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Peer Reviewed Scientific Journals | 2021

An adaptive short-term forecasting method for the energy yield of flat-plate solar collector systems

Unterberger V, Lichtenegger K, Kaisermayer V, Gölles M, Horn M. An adaptive short-term forecasting method for the energy yield of flat-plate solar collector systems. Applied Energy. 2021 Apr 16;2021(293). https://doi.org/10.1016/j.apenergy.2021.116891

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The number of large-scale solar thermal installations has increased rapidly in Europe in recent years, with 70 % of these systems operating with flat-plate solar collectors. Since these systems cannot be easily switched on and off but directly depend on the solar radiation, they have to be combined with other technologies or integrated in large energy systems. In order to most efficiently integrate and operate solar systems, it is of great importance to consider their expected energy yield to better schedule heat production, storage and distribution. To do so the availability of accurate forecasting methods for the future solar energy yield are essential. Currently available forecasting methods do not meet three important practical requirements: simple implementation, automatic adaption to seasonal changes and wide applicability. For these reasons, a simple and adaptive forecasting method is presented in this paper, which allows to accurately forecast the solar heat production of flat-plate collector systems considering weather forecasts. The method is based on a modified collector efficiency model where the parameters are continuously redetermined to specifically consider the influence of the time of the day. In order to show the wide applicability the method is extensively tested with measurement data of various flat-plate collector systems covering different applications (below 200 Celsius), sizes and orientations. The results show that the method can forecast the solar yield very accurately with a Mean Absolute Range Normalized Error (MARNE) of about 5 % using real weather forecasts as inputs and outperforms common forecasting methods by being nearly twice as accurate.


Technical Reports | 2021

Control of DHC networks and Reduction of the operating temperatures in DH systems

Task 55 Towards the Integration of Large SHC Systems into DHC Networks

Gölles M, Muschick D, Unterberger V, Leoni P, Schmidt R, Lennermo G. "Control of DHC networks and Reduction of the operating temperatures in DH systems". EA SHC FACTSHEET 55.A-D4.2. Date of Publication: 28.01.2021. https://task55.iea-shc.org/fact-sheets

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Overview on different approaches for the control of the heat distribution networks in case of the integration of large-scale solar thermal systems, and different possibilities for the reduction of the operating temperatures in DH systems.


Technical Reports | 2021

Control of large-scale solar thermal plants

Task 55 Towards the Integration of Large SHC Systems into DHC Networks

Gölles M, Unterberger V. "Control of large-scale solar thermal plants". IEA SHC FACTSHEET 55.B-D3.1. Date of Publication: 28.01.2021. https://task55.iea-shc.org/fact-sheets

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Overview on the control of large-scale thermal plants, limited to plants feeding into DH networks as well as theirkey components, i.e. the actual collector circuit and the heat exchanger between primary and secondary circuit.


Technical Reports | 2021

Endbericht: Heat Pumping system Control (HPC)

Modellbasierte Regelung von Absorptionswärmepump-Anlagen.

Zlabinger S, Wernhart M, Unterberger V, Rieberer R, Gölles M, Rohringer C, Poier H, Halmdienst C, Kemmerzehl C, Otto M. Heat Pumping system Control (HPC). Modellbasierte Regelung von Absorptionswärmepump-Anlagen. FFG, 4. Ausschreibung Energieforschungsprogramm, Projektnummer: 865095. Endbericht. 2021.

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Other publication | 2021

HPC - Workshop

Experimentelle Analyse, Simulation und Regelung von Absorptionswärmepumpen/-kältemaschinen

Zlabinger S, Unterberger V, Gölles M, Wernhart M, Rieberer R, Poier H, Rohinger C, Kemmerzehl C, Halmdienst C. Experimentelle Analyse, Simulation und Regelung von Absorptionswärmepumpen/-kältemaschinen. Online-Workshop im Rahmen des FFG-Projekts HPC ("4. Ausschreibung Energieforschung 2017") am 09.04.2021.

