Accounting for changes in the parameters of heating system water heaters when calculating the temperature schedule in district heating networks

   The operation mode of a water-to-water heater of a heating system is considered when it is independently connected to an external district heating network, ensuring reliable heat supply, stability of the hydraulic regime of the system and the necessary comfort in the premises. A mathematical model has been constructed and investigated that describes the variable operating modes of the heaters of the heating system during the heating period under the conditions of the implementation of this scheme and takes into account the change in the heat transfer coefficient of the unit and the mean temperature difference of the heat carriers in it. Based on the results of calculations using a computer program that implements an iterative algorithm based on the specified model, an analysis is provided of the behavior of the heat transfer coefficient of the heater during the cold period due to changes in the physical properties of water as a coolant when its temperature is regulated depending on current weather conditions. It is shown that at the beginning and end of the heating season, this coefficient decreases by about 20 percent compared to the mode of the coldest five-day period, but due to the non-linearity of the expression for the logarithmic mean temperature difference in the heat exchanger, its actual heat transfer under these conditions, when using a typical temperature schedule, is, on the contrary, about 20 percent higher than the required heat demand of the building. A solution to this problem is proposed through adjusting the temperature schedule downwards in both the supply and return pipelines at intermediate values of the outside temperature. The presentation is illustrated with numerical and graphical examples.

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