• Energy Research

District heating systems (DHS) are considered the best alternative to individual heat boilers as they have higher efficiency and enable the use of sustainable heat sources, like geothermal heat sources or waste heat from industry. Currently, most DHSs are operated by choosing a temperature once every day depending on the weather. This setting is chosen such that peak demand can be satisfied. However, when demand is lower, the supply temperature will be higher than necessary and heat will be wasted. In addition to this, heat production costs can be dynamic over time, which allows more cost-efficient heat production scheduling. By choosing a dynamic temperature over the day losses and operating costs can be reduced. However, determining these dynamic temperatures is not easy, as there are several factors that need to be taken into account to ensure that demand can always be fulfilled. In this research, the use of metaheuristics is explored for finding supply temperatures. Optimisation of DHS operations results in up to 5% savings with respect to typical heating curve operations. The second contribution is a method to determine a theoretical lower bound on the operating costs of a DHS, as this was not yet found in literature.

Decentralized surplus feed-in of solar heat into a District Heating Network (DHN) is here addressed. The heat collected from solar panels located on rooftops of DHN connected buildings may either be used locally for domestic hot water and space heating or fed into the DHN. Two-way substations able to transfer heat from and into the network seem then to be required utilities. The present paper presents the specifications (60kW capacity, return-to-supply connection) and promising architectures of such two-way substation based on a previous analysis. A first-of-a-kind Modelica-based dynamic model of the substation together with the consumer and the solar field connected to it is then detailed. Two-day simulations considering real operating conditions of DHN were then performed. The results highlighted i) the good match between the periods of solar heat reinjection with the periods of low supply temperature and differential pressure and ii) the decisive benefit of the reinjection to increase the part of useful solar energy.

Presented paper concerns the operational conditions of the District Heating System (DHS). The DHS consists of the Heating or CHP Plants and the District Heating Network (DHN) with substations and chambers. Usually, the substations are indirectly coupled with the heat consumers i. e., through heat exchangers. The chambers contain pipe fittings, controlling and monitoring accessories. The reference DHS are in operation annually for 200-230 days of heating season, and are supplying only hot water in the summer season. Heat supply to the consumers takes place through the same DHN during heating and summer seasons. The heat and hydraulic loads of the DHN is changing during operation and depend on present heat demand by the consumers. The heat demand for hot water supply during summer season is approximately 10 times less than nominal heat demand in the coldest wintertime. Different operational conditions of the DHS result in variable transportation losses by the DHN. On the basis of collected annual data (i. e. temperatures, pressures, water flow rates and weather conditions), operational analysis based on computer simulation for the DHS was performed. The result of the analysis allows verifying the models and calculation methods of fluid flow, heat losses and propagation of temperature waves in the DHN. Existing calculation methods of heat losses of the piping can be divided into two groups i. e., simplified and exact methods. The paper presents the results of the numerical calculation of the temperature distribution in the soil around the piping channel using FDA model. Also, the results of the numerical simulation of water and heat flow through the DHN, illustrated in the form of spatial diagram of temperature wave propagation in the particular section of piping, are presented in the paper. The DHN in Poland in the most cases are installed as underground, traditionally insulated piping placed in the concrete channels or underground, pre-insulated piping placed directly to the soil. Approximately, only 10\% of the piping are installed as above ground. The total quantity of the heat losses of the DHN is different for individual systems and depends on the size of the DHS, its heating loads and quality of insulation of the piping. Energy transportation through piping takes place in unsteady conditions. Changes in temperature and flowrate of water are observed. These changes have significant influence on the level of heat losses of the DHN. In order to compare the total quantity of the heat losses of the DHN for different systems, the indicator presented the percentage of the heat losses in the total heat transported through the DHN was defined. Results of numerical calculation show that : ・ Percentage of the heat losses in the total heat transported through the DHN in Poland are in the range 10-20\% for heating season and 25-50\% for summer season (usually the losses are two times higher in summer than in heating season), ・ Replacement of the existing channel piping for preinsulating piping could significantly reduce the percentages of heat losses to the level of 34\% in heating season and 7\% in summer, ・ Degree of cooling down of the network water could reach the level 12-16 K in summer season during night hours, ・ Changes of the network water parameters (decreasing temperature by 5-10 K, and appropriately increasing flow rate) in summer season could farther reduce the heat losses of the DHN.