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Durch die vermehrte Einbindung von Absorptionswärmepumpen und -kältemaschinen in bestehende und zukünftige Energiesysteme des Kälte- und Wärmesektors kann der Anteil erneuerbarer Energien deutlich gesteigert werden. Um dies erfolgreich umsetzen zu können, müssen die Betriebsstrategien und Regelungen dieser Systeme jedoch in der Lage sein, auch mit dynamischen und stark variierenden Betriebsbedingungen umgehen zu können. Dieser Herausforderung hat sich das von der FFG geförderte Projekt HPC – heat pumping system control gewidmet. Im Rahmen dieses Workshops sollen die Ergebnisse und deren Nutzen für die Praxis präsentiert und diskutiert werden.


Peer Reviewed Scientific Journals | 2021

Model-Based Estimation of the Flue Gas Mass Flow in Biomass Boilers.

Niederwieser H, Zemann C, Goelles M, Reichhartinger M. Model-Based Estimation of the Flue Gas Mass Flow in Biomass Boilers. IEEE Transactions on Control Systems Technology. 2021 Jul;19(4):1609 - 1622. https://doi.org/10.1109/TCST.2020.3016404

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Three estimators for the estimation of the flue gas mass flow in biomass boilers are presented and compared, namely a sliding-mode observer, a Kalman filter, and a so-called steady-state estimator. The flue gas mass flow is an important process variable in biomass boilers as it contains information about the supplied mass flows of air and decomposed fuel. It is also related to the generated heat flow. Furthermore, its knowledge may be exploited in model-based control strategies which allow one to keep pollutant emissions low, on the one hand, and to achieve high efficiency, on the other hand. However, due to fouling of the equipment over time, measurements and existing estimation methods are not suitable for long-term applications. The estimators proposed in this article are based on a dynamic model for gas tube heat exchangers. They are capable of handling the fouling of the heat exchanger and, additionally, they offer the possibility of monitoring the degree of fouling. By incorporating an additional differential pressure measurement and extending the aforementioned estimators, an improvement regarding the dynamic response and the estimation accuracy is achieved. The application of the estimators to real measurement data from both, a medium-scale and a small-scale biomass boiler, demonstrates their wide applicability.


Other Presentations | 2021

Operation of Coupled Multi-Owner District Heating Networks via Distributed Optimization

Muschick D, Gölles M, Kaisermayer V, Horn M. Operation of Coupled Multi-Owner District Heating Networks via Distributed Optimization.17th International Symposium on District Heating and Cooling. Nottingham Trent University, Nottingham, United Kingdom. 7. Sep 2021. Oral Presentation. [online]

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The simultaneous operation of multiple connected heating networks can be handled by optimization techniques. However, a global optimum might not represent a good operating strategy if the networks belong to different owners and thus might habe competing interests. An approach from game theory then needs to be applied, which finds a generalized Nash equilibrium instead.


Other Presentations | 2021

Optimal operation of cross-ownership district heating and cooling networks

Muschick D, Kaisermayer V, Gölles M, Horn M.Optimal operation of cross-ownership district heating and cooling networks. 20th European Roundtable on Sustainable Consumption and Production. 9. Sep 2021. Graz. Oral Presentation.

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Technical Reports | 2021

Supervisory control of large-scale solar thermal systems

Task 55 Towards the Integration of Large SHC Systems into DHC Networks

Gölles M, Unterberger V, Kaisermayer V, Nigitz T, Muschick D. "Supervisory control of large-scale solar thermal systems". IEA SHC FACTSHEET 55.A-D4.1. Date of Publication: 28.01.2021. https://task55.iea-shc.org/fact-sheets

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Overview on different approaches for supervisory control strategies,deciding on operating modes and set points for the controls of the different plants and componentsintegrated in solar thermal systems.


