| 1. |
- Hosain, Md Lokman, 1984-
(författare)
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Fluid Flow and Heat Transfer Simulations for Complex Industrial Applications : From Reynolds Averaged Navier-Stokes towards Smoothed Particle Hydrodynamics
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Optimal process control can significantly enhance energy efficiency of heating and cooling processes in many industries. Process control systems typically rely on measurements and so called grey or black box models that are based mainly on empirical correlations, in which the transient characteristics and their influence on the control parameters are often ignored. A robust and reliable numerical technique, to solve fluid flow and heat transfer problems, such as computational fluid dynamics (CFD), which is capable of providing a detailed understanding of the multiple underlying physical phenomena, is a necessity for optimization, decision support and diagnostics of complex industrial systems. The thesis focuses on performing high-fidelity CFD simulations of a wide range of industrial applications to highlight and understand the complex nonlinear coupling between the fluid flow and heat transfer. The industrial applications studied in this thesis include cooling and heating processes in a hot rolling steel plant, electric motors, heat exchangers and sloshing inside a ship carrying liquefied natural gas. The goal is to identify the difficulties and challenges to be met when simulating these applications using different CFD tools and methods and to discuss the strengths and limitations of the different tools.The mesh-based finite volume CFD solver ANSYS Fluent is employed to acquire detailed and accurate solutions of each application and to highlight challenges and limitations. The limitations of conventional mesh-based CFD tools are exposed when attempting to resolve the multiple space and time scales involved in large industrial processes. Therefore, a mesh-free particle method, smoothed particle hydrodynamics (SPH) is identified in this thesis as an alternative to overcome some of the observed limitations of the mesh-based solvers. SPH is introduced to simulate some of the selected cases to understand the challenges and highlight the limitations. The thesis also contributes to the development of SPH by implementing the energy equation into an open-source SPH flow solver to solve thermal problems. The thesis highlights the current state of different CFD approaches towards complex industrial applications and discusses the future development possibilities.The overall observations, based on the industrial problems addressed in this thesis, can serve as decision tool for industries to select an appropriate numerical method or tool for solving problems within the presented context. The analysis and discussions also serve as a basis for further development and research to shed light on the use of CFD simulations for improved process control, optimization and diagnostics.
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| 2. |
- Wang, Weilong, 1978-
(författare)
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Mobilized Thermal Energy Storage for Heat Recovery for Distributed Heating
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Conventional energy sources—oil and electricity—dominate the heat supply market. Due to their rising costs and their negative environmental effects on global climate change, it is necessary to develop an alternative heat supply system featuring low cost, high energy efficiency and environment friendliness. At present, it is often challenging to supply heat to detached buildings due to low energy efficiency and high distribution cost. Meanwhile, significant amounts of industrial waste and excess heat are released into the environment without recycling due to the difficulty of matching time and space differences between suppliers and end users. Phase change materials (PCMs), with the advantages of being storable and transportable, offer a solution for delivering that excess heat from industrial plants to detached buildings in sparse, rural areas. The objective of this thesis is to study PCMs and latent thermal energy storage (LTES) technology, and to develop a mobilized thermal energy storage (M-TES) system that can use industrial waste or excess heat for heat recovery and distribution to areas in need. Organic PCMs were chosen for study because they are non-toxic and non-corrosive, and they exhibit no phase separation and little sub-cooling when compared to inorganic PCMs. Two major issues including leakage of liquid PCMs and low thermal conductivity. Polyethylene glycol (PEG) was chosen to help analyze the thermal behavior of organic PCMs and PEG-based form-stable composites. To overcome the issue of low thermal conductivity, modified aluminum nitride (AlN) powder was added to the composites. Increased thermal conductivity traded off decreased latent heat. The PEG/EG composite, prepared by mixing the melted PEG into an expanded graphite (EG) matrix showed good thermal performance due to its large enthalpy and high thermal conductivity. To make a systematic study of the M-TES system, a compact lab-scale system was designed and built. Characteristics of PCM were studied, and the performance of the direct-contact TES container was investigated. A case study using an M-TES system to deliver heat from a combined heat and power (CHP) plant to a small village was conducted. A technical and economic feasibility study was conducted for an integrated heat supply system using the M-TES system. In addition, the options for charging a TES container at a CHP plant were analyzed and compared from the viewpoints of power output, heat output and incomes.
