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International audience; Partitioned approaches for the simulation of coupled conjugate heat transfer are gaining popularity in fields that require accurate thermal predictions. Considerable efforts have been put into determining stable coupling schemes, but performance enhancements have been neglected. This paper presents, for the first time, a detailed and comprehensive study of the numerical properties of Dirichlet-Robin coupling procedures, used in conjugate heat transfer simulation, with emphasis put on the optimal local coupling formulation that was recently derived from a stability analysis. This all-new optimal coupling approach provides local adaptability and has never been tested on a complex setup. This investigation looks to determine the relevance and the limitations of the theory when applied to complex conjugate heat transfer setups. The stability theory of the optimal Dirichlet-Robin coupling scheme is first recalled, then, a realistic 3D application, with complex geometry and flow structures, is used to evaluate the performance and sensitivity of Dirichlet-Robin couplings, with respect to various numerical parameters. This detailed study allows, for the first time, to evaluate the advantages and limitations of the recently proposed optimal procedure, when used on realistic 3D CHT problems. It turns out that the local optimal Dirichlet-Robin formulation outperforms all what is found in literature, and insures unconditional stability with monotone convergence for all considered setups of the 3D model.

International audience; Increasing penetration of distributed generation on the distribution network demands for a more flexible and efficient utilization of distributed energy resources. The development and deployment of Smart Grids technologies and solutions may provide solutions for significant changes in distribution operation within the near future. The Nice Grid project aims at implementing and testing a distributed energy resource management system, supporting hierarchical operation and control for a microgrid with high concentration of photovoltaic generators. The paper focuses on one use case of Load Reduction for TSO, from dispersed resources such as controllable loads and electrical storage units, which can be scheduled and operated through intermediaries, i.e. commercial aggregators. The business process, the project geographical footprint, the various supported standards and the overall architecture of the system are detailed in the following sections, with a strong emphasis on the transaction mechanism that supports the coordination process. The issues and lessons from the first two years are also discussed.

A district heating network has generally more than one production unit, and then there are different ways to fulfill the energy demand of the network. This paper deals with the planning problem which is a problem of optimization under constraints. The production units are modeled using MINLP (mixed integer non-linear programming), in particular the following technical aspects are considered: storage capacity (for municipal wastes and biomass), allowable operating range, allowable variation of power over time, partial load performances, minimum working time when a unit runs, and minimum waiting time when it is in stand-by mode. The environmental constraint is the annual share of renewable energies in the global energy mix (for example, at least 50% over a year). The model aims to minimize the operating cost of the network. The problem cannot be solved by a one-shot optimization, so the paper proposes a sequential approach: first, a target of renewable share is calculated for each month of the year; secondly, the planning production is determined each day according to the calculated target. The results of a case study show that the planning strategy that only aims to minimize the operating cost violates the environmental constraint. Using the developed planning model raises a little bit the cost (4.5%) but fulfills the heat demand and environmental constraint at the same time. Considering a reduced VAT eligible in France when the constraint on renewable share is met, the proposed planning is even better in term of the total cost (10% lower).

There is no reliable in situ measurement method of air-to-air heat pump seasonal heating performances. Several methods were previously developed but they were only validated in steady-state conditions. In real life, dynamic sequences such as defrost cycle and starting phases occur, which are not considered in these methods. The goal of this work is to complete one of the existing methods so that it can address both steady-state and dynamic phases. The compressor energy balance method is used here: in the standard heating phase, refrigerant fluid measurements determine the refrigerant flow rate by using the compressor thermal balance. Modeling hypothesis are formulated regarding performance evaluation during defrost and start-up sequences. An algorithm is developed in order to identify the operating mode (standard heating phase, stop, start-up, defrost). Default parameters for this algorithm are proposed. The developed method is assessed over a long term test by comparison with a reference method based on intrusive measurement on the refrigerant. The integrated heat pump performance measured with the in-situ method is within 1% of the reference measurement. Although large errors may occur in dynamic phases, their occurrence is low and some errors may compensate between the different phases. Leads on further work needed to bring this method closer to deployment are discussed. Better knowledge of the occurrence of the different operating modes is required. Further adaptation is also required for heat pumps using liquid injection at compressor suction.

International audience; The scenarios developed by the IPCC predict global warming of several degrees by the end of the century, which will increase the frequency and severity of heat waves. What will be the level of thermal comfort in buildings? Can we adapt them to reduce this overheating to an acceptable level? To answer these questions, climate projection data for 2050 and 2100 were developed using downscaling techniques. A list of adaptation measures was drawn up and a sample of typical buildings was created. Adaptation measures were assessed considering different indicators, for instance: degree-hours of discomfort evaluated by dynamic thermal simulation, CO2 balance, LCA indicators concerning health, biodiversity and resources, costs. The communication presents the first results obtained, showing the interest and limits of passive cooling according to the buildings, their location, andoccupants behaviour (in particular the management of solar protection and opening of windows).; Les scénarios élaborés par le GIEC prévoient un réchauffement planétaire de plusieurs degrés d’ici la fin du siècle, ce qui augmentera la fréquence et la sévérité des canicules. Quel sera alors le niveau de confort thermique dans les bâtiments ? Pourra-t-on les adapter pour réduire ces surchauffes à un niveau acceptable ? Pour répondre à ces questions, des données de projection climatique à l’horizon 2050 et 2100 ont été élaborées par des techniques de descente d’échelle. Une liste de mesures d’adaptation a été élaborée et un échantillon de bâtiments types a été constitué. Il s’agit alors d’évaluer les mesures d’adaptation par différents indicateurs, par exemple : degrés-heures d’inconfort évalués par simulation thermique dynamique, bilan CO2, indicateurs ACV concernant la santé, la biodiversité et les ressources, coûts. La communication présente les premiers résultats obtenus, montrant l’intérêt et les limites du rafraîchissement passif en fonction des bâtiments, de leur localisation, et du comportement des occupants (en particulier la gestion des protections solaires et l’ouverture des fenêtres).

