1,721,270 research outputs found
Framework to assess climate change impact on heating and cooling energy demands in building stock: A case study of Belgium in 2050 and 2100
Full text linkpeer reviewedClimate change has a broad impact on different aspects of energy use in buildings. This study explores potential changes in future heating and cooling energy demands. Increasing comfort expectations resulting from events like the extraordinary summer heatwaves in Europe are accelerating this trend to develop future scenarios for a better understanding of the relationship between future climate changes and the cooling need. This study used future weather data to estimate the heating and cooling energy demands in the Belgian building stock by 2050 and 2100 under base and business-as-usual scenarios using a dynamic building simulation model. The study showed that heating energy demand in the base scenario is expected to decrease by 8% to 13% in the 2050s and 13% to 22% in the 2090s compared to the 2010s. Additionally, the cooling energy demand is expected to increase by 39% to 65% in the 2050s and by 61% to 123% in the 2090s compared to the 2010s. Retrofit strategies applied to different building types contribute to lower the increase in cooling energy demand in the business-as-usual scenario compared to the base scenario. The cooling energy demand for an average building in the business-as-usual scenario is expected to increase with a range of 25% to 71% in the 2050s compared to 45% to 92% in the base scenario and 77% to 154% in the 2090s compared to 72% to 198% in the base scenario compared to the 2010s. The findings of the study provide insights to mitigate the impacts of climate change on heating and cooling energy demands.[OCCuPANt] Impacts of climate change on buildings in Belgium during summer13. Climate actio
Le rôle des piles à combustible de micro-cogénération résidentielle dans la transition énergétique - Cas d'études en Belgique
Full text linkCette thèse examine le rôle des systèmes de micro-cogénération à piles à combustible dans la transition énergétique via un travail théorique et expérimental. La thèse commence par définir la ‘décarbonisation’ à travers la notion de budgets carbone, en s'appuyant sur les derniers travaux du GIEC (AR6), qui sont ensuite contextualisés à l’échelle locale et individuelle, avec les exemples de la Belgique, de la Wallonie et de la France. En tenant compte des émissions importées, les engagements actuels de ces régions/pays ne sont en fait pas compatibles avec les recommandations du GIEC visant à limiter le réchauffement à +2°C. De plus, étant donné que certaines émissions de gaz à effet de serre ne pourront jamais être complètement atténuées, la neutralité carbone en 2050 ne pourrait être atteinte qu'en augmentant les puits de carbone à au moins 1 tCO2eq/an par habitant, ce qui représenterait une augmentation de +370% et +300% par rapport aux niveaux actuels (naturels) respectifs pour la France et la Wallonie, ce qui sera extrêmement difficile.
La thèse fournit des descriptions complètes des principaux types de piles à combustible existantes et de leurs caractéristiques respectives. De plus, les performances futures des piles à combustible de micro-cogénération sont étudiées. Les performances des systèmes PEMFC ne devraient pas augmenter de manière significative. Ce n'est pas le cas des systèmes SOFC, qui pourraient offrir une efficacité électrique théorique (DC) de 100% (LHV) pour l'oxydation électrochimique de biochar ou du méthane, qui peut être un vecteur d'hydrogène renouvelable. Par ailleurs, l'efficacité électrique LHV maximale démontrée (AC) d’une SOFC disponible commercialement depuis 2023 est déjà de 65%.
Ensuite, la thèse présente des travaux expérimentaux et de simulation réalisés sur deux systèmes actuellement commercialisés, à savoir le SOFC Bl***G*N et la PEMFC P*2 (noms donnés dans ce manuscript). Les travaux expérimentaux comprennent à la fois des campagnes de tests en laboratoire et un suivi des tests in situ, sur le terrain, dans des applications réelles, débouchant sur des modèles de performance qui peuvent spécifiquement être intégrés dans des outils de simulation de bâtiments ou de planification énergétique. Le système PEMC testé présente un niveau élevé d'hybridation avec une chaudière à condensation classique, ce qui est présumé empêcher un fonctionnement optimal et robuste de ces deux sous-systèmes. En revanche, le système SOFC testé est fiable et offre une efficacité électrique toujours proche de 60% (LHV) à sa puissance nominale, qui peut par ailleurs facilement être modulée dans la plage de 33% à 100%.
