Research On Hydraulic And Thermal Characteristics Of Existing Hot Water Heating System

In recent years, urban central heating is in rapid development in our country. However, with the expansion of the scale of central heat-supplying, heating pipe network systems increasingly highlighted some defects, such as lack of heat-supply capacity, high cost of heat-supplying, inappropriate regulation mode, ect. These problems have been seriously affecting the heating effect and causing highly waste of energy and resources.Hydraulic and thermal characteristics of hot water heating system affect not only the heating effect of heat consumers, but also the energy consumption at heat sources and cycling power consumption of pipe network. Therefore, the reserch on hydraulic and thermal characteristics of existing hot water heating systems is an inevitable demand for the development of central heating and is the necessary premise of formulating reasonable running or transforming programs.In this thesis, hydraulic and thermal characteristics of hot water heating system are the researching objects,the following contents are studied:(1) Hydraulic and thermal conditions for heating stations with indirect connection and water-mixing connection are analyzed. By deriving the mathematical model and calculating the example, the hydraulic and thermal characteristics in indirect connected heating stations under different regulating programs combination of first-degree and second-degree networks. For water-mixing heating systems under different regulating programs combination of first-degree and second-degree networks, the pipe impedance and power of water-mixing are calculated and analyzed.(2) Four-way water mixer, as a new type of connection device in heating systems, is introduced with its hydraulic and thermal characteristics. The objective situations that suitable for applying the Four-way water mixer to reform the heating system is proposed.(3) For the systems that radiant-floor-heating consumers and radiator-heating consumers are both existed, the affection to the heat gains and thermal comfort of both the two kinds of consumers that caused by the Difference between the actual parameters of heat medium and their design values. For the necessity of supplying heat medium with different parameters to radiant-floor-heating consumers and radiator-heating consumers, a new connecting form in heating station is proposed. Through the deriving of the formula, practicability of the new connecting form is illustrated. (4) From the viewpoints of both systems and users, the problem that the heat that needed and the heat that supplied don't match is being proposed. The significance of on-demand heating is analyzed. Then the energy conservation effect of using variable frequency pumps in the second-degree pipe network that the actual heating load is smaller than its designed load is calculated. The effect on energy saving by the structure of pipe network is analyzed. System monitoring schemes that correspondent with on-demand heating is proposed.