Analysis of operation of heat exchangers of hot water supply system in the scheme of reliable and safe heat supply of residential buildings

Abstract

The scheme of internal heat supply of residential buildings with independent connection of the heating system to the external heating networks and connection of the heater of the DHW system in a parallel single-stage arrangement, providing reliability of heat supply and the necessary comfort in the premises due to the unrelated regulation of heat supply for heating, ventilation and DHW even in case of fluctuations in water intake, is considered. A mathematical model describing the non-stationary modes of operation of DHW system heaters under the conditions of implementation of this scheme is constructed and investigated. 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, a decrease in the average heat transfer coefficient of the heater of the DHW system due to fluctuations in the flow of mains water following the daily change in water consumption at the DHW can be neglected, since this decrease lies within the usual error of engineering calculation, despite the fact that this coefficient depends on the flow in a nonlinear way, and its growth during the period of increased water intake for DHW does not fully compensate for the decrease during the reduction of water consumption. At the same time, it is proved that with a characteristic number of heat transfer units in a DHW system heater referred to the heated stream, the total amount of heat transferred can decrease quite noticeably, by an amount of 10 to 12 percent; however, with a rational choice of the heater size, such a decrease is within the limits allowed by the applied factors of margin when setting determination of the heat exchange surface.