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The temperature of the water returned to the heating network from consumers largely determines the energy efficiency of the heat supply system. It depends on a number of parameters: outside air temperature, hot water supply heaters connection scheme, daily water consumption in the hot water supply system. The calculation of this temperature is usually performed numerically, which makes it difficult to control the modes of the heat supply system. From a practical point of view, a simpler toolkit is needed. In this paper, equations are proposed that allow directly determining the change in the heat output of heat exchangers depending on the outside air temperature and the temperature of the network water returned to the heating network. These equations are obtained on the basis of systematic modeling of variable operating modes of the heat supply system, using the method previously proposed by the author. The operating characteristics of the heat station are taken into account by the coefficients of the equations, for the determination of which the calculation formulas were obtained. The equations used are valid for substations with a two-stage mixed scheme of hot water supply heaters in the mode of maximum water consumption.

Heat exchangers used in various industries, most often work in conditions of variable flows and temperatures. At the same time, the existing theories of calculation of heat exchanger modes are based on the use of constant dimensionless parameters in any mode of operation. The purpose of this work is to obtain dependencies to determine the effect of coolant temperatures on the variable parameter of the heat exchanger. Using the simulation method, dependencies were found that describe the change in the heat exchanger parameter which made it possible to obtain a general formula for the change in the heat exchanger parameter at varying coolant temperatures. To test the applicability of the existing relations describing the change in the heat exchanger parameter and the formula obtained, a large number of heat exchangers were calculated in variable operating modes. Comparison with the simulation results showed that the ratios of the known theories of heat exchangers do not work in all modes and their application can lead to significant errors. A formula has been obtained allows one to find the effect of coolant temperatures on the variable parameter of the heat exchanger. The formula can be used to predict the modes of large systems.

A screened enclosing structure of the outer wall of the building without the use of thermal insulation materials is proposed. To ensure the required thermal resistance of the outer fence, screens (cement-containing slabs) and closed air gaps between them are used. Using the ANSYS software package, the heat transfer processes were modeled in a shielded building envelope, consisting of the main (carrier) part and screens with air gaps closed between them. The features of the heat transfer process in the thickness of the outer enclosure are revealed.

The main task of energy-efficient heat supply is to ensure full compliance between the produced and consumed thermal power, subject to a minimum of reduced costs. To achieve this goal, various methods of central and local regulation are applied. Analysis of the thermal schemes of some cities in Russia showed that most of the heat sources of centralized heat supply systems are not able to support the design hightemperature graphs with central regulation. Therefore, the area of centralized qualitative method of regulation of heat load has decreased substantially. A perspective direction for the further development of heat supply systems is to appeal to the experience of foreign countries, i.e. the use of qualitative-quantitative and quantitative methods of central regulation and low-temperature heat supply. There is also an acute problem of the complete use of heat by consumers, since overstating of the temperature of the return water substantially reduces the efficiency of heat sources. A new formula has been obtained which makes it possible to predict the temperature of the return network water in variable operating modes of heating points. The resulting formula can be used to set up programmable regulators and will allow correcting irrational modes of operation of heat supply systems.