Optimal lay-out and operation of combined heat & power (CHP) distributed generation systems

The paper presents an optimization model of a distributed cogeneration system with a district heating network, applied to a real city centre situation. The distributed urban cogeneration system includes both a set of micro-gas turbines, located inside some public buildings, and a centralized cogeneration system based on a Internal Combustion Engine. The objective function adopted for the optimization is the Total Annual Cost for owning, maintaining and operating the whole system. To face the problem a Mixed Integer Linear Program (MILP) is defined and solved by a commercial software. Starting from the thermal and electrical demand of the buildings, the MILP model allows to define the possible installation of the centralized cogeneration ICE (Internal Combustion Engine) and the number of microturbines in the different buildings, the optimal lay-out of the district heating network and the optimal operation strategy for the whole system as well. In particular the energy performance and global CO₂ emissions are evaluated.     

The potential of district heating using geothermal energy. A case study, Greece

The purpose of this study is to investigate the possibility of using low-enthalpy geothermal energy from the geothermal field of Sousaki in the province of Korinthos, Greece, to cover the thermal needs of the nearby town of Ag. Theodori. The possibility of developing a system of district heating was examined based on a proposed town model. Total thermal demands were calculated on the basis of a model dwelling and prevailing weather conditions in the area. Subsequently, a heat transfer circuit is proposed, including the distribution network, the heat exchanger, the production and reinjection pumps, and the pumping station. Finally, energy indices are presented, such as demand in tons of equivalent oil and CO₂ emissions.     

District heating and energy efficiency in detached houses of differing size and construction

House envelope measures and conversion of heating systems can reduce primary energy use and CO₂ emission in the existing Swedish building stock. We analysed how the size and construction of electrically heated detached houses affect the potential for such measures and the potential for cogenerated district heating. Our starting point was two typical houses built in the 1970s. We altered the floor plans to obtain 6 houses, with heated floor space ranging between 100 and 306 m². One of the houses was also analysed for three energy standards with differing heat loss rates. CO₂ emission, primary energy use and heating cost were estimated after implementing house envelope measures, conversions to other heating systems and changes in the generation of district heat and electricity. The study accounted for primary energy, including energy chains from natural resources to useful heat in the houses. We showed that conversion to district heating based on biomass, together with house envelope measures, reduced the primary energy use by 88% and the CO₂ emission by 96%, while reducing the annual societal cost by 7%. The choice of end-use heating system was decisive for the primary energy use, with district heating being the most efficient. Neither house size nor energy standard did significantly change the ranking of the heating systems, either from a primary energy or an economic viewpoint, but did affect the extent of the annual cost reduction after implementing the measures.     

Operational optimisation of a complex trigeneration system connected to a district heating and cooling network

The combined production of electricity, heat and cold by polygeneration systems ensures maximum utilization of resources by reducing emissions and energy losses during distribution. Polygeneration systems are highly integrated systems characterized by the simultaneously production of different services (electricity, heating, cooling) by means of several technologies using fossil and renewable fuels that operates together to obtain a higher efficiency than that of an equivalent conventional system. The high number of distribution technologies available to produce electricity, heating and cooling and the different levels of integration make it difficult to select of the optimal configuration. Moreover, the high variability in the energy demand renders difficult the selection of the optimal operational strategy. Optimization methodologies are usually applied for the selection of the optimal configuration and operation of energy supply systems. This paper presents a scenario analysis using optimization models to perform an economic, energetic and environmental assessment of a new polygeneration system in Cerdanyola del Vallès (Spain) in the framework of the Polycity project of the European Concerto Program. This polygeneration system comprise high-efficiency natural gas cogeneration engines with thermal cooling facilities and it will provide electricity, heating and cooling for a new area in growth known as Alba park including a Synchrotron Light Facility and a Science and Technological park through a district heating and cooling network of four tubes. The results of the scenario analysis show that the polygeneration plant is an efficient way to reduce the primary energy consumption and CO₂ emissions (up to 24%).     

