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The current need for power-system control-room operational tools to increase real-time situational awareness has led to various proposals on data analytics algorithms to obtain operational information from SCADA and PMU power system networks. Most of the proposals are implemented in simulation, with reduced practical significance for system operators. This work proposes a web-based simple algorithm to identify the dynamic parameters of a reduced-order model of power system frequency dynamics that is implemented with industrial hardware on a PMU network in the Chilean power system. To demonstrate the applicability of the proposed tool, the algorithm is implemented in a web page with real-time monitoring of the frequency of the Chilean power system, so that utilities and academic institutions with access to PMU measurements can apply the proposed concepts regardless of the topology of the monitored system.

Die SIA erstellt neu die Norm 384/4 Klimakälte. Ein Teil dieser Norm ist die Mindesteffizienzanforderung für Kälteanlagen. Die EU hat mit der neuen Ökodesign-Verordnung neue Kennwerte für die Energieeffizienz einer Kälteanlage entwickelt, welche die verschiedenen Temperaturbedingungen und somit auch die Lastzustände berücksichtigen, den SEER (Komfort) und den SEPR (Prozess). Die neue Ökodesign-Verordnung dient damit als Grundlage für die Mindesteffizienzanforderungen in der Norm SIA 384/4. Um geeignete Grenzwerte (und die dazugehörigen Leistungsbereiche) zu definieren, wird eine Marktanalyse durchgeführt. Dafür werden die Daten von Kältemaschinen aus der Eurovent Certita Datenbank ausgewertet. Wie strikt die Mindesteffizienz der Kältemaschine sein soll, ist je nach Ausprägung der Anlage unterschiedlich. Deshalb wird der Grenzwert je nach Ausprägung mittels Bonus/Malus-Faktor angepasst. Die Faktoren werden anhand der Marktanalyse, Kreislaufsimulationen und Erfahrungswerte der Experten festgelegt. Abschliessend wird das Berechnungsmodell mit Beispielen überprüft und plausibilisiert. Neben dem Berechnungsmodell ist in diesem Bericht auch eine Zusammenfassung der neuen saisonalen Effizienzkennzahl SEER und SEPR erstellt worden, welche im Anhang zu finden ist. Ebenfalls im Anhang ist eine erweiterte Auswertung zur Marktanalyse für Komfortkühler, welche zusätzlich Informationen aus den vorhandenen Daten enthält.

Die SIA erstellt neu die Norm 384/4 Klimakälte. Ein Teil dieser Norm ist die Mindesteffizienz-anforderung für Kälteanlagen. Die EU hat mit der neuen Ökodesign-Verordnung neue Kennwerte für die Energieeffizienz einer Kälteanlage entwickelt, welche die verschiedenen Temperaturbedingungen und somit auch die Lastzustände berücksichtigen, den SEER (Komfort) und den SEPR (Prozess). Die neue Ökodesign-Verordnung dient damit als Grundlage für die Mindesteffizienzanforderungen in der Norm SIA 384/4. Um geeignete Grenzwerte (und die dazugehörigen Leistungsbereiche) zu definieren, wird eine Marktanalyse durchgeführt. Dafür werden die Daten von Kältemaschinen aus der Eurovent Certita Datenbank ausgewertet. Wie strikt die Mindesteffizienz der Kältemaschine sein soll, ist je nach Ausprägung der Anlage unterschiedlich. Deshalb wird der Grenzwert je nach Ausprägung mittels Bonus/Malus-Faktor angepasst. Die Faktoren werden anhand der Marktanalyse, Kreislaufsimulationen und Erfahrungswerte der Experten festgelegt. Abschliessend wird das Berechnungsmodell mit Beispielen überprüft und plausibilisiert. Neben dem Berechnungsmodell ist in diesem Bericht auch eine Zusammenfassung der neuen saisonalen Effizienzkennzahl SEER und SEPR erstellt worden, welche im Anhang zu finden ist. Ebenfalls im Anhang ist eine erweiterte Auswertung zur Marktanalyse für Komfortkühler, welche zusätzlich Informationen aus den vorhandenen Daten enthält.

Die Suche nach Sanie­rungs­poten­zialen bei Gebäuden ist auf eine gross­flächige und detail­lierte Gebäude-Energie­beur­teilung auf Basis hoch­auf­gelöster Thermal­auf­nah­men ange­wiesen. Solche Ther­mal­auf­nah­men ermög­lichen nun die Erstel­lung von Energie­ver­brauchs­karten und Wärme­katas­tern in Stadt-, Gemeinde- und Energie­ver­sor­gungs­gebieten.

This study presents a comparative accident risk assessment for different energy technologies, e.g., fossil fuels (incl. CCUS), Hydropower, H2, Nuclear, and new renewables, in the Organization for Economic Co-operation and Development (OECD) countries. The quantitative analysis is based on the historical observations collected in the Paul Scherrer Institute (PSI)'s ENergy-related Severe Accident Database (ENSAD) and updated using different sources, for the period 1970-2020, whereas for Nuclear a simplified level-3 Probabilistic Safety Assessment (PSA) is applied. Furthermore, for each energy technology, risk indicators, e.g., fatality rate and maximum consequences, are estimated to allow for comparison. Generally, fatality rates for Nuclear, Hydrogen, Hydropower and new renewables perform better than the fossil energy chains. In contrast, maximum consequences can be far highest for Nuclear, intermediate for fossil and Hydropower, and lowest for new renewables, which are less prone to severe accidents. Overall, no technology performs best or worst in all respects, thus trade-offs and priorities are needed to balance the conflicting objectives such as energy security, sustainability, and risk aversion to support rationale decision making.

Drinking water is becoming increasingly scarce as the world’s population grows and climate change continues. However, there is great potential to improve drinking water pipelines, as 30% of fresh water is lost between the supplier and consumer. While systematic process monitoring could play a crucial role in the early detection and repair of leaks, current practice requires manual inspection, which is both time-consuming and costly. This project envisages maintenance-free measurements at numerous locations within the underground infrastructure, a goal that is to be achieved through the use of a harvesting device mounted on the water pipe. This device extracts energy from the temperature difference between the water pipe and the soil using a TEG (thermoelectric generator), takes sensor measurements, processes the data and transmits it wirelessly via LoRaWAN. We built 16 harvesting devices, installed them in four locations and continuously evaluated their performance throughout the project. In this paper, we focus on two devices of a particular type. The data for a full year show that enough energy was available on 94% of the days, on average, to take measurements and transmit data. This study demonstrates that it is possible to power highly constrained sensing devices with energy harvesting in underground environments.

