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  • 51.
    Morandin, Matteo
    et al.
    Department of Mechanical Engineering, University of Padova.
    Toffolo, Andrea
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Meréchal, Francois
    LENI Industrial Energy Systems Laboratory.
    Ensinas, Adriano V.
    CECS, Federal University of ABC (UFABC).
    Nebra, Silvia A
    NIPE Interdisciplinary Centre for Energy Planning, University of Campinas.
    Synthesis and parameter optimization of a combined sugar and ethanol production process integrated with a CHP system2011Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 36, nr 6, s. 3675-3690Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The combined sugar and ethanol production process from sugar cane is a paradigmatic application for energy integration strategies because of the high number of hot and cold streams involved, the external hot utility requirement at two temperature levels for juice evaporation and crystallization, and the electricity demand for juice extraction by milling. These conditions make it convenient to combine the sugar-cane process with a CHP system fuelled by bagasse, the main by-product from juice extraction. The strategies, tools and expertise on energy integration developed separately by the research teams authoring this paper are applied here jointly to optimize the synthesis and the design parameters of the process and of the total site starting from the basic idea of dissociating the heat exchanger network design problem from the total site synthesis problem. At first the minimization of the external heat requirement for the process alone is pursued and results show that a one third reduction can be achieved by optimal heat integration. Then the use of the by-product bagasse for on-site power generation is considered and two bagasse-fuelled CHP systems are optimized along with some parts of the sugar and ethanol production process in order to obtain maximum total site net power. Results show a variety of interesting scenarios of combined sugar, ethanol and electricity production plants with considerably high electricity output.

  • 52.
    Nwachukwu, Chinedu M
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Grip, Carl-Erik
    Wang, Chuan
    Swerea MEFOS, Process Integration Department.
    Wetterlund, Elisabeth
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Systems analysis of sawmill by-products gasification towards a bio-based steel production2018Inngår i: ECOS 2018: Proceedings of the 31st International Conference on Efficiency, Cost, Optimisation, Simulation and Environmental Impact of Energy Systems / [ed] José Carlos Teixeira, Ana Cristina Ferreira, Ângela Silva, Senhorinha Teixeira, Universidade do Minho. Departamento de Engenharia Mecânica Campus Azurém, Guimarães Portugal , 2018Konferansepaper (Fagfellevurdert)
  • 53.
    Nwachukwu, Chinedu M
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Wetterlund, Elisabeth
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Biomass-based gas use in Swedish iron and steel industry: Supply chain and process integration considerations2020Inngår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 146, s. 2797-2811Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Substitution of fossil gaseous fuels with biomass-based gases is of interest to the iron and steel industry due to its role in the mitigation of anthropogenic CO2emissions. In switching from fossil fuels to biomass-based gases, a systems analysis of the full value chain from biomass supply to the production and supply of final gas products becomes crucial. This study uses process and heat integration methods in combination with a supply chain evaluation to analyse full value chains of biomass-based gases for fossil gas replacement within the iron and steel industry. The study is carried out as a specific case study in order to understand the implications of utilizing bio-syngas/bio-SNG as heating fuels in iron- and steel-making, and to provide insights into the most sensitive parameters involved in fuel switching. The results show a significant cost difference in the fuel production of the two gas products owing to higher capital and biomass use in the bio-SNG value chain option. When tested for sensitivity, biomass price, transportation distance, and capital costs show the most impact on fuel production costs across all options studied. Trade-offs associated with process integration, plant localisation, feedstock availability and supply were found to varying extents.

  • 54.
    Rech, Sergio
    et al.
    Department of Mechanical Engineering, University of Padova.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    TSO-STO: A two-step approach to the optimal operation of heat storage systems with variable temperature tanks2012Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 45, nr 1, s. 366-374Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mixed-Integer Linear Programming (MILP) has been generally used in the recent past to evaluate the optimal operation of heat storage systems for district heating. In fact, model equations and constraints can be linearized to strongly reduce the computational time without a significant loss in accuracy, and other simplifying hypotheses can be introduced, such as the constant value of the heat storage temperature.This paper presents instead a non-linear model of a Combined Heat and Power (CHP) system with a variable temperature heat storage serving a district heating network. Optimal operation for a fixed time-dependent demand is searched by varying CHP system loads. The objective is the maximization of management profit in a deregulated electricity market, taking into account investment (CHP and heat storage systems) and operating costs. The nature of the problem is investigated and a new approach for the decomposition of the objective function is proposed to simplify the solution procedure. The impact of different fuel costs and average electricity prices on the results is also analyzed.

  • 55.
    Sandberg, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Krook-Riekkola, Anna
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A bottom-up study of biomass and electricity use in a fossil free Swedish industry2019Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 167, s. 1019-1030Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    While previous research has focused on single industrial sectors or specific technologies, this study aims to explore the impacts of various industrial technology options on the use of biomass and electricity in a future fossil free Swedish industry. By building a small optimization model, that decomposes each industrial sector into site categories by type and technology to capture critical synergies among industrial processes. The results show important synergies between electrification, biomass and CCS/U (sequestration of CO2 is required to reach net-zero emissions). Reaching an absolute minimum of biomass use within the industry has a very high cost of electricity due to the extensive use of power-to-gas technologies, and minimising electricity has a high cost of biomass due to extensive use of CHP technologies. Meanwhile, integrated bio-refinery processes are the preferable option when minimising the net input of energy. There is, thus, no singular best technology, instead the system adapts to the given circumstances showing the importance of a detailed bottom-up modelling approach and that the decarbonisation of the industry should not be treated as a site-specific problem, but rather as a system-wide problem to allow for optimal utilisation of process synergies.