District heating systems (DHSs) have the potential to play a big part in the energy transition. The efficient operation of DHSs is therefore also an important subject of study. The operation of DHSs where combined heat and power (CHP) plants are used are particularly interesting, because CHPs can operate with high efficiency. In this work, the operational optimization of DHSs with CHP plants is considered. Determining the optimal heat and electricity production for CHPs for multiple time steps into the future is a complex problem. Because of the heat storage capabilities in the network many solutions are feasible, but determining which solutions are infeasible because of constraint violations in the DHS involves computing time delays that depend on complex network dynamics. In this work, the possibility of using an input convex neural network (ICNN) to learn the network dynamics of a DHS is explored. ICNNs have limitations on their learning capabilities, but theoretically allow for easier optimization. Experiments on the learning capabilities of ICNNs reveal that caution should be used when they are used to learn non-convex constraints, as the accuracy of the ICNN highly depends on how non-convex the function is. Experiments on the feasible space of supply temperatures to a small district heating network (DHN) reveal that although the network does not provide the same flexibility as heat storage tanks, still some flexibility in the operation can be found. This is due to the fact that water with a higher supply temperature is consumed by consumers at a slower pace and this increases the time delay between production and consumption. Supply temperatures that follow can then be lowered if the increased time delay causes this water to arrive when the heat demands are lower. In the experiments it was found that this flexibility in operation translates to non-convex areas in the feasible space. When this space would be learned by an ICNN, this space would be made convex. How much of the flexibility would be removed by ...

Liberated heat market works mainly like a liberated electric market in Nordic countries with the exception that heat market works within a local district heating network. There are producers, customers, a network operator and a system operator as there exist in the electric market. Physical actors are the traditional large scale producers that sell heat to customers connected to the district heating network, and the end users, that would also be small-scale producers using a micro-CHP or a boiler. They would buy heat from other producers or sell heat to customers through the network. The liberated heat energy market will also need the transmission-network-company that takes care of the temperatures, pressures and hydraulic balance of the heating network. A balance-sheet-operator is also needed to coordinate the heat contracts between producers and customers as well as to take care of reserve capacity, spot and future markets and billing. The requirements for the district heating network design in the heat trading context are an aspect that still requires further attention. Our simulations showed that temperature changes were occasionally quite rapid in some parts of the network. They were caused by stagnation of flow in some loops of the network, where flows come from different directions. Small producers seem to bring more time-varying factors into the system. This might lead to a new district heating network design approach where temperature variations can be minimized. The four different physical connection types for the small scale producer in the building side were studied and the recommended connection version was found. The recommended connection version is type 3, in which the small scale producer is connected to the DH-network via heat exchanger. This connection has advantages compared to the other versions: it does not bring any changes to the standard modular substation unit in buildings, it is a safe solution to the user (no water leaks) and to the DH network (no gas leak problems), it is easy to control, it is suitable for new installations and renovations, and maintenance of the CHP unit does not cause any problems to the DH operation. In general, we found out that the physical connection will need standardized rules, in which the quality and the performance of the connection unit are unambiguously defined, same way as the current Finnish Energy Industries/District Heating Department's (earlier Finnish District Heating Association) guidelines do for the district heating substations. However, these new building level guidelines of the small scale producer were not defined in this study. Real option analysis is adopted to evaluate the risks of investment when electricity price and heat price are uncertain.