Die vorliegende Arbeit befasst sich hauptsächlich mit dem Thema Energie, dazu wurde eine Literaturrecherche durchgeführt. Es wurde ein Konzept erarbeitet, welches aus einem Zusammenschluss erneuerbarer Energien und verschiedenen Technologien besteht, aber auch der Natur ihren Platz zugesteht. Dieses Konzept wird mittels technischer Zeichnungen dargestellt, anschliessend wurden, durch Berechnungen und Simulationen, die dazugehörigen Werte der verschiedenen Systeme und Anlagen ermittelt. Das Konzept besteht aus zwei Gebäudekomplexen die Platz für zirka 12'000 Personen bieten, sie sind mit einer Fassaden- und Dachbegrünung ausgestattet und von einem Pumpspeicherkraftwerk, welches durch einen Wald kaschiert wird, umgeben. Es wurde darauf geachtet, dass verschiedene Anlageteile des Gesamtprojekts multifunktionell sind, das heisst Energie produzieren, Platz für die Natur lassen und den Bewohnern als Naherholungsgebiet dienen. Die Gebäudekomplexe besitzen verschiedene Photovoltaikanlagen, welche in den oberen Südfassaden integriert wurden, sich auf den Süddächern oder auf dem Pumpspeicherkraftwerk befinden. Die tagsüber durch die Photovoltaik erzeugte Energie, wird in den Gebäuden etagenweise mittels Akkus/Batterien gespeichert und für die Nacht verfügbar gemacht. Energieüberschüsse, welche mehrheitlich durch die Photovoltaikanlage des Pumpspeicherkraftwerkes erzeugt wurden, werden in diesem als potentielle Energie gespeichert. Das heisst am Tag wird Wasser mittels «Solarstrom» hochgepumpt und in der Nacht mittels Turbinen wieder in elektrische Energie umgewandelt. Die zwei Gebäudekomplexe A+B, sind jeweils in drei Häuser für rund 2'000 Personen gegliedert und besitzen ein eigenes, von den anderen Häusern unabhängiges, Heizungs-/Kühlungs-, Lüftungs- und Warmwasserbereitungssystem. Dieses System besteht aus Wärmepumpen und sorgt dafür, dass die Heizung/Kühlung, Kontrollierte Wohnungslüftung, sowie die Warmwasserbereitung pro Haus möglichst «klimaneutral» betrieben werden. D, The present paper deals primary with the topic of energy, for this was a literature research carried out. A concept was developed, which results form a combine of renewables energies and different technologies, but also lets nature take its place. This concept is presented by technical drawings, subsequently, the corresponding values of the various systems and facilities were determined through calculations and simulations. The concept consists of two building complexes, which have space for 12’000 people, they are covered with a green façade and roof and surrounded by a pumped storage power station, which is hided through forest. Care was taken, to ensure that different parts of the overall project are multifunctional. That means, that they produce energy, leave space for nature and serve the inhabitants as local recreation area. The building complexes have various photovoltaic systems, which are integrated in the upper south façade and are located on the south roofs, or on the pump storage power plant. The energy, which is produced by the photovoltaic systems during the day, is stored with accumulators/batteries and made it available for the night, that for the whole building floor by floor. Energy surpluses, which are mostly generated by the pump storage power plant, are stored in it as potential energy. This means, that during the day water is pumped up using «solar power», and at night it is converted back into electrical energy with turbines. The two building complexes A+B are divided into three houses, with space for 2’000 persons and each of them has their own heating/cooling, ventilation and hot water preparation system, independent of the other houses. This system consists of heat pumps and ensures, that the heating/cooling, controlled domestic ventilation and hot water preparation system is as climate neutral as possible. For this purpose, the treated domestic waste water, which still has residual heat, is fed into a large service water tank, where the re

Evaporative cooling is a promising concept to improve proton exchange membrane fuel cells. While the particular concept based on gas diffusion layers (GDLs) modified with hydrophilic lines (HPILs) has recently been demonstrated, there is a lack in the understanding of the mass and heat transport processes. We have developed a 3-D, non-isothermal, macro-homogeneous numerical model focusing on one interface between a HPIL and an anode gas flow channel (AGFC). In the base case model, water evaporates within a thin film adjacent to the interfaces of the HPIL with the AGFC and with the hydrophobic anode GDL. The largest part of the generated water vapor leaves the cell via the AGFC. The transport to the cathode side is shown to be partly limited by the ab-/desorption into/from the membrane. The cooling due to the latent heat has a strong effect on the local evaporation rate. An increase of the mass transfer coefficient for evaporation leads to a transport limited regime inside the MEA while the transport via the AGFC is limited by evaporation kinetics.

Conference Proceedings available at: https://proceedings.open.tudelft.nl/index.php/clima2022, Technologies that can close the seasonal gap between summer renewable generation and winter heating demand are crucial in reducing CO2 emissions of energy systems. Borehole thermal energy storage (BTES) systems offer an attractive solution, and their correct sizing is important for their techno-economic success. Most of the BTES design studies either employ detailed modelling and simulation techniques, which are not suitable for numerical optimization, or use significantly simplified models that do not consider the effects of operational variables. This paper proposes a BTES modelling approach and a mixed-integer bilinear programming formulation that can consider the influence of the seasonal BTES temperature swing on its capacity, thermal losses, maximum heat transfer rate and on the efficiency of connected heat pumps or chillers. This enables an accurate assessment of its integration performance in different district heating and cooling networks operated at different temperatures and with different operating modes (e.g. direct discharge of the BTES or via a heat pump). Considering a case study utilizing air sourced heat pumps under seasonally varying CO2 intensity of the electricity, the optimal design and operation of an energy system integrating a BTES and solar thermal collectors were studied. The optimization, aiming at minimizing the annual cost and CO2 emissions of the energy system, was applied to two heating network temperatures and five representative carbon prices. Results show that the optimal BTES design changed in terms of both size and operational conditions, and reductions in emissions up to 43% could be achieved compared to a standard air-source heat pumps based system.

This presentation builds on an early work where we evaluated the potential of harvesting energy from concrete walls using temperature differences. We have now built and installed several LPWAN nodes that are powered solely from TEGs, using small temperature differences. With efficient harvesting, those nodes can scavenge sufficient energy to sense parameters in the civil infrastructure environment and communicate with gateways that are several kilometres away. This brings battery-free monitoring of walls and bridges one step closer to reality. After giving an overview of the technologies involved and discussing the basis of TEG harvesting, we will present first results and early conclusions of several weeks of measurement activity.

Triboelectric nanogenerators (TENG) have great potential to help enhancing the energy efficiency of buildings, and thus to contribute significantly to the reduction of global greenhouse gas emissions. However, there are major barriers against the adoption of such emerging energy technologies. Meeting the need for sustainable large-scale fabrication of high-performance products remains a critical challenge towards real-world TENGs’ building applications. To mitigate this challenge, we enhance the poor polarizability of native wood by a scalable plasma treatment, a facile approach which to the greatest degree preserves wood's warm colors, mechanical robustness while efficiently enhancing the triboelectric output. We demonstrate the enhancement of electric output by assembling wood triboelectric nanogenerators (W-TENGs) in both contact-separation and single-electrode operation modes. We show that when two radial-cut wood samples (L × R × T: 100 × 80 × 1 mm3), one treated with an O2 plasma and the other with a C4F8 + O2 plasma, are subjected to periodic contact and separation with an applied pressure as low as 0.0225 MPa, a maximum voltage of 227 V and a current of 4.8 µA are produced. Eventually, we showcase the real-world applicability of our approach with two prototypes of triboelectric wood floors, opening up new technological pathways towards a ‘net-zero emissions’ future.