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| 3. |
- Hosain, Md Lokman, 1984-
(författare)
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TOWARDS ACCELERATED SIMULATIONS FOR FLUID FLOW AND HEAT TRANSFER OF LARGE INDUSTRIAL PROCESSES
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The manufacturing sector is one of the biggest energy consumers. The iron and steel markets in China are growing very fast. Several studies have been performed to evaluate the Chinese steel sector in terms of energy savings and CO2 emissions. The results of the studies showed that the major energy savings expected within 2020 and 2030 timeframe will be from industrial furnaces in steel mills. For the Swedish steel industry, it is important to be very efficient in order to remain competitive. The hot rolling process in the steel industry is a long process, where big slabs are heated in a furnace above the recrystallization temperature to roll the metal into a thin sheet and then the sheet is cooled at the Runout table using water. The amount of energy used during the process directly influences the price of the products. Moreover, the government policy on energy usage and CO2 emissions, the competitive market and the water scarcity, demand an optimal process operation to reduce energy consumption and greenhouse gas emission. Computer simulation is the best and most convenient way to approximate real-world processes; therefore, there is a need to have a real-time online simulation tool for process optimisation, decision support and diagnostics in different industries.Computational fluid dynamics (CFD) is a robust tool for simulating almost any kind of real-world process related to fluid flow, heat transfer and combustion. However, simulating real-world processes in real-time using CFD is very challenging due to the complexity involved in the physical phenomena studied. In this thesis, CFD simulations have been performed in small scale to understand the physics and perceive the complexity involved in the heating process of steel slabs and the cooling process of the steel sheets at hot rolling steel industries. The results from the simulations are successfully validated using experimental and theoretical results published in open literature. Past experience suggests using mesh-based commercial CFD solvers for simulating industrial processes, only if accurate and detail results are desired. However, the computational performance of these solvers shows limitations from a real-time perspective and indicates the need for alternative CFD methods and solvers. In the literature review performed as part of the first stage of this work, we have identified different alternative methods which can be used to perform CFD simulations in real-time or near real-time for large industrial processes. The thesis discusses the limitations of different types of CFD methods and points out the difficulties and challenges in utilising these methods for simulating large industrial processes. Our preliminary simulation work brings light towards the goal of multi-phase multi-physics real-time simulations.
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| 4. |
- Avelin, Anders, 1966-
(författare)
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Process Modeling of Combustion and Digesters for On-line Applications
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of biomass has increased in recent years due to the efforts to reduce the high emissions of greenhouse gases, primarily carbon dioxide from combustion of fossil fuels. At the same time industrial processes have become more complex because of increased production rates and profitability requirements. A higher degree of automation is needed when the processes are too complex to be handled manually. There is a need to find modeling strategies that can automatically handle the challenges that the conversion of biomass in an industrial process entails, such as operational changes, decreasing component and overall system efficiency, drifting sensors, etc. The objective of this thesis is to develop a methodology for on-line applications in industrial processes. Dynamic process models have been developed for continuous digesters and boilers. Process models have been evaluated for their use in continuous industrial process. Applications that have been studied are monitoring and diagnostics, advanced control and decision support. The process models are designed for on-line simulations. The results shows that the use of mathematical simulation models can improve the use of both process data and process understanding, to achieve improved diagnostics, advanced control and process optimization. In the two examples of industrial processes covered in this thesis, we can see that similar types of models can be used for completely different types of processes, such as pulp digesters and boilers. It also demonstrates the ability to combine soft sensors and hard sensors with physical models to take the information to a higher level of utilization.