Conversion of individual natural gas to district heating: Geographical studies of supply costs and consequences for the Danish energy system

Replacing individual natural gas heating with district heating based to increasing shares of renewable energy sources may further reduce CO₂-emissions in the Danish Building mass, while increasing flexibility of the energy system to accommodate significantly larger amounts of variable renewable energy production. The present paper describes a geographical study of the potential to expand district heating into areas supplied with natural gas. The study uses a highly detailed spatial database of the built environment, its current and potential future energy demand, its supply technologies and its location relative to energy infrastructure. First, using a spatially explicit economic model, the study calculates the potentials and costs of connection to expanded district heating networks by supply technology. Then a comprehensive energy systems analysis is carried out to model how the new district heat can be supplied from an energy system with higher shares of renewable energy. It can be concluded on the basis of these analyses that the methods used proved highly useful to address issues of geographically dependent energy supply; however the spatio-economic model still is rather crude. The analyses suggest to expand district heating from present 46% to somewhere in between 50% and 70%. The most attractive potential is located around towns and cities. The study also suggests that CO₂-emissions, fuel consumption and socio-economic costs can be reduced by expanding district heating, while at the same time investing in energy savings in the building mass as well as increased district heating network efficiency.     

Optimisation of a Swedish district heating system with reduced heat demand due to energy efficiency measures in residential buildings

The development towards more energy efficient buildings, as well as the expansion of district heating (DH) networks, is generally considered to reduce environmental impact. But the combined effect of these two progressions is more controversial. A reduced heat demand (HD) due to higher energy efficiency in buildings might hamper co-production of electricity and DH. In Sweden, co-produced electricity is normally considered to displace electricity from less efficient European condensing power plants. In this study, a potential HD reduction due to energy efficiency measures in the existing building stock in the Swedish city Linköping is calculated. The impact of HD reduction on heat and electricity production in the Linköping DH system is investigated by using the energy system optimisation model MODEST. Energy efficiency measures in buildings reduce seasonal HD variations. Model results show that HD reductions primarily decrease heat-only production. The electricity-to-heat output ratio for the system is increased for HD reductions up to 30%. Local and global CO₂ emissions are reduced. If co-produced electricity replaces electricity from coal-fired condensing power plants, a 20% HD reduction is optimal for decreasing global CO₂ emissions in the analysed DH system.     

On the potential trade-offs between energy supply and end-use technologies for residential heating

In Sweden, where district heating accounts for a significant share of residential heating, it has been argued that improvements in end-use energy efficiency may be counter-productive since such measures reduce the potential of energy efficient combined heat and power production. In this paper we model how the potential trade-offs between energy supply and end-use technologies depend on climate policy and energy prices. The model optimizes a combination of energy efficiency measures, technologies and fuels for heat supply and district heating extensions over a 50 year period. We ask under what circumstances improved end-use efficiency may be cost-effective in buildings connected to district heating? The answer hinges on the available technologies for electricity production. In a scenario with no alternatives to basic condensing electricity production, high CO₂ prices result in very high electricity prices, high profitability of combined heat and power production, and little incentive to reduce heat demand in buildings with district heating. In contrast, in a scenario where electricity production alternatives with low CO₂ emissions are available, the electricity price will level out at high CO₂ prices. This gives heat prices that increase with the CO₂ price and make end-use efficiency cost-effective also in buildings with district heating.     

Conventional and advanced CO2 based district energy systems

District energy systems can potentially decrease the CO₂ emissions linked to energy services, thanks to the implementation of large polygeneration energy conversion technologies connected to buildings over a network. To transfer the energy from these large technologies to the users, conventional district energy systems use water with often two independent supply and return piping systems for heat and cold. However, sharing energy or interacting with decentralised heat pump units often results in relatively large heat transfer exergy losses due to the large temperature differences that are economically required from the water network. Besides, the implementation of two independent supply and return piping systems for heat and cold, results in large space requirements in underground technical galleries. Using refrigerants as a district heating or cooling fluid at an intermediate temperature could alleviate some of these drawbacks. A new system has been developed, that requires only two pipes, filled with refrigerant, to meet heating, hot water and cooling requirements. Because of the environmental concerns about conventional refrigerants, CO₂, a natural refrigerant, used under its critical point, is considered an interesting candidate. A comparative analysis shows that both in terms of exergy efficiency and costs the proposed CO₂ network is favourable.     