eTanks als saisonale thermische Energiespeicher sind eine vielversprechende Technologie, um die beinahe unendliche Energie der Sonne über das ganze Jahr zu nutzen. Mit einer grossen Speicherkapazität, relativ einfacher Bauform und ohne komplizierte Bauteile, sind sie ideal für solarthermische Systeme geeignet. Die Nutzung der Sonne im Winter ist jedoch aufgrund der tiefen Aussentemperaturen und Einstrahlungswinkel mangelhaft. Die tiefen Rücklauftemperaturen der Solaranlage sind aufgrund des niedrigen Temperaturunterschiedes zum eTank nicht gut speicherbar. Abhilfe bietet in diesem Szenario die Kombination des eTanks mit Phasenübergangsmaterialien (PCM). Mithilfe dieser Materialien kann die Speicherkapazität bei niedrigen Temperaturen erhöht werden. Das PCM wird so gewählt, dass der Phasenübergang präzise bei den tiefen Wintertemperaturen stattfindet, welche die Sonne zu diesem Zeitpunkt liefern kann. Um den Effekt zu quantifizieren, werden zwei Modell-eTanks gebaut. Das PCM wird mit einem Doppelrohrsystem in einem der zwei Modelltanks eingebracht. Im Solarlabor der ZHAW werden Testdurchläufe durchgeführt, bei denen die Tanks parallel be- und entladen werden. Sämtliche relevante Daten werden während den Tests geloggt, ausgewertet und anschliessend bei der Auswertung mit berechneten, theoretischen Werten abgeglichen. Aufgrund von Ungenauigkeiten bei den Messungen, Frostschäden und Dichtigkeitsproblemen, konnten quantitativ nur eine reduzierte Anzahl Messungen durchgeführt werden. Diese Faktoren beeinflussen auch die Relevanz der Daten. Das Modell ist grundsätzlich funktionstüchtig, was durch den erfolgreichen Phasenübergang sichtbar wird. Dieser konnte bei der Demontage beobachtet werden. Die Resultate zeigen bei mehreren Testläufen eine grosse Abweichung zwischen den gemessenen und den berechneten Werten. Auch in den grafischen Darstellungen der Temperaturen ist der Phasenübergang schlecht sichtbar. Die Bauart der Modelltanks ist jedoch vielversprechend. Mit der Kali, eTanks as seasonal thermal energy storage systems are a very promising technology to use the almost infinite energy from the sun over the whole year. With their large storage capacity, relatively easy construction and lack of complicated parts, they are ideally suited in combination with solar thermal systems. The system still has disadvantages when it comes to the usage of solar power in Winter while temperatures are cold and angle of incidence to the panels are low. The colder return temperatures are difficult to store because of the low temperature difference to the eTank. A promising remedy for this scenario is the combination of an eTank with phase-changing-materials (PCM). These materials provide the possibility to increase the storage capacity at low temperatures. The PCM is selected according to its phase-change-temperature which can be precisely the return temperatures that are expected to be provided by the solar thermal system. Two model-eTanks are built to quantify this effect. The PCM is built in one of the tanks using a double-pipe system. Test runs are carried out at the solar laboratory at ZHAW. During these test runs, the tanks are thermally loaded and unloaded in parallel. All relevant data are logged during the test runs and later analyzed. During the evaluation, the measured data is compared to calculated possible values. Because of inaccuracies with the measurements, frost damage and leaks in the pipes, the quantity of the test runs was limited. These factors also affect the relevancy of the data. Based on observations during the disassembly, the PCM has successfully carried out the phase-change. This means that the model-tanks work. The results show a big difference between the measured and the calculated values in multiple test runs. The graphical analysis of the temperatures also shows no conclusive evidence of if, and at what temperature, the phase change happened.

To apply phase-change thermal storage in heat-pump systems, a low heat-transfer temperature difference is required. The typical temperature material requirements for phase change limit the application of its thermal storage in heat pump energy supply systems. This study introduces a novel phase-change thermal storage device suitable for a renewable energy supply system composed of multichannel flat tubes and closed rectangular fins. Performance experiments and optimisation of the connection geometry of the thermal storage units under low heat-transfer temperature differences were carried out. When the inlet temperature of the heat transfer fluid was 55 °C (the melting point of the phase change material is 50 °C), the energy storage density and gravimetric specific power can reach 175.16 kJ/kg and 27.93 W/kg respectively, which has obvious advantages compared to relevant devices in the literature. A dimensionless energy-efficiency ratio was used to optimise the device. It was shown that the series type can significantly increase pressure loss while improving heat storage performance, and optimising the structure and operation design parameters of parallel components is more beneficial in terms of device performance improvement. The optimal operating flow corresponding to different heights of the novel thermal storage unit in parallel was provided, thus laying a theoretical foundation for practical applications.

Conference Proceedings available at: https://proceedings.open.tudelft.nl/index.php/clima2022, Technologies that can close the seasonal gap between summer renewable generation and winter heating demand are crucial in reducing CO2 emissions of energy systems. Borehole thermal energy storage (BTES) systems offer an attractive solution, and their correct sizing is important for their techno-economic success. Most of the BTES design studies either employ detailed modelling and simulation techniques, which are not suitable for numerical optimization, or use significantly simplified models that do not consider the effects of operational variables. This paper proposes a BTES modelling approach and a mixed-integer bilinear programming formulation that can consider the influence of the seasonal BTES temperature swing on its capacity, thermal losses, maximum heat transfer rate and on the efficiency of connected heat pumps or chillers. This enables an accurate assessment of its integration performance in different district heating and cooling networks operated at different temperatures and with different operating modes (e.g. direct discharge of the BTES or via a heat pump). Considering a case study utilizing air sourced heat pumps under seasonally varying CO2 intensity of the electricity, the optimal design and operation of an energy system integrating a BTES and solar thermal collectors were studied. The optimization, aiming at minimizing the annual cost and CO2 emissions of the energy system, was applied to two heating network temperatures and five representative carbon prices. Results show that the optimal BTES design changed in terms of both size and operational conditions, and reductions in emissions up to 43% could be achieved compared to a standard air-source heat pumps based system.