Conference contributions | 2020

"Long-term verification of a new modular method for CO-lambda-optimisation"

Zemann C, Hammer F, Gölles M. Long-term verification of a new modular method for CO-lambda-optimisation. 6th Central European Biomass Conference CEBC 2020 (Oral Presentation). 2020.

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Peer Reviewed Scientific Journals | 2020

A MILP-based modular energy management system for urban multi-energy systems: Performance and sensitivity analysis

Moser AGC, Muschick D, Gölles M, Nageler PJ, Schranzhofer H, Mach T et al. A MILP-based modular energy management system for urban multi-energy systems: Performance and sensitivity analysis. Applied Energy. 2020;2020(261). 114342.

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The continuous increase of (volatile) renewable energy production and the coupling of different energy sectors such as heating, cooling and electricity have significantly increased the complexity of urban energy systems. Such multi-energy systems (MES) can be operated more efficiently with the aid of optimization-based energy management systems (EMS). However, most existing EMS are tailor-made for one specific system or class of systems, i.e. are not generally applicable. Furthermore, only limited information on the actual savings potential of the usage of an EMS under realistic conditions is available. Therefore, this paper presents a novel modular modeling approach for an EMS for urban MES, which also enables the modeling of complex system configurations. To assess the actual savings potential of the proposed EMS, a comprehensive case study was carried out. In the course of this the influence of different user behavior, changing climatic conditions and forecast errors on the savings potential was analyzed by comparing it with a conventional control strategy. The results showed that using the proposed EMS in conjunction with supplementary system components (thermal energy storage and battery) an annual cost savings potential of between 3 and 6% could be achieved.


Peer Reviewed Scientific Journals | 2020

Control of biomass grate boilers using internal model control

Schörghuber C, Gölles M, Reichhartinger M, Horn M. Control of Biomass Grate Boilers using Internal Model Control. Control engineering practice. 2020.

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A new model-based control strategy for biomass grate boilers is presented in this paper. Internal model control is used to control four outputs of the plant and to achieve a control structure with fewer control parameters needing to be experimentally tuned. A nonlinear state–space model describing the essential behaviour of the biomass grate boiler is used for controller design. The inverse system dynamics representing the main part of internal model control are designed with the help of this model. In doing so the properties of differentially flat systems are used. Due to a time delayed input, the inverse system is determined only for three input output channels. The stabilization of the inverse system dynamics, however, is a challenging task. A stabilization method with the help of the time delayed input is suggested and a stability analysis is given. The new control strategy has only three parameters to be tuned, representing a major reduction of complexity in comparison to existing model-based approaches. Finally, experimental results of the implemented control strategy on representative biomass grate boiler with a nominal capacity of 180 kW are presented and compared to an existing model-based control strategy based on input output linearization. The experimental evaluation proves that it is possible to operate the biomass boiler in all load ranges with high efficiency and low pollutant emissions.


Peer Reviewed Scientific Journals | 2020

Decentralized heating grid operation: A comparison of centralized and agent-based optimization

Lichtenegger K, Leitner A, Märzinger T, Mair C, Moser A, Wöss D, Schmidl C, Pröll T. Decentralized heating grid operation: A comparison of centralized and agent-based optimization. Sustainable Energy, Grids and Networks. 2020;2020(21).

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Moving towards a sustainable heat supply calls for decentralized and smart heating grid solutions. One promising concept is the decentralized feed-in by consumers equipped with their own small production units (prosumers). Prosumers can provide an added value regarding security of supply, emission reduction and economic welfare, but in order to achieve this, in addition to advanced hydraulic control strategies also superordinate control strategies and appropriate market models become crucial.

In this article we study methods to find a global optimum for the local energy community or at least an acceptable approximation to it. In contrast to standard centralized control approaches, based either on expert rules or mixed integer linear optimization, we adopt an agent-based, decentralized approach that allows for incorporation of nonlinear phenomena. While studied here in small-scale systems, this approach is particularly attractive for larger systems, since with an increasing number of interacting units, the optimization problem becomes more complex and the computational effort for centralized approaches increases dramatically.