  • 56.
    Tanaka, Yasuto
    et al.
    Department of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama.
    Mesfun, Sennai
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Umeki, Kentaro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Tamura, Yutaka
    Department of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama, Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1 Ookayama.
    Yoshikawa, Kunio
    Department of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama, Tokyo Institute of Technology, Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology.
    Thermodynamic performance of a hybrid power generation system using biomass gasification and concentrated solar thermal processes2015Inngår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 160, s. 664-672Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes the investigation of a hybrid power production system from biomass and solar energy. This paper suggests integration through heat exchanger network as a useful approach to obtain the synergy between biomass and solar. Biomass is first gasified in a bubbling fluidized bed (BFB) gasifier, and then syngas is used in a gas turbine. Excess heat exists in this sub-system and concentrated solar thermal process (CSTP) while there is a demand of steam for generating gasifying agent. Steam Rankine cycle exploits the heat created by these thermal streams to generate power while satisfying the steam demands. Thermodynamic performance was analyzed by process modelling with a semi-kinetic model of BFB gasifier and pinch analyses. The composition and temperature of gasifying agent showed some effect on the overall efficiency of the system. Higher overall efficiency of the system was achieved at higher temperature and higher O2 fraction in the O2-steam mixture as gasifying agent. The increase in thermal input from CSTP had positive effect on overall efficiency of the hybrid system until thermal input from CSTP becomes dominant against thermal stream related to the gasifier and the gas turbine.

  • 57.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A synthesis/design optimization algorithm for Rankine cycle based energy systems2014Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 66, s. 115-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The algorithm presented in this work has been developed to search for the optimal topology and design parameters of a set of Rankine cycles forming an energy system that absorbs/releases heat at different temperature levels and converts part of the absorbed heat into electricity. This algorithm can deal with several applications in the field of energy engineering: e.g., steam cycles or bottoming cycles in combined/cogenerative plants, steam networks, low temperature organic Rankine cycles. The main purpose of this algorithm is to overcome the limitations of the search space introduced by the traditional mixed-integer programming techniques, which assume that possible solutions are derived from a single superstructure embedding them all. The algorithm presented in this work is a hybrid evolutionary/traditional optimization algorithm organized in two levels. A complex original codification of the topology and the intensive design parameters of the system is managed by the upper level evolutionary algorithm according to the criteria set by the HEATSEP method, which are used for the first time to automatically synthesize a “basic” system configuration from a set of elementary thermodynamic cycles. The lower SQP (sequential quadratic programming) algorithm optimizes the objective function(s) with respect to cycle mass flow rates only, taking into account the heat transfer feasibility constraint within the undefined heat transfer section. A challenging example of application is also presented to show the capabilities of the algorithm

  • 58. Toffolo, Andrea
    Fuzzy expert systems for the diagnosis of component and sensor faults in complex energy systems2009Inngår i: Proceedings of the ASME International Mechanical Engineering Congress and Exposition - 2008: presented at 2008 ASME International Mechanical Engineering Congress and Exposition, October 31 - November 6, 2008, Boston, Massachusetts, USA, New York: American Society of Mechanical Engineers , 2009, Vol. 6: Electronics and photonics, s. 237-247Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Locating the causes of malfunctions in complex energy systems is an extremely difficult task, since more than one fault mode may produce similar and possibly undistinguishable patterns of effects. This paper shows how fuzzy expert systems can exploit the available measurements from the data acquisition system to identify different component and sensor fault modes. Real sensor data (mass flow rates, pressures, temperatures, and key operating parameters) are compared to the expected values of the same quantities that are calculated using numerical models of local subsystems. This comparison simply determines if the differences between measured and expected values are "negative", "zero" or "positive" in fuzzy logic terms. The final objective is to verify the existence of some patterns of these attributes that univocally identify the considered fault modes. These patterns are then implemented as the set of rules forming the knowledge base of a fuzzy expert system. The proposed diagnostic methodology is tested on the gas section of a real combined-cycle cogeneration plant and the effect of measurement noise is also discussed.

  • 59. Toffolo, Andrea
    Fuzzy Expert Systems for the Diagnosis of Component and Sensor Faults in Complex Energy Systems2007Inngår i: Proceedings of the ASME International Mechanical Engineering Congress and Exposition - 2007: presented at 2007 ASME International Mechanical Engineering Congress and Exposition, November 11 - 15, 2007, Seattle, Washington, USA, New York: American Society of Mechanical Engineers , 2007, Vol. 6 : Energy systems : analysis, thermodynamics and sustainability, s. 237-247Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Locating the causes of malfunctions in complex energy systems is an extremely difficult task, since more than one fault mode may produce similar and possibly undistinguishable patterns of effects. This paper shows how fuzzy expert systems can exploit the available measurements from the data acquisition system to identify different component and sensor fault modes. Real sensor data (mass flow rates, pressures, temperatures, and key operating parameters) are compared to the expected values of the same quantities that are calculated using numerical models of local subsystems. This comparison simply determines if the differences between measured and expected values are “negative”, “zero” or “positive” in fuzzy logic terms. The final objective is to verify the existence of some patterns of these attributes that univocally identify the considered fault modes. These patterns are then implemented as the set of rules forming the knowledge base of a fuzzy expert system. The proposed diagnostic methodology is tested on the gas section of a real combined-cycle cogeneration plant and the effect of measurement noise is also discussed.