This presentation builds on an early work where we evaluated the potential of harvesting energy from concrete walls using temperature differences. We have now built and installed several LPWAN nodes that are powered solely from TEGs, using small temperature differences. With efficient harvesting, those nodes can scavenge sufficient energy to sense parameters in the civil infrastructure environment and communicate with gateways that are several kilometres away. This brings battery-free monitoring of walls and bridges one step closer to reality. After giving an overview of the technologies involved and discussing the basis of TEG harvesting, we will present first results and early conclusions of several weeks of measurement activity.

eTanks als saisonale thermische Energiespeicher sind eine vielversprechende Technologie, um die beinahe unendliche Energie der Sonne über das ganze Jahr zu nutzen. Mit einer grossen Speicherkapazität, relativ einfacher Bauform und ohne komplizierte Bauteile, sind sie ideal für solarthermische Systeme geeignet. Die Nutzung der Sonne im Winter ist jedoch aufgrund der tiefen Aussentemperaturen und Einstrahlungswinkel mangelhaft. Die tiefen Rücklauftemperaturen der Solaranlage sind aufgrund des niedrigen Temperaturunterschiedes zum eTank nicht gut speicherbar. Abhilfe bietet in diesem Szenario die Kombination des eTanks mit Phasenübergangsmaterialien (PCM). Mithilfe dieser Materialien kann die Speicherkapazität bei niedrigen Temperaturen erhöht werden. Das PCM wird so gewählt, dass der Phasenübergang präzise bei den tiefen Wintertemperaturen stattfindet, welche die Sonne zu diesem Zeitpunkt liefern kann. Um den Effekt zu quantifizieren, werden zwei Modell-eTanks gebaut. Das PCM wird mit einem Doppelrohrsystem in einem der zwei Modelltanks eingebracht. Im Solarlabor der ZHAW werden Testdurchläufe durchgeführt, bei denen die Tanks parallel be- und entladen werden. Sämtliche relevante Daten werden während den Tests geloggt, ausgewertet und anschliessend bei der Auswertung mit berechneten, theoretischen Werten abgeglichen. Aufgrund von Ungenauigkeiten bei den Messungen, Frostschäden und Dichtigkeitsproblemen, konnten quantitativ nur eine reduzierte Anzahl Messungen durchgeführt werden. Diese Faktoren beeinflussen auch die Relevanz der Daten. Das Modell ist grundsätzlich funktionstüchtig, was durch den erfolgreichen Phasenübergang sichtbar wird. Dieser konnte bei der Demontage beobachtet werden. Die Resultate zeigen bei mehreren Testläufen eine grosse Abweichung zwischen den gemessenen und den berechneten Werten. Auch in den grafischen Darstellungen der Temperaturen ist der Phasenübergang schlecht sichtbar. Die Bauart der Modelltanks ist jedoch vielversprechend. Mit der Kali, eTanks as seasonal thermal energy storage systems are a very promising technology to use the almost infinite energy from the sun over the whole year. With their large storage capacity, relatively easy construction and lack of complicated parts, they are ideally suited in combination with solar thermal systems. The system still has disadvantages when it comes to the usage of solar power in Winter while temperatures are cold and angle of incidence to the panels are low. The colder return temperatures are difficult to store because of the low temperature difference to the eTank. A promising remedy for this scenario is the combination of an eTank with phase-changing-materials (PCM). These materials provide the possibility to increase the storage capacity at low temperatures. The PCM is selected according to its phase-change-temperature which can be precisely the return temperatures that are expected to be provided by the solar thermal system. Two model-eTanks are built to quantify this effect. The PCM is built in one of the tanks using a double-pipe system. Test runs are carried out at the solar laboratory at ZHAW. During these test runs, the tanks are thermally loaded and unloaded in parallel. All relevant data are logged during the test runs and later analyzed. During the evaluation, the measured data is compared to calculated possible values. Because of inaccuracies with the measurements, frost damage and leaks in the pipes, the quantity of the test runs was limited. These factors also affect the relevancy of the data. Based on observations during the disassembly, the PCM has successfully carried out the phase-change. This means that the model-tanks work. The results show a big difference between the measured and the calculated values in multiple test runs. The graphical analysis of the temperatures also shows no conclusive evidence of if, and at what temperature, the phase change happened.

Evaporative cooling is a promising concept to improve proton exchange membrane fuel cells. While the particular concept based on gas diffusion layers (GDLs) modified with hydrophilic lines (HPILs) has recently been demonstrated, there is a lack in the understanding of the mass and heat transport processes. We have developed a 3-D, non-isothermal, macro-homogeneous numerical model focusing on one interface between a HPIL and an anode gas flow channel (AGFC). In the base case model, water evaporates within a thin film adjacent to the interfaces of the HPIL with the AGFC and with the hydrophobic anode GDL. The largest part of the generated water vapor leaves the cell via the AGFC. The transport to the cathode side is shown to be partly limited by the ab-/desorption into/from the membrane. The cooling due to the latent heat has a strong effect on the local evaporation rate. An increase of the mass transfer coefficient for evaporation leads to a transport limited regime inside the MEA while the transport via the AGFC is limited by evaporation kinetics.

Übersicht über Energy Harvesting-Methoden, Möglichkeiten und Restriktionen anhand von Beispielen aus der Praxis

Triboelectric nanogenerators (TENG) have great potential to help enhancing the energy efficiency of buildings, and thus to contribute significantly to the reduction of global greenhouse gas emissions. However, there are major barriers against the adoption of such emerging energy technologies. Meeting the need for sustainable large-scale fabrication of high-performance products remains a critical challenge towards real-world TENGs’ building applications. To mitigate this challenge, we enhance the poor polarizability of native wood by a scalable plasma treatment, a facile approach which to the greatest degree preserves wood's warm colors, mechanical robustness while efficiently enhancing the triboelectric output. We demonstrate the enhancement of electric output by assembling wood triboelectric nanogenerators (W-TENGs) in both contact-separation and single-electrode operation modes. We show that when two radial-cut wood samples (L × R × T: 100 × 80 × 1 mm3), one treated with an O2 plasma and the other with a C4F8 + O2 plasma, are subjected to periodic contact and separation with an applied pressure as low as 0.0225 MPa, a maximum voltage of 227 V and a current of 4.8 µA are produced. Eventually, we showcase the real-world applicability of our approach with two prototypes of triboelectric wood floors, opening up new technological pathways towards a ‘net-zero emissions’ future.

To apply phase-change thermal storage in heat-pump systems, a low heat-transfer temperature difference is required. The typical temperature material requirements for phase change limit the application of its thermal storage in heat pump energy supply systems. This study introduces a novel phase-change thermal storage device suitable for a renewable energy supply system composed of multichannel flat tubes and closed rectangular fins. Performance experiments and optimisation of the connection geometry of the thermal storage units under low heat-transfer temperature differences were carried out. When the inlet temperature of the heat transfer fluid was 55 °C (the melting point of the phase change material is 50 °C), the energy storage density and gravimetric specific power can reach 175.16 kJ/kg and 27.93 W/kg respectively, which has obvious advantages compared to relevant devices in the literature. A dimensionless energy-efficiency ratio was used to optimise the device. It was shown that the series type can significantly increase pressure loss while improving heat storage performance, and optimising the structure and operation design parameters of parallel components is more beneficial in terms of device performance improvement. The optimal operating flow corresponding to different heights of the novel thermal storage unit in parallel was provided, thus laying a theoretical foundation for practical applications.

