Modeling toolkit for comparing AC vs. DC electrical distribution efficiency in buildings, A

2021 Summer.Includes bibliographical references.An increasing proportion of electrical devices in residential and commercial buildings operate from direct current (DC) power sources. In addition, distributed power generation systems such as solar photovoltaic (PV) and energy storage natively produce DC power. However, traditional power distribution is based on an alternating current (AC) model. Performing the necessary conversions between AC and DC power to make DC devices compatible with AC distribution results in energy losses. For these reasons, DC distribution may offer energy efficiency advantages in comparison to AC distribution. However, reasonably fast computation and comparison of electrical efficiencies of AC-only, DC-only, and hybrid AC/DC distributions systems is challenging because DC devices are typically (nonlinear) power-electronic converters that produce harmonic content. While detailed time-domain modeling can be used to simulate these harmonics, it is not computationally efficient or practical for many building designers. To address this need, this research describes a toolkit for computation of harmonic spectra and energy efficiency in mixed AC and DC electrical distribution systems, using a Harmonic Power Flow (HPF) methodology. The toolkit includes a library of two-port linear and nonlinear device models which can be used to construct and simulate an electrical distribution system. This dissertation includes a description of the mathematical theory and framework underlying the toolkit, development and fitting of linear and nonlinear device models, software implementation in Modelica, verification of the toolkit with laboratory measurements, and discussion of ongoing and future work to employ the toolkit to a variety of building designs

EOOLT 2007 – Proceedings of the 1st International Workshop on Equation-Based Object-Oriented Languages and Tools

Computer aided modeling and simulation of complex systems, using components from multiple application domains, such as electrical, mechanical, hydraulic, control, etc., have in recent years witness0065d a significant growth of interest. In the last decade, novel equation-based object-oriented (EOO) modeling languages, (e.g. Mode- lica, gPROMS, and VHDL-AMS) based on acausal modeling using equations have appeared. Using such languages, it has become possible to model complex systems covering multiple application domains at a high level of abstraction through reusable model components. The interest in EOO languages and tools is rapidly growing in the industry because of their increasing importance in modeling, simulation, and specification of complex systems. There exist several different EOO language communities today that grew out of different application areas (multi-body system dynamics, electronic circuit simula- tion, chemical process engineering). The members of these disparate communities rarely talk to each other in spite of the similarities of their modeling and simulation needs. The EOOLT workshop series aims at bringing these different communities together to discuss their common needs and goals as well as the algorithms and tools that best support them. Despite the short deadlines and the fact that this is a new not very established workshop series, there was a good response to the call-for-papers. Thirteen papers and one presentation were accepted to the workshop program. All papers were subject to reviews by the program committee, and are present in these electronic proceedings. The workshop program started with a welcome and introduction to the area of equa- tion-based object-oriented languages, followed by paper presentations and discussion sessions after presentations of each set of related papers. On behalf of the program committee, the Program Chairmen would like to thank all those who submitted papers to EOOLT'2007. Special thanks go to David Broman who created the web page and helped with organization of the workshop. Many thanks to the program committee for reviewing the papers. EOOLT'2007 was hosted by the Technical University of Berlin, in conjunction with the ECOOP'2007 conference

Design of a mechatronic system for application of hardware-in-the-loop simulation technique

Classical approaches, using Simulation analysis technique, use a controller model that can – or not – be coupled with a plant model. Usually, the controller and plant models are connected, in a closed-loop behavior, and this kind of Simulation is called Software-in-the-loop Simulation (SIL). However, recently, some directions are being assumed and some recent works deal with Simulation considering the real controller, instead of the controller model, in the closed loop behavior with the plant model and this kind of approach is called Hardwarein- the-loop simulation (HIL). In order to study and to propose some rules about the simulation of real-time systems considering HIL simulation, at the Automation Laboratory of the Centre for Mechanics and Materials Technologies of the University of Minho, Portugal – a workbench especially devoted to this study is being developed. This workbench considers an environment for Simulation, and the respective programming language, and a real controller that interacts with the simulation environment running on a PC. After looking at the available software tools and modeling languages, Dymola simulation environment and Modelica modeling language were chosen. The main reasons for this choice are associated with the unique multi-domain engineering capabilities of Dymola and Modelica that allow to deal, on the same environment, with many different engineering domains like hydraulics, power train, thermodynamics, air-conditioning, vehicle dynamics, mechanical, electrical, electronic, control, thermal, pneumatic, among others... As real controller, the choice was a Programmable Logic Controller (PLC) from OMRON company, the CPM2A model. This paper presents the first step, of this ongoing work, and is focused, mainly, on studying how to exchange information between a real PLC (used, as controller, on the designed workbench) and Dymola software that will run specific plant models, developed in Modelica language, on a Personal Computer.(undefined

