China is the largest energy consumer worldwide, with a fast-growing rate. But the energy and environmental problems brought by its unbalanced energy structure and low energy efficiency restrict the sustainable development of China. The Distributed Energy System (DES) is one of the internationally recognized solutions to the problems. To enhance the implementation of the DES under China’s scenario, the thesis develops computational models for the Combined Cooling, Heat, and Power (CCHP) and Separated Cooling, Heat, and Power (SCHP) systems for a Micro Energy Grid in northeast China using MATLAB. The objective is to minimize the overall expenditure, energy use, and carbon emission equivalents. The results show that the CCHP system reduces 18.62% of the overall expenditure and 35.02% of the carbon emission equivalents than the SCHP system. The CCHP system has a promising prospect in China with better Greenhouse Gas emissions reduction and economic performance. / Kina är världens största energikonsument, med en snabb tillväxttakt. Men de energi- och miljöproblem som orsakas av den obalanserade energistrukturen och den låga energieffektiviteten begränsar Kinas hållbara utveckling. Distribuerade energisystem (DES) är en av de internationellt erkända lösningarna på dessa problem. För att förbättra implementeringen av DES enligt Kinas scenario utvecklar avhandlingen beräkningsmodeller för kombinerad kylning, värme och kraft (CCHP) och separerad kylning, värme och kraft (SCHP) för ett mikroenerginät i nordöstra Kina med hjälp av MATLAB. Målet är att minimera de totala kostnaderna, energianvändningen och koldioxidutsläppen. Resultaten visar att CCHP-systemet minskar de totala utgifterna med 18,62 % och koldioxidutsläppen med 35,02 % jämfört med SCHP-systemet. CCHP-systemet har lovande utsikter i Kina med bättre minskning av växthusgasutsläpp och ekonomisk prestanda.

Klimatförändring ställer idag krav på högre energieffektivitet vilket lett till utbyggnaden av ett distribuerat energisystem. Samtidigt introduceras framväxande teknologier som digitala tvillingar till det nya energisystemet i hopp om att ytterligare effektivisera systemet. För att främja samarbete mellan industrin och akademin, och således stödja utvecklingen och implementeringen av digitala tvillingar, bör aktörernas syner sammanföras. Syftet med arbetet är därav att undersöka ifall det finns några likheter och skillnader mellan industri och akademi i hur de uppfattar användningsområdena och utmaningarna med digitala tvillingar av distribuerade energisystem. För att besvara forskningsfrågan utfördes inledningsvis en systematisk litteraturstudie. Studien utgör arbetets underlag för akademins uppfattning om digitala tvillingars användningsområden och utmaningar. Vidare utfördes fem intervjuer med olika industriaktörer med insikt i digitala tvillingar och distribuerade energisystem för att avgöra deras uppfattning om teknologin. Insikterna från litteraturstudien och intervjuerna ställdes sedan mot varandra för att identifiera eventuella likheter och skillnader. De användningsområden som identifierades av akademin och industrin var simulering, felidentifiering och prediktivt underhåll, visualisering och styrning, cybersäkerhet, optimering av kraftnätet samt prognostisering och estimering. Utmaningarna som identifierades av akademin var standardiserade ramverk för modellering och för datahantering, brist på passande sensorer, datalagringsmöjligheter, datorers beräkningskapacitet och cyberattacker. Industrin identifierade motstånd till ny teknologi, kompetensbrist, silotänk, teknologins värdeskapande, datahantering och cyberattacker som huvudutmaningarna med digitala tvillingar. Utifrån analysen har industrin och akademin en liknande uppfattning om digitala tvillingars användningsområden inom distribuerade energisystem men uppfattningen om utmaningarna med digitala tvillingar var, inom akademin, mer teknikbaserad medan den inom industrin var främst icketeknisk. / Today, the increasing threat of climate change has created a greater need for higher energy efficiency, which has led to the development of a distributed energy system. At the same time, emerging technologies such as digital twins are being introduced into the new energy system in the hope of further improving the efficiency of the system. To promote cooperation between industry and academia, and thus support the development and implementation of digital twins, the views of the actors should be brought together. The purpose of this work is therefore to investigate whether there are any similarities and differences between industry and academia in how they perceive the applications and challenges of digital twins of distributed energy systems.  To answer the research question, a systematic literature study was initially conducted. The study constitutes the basis for the academia's perception of the use cases and challenges of digital twins. Furthermore, five interviews were conducted with different industrial actors with insight into digital twins and distributed energy systems to determine their perception of the technology. The insights from the literature study and interviews were then compared to identify any similarities and differences.  The application areas identified by academia and industry were simulation, fault identification and predictive maintenance, visualization and control, cyber security, grid optimization, and forecasting and estimation.  The challenges identified by academia were standardized modelling and data management frameworks, lack of suitable sensors, data storage capabilities, computational capacity of computers and cyber-attacks. Industry identified resistance to new technologies, skills shortages, silo thinking, technology value creation, data management and cyber-attacks as the main challenges of digital twins. Based on the analysis, industry and academia have a similar perception of the use cases of digital twins of distributed energy systems but the perception of the challenges of digital twins was, in academia, more technology-based while in industry it was mainly non-technical.

