Investigating the Possibility of Using Low-Temperature Heat Supply with the Central Qualitative Regulation

Nowadays, most heat sources of centralized heat-supply systems are unable to maintain the designed high-temperature schedules of the centralized regulation. Therefore, the area of qualitative regulation of the heat load has considerably reduced. The low-temperature heat-supply system is treated as the most plausible alternative to the high-temperature heat-supply system; however, no detailed calculations of the thermal and hydraulic modes for low-temperature schedules of qualitative regulation were carried out. This paper is devoted to the problems of providing the qualitative regulation of heat-supply systems and the possibility of switching to schedules with a lower design temperature without upper cutoff. The analysis of thermal schemes for some cities of the Russian Federation showed that the implementation of schedules with low design temperature of water in the supply line without upper cutoff does not increase the range of qualitative regulation and even reduces it in some cases. In a schedule without cutoff, the area of regulation is shifted to the region of lower outdoor temperatures, which allows for providing the optimum internal temperature. However, at low temperatures, the load of the second stage of the hot water heat exchanger is small, which makes it possible to provide the acceptable internal temperature even in a schedule with cutoff and with lower consumption of the water of heat-supply network. The most unfavorable internal temperature regime is observed near the breakpoint of the temperature graph when the load in the second stage of the hot water supply system's heater is at its maximum. At the same time, the breakpoint in the temperature graph without cutoff is located in the region of lower outdoor temperatures, when the heat losses are still high and even the acceptable values of the internal temperature are unavailable.