The agent-based optimization approach is compared to centralized optimization of the same prosumer-based setting as well as to a purely central setup. The comparison is based on the quality of the optimization solution, the computational effort and the scalability. For the comparison of these three approaches, three different scenarios have been set up and analysed for four seasons. In this analysis, no approach has emerged as clearly superior to the others; thus each of them is justified in certain situations.


Conference Papers | 2020

Dynamische Simulation von Absorptionskälteanlagen – Dymola-Modell einer H2O/LiBr-Absorptionskälteanlage

Wernhart M, Rieberer R, Zlabinger S, Unterberger V, Gölles M. Dynamische Simulation von Absorptionskälteanlagen: Dymola-Modell einer H2O/LiBr-Absorptionskälteanlage. in Proc. Deutsche Kälte-Klima-Tagung 2020. Deutscher Kälte- und Klimatechnischer Verein e.V. 2020

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Absorptionskälteanlagen können einen wesentlichen Beitrag zur Verringerung von CO2-Emissionen leisten, wenn Wärme aus regenerativen Energieträgern oder Abwärme aus industriellen Prozessen zum Antrieb verwendet wird. Absorptionskälteanlagen weisen bereits jetzt eine hohe Effizienz auf, bei veränderlichen Betriebsbedingungen kann diese je nach vorhandenen Stellgliedern weiter gesteigert werden. Dazu werden im Rahmen des Forschungsprojektes „Heat Pumping Systems Control (HPC)“ zwei Absorptionskälteanlagen – eine mit der Stoffpaarung Ammoniak/Wasser (NH3/H2O) und eine mit der Stoffpaarung Wasser/Lithiumbromid (H2O/LiBr) – untersucht, um für unterschiedliche Anwendungen optimale Betriebsstrategien zu entwickeln. Zur Berücksichtigung der Zustandsänderungen in der Absorptionskälteanlage, werden dynamische Simulationsmodelle in der Modellierungssprache Modelica entwickelt und mit Messdaten validiert.

Im Rahmen dieses Konferenzbeitrags werden Komponentenmodelle für die NH3/H2O-Absorptionskälteanlage und Simulationsrechnungen bei veränderlichen Randbedingungen präsentiert, sowie ein Vergleich mit Messdaten diskutiert.


Conference Papers | 2020

Evaluation of the Transient Behaviour of a Fixed-Bed Biomass Gasifier for Demand-Oriented Electricity Production

Hollenstein C, Zemann C, Antolini D, Patuzzi F, Martini S, Baratieri M, Gölles M. Horn M. Evaluation of the Transient Behaviour of a Fixed-Bed Biomass Gasifier for Demand-Oriented Electricity Production. 28th European Biomass Conference & Exhibition. 6-9 July 2020.

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The majority of renewable energy technologies are volatile in nature. External factors such as weather conditions lead to fluctuations in their produced electricity and heat. This results in a demand either not being covered or dissatisfied since too much electricity and heat is produced in the energy system. Although energy storages can counteract these fluctuations, renewable energy technologies that are capable of producing energy on demand are needed as well. As such, technologies based on the thermochemical conversion of biomass are especially relevant as they are considered to be CO2-neutral. Although most existing implementations are based on combustion of biomass, fixed-bed biomass gasification is of growing relevance due to higher overall efficiencies and low pollutant emissions. Currently, fixed-bed biomass gasifiers are usually operated at steady-state operation to produce the maximum amount of energy possible. This contribution investigates, whether they can be used as a technology for demand-oriented electricity and heat production


Conference Papers | 2020

Experimentally verified dynamic simulation model of a NH3/H2O-absorption refrigeration system