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| 5. |
- Blomqvist, Stefan, 1988-
(författare)
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Energy Efficiency in the Residential, Service and Energy Sectors : Barriers, Drivers and System Studies
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increased energy efficiency is a prerequisite for achieving the national energy and climate goals, the goals set by the European Union, and the Sustainable Development Goals adopted by the United Nations. Close to 40% of Sweden’s total energy use and approximately 20% of domestic greenhouse gas emissions are allocated to the residential and service sector. There is great potential for increased energy efficiency within the sector. Almost half of Swedish households are situated in multifamily buildings, where district heating is the predominant heating solution, as well as in service buildings.This thesis uses a system perspective to explore energy efficiency work and end-use measures in an energy system, focusing on district heated regions that include combined heat and power production, and the residential and service sector, focusing on multifamily buildings and non-residential buildings. The research explores energy and climate goals in relation to the integration of the Sustainable Development Goals and potential barriers between organizations’ different objectives. In addition, the research focuses on barriers and drivers for energy efficiency. How type of ownership, size of the organization, and degree of urbanization can differentiate this work is also studied. Finally, the research explores potential conflicting objectives by studying energy end-use measures based on different system boundaries.The results show that around 70% of organizations in the Swedish residential and service sector had integrated the Sustainable Development Goals. However, depending on ownership, the integration rate ranges from 60% in public organizations with predominantly rental properties to 77% in private organizations, and 84% in cooperative organizations with predominantly tenant-owned properties. Only 48% of the small organizations had integrated the goals, compared to 73% of medium-sized organizations and 90% of large organizations. 49% of organizations in rural areas had integrated the goals, compared to 63% in towns and suburbs, and 80% in cities. The results show different use of terminology and timelines, and conflicting objectives are seen as different system boundaries are applied. This may inhibit understanding and communication, and hinder integration.Despite the need for energy efficiency, cost-efficient energy conservation measures are not always implemented. This is explained by the existence of barriers to energy efficiency. The perception of a lack of time or other priorities is the most hindering factor, along with the experience of a slim organization. On the other hand, the major drivers are reducing costs, followed by drivers of an organizational or behavioral nature. The results illustrate a challenging situation among publicly owned organizations, small organizations, and those in rural areas, as - relative to other groups - they experience barriers to a greater degree and drivers to a lesser extent. Positive factors that emerge between 2010 and 2020 are that energy strategies are integrated, and energy efficiency is given high priority throughout the organizations’ working methods.Lastly, by using simulation and optimization models, energy end-use measures of (1) large-scale renovation of a multifamily building stock and (2) the use of a hydronic pavement system for snow and ice clearance are studied. The results of the large-scale renovation of multifamily buildings reveal a potential conflict. The measure resulting in the best energy performance of the building, which may be the most desirable measure from a building owner’s perspective, risks leading to larger greenhouse gas emissions. A hydronic pavement system - a rarely used application in present-day district heating systems - proves to be a possible sustainable solution and a suitable application for the future generation of a low-temperature district heating system. The results underline the importance of understanding system boundaries in general, but also when considering energy efficiency improvements.
