Analysis of operation of heat exchangers of a heating system in the arrangement of reliable and safe heat supply of residential buildings

Abstract

The arrangement of heat supply of residential buildings with independent connection to external heating networks is considered, which ensures the reliability of heat supply and the necessary comfort in the premises in cold weather conditions after the official termination of the heating season or before it begins due to the supply of water from the return main of the heating network after the DHW heat exchangers. A mathematical model describing the non-stationary modes of operation of heaters of the heating system under the conditions of the implementation of this arrangement is constructed and studied. Calculations were carried out using this model, including numerical simulation on a computer using the Monte Carlo method. It is established that in this case, due to fluctuations in the waste water consumption following the daily variation in water consumption at the DHW, there occurs a decrease in the average heat transfer coefficient of the heater of the heating system and its temperature efficiency due to the fact that these values depend on the flow rate in a non-linear way, and their growth during the period of increased water intake at the DHW does not compensate for the decrease during the reduction of water consumption. It is noted that in this case, the reduction of the heat transfer coefficient lies within the usual error of engineering calculation, and this effect can be neglected. It is proved that, with a small number of heat transfer units in the heater of the heating system attributed to the heated flow, the total amount of heat transferred can decrease quite significantly (by up to 30 percent); however, with a rational choice of the heater size, such a decrease is within the limits allowed by the margins applied when setting the flow rate of delivery water and determining the heat transfer area.