En s'appuyant sur ces performances expérimentales et sur les progrès anticipés des systèmes de piles à combustible, la thèse démontre que leur potentiel de réduction des gaz à effet de serre sur l’empreinte carbone individuelle moyenne reste relativement insignifiant si leur combustible n'est pas décarboné. Même dans ce cas, la réduction resterait insuffisante, et d'autres actions devraient encore être mises en œuvre.
Cependant, certaines piles, telles que les SOFC à ‘Direct Carbon’ (DCSOFC) ou les PEMFC à ‘Direct Formic Acid’ (DFAFC), offrent la possibilité capturer du pure CO2 à leur échappement anodique. Avec l'étude de cas de la demande électrique moyenne d'un logement belge et de l'utilisation d'une voiture électrique (pour environ 20000 km/an) fournie par une DCSOFC avec une efficacité électrique LHV de 80% alimenté en biomasse, ces émissions négatives pourraient atteindre environ 3 MtCO2eq/an. Vu le niveau minimal d'absorption de carbone requis par l'objectif de neutralité carbone (spécifié plus haut), le potentiel d'émissions négatives de ces systèmes de piles à combustible devra absolument être davantage développé et mis en œuvre en parallèle d’une augmentation significative des puits carbone naturels.Through theoretical, simulation, and experimental work, this thesis investigates the role of fuel cell micro-cogeneration systems in driving the energy transition. The thesis begins by defining the ‘decarbonization’ though the notion of carbon budgets, drawing insights from IPCC's latest work (AR6), which is then contextualized at both local and individual scales, with the examples of Belgium, Wallonia, and France serving as frequent case studies throughout this research. Considering imported emissions, the current commitments of those regions/countries is in fact not compatible with IPCC’s +2°C recommendations. Also, since some greenhouse gases emissions could never be fully mitigated, 2050 carbon neutrality could only be reached by increasing carbon sinks to at least 1 tCO2eq/year per capita, which will be highly challenging for France or Wallonia as it represents +370% and +300% increases against respective current (natural) levels.
Introducing the concept of fuel cells, the thesis provides comprehensive descriptions of main existing fuel cell types and their respective characteristics. Furthermore, the future performance of micro-cogeneration fuel cells is reviewed according to their underlying technology. PEMFC (Polymer Electrolyte Membrane Fuel Cell) systems performance are not expected to be significantly increased. This is not the case for SOFC (Solid Oxide Fuel Cell) systems, that exhibit no Carnot limit and could offer theoretical electrical LHV (Low Heating Value) efficiency close to 100% (DC) for the dry electrochemical oxidation of biochar or methane, which can be a renewable hydrogen carrier. Maximum demonstrated LHV electrical efficiency (AC) of any commercially available fuel cell systems is already of 65%, for a utility scaled methane-fed SOFC system launched on the market in 2023.
The thesis then presents experimental and simulation work performed on two presently available fuel cell systems, namely (in this thesis) the Bl***G*N SOFC and the P*2 PEMFC. The experimental work encompasses both laboratory test campaigns and in-situ field-test monitoring in real applications, yielding dedicated performance models that can be integrated into building performance simulation or energy planning tools. The tested PEMC system exhibits a high-level of hybridization with a classical condensing boiler, which is assumed to prevent both sub-systems to operate as optimally and reliably as they would have as standalone units. Oppositely, the tested SOFC system exhibited no troubleshooting and a reliable electrical efficiency always close to 60% (LHV) at its nominal power outputs, which can also easily even be modulated in the 33-100% range.
Building on those experimental performance and anticipated advancements of fuel cell systems, the thesis demonstrates that their greenhouses gases mitigation potential over the average individual carbon footprint remains quite unsignificant if their fuel is not decarbonized. Even so, their mitigation potential would still be way insufficient, and other actions, including behavioural changes, would still have to be implemented.