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| 6. |
- Ghaviha, Nima, 1987-
(författare)
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Energy Optimal Operation of Electric Trains : Development of a Driver Advisory System
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electric traction system used in trains is the most energy efficient traction system in the transportation sector. Moreover, it has the least NOx and CO2 emissions in comparison to other transportation systems (e.g. busses, passenger cars, airplanes, etc.). On the other hand, they are extremely expensive, mainly due to high installation and maintenance cost of the catenary system, including e.g. overhead lines and substations. Consequently, the share of electrified lines is only slightly higher than non-electrified lines. For instance in Europe, 60% of the railway networks are electrified, and the percentage is much lower in other continents. Battery driven trains are a new generation of electric trains that can overcome such high costs while keeping CO2 emissions and energy consumption low.At the moment, there are only two battery driven electric trains developed and both of the trains are passenger electric multiple units (EMUs). An EMU is an electric train with a traction system in more than one wagon, in contrast to loco-haul electric trains which have a traction system in one wagon only. Energy management during the operation of battery driven trains is a crucial task, as energy optimal operation of trains considering the optimal use of batteries can increase both the operating time and the lifetime of batteries. Energy efficient train operation is realized using driver advisory systems (DAS) that instructs drivers on how to drive trains for minimum energy consumption. The aim of this research is to propose an algorithm for speed profile optimization of both EMUs and battery driven EMUs. The desired algorithm should be suitable as a core component for an online DAS with short response time.Several approaches are proposed in the literature for speed profile optimization of electric trains, and a few of these have been proposed for speed profile optimization of battery driven electric trains. The trains modeled in almost all of the approaches are trains using a notch system for controlling tractive effort. The proposed solution in this research project is to use discrete dynamic programming (DP) to find the optimum speed profile. The application of DP is studied for speed profile optimization of EMUs with a notch system as well as EMUs with a smooth gliding handle for controlling tractive effort. The problem is solved for both normal EMUs and battery driven EMUs.The results of this research show that DP can provide accurate results in a reasonably short time. Moreover, the proposed algorithm can be used as a base for a DAS with fast response time (real-time).
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| 7. |
- Guziana, Bozena, 1963-
(författare)
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Corporate Greening : Product and Production Perspectives
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes corporate greening in general, and specifically the environmental technology (ET) sector as a green sector. The thesis has also particular focus on production and products related aspects and the influence of the environmental profile of the ET sector on the environmental engagement of companies in the sector. The study is based on a questionnaire-based survey, online surveys and on semi-structured open-ended interviews. The organizations within the ET sector were identified using existing platforms within this sector: Sustainability Sweden and Swentec. The results show that not all companies and industry associations in the ET sector clearly distinguish between product and production related environmental aspects. Furthermore, the product related environmental profile, which constitutes the legitimacy for the sector, can influence companies’ environmental strategy, not only positively but also negatively. The results from the survey on Global Supersector Leaders 2009/2010 in Dow Jones Sustainability Indexes (DJSI) show that all companies are aware of production and product related environmental issues. Based on results from this survey a model of corporate environmental profile consisting of product and production oriented activities as well as initiatives that go beyond the core business operations is proposed. These initiatives can be divided into two groups: environmental education and environmental projects and sponsorship. This thesis proposes products and production related impacts and environmental activities as bases for defining corporate environmental profiles, corporate greening, and for defining ‘green’ and ‘green-green’ business as well as environmental leaders. The distinction between product and production related environmental initiatives as well as the other dimensions of the proposed model in this thesis can support companies in their communication of environmental performance and environmental activities. Furthermore, ‘competitive advantage’, ‘environmental responsibility’ and ‘environmental leadership’ should motivate companies within the ET sector to be ‘vocal’ green-green firms.