A novel purification technology for raw biogas streams is proposed and it is based on the use of a superacid solution within a bubble column reactor. The solvent is a mixture of sulfuric acid (H2SO4(aq), 95.0 wt.%) and acetic acid glacial (CH3COOH(l), ≥ 99.8 vol.%), both commercial grades. A mixture with a molar ratio of 9/1 for H2SO4(aq), / CH3COOH(l) respectively, leads to the interesting physical and chemical absorption properties for biogas treatment. Process simulations of the technology within a frequently used biomethane production process showed simultaneous capabilities for H2S elimination, CO2 absorption and, siloxanes and volatile organic compounds (NMVOCs) complete degradation. A single bubble column reactor was designed for treating 500 N m 3 / h of raw biogas with H2S content between 400 and 1500 ppmv (dry basis) and for handling a solvent volume flow between 10.23 and 23.39 L/min, depending on the H2S gas content. Proper functioning and hydrodynamic stability of this unit were evaluated in order to avoid possible issues related to bubbles coalescences or break-up, liquid backmixing and mass transfer limitations. Comparison of the proposed technology with methanol-based and monoethanolamine (MEA(aq))-based absorption processes allowed proving the low energy demands of the proposed unit and the feasible implementation of the technology.

SPIRAL2 is a superconducting LINAC subject to cryogenic thermo-acoustic oscillations occurring in its valves-boxes. 4 years of monitoring and experimental investigations with thousands of datasets turned these unwanted effects into an opportunity to study and understand thermo-acoustics in a complex environment such as a real life accelerator. Without digging deep into Rott's thermo-acoustics theory, thoroughly shown in other works, this paper describes the instrumentation and the methods that prepare more advanced modelling of these phenomena either to damp or to harness the energy of cryogenic thermo-acoustics., 8 pages, 10 figures. arXiv admin note: text overlap with arXiv:2101.10768

In order to contribute to the decarbonization of heating consumption, France has set some objectives to develop District heating and/or cooling networks (DHCN). In this context, it is useful to identify the most appropriate district areas for implementing DHCN, and to assess their potential of development. After introducing the situation of DHCN in France, this paper presents a typology to assess the potential of development of those networks in France, based on an original method that involves the calculation of 3 variables: the linear heating/cooling density (LHD/LCD), the Proportion of Buildings anterior to 1990 and the share of energy consumption from the residential sector, to assess respectively the energy density, the supply temperatures and the energy mix between the different sectors of activities. LHD and LCD are calculated using a Delaunay triangulation and Kruskal's algorithm applied to buildings whose heating and cooling demands are calculated at a local scale. 18 different types of districts are defined for both DHN and DCN, among which 9 have a sufficient LHD/LCD. Then, the potential of development for DHN and DCN is calculated on the French territory. Thus, the DHN potential is assessed to 132 TWh/y while the DCN potential is assessed to 7.8 TWh/y.

The building stock is a major contributor to energy consumption and greenhouse gases emissions (GHG), which can be evaluated using life cycle assessment (LCA). Electrification of buildings, e.g. replacing fuel and gas boilers with heat pumps, in order to reduce these emissions is often seen as an option, but this will have short term effects by increasing peak demand, and long term effects by requiring more electricity production capacities. In this paper, a methodology to account for such interaction in LCA is presented. It connects three models addressing: market allocation on a national scale over a long term period, short term variation (i.e. seasonal, daily and hourly) of the electricity mix also on a national scale, and building energy simulation at the scale of one building. This methodology has been applied to a case study including a sample of buildings in the French context, but it can be used in other countries. Six buildings have been studied over 100 years considering 50 energy transition scenarios. Results show that the environmental impacts vary more depending on the scenarios than on the types of the building. Marginal mixes considered in consequential LCA are mainly composed of coal, gas, nuclear and peak technology production which explains the highest values of the different impacts compared to average mixes used in attributional LCA. This approach allows to address uncertainties related to electricity production.

The main drawback of conventional alkanolamines for post combustion CO2 capture is that they cannot combine a low energy consumption for regeneration and a high reactivity. Blends of tertiary and primary amines provide these two advantages at the same time. This study considers a new composition of solvent for carbon capture: methyldiethanolamine (MDEA) 30 wt.% and hexylamine (HA) 10 wt.%. MDEA acts as regeneration promoter and HA as activator. The kinetics of this solvent is assessed through an optimization method based on a genetic algorithm and at different temperatures (25 °C, 40 °C and 60 °C), in order to determine the Arrhenius law. The reaction considered is a first order reaction where each amine reacts with CO2 in parallel. The composition studied does not give better results than MDEA alone. This is probably due to the addition of a too large amount of hexylamine.

Carbon dioxide released by the transportation sector has a significant impact on the environment. Nowadays, the research efforts are thoroughly investing in the capability of series hybrid electric vehicles in reducing CO2 and NOX emissions. Many regulations are encouraging automakers to substitute internal combustion engines with electric vehicles. Although the latter are zero-emissions energy sources, they are expensive and have a limited autonomy range. Therefore, recent studies are interested in gas turbines (GTs) in series hybrid electric vehicles (SHEV). A gas turbine (GT) coupled to an alternator is considered as an auxiliary power unit capable of charging the battery of the electric vehicle once depleted. The microturbine is generally composed of a centrifugal compressor and a radial turbine mounted on the same shaft with a recuperator and air bearings. Based on previous researches and thermodynamic analysis, the most suitable gas turbine cycle with regard to the efficiency and the net specific work is composed of two compression stages with an intercooler, a regenerator, and two expansion stages with a reheater. It can be deduced that by increasing the turbine inlet temperature, the system efficiency increases. However, the inlet temperature is limited by turbine materials constraints and specifications. The present paper focuses on developing a more efficient GT cycle by reaching higher inlet temperatures by cooling the turbine blade. It consists of using compressed gas from the compressor and introduce them into the turbine blades. This technology takes into consideration the influence of the extracted mass of compressed air, the effectiveness of the coolant, and the turbine blade temperature on thermal efficiency. An increase of the cycle efficiency of 4.78 points is obtained for a turbine inlet temperature of 1,450 °C.

