Analysis of reliable and safe heat supply of residential buildings using waste water after DHW heat exchangers

A modified scheme of heat supply of residential buildings with dependent connection to external heating networks, providing reliability of heat supply and the necessary comfort in the premises due to mixing of waste water after domestic hot water (DHW) heaters at an outdoor temperature exceeding the temperature graph break point, is considered. A review of possible ways to improve the reliability and safety of heat supply, improve the efficiency of heat sources, as well as regulate heat supply and prevent "overheating" near the beginning and end of the heating period is carried out. Calculations are carried out to determine the actual amplitude of temperature fluctuations in residential buildings with a daily variation in water flow rate after hot water heaters in the conditions of application of the considered scheme of connecting buildings to the heating network. Analysis of obtained results is given, and conclusions are drawn concerning the expediency of application of the above scheme. It is established that, given the thermal stability of enclosing structures, the daily flow rate fluctuations have no significant effect on the stability of the temperature regime of residential buildings and the comfort of their indoor microclimate at high outdoor air temperatures. It is shown that, in terms of reliability of heat supply of the main group of residential buildings and ensuring the life safety, the offered scheme is not inferior to the standard two-stage scheme of connection of DHW heat exchangers, with restriction of the total consumption of network water and with dependent control of heat supply to DHW, heating and ventilation. It is noted that in the scheme under consideration, the daily average consumption of network water to domestic hot water heaters over most of the heating period is higher or equal to the estimated consumption for heating and ventilation systems, which minimizes the time of using the mixing pump and provides for the regulation of heat supply only at the expense of the wastewater circuit.

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