The Doctoral Thesis "Management and Control Methodology of the District Heating System", where the subject of research is the district heating network of Riga City district heating system (DHS) in the heat supply area of CHPP-1 and CHPP-2, is focused on a DHS with subjective necessary needs of consumers to have comfortable indoor temperature in buildings under our climate conditions, as well as to have hot water, by ensuring safe and efficient production and transmission of heat at the same time. The topicality of the subject matter of the Doctoral Thesis is based on the necessity to improve the DHS efficiency, which is related to the guidelines of the UN Convention on the Climate Change, to reduce emission of gases harmful to the climate into the atmosphere and to reduce consumption of primary energy resources. The objective of the Doctoral Thesis is to assess the interaction of all the DHS elements and to develop a methodological solution for management and control of DHS processes providing a higher contribution for reduction of CO2 emissions and improvement of the DHS efficiency. By performing a study on changes of the return temperature in the transmission system it is possible to reveal deviations from the normal condition. This means that there are changes in the system that need to be identified by other practical methods, for example: - examination of the consumers' systems by applying reading of heat meter data; - survey of the consumers' systems, compliance with the return temperature regime; - analysis of the results of monitoring of the control systems of transmission systems (heat pipelines without channels); - survey of heat pipelines above the ground and in channels; - inspection of the condition of shut-off fittings of heat chambers (verification of unauthorised interferences). The study demonstrates that trend graphs can be prepared for each heat supply system by using historical data and the limits of deviations of the return temperature can be established. As the return temperature is reduced, heat losses decrease electricity consumption for the network pumps decreases and energy consumption by the heat supply system decreases leading to reduction of CO2 emissions and consumption of primary energy resources. The operator of each system can identify the deviation fast by following the return temperature and comparing it to the trend graph margins and respond fast in order to prevent deficiencies in the DHS management. For more efficient use of the developed system it is necessary to develop a technical data management system which automatically follows and notifies deviations from settings. The Thesis also reviews availability of DHS energy sources, including renewable energy resources (wood chips), and the possibilities of their future use, the possibilities of improving efficiency of the use of fuel, assesses the role of heat transmission in the DHS development and the impact of existing and perspective heat consumers on the DHS development in the area subject to study. The Thesis consist of an introduction, four chapters reviewing the district heating system energy sources, the possibilities of improving efficiency of heat production, the role of heat transmission in the district heating system development and the impact of existing and perspective heat consumers on the district heating development, an experimental section, the result evaluation, conclusions, the list of references and annexes. The first chapter describes the availability of and the demand for energy resources used in district heating systems, in particular, availability of and demand for renewable energy resources and fossil energy resources. The potential of major renewable energy sources in Latvia, i.e. wood biomass, hydro energy and wind energy, and the possibilities of their use in energy are assessed. The second chapter assesses the possibilities of improving of fuel efficiency by using biofuel (wood chips) for heat production in the heat sources of Riga City district heating system. Within this chapter the forms of heat production in district heating, namely, combined cycle natural gas fired cogeneration, cogeneration units using wood chips, natural gas fired water heating boilers and water heating boilers using wood chips as the fuel, were compared. The study of the heat production units installed in the district heating system where wood chips are used as the fuel leads to the conclusion that, along with development of technologies, equal efficiency indices of fuel combustion to those of natural gas fired units can be achieved. The third chapter contains assessment of the role of heat transmission in the development of a district heating system, the analysis of specific and absolute heat losses and various measures of reduction of heat losses has been performed. The chapter summarises and analyses the results of the experiment identifying the link between the difference of the heat carrier temperature (T1 and T2) and the ambient air temperature in heat production sources CHPP-1 and CHPP-2 operating in Riga. The performed studies demonstrated that deviations from the normal condition, upon the change of the temperature difference in the transmission system can be revealed by applying the developed methodology. The developed DHS management and control methodology defines the function of the DHS at a particular difference of temperatures (ΔT). Curves above and below the regression curve correspond to the mean forecasted values of 95 % reliability interval and between them there is the optimum zone defining the operation of the district heating system. The fourth chapter contains the study of impact of heat consumers upon development of the district heating system, including the study of impact of change of the number of population, study of demand regarding the people's perceived quality of life, summarises information about housing development projects funded by the municipality and development territories, forecast of quantitative indices of living spaces, demand for non-residential areas and trends thereof. The chapter contains study of impact of improvement of energy efficiency of heat consumers upon the district heating system, including assessment of the current level of energy efficiency of buildings, technical possibilities of securing improvement of energy efficiency of buildings, sufficiency and conditions of funding, forecasted specific heat consumption in residential buildings in Riga. Forecasting of effective heat consumption is done according to a particular sequence of assessment due to the impact of multiple factors and uncertainties: forecast of heat demand in the residential sector of Riga city, forecast of heat demand by the non-residential sector in Riga; forecast of heat demand in particular heat supply areas of Riga city. The Doctoral Thesis has been developed in Latvian on 122 pages. The Thesis contains 57 Figures, 33 Tables, 83 formulas, 4 Annexes and 111 sources of reference have been used.