Energy Planning of Future District Heating Systems with Various Energy Sources

The successful development of a district heating (DH) system requires deep understanding of operation issues. This includes the integration of new energy conversion technologies, control strategies, and economic issues. Different energy sources can be utilized as a primary energy input in the DH systems. Nowadays, the focus is on reduction of the use of fossil fuels and a shift toward renewable alternatives. New developments in the building sector emphasize the application of new design forms and materials, trying to reach the desired lower certified level of energy use. This is corroborated by European Directive 2010/31/EU, stating that, by the end of 2020, all new buildings should be nearly Zero-Energy Buildings (nZEB). The directive pushes society toward the rational use of energy in the building sector. In its deeper analysis, it can be concluded that the DH companies experience the reduction in heat demands. Furthermore, much discussion has taken place regarding the lowering of temperature levels in the DH network, allowing better energy utilization and the application of low temperature excess heat. In this context, DH systems and energy units are becoming more complex and sophisticated; therefore, the need for profound knowledge of DH operation arises. This thesis discussed different issues associated with the operation of energy production units integrated to DH systems. Therefore, the studies presented in this thesis shed light on operation of DH systems under the three main points. The first concentrates on customers’ impact on DH operation. Hence, the reduction in heat demand, different temperature levels, and available control strategies were analyzed. Next, debates were held about the investment decisions that DH companies face when there is a need to extend or develop energy production units. This included the analysis of units’ sizes, heat load fluctuations, fuel price volatility, mutual effects, and technical limitations. The third research point demonstrated how DH operation could question existing legislation guidelines. In this thesis, Aspen HYSYS process simulation software was employed for the simulation of energy units. Data post-processing was carried out by MATLAB. Sensitivity analyses of the performed studies were performed under the annual heat and electricity loads obtained from the energy monitoring system of the university campus. The results found that effective plant operation was highly dependent on heat load profile. The operation of a Combined Cycle Power Plant (CCPP) connected to low energy building stock was rather difficult. This means that the CCPP is suitable for high-density heat areas, while it has poor energy performance indicators in low heat density areas. Further, the analysis of possible solutions for supplying the DH system with several energy supply technologies found that proper evaluation of all the risks associated with the choice of installation and investment could lead to significant savings in a long-term operation of a DH system. This is highly relevant due to changes in heat load profiles, legislation amendments, and improvements in energy saving measures. The existing method for heat supply optimization, which is based on the methodology of finding the optimal generation mix in some target year, is found to be a simple way to deal with the costs and operation issues. A number of additional important factors affecting plant operation are missing. Analysis of the allocation factors found that the allocation of fuel, emissions, and operation expenses in Combined Heat and Power (CHP) plants, performed according to standard EN15603 was sensitive when annual operation was considered. Therefore, the decision regarding allocation methods should be carefully analyzed before implementation in the standards, pricing models, and different policies. Mistaken allocation could disable benefits from cogeneration technology and distribution systems. The results of the allocation analysis presented in this work could be used by designers of CHP systems and policy makers, as a tool for developing an emission trading system for CHP plants and for the pricing of heat and power. The literature review of different factors leading to the premature breakup of the distribution network showed that it is very important to be aware of existing degradation mechanisms and prevent them in good time. Operation of the DH system with the various energy sources, following different control strategies, is a rather complicated process. In addition, legislation amendments put an extra pressure on DH companies. Based on the process simulation and feasibility studies, the presented information fits well within the issues associated with the operation of DH systems. Further, the performed studies provided valuable information, applicable for operation analysis, control strategy development, and growth of DH networks

Uncertainty of the allocation factors of heat and electricity production of combined cycle power plant

There are many different methods for the allocation of CO2 emissions in Combined Heat and Power plants. The choice of allocation method has a great effect on energy pricing and CO2 allocation in Combined Heat and Power plants. The power bonus method is the main method used for the allocation of CO2 emissions between heat and power production in the European Union and given as a standard. Aside from this method, six different allocation methods were tested on the Combined Cycle Power Plant in this study. Operational and design parameters of the Combined Cycle Power Plant were taken into consideration during analysis. The District Heating system, with an annual heat load of 27 GWh and maximum heat effect requirement of 14 MW, was chosen for the simulation model. This load was represented by the university campus. The energy source for District Heating was a Combined Cycle Power Plant with supplementary firing technology and natural gas as a fuel. The modeling of the system was carried out by the simulation software Aspen HYSYS, while data post-processing was done by MATLAB. Sensitivity analysis of the different allocation methods was performed for the Combined Cycle Power Plant under a yearly heat and electricity load. It was noted that different allocation methods produce different allocation factors. The differences between heat allocation factors for design and operational conditions were small. The most sensitive method was the power bonus method. The study showed that the decision regarding allocation method should be carefully analyzed before implementation in the standards and different policies, because benefits from cogeneration technology and distribution systems should be enabled. The results obtained in this study can be used by designers of Combined Heat and Power systems and policy makers, as a tool for developing an emission trading system for Combined Heat and Power plants and for the pricing of heat and power