Removal of carbon dioxide to upgrading biogas is possible by cryogenics and frost formation. In this work, it is targeted removing carbon dioxide by frost deposition (physical transition from gas to solid state) at low pressure and temperature from biogas, as well as assessing the impact of mass flow rate, temperature and the initial CO2 content in biogas on the carbon dioxide removal process. The Solid-Gas phase equilibrium between CH4 and CO2 is presented. It is followed by a sensitivity study of CO2 deposition on a flat plate and the assessment of different geometries of the heat exchanger generating frost. The global process including CO2 removal and biomethane liquefaction is simulated in AspenTech tools that are linked to a specific module modelling frost formation phenomenon. This module is coded in Dymola (Modelica language). Different operating modes of the heat exchanger are compared: thermal inertia or by direct cooling by nitrogen gas obtained after liquefaction of the biomethane. The temperature of the heat exchanger increases as CO2 deposits. Results show that cryogenic CO2 frost formation can be used for simultaneous liquefaction and upgrading of methane at 97% vol. minimum of purity and a reduction of cooling cycles on site by cold recovery from frost. This implies a reduction of energy intensity to remove carbon dioxide compared to conventional cryogenic technologies.

The increase in energy demand and the need for lower CO2 emissions have increased the importance of natural gas as the cleanest fossil fuel in the energy market. Natural gas is mainly transported using pipelines or as liquefied natural gas (LNG). LNG is stored and transported in cryogenic storage tankers, where a part of the LNG evaporates, generating boil-off gas (BOG). The BOG is used normally as fuel for propulsion engines, but at low navigation speed, it is more than the engines’ fuel needs, and the excess quantity is either burnt or reliquefied. Existing technologies for on-board reliquefaction consume a large amount of energy and are costly, which arises the need for new concepts of reliquefaction technologies. The new proposed system operates on two modes; the first is the charging mode in which cold energy is stored when the LNG is evaporated to supply the LNG carrier propulsion system at high speed. The second is the discharging mode, in which the stored cold energy is used to condense the excess BOG at low navigation speed. The novel reliquefaction system utilizes latent or sensible heat storage materials that haven’t been examined before for cryogenic applications. A preliminary energetic assessment for the system is carried out using Aspen HYSYS, Excel and VBA, to study the impact of the variation of the operating conditions on the choice of suitable storage material and its performance. Results showed that low LNG evaporation and high BOG liquefaction pressures offer higher energy storage capacity for all types of thermal energy materials, with better performance for the latent ones. Further investigation on this technology helps in providing a suitable replacement for the costly available reliquefaction systems and avoids the burning of BOG with its consequent high CO2 emissions.

Combining a methanation step with biomass gasification requires an intensive tar removal process that reduces its content down to 1 mg/Nm3. In this paper, low temperature processes are suggested for treating tar and reducing its content to the acceptable limit. However, the gas must be pre-treated prior to the low temperature process in order to reduce its temperature, its moisture content and the heavy tar fraction. Two water scrubbers are placed prior to the low temperature tar removal process. Benzene and toluene remains in the producer gas after the scrubbers. Those two components can be valorised if separated from the producer gas at low temperature. The tar removal, at low temperature, induces the water vapour frosting remaining in the producer gas. The simultaneous frosting and condensation takes place over a cold plate. Modelling simultaneously the multi-component frost growth and condensation requires complex mathematical approach. A parametric study is completed to assess the impact of the wall temperature and the producer gas flow rate on the tar removal process function of time and plate length. Results showed that a wall temperature of -20 (C is required to lead to the benzene frost formation for an initial molar fraction of 0.024. After one hour, the thicknesses of benzene and ice frost layers reach 1.5 and 2.5 mm, respectively. Therefore, the heat transfer between the gas and the cold surface is reduced.

The building sector has a great potential to reduce energy consumptions and environmental impacts on a global level. Despite the progress in dynamic building energy simulation (DBES) models concerning deterministic phenomena [1–8], the ability to predict energy consumption is limited by the non-deterministic boundary conditions, especially those related to occupants’ behaviour

For residential heat pumps, R32 becomes one of the most widely used refrigerant, thanks to an environmental impact much lower than R410A. However, with a classic suction superheat control, R32 induces higher discharge temperatures. Two-phase suction is thus generally allowed in rotary compressors to lower the discharge temperature. In theory, this process can also improve the heat pump performances. However, using two-phase suction for real-time performance optimization implies to identify and control the suction vapour quality. In this study, an iterative method using the compressor energy balance and the compressor efficiencies is presented to determine the suction vapour quality and refrigerant mass flow rate without using a flowmeter. An R32 air-to-air heat pump is then experimentally tested. The reference values are indirectly measured through the mass flow rate measurement and the compressor energy balance. A correlation is thus presented, giving the vapour quality from the operating parameters. If the volumetric or global compressor efficiencies are known, the proposed iterative method allows to calculate the vapour quality with a 0.4 % accuracy. Moreover, this method gives the refrigerant mass flow rate and heating capacity with a 1 % accuracy. The sensitivity of the method is evaluated considering a 10 % error on the volumetric or global efficiency values. In this case, the suction vapour quality values are kept within 2.5 % of the reference measurement. In addition of allowing a precise control of two-phase suction, this method can also make the in-situ performance measurement of these heat pumps possible.

The use of two-phase nozzles for low-grade heat valorization by electricity production increases the energy recovery rate using Trilateral Flash or Wet to Dry cycles. A model benchmark for nozzle flow rate and efficiency estimation was conducted on experimental data from the literature. These data come from a series of tests made on geothermal energy production water two-phase nozzles. A new transitional bubble-to-droplet interfacial area density formulation (TA-BD model) is presented by the paper. It is compared to three models from literature. Two nozzles operating with different inlet and outlet conditions were modeled. The calibration flexibility and the robustness of the models are discussed in association with physical analysis. The paper shows how the models using single or redundant adaptation parameters fail to provide good results simultaneously on flow rate and efficiency. It appeared that the TA-BD model is the more flexible and robust. The Homogeneous Relaxation Model (HRM) model gives also good results. Furthermore, TA-BD model gives the lowest average discrepancies. Especially at the best efficiency point of the first test case, TA-BD model shows less than 1% discrepancy where the HRM model has 18% discrepancy in efficiency. The TA-BD model appeared to be easier to calibrate than the HRM model. Finally, regarding the proposed TA-BD model, the sensitivity to the geometry and operating conditions shows that the interfacial area density formulation could be completed to include the effect of nozzle's section profile, the effect of the inlet temperature on bubbles number density, and the effect of outlet pressure on the droplets number density.