Performance assessment of a Stirling engine plant for local micro‐cogeneration

In this paper, we evaluate the viability of a 9.5‐kW_e wooden pellet‐fueled Stirling engine‐based micro‐cogeneration plant as a substitute for small‐scale district heating. The district heating systems against which the micro‐cogeneration plant is compared are based either on a pellet‐fueled boiler or a ground‐source heat pump. The micro‐cogeneration and district heating plants are compared in terms of primary energy consumption, CO₂ emissions, and feasibility of the investment. The comparison also considers an optimally operated individual 0.7‐kW_e pellet‐fueled Stirling engine micro‐cogeneration system with exhaust gas heat recovery. The study is conducted in two different climates and contributes to the knowledge base by addressing: (i) hourly changes in the Finnish electricity generation mix; and (ii) uncertainty related to what systems are used as reference and the treatment of displaced grid electricity. Our computational results suggest that when operated at constant power, the 9.5‐kW_e Stirling engine plant results in reduced annual primary energy use compared with any of the alternative systems. The results are not sensitive to climate or the energy efficiency or number of buildings. In comparison with the pellet‐fueled district heating plant, the annual use of primary energy and CO₂ emissions are reduced by a minimum of 25 and 19%, respectively. Owing to a significant displacement of grid electricity, the system's net primary energy consumption appears negative when the total built area served by the plant is less than 1200 m². On the economic side, the maximum investment cost threshold of a CHP‐based district heating system serving 10 houses or more can typically be positive when compared with oil and pellet systems, but negative when compared with a corresponding heat pump system. Copyright © 2010 John Wiley & Sons, Ltd.     

Regional energy system optimization – Potential for a regional heat market

Energy supply companies and industrial plants are likely to face new situations due to, for example, the introduction of new energy legislation, increased fuel prices and increased environmental awareness. These new prerequisites provide companies with new challenges but also new possibilities from which to benefit. Increased energy efficiency within companies and increased cooperation between different operators are two alternatives to meet the new conditions. A region characterized by a high density of energy-intensive processes is used in this study to find the economic potential of connecting three industrial plants and four energy companies, within three local district heating systems, to a regional heat market, in which different operators provide heat to a joint district heating grid. Also, different investment alternatives are studied. The results show that the economical potential for a heat market amounts to between 5 and 26 million EUR/year with payback times ranging from two to eleven years. However, the investment costs and the net benefit for the total system need to be allotted to the different operators, as they benefit economically to different extents from the introduction of a heat market. It is also shown that the emissions of CO₂ from the joint system would decrease compared to separate operation of the systems. However, the valuation of CO₂ emissions from electricity production is important as the difference of emitted CO₂ between the accounting methods exceeds 650 kton/year for some scenarios.     

Economic and environmental impacts of insulation in district heating pipelines

The determination of optimum thickness of insulation is often applied to energy technologies and building projects. In this study, the energy, economic and environmental evaluations of thermal insulation in district heating pipeline are discussed. The optimum insulation thickness, energy saving over a lifetime of 10 years, payback period and emissions of CO₂, CO and SO₂ are calculated for nominal pipe sizes and fuel types based on heating loads in Afyonkarahisar/Turkey. The life cycle cost analysis is used to determine the optimum thickness of the pipeline material in order to take into account the change in inflation that directly affect both the cost of pipeline material and fuels depending on fuel type. The results show that the highest value of optimum insulation thickness, energy savings, emissions and the lowest payback period are reached for a nominal pipe size of 200 mm. About three times more energy saving results by making 200 mm nominal pipe instead of 50 mm. Considering the economical and environmental advantages, the geothermal energy is a better choice and then fuel-oil. When thermal insulation is done in a district heating pipeline, there will be a significant reduction of 21% in the amount of CO₂ emitted to the atmosphere.     

Fossil fuels substitution by the solar energy utilization for the hot water production in the heating plant “Cerak” in Belgrade

The main objective of this paper is to evaluate energy and environmental benefits of the large-scale solar heating system connection with district heating system. The assessment of fossil fuels substitution by the solar energy for the hot water production for domestic use, during the summer period, is done. Hot water for district heating and domestic use is produced in heating plant “Cerak” placed in the suburb of Belgrade. The existing production and distribution system are based on fossil fuel energy, mainly on the natural gas. In the first phase of the project plan was to install about 10,000 m² of solar collectors to substitute nearly 25% of natural gas consumption. During the summer period, the saving of natural gas calculated for presented system is approximately 430,000 m³ and in this way 900 t of the CO₂ emissions would be reduced.     