  • 60. Toffolo, Andrea
    Fuzzy expert systems for the diagnosis of component and sensor faults in complex energy systems2009Inngår i: Journal of energy resources technology, ISSN 0195-0738, E-ISSN 1528-8994, Vol. 131, nr 4, s. 0420021-04200210Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Locating the causes of malfunctions in complex energy systems is an extremely difficult task, since more than one fault mode may produce similar and possibly undistinguishable patterns of effects. This paper shows how fuzzy expert systems can exploit the available measurements from the data acquisition system to identify different component and sensor fault modes. Real sensor data (mass flow rates, pressures, temperatures, and key operating parameters) are compared with the expected values of the same quantities that are calculated using numerical models of local subsystems. This comparison simply determines if the differences between measured and expected values are "negative," "zero," or "positive" in fuzzy logic terms. The final objective is to verify the existence of some patterns of these attributes that univocally identify the considered fault modes. These patterns are then implemented as the set of rules forming the knowledge base of a fuzzy expert system. The proposed diagnostic methodology is tested on the gas section of a real combined-cycle cogeneration plant, and the effect of measurement noise is also discussed

  • 61. Toffolo, Andrea
    Multi-Objective Synthesis Optimization of Heat Exchanger Networks With Arbitrary Topology2008Inngår i: Proceedings of the ASME International Mechanical Engineering Congress and Exposition - 2008: presented at 2008 ASME International Mechanical Engineering Congress and Exposition, October 31 - November 6, 2008, Boston, Massachusetts, USA, New York: American Society of Mechanical Engineers , 2008, Vol. 8 : Energy systems: analysis, thermodynamics and sustainability, sustainable products and processes, s. 307-319Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The synthesis of heat exchanger networks (HENs) is one of the most studied problems in process synthesis, because a high level of integration of the internal heat transfer is necessary to reduce both primary energy consumption and total costs. This work develops a methodology for the multi-objective optimization of HEN synthesis. A two-level hybrid algorithm operating on a population of candidate HEN topologies is proposed to search for the best tradeoffs between the maximization of energy recovery and the minimization of total HEN costs. The advantages deriving from graph representations of a HEN are fully exploited in order to handle topologies with arbitrary complexity and to simplify the optimization procedure required to evaluate the objective functions for a given topology. The Aromatics Plant problem, a well-known test case in the literature about HEN synthesis, is used as a test case to show the potentialities of the proposed methodology.

  • 62. Toffolo, Andrea
    Multi-objective synthesis optimization of heat exchanger networks with arbitrary topology2009Inngår i: Proceedings of the ASME International Mechanical Engineering Congress and Exposition - 2008: presented at 2008 ASME International Mechanical Engineering Congress and Exposition, October 31 - November 6, 2008, Boston, Massachusetts, USA, New York: American Society of Mechanical Engineers , 2009, Vol. 8 : Energy systems: analysis, thermodynamics and sustainability, sustainable products and processes, s. 307-319Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The synthesis of heat exchanger networks (HENs) is one of the most studied problems in process synthesis, because a high level of integration of the internal heat transfer is necessary to reduce both primary energy consumption and total costs. This work develops a methodology for the multi-objective optimization of HEN synthesis. A two-level hybrid algorithm operating on a population of candidate HEN topologies is proposed to search for the best tradeoffs between the maximization of energy recovery and the minimization of total HEN costs. The advantages deriving from graph representations of a HEN are fully exploited in order to handle topologies with arbitrary complexity and to simplify the optimization procedure required to evaluate the objective functions for a given topology. The Aromatics Plant problem, a well-known test case in the literature about HEN synthesis, is used as a test case to show the potentialities of the proposed methodology.

  • 63. Toffolo, Andrea
    On cross-flow fan theoretical performance and efficiency curves: An energy loss analysis on experimental data2004Inngår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 126, nr 5, s. 743-751Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Contrary to conventional turbomachinery, cross-flow fan flow field is non-axisymmetrical and its complex configuration strongly affects performance and efficiency characteristic curves. The formulation of a theory on cross-flow fan operation is made even tougher since the strength and the eccentricity of the vortex that forms within the impeller are deeply influenced by the geometry of the impeller and of the casing as well. In this paper a numerical reconstruction of the flow field, validated against an extensive systematic database of global and local experimental measurements, is analyzed. The aim is to achieve a general interpretation of performance and efficiency curves, and to lead them back to one theoretical archetype, whatever the fan configuration being considered.

  • 64. Toffolo, Andrea
    On the theoretical link between design parameters and performance in cross-flow fans: A numerical and experimental study2005Inngår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 34, nr 1, s. 49-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cross-flow fan performance strictly depends on the complex configuration of the non-axisymmetrical flow field within the machine. The flow field, in turn, is deeply influenced by the design parameters of both casing and impeller geometry. In this paper, the relationship between the design parameters of the geometrical configuration and fan performance is discussed in a theoretical perspective, analyzing the features of the corresponding flow fields. These are reconstructed by a numerical study on cross-flow fan operation carried out for a representative set of configurations at different throttling conditions. Time-accurate solutions for a two-dimensional viscous and incompressible model of the fan using a sliding mesh technique are calculated with a commercial CFD code. The numerical results are validated with experimental data obtained from tests on performance and from local measurements of the flow field

  • 65. Toffolo, Andrea
    The synthesis of cost optimal heat exchanger networks with unconstrained topology2009Inngår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 29, nr 17-18, s. 3518-3528Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The optimization of heat exchanger network (HEN) synthesis still remains an open problem because of the complexity of the space comprising all the possible solutions, and most of the proposed methods introduce simplifying assumptions that mainly affect the topological features of the candidate solutions considered and thus artificially limit the boundaries of the search space. This work is devoted to the pursuit of cost-optimal HENs with unconstrained topology, exploiting the advantages deriving from two graph representations of a HEN. One representation is used by an evolutionary algorithm to manage HEN topology and the other is used by a NLP algorithm to manage heat load distribution among the exchangers. The proposed two-level hybrid optimization method is applied to four test cases taken from the literature about HEN synthesis, among which the well-known Aromatics Plant problem