Biomass gasification is the thermo-chemical conversion of biomass into producer gas. The latter can be then integrated in a combined heat and power unit or chemically converted into biofuels. Tar formation during biomass gasification is the main process disadvantage. Tar leads to fouling and clogging problems in the process, in addition to catalyst deactivation when production of chemicals is envisaged. Eliminating tar from the producer gas forms the trigger point for any further valorization. This work hence evaluates the efficiency of wet scrubbers on tar removal from producer gas, based on simulations conducted using Aspen Plus. Wet scrubbers are highly efficient tar removal methods suitable for small scale gasifiers and having a low cost. Two scrubbers are placed in series to increase the tar removal efficiency. The tar reduction efficiency is assessed function of the scrubbing liquid: rapeseed methyl ester and water. Sensitivity studies handling the variation of the liquid to gas ratio and the scrubbing liquid temperature were conducted to study their impact on the tar removal efficiency. Results showed that increasing the liquid to gas ratio and decreasing the scrubbing liquid temperature leads to higher tar removal efficiencies. However, the conducted economic analysis indicated that the operational cost increases as well. A balance between the non-aqueous scrubbing liquid higher tar removal efficiencies with lower utilities cost and the actual liquid cost makes water an alternative scrubbing liquid choice. Finally, the selection of the optimal conditions depends mainly on the required tar limit set for the producer gas application.

This paper presents the simulations and experiments for the development of a hybrid and reversible mobile air conditioning, organic Rankine cycle (ORC), and ejector refrigeration cycle (ERC) system. This flexible and compact system may be the solution to the introduction of waste heat recovery in passenger cars. The cycle fuel economy is calculated for series hybrid electric vehicles (SHEVs). A global vehicle model is used to simulate the annual weather conditions of different climatic regions. The reference driving cycle is the Worldwide Harmonized Light Vehicle Test Cycle. The cycle fuel economy is maximized in temperate and cold climatic regions. In the hypothesized engine cold-start initial condition, the SHEV ReverCycle maximum fuel economy is 1.2% in Paris. In the hot-start initial condition, the SHEV ReverCycle maximum fuel economy is 2.2% in Moscow. The experimental results of the ReverCycle proof of concept are then presented. The maximum measured net efficiency in the ORC mode is 3.9%. The ERC mode can satisfy cabin cooling requirements at an ambient temperature below 20 °C. The estimated fuel economy in the ERC mode is 1.4%.

International audience; The aim of this study is to develop real-time energy management strategies for HVAC systems taking into account the heat storage in building thermal mass. In fact, thermal energy production represents up to 50 % of building's total energy consumption and 75 % of Greenhouse Gases (GHG) emissions. Different systems and storage methods can be integrated to reduce the cost and the GHG emissions related to heating, cooling and Domestic Hot Water (DHW) production in buildings. In this context, multiple studies have developed optimal control systems (such as Model Predictive Control) for optimising thermal production and/or storage systems. The results presented in these studies showed a wide range of reduction rates due to different hypotheses, models, methods and systems taken into consideration. In real time optimisation, the building model is usually separated from the thermal system. In this study, a reduced model and a continuous optimisation method were used to minimise the cost of the building's heating. The applied strategy combined the building model and thermal mass with a Ground Source Heat Pump (GSHP) and a Borehole Thermal Energy Storage (BTES). This first approach showed promising results by reducing the cost between 10 % and 15 %. This method will be used to combine different systems and improve their performance in real-time. Key Innovations  Real time simultaneous multi-system optimisation using Pontryagin Minimum Principal.  BTES and GSHP operation optimisation taking into consideration building thermal mass energy storage under variable electricity pricing. Practical Implications Real time optimal control is an interesting solution for cost and GHG emissions reduction. When it comes to such simulations, the results can vary on the models, hypotheses and algorithms used. Every project should be analysed separately, and the building properties taken into consideration in the application of the optimal control.

International audience; The building sector is the economic sector of the EU that has the highest final energy consumption. In response to concerns about climate change, energy security and social equity, most countries plan to substantially reduce energy demand and greenhouse gas emissions. Moreover, 55 % of the world’s population lives in urban areas, a proportion that is expected to rise to 68 % by 2050. Finally, there are effective catalysts to improve environmental performance at the scale of urban projects. For these reasons, environmental impacts of the neighbourhood have to be minimised using reliable tools offering economically viable solutions. This paper presents a multicriteria optimisation methodology that has been developed to reduce both investment and environmental costs of buildings. The life cycle assessment methodology used in this study enables the evaluation environmental impacts over the whole life cycle of buildings. The optimisation of an individual building and the simultaneous optimisation of several buildings were carried out considering various criteria such as environmental impacts and construction cost, in the case of a 5-hectare urban project. A genetic algorithm was implemented in order to identify Pareto-optimal solutions associating a life cycle assessment tool to building energy simulation. The first step was to implement the NSGA-II algorithm and a comparison with the NSGA-III algorithm is considered in perspective. Results present optimal Pareto fronts minimising investment costs and CO2 emissions of buildings. In this way, a decision-making aid is proposed to urban planners.

The present energy mix is leaning towards natural gas as solution to reduce our carbon footprint due to its relatively low GHG emission factor. Gas Turbines could therefore be a great short-to-mid-term solution to fight climate change. The gas turbine flexibility, or part-load operation, is an indispensable asset in some OG however, it is also showed the potential part-load efficiency compensation due to the IAH effect that could improve by 1 point the efficiency at 50 % load and 50 % recirculation rate.

