Future energy systems and thus the climate are affected by many factors, such as energy resources, energy demand, energy policy and the choice of energy technologies. Energy systems of the future are facing three main challenges; the steady growth of global energy demand, the energy resource depletion, as well as the increasing emissions of carbon dioxide (CO2) and other greenhouse gases and their impact on climate change. To meet the mentioned challenges with sustainability in mind, actions that increase energy efficiency and choosing an energy-efficient energy system which is cost efficient will be essential. Combined heat and power (CHP) plants and district heating and cooling could contribute greatly to increased system efficiency by using energy otherwise wasted.

The aim of this study is to increase the understanding of how CHP-based district heating and cooling systems using different primary energy sources can contribute to more cost-efficient energy systems, which reduce global CO2 emissions, and to highlight the impact of some important parameters and measures on Swedish municipal district heating systems. An important assumption in this study is the estimation of CO2 emissions from electricity production, which is based on marginal electricity perspectives. In the short term, the marginal electricity is assumed to come from coal-fired condensing power plants while in the long term it consists of electricity produced by natural gas-fired combined cycle condensing power plants. This means that the local electricity production will replace the marginal electricity production. The underlying assumption is an ideal fully deregulated European electricity market where trade barriers are removed and there are no restrictions on transfer capacity.

The results show that electricity generation in CHP plants, particularly in higher efficiency combined steam and gas turbine heat and power plants using natural gas, can reduce the global environmental impact of energy usage to a great extent. The results confirm, through the scenarios presented in this study, that waste as a fuel in CHP-based district heating systems is fully utilised since it has the lowest operational costs. The results also show how implementation of a biogas-based CHP plant in a biogas system contributes to an efficient system, as well as lowering both CO2 emissions and system costs. The results show that replacing electricity-driven (e.g. compression) cooling by heat-driven cooling using district heating (e.g. absorption chillers) in a CHP system is a cost-effective and climate friendly technology as electricity consumption is reduced while at the same time the electricity generation will be increased. The results of the study also show that there is potential to expand district heating systems to areas with lower heat density, with both environmental and economic benefits for the district heating companies.

The results reveal that the operation of a studied CHP-based district heating system with an imposed emission limit is very sensitive to the way CO₂ emissions are accounted, i.e., local CO₂ emissions or emissions from marginal electricity production. The results show how the electricity production increases in the marginal case compared with the local one in order to reduce global CO₂ emissions. The results also revealed that not only electricity and fuel prices but also policy instruments are important factors in promoting CHP-based district heating and cooling systems. The use of electricity certificates has a large influence for the introduction of biogas-based cogeneration. Another conclusion from the modelling is that present Swedish policy instruments are strong incentives for cogeneration with similar impact as applying external costs.

The objectives of this study are to present a model for biogas production systems to help achieve a more cost-effective system, and to analyse the conditions for connecting combined heat and power (CHP) plants to the biogas system. The European electricity market is assumed to be fully deregulated. The relation between connection of CHP. increased electricity and heat production, electricity prices, and electricity certificate trading is investigated. A cost-minimising linear programming model (MODEST) is used. MODEST has been applied to many energy systems, but this is the first time the model has been used for biogas production. The new model, which is the main result of this work, can be used for operational optimisation and evaluating economic consequences of future changes in the biogas system. The results from the case study and sensitivity analysis show that the model is reliable and can be used for strategic planning. The results show that implementation of a biogas-based CHP plant result in an electricity power production of approximately 39 GW h annually. Reduced system costs provide a profitability of 46 MSEK/year if electricity and heat prices increase by 100% and electricity certificate prices increase by 50%. CO2 emission reductions up to 32,000 ton/year can be achieved if generated electricity displaces coal-fired condensing power.

The objective of the study is to analyse the conditions for connection of residential buildings in heat sparse areas to district heating systems in order to increase electricity production in municipal combined heat and power plants. The European electricity market has been assumed to be fully deregulated. The relation between connection of heat sparse areas, increased electricity and heat production as well as electricity prices, fuel prices and emissions rights is investigated. The results of the study show that there is potential to expand the district heating market to areas with lower heat concentrations in the cities of Gavle, Sandviken and Borlange in Sweden, with both economic and environmental benefits. The expansion provides a substantial heat demand of approximately 181 GWh/year, which results in an electricity power production of approximately 43 GWh/year. Since the detached and stand-alone houses in the studied heat sparse areas have been heated either by oil boiler or by direct electricity, connection to district heating also provides a substantial reduction in emissions of CO(2). The largest reductions in CO(2) emissions are found to be 211 ktonnes/year assuming coal-fired condensing power as marginal electricity production. Connection of heat sparse areas to district heating decrease the system costs and provide a profitability by approximately 22 million EURO/year for the studied municipalities if the price of electricity is at a European level, i.e. 110 EURO/MWh. Sensitivity analysis shows, among other things, that a strong relation exists between the price of electricity and the profitability of connecting heat sparse areas to district heating systems.