  • 66. Toffolo, Andrea
    et al.
    Benini, Ernesto
    Department of Mechanical Engineering, University of Padova.
    Genetic diversity as an objective in multi-objective evolutionary algorithms2003Inngår i: Evolutionary Computation, ISSN 1063-6560, E-ISSN 1530-9304, Vol. 11, nr 2, s. 151-167Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A key feature of an efficient and reliable multi-objective evolutionary algorithm is the ability to maintain genetic diversity within a population of solutions. In this paper, we present a new diversity-preserving mechanism, the Genetic Diversity Evaluation Method (GeDEM), which considers a distance-based measure of genetic diversity as a real objective in fitness assignment. This provides a dual selection pressure towards the exploitation of current non-dominated solutions and the exploration of the search space. We also introduce a new multi-objective evolutionary algorithm, the Genetic Diversity Evolutionary Algorithm (GDEA), strictly designed around GeDEM and then we compare it with other state-of-the-art algorithms on a well-established suite of test problems. Experimental results clearly indicate that the performance of GDEA is top-level.

  • 67. Toffolo, Andrea
    et al.
    Benini, Ernesto
    Dipertemento di Ingegneria Meccanica, Università di Padova.
    Towards a reduction of compressor blade dynamic loading by means of rotor-stator interaction optimization2002Inngår i: Proceedings of the ASME Turbo Expo 2002 Turbomachinery: presented at the 2002 ASME Turbo Expo, June 3 - 6, 2002, Amsterdam, the Netherlands, New York: American Society of Mechanical Engineers , 2002, Vol. 5A, s. 667-674Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a two-dimensional procedure for minimizing dynamic loading and maximizing time-averaged isentropic efficiency in multi-stage compressors. The procedure arises from the combination of an evolutionary algorithm and a CFD code in which a sliding mesh technique and a time-dependent approach are implemented enabling the study of unsteady rotor stator interaction. The method is then applied to a two-stage compressor cascade (rotor-stator-rotor-stator). The results concerning the optimal set of geometrical parameters considered for optimization (axial distances between successive cascades, circumferential clocking between stators and between rotors) are finally presented and discussed.

  • 68.
    Toffolo, Andrea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lazzaretto, A.
    University of Padova, Padova, Italy.
    A practical tool to generate complex energy system configurations based on the synthsep methodology2019Inngår i: International Journal of Thermodynamics, ISSN 1301-9724, Vol. 22, nr 1, s. 45-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Traditional fossil fueled power plants are commonly based on steam Rankine cycle or Brayton Joule cycle. Using water or air as working fluid is obviously the most obvious choice for the wide availability of these substances in nature. However, the scarcity of natural energy sources and the strong need of reducing environmental impact have necessarily drawn the research to new energy systems configurations operating with other working fluids, which are able to recover lower temperature sources, such as Sun or industrial wasted heat. The variety of new working fluids (refrigerants or organic fluids) widens the choice to a variety of configurations that can be tailored to the specific source characteristics and boundary constraints. It is not always easy or even possible to conceive the best configuration for given specifications with the mere experience of a common designer. To design a new system configuration, the designer normally uses some “non-codified rules” deriving from his knowledge of basic thermodynamics and energy engineering. This paper aims instead at showing a practical tool that is based on a new methodology, named SYNTHSEP, to generate new energy system configurations. This methodology starts from the simple thermodynamic cycles operated by a given fluid made up of the four fundamental processes (compression, heating, expansion and cooling) and uses a rigorous set of codified rules to build the final system configuration. The paper presents the basics of the new methodology and how it has been implemented in a practical tool that simply requires the information about the elementary cycles and their shared processes as input data.

  • 69. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    A global and a local approach with evolutionary algorithms to locate malfunction causes in energy systems2009Inngår i: Journal of energy resources technology, ISSN 0195-0738, E-ISSN 1528-8994, Vol. 131, nr 4, s. 0420011-0420017Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Energy system performance may differ from the expected one during actual operation because of the effects of faults, anomalies, and wear and tear due to normal use. One of the main issues of diagnosis, i.e., the procedure to discover the causes of malfunctions, is to find the way back from measured altered performance to the original cause. Several procedures were proposed in the literature to solve the diagnostic problem, usually based on the comparison between a reference nonmalfunctioning condition and an actual, possibly malfunctioning, condition. A different strategy is suggested in the paper. A direct search of the possible causes of malfunctions is performed by means of an evolutionary algorithm: a component fault is arbitrarily introduced in a model of the healthy system by substituting the reference characteristic curve with an altered one, and the algorithm is used to search for a combination of different kinds of performance modifiers that generates the same measured effects of the actual anomaly. A global and a local approach are proposed and applied to a real test case plant, also in presence of measurement noise. The local approach demonstrates to be more effective in terms of accuracy and computational effort.