International audience; The climate data used for dynamic energy simulation of buildings located in urban areas are usually collected in meteorological stations situated in rural areas, which do not accurately represent the urban microclimate (e.g. urban heat island effect), leading to potential simulation errors. This paper aims at quantitatively evaluating the effects of heat island on a high-rise building energy performance, based on the microclimate simulation tool ENVI-met and building energy simulation tool COMFIE. However the computation of microclimate is time consuming; it is not possible to simulate every day of a year in a reasonable time. This paper proposes a method that generates hourly "site-specific climate data" to avoid long microclimate simulation time. A coupling method of ENVI-met and COMFIE was developed for more precise simulation, considering the effects of heat island on buildings energy performance. It was applied to a high-rise building in Wuhan, China. The results showed that the yearly average urban heat island effect intensity at the height of 3 m was estimated to be 0.45 °C and decreased with the height. Compared to the simulation considering the outdoor temperature variation with the height and orientation, using the original climate data collected in rural areas led to an overestimation of the heating load by around 3.5 % and an underestimation of the cooling load by around 3.9 %. Compared to the weather file at the height of 3 m in the south neglecting the temperature variation along the height, the heating load was overestimated by 5.4 % and the cooling load was underestimated by 6.9 %. The methods proposed in this paper can be used for a more precise application of urban building energy simulation.

A multi-period mixed-integer-linear-programming problem for the design of mass networks is proposed in this paper. Design of mass networks, conversion systems and storages is done so as to minimize the capital expenses and operating costs and fulfill demand in resources. This work provides a detailed model of compressed gas storage, considering pressure state inside gas tank, compression costs and compressor design, which have not been considered before in a linear model, with a discrete pressure scale. The performance of the model is assessed on a hydrogen network design problem, including renewable electricity, electrolyzer design and hydrogen storage. The share of renewable electricity use increases from 60% to 90% with hydrogen storage. Different compressed gas storage linearized models are compared with different pressure scales and the linearization error is assessed. The introduction of discrete intermediate pressures reduces the committed error on compressor power and operating costs, due to the linearization.

Following the tendency of sustainable development, compressed natural gas as an alternative fuel has been expanded applied in the transportation sector these years. Although several studies on the life cycle are quite comprehensive for passenger vehicles, it is problematic to apply these results to heavy-duty electric hybrid trucks. This study applies the Well-to-Wheel methodology on compressed natural gas fuel. The optimized hybrid electric truck model is built up to minimize the truck performance variation. The total CO2 equivalent emissions and the methane leakage as indicators are compared among the three largest emitting countries. The results indicate that compressed natural gas-based hybrid trucks have 9.1%–18.7% less CO2 equivalent emissions than diesel-based ones and the results are more obvious for heavy-duty trucks. Nevertheless, this advantage may be minimized by methane leakage, particularly in the recovery process, accounted for 7.3% Total CO2 equivalent emissions increase in North America, 5.1% in Europe, 5.3% in China from well to wheel. Applying natural gas in hybrid electric trucks does have environmental benefits. Methane capturing and compression efficient improving can be the faster ways to help reach the emission reduction target.

International audience

The limited driving range (DR) of battery-electric buses (BEB) is the main barrier preventing their wide deployment. The bus operating conditions (driving conditions, passenger occupancy, and weather conditions) directly impact its energy needs and battery size requirements, and thus affect the BEB DR. For this sake, it is important to evaluate the BEB energy consumption in detail. This paper provides a comprehensive energy analysis for city and intercity battery-electric buses under real-world operating conditions. The analysis helps in properly sizing the battery based on the bus's real-world energy needs. The results show that there is room to significantly reduce the required battery size for the city bus, unlike intercity buses.

International audience

International audience

International audience; In refrigeration systems ejectors are used to increase the pressure of an entrained or secondary stream using the energy of a high pressure and high temperature primary stream. The lack of flexibility of ejectors contributes to their modest deployment in the refrigeration market and more widely in industry. In general, for gas-gas ejectors, the highest ejector performance is obtained at the critical pressure ratio. For lower pressure ratios the entrainment ratio remains constant, and for higher pressure ratios it drops rapidly to zero. This behavior makes the load control hard to handle. In order to increase the flexibility of ejectors and also the average entrainment ratio, variable geometry solutions exist. Those solutions allow the variation of the primary stream nozzle throat section or the nozzle axial position. With those solutions the secondary mass flow remains limited to a maximum fixed by the mixing chamber diameter. In this paper, a new variable geometry ejector concept is explored that allows increasing the secondary stream flow rate as the discharge pressure decreases. The ejector performance is estimated by computational fluid mechanics. This is compared to a geometry from literature. The case study is an R134a ejector driven refrigeration cycle using waste heat. The interest of the new variable geometry ejector on the seasonal Energy Efficiency Ratio is analyzed.

International audience; The reduction of global warming potential gases emissions in industrial refrigeration devices requires the development of efficient cycles using low GWP gases. The supercritical C02 cycle assisted by a transcritical two phase ejector is a nice example of such cycles. The design of such ejectors is not obvious and an intense development of performance prediction tools is observed in literature especially regarding two-phase CFD modeling. The two phase flow CFD models are limited today by their lack of flexibility and difficulties to empirically calibrate them. The main drawback of classical Hertz-Knudsen or HRM phase change models is their difficulty to simultaneously predict the mass flow rate and the outlet velocity of the primary flow of the ejector. These two parameters are responsible of the entrainment ratio an ejector at given operating conditions and geometry. This paper presents a thermal phase change model that introduces a non symmetric interfacial area density formulation for two-phase liquid-gas CO 2 ejectors. This formulation describes the gas-liquid interface as bubbles at low void fractions and as droplets at high void fractions. The model results are compared to experimental results of literature. It appeared that bubbles number density affects mainly the primary flow rate and the droplets number density affects the outlet velocity of the primary nozzle and thus the mixture pressure and the secondary flow rate.

International audience; A bubble to droplet transition non-symmetric interfacial area density formulation was developed for flash boiling nozzles CFD modeling. This formulation is used in a two fluid Euler-Euler modeling with a thermal phase change model. The regime transition formulation is based on the number of bubbles density and number of droplet density values. The first affects mainly the flow regime close to the nozzle throat and the second parameter affects mainly the flow close to the outlet. The physical factors affecting the calibration values of these parameters are analyzed in this paper with the aim of defining appropriate closure models. The analysis is done using experimental data available in literature. The comparison is done on the mass flow rate and the nozzle outlet velocity. It appears that the number of bubbles density is related to the inlet sub-cooling conditions and that the number of droplets density is affected by the outlet pressure and Reynolds number.

