Reliability analysis in subsystem of heat supply

A set of mathematical models for calculating the reliability indexes of structurally complex multifunctional combined installations in heat and power supply systems was developed. Reliability of energy supply is considered as required condition for the creation and operation of heat and power supply systems. The optimal value of the power supply system coefficient F is based on an economic assessment of the consumers’ loss caused by the under-supply of electric power and additional system expences for the creation and operation of an emergency capacity reserve. Rationing of RI of the industrial heat supply is based on the use of concept of technological margin of safety of technological processes. The definition of rationed RI values of heat supply of communal consumers is based on the air temperature level iside the heated premises. The complex allows solving a number of practical tasks for providing reliability of heat supply for consumers. A probabilistic model is developed for calculating the reliability indexes of combined multipurpose heat and power plants in heat-and-power supply systems. The complex of models and calculation programs can be used to solve a wide range of specific tasks of optimization of schemes and parameters of combined heat and power plants and systems, as well as determining the efficiency of various redundance methods to ensure specified reliability of power supply.

Introduction. Renovation of housing stock supposes construction of new buildings, where the main utilities consuming heat energy will be heating and hot water supply (HWS) systems. Under such conditions the task of heat consumption reduction by transfer to low-temperature and use of the associated procedures is relevant. Materials and Methods. Research was performed on the basis of residential and administration buildings designed within the whole Russia, the facilities were selected based on the year of putting into operation and their purpose. The source of data concerning buildings became documents included into the scope of the design and detailed documentation: plans, drawings and explanatory notes. As meeting the demands of hot water supply makes the main contribution to daily nonuniformities of heat energy consumption, the attention was paid to equipment of hot water supply systems. For calculations, the commercial product of Microsoft Office Excel 2010 was used. Results. During selection of roof boiler house as a source of heat supply increase in consumption of equivalent fuel in relation to the variant of connection to heat power plant operating on solid fuel by 187,314 tons of fuel oil equivalent is possible. General refusal from power-and-heat generation complicates operation of large district heat supply systems. The design parameters of coolant in building heating system differ from project to project: from 95/70 °С, used everywhere till the beginning of the XXI century, up to 90/65 °С corresponding to existing practice of designing or 80/60 °С as at the facility in Sevastopol. Reduction of design temperatures by 5 % is insufficient to decrease general heat consumption of the building. Reduction of heat consumption is explained by selection of advanced materials for pipeline heat insulation. Use of automation diagrams for heat points on the basis of regulator ECL Comfort 310 contributes to improvement of hydraulic control for heating systems, however, concealed automation results in violation of high-quality mode for heat network control and decrease of coolant parameters on adjacent (often non-automated) consumers. Conclusions. Supplement of central high-quality control by local constant temperature/variable flow control at individual heat unit and installation of temperature controllers on heating radiators with mechanical thermostatic head have potential for reduction of the heat energy volume used ineffectively. Increase in level of controllability for heating system together with cheaper and responsive automation systems are basic conditions for increase in quality of heat supply in future.

