Research On Diversity Of Hot Water Heating System Forms

This paper studied the diversity of central heating network forms, including heating network structures, connection types of heating networks and consumers and circulation power.Firstly, connection facilities in the heating substation are studied. Three types of network configurations, e.g. the unidirectional ring-shaped heat-supply network, the traditional supply-return two-pipe heating network and the cascade mixing water heating network, are studied in detail. Thermo-hydraulic model and thermo-dynamic accessibility of the unidirectional ring-shaped network are established respectively and then compared with the traditional two-pipe heating network. The definition and characteristics of the cascade mixing water heating network are studied. For the mixed one-pipe and two-pipe heating network, the method of thermal accessibility and flowrate accessibility judgment is proposed.Secondly, this paper classified the forms of heating network from the perspective of circulation and summarized the definitions and characteristics of different systems. Considering the variation of different circulation grades, the calculation pump power formulas are derived. The proper installation positions of mixing pump in three-way mixer system are studied according to the suitable pressure condition, and the pump power calculation formula is derived consequently. For the four-way mixing facilities, the pump power calculation formulas are derived which involving with water diversion ratio and heat user resistance.Then, economic index of different heating network forms are analyzed. The metal expense, annual operation cost of pump, annual operation cost of heating networks are compared in different heating areas to conclude the reasonable heating areas of different heating network forms. When the total heating load is constant and the proportion of heat users which require different water temperature is variable, the economy of different heating network forms(the unidirectional ring-shaped heat-supply network, the traditional supply-return two-pipe heating network and the mixed one-pipe and twopipe heating network) are compared. Optimal transformation schemes of expansions of two-pipe branch-shaped heating network are studied.At last, pump reforms and network expansion of a case study in Shenyang are conduted. Three pump reforms options are proposed, and based on the hydraulic simulation results, the pressure diagrams of the three programs are drawn and compared. The optimal schemes are evaluated from the perspective of economics. Three expansion schems are proposed for the western line and the best one is chosen via economic index analysis.