Wernhart M, Rieberer R, Zlabinger S, Unterberger V, Gölles M. Experimentally verified dynamic simulation model of a NH3/H2O-absorption refrigeration system. in Japan Society of Refrigerating and Air Conditioning Engineers, Hrsg., 14th IIR Gustav-Lorentzen Conference on Natural Fluids, GL 2020 - Proceedings. International Institute of Refrigeration. 2020. S. 103-109. (Refrigeration Science and Technology). https://doi.org/10.18462/iir.gl.2020.1145

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The operation characteristics of thermally driven absorption refrigeration systems (ARS) are strongly dependent on their hydraulic integration. Therefore, varying operating conditions of the hydraulic supply have a great influence on the behaviour of ARS and lead to dynamic operation, which can affect the efficiency and is largely unexplored so far. To enable a simple investigation of ARS integration considering their dynamic behaviour and to develop modern, efficiency-enhancing control strategies, dynamic simulation models of ARS are developed in Modelica Code.

In this paper, a dynamic simulation model of an ARS with the working pair ammonia/water (NH3/H2O) is presented. The parameterization and the physical correlations of selected components of the simulation model are described. Afterwards, the simulation model is verified by comparing simulation results with measurement data of the NH3/H2O-ARS. Finally, the capabilities of the simulation model are demonstrated by performing a simulation-based analysis of the temperature glide of the refrigerant in the evaporator.


Peer Reviewed Scientific Journals | 2020

Increased efficiency of dual fluidized bed plants via a novel control strategy

Nigitz T, Gölles M, Aichernig C, Schneider S, Hofbauer H, Horn M. Increased efficiency of dual fluidized bed plants via a novel control strategy. Biomass & Bioenergy. 2020 Okt;141. 105688. https://doi.org/10.1016/j.biombioe.2020.105688

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Industrial plants using DFB biomass gasification are on the verge of profitability. These plants should be operated more economically in order to support the industrial applications for renewable technologies of this kind. Since some parts of such plants are typically difficult to control, a state-of-the-art control strategy is analyzed here in the context of its potential for increased economic efficiency. The DFB gasification plant “HGA Senden” in Ulm, Germany is considered on an exemplary basis here. A process analysis reveals a high potential in the synchronization of product gas generation and utilization. At the present time a relevant surplus of product gas is burned in an auxiliary boiler for synchronization purposes and regular manual adjustments at the fuel feed are necessary by the plant operators. For this synchronization a novel control strategy is developed that actuates the auxiliary boiler and the fuel feed simultaneously. The novel control strategy was experimentally validated for a period of over one month. Due to this long-term evaluation the fuel consumption was reduced by 5% and the manual adjustments of the fuel feed that were necessary on average every 30min were eliminated. As a result DFB gasification plants can be operated more economically by applying the novel control strategy for synchronization of product gas generation and utilization.


Conference Papers | 2020

Long-term validation of a new modular approach for CO-lambda-optimization

Zemann C, Hammer F, Gölles M, Horn M. Long-term validation of a new modular approach for CO-lambda-optimization. 28th European Biomass Conference & Exhibition. 6-9 July 2020.

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Long Term Validation of a New Modular Approach for CO-Lambda-Optimization

The optimization of existing biomass boilers in terms of efficiency and pollutant emissions is essential for their continued economic and ecological viability in future energy systems. These improvements are typically achieved by constructive changes which are expensive and can require prolonged downtimes. A well-known method for optimizing biomass boilers in terms of efficiency and pollutant emissions without constructive changes is the so-called CO-lambda-optimization. While multiple approaches for CO-lambda-optimization have been presented in literature, they are still rarely used in real biomass boilers. This is partly due to the fact that these approaches do not meet the requirements associated with their long-term operation in real biomass boilers. This contribution presents a new and modular approach for the CO-lambda-optimization which is specifically designed to meet these requirements. Particular emphasis in this contribution is laid on the long-term validation of the presented approach for CO-lambda-optimization at a medium-scale fixed-bed biomass boiler.