Modelling and Simulation of the Fifth-Generation District Heating and Cooling

District heating and cooling are efficient systems for distributing heat and cold in urban areas. They are a key solution for planning future urban energy-efficient systems due to their high potential for integrating renewable energy sources. The systems also play an important role in community resilience, which makes them a multidisciplinary research topic. The continuous development of these systems has now reached the fifth-generation whereby end-customers can benefit from the intrinsic synergies this generation offers. A typical Fifth-Generation District Heating and Cooling (5GDHC) system consists of connected buildings that together have simultaneous heating and cooling demands. Local heat pumps and chillers in decentralised substations modulate the low network temperature to the desired building supply temperatures. The demands are potentially balanced by the means of recovering local waste heat from chillers, while also utilising heat pumps to provide direct cooling. The heat carrier fluid in the distribution pipes can therefore flow in either direction in the so-called bidirectional low-temperature network. A balancing unit is incorporated to compensate for network energy imbalances. The exchange of energy flows is realised at different stages within the individual building and across connected buildings. Numerous factors influence the quantity and quality of the exchanged energy flows. Demand profiles in each building, the efficiency of building energy systems, and control logics of system components are some examples of these factors. Investigating this generation using traditional computational tools developed using imperative programming languages is no longer suitable due to system complexity, size variability, and changes adopted in different use cases. Modelica is a free open-source equation-based object-oriented language used for the modelling and simulation of multi-domain physical systems. Models are described by differential-algebraic and discrete equations. The mathematical relations between model variables are encapsulated inside an icon that represents the model. Different component models interface variables through standardised interfaces and connection lines. Large complex systems are composed by the visual assembly of components in a Lego-like approach. Models developed in Modelica can be easily inherited for rapid virtual prototyping and/or edited to adopt changes in the model use. This dissertation has a fourfold objective. Firstly, it demonstrates the development of a simulation model for an installed 5GDHC system located in Lund, Sweden. Secondly, it characterises the components that constitute a 5GDHC system. Thirdly, it unravels the exchange of energy flows at different system levels and describes, in a logical progression, the modelling of 5GDHC with Modelica. Fourthly, it presents ethical risk analyses of the different role-combinations that may arise in 5GDHC business models. The developed model is used in performing annual simulations and to evaluate the system performance under two different substation design cases. The results indicate that adding a direct cooling heat exchanger in each substation can reduce the electric energy consumption at both substation and system levels by about 10 and 7 %, respectively. Moreover, the annual waste heat to ambient air can be decreased by about 17 %. The dissertation fosters an ethical discourse that engages the public and all who take part in the multidisciplinary research on 5GDHC to guarantee safe operation and appropriate services. Future research will build on the models presented in this dissertation to investigate different network temperature and pressure control strategies, in addition to adopting several design concepts for balancing units and thermal energy storage systems

Expert survey and classification of tools for modeling and simulating hybrid energy networks

Sector coupling is expected to play a key role in the decarbonization of the energy system by enabling the integration of decentralized renewable energy sources and unlocking hitherto unused synergies between generation, storage and consumption. Within this context, a transition towards hybrid energy networks (HENs), which couple power, heating/cooling and gas grids, is a necessary requirement to implement sector coupling on a large scale. However, this transition poses practical challenges, because the traditional domain-specific approaches struggle to cover all aspects of HENs. Methods and tools for conceptualization, system planning and design as well as system operation support exist for all involved domains, but their adaption or extension beyond the domain they were originally intended for is still a matter of research and development. Therefore, this work presents innovative tools for modeling and simulating HENs. A categorization of these tools is performed based on a clustering of their most relevant features. It is shown that this categorization has a strong correlation with the results of an independently carried out expert review of potential application areas. This good agreement is a strong indicator that the proposed classification categories can successfully capture and characterize the most important features of tools for HENs. Furthermore, it allows to provide a guideline for early adopters to understand which tools and methods best fit the requirements of their specific applications

A Modelica based computational model for evaluating a renewable district heating system

District heating (DH) systems are considered a viable method for mitigating long-term climate change effects, through reduction of CO2 emissions, their high conversion efficiencies and their ability to be integrated with renewable energy sources (RES). The current evolution towards sustainable DH, e.g. integration of RES, results in increased complexity and diversity during the early-design phase. In the early-design phase of DH systems a feasibility study is conducted to assess if the economic and environmental factors of the project meet the given requirements. This assessment is generally conducted with traditional district heating computational models (DHCM), utilizing a simulation language which limits the evaluation of sustainable DH systems in terms of flexibility and comprehensibility. The need for an alternative language capable of effectively modeling DH systems with integrated RES led to the use of Modelica, which offers improved flexibility, reusability as well as hierarchical and multi-domain modeling. This paper presents a case study, for the evaluation of a new DHCM analyzing its modeling capabilities and system performance, of an educational campus formed by eight institutional buildings connected to a centralized power plant, holding among others a biomass gasifier and a gas boiler. For an optimum utilization of the biomass gasifier, two power plant configurations are assessed: a biomass gasifier system with and without thermal energy storage (TES). The system performance evaluation indicates a significant increase in the utilization of the biomass gasifier with 8.2% (353 hours) compared to results obtained from the traditional DHCM. This deviation is due to a more accurate consideration of the DH thermal capacity and the space heating demand. Furthermore, the models in this DHCM enable assessments of the impact of building retrofits or climate change scenarios. Thus, the increased modeling capabilities and system performance demonstrate that this new DHCM is suitable and beneficial for early-design feasibility studies of innovative RES integrated DH systems