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| 8. |
- He, Jie, 1979-
(författare)
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GASIFICATION-BASED BIOREFINERY FOR MECHANICAL PULP MILLS
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The modern concept of "biorefinery" is dominantly based on chemical pulp mills to create more value than cellulose pulp fibres, and energy from the dissolved lignins and hemicelluloses. This concept is characterized by the conversion of biomass into various biobased products. It includes thermochemical processes such as gasification and fast pyrolysis. In mechanical pulp mills, the feedstock available to the gasification-based biorefinery is significant, including logging residues, bark, fibre material rejects, biosludges and other available fuels such as peat, recycled wood, and paper products. This work is to study co-production of bio-automotive fuels, biopower, and steam via gasification in the context of the mechanical pulp industry. Biomass gasification with steam in a dual-fluidized bed gasifier (DFBG) was simulated with ASPEN Plus. From the model, the yield and composition of the syngas and the contents of tar and char can be calculated. The model has been evaluated against the experimental results measured on a 150 KWth Mid Sweden University (MIUN) DFBG. The model predicts that the content of char transferred from the gasifier to the combustor decreases from 22.5 wt.% of the dry and ash-free biomass at gasification temperature 750 ℃ to 11.5 wt.% at 950 ℃, but is insensitive to the mass ratio of steam to biomass (S/B). The H2 concentration is higher than that of CO under normal DFBG operating conditions, but they will change positions when the gasification temperature is too high above about 950 ℃, or the S/B ratio is too far below about 0.15. The biomass moisture content is a key parameter for a DFBG to be operated and maintained at a high gasification temperature. The model suggests that it is difficult to keep the gasification temperature above 850 ℃ when the biomass moisture content is higher than 15.0 wt.%. Thus, a certain amount of biomass needs to be added in the combustor to provide sufficient heat for biomass devolatilization and steam reforming. Tar content in the syngas can also be predicted from the model, which shows a decreasing trend of the tar with the gasification temperature and the S/B ratio. The tar content in the syngas decreases significantly with gasification residence time which is a key parameter. Mechanical pulping processes, as Thermomechanical pulp (TMP), Groundwood (SGW and PGW), and Chemithermomechanical pulp (CTMP) processes have very high wood-to-pulp yields. Producing pulp products by means of these processes is a prerequisite for the production of printing paper and paperboard products due especially to their important functional properties such as printability and stiffness. However, mechanical pulping processes consume a great amount of electricity, which may account for up to 40% of the total pulp production cost. In mechanical pulping mills, wood (biomass) residues are commonly utilized for electricity production through an associated combined heat and power (CHP) plant. This techno-economic evaluation deals with the possibility of utilizing a biomass integrated gasification combined cycle (BIGCC) plant in place of the CHP plant. Integration of a BIGCC plant into a mechanical pulp production line might greatly improve the overall energy efficiency and cost-effectiveness, especially when the flow of biomass (such as branches and tree tops) from the forest is increased. When the fibre material that negatively affects pulp properties is utilized as a bioenergy resource, the overall efficiency of the system is further improved. A TMP+BIGCC mathematic model is developed based on ASPEN Plus. By means of this model, three cases are studied: 1) adding more forest biomass logging residues in the gasifier,2) adding a reject fraction of low quality pulp fibers to the gasifier, and3) decreasing the TMP-specific electricity consumption (SEC) by up to 50%. For the TMP+BIGCC mill, the energy supply and consumption are analyzed in comparison with a TMP+CHP mill. The production profit and the internal rate of return (IRR) are calculated. The results quantify the economic benefit from the TMP+BIGCC mill. Bio-ethanol has received considerable attention as a basic chemical and fuel additive. It is currently produced from sugar/starch materials, but can also be produced from lignocellulosic biomass via a hydrolysis--fermentation or thermo-chemical route. In terms of the thermo-chemical route, a few pilot plants ranging from 0.3 to 67 MW have been built and operated for alcohols synthesis. However, commercial success has not been achieved. In order to realize cost-competitive commercial ethanol production from lignocellulosic biomass through a thermo-chemical pathway, a techno-economic analysis needs to be done. In this work, a thermo-chemical process is designed, simulated, and optimized mainly with ASPEN Plus. The techno-economic assessment is made in terms of ethanol yield, synthesis selectivity, carbon and CO conversion efficiencies, and ethanol production cost. Calculated results show that major contributions to the production cost are from biomass feedstock and syngas cleaning. A biomass-to-ethanol plant should be built at around 200 MW. Cost-competitive ethanol production can be realized with efficient equipments, optimized operation, cost-effective syngas cleaning technology, inexpensive raw material with low pretreatment cost, high-performance catalysts, off-gas and methanol recycling, optimal systematic configuration and heat integration, and a high-value byproduct.