Peer Reviewed Scientific Journals | 2020

Model-based control of hydraulic heat distribution systems — Theory and application

Unterberger V, Muschick D, Loidl A, Poms U, Gölles M, Horn M. Model-based control of hydraulic heat distribution systems — Theory and application. Control Engineering Practice. 2020;2020(101).104464. https://doi.org/10.1016/j.conengprac.2020.104464

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With the share of renewable energy sources increasing in heating and hot water applications, the role of hydraulic heat distribution systems is becoming more and more important. This is due to the fact that in order to compensate for the often fluctuating behaviour of the renewables a flexible heat transfer must be ensured by these distribution systems while also taking the optimal operating conditions (mass flow, temperature) of the individual components into consideration. This demanding task can be accomplished by independently controlling the two physical quantities mass flow and temperature. However, since there exists an intrinsic nonlinear coupling between these quantities this challenge cannot be handled sufficiently by decoupled linear PI controllers which are currently state-of-the-art in the heating sector. For this reason this paper presents a model-based control strategy which allows a decoupled control of mass flow and temperature. The strategy is based on a systematic design approach from models described in this contribution, which are validated by commercially available components from which most of them can be parametrized by the data sheet. The control strategy is designed for a typical hydraulic configuration used in heating systems, which will allow the accurate tracking of the desired trajectories for mass flows, temperatures and consequently heat flows. The controllers are validated experimentally and compared to well-tuned state-of-the-art (PI) controllers in order to illustrate their superiority and prove their decoupling of the control of mass flow and temperature in real world applications.


Peer Reviewed Scientific Journals | 2020

Optimal operation of residential heating systems with logwood boiler, buffer storage and solar thermal collector

Zemann C, Deutsch M, Zlabinger S, Hofmeister G, Gölles M, Horn M. Optimal operation of residential heating systems with logwood boiler, buffer storage and solar thermal collector. Biomass and Bioenergy, 2020,140:105622.

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Modern central heating systems with logwood boilers are comprised of the boiler, a buffer storage and solar thermal collectors. Conventional control strategies for these heating systems do not coordinate the utilization of all components. This can lead to a sub-optimal operation of the entire heating system resulting in a loss of efficiency and increased pollutant emissions. This contribution presents a control strategy which considers all components of the heating system including the user and forecasts for the solar yield and heat demand. It determines and carries out an optimal operating strategy that improves the user utility and maximizes the heating system efficiency while also ensuring a clean and efficient combustion. The control strategy continuously learns the user behavior and instructs the user when to refill the logwood boiler and how much fuel to use. The new control strategy was verified through test runs performed at an experimental setup consisting of a commercially available logwood boiler with a nominal capacity of 28 kW , two buffer storages with a capacity of 1.5 m3 each and a heating device with a thermal output of up to 12 kW simulating a solar thermal collector. During these test runs, the CO emissions were reduced 93.6 %by in the main combustion phase, 7.1 % more solar yield was utilized, the buffer losses were reduced by - 16.9 % and the overall efficiency was increased by 3.1 % . Thus, the application of this control strategy resulted in a significantly improved user utility and heating system efficiency.


Conference Papers | 2020

Power Systems in the context of district heating and cooling networks as an integrated energy system approach -Regulations and Business Cases within the IEA DHC Annex TS3

Kneiske T, Kallert A, Cronbach D, Yu Y, Schmidt D, Johannsen R, Sorknæs P, Muschick D, Ianakiev A, Svensson I, Schmidt R, Terreros O, Widl E. Power Systems in the context of district heating and cooling networks as an integrated energy system approach - Regulations and Business Cases within the IEA DHC Annex TS3. 48. CIGRE conference 2020. July 2020.