International audience

International audience

The balance between supply and demand for electricity is mainly disrupted by the growing contribution of renewable energy sources to the electrical grid since these sources are intermittent by nature. Therefore, the energy storage systems, mainly those of considerable size, become essential to restore the electricity balance. The compressed air energy storage (CAES) system is one of the mature technologies used to store electricity on a large scale. Therefore, this article discusses the energy and exergy analysis of different configurations of a constant-pressure CAES system to improve its overall efficiency and energy density. The exergy efficiency of our basic adiabatic configuration using water as thermal storage medium is 56.4% and the energy density is 12.17 kWh/m3. The results show that the CAES system using a packed bed of quartzite rock as thermal storage medium has the best efficiency (67.2%) and energy density (17 kWh/m3) among adiabatic systems. The diabatic CAES systems could have a net efficiency up to 70.1% and an energy density up to 31.95 kWh/m3 by using combustion chambers. Finally, the waste heat recovery from other installations such as a gas turbine power plant has the potential to improve the energy density to 20.53 kWh/m3 without using fossil fuel sources.

International audience

The integration of thermodynamic systems in industrial processes can help increasing the energy recovery and provide more integration opportunities. However, designing such technologies in a simultaneous mass and heat integration is a large-scale and complex problem. Indeed, the heat requirements created by the mass allocation network are unknown prior to the whole design. Besides, designing sequentially the mass allocation network (MAN) and the heat exchanger network (HEN) can lead to sub-optimal solutions. This paper proposes a three-step methodology based on mixed-integer-linear-programming (MILP) models to evaluate economically suitable technologies, reducing strongly the computational time. After a preliminary step, a first MILP model evaluates economically a great number of technologies simultaneously. In this model, the simplified total cost, including thermodynamic systems capital costs, is minimized. Then, the best thermodynamic systems candidates are identified and used in a second MILP solving the larger problem including the simultaneous MAN and HEN design. The performances of the methodology are assessed on an ammonia recovery case study: 3 economically relevant technologies among 74 are selected in a few seconds. Then, the MAHEN (mass allocation and heat exchange network) is designed with these technologies, showing a decrease of total annualized cost of 3.6%.

International audience; In France, buildings account for a significant portion of the electricity consumption (around 68%), due to an important use of electrical heating systems. This results in high peak load in winter and causes tensions on the production-consumption balance. In view of reducing such fluctuations, advanced control systems (including the Model Predictive Control framework) have been developed to shift heating load while maintaining indoor comfort and taking advantage of the building thermal mass. In this paper, a framework for developing optimisation-based control strategies to shift the heating load in buildings is introduced. The balanced truncation method and a time-continuous optimisation method were used to develop a real-time control of the heating power. These two methods are well suited for control problems and yield precise results. The novelty of the approach is to use reduced models derived from advanced building simulation software. A simulation case study demonstrates the controller performance in the synthesis of a predictive model-based optimal energy management strategy for a single-zone test building of the "INCAS" platform built in Le Bourget-du-Lac, France, by the National Solar Energy Institute (INES). The controller exhibits excellent performance, reaching between 6 and 13% cost reduction, and can easily be applied in real-time.

Due to the foreseen growth of sustainable energy utilization in the upcoming years, storage of the excess production is becoming a rather serious matter. In this work, a promising solution to this issue is investigated using one of the most emerging technologies of electricity conversion: reversible solid oxide cells (RSOC). A detailed model was created so as to study the RSOC performance before implementing it in the global co-electrolysis Aspen PlusTM model. The model was compared to experimental results and showed good agreement with the available data under steady state conditions. The system was then scaled up to a 10MWco-electrolysis unit operating at 1073 K and 3 bar. The produced syngas is subsequently directed to a methanation unit to produce a synthetic natural gas (SNG) with an equivalent chemical power of 8.3 MWth. Additionally, as a result of a heat integration analysis, the methanation process provides steam and electricity to operate the rest of the units in the process. A final CO2 capture step is added to ensure the required specifications of the produced SNG for gas network injection. Lastly, the overall performance of the power-to-gas process was evaluated taking into account the energy consumption of each unit.

The liquid desiccant membrane cooled ceiling (LDMC-C) and displacement ventilation (DV) system removes humidity directly from the space. However, LDMC-C/DV system does not control humidity in the lower occupied zone. In this work, a method for humidity control is proposed where fraction of the dehumidified cool dry air adjacent to the LDMC ceiling is extracted from the exhaust stream and mixed with the DV supply air stream. This leads to re-establishing of the thermal comfort; reducing the DV cooling requirements, and saving energy. A time-dependent mathematical model of the LDMC-C was developed and validated experimentally. The LDMC-C transient model was then integrated to the mixed DV space model and was applied to a case study. When mixing strategy was applied, the relative humidity dropped by an average of 8.72% in the occupied zone within 12 min and energy saving of 24% was achieved compared to in-duct conventional dehumidification.