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| 9. |
- Lidberg, Tina, 1982-
(författare)
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Building Energy Efficiency Measures in District Heating Systems
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improving energy performance of existing buildings is an important part in decreasing energy use and in turn reducing greenhouse gas emissions and primary energy use. To be able to evaluate how energy refurbishment influences greenhouse gas emissions and primary energy use a wider system perspective is needed which puts the building in its context. This thesis deals with energy efficiency refurbishment performed on multi-family buildings within district heated areas and how greenhouse gas emissions and primary energy use is influenced. Both energy demand and temperature levels are considered.A simulated building is used to evaluate energy refurbishment packages. The results are used as input data for models of district heating systems to cost optimize district heating production. One district heating system model is also used to evaluate the impact of lowered district heating supply temperatures. The results from the cost optimizations are used to evaluate the impact on greenhouse gas emissions and primary energy use.The results show that all refurbishment packages decreases greenhouse gas emissions and primary energy use, but to a different extent. Depending on the fuel types used and to which extent electricity is co-produced in the district heating system, the results of implementing the refurbishment packages vary. The largest reduction of greenhouse gas emissions and primary energy use occurs in a district heating system with a high share of biofuel and no electricity production. Another result is that the temperature levels of a building’s heating system can be reduced when refurbished which promotes low-temperature district heating. The results also indicates that greenhouse gas emissions and primary energy use can be decreased from a short- and medium term perspective if the supply temperature of a district heating system is lowered. From a long term perspective primary energy use is still decreased while greenhouse gas emissions are increased.
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| 10. |
- Lundström, Lukas, 1980-
(författare)
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Heat demand profiles of buildings' energy conservation measures and their impact on renewable and resource efficient district heating systems
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increased energy performance of the building stock of European Union is seen as an important measure towards mitigating climate change, increasing resource utilisation efficiency and energy supply security. Whether to improve the supply-side, the demand-side or both is an open issue. This conflict is even more apparent in countries such as Sweden with a high penetration of district heating (DH). Many Swedish DH systems have high share of secondary energy resources such as forest industry residuals, waste material incineration and waste heat; and resource efficient cogeneration of electricity in combined heat and power (CHP) plants. When implementing an energy conservation measure (ECM) in a DH connected building stock, it will affect the operation of the whole DH system. If there are CHP plants and the cogeneration of electricity decreases due to an ECM, and this electricity is valued higher than the fuel savings, the consequences of the ECM would be negative. These complex relationships are investigated by conducting a case study on the Eskilstuna DH system, a renewable energy supply system with relatively high share of cogenerated electricity. Heat demand profiles of ECMs are determined by building energy simulation, using recently deep energy retrofitted multifamily buildings of the “Million Programme”-era in Eskilstuna as model basis. How implementing ECMs impact on the DH system’s heat and electricity production under different electricity revenue scenarios has been computed and evaluated in terms of resource efficiency and CO2 emissions. The results show that different ECMs in the buildings impact differently on the DH system. Measures such as improved insulation level of the building’s envelope, that decrease the heat demand’s dependence to outdoor temperature, increase the amount of cogenerated electricity. While measures such as thermal solar panels, which save heat during summer, affects the absolute amount of cogenerated electricity negatively. Revenues from cogenerated electricity influence the amount of cost-effectively produced electricity much more than the impact from ECMs. Environmental benefits of the ECMs, measured in CO2 emissions and primary energy consumption, are quite small in DH systems that have high share of forest residual fuels and electricity cogeneration. The consequences can even be negative if ECMs lead to increased need of imported electricity that is produced resource inefficiently or/and by fossil fuels. However, all studied ECMs increase the relative amount of cogenerated electricity, the ratio between amount of cogenerated electricity and the heat load. This implied that all ECMs increase the overall efficiency of the Eskilstuna DH system.
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