A. The principle of distributed variable frequency pump system
In the traditional heating branch pipe network system, a group of circulating pumps are generally installed at the heat source or in the heat exchange station, and the flow rate, head and number of circulating pumps are selected according to the flow rate of the pipe network system and the resistance of the most unfavorable loop; Each user end of the pipe network system is equipped with adjustment equipment such as manual regulating valve or self-operated flow control valve to consume the remaining pressure head of the user and achieve the hydraulic balance among the users in the system; individual existing heating networks are due to the user's heat load. Due to the change of the pressure head, the water supply or return water chemical pump is added, but because it is not easy to adjust, it often has an adverse effect on the upstream or downstream users.
With the emergence of new regulating equipment and control methods, it is possible to digitally control the water pump. In this way, the regulating equipment in the pipe network can theoretically be cancelled, and the speed-adjustable water pump can be replaced by a water pump with adjustable speed. Meet the requirements of subsequent hydraulic conditions. If the pressure difference of the appropriate node in the pipe network is controlled, this point is called the pressure difference control point. For the selection of the main circulating pump, as long as the resistance from the flow rate and the heat source to the pressure difference control point can be satisfied, the circulating pump can be greatly reduced. The lift of the main circulation pump reduces a lot; each user after the economic control point sets up a corresponding distributed variable frequency pump to become a distributed variable frequency pump system, so that the energy throttling by the original valve is no longer lost in vain, because the pump can be used with variable frequency The main circulation pump can greatly reduce the power consumption, and theoretically, the adjustment equipment can be omitted. At the same time, the heating system can work at a lower pressure level, and the system is safer. China Urban Heating Association has also listed the research and development of distributed variable frequency pump system as the "Tenth Five-Year" scientific and technological plan.
B. Design of distributed variable frequency pump system
In the distributed variable frequency pump system, the design should be carried out according to the following steps:
1. Pipe network system design, calculate the resistance of the pipe network.
2. Select the pressure difference control point. Different pressure difference control points correspond to different equipment initial investment and pipe network operating costs, and should be selected according to technical and economic analysis.
3. Choose the main circulating pump. The selection of the main circulating pump considers two aspects:
A: The flow requirements should be able to provide all the circulating flow of the pipe network;
B: The lift requirement should meet the resistance of the pipe network between the heat source and the pressure difference control point.
4. The selection of the distribution pump mainly considers the resistance and flow of the branch users.
C. Realization of distributed variable frequency pump system
1.The heating system consists of a 4×10t/h hot water boiler room and two inter-supply stations. The basic parameters are as follows:
(1) Heating building area:
Longnan Station: 181814.31m2
Longbei Station: 139891.62m2
Total: 321705.93m2
(2) Equipment: two main circulating pumps, one open and one standby, ISR200-150-400, power N is 90KW, flow rate Q is 400m3/h, lift H is 50m water column.
(3) Pipe network:
1-2 Pipe diameter DN300, groove length L=500m
2-3 pipe diameter DN250, groove length L=536m
3-4 pipe diameter DN250, groove length L=650m
According to the actual operation in recent years, the temperature of the heat source supply and return water is 105℃/65℃, the internal resistance loss of the boiler room is 10m water column, the resistance loss in Longbei Station is 10m water column, the internal resistance loss in Longnan Station is 5m water column, and the building heat index is 55kcal /m2h.
2. From the above parameters, the experimental transformation scheme is selected as follows:
1. Replace the main circulating pump of the boiler room with H=24m, Q=480m3/h, N=45KW variable frequency pump
2. One water supply plus one variable frequency pump in Longnan Station, H=12.5m Q=200m3/h N=15KW
3. One water supply plus one variable frequency pump at Longbei Station, H=24m Q=240m3/h N=22KW
4. The frequency conversion pumps of Longnan and Longbei stations are connected in parallel with the original pipe sections, and valves are added to the original pipe sections.
It should be pointed out that since the parameters of the pump cannot exactly meet the needs of the pipe network, there are different degrees of rounding in the process of equipment selection.
