (PCM), initially liquid, at a temperature above its melting temperature. The solidification process was initiated by cooling the left wall and fins to a temperature lower than the melting temperature. In order to study and examine the thermal behavior and thermal performance of the proposed system, a mathematical model, based on the conservation equations of mass, momentum and energy was developed. The governing equations and their associated boundary and initial conditions were next non-dimensionlaized. Therefore, several controlling parameters were appeared. The volume control method was used to discretize the equations. The resulting algebraic equations were solved iteratively. Numerical investigations were carried out to study and examine the effect of the dimensionless fin length on the hydrodynamic and thermal fields of the flow, the dimensionless heat flux, the solidified mass fraction and the dimensionless time of complete solidification.

In building environments, several research on dynamic moisture storage in hygroscopic building materials has improved interest in moisture buffering capacity of bio-based materials and demonstrated the potential of these materials to improve thermal comfort and buildings energy consumption. This paper presents an investigation, which aims to compare the hygroscopic behavior of different bio-based materials to identify their hygric proprieties. For this, an experimental facility is used to measure the moisture buffer value (MBV) for different categories of building materials. Thereafter, a dynamic simulation has been carried out by using TRNSYS software in order to evaluate heating and cooling loads. The results showed that the wood-cement composite still has excellent moisture regulator when compared to wood panels or fibrous materials. It has a buffer capacity superior to 3 [g/m2.% RH] very close to that of wood fiber panels. The simulation results of the different cases showed that the insulation reduces significantly total energy demand, but it does not lead heat evacuation in the summer season. Thus, from this study, it can be concluded that a natural ventilation mechanism is recommended to improve energy efficiency in the building.

Located on the Southern shore of the Mediterranean, and at the same time at the gates of Europe and the North of the African continent, Morocco is distinguished by its richness in terms of climate and geography which constitute specific features providing a diversity of local materials required in the eco-construction and renovation. In this regard, the Kingdom of Morocco has launched a transition to a new development model that is more respectful of its human and natural resources through the strategy of energy and energy efficiency. This leads it to deploy an important part of research and development to choose innovative and pragmatic solutions adapted to different sectors. Including the building and thermal comfort. The innovative solutions are based on the choice of an energy mix associated with local materials. The objective of this communication is to realize the variety of materials potentially available in the northern region of Morocco and to evaluate their contribution in terms of thermal comfort and by listing the constraints of short circuit, environmental preservation and possible fields (concrete, wood, bricks...). Then comes the scientific contribution which consists in quantifying, characterizing, understanding and certifying between Universities and other organizations. Focusing on multi-physical characterization methods. The reflection closes with a study about the cost and the global socio-economic benefits of this approach and the implementation of a methodology for the selection of eco-materials in order to establish later a chain of eco-renovation and eco-construction operating on the trans-border area of northern Morocco.

Our study focuses on the thermal performance evaluation of a solar room built using a new bio-based composite wall coupled with a phase change material (PCM) layer during the cooling season in Nancy city France. This composite wall consists of a bio-based panel IBS-IZOLOX developed by the Belgium company ISOLHABITAT. The inner side of this bio-based composite wall should be coupled with a PCM layer in order to improve the thermal inertia of the room envelope. The results show that this system wall can improve significantly the thermal comfort performance of the passive solar room during the cooling season.

Morocco has adopted a national energy strategy for the promotion of renewable energy and the energy efficiency. The building’s sector is an area targeted by this strategy, since it is one of the major energy consumers in the Moroccan level. With a 25% share of final consumption countries (ADEREE) Its consumption is set to increase further in the future years. In addition the building is a strategic energy sector taking into account the long life of buildings. In this perspective, in order to establish a regulatory and legal framework governing the energy efficiency in the building sector, this regulation was based on several steps among them, the establishment of a climate zoning based on the degrees of heating-days and zoning. This zoning has left Morocco in six climatic zones. In this context, the present work aims to make a contribution in packaging useful climate data for the evaluation of the building thermal requirements, specifically the production of hot water. To achieve this goal, we developed a solar radiation calculation model for the six Moroccan climate zones based on the model of "Capderou". However, from these data, was developed another model for calculating the water heater solar performances and the production of domestic hot water in these different zones. This model is based on the platform "ENERBAT" Laboratory "LERMAB" at the University of Nancy Lorraine.

Numerical simulations were carried out to explain the behavior exhibited in experimental work on the dissolution process of silicon into a germanium melt. The experimental work utilized a material configuration similar to that used in the Liquid Phase Diffusion (LPD) and Melt-Replenishment Czochralski (Cz) growth systems. The numerical simulations were carried out under the assumption of 2D. The mathematical model equations were developed using Lattice Boltzmann Method (namely the BGK approximation was adopted). Measured concentration profiles and dissolution height from the samples processed with and without the application of magnetic field show that the amount of silicon transported into the melt is slightly higher in the samples processed under magnetic field, and there is a difference in dissolution interface shape indicating a change in flow structure. This change in flow structure was predicted by the present LB model. In the absence of magnetic field a flat stable interface is observed. In the presence of an applied field, however, the dissolution interface remains flat in the center but curves back into the source material near the edge of the wall. This indicates a far higher dissolution rate at the edge of the silicon source.