Integrating energy across different sectors is an efficient solution for improving energy systems to meet energy demands with low CO2 emissions. Such integration includes combining the supply and demand of heating, cooling, and electricity by implementing appropriate equipment, as well as combining the energy systems of civic and industrial sectors. This thesis develops various optimization approaches to identify the optimal design and operation of distributed energy systems and the integration of energy systems across commercial, industrial, and transportation sectors, which minimize CO2 emissions and costs of the systems. Available equipment of the energy systems includes combined cooling, heating, and power system, absorption chiller, solar thermal collector, photovoltaic, boiler, electric chiller, battery, ground source heat pump, and air source heat pump. This thesis provides the following contributions to this area. (1) Identify optimal structures of distributed energy systems under different electric grid CO2 footprints. The work implements representative periods when formulating the energy system, which reduces computation time. (2) Differentiate heating demands of entities in the integrated system at different temperature levels to ensure feasible heat transfer. It removes the simplified assumptions in existing studies on the integrated energy system that assume all heating demands are at a uniform temperature. (3) Optimize production rates of plants instead of assuming steady industrial production rates. The switchable production rates lead to a further reduction in CO2 emissions of the integrated system. (4) Identify the environmental and economic benefits of the integrated operation under different electric grid CO2 footprints. It presents that integrated operation reduces more CO2 emissions when the electric grid has higher CO2 footprints. (5) Identify the optimal relative sizes of entities in the integrated system that maximize the CO2 emissions reduction benefits brought by the integrated system. (6) Prove the integrated system has lower CO2 emissions than individual energy systems both under deterministic and stochastic scenarios. Overall, the work in this thesis contributes to developing energy systems and integrated energy systems with the lowest possible CO2 emissions under various scenarios. / Thesis / Doctor of Philosophy (PhD) / As the total population continues to increase worldwide, it is necessary to improve community energy systems to reduce CO2 emissions when meeting energy demands. An efficient solution is integrating energy systems across different sectors. This work explores novel structures of energy systems – integrated energy systems that combine the supply and demand of heating, cooling, and electricity in residential, commercial, industrial, and transportation sectors. The optimal energy system configurations, sizes of subsystems, production rates of plants, heat transfer and electricity transfer, as well as capacity and operation of the equipment, have been identified by developing optimization approaches that minimize CO2 emissions and costs of the integrated system. The optimal design and operation are found under both deterministic and stochastic scenarios and different grid electricity generation scenarios, which provide references for developing community energy systems with the lowest possible CO2 emissions under various scenarios.

A l'heure actuelle, l'industrie représente environ le tiers de la consommation énergétique et des émissions de CO2. Des opportunités substantielles existent pour faire face aux enjeux environnementaux et économiques, passant par l'efficacité énergétique en général et l'utilisation de l'énergie, en particulier dans les parcs industriels. Les Systèmes à Energie Distribuée (SED) correspondent en ce sens à une solution courante et prometteuse. Nous avons donc entrepris une démarche d'approche globale de site, incluant l'agrégation de l'ensemble des variables énergétiques, économiques, environnementales et managériales influentes dans une installation de ce type. Une mise en application sur une installation pilote et sa validation ont permis d'identifier les verrous scientifiques et techniques et de mesurer pertinence et efficacité des éléments et modes opératoires des systèmes en mode stationnaire. Cette étude offre une méthode d'utilisation coopérative des indicateurs des domaines impactés et ouvre également des perspectives sur des développements en mode dynamique à des fins d'aide à la conduite optimale. / Nowadays, industry accounts for about one third of energy consumption and CO2 emissions. Substantial opportunities exist to address environmental and economic challenges, including energy efficiency in general and the use of energy, especially in industrial parks. Distributed Energy Systems (DES) correspond in this sense to a common and promising solution. We have therefore undertaken a global site approach, including the aggregation of all influential energy, economic, environmental and managerial variables in an installation of this type. Implementation on a pilot plant and its validation have made it possible to identify the scientific and technical locks and to measure the relevance and efficiency of the elements and stationary operating modes of the systems. This study offers a method of cooperative use of the indicators of impacted domains and also opens perspectives on developments in dynamic mode for the purposes of optimum driving assistance.