Solar and geothermal energy systems are shown to have received the widest use among all kinds of renewable sources of energy for heat supply purposes around the world. The power capacities and amounts of thermal energy generated by solar and geothermal heat supply systems around the world are presented by way of comparison. The thermal power capacity of solar heat supply systems installed around the world as of 2015 totaled 268.1 GW, and the thermal energy generated by them amounted to 225 TW h/year. The thermal power capacity of geothermal heat supply systems installed around the world totaled 70.3 GW, and the thermal energy generated by them amounted to 163 TW h/year. Information on the geothermal heat supply systems in the leading countries around the world based on the data reported at the World Geothermal Congress held in 2015 is presented. It is shown that China, with the installed thermal power capacities of its geothermal heat supply stations totaling 17.87 GW and the amount of thermal energy generated per annum equal to 48.435 TW h/year, is the world’s leader in this respect. The structures of geothermal heat supply systems by the kinds of heat consumption used around the world are presented. The systems equipped with geothermal heat pumps accounted for 70.95% in the total installed capacity and for 55.3% in the total amount of generated heat. For systems that do not use heat pumps, those serving for pools account for the largest share amounting to 44.74% in installed capacity and to 45.43% in generated heat. A total of 2218 geothermal wells with the total length equal to 9534 km (with 38.7% of them for heat supply purposes) were drilled in 42 countries in the period from 2010 to 2014. In Russia, geothermal heat supply systems are in operation mainly in Dagestan, in Krasnodar krai, and in Kamchatka. The majority of these systems have been made without breaking the stream after the well outlet. A cyclic control arrangement is also used. The combined geothermal and solar heat supply system with an installed thermal power capacity of 5 MW that is in operation in the Rozovyi settlement, Krasnodar krai, is described. In the summer time, the solar installation with a capacity of 115 kW is used for supplying hot water to residential houses and for restoring the geothermal well pore pressure. The basic process circuit and characteristics of the geothermal heat supply system with the installed thermal power capacity of 8.7 MW operating in the Khankala settlement, the city of Groznyi, are given. The specific feature of this system is that the spent geothermal heat carrier is reinjected into a specially drilled inclined well. Advanced geothermal heat supply technologies involving reinjection of the spent geothermal heat carrier, combination with binary power units, use of heat pumps for recovering the spent heat carrier, and protection of equipment from corrosion and deposits are proposed.

In this work results of mathematical modeling and results of the pilot studies conducted at the laboratory stand for the system of heat supply of Kazan, the development of power of the large cities directed to development of an integrated approach at a research of problems are integrated. By means of the program Zulu complex the mathematical model intended for optimization of work of power systems during their operation has been created.Results of the conducted researches have allowed to analyse influence of stage-by-stage introduction at consumers of automatic metering stations and weather regulation (AITP) on a hydraulic operating mode of system of heat supply for large municipal associations. In this work the main criteria are also considered, the algorithm and a method of calculation of power efficiency is developed by optimization of systems of municipal heat supply by introduction of the automated individual thermal points (AITP). The questions of influence of the made technical solutions on financial and economic and investment indicators are raised. The considered actions for energy resources saving are investigated for the purpose of reduction of volumes of consumption or more rational use of fuel and energy resources.

Objectives. The aim is to justify the expediency of a transition en masse to independent connection of heat consumption systems under the conditions of pulse circulation of the coolant through the equipment of a heat supply unit in order to increase the overall energy efficiency of district heat supply systems.Methods. The research is based on methodologies for the effective use of technologies providing a means of effecting a pulsed motion of the coolant in the heat supply system. The advantages and disadvantages of known technical solutions are identified and summarised. Hydraulic accumulators or any other devices for damping a hydraulic shock can be used as devices for preventing the propagation of a wave of hydraulic shock into the transport mainline.Results. An analysis of approaches to heat consumption system connection is carried out in order to assess power efficiency; the most effective ways for improving the efficiency of heat and power devices are identified; a synthesis of the technical solution for the implementation of a technological connection of heat consumption systems is performed. The expediency of transition to independent connection of heat consumption systems under the conditions of pulse circulation of coolant in heat supply units is demonstrated. The independent scheme of connection of subscribers to the heat network is indicated as the most appropriate. The factors constraining the en masse transition to independent connection of the heat load are determined. Based on the analysis and scientific research in the field of increasing the energy efficiency of heat and power systems, the transition to pulse circulation of the coolant in the heat supply unit of the independent heat consumption system is selected. The presented technical solutions are confirmed by Russian Federation patents of inventions and utility models.Conclusion. It is shown that the use of pulse coolant circulation in the equipment of heat supply units for independent connection of heat consumption systems will increase the reliability and long-term operation of the recuperative heat exchanger, as well as increase the overall energy efficiency of the heat supply system.