  • 70. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    A new thermoeconomic method for the location of causes of malfunctions in energy systems2003Inngår i: 2003 advances in bioengineering: presented at the 2003 ASME International Mechanical Engineering Congress, November 15 - 21, 2003, Washington, D.C. / [ed] Robert Boehm, New York: American Society of Mechanical Engineers , 2003, s. 355-364Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Diagnosis procedures primarily aim at locating the control volumes where anomalies occurred. This is not a simple task, since the effects of anomalies generally propagate through the whole system and affect the behavior of several components. Some components may therefore present a reduced efficiency, although they are not sources of operation anomalies, due to non flat efficiency curves. These induced effects are a big obstacle in the use of thermoeconomic techniques for the search of the origin of the anomalies. On the other hand, the real cause of the alteration of component behavior is the modification of its characteristic curve, due to degradation or failures. According to this concept, a new approach, based on an indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly, is proposed and applied to a test case power plant.

  • 71. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    A new thermoeconomic method for the location of causes of malfunctions in energy systems2007Inngår i: Journal of energy resources technology, ISSN 0195-0738, E-ISSN 1528-8994, Vol. 129, nr 1, s. 1-9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Diagnosis procedures primarily aim at locating the control volumes where anomalies occurred. This is not a simple task since the effects of anomalies generally propagate through the whole system and affect the behavior of several components. Some components may therefore present a reduced efficiency, although they are not sources of operation anomalies, due to nonflat efficiency curves. These induced effects are a big obstacle in the use of thermoeconomic techniques for the search of the origin of the anomalies. On the other hand, the real cause of the alteration of component behavior is the modification of its characteristic curve, due to degradation or failures. According to this concept, a new approach, based on an indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly, is proposed and applied to a test case power plant

  • 72. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Energy system diagnosis by a fuzzy expert system with genetically evolved rules2008Inngår i: International Journal of Thermodynamics, ISSN 1301-9724, Vol. 11, nr 3, s. 115-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The problem of malfunction diagnosis in energy systems can be approached using an expert system which compares the experimental data measured by the plant acquisition system and the calculated data evaluated by a plant simulator under the same operating conditions. In this paper the rules that form the "knowledge base" of the expert system are not assigned heuristically by trying to code the expertise of plant personnel, as it is usually done, but they are artificially and randomly generated by the recombination and selection operators of an evolutionary algorithm. A two-objective optimization problem is set up, in order to search for the optimal sets of rules having the minimum complexity but simultaneously maximizing the number of correct fault identifications for a given set of malfunctioning operating conditions. A global and a local approach are applied to a real test case, a two-shaft gas turbine used as the gas section of a combined-cycle cogeneration plant, in order to evaluate the potentialities and the limits of this methodology.

  • 73. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Evolutionary algorithms for multi-objective energetic and economic optimization in thermal system design2002Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 27, nr 6, s. 549-567Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermoeconomic analyses in thermal system design are always focused on the economic objective. However, knowledge of only the economic minimum may not be sufficient in the decision making process, since solutions with a higher thermodynamic efficiency, in spite of small increases in total costs, may result in much more interesting designs due to changes in energy market prices or in energy policies. This paper suggests how to perform a multi-objective optimization in order to find solutions that simultaneously satisfy exergetic and economic objectives. This corresponds to a search for the set of Pareto optimal solutions with respect to the two competing objectives. The optimization process is carried out by an evolutionary algorithm, that features a new diversity preserving mechanism using as a test case the well-known CGAM problem.

  • 74. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Locating causes of malfunctions in energy systems with evolutionary algorithms: A global and a local approach2006Inngår i: 2006 International Mechanical Engineering Congress & Exposition: November 5-10, 2006, Chicago, Ilinois USA, New York: American Society of Mechanical Engineers , 2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Energy system performance may differ from the expected one during actual operation because of the effects of faults, anomalies, wear and tear due to normal use. One of the main issues of diagnosis, i.e. the procedure to discover the causes of malfunctions, is to find the way back from measured altered performance to the original cause. Several procedures were proposed in the literature to solve the diagnostic problem, usually based on the comparison between a reference nonmalfunctioning condition and an actual, possibly malfunctioning, condition. A different strategy is suggested in the paper. A direct search of the possible causes of malfunctions is performed by means of an evolutionary algorithm: a component fault is arbitrarily introduced in a model of the healthy system by substituting the reference characteristic curve with an altered one, and the algorithm is used to search for a combination of different kinds of performance modifiers that generates the same measured effects of the actual anomaly. A global and a local approach are proposed and applied to a real test case plant, also in presence of measurement noise. The local approach demonstrates to be more effective in terms of accuracy and computational effort

  • 75. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    On the thermoeconomic approach to the diagnosis of energy system malfunctions indicators to diagnose malfunctions: Application of a new indicator for the location of causes2004Inngår i: International Journal of Thermodynamics, ISSN 1301-9724, Vol. 7, nr 2, s. 41-49Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Diagnosis procedures primarily aim at locating the control volumes where anomalies occurred. This is not a simple task, since the effects of anomalies generally propagate through the whole system and affect the behavior of several components. Some components may therefore present a reduced efficiency, although they are not sources of operation anomalies, due to non-flat efficiency curves. These induced effects are a big obstacle in the use of the thermoeconomic indicators for the search of the origin of the anomalies. As discussed in a brief overview of the several thermoeconomic indicators suggested in the literature, the reason for this inability is the focus on specific exergy consumptions as independent variables of the thermoeconomic model of the energy system. Instead, the real cause of the alteration of component behavior is the modification of its characteristic curve. Based on this concept, a new indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly is discussed and applied to the combined cycle power plant of the TADEUS problem

