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Providing consumers with heat of the required quality in the required quantity is quitea tall order. This is due to various laws of time variation in thermal loads of residential, public and industrial buildings, and the high inertia of district heating systems. Currently, new technical capabilities have appeared that make it possible to implement methods of quantitative and qualitative regulation of heat load in heat supply systems, which have a number of advantages over qualitative regulation. Based on the equations of heat transfer, thermal and hydraulic balance, the article shows the interactions between the parameters of various types of heat supply systems, viz. valve opening degree, throughput capacity, flow rate, and coolant temperature. The type of flow characteristics of the control valve, temperature characteristics of heat supply systems, temperature control characteristics, thermal and hydraulic characteristics of the regulated area are determined. The purpose of the article was to consider the influence of the maximum throughput capacity of the control valve on the thermal and hydraulic characteristics of dependent and independent water heating systems. As a result of the analysis of the thermal and hydraulic characteristics of heating systems, recommendations have been developed for selecting valve parameters to ensure high-quality temperature control. For independent heat supply systems with a heat exchanger, it is recommended to install a control valve with a concave (logarithmic, parabolic or other) characteristic. In the case of installing a valve with a linear characteristic, the heat exchanger throughput capacity need to be greater than the maximum throughput capacity of valve (the pressure loss of the medium flow in open valve is higher than the pressure loss in the heat exchanger). For dependent heat supply systems, it is recommended to install a control valve with a linear characteristic and a maximum throughput capacity five times less than the throughput capacity of the jumper.
Providing consumers with heat of the required quality in the required quantity is quitea tall order. This is due to various laws of time variation in thermal loads of residential, public and industrial buildings, and the high inertia of district heating systems. Currently, new technical capabilities have appeared that make it possible to implement methods of quantitative and qualitative regulation of heat load in heat supply systems, which have a number of advantages over qualitative regulation. Based on the equations of heat transfer, thermal and hydraulic balance, the article shows the interactions between the parameters of various types of heat supply systems, viz. valve opening degree, throughput capacity, flow rate, and coolant temperature. The type of flow characteristics of the control valve, temperature characteristics of heat supply systems, temperature control characteristics, thermal and hydraulic characteristics of the regulated area are determined. The purpose of the article was to consider the influence of the maximum throughput capacity of the control valve on the thermal and hydraulic characteristics of dependent and independent water heating systems. As a result of the analysis of the thermal and hydraulic characteristics of heating systems, recommendations have been developed for selecting valve parameters to ensure high-quality temperature control. For independent heat supply systems with a heat exchanger, it is recommended to install a control valve with a concave (logarithmic, parabolic or other) characteristic. In the case of installing a valve with a linear characteristic, the heat exchanger throughput capacity need to be greater than the maximum throughput capacity of valve (the pressure loss of the medium flow in open valve is higher than the pressure loss in the heat exchanger). For dependent heat supply systems, it is recommended to install a control valve with a linear characteristic and a maximum throughput capacity five times less than the throughput capacity of the jumper.
The article discusses the current problems of transformation of existing district heating systems for the CIS countries within the framework of the development of trends in the integration of energy sectors, increasing the consumption of renewable energy resources, “decarbonizing” industry and digitalization of the economy. The experience of Western European countries in terms of the transition to “4th and 5th generation” district heating systems is considered. The technical aspects of the creation of hybrid control systems are analyzed, generalized structural technological schemes of hybrid district heating systems and the main measures, the implementation of which is necessary during their transition to the state of a new generation of district heating systems, are introduced. It is noted that the hybridity of the district heating system implies the presence of regenerative properties in terms of the production of energy carriers for use in adjacent systems, in particular hydrogen. In turn, the flexibility of the district heating system is largely realized via the development of accumulative properties, which leads to the invariance of the use of available energy storage technologies. It is argued that, despite the constantly decreasing costs of creating and operating an electric power storage system, thermal energy storage systems remain a priority in heat supply, especially when using renewable energy sources. The issue of using electricity in district heating systems as an excess resource of integrated energy systems within the framework of equalizing the daily and seasonal schedule of energy consumption is also considered. Also, a diagram is presented reflecting the technical solutions in terms of the equipment used to implement the “electricity – heat” technology. The problem of management of heat supply systems of a new generation is discussed. It is indicated that in order to ensure the required maneuverable properties of heat supply systems, it is necessary to develop and apply new methods of planning and managing heat supply systems, excluding a single-purpose approach in the organization of hybrid systems, which manifests a synergistic effect with new possibilities for finding optimal solutions aimed at reducing fuel consumption. The need to create an intersystem information space, which would include the creation of intelligent process control systems based on the analysis of large amounts of data, is demonstrated. It is noted that the main goal of operational management of hybrid thermal networks is to achieve a dynamic balance between the required value of the thermal load of consumers, the production of thermal energy and the volume of accumulation. The use of hybrid systems in heat supply makes it possible to solve the multifunctional task of increasing the reliability of energy supply and the stability of the functioning of the energy system, which is primarily achieved by solving the problem of balancing production and energy consumption capacities from the point of alignment of generation and energy consumption schedules. A separate consideration of the prospects for the use of hybrid district heating systems in the conditions of the Republic of Belarus is highlighted. The need for additional research to adapt known and develop new technical solutions within the framework of the transition of district heating systems to a new quality is shown.
The article discusses the methods of substitution of a compound motor load as a consumer of higher harmonics. Two substitution schemes were used. The calculation of the complex resistance against them was compared with the results of simulation modeling. The simulation was carried out in the MATLAB Simulink environment, with the use of the Specialized Power Systems library, in which a simulation model with motors and a source of harmonic distortion was developed. Five asynchronous motors with a squirrel-cage rotor of the AIR brand with powers varying from 0.75 to 5.50 kW were selected for the study. The simulation was carried out at different motor loads. The shaft torque varied with values of 50; 70; 90 and 100 % of the nominal values of each motor. A six-pulse diode rectifier was used as a source of harmonic currents in the network, generating harmonics with numbers 5, 7, ..., 25, corresponding to a pulse rate equal to six. Oscillograms of currents and voltages were recorded at the point of common connection of asynchronous motors and the rectifier, which were subsequently used to calculate the complex resistance. Based on the results of the work, amplitude-frequency and phase-frequency characteristics of the impedance of a composite motor load were obtained, the analysis of which revealed the incongruence of calculation methods with simulation modeling. Conclusions have been drawn on the need to continue research in this direction, since there are qualitative discrepancies in the functional dependence of the complex resistance on the harmonic number with the experimental data obtained for a single asynchronous motor. The results of the work can be used in calculating the voltage distortion factor and modeling modes associated with higher harmonics both at existing enterprises and during their design, which will increase the reliability and efficiency of electrical networks.
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