One of the main directions for improving heat supply systems is the tendency to switch to low-temperature heating systems by using heat pump units is the tendency of implementation the low-temperature heating systems based on the use of heat pump units. In the work, the main attention is focused on the improvement of thermal parameters and circuit design features of elements of the heat pump system of heat supply using soil energy. For this purpose, the toolkit of mathematical modelling of processes in ground heat pumps is applied, taking into account the climatic conditions of Ukraine. The paper proves the technical possibility of creating an autonomous system of alternative heat supply for energy-saving technologies with the possibility of using ground energy, taking into account environmental requirements. It is substantiated that the use of the proposed systems is a promising direction for Ukraine, which is experiencing a shortage of its own energy resources, because it provides an opportunity to increase the share of organic fuel substitution and reduce the volume of heat emissions into the environment. A mathematical model of heat processes in the elements of the heat exchange equipment of the heat pump system based on renewable energy (soil energy) and secondary energy (wastewater) was developed, taking into account environmental requirements (preventing hypothermia of the soil during the operation of soil pipes and damage to vegetation, respectively), which allows choosing a rational mode of operation of the system under seasonal climatic changes and technological conditions. Numerical modelling of heat processes in elements of the heat exchange equipment of the heat pump system using groundwater and waste water was performed, and the energy and environmental efficiency of the system under variable climatic and technological factors was determined. Analysis and generalization of the calculation results of the heat pump heat supply systems using alternative energy based on the proposed mathematical model, taking into account environmental requirements (preventing thermal relaxation of the soil) allows to take into account the change in the temperature gradient around the soil heat exchanger and more accurately determine the heat flow from each section of the heat exchanger. It has been established that for heat pumps with soil heat exchangers, the maximum substitution ratio of the traditional fuel is 75 %, and the economically feasible quantity of soil heat exchangers is 9 units. Heat pumps using waste water can completely replace traditional heat supply systems. For individual consumers, it is possible to recommend heat pump units with soil heat exchangers, at the same time, it is necessary to provide a backup source of energy to increase the reliability of heat supply.

The paper considers the mathematical foundations of optimization of the geometric parameters of networks of centralized heat supply systems. As the target function of the optimization process, it is proposed to take the total heat losses that occur along the entire length of the studied section of the heat pipe from the source of heat supply to each of the consumers. Based on this, the geometric parameters of heat networks are modeled using instrumental means of determining the most rational positions of their branching nodes in order to identify economically feasible directions for laying each of the fragments of the corresponding networks. In order for the proposed approach to the optimization of heat networks to be conveniently applied in practice, additional mathematical tools should be introduced that allow taking into account specific urban planning conditions and restrictions imposed on heat supply systems and must be taken into account in the design process. In order to illustrate the simplicity of the proposed approach, the sequence of actions that must be performed to optimize the geometric parameters of the heat network is given. The corresponding sequence of actions was considered when modeling the elementary heat supply network. The application of the developed algorithm allows not only to reduce heat losses during transportation of the coolant from boiler rooms to consumers, but also, as a result, to increase the level of energy efficiency of the entire heat supply system, to achieve higher savings rates, and also to indirectly achieve tangible environmental and social effects due to the reduction of greenhouse gas emissions ( which could be formed during the burning of fuel for the production of additional thermal energy) into the atmospheric air and a potential reduction of costs for the heating needs of buildings on the part of subscribers (consumers). Obviously, the use and further improvement of the proposed algorithm will contribute to the gradual achievement of the goals of sustainable development.

An imbalance of thermal operating conditions in a subway has a negative effect on the microclimate in tunnels and stations and eventually leads to accumulation of “thermal pollution” of the soil strata surrounding the subway tunnels and facilities. In turn, such “thermal pollution” results in less intense heat removal to the soil and in air overheating in stations. One of the efficient methods for achieving better energy efficiency of the climate systems and for improving the microclimate in the Moscow Subway’s underground facilities is to use heat pump systems with recovery of the tunnel air heat for supplying heat and cold for station complexes. The article presents the main results obtained from experimental investigations of the thermal operating conditions at some stations of the Moscow Subway. In particular, air temperature in the subway tunnel spaces was measured in the summer and winter seasons. As a result, the main factors influencing the temperature operating conditions in the subway tunnels have been revealed. Based on the results of the experiments, it can be recommended to put heat pumps into operation in the tunnels for setting up a comfortable microclimate in the subway. As an example, the results from testing this process solution are presented through analyzing the efficiency of the heat pump-based heat supply system of the Salar’evo experimental station’s complex. The analysis of the Salar’evo station’s heat pump-based heat supply system has demonstrated its successful operation in the subway along with good compatibility between the subway systems and heat pump unit at the design and operation stages. Application of heat pump equipment in the heat and cold supply systems of subway facilities is not only significantly cheaper than the conventional technology in terms of one-time capital investments but also makes it possible to save more than 80% of energy in the course of operation.