Research has to address global energy issues in order to reduce energy consumption and greenhouse gas emissions to limit climate change. This research includes the development of new urban simulation tools, called UBEM (Urban Building Energy Modelling), to help the collectivities, study offices and other energy transition stakeholders reduce energy consumption in the building sector. These UBEMs are composed of models that have to deal with the problems of lack of parametrization data and calculation costs related to urban simulation. Many models exist with different levels of detail, to simulate all the physical phenomena linked to the building, energetic systems or external solicitation while respecting these constraints. Due to the wide variety of models available, the user/modeler may find himself in situations where the selection of the most suitable models for his study can be tedious and complex. Thus, a methodology for carrying out a "parsimonious" simulation is proposed in this thesis. This parsimony of simulation aims at finding the right level of modelling by determining the trade-off point between: the number of input parameters and their uncertainty, the level of detail of the model with its simplifying hypotheses, the precision obtained and the simulation time, all for a given output and context. Key guidance indicators (KGI) are created from district characteristics and used to determine threshold values for the selection of the model complexity to be used. This contribution allows to advise and guide various users and modelers in their urban modelling, so as to promote a simulation which is not the most accurate, but the most suitable for the case study. Thus, the thesis proposes a methodology for the development of more parsimonious and therefore more effective decision support tools, allowing to make the various stakeholders aware of all the parsimony challenges: move from the logic of always more to just the right thing.; La recherche doit répondre aux enjeux énergétiques globaux afin de réduire les consommations énergétiques et les émissions de gaz à effet de serre pour limiter l’impact du changement climatique. Cette recherche s’appuie notamment sur le développement de nouveaux outils de simulation urbaine, appelés UBEM (Urban Building Energy Modelling), afin d’aider les collectivités, les bureaux d’études et autres acteurs de la transition énergétique à réduire les consommations d’énergie du secteur du bâtiment. Ces UBEM sont composés de modèles devant intégrer les problématiques de manque de données de paramétrage et de coût de calcul liés à la simulation urbaine. De nombreux modèles existent avec des niveaux de détail différents, afin de simuler l’ensemble des phénomènes physiques liés au bâti, aux systèmes énergétiques ou encore aux sollicitations extérieures, en respectant ces contraintes. De par cette grande diversité de modèles à disposition de l’utilisateur, ce dernier peut se retrouver dans des situations où la sélection des modèles les plus adaptés à son étude peut s’avérer fastidieuse et complexe. Ainsi, une méthodologie permettant de réaliser une simulation dite « parcimonieuse » est proposée dans cette thèse. La parcimonie de simulation a pour objectif de trouver le bon niveau de modélisation en déterminant le point d’équilibre entre : le nombre de paramètres d’entrée et leurs incertitudes, le niveau de détail du modèle avec ses hypothèses simplificatrices, la précision obtenue vis-à-vis d’une référence et le temps de simulation, le tout pour une sortie et un contexte donnés. Pour cela, des KGI (Key Guidance Indicators), créés à partir des caractéristiques liées à l’échelle quartier, sont utilisés afin de déterminer des valeurs seuils permettant de choisir quel niveau de modélisation utiliser suivant le quartier. Cette contribution permet de pouvoir conseiller et guider divers utilisateurs et modélisateurs, dans leurs modélisations urbaines, afin de proposer une simulation non pas la plus précise, mais la plus adaptée au cas d’étude. Cette thèse propose ainsi une méthodologie pour le développement d’outils d’aide à la décision plus parcimonieux et donc plus efficaces, permettant passer de la logique du toujours plus à juste ce qu’il faut.

Energy efficiency and decarbonation of energy use in the building sector is a strategic issue of the ecological transition in France. In 2019, the French building stock accounts for 45% of the final energy consumption, with the tertiary sector alone accounting for about one third of this or 17% of national consumption. The energy consumption of the tertiary stock and its determining factors are poorly documented. Existing tertiary stock models are mostly based on an aggregated representation of the total heated surface of the building stock subdivided by its economic activity and heating energy fuel. This aggregation makes it impossible to represent the extreme heterogeneity of the sector. This work aims at reconciling different accessible databases to establish a tertiary building stock model, its consumption and its load curve. The developed method allows to represent the building stock as a collection of buildings, in which each of them is characterized individually in terms of area, constructive and thermal characteristics, occupants, main activity sector and equipment. This method allows to take account of the link between building, system and occupancy, which contributes to the heterogeneity of the tertiary sector. The methodology is designed to be applicable to any territory in metropolitan France. The results of surface area modelling and energy consumption simulation could thus be compared with existing references for the Île-de-France region. Two applications of the method are presented: the study of the energy saving potential of the tertiary sector in the Île-de-France region, and the study of photovoltaic self-consumption in the tertiary sector for the agglomeration of Orleans.; L’efficacité énergétique et la décarbonation des usages de l’énergie dans le secteur du bâtiment constituent un enjeu stratégique dans le cadre de la transition écologique en France. En 2019, le parc de bâtiments français représente 45% de la consommation finale d’énergie, le secteur tertiaire à lui seul compte pour 17%. La consommation d’énergie des bâtiments du secteur tertiaire et ses déterminants sont très peu documentés. La représentation du parc de bâtiments tertiaire français est aujourd’hui essentiellement basée sur des estimations de surface chauffée segmentées selon les activités économiques et l’énergie de chauffage. Ceci rend impossible la représentation de l’extrême hétérogénéité du secteur tertiaire. La difficulté majeure est liée au manque de données et d’études sur ce secteur. Ce travail vise à réconcilier différentes sources de données facilement accessibles pour modéliser le parc tertiaire, ses consommations et sa courbe de charge. La méthode développée permet de représenter le parc sous forme d’une collection de bâtiments dont chaque individu est caractérisé de manière techno-explicite par sa surface, ses caractéristiques constructives et thermiques, ses occupants, son secteur d’activité principal et ses équipements. Cette méthode permet la prise en compte des singularités du lien bâti-système-occupant qui participent à l’hétérogénéité du parc tertiaire. La méthodologie est conçue pour être applicable à tout territoire en France métropolitaine. Les résultats de modélisation des surfaces et de simulation de la consommation d’énergie ont ainsi pu être comparés aux sources existantes pour la région Île-de-France. Deux applications de la méthode sont présentées : l’étude du gisement d’économie d’énergie du secteur tertiaire de la région Île-de-France, et celle de l’autoconsommation photovoltaïque du secteur tertiaire pour la métropole d’Orléans.

International audience; This chapter describes the research experience of the International Energy Agency-Energy in Buildings and Communities Programme Annex 72 members on the application of multi-objective optimization processes for the selection of design or retrofit actions that allow for improving different aspects (energy, environmental, economic, etc.) of buildings in a life cycle perspective. Thirteen case studies were examined focussing on methodologies, applications and results and deriving generic conclusions and guidelines for building designers and decision-makers.