  • 76.
    Toffolo, Andrea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lazzaretto, Andrea
    University of Padova, Department of Industrial Engineering.
    Manente, Giovanni
    University of Padova, Department of Industrial Engineering.
    Paci, Marco
    ENEL Engineering and Innovation, via Andrea Pisano 120, 56126 Pisa.
    A multi-criteria approach for the optimal selection of working fluid and design parameters in Organic Rankine Cycle systems2014Inngår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 121, s. 219-232Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The selection of the cycle configuration, working fluid and operating parameters is crucial for the economic profitability of Organic Rankine Cycle systems using low to medium temperature heat sources. The aim of this paper is to show a method that improves this selection taking into account several criteria at a time: an original thermodynamic optimization procedure of the system configuration and design parameters which explores all possible configurations, the design options around the optimum values of the objective function, an economic modeling technique validated on real cost data, and the consideration of the off-design behavior. The method is applied to comparatively assess the performance of two working fluids, isobutane and R134a, in the temperature interval between 130 and 180 °C. The results show that the optimal cycle configuration is in most cases subcritical for isobutane and supercritical recuperated for R134a. The maximum power output of R134a is higher than isobutane for all the temperatures considered. The analysis of the objective function around the optimum shows the extent of the best range of turbine inlet pressures and enthalpies. These results highlight alternative design conditions to those maximizing the power output which might be preferred for technical and economic reasons.

  • 77.
    Toffolo, Andrea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lazzaretto, Andrea
    University of Padova.
    Manente, Giovanni
    University of Padova.
    Paci, Marco
    ENEL Engineering and Innovation, via Andrea Pisano 120, 56126 Pisa.
    An organic rankine cycle off-design model for the search of the optimal control strategy2012Inngår i: ECOS 2012: The 25th International Conference on Efficiency, Cost, Optimization and Simulation of Energy Conversion Systems and Processes (Perugia, June 26th-June 29th, 2012) / [ed] Umberto Desideri; Giampaolo Manfrida; Enrico Sciubba, Firenze: Firenze University Press, 2012, s. 28-41Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Power generation from low enthalpy geothermal resources using Organic Rankine Cycle systems is markedly influenced by the temperature level of the heat source and heat sink. During plant operation the actual temperature of the geofluid may be different from the value assumed in the design phase. In addition, the seasonal and daily variations of the ambient temperature greatly affect the power output especially when a dry condensation system is used. This paper presents a detailed off-design model of an Organic Rankine Cycle that includes the performance curves of the main plant components. Two capacitive components in the model have the key function of damping the temporary disequilibrium of mass and energy inside the system. Isobutane and R134a are considered as working fluids, mainly operating in subcritical and supercritical cycles, respectively. The off-design model is used to find the optimal operating parameters that maximize the electricity production in response to changes of the ambient temperatures between 0 and 30°C and geofluid temperatures between 130 and 180°C. This optimal operation strategy can be conveniently applied both to already existing plants and in the choice of new design plant configurations. --------------------------------------------------------------------------------

  • 78. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Martegani, A.D.
    Department of Mechanical Engineering, University of Padova.
    Cross-flow fan design guidelines for multi-objective performance optimization2004Inngår i: Proceedings of the Institution of mechanical engineers. Part A, journal of power and energy, ISSN 0957-6509, E-ISSN 2041-2967, Vol. 218, nr 1, s. 33-42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    More than one century has passed since Mortier's first cross-flow fan patent in 1891, but the design is still based on empirical considerations and on the re-adaptation of previously developed configurations. The complexity of the flow field inside the machine is the main reason for the lack of an established design procedure, because the characteristics of the eccentric vortex that forms within the impeller are deeply influenced by the geometry of the impeller and also of the casing. In this paper, the objectives that should be pursued in the design procedure are discussed and defined, and guidelines for crossflow fan design are determined through the analysis of an experimental database of fan performance and efficiencies, which is obtained by the systematic variation of the most important geometric parameters of the casing in combination with different impellers

  • 79. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Martegani, Antonio Dario
    Department of Mechanical Engineering, University of Padova.
    An experimental investigation of the flow field pattern within the impeller of a cross-flow fan2004Inngår i: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 29, nr 1, s. 53-64Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cross-flow fan performance is strongly influenced by the geometry of the casing, as the latter, in turn, affects the position and the strength of the eccentric vortex that characterizes the operation of this category of fans. The paper presents a systematic experimental investigation of the flow field within the impeller at different throttling conditions and for different geometries of the fan casing. Both pressures and velocities are measured using a three-dimensional five-hole probe that is inserted in the flow. This study helps determine the relationship between the design parameters of the casing and the flow field pattern, and it is part of an extensive work, by the same research group, aimed at establishing a general theory on cross-flow fan operation and at outlining the design guidelines for this particular type of turbomachines

  • 80. Toffolo, Andrea
    et al.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Morandin, Matteo
    Department of Mechanical Engineering, University of Padova.
    The HEATSEP method for the synthesis of thermal systems: An application to the S-Graz cycle2010Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 35, nr 2, s. 976-981Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the last decades component synthesis has become a critical issue in the research field about new highly integrated energy conversion systems. Several heuristic methodologies following experience-based guidelines have been proposed to simplify the problem of synthesis optimization. This paper describes an application of the HEATSEP method, which consists in the isolation of all the heat transfer processes of an energy system in an undefined "black-box". Then, synthesis optimization can be split in two subproblems, the first about the synthesis/design optimization of the basic plant configuration (which is made up of all the components but heat transfer devices) and the other about the synthesis of the heat exchanger network inside the black-box. The chosen test case is the design optimization of the basic plant configuration of an S-Graz cycle based power plant, as it is suitable to show the potentialities of the method

  • 81.
    Toffolo, Andrea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lazzaretto, Andrea
    University of Padova.
    Spakovsky, Michael R. von
    Virginia Polytechnic Institute and State University.
    On the nature of the heat transfer feasibility constraint in the optimal synthesis/design of complex energy systems2012Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 41, nr 1, s. 236-243Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the formulation of the constraint on heat transfer feasibility in the synthesis/design optimization of complex energy systems is discussed, with particular emphasis on the case in which the matching among the hot and cold thermal streams within the system is not defined a priori. The mathematical nature of the set of inequality constraints expressing the internal availability of thermal power at different temperature levels is examined and some examples are shown illustrating the way these constraints bound the feasible region of the search space and affect the hypersurface of the so-called optimum response surface, which results from considering a reduced number of degrees of freedom of the optimization problem. A brief discussion is also proposed about the choice of the algorithm and the variables for the optimization process.