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Integrated energy systems 1 couples power systems, district heating and cooling (DHC), and gas grids, thereby enabling the storage and distribution of energy across different infrastructure types. Supply and demand follow different patterns in these different domains, which can lead to synergies in generation, storage and consumption, if planned and managed as one energy system. An integrated approach has the potential to increase reliability, flexibility and supply safety and efficiency. Moreover, network coupling increases local utilization of renewables, avoiding problems in the distribution networks, as well as transmission losses. In addition, hybrid energy networks are a promising opportunity to manage and mitigate temporal imbalances of supply and demand in energy systems with a high share of volatile renewables, mainly PV and wind energy. The IEA DHC Annex TS3 provides a holistic approach for designing and assessing hybridization schemes, focusing on the district heating and cooling (DHC) networks and considering both technical (system configuration, operational strategy) and strategic aspects (business models, regulatory frame). These aspects will be discussed within the framework of the IEA DHC Annex TS3 in order to promote the benefits of DHC networks in an integrated energy system. Furthermore we can establish a common direction for the development and implementation of hybrid energy concepts. The IEA DHC Annex TS3 will connect existing national and international projects and thus benefit from interdisciplinary experience and exchange. The primary result of the IEA DHC Annex TS3 will be a guidebook including:  Analyses of available technologies and synergies / application areas  An overview of international case studies including simulation scenarios 1 Different alternative notations can be found in literature, e.g. multi-energy networks, hybrid energy networks, sector coupling, multi-domain networks, cross energy systems. However, since no standard definition is available, those notations are used synonymously.


Peer Reviewed Scientific Journals | 2020

Progressive Hedging for Stochastic Energy Management Systems: The Mixed-Integer Linear Case

Kaisermayer V, Muschick D, Gölles M, Horn M. Progressive Hedging for Stochastic Energy Management Systems: The Mixed-Integer Linear Case. Energy Systems. 2020 Aug 29. https://doi.org/10.1007/s12667-020-00401-z

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Energy systems have increased in complexity in the past years due to the everincreasing integration of intermittent renewable energy sources such as solar thermal or wind power. Modern energy systems comprise different energy domains such as electrical power, heating and cooling which renders their control even more challenging. Employing supervisory controllers, so-called energy management systems (EMSs), can help to handle this complexity and to ensure the energy-efficient and cost-efficient operation of the energy system. One promising approach are optimization-based EMS, which can for example be modelled as stochastic mixed-integer linear programmes (SMILP). Depending on the problem size and control horizon, obtaining solutions for these in real-time is a difficult task. The progressive hedging (PH) algorithm is a practical way for splitting a large problem into smaller subproblems and solving them iteratively, thus possibly reducing the solving time considerably. The idea of the PH algorithm is to aggregate the solutions of subproblems, where artificial costs have been added. These added costs enforce that the aggregated solutions become non-anticipative and
are updated in every iteration of the algorithm. The algorithm is relatively simple to implement in practice, re-using almost all of a possibly existing deterministic implementations and can be easily parallelized.
Although it has no convergence guarantees in the mixed-integer linear case, it can nevertheless be used as a good heuristic for SMILPs. Recent theoretical results shown that for applying augmented Lagrangian functions in the context of mixed-integer programmes, any norm proofs to be a valid penalty function. This is not true for squared norms, like the squared L 2 -norm that is used in the classical progressive hedging algorithm. Building on these theoretical results, the use of the L 1 and L-infinity-norm in the PH algorithm is investigated in this paper. In order to incorporate these into the algorithm an adapted multiplier update step is proposed. Additionally a heuristic extension of the aggregation step and an adaptive penalty parameter update scheme from the literature is investigated. The advantages of the proposed modifications are demonstrated by means of illustrative examples, with the application to SMILP-based EMS in mind.


Conference Papers | 2020

Simultaneous state and fuel property estimation in biomass boilers - theory and practice

Zemann C, Gölles M, Horn M. Simultaneous state and fuel property estimation in biomass boilers - theory and practice. 1st Virtual IFAC World Congress. 2020.