Macro-homogenous models enable the study of the complex interplay between operating conditions, materials response and cell performance, which is needed for the optimisation of the cell performances. However, input parameters to the macro-homogenous models are needed to account for the micro-scale properties of the single components and interfaces. For this purpose the water filled and open pore domains of gas diffusion layers (GDL) are determined depending on the boundary (and operating) conditions using the geometric input of the fiber/pore morphologies provided by tomography. The ultimate aim is to calculate the effective transport properties for different degrees of saturation, based on water distributions that are obtained with pore-scale modeling and from tomography. Considering the liquid water as statistical ensemble, a Monte Carlo-based approach based on the energetic balance between solid, liquid and gaseous phases in the porous medium, has been used to determine water distribution. PSMC (Pore Scale Monte Carlo) code we developed, is shown to be able to simulate the equilibrium distribution of the water (EWD) in the porous structure, minimizing the surface free energy of the water-solid-air system. Such an information will be later used to calculate the effective transport properties (e.g. permeability, conductivity) needed for a macroscopic simulation of the full PEM fuel cell.

In almost 30 years of PEM fuel cell modeling, countless numerical models have been developed in science and industrial applications, almost none of which have been fully disclosed to the public. There is a large need for standardization and establishing a common ground not only in experimental characterization of fuel cells, but also in the development of simulation codes, to prevent each research group from having to start anew from scratch. Here, we publish the first open standalone implementation of a full-blown, steady-state, non-isothermal two-phase model for low-temperature PEM fuel cells. It is based on macro-homogeneous modeling approaches and implements the most essential through-plane transport processes in a five-layer MEA. The focus is on code simplicity and compactness with only a few hundred lines of clearly readable code, providing a starting point for more complex model development. The model is implemented as a standalone MATLAB function, based on MATLAB’s standard boundary value problem solver. The default simulation setup reflects wide-spread commercially available MEA materials. Operating conditions recommended for automotive applications by the European Commission are used to establish new fuel cell simulation base data, making our program a valuable candidate for model comparison, validation and benchmarking.

Underground infrastructure networks form the backbone of vital supply and disposal systems. However, they are under-monitored in comparison to their value. This is due, in large part, to the lack of energy supply for monitoring and data transmission. In this paper, we investigate a novel, energy harvesting system used to power underground sewer infrastructure monitoring networks. The system collects the required energy from ambient sources, such as temperature differences or residual light in sewer networks. A prototype was developed that could use either a thermoelectric generator (TEG) or a solar cell to capture the energy needed to acquire and transmit ultrasonic water level data via LoRaWAN. Real-world field trials were satisfactory and showed the potential power output, as well as, possibilities to improve the system. Using an extrapolation model, we proved that the developed solution could work reliably throughout the year.

In dieser Arbeit wurde das Potential von Free Cooling für die drei Schweizer Standorte Bern, La Chaux-de-Fonds und St. Gallen in Abhängigkeit von der Vorlauftemperatur, Anwendungsart, Schaltung und Art der Rückkühlung untersucht. Hierfür wurde die gleiche Methodik wie in der Untersuchung: “Free Cooling in der Klimakälte - Untersuchung des Potentials in der Schweiz” angewendet.

Numerical simulations of laminar premixed flames burning hydrogen and methane in spontaneous ignition mode are performed by harmonically exciting the reactants’ temperature at the domain inlet. The results are compared to an analytical model representing the same reactive flow configuration. The model provides a simplified but nevertheless accurate representation of reheat combustion taking place in sequential gas turbine combustors. An analytic expression for autoignition flames transfer functions to entropy waves is derived and used to extend transfer function models from the literature. For validation purposes, results from fully compressible Direct Numerical Simulations (DNS), including a complete representation of the fluctuating acoustic and entropic fields of the reactive flow, are analyzed and compared to incompressible Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations that only take into account the fluctuating entropic field. Methane flames are found to be more sensitive to entropic forcing than hydrogen flames, featuring nonlinear phenomena even for low excitation amplitudes. In the linear regime, all flames behave as predicted by the analytical model and the URANS simulations are found to correctly predict the fluctuating entropic field. The transition from linear to nonlinear flame response is described in detail and its physical mechanisms are explained. Comparisons with results available in the literature show good prediction capabilities, both in terms of flame describing function and integrated heat release rate. Limitations of the proposed analytical model with respect to real combustion systems are discussed and a simple correction is proposed.

Direct Numerical Simulations (DNS) are performed to investigate the process of spontaneous ignition of hydrogen flames at laminar, turbulent, adiabatic and non-adiabatic conditions. Mixtures of hydrogen and vitiated air at temperatures representing gas-turbine reheat combustion are considered. Adiabatic spontaneous ignition processes are investigated first, providing a quantitative characterization of stable and unstable flames. Results indicate that, in hydrogen reheat combustion, compressibility effects play a key role in flame stability and that unstable ignition and combustion are consistently encountered for reactant temperatures close to the mixture’s characteristic crossover temperature. Furthermore, it is also found that the characterization of the adiabatic processes is also valid in the presence of non-adiabaticity due to wall heat-loss. Finally, a quantitative characterization of the instantaneous fuel consumption rate within the reaction front is obtained and of its ability, at auto-ignitive conditions, to advance against the approaching turbulent flow of the reactants, for a range of different turbulence intensities, temperatures and pressure levels.

A significant amount of energy consumption in buildings is due to heating, ventilation and air-conditioning systems. Among other systems, refrigeration plants are subject of efficiency improvements. However, actual operating conditions of such plants and the performance must be known as well as any eventual optimization potential identified before enhancements can take place. Energy and exergy analyses have been widely used to assess the performance of refrigeration systems. Among others, exergy efficiency is used as an indicator to determine the system performance; however, the practical achievable values are unknown. Therefore, this work proposes a practice-oriented evaluation method for refrigeration plants, based on exergy analysis and technical standards as baseline. The identification of possible enhancements is highly relevant in practice, as measures which improve the system effectiveness most likely prevent frequent shortcomings during refrigeration plant operation. With the introduced optimization potential index (OPI), the achievable enhancements compared to the state of the art in technology and the performance are identified at a glance regardless the complexity of the system. By dividing the plant into different subsystems, each of them can be assessed individually. Laypersons can easily determine the system operating state and subsequently, if needed, initiate a detailed analysis as well as appropriate countermeasures by specialist. Moreover, modeling is seen as an appropriate method to determine additional reference values for refrigeration machines if none are available according to technical standards. Among different modeling techniques, artificial neural network models reveal the best performance for the present application. The application, functionality and purpose of the presented method is exemplified on two numerical test cases and on a real field plant as a case study. The investigation reveals an adequate operation of the studied field pla

Heat release from absorption storage heat pump by means of absorption of water vapor into aqueous sodium hydroxide is limited by uptake kinetics affecting temperature gain, as well as power- and energy density of the method. Earlier studies pinpoint that natural diffusion alone is not sufficient to reach higher uptake rate, and that the surface to bulk exchange has to be enforced. In this paper, different technical solutions to this problem for the heat storage application are introduced and studied by neutron imaging, enabling visual observation of water vapor uptake and diffusion. The experiments brought to the fore that the buoyancy changes associated with water uptake may be utilized to markedly enhance kinetics. This concept was applied on a vertically installed spiral finned tube operating as heat and mass exchanger for the absorption storage heat pump, also referred to as sorption heat storage. By flooding the space between the spiral fin with absorbent, water absorption into the vertical surface leads to a buoyancy driven movement of the liquid, supplying unspent aqueous NaOH to the vertical surface and exchanging it with the diluted liquid. This is found to increase the rate of absorption markedly. Under realistic heat storage specific operating conditions, a temperature gain of 12.5 K, an active area specific power of 1.28 kW/m2 and an energy density of 243 kWh/m3 in respect to the volume of charged absorbent (greatest volume) is reached. It is proposed that carful design of the spiral finned tube to enhance buoyancy movement will further improve overall sorption heat storage performance.