International audience

International audience; Highlights  A tool was developed to help real estate owners plan refurbishment  The tool identifies priorities in terms of actions and buildings to be retrofitted  It combines dynamic building energy simulations and multi-objective optimisation  It was applied to a social housing stock with a multi-year budget constraint  Priorities are set based on the identified optimal renovation schedules

International audience

Heat pumps are a key system for reducing energy consumption and greenhouse gas emissions in buildings. Their performances depend on many factors that cannot always be predicted, therefore in-situ measurement is necessary to know the real performances of each equipment. A previously developed method is presented and validated. It is able to measure accurately the heating power in steady-state for superheated vapour compression. However, it is not functional for transitory state and for two-phase suction. Thus, complementary methods are studied and evaluated to extend the performance measurement to these cases. A complete method is then suggested, allowing a better consideration of wet compression cycles and transitory operation in seasonal performance assessment.; La pompe à chaleur est l’une des clés de la réduction des émissions de gaz à effet de serre dans les bâtiments. Ses performances in-situ dépendent de nombreux facteurs, et la mesure embarquée est alors nécessaire afin de connaître les performances réelles de chaque installation. Une méthode de mesure précédemment développée est présentée puis validée. Elle permet de mesurer de façon fiable la puissance calorifique en régime pseudo-stabilisé pour des cycles avec surchauffe. Cependant, elle n’est pas fonctionnelle en régime transitoire et dans le cas de compression avec aspiration diphasique. Ainsi, des méthodes alternatives complémentaires permettant d’estimer les performances des PAC dans ces conditions particulières sont étudiées et évaluées. Une méthode globale d’évaluation des performances est alors proposée, permettant une meilleure prise en compte de l'aspiration diphasique et des phases transitoires.

Heat pumps are a key system for reducing energy consumption and greenhouse gas emissions in buildings. Their performances depend on many factors that cannot always be predicted, therefore in-situ measurement is necessary to know the real performances of each equipment. A previously developed method is presented and validated. It is able to measure accurately the heating power in steady-state for superheated vapour compression. However, it is not functional for transitory state and for two-phase suction. Thus, complementary methods are studied and evaluated to extend the performance measurement to these cases. A complete method is then suggested, allowing a better consideration of wet compression cycles and transitory operation in seasonal performance assessment.; La pompe à chaleur est l’une des clés de la réduction des émissions de gaz à effet de serre dans les bâtiments. Ses performances in-situ dépendent de nombreux facteurs, et la mesure embarquée est alors nécessaire afin de connaître les performances réelles de chaque installation. Une méthode de mesure précédemment développée est présentée puis validée. Elle permet de mesurer de façon fiable la puissance calorifique en régime pseudo-stabilisé pour des cycles avec surchauffe. Cependant, elle n’est pas fonctionnelle en régime transitoire et dans le cas de compression avec aspiration diphasique. Ainsi, des méthodes alternatives complémentaires permettant d’estimer les performances des PAC dans ces conditions particulières sont étudiées et évaluées. Une méthode globale d’évaluation des performances est alors proposée, permettant une meilleure prise en compte de l'aspiration diphasique et des phases transitoires.

Thermal comfort of drivers and passengers inside cars compartments is a subject bouncing back to the spotlight with the electrification of vehicles. In fact, air conditioning and heating systems can reduce the battery autonomy of electric vehicles by up to 50% under certain conditions. On the other hand, the most used thermo-physiological models nowadays are still those that consider a standard average person. Many studies showed the limitations of these models in predicting thermal comfort for different populations in complex environments. Therefore, if a personal thermal comfort at minimum vehicle energy consumption is required, a deep consideration should be given to the understanding of the individualization of the thermo-physiological model and to identifying key parameters that have the most influence on thermal comfort. An individualization procedure followed by an experimental validation of the customized model is presented. Considering individual characteristics was shown to improve the model by 20% on average.; Le confort thermique des conducteurs et des passagers dans les compartiments de la voiture est un sujet qui redevient d’actualité avec l'électrification des véhicules. En fait, les systèmes de climatisation et de chauffage peuvent réduire l'autonomie des véhicules électriques jusqu'à 50% dans certaines conditions. D'autre part, les modèles de représentation des personnes les plus utilisés sont encore ceux qui considèrent une personne moyenne standard. De nombreuses études ont montré les limites de ces modèles dans la prévision du confort thermique de différentes populations dans des environnements complexes. Par conséquent, si un confort thermique personnel correspondant à une consommation minimale d’énergie du véhicule est requis, il convient d’accorder une attention particulière à la compréhension de l’individualisation du modèle thermo-physiologique et à l’identification des paramètres clés ayant le plus d’influence sur le confort thermique. Une procédure d’individualisation a été exposée suivi d’une validation expérimentale du modèle personnalisé. La prise en compte des caractéristiques individuelle améliore la prédiction du modèle de 20% en moyenne.

To fulfill the objectives of reducing greenhouse gases and renewable energy consumption, the performances improvement of heat productions systems such as district heating network is required. Ones of the solutions is to detect the malfunctions and to optimize the control. This thesis gives 4 performance indicators to detect common malfunctions. They have been developed through a generic numerical test bench of a french district heating network, and tested on in-situ data. The malfunctions correction enables to apply an optimization strategy on the supply temperature control of the network. The method has been tested on a numeric twin of a real network. The results show the control strategy leads to an improvement of the networks performances.; Pour atteindre les objectifs de réduction de gaz à effet de serre et de consommation d’énergie renouvelable, il est nécessaire d’améliorer les performances des systèmes de production de chaleur tels que les réseaux de chaleur. Cela passe par la détection de dysfonctionnement et par l’optimisation du pilotage. Cette thèse propose 4 indicateurs de performance afin de détecter les dysfonctionnements courants. Ceux-ci ont été développés à l’aide d’un banc d’essai numérique générique d’un réseau francilien en incluant le côté secondaire, puis validés sur des données in-situ. La correction des dysfonctionnements a permis la mise en place d’une stratégie d’optimisation sur le pilotage de la température de départ d’un réseau. La méthode a pu être testée numériquement sur un jumeau numérique d’un réseau existant. Les résultats montrent que la stratégie de pilotage amène des gains de performances sur le réseau.