Thanks to the advantages of storing the latent heat of melting, phase change materials (PCMs) are used in many applications including building air conditioning systems. This study examines the process of solidification of a PCM in an internally finned rectangular cold storage unit. The PCM, placed in the enclosure, is initially in heated liquid state having a temperature, Ti, higher than the melting point, Tm. Heat is transferred from the energy storage unit through the left vertical wall on which fins are attached. These fins, embedded in the PCM, allow increasing heat transfer thanks to their additional exchange surface. The left wall is in contact with a vertical duct through which heat transfer fluid (air), having an inlet temperature, Ta, in, lower than the melting point, Tm, flows in the downward direction. A parametric study was conducted in order to highlight the impact of operating parameters such as air inlet temperature and flow rate on the thermal behavior and thermal performance of the cold storage unit.

The most diverse fuels in different state among the most common are wood, coal, hydrocarbons (methane CH4, propane C3H8, gasoline, gas oil, kerosene, fuel oil ...), hydrogen (H2). The oxidizer is most often oxygen from the air, more exceptionally pure oxygen (rocket engine, some industrial furnaces) which allows reaching higher temperatures but poses safety problems. Combustion is one of the main themes of energy. This paper study a numerical simulation of combusting hydrogen and various hydrocarbons with air in a burner and the numerical solution of the local entropy generation rate due to the high temperature and velocity gradients in the combustion chamber. In this work the calculations showed that the maximum reaction rates reduce with the augment of φ or the reduce of the oxygen percentage. The temperatures gradients take place in the axial direction, however, the raise of φ considerably minimize them also the increase of φ from 0.5 to 1.0 decrease the entropy generation rates.

This paper presents the results of heat transfer process modelling for Photovoltaic/Thermal PV/T hybrid system in state-space. The heat transfer process in solid materials can be described by an integer-order partial differential equation. However, in Photovoltaic (PV/T) hybrid systems, which is characterized by heterogeneous media due to the multilayers that make up the system, it can be described by a fractional-order partial differential equation. The major objectives of this study were to establish a new mathematical model of the Photovoltaic/Thermal (PV/T) hybrid systems and their fractional-order observers in time domain. This model has been constructed in the context of a new consideration of heat conduction with a time fractional-order derivative. On the other hand, after obtained the general model of the system in state-space, the existence conditions of the fractional-order observer of such systems are given. Then, a necessary and sufficient condition for the asymptotic stability of the estimation error is given in a Linear Matrix Inequality (LMI) formulation.

A solution based on the incorporation of a phase change material with ventilation tubes is proposed. This coupling is tested on a building material "concrete block" to increase the thermal inertia of the building walls. In the first part of the study, an experimental device is designed to compare the thermal response of different configurations depending on the condition of the tubes (open, closed, ventilated). The second part concerns a 3D numerical simulation. The results show potential solutions to ensure a large thermal inertia of a building.

nanoparticles in a rectangular latent heat storage unit (LHSU). The storage unit consists of a number of identical plates of Nano-PCM separated by rectangular channels in which water flows as a heat transfer fluid (HTF). A mathematical model based on the conservation equations of mass, momentum and energy has been developed and validated by experimental and numerical data available in literature. The phase change problem was formulated using the enthalpy porosity technique and the resulting equations were discretized according to the finite volume approach. Numerical investigations were conducted to evaluate the effect of the nanoparticles volume fraction on the heat transfer features and thermal performance of the storage unit.

This work aims to optimize the design of an air-conditioned multi-zone house integrated phase change materials (PCMs) considering the north Moroccan climate conditions. The objective of this optimization is to minimize the heating and cooling loads. The methodology of this optimization is based on the coupling between Energyplus® as a dynamic simulation tool and GenOpt® as an optimization tool. The results show that the obtained optimal design allows minimizing the energy consumption regarding reference house without PCM.

This study investigates the thermal energy potentials and economic feasibility of an air-conditioned family household-integrated phase change material (PCM) considering different climate zones in Morocco. A simulation-based optimisation was carried out in order to define the optimal design of a PCM-enhanced household envelope for thermal energy effectiveness and cost-effectiveness of predefined candidate solutions. The optimisation methodology is based on coupling Energyplus® as a dynamic simulation tool and GenOpt® as an optimisation tool. Considering the obtained optimum design strategies, a thermal energy and economic analysis are carried out to investigate PCMs’ integration feasibility in the Moroccan constructions. The results show that the PCM-integrated household envelope allows minimising the cooling/heating thermal energy demand vs. a reference household without PCM. While for the cost-effectiveness optimisation, it has been deduced that the economic feasibility is stilling insufficient u...

The use of Phase Change Materials (PCMs) in the building sector is an attractive solution contributing to the reduction of energy consumption as well as the improvement of the thermal comfort. To achieve this objective, it is required to study the complex phenomena of phase changes when PCM incorporated in different types of building materials. In this study, PCM is incorporating in a cavity of hollow brick and check the effect of natural convection during melting process by compared between two cases, the first the case when there is only a pure conduction and for the second case is when natural convection is not neglected in the upper part of this cavity. For the numerical model, the finite element method is using with modification in the specific heat of PCM accounting for the increase amount of energy, in the form of latent heat, needed to melt the PCM over its melting temperature range. The result showed that the effect of natural convection is limited and can represented by using un equivalent thermal conductivity.