Optimization of the Parameters of the Heat Network Under a Reduced Temperature Schedule

Abstract

The economic and environmental problems of Ukraine lead to decrease the water temperature in heat supply systems. Increasing the cost of fuel made it inappropriate to schedule temperature 95/70. To switch to a lower temperature schedule, at first it is necessary to ensure the automation of the regulation of individual heat points. Only after that it is possible to use reduced temperature schedules. This is confirmed by the successful experience of countries where central heating is widely used: Denmark, Germany, Finland, Sweden, Holland, etc. Modernization of the heat supply systems of Ukraine should go through transition to independent heating systems with qualitative and quantitative regulation, after which the temperature schedule can be reduced to appropriate values. A numerical study of the optimal temperature and water flow in the heat network depending on the design and operating parameters has been carried out. In addition, the results of field studies of the heating characteristics of residential buildings and administrative buildings, the heat supply of which is carried out from two big sources of Kharkov, were used. The entropy production in the heat supply system is numerically determined depending on the design and operating parameters. As a result of the computational experiment, when using entropy production as an optimization criterion, the parameters of the reduced temperature schedule of the heat supply system for the conditions of Kharkiv were determined and substantiated. The results of the numerical study show that the parameters of the heat network at maximum heat load and outdoor air temperature (-25 °C) are as follows: the temperature of the supply network water is 76.7 °C; heat carrier flow rate is 5.7 kg/s, velocityis 0.73 m/s, specific pressure loss is 85.3 Pa/m, specific consumption of electric power to transport the heat carrier is 0.81 W/m, specific heat loss is 33.8 W/m.