In the modern world, the efficient use of energy is an extremely important aspect of human activity. In particular, heat supply systems have significant economic, environmental and social importance for both heat consumers and heat supply organizations. The economic status of all participants in the heat supply process depends on the efficiency of the functioning of the heat supply-systems. The reliability of the functioning of systems depends on vital processes such as the work of hospitals and industrial enterprises. With such a close network communication, reliable and efficient operation of power supply systems is critical. In this article, ways to improve the efficiency of heat supply systems are considered. A mathematical model for improved planning of heat supply systems by connecting the optimal set of new heat consumers is presented. For each single customer, when there is an alternative option for connecting this consumer to the existing heat network, it is possible to choose the only optimal solution. This becomes possible due to the restrictions and the procedure for selecting variants from a subset of binary variables corresponding to alternatives. The procedure for finding the optimal number of consumers for connection to the existing heat network is presented, which is the rationale for increasing the number of existing consumers of the heat network. The testing was carried out and the results of the mathematical model by an example of test heat networks are presented. Directions of further study of increasing the efficiency of heat supply systems and integrating the presented mathematical model with modern software complexes are determined.

Heat supply is the most important area for the provision of energy services to a wide range of consumers. This industry determines the well-being of society, social stability and competitiveness of the economies of many countries of the world. The processes of energy liberalization initiated in the early 1990s led to the emergence of new forms of heat supply management based on market interaction among producers and consumers of heat energy. In market conditions, the problem of optimizing heat supply systems becomes much more complicated, and its structuring becomes multivariate depending on the characteristics of the industry organization. To solve the problems of optimal functioning and development of heat supply systems in changing conditions, along with existing optimization methods, it becomes necessary to use new approaches focused on solving problems in some specific uncertain situations characterized by conflicting interests of the parties, and often defined as conflict. The paper presents a comprehensive scientific and methodological approach based on mathematical modeling for solving problems of managing the development and functioning of heat supply systems in a market economy.

Introduction. Despite the significant scale and importance of the heat supply sector for the country’s housing and public utilities, a number of persistent issues have accumulated in its operation, reducing both its reliability and economic efficiency. This underscores the need to identify directions for enhancing the performance and dependability of heat supply systems through the rational use of energy resources and to develop a comprehensive system of performance indicators. In line with Russia’s strategic policy documents, energy conservation is a priority for the development of the national energy sector, including urban heat supply, which creates opportunities to improve system reliability by reducing failures across networks and sources and to enhance cost-effectiveness through the rational use of energy resources. Materials and methods. The research applied logical analysis and systematisation methods. An analysis of publicly available data sources and expert studies in the field of heat supply made it possible to summarise and systematise practical experience in implementing energy-saving measures across the generation, transmission, and consumption stages of thermal energy. Results. A comprehensive set of measures aimed at improving the reliability and cost-effectiveness of heat supply through the rational use of energy resources has been developed and systematised. In addition, a framework of performance indicators has been designed to assess the effectiveness of heat-supply operations in the urban and municipal sectors, reflecting improvements in reliability and cost-effectiveness resulting from the proposed measures. Conclusions. Implementing the proposed energy-conservation and energy-efficiency measures across the stages of heat generation, transmission, and consumption will enhance both the reliability and cost-effectiveness of urban and municipal heat-supply systems. The suggested system of performance indicators will enable a comprehensive evaluation of the effectiveness of these measures in terms of the improvements achieved.