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A key factor for the further distribution of biomass boilers in modern energy systems is the capability of changing the applied feedstock during normal plant operation. This is only possible with the application of advanced control strategies that utilize knowledge about the state variables and varying fuel properties. However, neither the state variables nor the fuel properties are measurable during plant operation and, thus, need to be estimated. This contribution presents a method for the simultaneous real-time estimation of the state variables and the fuel properties in fixed-bed biomass boilers which is a novel approach in the field of biomass boilers. The method bases on an Extended Kalman Filter using a nonlinear dynamic model and measurement data from the combustion process. The estimated variables are the masses of dry fuel and water in the fuel bed as well as the fuel's bulk density, water content, chemical composition and lower heating value. The proposed method is easy to implement and requires moderate computational effort which increases the potential of its application at actual biomass boilers. The proposed method is verified with simulation studies and by test runs performed at a representative small-scale fixed-bed biomass boiler. The estimation results show a good agreement with the actual values, demonstrating that the proposed method is capable of accurately estimating the biomass boiler's state variables and simultaneously its fuel properties. For this reason, the presented method is a key technology to ensure the further distribution of biomass boilers in modern energy systems.


Conference Papers | 2020

Soft-Sensor for the on-line estimation of the flue gas mass flow in biomass boilers with additional monitoring of the heat exchanger fouling

Niederwieser H, Zemann C, Gölles M, Reichhartinger M. Soft-Sensor for the On-Line Estimation of the Flue Gas Mass Flow in Biomass Boilers with Additional Monitoring of the Heat Exchanger Fouling. In Proceedings of the 28th European Biomass Conference and Exhibition 2020 (eEUBCE 2020). 2020. p. 280 - 284

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The flue gas mass flow is one of the fundamental quantities of the combustion process in biomass boilers. Since it directly relates to the enthalpy flow entering the heat exchanger, its knowledge is highly advantageous for a sophisticated load control of the biomass boiler. It also includes information regarding the primary and secondary air mass flows as well as the mass flows of potentially occurring leakage air and thermally decomposed fuel. However, in practical application it is not possible to obtain a reliable measurement of the flue gas mass flow. For this reason, this work presents a soft-sensor for the on-line estimation of the flue gas mass flow in biomass boilers. The approach is robust against fouling of the relevant boiler components and is based on standard measurements which are typically available in biomass boilers. In addition, the soft-sensor offers the possibility of monitoring the degree of heat exchanger fouling.


Peer Reviewed Scientific Journals | 2020

The effect of the reaction equilibrium on the kinetics of gas-solid reactions — A non-parametric modeling study.

Birkelbach F, Deutsch M, Werner A. The effect of the reaction equilibrium on the kinetics of gas-solid reactions — A non-parametric modeling study. Renewable Energy 2020.152:300-307.

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The viability of thermochemical energy storage for a given application is often determined by the reaction kinetics under process conditions. For high exergetic efficiency the process needs to operate in close proximity to the reaction equilibrium. Thus, accurate kinetic models that include the effect of the reaction equilibrium are required.

In the present work, different parametrization methods for the equilibrium term in the General Kinetic Equation are evaluated by modeling the kinetics of two reaction systems relevant for thermochemical energy storage (CaC2O4 and CuO) from experimental data. A non-parametric modeling method based on tensor decompositions is used that allows for a purely data driven assessment of different parametrization methods.

Our analysis shows that including a suitable equilibrium term is crucial. Omitting the equilibrium term when modeling formation reactions can lead to seemingly negative activation energies. Our tests also show that for formation reactions, the reaction rate decreases much faster towards the equilibrium than theory predicts. We present an empirical modeling approach that can predict the reaction rate of gas-solid reactions, regardless of the shortcomings of theory. In this way, non-parametric modeling offers a powerful tool for applied research and may contribute to the advancement of the thermochemical energy storage technology.