This article presents a numerical study on the building integration of a liquid sorption storage combined with an air-source electric heat pump. The double staging of the sorption storage (i.e. a chemical heat pump) and an electric heat pump leads to significant electricity demand and CO2 emission reductions. Further, it provides an effective coupling between the heat demand of the building and the electricity supply, allowing for optimal integration of solar energy using photovoltaics. For the buildings analyzed, an autarky level of up to 83% is achieved. Winter electricity demand and emission reductions respectively reached values of up to 41%. The storage integration was studied performing dynamic building simulations. The simulation model for the liquid sorption storage was based on a grey box approach. This features a simple analytical model being tuned to match with performance data available from experiments conducted on a lab scale test rig. The presented integration of a compact seasonal thermal energy storage at the building scale represents a promising approach for a grid compliant integration of renewable energy, significantly reducing electricity demand peaks and related CO2 emissions in winter.

Seasonal thermal energy storage is an effective measure to enable a low carbon future through the integration of renewables into the energy system. Borehole thermal energy storage (BTES) provides a solution for long-term thermal energy storage and its operational optimization is crucial for fully exploiting its potential. This paper presents a novel linearized control-oriented model of a BTES, describing the storage temperature dynamics under varying operating conditions, such as inlet temperature, mass-flow rate and borehole connection layouts (e.g. in-series, in-parallel or mixed). It supports an optimization framework, which was employed to determine the best operating conditions for a heat pump-driven BTES, subject to different intensity profiles of the electricity. It was demonstrated that this boundary condition, due to its seasonal variation, is critical for the optimal operation of the system, as increasing heat pump efficiency in winter while accepting a lower one in summer can be beneficial. Results for an exemplary district case, subject to two different intensity profiles, show that a lower relative intensity in summer compared to the one in winter leads to a higher optimal operating temperature of the storage. The district system studied is heating-dominated, effectively enabling the BTES to cover only 20% of the total heat demand, leading to limited total yearly CO2 emissions savings of 2.2% to 4.3%. When calculating the benefits associated with the heating and cooling demand handled by the BTES, a higher emission reduction in the range of 12.8%–19.9% was found. This highlights the BTES potential when subject to more balanced loads.

This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular, the amplitude, orientation, and nature of the acoustic field of azimuthal order n are characterized. The dependence of the pulsa- tion amplitude on the azimuthal location in the chamber is discussed, and a protection scheme making use of just one sensor is proposed. The governing equations are then introduced, and a low-order model of the instabilities is discussed. The model accounts for the nonlinear response of M distinct flames, for system acoustic losses by means of an acoustic damping coefficient a and for the turbulent combustion noise, modeled by means of the background noise coefficient r. Keeping the response of the flames arbitrary and in principle different from flame to flame, we show that, together with a and r, only the sum of their responses and their 2n Fourier component in the azimuthal direction affect the dynamics of the azimuthal instability. The existing result that only this 2n Fourier compo- nent affects the stability of standing limit-cycle solutions is recovered. It is found that this result applies also to the case of a nonhomogeneous flame response in the annulus, and to flame responses that respond to the azimuthal acoustic velocity. Finally, a parametric flame model is proposed, depending on a linear driving gain b and a nonlinear saturation constant j. The model is first mapped from continuous time to discrete time, and then recast as a probabilistic Markovian model. The identification of the parameters fa; b; j; rg is then carried out on engine time-series data. The optimal four parameters fa;r;b;jg are estimated as the values that maximize the data likelihood. Once the parameters have been estimated, the phase space of the identified low-order problem is discussed on selected invariant manifolds of the dynamical system.

Thermodynamic properties of the bromine electrode in an exemplary hydrogen–bromine flow battery (HBFB) are investigated in detail. Open-circuit potential (OCP) measurements of HBRB electrolytes in a liquid junction-free setup and electrolyte Raman spectra are employed to estimate polybromides speciation. An improved mathematical description of the bromine electrode OCP versus state of charge is provided. This paper addresses the phenomenon of polybromides formation at concentrations up to 7.7 mol L-1 HBr and 3.85 mol L-1 Br2 and their significant impact on the OCP. The model takes into account tri-, penta- and heptabromides formation, precisely modelled electrolyte activity coefficients (up to 11-molal HBr), electrolyte density, and temperature. It is elucidated that the polybromide formation constants found in literature treating dilute electrolytes are substantially too low. Newly determined equilibrium constants, applicable over a wider concentration range are provided for 25 and 43 °C together with their standard enthalpy changes. The model is successfully validated in an independent experiment using a real, pilot-scale HBFB. It is concluded that the usage of a simple Nernst-like equation to calculate the OCP of flow battery electrodes containing concentrated electrolytes leads to erroneous results.

Sorption heat storage system performance heavily depends on the operating temperature. It is found that testing temperatures reported in literature vary widely. In respect to the building application for space heating, reported testing temperatures are often outside of application scope and at times even incomplete. This has led to application performance overestimation and prevents sound comparison between reports. This issue is addressed in this paper and a remedy pursued by proposing a static temperature and vapor pressure-based testing guideline for building-integrated sorption heat storage systems. By following this guideline, comparable testing results in respect to temperature gain, power and energy density will be possible, in turn providing a measure for evaluation of progress.

In this paper we will describe didactic elements in the Horizon 2020 project FCHgo. This project is directed at children and adolescents between 8 and 18 years old. Its ultimate goal is to raise awareness for renewable energy sources, in particular hydrogen as a fuel and fuel cells for electric power. As part of the project, we are developing a toolkit for teachers and pupils, based upon a narrative approach to physical science and engineering. We believe the narrative approach to be best suited for this project because it allows us to take into account the cognitive tools available to pupils at various stages of their development.

Heat release from absorption storage heat pump by means of absorption of water vapor into aqueous sodium hydroxide is limited by uptake kinetics affecting temperature gain, as well as power- and energy density of the method. Earlier studies pinpoint that natural diffusion alone is not sufficient to reach higher uptake rate, and that the surface to bulk exchange has to be enforced. In this paper, different technical solutions to this problem for the heat storage application are introduced and studied by neutron imaging, enabling visual observation of water vapor uptake and diffusion. The experiments brought to the fore that the buoyancy changes associated with water uptake may be utilized to markedly enhance kinetics. This concept was applied on a vertically installed spiral finned tube operating as heat and mass exchanger for the absorption storage heat pump, also referred to as sorption heat storage. By flooding the space between the spiral fin with absorbent, water absorption into the vertical surface leads to a buoyancy driven movement of the liquid, supplying unspent aqueous NaOH to the vertical surface and exchanging it with the diluted liquid. This is found to increase the rate of absorption markedly. Under realistic heat storage specific operating conditions, a temperature gain of 12.5 K, an active area specific power of 1.28 kW/m2 and an energy density of 243 kWh/m3 in respect to the volume of charged absorbent (greatest volume) is reached. It is proposed that carful design of the spiral finned tube to enhance buoyancy movement will further improve overall sorption heat storage performance.