However, emerging technologies, such as Direct Carbon Solid Oxide Fuel Cells (DCSOFCs) or Direct Formic Acid Fuel Cells (DFAFCs) offer the capability of facilitating pure CO2 capture at their anode exhaust and thus allow for potential negative emissions. With the case study of an average Belgian dwelling’s electrical demand and the use of an electric car (for about 20000 km/year) provided by a DCSOFC with an electrical LHV efficiency of 80% fed by biomass, those negative emissions could be up to about 3 MtCO2eq/year. In view of the minimal carbon absorption level implied by the carbon neutrality target (reported above), which will unlikely rely only on natural sinks in densely populated western countries, the negative emissions potential of such fuel cell systems shall absolutely be further developed and implemented (in addition to the maximization of natural sinks).7. Affordable and clean energy11. Sustainable cities and communities12. Responsible consumption and production13. Climate actio
Carnot batteries for integrated heat and power management in residential applications: A techno-economic analysis
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Carnot battery technology : a state-of-the-art review
Full text linkThe growth of renewable energy requires flexible, low-cost and efficient electrical storage to balance the mismatch between energy supply and demand. The Carnot battery buffers electrical energy by storing thermal energy (charging cycle mode) from a resistive heater or a heat pump system when the electricity production is higher than the demand. When electricity demand is higher than the production, the Carnot battery generates power from the stored thermal energy (power cycle mode). This paper is a review of this emerging and innovative technology, including a market analysis. First, the different possible technologies and configurations of Carnot batteries are described. This includes charging cycles, power cycles and thermal energy storage systems. Furthermore, a state-of-the-art of the existing prototypes in the world is given. The performance indicators for this technology are unclear, and this paper tries to define objective performance indicators. Finally, all the described technologies are compared, and conclusions are drawn to help engineers select the optimal technology for a given case
Data-driven Modeling and Control of Waste Heat Recovery Organic Rankine Cycle Systems
No full textHumanity has experienced a drastic growth during the last decades, faster than what was experienced in previous centuries. Increment concerns not only the population number but the amount of developments in areas such as computation capacity, automation, robotics, precision agriculture, material science, among others. These innovative solutions bring together a higher energy demand, hence in order to diminish the green house effect, global warming and other impacts caused by industry and oil based transportation system to the natural resources, it is deemed necessary to achieve sustainable and more efficient manufacturing processes.
Regarding energy efficiency organic Rankine cycle (ORC) power systems appear as an interesting technology to recover waste heat available at low-grade temperature, thus increasing the overall system efficiency. The ORC unit operates under the same principle as classical Rankine cycle for electricity generation, the main difference being the use of refrigerants with low boiling point as working fluid instead of water, allowing to reach superheated state for low temperature heat source conditions, thus becoming ideal for waste heat recovery (WHR) applications in the range from 100 400 C. The optimal thermodynamic design of such machines represents a first challenge, since cycle architecture, components and refrigerant selection, are an important aspect to look at. However such decisions are often considered at steady-state design, while ORC operates outside the designed range due to varying waste heat profiles, thus making necessary to consider a suitable control strategy aiming to guarantee safety operation and optimal
performance during transient conditions. The main contributions of this PhD thesis include: experimental validation of the proposed strategies, open-loop tests to illustrate the dynamics that represent a real challenge for modeling and control, presenting the conditions to achieve optimal ORC operation by building an optimizer, defining gain-scheduling and adaptive strategies based on classical PID and more advanced Model Predictive Control (MPC) to deal with nonlinear time-varying ORC dynamics. In order to
provide additional robustness against modeling errors a multiple model predictive controller is designed, where a Bayesian weighting scheme is applied to obtain an average prediction trajectory from a model bank built with models identified at different operating points. In order to better explain the complex ORC dynamics an sparse identification algorithm is proposed aiming to built a global nonlinear description of the process.
This research work is thus an attempt to present a user-friendly methodology for waste heat recovery organic Rankine cycle (WHR-ORC) modeling and control trol, a guide for practitioners and researchers interested on understanding from a data-driven perspective why is this power unit a nonlinear time-varying system, how to define a suitable low-order model for control, and how to design an advanced control strategy to achieve optimal performance under drastic waste heat variations. As well as to provide some ideas and future perspectives to optimize the ORC performance.The Next Generation of Organic Rankine Cycles7. Affordable and clean energ
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Frost Accretion and Distribution in Heat Exchangers of Refrigeration Systems, Accounting for Surface Wettability
Full text linkFrost accretion in heat exchangers of refrigeration systems is a major issue involv- ing energy consumption penalty in the heating or cooling devices. Numerous studies try to suppress, or at least delay, this frost formation. Among them, the use of (super-)hydrophobic coatings has shown encouraging results. The present thesis aims at investigating one step further the use of such materials in a heat pump evaporator.