Energy planning of district heating for future building stock based on renewable energies and increasing supply flexibility

This paper discusses factors associated with the decisions on energy supply plants in new or existing district heating (DH) systems. Three highly efficient energy conversion technologies were considered. The study focused on an assessment of the heat supply units, considering the economic aspects and technical limitation of the technologies. Further, risks associated with the changes in heat load profiles and fuel price volatility were investigated. The existing method for heat supply optimization was compared with a new method, suggested in this paper. The new method was based on detailed performance simulation models developed in Aspen HYSYS software and data post-processing in MATLAB. The results showed that the existing method for the heat supply optimization cannot demonstrate all the advantages of highly efficient conversion technologies. The study on the new method examined 36 plant combinations and identified eight with a levelized cost of energy (LCOE) under 0.15 EUR/kWh. The results showed that an increase in the flexibility of DH provided better heat supply reliability, while increasing the heat cost. The total deviation in LCOE due to fuel and electricity price volatility was in the range of 1.6%–3.6%. Further, a change of 20% in the plant investment costs induced almost the same variation in LCOE

Energy planning of district heating for future building stock based on renewable energies and increasing supply flexibility

This paper discusses factors associated with the decisions on energy supply plants in new or existing district heating (DH) systems. Three highly efficient energy conversion technologies were considered. The study focused on an assessment of the heat supply units, considering the economic aspects and technical limitation of the technologies. Further, risks associated with the changes in heat load profiles and fuel price volatility were investigated. The existing method for heat supply optimization was compared with a new method, suggested in this paper. The new method was based on detailed performance simulation models developed in Aspen HYSYS software and data post-processing in MATLAB. The results showed that the existing method for the heat supply optimization cannot demonstrate all the advantages of highly efficient conversion technologies. The study on the new method examined 36 plant combinations and identified eight with a levelized cost of energy (LCOE) under 0.15 EUR/kWh. The results showed that an increase in the flexibility of DH provided better heat supply reliability, while increasing the heat cost. The total deviation in LCOE due to fuel and electricity price volatility was in the range of 1.6%–3.6%. Further, a change of 20% in the plant investment costs induced almost the same variation in LCOE.acceptedVersion© 2016. This is the authors’ accepted and refereed manuscript to the article. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0

Analysis of energy signatures and planning of heating and domestic hot water energy use in buildings in Norway

Widespread introduction of low energy buildings (LEBs), passive houses, and zero emission buildings (ZEBs) are national target in Norway. In order to achieve better energy performance in these types of buildings and successfully integrate them in energy system, reliable planning and prediction techniques for heat energy use are required. However, the issue of energy planning in LEBs currently remains challenging for district heating companies. This article proposed an improved methodology for planning and analysis of domestic hot water and heating energy use in LEBs based on energy signature method. The methodology was tested on a passive school in Oslo, Norway. In order to divide energy signature curve on temperature dependent and independent parts, it was proposed to use piecewise regression. Each of these parts were analyzed separately. The problem of dealing with outliers and selection of the factors that had impact of energy was considered. For temperature dependent part, the different methods of modelling were compared by statistical criteria. The investigation showed that linear multiple regression model resulted in better accuracy in the prediction than SVM, PLS, and LASSO models. In order to explain temperature independent part of energy signature the hourly profiles of energy use were developed.The authors gratefully acknowledge the support from the Research Council of Norway through the research projects: the Research Centre on Zero Emission Neighbourhoods in Smart Cities (FME ZEN) and Energy for domestic hot water in the Norwegian low emission society under VarmtVann2030 within EnergiX program.publishedVersio