A review of the current world state of application of various heat supply regimes for public buildings is conducted. The efficiency analysis of the use of various renewable energy sources in combined heat supply systems is analyzed. An integrated heat supply system with successive heating of the coolant from low-potential renewable sources of heat (solar system) to high-temperature traditional heat sources (gas and pellet boilers) is developed. A mathematical model of the integrated heat supply system using renewable sources of heat is proposed. This model can be used to simulate the processes of heating rooms in the intermittent heat supply mode. The dynamics of heating of premises with various heating devices: with natural convection (radiator) and forced convection (fan coils) is carried out. During the heating season (2016–2017), the operation modes of integrated systems of alternative intermittent heat supply (ISAIHS) are studied. These studies are extremely relevant for solving the issues of rational use of energy resources. The proposed solutions show that the most effective use of renewable sources of heat can be only in an integrated approach to solving this issue. Also it should be noted the interaction of ISAIHS components: the heat source – the heating system – the characteristics of the building – the operating modes of the premises. As a result of the research, the boundaries of the effective use of various heat generators in ISAHS are established. The influence of the type of heating devices and insulation of internal walls on the effectiveness of ISAIHS operation is revealed. The full-scale tests of a pilot installation of an integrated heat supply system are carried out. The obtained results will help to use heat sources more efficiently with a two-period operation regime for new houses. This can be used to improve the energy efficiency of existing buildings.

The district heating system of Karaganda (Kazakhstan) is considered in the article. The characteristics of the existing cogenerators and the state of the pipeline networks are given. Given the analysis of the existing state of the entire district heating of Karaganda. Proposed the program for the integrated development of the heat supply system bringing world experience in implementing the main development and modernization of heating networks. Shown the experience of reconstruction of heat supply facilities in the city of Karaganda within the framework of the state loan program “Nurly Zhol”. Based on the statistical data on the development of the city of Karaganda and its heat supply system the predicted heat loads are given until 2030. Due to the shortage of available heat capacity, options for the development of a centralized heat supply system in Karaganda are given and analyzed.

The synthesis problem of energy supply systems includes the selection of proper heating and power generating units as well as energy integration. Such problems have been generally formulated as a linear programming (LP) problem. The structural analysis of the problem and solutions is focussed on rather than merely solved. As a practical consideration for preliminary selection of technologies, a problem regarding the selection of heating devices such as electric heaters, furnaces, steam heaters, or heaters with a heating medium under given loads is defined as a synthesis problem of optimal heat and power supply systems and formulated into an LP form with an objective function of minimum fuel. The results of analysis of the LP problem clarify essential structures of heat and power supply systems under arbitrary heat and power demands.

An important area of energy conservation is the use of energy efficient heat supply systems. Such systems are systems with heat pumps to utilize the low-potential heat of the upper layers of the earth's crust. The urgent scientific task is the development of designs of heat pumps to increase their efficiency. The distribution of heat pumps is acquired on the basis of vertical ground heat exchangers, with the promising implementation of these heat exchangers in the form of building piles, so-called power piles. The issue of their interaction is very important when designing heat pumps based on power piles, since the structural and bearing capacity establishes certain boundaries for the separation of foundation piles. Research of vertical soil heat exchangers is a popular theme of scientific developments, in particular, the most profound studies are conducted in the USA. Also, Belarusian specialists are specifically involved in the modelling of energy piles. Finnish companies make a major contribution to the development of geothermal energy based on power piles. The article deals with the systems of heat supply with a soil heat pump, which used as a evaporator building foundation piles, so-called power piles. The robots have constructively developed energy parameters of energy fingers. Considered basic working parameters: the number of U-piping tubes in the design of the piles; tube diameter; crock between piles; heat supply of the piles; distance between piles. Well-known studies on the design features of power piles and their impact on the energy performance of heat pumps are analysed. It was established that the least investigated area in this field is the method of engineering calculations of energy piles, namely, the mutual influence of energy piles one by one, that is, the minimum allowable distance between the foundation energy piles. For the mass implementation of power piles in the new construction, a scientifically sound method of selecting the optimal structure of the foundation energy piles is necessary.