In this paper we will describe didactic elements in the Horizon 2020 project FCHgo. This project is directed at children and adolescents between 8 and 18 years old. Its ultimate goal is to raise awareness for renewable energy sources, in particular hydrogen as a fuel and fuel cells for electric power. As part of the project, we are developing a toolkit for teachers and pupils, based upon a narrative approach to physical science and engineering. We believe the narrative approach to be best suited for this project because it allows us to take into account the cognitive tools available to pupils at various stages of their development.

In dieser Arbeit wurde das Potential von Free Cooling für die drei Schweizer Standorte Bern, La Chaux-de-Fonds und St. Gallen in Abhängigkeit von der Vorlauftemperatur, Anwendungsart, Schaltung und Art der Rückkühlung untersucht. Hierfür wurde die gleiche Methodik wie in der Untersuchung: “Free Cooling in der Klimakälte - Untersuchung des Potentials in der Schweiz” angewendet.

This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular, the amplitude, orientation, and nature of the acoustic field of azimuthal order n are characterized. The dependence of the pulsa- tion amplitude on the azimuthal location in the chamber is discussed, and a protection scheme making use of just one sensor is proposed. The governing equations are then introduced, and a low-order model of the instabilities is discussed. The model accounts for the nonlinear response of M distinct flames, for system acoustic losses by means of an acoustic damping coefficient a and for the turbulent combustion noise, modeled by means of the background noise coefficient r. Keeping the response of the flames arbitrary and in principle different from flame to flame, we show that, together with a and r, only the sum of their responses and their 2n Fourier component in the azimuthal direction affect the dynamics of the azimuthal instability. The existing result that only this 2n Fourier compo- nent affects the stability of standing limit-cycle solutions is recovered. It is found that this result applies also to the case of a nonhomogeneous flame response in the annulus, and to flame responses that respond to the azimuthal acoustic velocity. Finally, a parametric flame model is proposed, depending on a linear driving gain b and a nonlinear saturation constant j. The model is first mapped from continuous time to discrete time, and then recast as a probabilistic Markovian model. The identification of the parameters fa; b; j; rg is then carried out on engine time-series data. The optimal four parameters fa;r;b;jg are estimated as the values that maximize the data likelihood. Once the parameters have been estimated, the phase space of the identified low-order problem is discussed on selected invariant manifolds of the dynamical system.

Sorption heat storage system performance heavily depends on the operating temperature. It is found that testing temperatures reported in literature vary widely. In respect to the building application for space heating, reported testing temperatures are often outside of application scope and at times even incomplete. This has led to application performance overestimation and prevents sound comparison between reports. This issue is addressed in this paper and a remedy pursued by proposing a static temperature and vapor pressure-based testing guideline for building-integrated sorption heat storage systems. By following this guideline, comparable testing results in respect to temperature gain, power and energy density will be possible, in turn providing a measure for evaluation of progress.

This article presents a numerical study on the building integration of a liquid sorption storage combined with an air-source electric heat pump. The double staging of the sorption storage (i.e. a chemical heat pump) and an electric heat pump leads to significant electricity demand and CO2 emission reductions. Further, it provides an effective coupling between the heat demand of the building and the electricity supply, allowing for optimal integration of solar energy using photovoltaics. For the buildings analyzed, an autarky level of up to 83% is achieved. Winter electricity demand and emission reductions respectively reached values of up to 41%. The storage integration was studied performing dynamic building simulations. The simulation model for the liquid sorption storage was based on a grey box approach. This features a simple analytical model being tuned to match with performance data available from experiments conducted on a lab scale test rig. The presented integration of a compact seasonal thermal energy storage at the building scale represents a promising approach for a grid compliant integration of renewable energy, significantly reducing electricity demand peaks and related CO2 emissions in winter.

Direct Numerical Simulations (DNS) are performed to investigate the process of spontaneous ignition of hydrogen flames at laminar, turbulent, adiabatic and non-adiabatic conditions. Mixtures of hydrogen and vitiated air at temperatures representing gas-turbine reheat combustion are considered. Adiabatic spontaneous ignition processes are investigated first, providing a quantitative characterization of stable and unstable flames. Results indicate that, in hydrogen reheat combustion, compressibility effects play a key role in flame stability and that unstable ignition and combustion are consistently encountered for reactant temperatures close to the mixture’s characteristic crossover temperature. Furthermore, it is also found that the characterization of the adiabatic processes is also valid in the presence of non-adiabaticity due to wall heat-loss. Finally, a quantitative characterization of the instantaneous fuel consumption rate within the reaction front is obtained and of its ability, at auto-ignitive conditions, to advance against the approaching turbulent flow of the reactants, for a range of different turbulence intensities, temperatures and pressure levels.

Numerical simulations of laminar premixed flames burning hydrogen and methane in spontaneous ignition mode are performed by harmonically exciting the reactants’ temperature at the domain inlet. The results are compared to an analytical model representing the same reactive flow configuration. The model provides a simplified but nevertheless accurate representation of reheat combustion taking place in sequential gas turbine combustors. An analytic expression for autoignition flames transfer functions to entropy waves is derived and used to extend transfer function models from the literature. For validation purposes, results from fully compressible Direct Numerical Simulations (DNS), including a complete representation of the fluctuating acoustic and entropic fields of the reactive flow, are analyzed and compared to incompressible Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations that only take into account the fluctuating entropic field. Methane flames are found to be more sensitive to entropic forcing than hydrogen flames, featuring nonlinear phenomena even for low excitation amplitudes. In the linear regime, all flames behave as predicted by the analytical model and the URANS simulations are found to correctly predict the fluctuating entropic field. The transition from linear to nonlinear flame response is described in detail and its physical mechanisms are explained. Comparisons with results available in the literature show good prediction capabilities, both in terms of flame describing function and integrated heat release rate. Limitations of the proposed analytical model with respect to real combustion systems are discussed and a simple correction is proposed.

Seasonal thermal energy storage is an effective measure to enable a low carbon future through the integration of renewables into the energy system. Borehole thermal energy storage (BTES) provides a solution for long-term thermal energy storage and its operational optimization is crucial for fully exploiting its potential. This paper presents a novel linearized control-oriented model of a BTES, describing the storage temperature dynamics under varying operating conditions, such as inlet temperature, mass-flow rate and borehole connection layouts (e.g. in-series, in-parallel or mixed). It supports an optimization framework, which was employed to determine the best operating conditions for a heat pump-driven BTES, subject to different intensity profiles of the electricity. It was demonstrated that this boundary condition, due to its seasonal variation, is critical for the optimal operation of the system, as increasing heat pump efficiency in winter while accepting a lower one in summer can be beneficial. Results for an exemplary district case, subject to two different intensity profiles, show that a lower relative intensity in summer compared to the one in winter leads to a higher optimal operating temperature of the storage. The district system studied is heating-dominated, effectively enabling the BTES to cover only 20% of the total heat demand, leading to limited total yearly CO2 emissions savings of 2.2% to 4.3%. When calculating the benefits associated with the heating and cooling demand handled by the BTES, a higher emission reduction in the range of 12.8%–19.9% was found. This highlights the BTES potential when subject to more balanced loads.