The aim of this study is to investigate the potential use of natural gas for heat and power production for the municipality of Linkoping, Norrkoping and Finspang in the County of Ostergotland, Sweden. The results of the study revealed that these three municipalities with the present heating demand can convert 2030 GWh/year of the present fuel mixed to natural gas. The expansion of natural gas provides the possibility to increase the electricity generation with approximately 800 GWh annually in the County of Ostergotland. The global emissions of CO(2) reduce also by approximately 490 ktonne/year by assuming the coal condensing power plant as the marginal power plant. The total system cost decreases by 76 Mkr/year with the present electricity price which varies between 432 and 173 SEK/MWh and with 248 Mkr/year if the present electricity price increases to 37% which is approximately corresponding to European electricity prices. Sensitivity analysis is done with respect to the different factors such as price of electricity, natural gas, etc. The findings show that increased price of electricity and increased district heating demand increases the profitability to convert to natural gas using CHP plant. (C) 2008 Elsevier Ltd. All rights reserved.

The present study of the district heating (DH) system in the city of Kisa, Sweden, shows how, through energy cooperation with a nearby sawmill and paper mill, a local energy company contributes to energy-efficient DH and cost-effective utilization of a new biofuel combined heat and power (CHP) plant. Cases of stand-alone and integrated energy systems are optimized with the linear program MODEST. The European power market is assumed to be fully deregulated. The results show clear advantages for the energy company to cooperate with these industries to produce heat for DH and process steam for industry. The cooperating industries gain advantages from heat and/or biofuel by-product supply as well. The opening to use a biofuel CHP plant for combined heat supply results in cogenerated electricity of almost 29 GWh/a with an increased biofuel use of 13 GWh/a, zero fuel oil use and CO₂ emission reductions of 25,800 tons CO₂/a with coal-condensing power plant on the margin and biofuel as limited resource. The total system cost decreases by −2.18 MEUR/a through extended cooperation and renewable electricity sales. The sensitivity analysis shows that the profitability of investing in a biofuel CHP plant increases with higher electricity and electricity certificate prices.

A hydronic pavement system (HPS) is an alternative method to clear snow and ice, which avoids the use of salt, sand, and fossil fuel in conventional snow clearance, and minimizes the risk of accidents. The aim is to analyze the performance of different control strategies for a 35,000 m2 HPS utilizing heat from a district heating and cooling (DHC) system. The key performance indicators are (1) energy performance of the HPS, and (2) primary energy use, (3) electricity production and (4) greenhouse gas (GHG) emissions from the DHC system. The methodology uses a simulation model of the HPS and an optimization model of the DHC system. Three operational strategies are analyzed: A reference scenario based on the current control strategy, and scenarios where the HPS is shut down at temperatures below −10 ◦C and −5 ◦C. The study shows that the DHC return temperature is suitable for use. By operational strategies, use during peak demand in the DHC system can be avoided, resulting in reduced use of fossil fuel. Moreover, the energy use of the HPS could be reduced by 10% and the local GHG emissions by 25%. The study emphasizes that the HPS may have positive effects on global GHG emissions, as it enables electricity production from renewable resources. 

In Sweden, 90% of multifamily buildings utilize district heat and a large portion is in need of renovation. The aim is to analyze the impact of renovating a multifamily building stock in a district heating and cooling system, in terms of primary energy savings, peak power demands, electricity demand and production, and greenhouse gas emissions on local and global levels. The study analyzes scenarios regarding measures on the building envelope, ventilation, and substitution from district heat to ground source heat pump. The results indicate improved energy performance for all scenarios, ranging from 11% to 56%. Moreover, the scenarios present a reduction of fossil fuel use and reduced peak power demand in the district heating and cooling system ranging from 1 MW to 13 MW, corresponding to 4–48 W/m2 heated building area. However, the study concludes that scenarios including a ground source heat pump generate significantly higher global greenhouse gas emissions relative to scenarios including district heating. Furthermore, in a future fossil-free district heating and cooling system, a reduction in primary energy use will lead to a local reduction of emissions along with a positive effect on global greenhouse gas emissions, outperforming measures with a ground source heat pump.

Both energy supply and waste treatment give rise to negative effects on the environment, so-called external effects. In this study, monetary values on external costs collected from the EU's ExternE project are used to evaluate inclusion of these costs in comparison with an energy utility perspective including present policy instruments. The studied object is a municipal district heating system with a waste incineration plant as the base supplier of heat. The evaluation concerns fuels used for heat production and total electricity production, for scenarios with external costs included and for a scenario using the present policy instrument. Impacts of assumptions on marginal power producers (coal or natural gas power plants) are investigated, since locally produced electricity is assumed to replace marginal power and thus is credited for the avoided burden. Varying levels of external costs for carbon dioxide emissions are analysed. The method used is an economic optimisation model, MODEST. The conclusion is that present policy instruments are strong incentives for cogeneration, even when external costs are included. Waste is fully utilised in all scenarios. In cases where coal is the marginal power producer, more electricity is produced; when natural gas is the marginal power producer, less is produced. There are several uncertainties in the data for external costs, both methodological and ethical. In the ExternE data, not all environmental impacts are included. For waste incineration, ashes are not included, and another difficulty is how to treat the avoided burden of other waste treatment methods. 

