Abstract
The lowering of the temperature graph in the lower-level heat networks is often carried out by a mixture of coolant from the return pipeline at mixing pumping stations in order to maintain the set temperature of the mixed water. In this case, part of the heat carrier is not returned to the source of thermal energy, but it circulates in the circuits from the mixing station to the lower consumption nodes. The presence of such circulation flows leads to the absence of a stabilizing moment of the temperature field when it is calculated by traditional methods, as well as to the “looping” of the computational process and the impossibility of obtaining a solution. In work to overcome these problems, a new computational scheme for commissioning calculation is proposed, which is based on: (a) decomposing the calculation of the thermal-hydraulic regime into calculations of the hydraulic and temperature conditions; (b) using the conditional regulator of the ratio of the mixing station’s output costs in calculating the hydraulic regime; (c) fixing the temperature at the station’s output when calculating the temperature regime; (d) iterative calculation with correction of the setpoint of the ratio controller of the flow rate based on the calculation of the temperature regime.
Highlights
Schemes of many heat supply systems (HSS) of large cities include such control elements as mixing pump stations (MPS)
The need for such a transition is dictated by the type of heat insulation of the pipelines, which is sometimes not designed for high temperatures, and/or the scheme for connecting heat consumers to the heat network (HN)
MPS are common in systems that have many compactly located consumers with direct connection to the HN and low heat load, when it is impossible to organize elevator water mixing at the consumer due to low flow of coolant or insufficient available pressure
Summary
Schemes of many heat supply systems (HSS) of large cities include such control elements as mixing pump stations (MPS) These elements are used to lower the temperature in the supply line due to the addition of water from the return pipeline. The installation of pumps in the MPS is not on the jumper but on the return pipeline up to (along the coolant path) the mixing jumper (together with an uncomplicated automation circuit) allows to provide a return water pile, and to reduce the pressure in the return pipeline for consumers after the MPS, it requires installation of larger pumps. When controlling the HSS mode, the value of the water admixture from the return pipeline maintains the temperature of the mixed water at the outlet of the MPS for consumers in the supply zone In this case, part of the coolant, not reaching the sources of heat energy (SH), returns to consumers (Figure 2). The required calculation time increases very significantly, and the solution cannot be obtained in some cases, for example, if the MPS is installed on a ring network in a HSS with several sources
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