Importance of Increased Knowledge on Reliability of District Heating Pipes

District heating (DH) is a service that satisfies customers’ demands in the areas of heating, hot water preparation and the supply of heat to ventilation systems. Three generations of DH distribution technology are already in operation; the next generation of low temperature district heating (LTDH) will soon be upon us. However, without a reliable distribution system, it is quite difficult to utilize the concept of LTDH and remain competitive in the energy market. For that reason, this paper provides a comprehensive review of pipe reliability issues associated with DH systems. In this regard, discussions have been concentrated on factors leading to pipe degradation processes. Three groups of factors, namely physical, environmental and operational, were identified and examined. Allowable heat losses in the DH network and the creation of a pipe failure database were also discussed. The information collected in this paper leads to a better understanding of pipe degradation mechanisms and can be used as a tool for pipe failure prevention

Future Trends in District Heating Development

Purpose of Review: This article describes challenges that should be overcome towards implementation of low-temperature district heating (LTDH). The trends in development, operational issues, and legislative framework were revised. Recent Findings: The new substation design with solutions to avoid legionella bacteria issue, improved network topology and control strategies, opportunities of LTDH for buildings under various renovation stages and construction year were identified as the most crucial for the transition to 4th generation district heating (DH). Importance of heat load aggregation to avoid peak load issue in the areas with low-energy buildings (LEB) and solutions for transition from high temperature to low temperatures in the DH network have been shown. Summary: The findings indicate that there is a huge potential for achieving low-carbon society and improvement in energy efficiency under transition to LTDH. The solutions for transition from high-temperature DH to LTDH exist; however, they need good policies and market availability to be implemented

Implementation of CCPP for energy supply of future building stock

European Directive 2010/31/EU stated that by the end of 2020 all new buildings should be nearly Zero-Energy Buildings (nZEB). Since such buildings require a low quantity of energy for heating, they can utilize energy from the return line of a District Heating (DH) system. Further, this new type of buildings can successfully be integrated into the fourth generation of heat distribution technology, which is the new trend in the DH industry. On the other hand, existing building stock has a service lifetime of around 50 years, indicating that the required supply temperature in the DH system cannot be lowered beneath a certain level. Hereafter, together with new types of buildings and different policies, this could lead to changes in heat demand profiles of the DH system. The above-mentioned situation in the building market will lead to changes in heat load profiles and unavoidably influence the performance indicators of energy conversion units. Therefore, the focus in this paper was devoted to operation analysis of ethanol-based a Combined Heat and Power (CHP) plant with combined cycle technology under changeable demand conditions and different temperature levels in the DH system. In this paper different temperature levels of the DH system together with two temperature control strategies were considered. Further, the analysis included different heat demand profiles. The analysis was performed in Aspen HYSYS simulation software and data post processing was made by MATLAB. The results found that effective plant operation is highly dependent on heat load profile. Temperature control strategies did not induce a significant change in overall power production in CHP. The decrease in the supply temperature did not show a significant impact on plant performance. However, increase in temperature difference between supply and return lines led to higher power production and better overall plant performance. Further, it was concluded that it is rather difficult to operate CCPP connected to low energy building stock. This means that the CCPP is suitable for high-density heat areas, while it has poor energy performance indicators in low heat density areas

Challenges and potentials for low-temperature district heating implementation in Norway

Current district heating (DH) systems with high temperatures are facing many challenges that may decrease its competitiveness. Some of the challenges are decreased heat demands due to energy efficient buildings and high return temperatures that decrease possibilities for utilization of renewable heat sources. Low temperature DH (LTDH) systems have opportunities for utilization of waste heat and renewables and lower distribution losses. Therefore, the aims of the study were to analyze the challenges in the transition to LTDH and to estimate the increased competitiveness in low heat density areas. Since the heating density is an important factor for the DH competitiveness, the high and the low heat density area were analyzed. A building area consisting of the passive house and low energy buildings in Trondheim, Norway, was analyzed. The hourly DH network model was developed included both thermal and pressure losses. The results showed that the heat loss could be reduced by lowering the supply temperature from 80 °C to 55 °C. Analysis of the return temperature showed that LTDH could provide a lower return temperature than the existing DH system, regardless of the faults. Competitiveness of LTDH might be decreased for the heat densities lower than 1 MWh/m. © 2018 Elsevier LtdChallenges and potentials for low-temperature district heating implementation in NorwayacceptedVersio