  • 82. Toffolo, Andrea
    et al.
    Masi, Massinmo
    Department of Mechanical Engineering, University of Padova.
    Lazzaretto, Andrea
    Department of Mechanical Engineering, University of Padova.
    Low computational cost CFD analysis of thermoacoustic oscillations2010Inngår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 30, nr 6-7, s. 544-552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The numerical analysis of thermoacoustic oscillation phenomena by means of time-dependent CFD simulations usually requires a great computational effort, which may not be reasonable in industrial design. On the other hand, CFD tools provide the only approach that includes all the physical and chemical aspects involved in the thermoacoustic coupling between flame heat release and the acoustic modes of the burner/combustion chamber system. This paper presents some guidelines to reduce the computational effort required to perform a CFD analysis of the thermoacoustic oscillations with commercial codes. These guidelines are organized in a procedure that can be followed to analyze thermoacoustic coupling conditions that actually lead to unstable oscillations or are identified as potentially critical in the design phase. This procedure is also illustrated by an example of application, the partially-premixed flame type burner of a real 10 MW industrial boiler which shows noisy pressure fluctuations at a low frequency

  • 83.
    Toffolo, Andrea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rech, S.
    Department of Industrial Engineering, University of Padova, Italy.
    Lazzaretto, A.
    Department of Industrial Engineering, University of Padova, Italy.
    Generation of Complex Energy Systems by Combination of Elementary Processes2018Inngår i: Journal of energy resources technology, ISSN 0195-0738, E-ISSN 1528-8994, Vol. 140, nr 11, artikkel-id 112005Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fundamental challenge in the synthesis/design optimization of energy systems is the definition of system configuration and design parameters. The traditional way to operate is to follow the previous experience, starting from the existing design solutions. A more advanced strategy consists in the preliminary identification of a superstructure that should include all the possible solutions to the synthesis/design optimization problem and in the selection of the system configuration starting from this superstructure through a design parameter optimization. This top–down approach cannot guarantee that all possible configurations could be predicted in advance and that all the configurations derived from the superstructure are feasible. To solve the general problem of the synthesis/design of complex energy systems, a new bottom–up methodology has been recently proposed by the authors, based on the original idea that the fundamental nucleus in the construction of any energy system configuration is the elementary thermodynamic cycle, composed only by the compression, heat transfer with hot and cold sources and expansion processes. So, any configuration can be built by generating, according to a rigorous set of rules, all the combinations of the elementary thermodynamic cycles operated by different working fluids that can be identified within the system, and selecting the best resulting configuration through an optimization procedure. In this paper, the main concepts and features of the methodology are deeply investigated to show, through different applications, how an artificial intelligence can generate system configurations of various complexity using preset logical rules without any “ad hoc” expertise.

  • 84.
    Toffolo, Andrea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rech, Sergio
    Universita degli Studi di Padova, Interdepartmental Center “Giorgio Levi Cases” for Energy Economics and Technology, Padua, Italy.
    Lazzaretto, Andrea
    Universita degli Studi di Padova, Department of Industrial Engineering, Padua, Italy.
    Combination of elementary processes to form a general energy system configuration2017Inngår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE): Proceedings (IMECE), ASME Press, 2017, artikkel-id IMECE2017-71653Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The fundamental challenge in the synthesis/design optimization of energy conversion systems is the definition of the system configuration and design parameters. The traditional way to operate in system engineering practice is to follow the previous experience, starting from design solutions that already exist. A more advanced strategy consists in the preliminary identification of a superstructure that should include all the possible solutions to the synthesis/design optimization problem, and in the selection of the system configuration starting from this superstructure through a design parameter optimization. This top-down approach cannot guarantee that all possible configurations could be predicted in advance and that all the configurations derived from the superstructure are really feasible. To solve the general problem of the synthesis/design of complex energy systems a new bottom-up methodology is proposed, based on the original idea that the fundamental nucleus in the construction of any energy system configuration is the elementary thermodynamic cycle (compression, heat transfer with the hot source, expansion, heat transfer with the cold source). So, any configuration can be built by generating, according to a rigorous set of rules, all the combinations of the elementary thermodynamic cycles operated by different working fluids that can be identified within the system, and selecting the best resulting configuration through an optimization procedure. In this paper a deep analysis of the major features of the methodology is presented to show, through different examples of applications, how an artificial intelligence is able to generate system configurations of various complexity using preset logical rules without any "ad hoc" expertise. 