In order to reduce CO2 emission, district heat networks and carbon-neutral heat energy production are being developed in the Netherlands. This resulted in an increasing amount of district heating systems (DHS) in the horticulture areas. A DHS in a region called the ”B3-Hoek” connects multiple producers with horticulture companies in a single-buyer market model with long term bilateral contracts. This market model has some undesirable aspects that contribute to the willingness of introducing a short term heat market model in the system. However, such a short term market is still prone to market failures, if producers have considerable market power. The aim of this research is to investigate how a short term market can be designed for a DHS in the Netherlands, how producers and large consumers behave on a short term market and how this affects the performance of the market. An interactive simulation of a short term heat market was created, based on the DHS in the B3-Hoek to investigate this. The findings in this research give a conceptual model of the new market design and it showt that in a short term heat market prices will converge to marginal cost levels when market conditions are not tight. There is a balance of market power between the producers and the horticulture companies collectively. The results of short term market will not be comparable to the case of a perfectly competitive market due to Cournot competitive behaviour, but they can still be considered desirable for both horticulture companies and producers. ; Complex Systems Engineering and Management (CoSEM)

Työssä on esitetty pääpiirteissään Joutsenon Energia Oy:n kaukolämpöjärjestelmä lämpökeskuksineen ja kaukolämpöverkkoineen sekä toimintaa ohjaava lainsäädäntö. Kunnossapitoa on käsitelty ensin teoreettisesti yleisellä tasolla, keskittyen kunnossapitostrategioihin ja niiden valintaan, kunnossapitotiedon hallintaan sekä kunnossapidon organisointiin. Työn puitteissa otettiin käyttöön myös Komartekin kaukolämmön kunnossapito-ohjelma Lämpökunto sekä graafinen informaatiojärjestelmä MAP, johon mallinnettiin mm. Joutsenon kaukolämpöverkkojen johdot ja kaivot. Tutkimustuloksina on esitelty mahdollisuuksia tehostaa kaukolämpöverkkojen ja –keskusten kunnossapitoa ja käyttää Lämpökuntoa tässä apuvälineenä. Kaukolämpöverkoille tehtiin perusparannustarpeen kartoitus sekä keskustaajaman kaukolämpöverkon uusimiselle aikatauluehdotus. Lämpökeskuksia tarkasteltiin niiden energiataloudellisuuden ja käyttöluotettavuuden kannalta ja pyrittiin löytämään keinoja näiden tekijöiden parantamiseksi. The thesis was made for a municipal corporation, Joutsenon Energia Oy, which pro-vides its customers with electricity, district heat and natural gas. To begin with, the district heating system including the district heating centres and networks, as well as the binding legislation, are described in the work. Secondly, the general maintenance theory is presented. The main aspects covered in the section include the basic strategies, data systems and organising of maintenance. Subsequently, the maintaining of the district heating centres and networks is examined. The district heating centres are considered mainly in order to define their energy efficiency and reliability and also to discover potential to improve operations. Networks are studied in order to recognise the needs for fundamental improvement and if needed, the timetable for improvement is presented. In addition to all this, a maintenance software with a graphic interface was installed and adopted including the modelling of the district heating networks.

Tämän diplomityön tarkoituksena on selvittää mahdollisuuksia Kotkan Energia Oy:n kaukolämpöverkon ja aivan erityisesti sen käytön kehittämiseen. Kaukolämmön optimaalinen toimittaminen on tasapainoilua kaukolämpöveden virtausten ja lämpötilojen välillä. Kaukolämpöverkon käyttöä voidaan parantaa laskemalla syötettävän kaukolämpöveden menolämpötilaa muu tuotanto ja asiakkaiden tarpeet huomioiden. Lämpötiloja laskiessa verkon oikein ajoitettu varaaminen muuttuu entistä tärkeämmäksi tekijäksi, koska sen avulla voidaan vähentää varatehon käyttöä. Alhaisempi menolämpötila laskee kaukolämpöverkon lämpöhäviöitä, mutta lisää kaukolämpöveden virtausta kuluttajien tehontarpeen pysyessä vakiona. Välipumppauksen käyttö sekä matalammat paine-erot laskevat pumppaushäviöitä, mutta työssä tehtyjen havaintojen perusteella selvästi suurin vaikutus kustannuksiin on lämpöhäviöillä. Laitoskäytöstä vastaavat operaattorit ohjaavat myös kaukolämpöverkon käyttöä, mikä tekee heidän toiminnastaan kriittisen tärkeää kaukolämpöverkon käytön optimoinnin kannalta. Kaukolämpöakku havaittiin myös kannattavaksi investoinniksi, joka samalla vähentäisi tuotannon riippuvuutta operaattorien päätöksistä. The purpose of this master’s thesis is to examine the possibilities to improve the district heating network of Kotkan Energia Ltd and especially the way it is being used. Optimal supply of district heat is a balancing act between the flow and temperature of district heating water. District heating network usage can be improved by lowering the temperature of the water supplied. When doing so, other production and customer needs will have to be taken into consideration. As temperatures used in the network fall, heat storing becomes an increasingly important factor because it can be used to lower the need for backup heat production capacity. Lower feed water temperatures reduce the district heating network heat losses, but increase water flow as power demand remains constant. Use of intermediate pumping as well as lower pressure differences decrease pumping losses, but the costs of heat losses were found to be the most significant factor. Operators in charge of plant operation are also in control of district heating network usage. This makes their work extremely important considering the optimization of district heating network usage. District heat storage was also found to be a profitable investment that would help reduce the dependence on the production decisions of operators.

