Design and Application of Distributed Variable Frequency Pump System

1. The principle of distributed variable frequency pump system

　　In the traditional heating branch pipe network system, a set of circulating pumps are generally installed at the heat source or in the heat exchange station, and the flow, head and number of circulating pumps are selected according to the flow of the pipe network system and the resistance of the most unfavorable loop; The end of each user of the pipe network system is equipped with manual control valves or self-operated flow control valves and other adjustment equipment to consume the remaining pressure head of the user and achieve the hydraulic balance between the users in the system; individual existing heating networks are due to the user’s thermal load Due to the change of the pressure head, the capital pressure head is not enough, and the water supply or return water pressure pump is added. However, because it is not easy to adjust, it often has an adverse effect on upstream or downstream users.

　　With the emergence of new regulating equipment and control methods, digital control of water pumps has become possible. In this way, the regulating equipment in the pipe network can be eliminated in theory, and the water pump with adjustable speed can be replaced by the appropriate node of the pipe network. 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 choice of the main circulating pump, as long as the resistance of the flow and heat source to the pressure difference control point can be met, this can greatly reduce the circulation pump. The power of the main circulating pump motor drops a lot; each user after the economic control point sets the corresponding distributed variable frequency pump to become a distributed variable frequency pump system, so that the energy of the original valve throttling is no longer lost in vain, because the pump can be variable frequency The speed of the main circulating pump can be adjusted greatly, and the power consumption can be greatly reduced by the main circulating pump. In theory, 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. The China Urban Heating Association has also listed the research and development of the distributed variable frequency pump system as the “Tenth Five-Year Plan”.

　　2. 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 differential pressure control point. Different differential pressure control points correspond to different initial equipment investment and pipe network operating costs. The selection should be based on technical and economic analysis.

　　3. When choosing the main circulating pump, the choice of the main circulating pump considers two aspects:

　　A: Flow requirements, should be able to provide all the circulating flow of the pipe network;

　　B: The head requirements should meet the resistance of the pipe network from the heat source to the pressure difference control point.

　　4. The choice of distributed pumps mainly considers meeting the resistance and flow of users in this branch.

　　Third, the realization of distributed variable frequency pump system

　　In accordance with the above thoughts, Tangshan City Heating Power Corporation reformed the heating system of its Longdong boiler room. This article uses this as an example to illustrate the realization process of the distributed variable frequency pump system.

　　1. The Longdong heating system is composed of a 4×10t/h hot water boiler room and two intermediate 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 circulation pumps, one open and one standby, ISR200-150-400, power N is 90KW, flow Q is 400m3/h, and head 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

根据近几年实际运行情况，取热源供回水温度105℃/65℃，锅炉房内部阻力损失10m水柱，龙北站内阻力损失10m水柱，龙南站内部阻力损失5m水柱，建筑热指标取55kcal/m2h。

2、由以上参数，经计算选择实验改造方案如下：

1锅炉房主循环泵换成H=24m，Q=480m3/h,N=45KW变频泵

2龙南站一次供水加一台变频泵，H=12.5m　Q=200m3/h　N=15KW

3龙北站一次供水加一台变频泵，H=24m　Q=240m3/h　N=22KW

4龙南、龙北站变频泵与原有管段并联，并在原有管段增加阀门。

需要指出的是，由于水泵的参数不可能完全正好满足管网的需要，在设备选择过程中均有不同程度的取整。

3、按照锅炉房主循环泵提供锅炉房内部和1－2点阻力损失，各站分布变频泵分别克服2－3、2－4及站内阻力损失的原则，本年度我公司对改造后的龙东供热系统进行了调试运行。在调试过程中，我们本着在满足供热要求的前提下，尽量使两个热力站的一次回水温度平衡，并且在可能的情况下尽量提高分布变频泵的负荷，减少主循环泵的负荷，以期尽可能节约电能消耗。分布式变频泵系统投运后，与原有单点设置循环泵系统相比，电流消耗实测如下：

系统单点循环泵一台运行时消耗电流为130A；

分布式变频泵多点运行时，实测数据表如下：

4、分布式变频泵系统投运前后主循环泵出口压力由0.6Mpa下降为0.39Mpa。

5、分析

几台泵电机的功率因数差别不大，均在0.78－0.81之间，如不考虑其差异，节能率为(130－56－17.1－26.8)/130×100％=23.15％

四、结论

分布式变频泵系统是一种新型的水泵布置型式，与传统的单点布置相比具有如下优点：

1、节约电能；

2、系统整体压力水平较低，系统更加安全。

五、几点体会

1、由于主循环泵一般布置在热源回水，对于分布泵的布置（除主循环泵以外）应在热力站的供水或尽量靠近经济控制点处的供水管。

　　2. The constant pressure value of water at the water replenishment point should be recalculated. As it is generally difficult to arrange the distributed pump at the economic control point of the pipe network, when the distributed pump is arranged in the station, for the long branch line, It may cause the drift of the replenishment point. For this working condition, one method is to set the water replenishment point at the lowest point of the pipe network pressure, and the other method is to concentrate the water replenishment at the total return water of the heat source, and appropriately increase the constant pressure value of the water replenishment.

　　3. In the selection of equipment, the technical parameters of the main circulating pump should have a proper margin.

　　4. The control of the pressure difference at the pressure difference control point: due to the long distance of the heating pipe network, the signal transmission is not easy to realize or the realization cost is high, the calculated value is converted to the inlet and outlet of the main circulating pump; or the pressure difference control point is used for return Install a pressure gauge on the water pipe, and adjust the pressure difference between the inlet and outlet of the main circulation pump by referring to the value of the pressure gauge.

　　5. In the distributed variable frequency pump system, because the technical parameters of the water pump product are not continuous, it is impossible to meet the actual needs. Even if the frequency conversion adjustment is performed, it is impossible to meet the requirements. The valve adjustment of individual points in the system is still necessary. .