The economic and environmental performance of a district heating (DH) system is to a great extent affected by the size and dynamic behavior of the DH load. By implementing energy efficiency measures (EEMs) to increase a building’s thermal performance and by performing cost-optimal energy renovation, the operation of the DH system will be altered. This study presents a systematic approach consisting of building categorization, life cycle cost (LCC) optimization, building energy simulation and energy system optimization procedures, investigating the profitability and environmental performance of cost-optimal energy renovation of a historic building district on the DH system. The results show that the proposed approach can successfully be used to predict the economic and environmental effects of cost-optimal energy renovation of a building district on the local DH system. The results revealed that the financial gains of the district are between 186 MSEK (23%) and 218 MSEK (27%) and the financial losses for the DH system vary between 117–194 MSEK (5–8%). However, the suggested renovation measures decrease the local and global CO2 emissions by 71–75 metric ton of CO2eq./year (4%) and 3545–3727 metric ton of CO2eq./year (41–43%), respectively. Total primary energy use was decreased from 57.2 GWh/year to 52.0–52.2 GWh/year.

Jets are often used for supplying air to buildings. For designing ventilation systems it is therefore of great importance to have a good understanding of air jets to avoid draught, which might lead to discomfort. At the same time as we want a good indoor climate, we also want to reduce energy consumption. The purpose of this study is to investigate the flow and thermal characteristics of warm air jets supplied under the ceiling, as a heating method, by means of numerical prediction and full-scale experiments. Together with the warm wall jet, an isothermal wall jet will also be examined. For the calculations, three different k-ε models have been used and evaluated, namely the standard k-ε, the Chen-Kim k-ε model and the Renormalization Group k-ε model. The experiments have been carried out in a full-scale room where the temperature and velocity within the air jet are conducted. For the isothermal wall jet, the Chen model gives best agreement for the growth rate, while the standard k-ε model gives the best result for the velocity decay of the jet. The evaluation of the warm jet provided best results for the Chen model regarding both the growth rate and the velocity decay. The velocity and temperature profiles for the warm jet provided similar results for all models, but also some differences between the predicted and measured temperatures.

Studying energy renovation of older residential building stocks together with the surrounding district heating (DH) system is essential to fully understand implications from a reduced district heat demand and for involved actors. This study reveals the benefit of integrating the simulation and optimization tools OPERA-MILP, IDA ICE, and MODEST to investigate thoroughly the effect of energy renovation strategies on heat load supply, building and DH system-based life cycle costs (LCCs), primary energy use, and total of direct and indirect CO2 emissions. Energy renovation considered different cluster combinations of slab and tower blocks of a stock of 343 apartment buildings in two Swedish municipalities and strategies for lowest LCC and code compliance. Applied tools were thoroughly validated and verified including heat demand and load duration curves and numerical accuracy. Results with all aggregated clusters and renovation strategy for code compliance showed a reduced combined heat and power production with 35.7 GWh/a (heat) and 6.5 GWh/a (electricity), deceased primary energy use with 36.2 GWh/a and reduction of marginal CO2 emissions with 8.4 kton/a mainly from released biofuels substituting for fossil fuels in power plants, increased CO2 emissions of 0.5 kton/a with electricity production mix, and financial deficit for building owners, energy companies, and industries of respective 44, 33.9, and 2.2 M€/50a.

Energy-related cooperation using industrial excess heat (IEH) in district heating (DH) networks shows economic and environmental benefits. A rarely investigated approach is the energy cooperation which incorporates a jointly operated CHP plant also producing process steam for nearby industry. The present study aims to evaluate economic and environmental effects on the Hofors DH system with jointly operated CHP plant when the nearby steel mill extends the supply of recovered IEH. Various IEH supply opportunities with different capacities of hot water and steam were designed and compared with existing IEH utilization, plant heat and electricity production and DH system performance. The energy system model MODEST is used for cost-optimization. A parametric study is used to analyze influences of increasing IEH cost and fluctuating electricity prices. The results show advantages for the DH system to utilize IEH for deliveries of DH and process steam and the cogeneration of electricity. Economic and environmental benefits are decreased total system cost (-1.67 MEUR/a), less use of fuels and electricity, and reduced CO₂ emissions with a maximal reachable amount of 28,200 ton/a when the use of biofuel is assumed as limited resource and the substituted marginal electricity production is based on coal condensing power plants. The results also show that industrial steam is a preferred heat supply source as long as the steam cost is below the alternative heat production cost, irrespective of the electricity price. While the cost-effective utilization of industrial hot water for DH is more sensitive and affected by a beneficial CHP production based on higher electricity price segments, it is also shown that utilization of continuously supplied industrial hot water is limited during seasons of low DH demand.