Increasing the building energy efficiency in recent years results in noticeably reduction in their heating demand. Combined with the current trend for utilizing low temperature heat sources, it raises the necessity of introducing a new generation of district heating [DH] systems with lowered operational temperature. However, in order to implement low temperature concept for existing DH systems, there is a need to apply a stepwise changes in the existing systems. This study emphasis on improving the existing DH pipes networks. For this purpose the first step is developing a model, which comprises district heating networks [DHN] characteristics.This paper is presenting a new developed model, which reflects the thermo-dynamic behavior of DHN. It is designed for tree network topologies. The purpose of the model is to serve as a basis for applying a variety of scenarios towards lowering the temperature in DH systems. The main focus is on modeling transient heat transfer in pipe networks regarding the time delays between the heat supply unit and the consumers, the heat loss in the pipe networks and the consumers’ dynamic heat loads. A pseudo-dynamic approach is adopted and also the implicit finite element method is applied to simulate transient temperature changes in pipe networks. The model is calculating time series data related to supply temperature to the DHN from heat production units, heat loads and return temperature related to each consumer to calculate dynamic temperature changes in the network, heat loss and temperature loss through the pipe networks. To validate the model and to demonstrate its competences, the model is applied for Studstrup district heating networks. Studstrup is a suburban area in Aarhus, Denmark where 320 consumers are connected to the DHN through approximately 14 km pipelines (supply and return pipes). At the first stage, the Studstrup DH system is developed in TERMIS, which is commercial software for district heating system simulation, and then the developed model is validated and compared with the results obtained from TERMIS and measurements. The TERMIS model is already validated towards measurements.This paper explains the developed model, which is going to be used for performing possible scenarios to improve the existing DHN from heat and temperature loss viewpoints. Moreover, it provides a platform to add and extend different aspect of DH systems.

With the decarbonisation of electricity generation, large scale heat pumps are becoming increasingly viable for district heating combined with thermal energy storage, district heating can provide flexibility to the electricity grid by decoupling demand from supply. This thesis examines how district heating with heat pumps and thermal energy storage can integrate with and provide a benefit to an electricity system with predominantly renewable generation. The scope of work comprises three interlinked models underpinned by the same set of meteorology data, fundamentally coupling supply and demand. First, heat load data are surveyed, and an hourly demand profile is simulated. Disaggregation of district heating loads from the national demand is accomplished via segmentation of the building stock to model heat demand at high spatiotemporal resolution. Second, a novel method of pricing hourly electricity in a zero carbon, capital-intensive renewable system with electricity storage is developed and applied to a dispatch simulation to generate hourly electricity prices. Third, a dynamic model of district heating is constructed to simulate the meeting of heat loads with different design configurations using electricity as the energy source. Model predictive control is applied with varying forecast horizons so as to minimise the cost of electricity to meet the heat demand given a time series of hourly prices and consequently optimising the capacity of thermal energy storage. It was found that a thermal energy storage capacity equivalent to 1.3% of annual demand is sufficient to minimise operating costs. Finally, the potential impact of district heating on balancing the electricity system is analysed and an equivalence between thermal and electric storage is examined. While this is highly dependent on annual conditions, it can be as much as 3.5 units of thermal storage for every unit of electrical grid storage on the system. This could potentially reduce the investment in grid storage by £36 billion, underlining the ...