The first step is to understand the physical phenomena involved in such process. A first classical heat pump has been built and has been highly instrumented, especially around the evaporator. At this stage, the surface of the fins and tubes evaporator is classical aluminum. It allows to get a very fine understanding of the frost problematic in these devices. In parallel another test rig is set up, to understand how frost may behave on superhydrophobic surfaces on elementary geometries, such as flat plates. Beside the the physical phenomena observation, those test benches allow to build a experimental data set.
Based on observations, new simulation models are implemented. A segment-by- segment discretization is envisaged for the modeling of the evaporator. It allows to get independent frost layers on each tubes, as observed during the experimental campaign. An originality of this model is to account for the fin thermal conductivity, which is determinant in the frost distribution through the device. For numerical robustness, the model is implemented as a dynamic one. A modeling work is also conducted at the surface scale. It accounts for major parameters impacting the macroscopic scale, such as contact angles or roughness. The major objective of this model is to predict the nucleation time (defined here as the time necessary, for a given surface, to be fully covered by frost nuclei).
The next step is, still separately, to compare the measurement results to the model predictions. At the evaporatior scale, the results are compared for the refrigerant side and for the air side in dry, wet or frosted conditions. This allows to successfully val- idate the model and clearly underline the effect of the fin thermal conductivity. At the surface scale, the same task is conducted, leading to the validation of the model.
As models can now be trusted, the ultimate step of the work is to merge them to predict the performance of heat exchanger in frost conditions, with different surface characteristics. The main result found there is that a real frost delay can be observed compared to regular surfaces, only if the hydrophobic level is sufficiently high. Slightly hydrophobic materials do not have any significant impact while superhydrophobic ones are game changers
Conversion de l’énergie thermique des gaz d’échappement en travail mécanique par un cycle de Rankine afin de réduire les émissions des gaz à effet de serre
Full text linkDans le cadre de la diminution des émissions des gaz à effet de serre, les constructeurs automobiles étudient le développement de solutions innovantes permettant la récupération de La chaleur perdue, notamment, celle des gaz d’échappement. Dans ce contexte, un système de conversion de l’énergie basé sur un cycle de Rankine est proposé. Il s’avère que l’intégration d’un tel système est limitée par les contraintes d’architecture mécanique du véhicule. Le choix des technologies des échangeurs de chaleur pour une boucle de Rankine a été réalisé via la modélisation quasi-statique sous EES®. Il en ressort que les technologies à faisceau de tubes pour l’évaporateur et à plaques corruguées pour le condenseur sont les mieux adaptées pour un système de Rankine automobile. Une étude approfondie du dimensionnement de l’évaporateur a été effectuée. Une machine de détente volumétrique à pistons axiaux à été retenue. Elle a fait l’objet de travaux de modélisation quasi-statique sous EES® et dynamique sous AMESim®. Les modèles ont été recalés à partir des données du fournisseur. Ensuite, les cartographies de fonctionnement de la machine ont été obtenues. Enfin, une étude de l’intégration de la boucle de Rankine dans une automobile a été réalisée grâce à une modélisation de la boucle complète de Rankine sous EES®. En fonction de la source froide, le système proposé peut produire entre 1 et 5 kW de puissance mécanique. Dans le but d’optimiser les performances du système de Rankine, des leviers du pilotage ont été proposés./In order to decrease the emissions of greenhouse effect gases, automotive manufacturers study the development of innovative solutions which enable the recovery of waste heat, in particular that of the exhaust gases. Within this context, a recovery system based on a Rankine cycle is proposed. Nonetheless, the integration of such system within a vehicle is limited by the available room inside the vehicle. The choice of technologies and dimensions of the heat exchangers were done by means of steady state modelling under EES® environment. This study showed that the tubes bundles type evaporator and corrugated plate type condenser are the appropriate technologies for an automotive application of the Rankine cycle. A detailed study of the evaporator was carried out as well. A reciprocating wobble plate machine was chosen as an expansion device. The detailed study of the expander performance was carried out by means of steady-state modelling under EES® environment and dynamic modelling under AMESim® environment. The models were calibrated with the sets of measures provided by the supplier. Maps of expander was then obtained. Thus, the implementation study of a Rankine cycle within a vehicle was carried out by means of modelling of a Rankine cycle model under EES® environment. We obtained that depending of the thermodynamic state of the cold source; the recovery system could produce between 1 to 5 kW of additional mechanical power. In order to optimize the performance of the Rankine system, different ways of operating the Rankine system were proposed
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