Potential of power-to-heat from excess wind energy on the city level

ABSTRACT

This study discusses the potential of power-to-heat (P2H) as an effective option to reduce greenhouse gas emissions in the heating sector and energy curtailment. P2H promotes the integration of electricity from renewable energy sources into the power grid by utilizing otherwise unused electricity (excess energy) for space heating. To estimate the contribution of this effect from a techno-economic perspective, a linear problem is defined by minimizing the overall heating costs and solved by an open source model generator. Four different scenarios are modeled on a city level, using real heat demand data from a case study regarding the municipality of Greifswald, a region with dominant wind-energy. Results indicate that district heating networks are an important technology for coupling power and heat to meet CO₂ reduction targets. In addition, further integration of renewable energy is promoted to reduce overall emissions and achieve Germany’s climate protection goals by 2050.     

Pathways to a sustainable European kraft pulp industry: Trade-offs between economy and CO2 emissions for different technologies and system solutions

In this paper the trade-off, in terms of annual net profit for the mill and global emissions of CO₂, between different technology pathways for utilization of excess steam and heat at kraft pulp mills is investigated for a case depicting a typical Scandinavian mill of today. The trade-off is analysed for four future energy market scenarios having different levels of CO₂ charge. The technology pathways included in this study are increased electricity production in new turbines, production of district heating, increased sales of biomass in the form of bark and/or lignin, and carbon capture and storage (CCS). The results show that the proven pathways, increased electricity production, bark export and district heating production, are economically robust, i.e. they are profitable for all of the studied energy market scenarios. The new and emerging technology pathways, that are CCS and lignin extraction, hold a larger potential for reduction of global CO₂ emissions, but their economic profitability is more dependent on the development of the energy market. All in all, it can be concluded that to realize the larger potential of reduction of global CO₂ emissions a high carbon cost alone may not be sufficient. Other economic stimulations are required, e.g. technology-specific subsidies.     

Heat Roadmap Europe: Combining district heating with heat savings to decarbonise the EU energy system

Six different strategies have recently been proposed for the European Union (EU) energy system in the European Commission's report, Energy Roadmap 2050. The objective for these strategies is to identify how the EU can reach its target of an 80% reduction in annual greenhouse gas emissions in 2050 compared to 1990 levels. None of these scenarios involve the large-scale implementation of district heating, but instead they focus on the electrification of the heating sector (primarily using heat pumps) and/or the large-scale implementation of electricity and heat savings. In this paper, the potential for district heating in the EU between now and 2050 is identified, based on extensive and detailed mapping of the EU heat demand and various supply options. Subsequently, a new ‘district heating plus heat savings’ scenario is technically and economically assessed from an energy systems perspective. The results indicate that with district heating, the EU energy system will be able to achieve the same reductions in primary energy supply and carbon dioxide emissions as the existing alternatives proposed. However, with district heating these goals can be achieved at a lower cost, with heating and cooling costs reduced by approximately 15%.     

Towards a low-carbon future in China's building sector—A review of energy and climate models forecast

This article investigates the potentials of energy saving and greenhouse gases emission mitigation offered by implementation of building energy efficiency policies in China. An overview of existing literature regarding long-term energy-demand and carbon dioxide (CO₂) emission forecast scenarios is presented. Energy consumption in buildings could be reduced by 100–300 million tons of oil equivalent (mtoe) in 2030 compared with the business-as-usual (BAU) scenario, which means that 600–700 million metric tons of CO₂ emissions could be saved by implementing appropriate energy policies within an adapted institutional framework. The main energy-saving potentials in buildings can be achieved by improving a building's thermal performance and district heating system efficiency. The analyses also reveal that the energy interchange systems are effective especially in the early stage of penetration. Our analysis on the reviewed models suggests that more ambitious efficiency improvement policies in both supply- and demand-side as well as the carbon price should be taken into account in the policy scenarios to address drastic reduction of CO₂ emission in the building sector to ensure climate security over the next decades.     