  • 85.
    Valero, A.
    et al.
    CIRCE, University of Zaragoza.
    Correas, L.
    University of Padova.
    Lazzaretto, Andrea
    University of Padova.
    Rangel, V.
    CIRCE, University of Zaragoza.
    Reini, M.
    University of Trieste.
    Taccani, R.
    University of Trieste.
    Toffolo, Andrea
    Verda, V.
    Politecnico di Torino.
    Zaleta, A.
    University of Guanajuato.
    Thermoeconomic philosophy applied to the operating analysis and diagnosis of energy utility systems2004Inngår i: International Journal of Thermodynamics, ISSN 1301-9724, Vol. 7, nr 2, s. 33-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the objectives of thermoeconomic diagnosis are presented. The paper is part of a project, started in 2001 and named TADEUS (Thermoeconomic Approach to the Diagnosis of Energy Utility Systems), aimed at integrating various experiences accumulated by a group of researchers working on thermoeconomic diagnostics, a field of research started by Antonio Valero and co-workers in 1990 and followed by various researchers all over the world. It is shown how, starting from the same basic set of ideas, researchers developed different approaches, each one having particular characteristics that are, nonetheless, complementary to each other.

  • 86.
    Vesterlund, Mattias
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Design optimization of a district heating network expansion: a case study for the town of Kiruna2017Inngår i: Applied Sciences, E-ISSN 2076-3417, Vol. 7, nr 5, artikkel-id 488Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The urbanization of new areas beyond the existing perimeter of a town implies the expansion of several infrastructures, including the district heating network. The main variables involved in the design of the district heating network expansion are the layout of the new pipes, their diameters, and the capacity of the new heat production sites that are required to satisfy the increased demand of room heating and hot tap water. In this paper, a multi-objective evolutionary algorithm is applied to the minimization of the costs related to the expansion of the district heating network of the town of Kiruna, in northern Sweden. The results show that the spectrum of the optimal design compromises between investment costs for the new pipes and the new heat generation site on one side, and operating costs due to overall fuel consumption and pumping power in the network on the other. The presented methodology is a tool meant for the decision makers in the company who own the district heating network, to evaluate all the possible best design alternatives before making a decision.

  • 87.
    Vesterlund, Mattias
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Dahl, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Optimization of multi-source complex district heating network: a case study2016Inngår i: Proceeding of 29th International Conference on efficiency, Cost, Optimization, Simulation and Enviromental Impact of Energy Systems, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The level of complexity for a district heating network increases with the maturity of the network, and this affects the pattern of the distribution of the hot water from the heat production sites to the end users. The majority of district heating systems are also multi-source networks, typically supported with heat from one main production site and other smaller satellite sites that are activated when required. In general, local energy companies have a lack of knowledge regarding how a meshed network behaves when different production sites are operated. The schedule of heat generation at the different sites is often based on staff experience and some general rules of thumb.

    In this paper a method for modeling and simulating complex district networks is further developed in order to optimize the total operating costs of a multi-source network, with constraints on the pressure and temperature levels in the user areas and on the heat generation characteristics at each production site.

    The optimization results show that the usage of the cheapest resources is preferred to a distributed generation of heat, even if some of the pipes may exceed the recommended thermal load capacity. The main site water supply temperature is found to be the lowest allowed by the constraint on the temperature of the water supplied to the end users, since the decrease of the costs associated with the lower thermal losses in the network is not counterbalanced by the increase of those associated with the pumping power of a larger water mass flow rate.

  • 88.
    Vesterlund, Mattias
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Dahl, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Optimization of multi-source complex district heating network, a case study2017Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 126, s. 53-63Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The level of complexity for a district heating network increases with the maturity of the network, and this affects the pattern of the distribution of the hot water from the heat production sites to the end users. The majority of district heating systems are also multi-source networks, typically supported with heat from one main production site and other smaller satellite sites that are activated when required. In general, local energy companies have a lack of knowledge regarding how a meshed network behaves when different production sites are operated. The schedule of heat generation at the different sites is often based on staff experience and some general rules of thumb.

    In this paper a method for modeling and simulating complex district networks is further developed in order to optimize the total operating costs of a multi-source network, with constraints on the pressure and temperature levels in the user areas and on the heat generation characteristics at each production site.

    The optimization results show that the usage of the cheapest resources is preferred to a distributed generation of heat, even if some of the pipes may exceed the recommended thermal load capacity. The main site water supply temperature is found to be the lowest allowed by the constraint on the temperature of the water supplied to the end users, since the decrease of the costs associated with the lower thermal losses in the network is not counterbalanced by the increase of those associated with the pumping power of a larger water mass flow rate.

  • 89.
    Vesterlund, Mattias
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Dahl, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Simulation and analysis of a meshed district heating network2015Inngår i: ECOS 2015: 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems , 2015Konferansepaper (Fagfellevurdert)
  • 90.
    Vesterlund, Mattias
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Toffolo, Andrea
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Dahl, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Simulation and analysis of a meshed district heating network2016Inngår i: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 122, s. 63-73Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The flow distribution in a district heating network tends to become no longer obvious when system design is developed and its complexity increased. As a consequence, the network owner, often the local energy company, is in need of a simulation program to have the possibility of analysing network behaviour and expand the understanding about the operation of district heating system. In this paper, a simulation tool developed in MATLAB/Simulink is applied in order to analyse the flow distribution in the district heating network of the town of Kiruna (Sweden). The network in Kiruna has been developing since the 60s and is today a complex network with a meshed structure, i.e. it is formed by a set of loops from which secondary branches depart. The simulation tool is part of a methodology that has specifically been developed to analyse the flow pattern in such kind of networks without altering their physical structure, and it is expected to be a valuable tool for the redesign of the network in the forthcoming relocation of some of the urban districts. The results about the current network configuration show that only a few pipes in the network are exceeding the levels of heat flow recommended by pipe manufacturers. The largest drops in pressure and temperature from the heat production site to the nodes serving the main consumer areas are within 1.2 bar and 9 °C in the days of highest demand.

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