Thermodynamic properties of the bromine electrode in an exemplary hydrogen–bromine flow battery (HBFB) are investigated in detail. Open-circuit potential (OCP) measurements of HBRB electrolytes in a liquid junction-free setup and electrolyte Raman spectra are employed to estimate polybromides speciation. An improved mathematical description of the bromine electrode OCP versus state of charge is provided. This paper addresses the phenomenon of polybromides formation at concentrations up to 7.7 mol L-1 HBr and 3.85 mol L-1 Br2 and their significant impact on the OCP. The model takes into account tri-, penta- and heptabromides formation, precisely modelled electrolyte activity coefficients (up to 11-molal HBr), electrolyte density, and temperature. It is elucidated that the polybromide formation constants found in literature treating dilute electrolytes are substantially too low. Newly determined equilibrium constants, applicable over a wider concentration range are provided for 25 and 43 °C together with their standard enthalpy changes. The model is successfully validated in an independent experiment using a real, pilot-scale HBFB. It is concluded that the usage of a simple Nernst-like equation to calculate the OCP of flow battery electrodes containing concentrated electrolytes leads to erroneous results.

A significant amount of energy consumption in buildings is due to heating, ventilation and air-conditioning systems. Among other systems, refrigeration plants are subject of efficiency improvements. However, actual operating conditions of such plants and the performance must be known as well as any eventual optimization potential identified before enhancements can take place. Energy and exergy analyses have been widely used to assess the performance of refrigeration systems. Among others, exergy efficiency is used as an indicator to determine the system performance; however, the practical achievable values are unknown. Therefore, this work proposes a practice-oriented evaluation method for refrigeration plants, based on exergy analysis and technical standards as baseline. The identification of possible enhancements is highly relevant in practice, as measures which improve the system effectiveness most likely prevent frequent shortcomings during refrigeration plant operation. With the introduced optimization potential index (OPI), the achievable enhancements compared to the state of the art in technology and the performance are identified at a glance regardless the complexity of the system. By dividing the plant into different subsystems, each of them can be assessed individually. Laypersons can easily determine the system operating state and subsequently, if needed, initiate a detailed analysis as well as appropriate countermeasures by specialist. Moreover, modeling is seen as an appropriate method to determine additional reference values for refrigeration machines if none are available according to technical standards. Among different modeling techniques, artificial neural network models reveal the best performance for the present application. The application, functionality and purpose of the presented method is exemplified on two numerical test cases and on a real field plant as a case study. The investigation reveals an adequate operation of the studied field pla

Exergy analysis allows us to determine the quality of energy sources and losses due to irreversibilities through a system. However, the quantification of possible improvements as compared with the state of the art in technology is complicated. Typically, it is referred to the thermodynamic ideal, which is not achievable in practice. Therefore, this paper introduces the exergy optimization potential index, a new key figure based on exergy analysis and technical standard values, in order to assess the achievable performance and to determine possible improvements in vapor compression refrigeration plants with cold water distribution. By dividing the plant into different subsystems (dry cooler, refrigeration machine, cold storage & transport and cooling location), each of them can be assessed individually. Furthermore, by comparing the actual exergy effort with reference values, the interpretation of the results becomes straightforward. The applicability of the method is demonstrated on two theoretical test cases and on a real system. The investigated refrigeration plant performs well in general, which is revealed with an average optimization potential index inferior to 0. However, the subsystem dry cooler shows potential for improvement in the period of May to mid of July. Also, three out of seven cooling locations have performance issues, which is indicated with an average optimization potential index of at least 0.07. Overall, the electrical exergy input has a major impact on the optimization potential index. This reveals the importance of minimizing the electrical energy usage, as it is the main overhead in the operating cost of refrigeration plants.

A review of wind turbine technology showed that many flaws in both the flow models and computations are involved in the traditional fundamentals. While traditional methods for design and computation are all based on the airfoil theory, a new method based on turbine theories has been developed and is shown to be ideally applicable. Against the traditional method, the new method also considers non-uniform pressure distribution in flows downstream of the rotor plane and is thus highly accurate. The blade efficiency or tip swirl number has been introduced. It enables computation of the power coefficient to be very reasonable. Its optimum can be directly applied to the geometrical design of turbine blades. Between the tip speed ratio blade efficiency and power coefficient cp, a closed solution of both the optimum design and the operation of wind turbines exists. It is demonstrated that the maximum achievable power coefficient can be 10% larger than that predicted by all previous theories.

In the design phase of the photovoltaic field for a bifacial photovoltaic power plant (B-PV), the influence of installation parameters on both the energetic and economic performance must be considered, which makes determining the cost-optimal field design a challenge. Although some studies have dealt with this topic, many questions remain unanswered. Therefore, this work investigated the site-dependent impact of the installation parameters row spacing, module elevation, tilt angle and soil reflectivity of a fixed-tilt and a single-axis tracked B-PV with an east–west and north south-axis on the energy yield, the levelized cost of electricity (LCOE) and the bifacial gain. Based on the results, the magnitude of the influence of an installation parameter on the energy yield and LCOE could be quantified for all three system designs. However, three findings are particularly noteworthy: 1. in the case of the fixed-tilt design, the relative energy yield gain caused by a larger row spacing increases with increasing latitude; 2. depending on PV field’s configuration, soil brightening measures can significantly increase the energy yield of all three system designs, practically independent of location, and at the same time reduce the LCOE; 3. the choice of a too high module elevation can lead to small yield losses. Finally, the simulation model used was validated with the Swiss BIFOROT test array. In summary, it can be said that the complex interactions of installation parameters must be thoroughly investigated in order to avoid energy yield losses and unnecessarily high LCOE.

Exergy analysis has been widely used to assess refrigeration systems by evaluating exergy losses or exergy efficiency. The latter is mostly used as an indicator to determine the system performance, which requires the comparison of the actual system with its idealized reversible version, but not the practical achievable efficiency. Therefore, a practice-oriented evaluation method for refrigeration plants in free cooling operation is proposed, based on exergy analysis and technical standards as baseline. By considering the exergy input of auxiliary devices, the overall design of hydraulic circuits can be assessed on subsystem level. The achievable optimization potential compared to the state of the art in technology and the performance is revealed with the introduced optimization potential index (OPI). The application is demonstrated on a case study, where the analysis reveals an adequate operation of the field plant in general. Most cooling locations show potential for improvement, which is indicated by an OPI superior to zero. Moreover, the auxiliary electrical exergy input shows the same magnitude as the thermal exergy input, which emphasizes the importance of reducing the electrical energy usage of auxiliary devices in refrigeration plants to increase the performance.