Energy and environmental sustainability assessment of a crude oil refinery by thermodynamic analysis

This study presents the assessment of energy and environmental sustainability metrics for a crude oil refinery consisting of three distillation columns. The assessments of the current operation and the retrofits for possible improvements are suggested by the thermodynamic analysis and energy analyzer. The main objective is to explore the scope of reducing the thermal energy consumption and CO₂ emissions for a more sustainable refinery operation. Thermodynamic analysis is carried out by using the thermal analysis capability of ‘column targeting tool’ to address the ‘energy intensity metrics’ and the ‘energy analyzer’ to design and improve the performance of the heat exchanger network system for process heat integration. Environmental pollution impact metrics are estimated from the ‘carbon tracking’ options with a selected CO₂ emission data source of US‐EPA‐Rule‐E9‐5711 and using crude oil as a primary fuel source for the hot utilities. The results indicate that column targeting tool, energy analyzer, and carbon tracking can estimate the energy and environmental sustainability metrics of an existing design and determine the scope of considerable improvements for reducing the costs of thermal energy required and emissions of carbon dioxide in a crude oil refinery operation. Copyright © 2015 John Wiley & Sons, Ltd.     

Energy efficiency measures and conversion of fossil fuel boiler systems in a detached house

There is a large potential to reduce primary energy use and CO₂ emissions from the Swedish building stock. Here detached houses heated by oil, natural gas or electric boilers were assessed. CO₂ emissions, primary energy use and heating costs were evaluated before and after implementing house envelope measures, conversions to more efficient heating systems and changes to biomass fuel use. The study included full energy chains, from natural resources to usable heat in the houses. The aim was to evaluate the societal economic cost effectiveness of reducing CO₂ emission and primary energy use by different combinations of changes. The results demonstrated that for a house using an electric boiler, a conversion to a heat pump combined with house envelope measures could be cost efficient from a societal economic perspective. If the electricity was based on biomass, the primary energy use was at the same time reduced by 70% and the CO₂ emission by 97%. Large emission reductions were also seen for conversions from oil and gas boilers to a biomass-based system. However, for these conversions the heating cost increased, leading to a mitigation cost of around €50/tonne C avoided. The price of oil and natural gas greatly influenced the competitiveness of the alternatives. House envelope measures were more cost-effective for houses with electric boilers as the cost of energy for this system is high. The results are specific to a Swedish context, but also give an indication of the potential in other regions, such as northern European and large parts of North America, which have both a cold climate and a widespread use of domestic boilers.     

Excess heat from kraft pulp mills: Trade-offs between internal and external use in the case of Sweden—Part 2: Results for future energy market scenarios

In this paper the trade-off between internal and external use of excess heat from a kraft pulp mill is investigated for four different future energy market scenarios. The work follows the methodology described in Svensson et al. [2008. Excess heat from kraft pulp mills: trade-offs between internal and external use in the case of Sweden—Part 1: methodology. Energy Policy, submitted for publication], where a systematic approach is proposed for investigating the potential for profitable excess heat cooperation. The trade-off is analyzed by economic optimization of an energy system model consisting of a pulp mill and an energy company (ECO). In the model, investments can be made, which increase the system's energy efficiency by utilization of the mill's excess heat, as well as investments that increase the electricity production. The results show that the trade-off depends on energy market prices, the district heating demand and the type of existing heat production. From an economic point of view, external use of the excess heat is preferred for all investigated energy market scenarios if the mill is studied together with an ECO with a small heat load. For the cases with medium or large district heating loads, the optimal use of excess heat varies with the energy market price scenarios. However, from a CO₂ emissions perspective, external use is preferred, giving the largest reduction of global emissions in most cases.     

Stated preferences of Finnish private homeowners for residential heating systems: A discrete choice experiment

Our aim is to examine how different attributes of residential heating systems affect private homeowners' choice of heating system following renovations when heterogeneity in the homeowners' preferences is considered. Utilizing the results of our choice model, we then aim to simulate the market shares of different heating systems under various policy scenarios. The data were retrieved by a questionnaire mailed to a random sample of Finnish private owners of detached houses built in the 1960s–1990s with a response rate of 52%. The labeled choice sets in the discrete choice experiment (DCE) had 6 heating system alternatives (wood pellet boiler, solid wood fired boiler, district heat, electricity, ground heat (pump) and oil boiler) with varying levels of predetermined attributes (investment cost, annual operating cost, CO₂ emissions, fine particle emissions and required own work). The choice modeling results emphasized the role of the investment cost as the main attribute affecting the decisions, although nonfinancial attributes also had a considerable effect. Systematic preference heterogeneity was caused by the availability of district heat, the existing heating system and the homeowner's forest ownership. In addition, the results indicated a significant unobserved preference heterogeneity. Based on the simulation of market shares, the use of wood pellets in residential heating is projected to increase threefold during 2009–2020.