Application in Water supply

1. Overview for energy saving of water supply system

In the water supply system, the basic control object is water flow, water Supply System’s basic task is to meet the demands of users of consumption of water. Currently, there are two common modes of flow control: valve control and speed control.

1) Valve control

By adjusting the valve opening range to control the water flow. At this point, the pipe resistance of the water system will be changed with the change of valve opening and lift characteristics remain unchanged. When design the water supply system, the pump lift and water flow is selected the maximum extent possible to meet user’s demands, and have a certain margin. But practical application of the system is running at full capacity in most time. Then must reduce the valve opening range and adjusting the water flow. In this way, pipe resistance will be increased, resulting in closure of a large number of losses. By this control mode not only waste a lot of output power of the motor, but also because the characteristics of pipe resistance to change, the efficiency of water supply system will be greatly reduced.

2) Speed control.

By changing pump’s rotate speed to regulate the flow, and the opening of the valve remains the same ( generally keep the maximum opening). When pumping speed is changed, lift characteristics of water supply systems will be changed with it, and the pipe characteristics is unchanged.
In this control mode, use VVVF technology to change the speed of water pump motor, water pump flow can be changed with the change of water flow, to achieve real balance between supply and demand. In energy saving, also can make whole system achieve the best efficiency at the same time. With variable frequency regulating speed technology matures, this control method has gained more and more application.

2. Principle of energy-saving

Hydrodynamic theory shows that most of the fluid transfer equipment ( such as centrifugal water pump, fan, etc ) is proportional to the speed of the output flow rate Q and N; The output pressure or head P and its speed is proportional to the square of n; Power output is proportional to the cube of its speed N N, using a mathematical formula can be expressed as :

Q = K1 x N
P = K1 x n2
N = Q x P = K3 x n3(K1 ,K2 ,K3 are proportionality constants)

From the above principle we know if reduce the pump speed, pump’s output power will fall more accordingly. For example, if change the motor power supply frequency from 50hz down to 45hz, then, in theory, before and after the frequency change ratio of output power is ( 45/50 ) 3 = 72.9%. The long-term practice has been proved that, insert frequency conversion energy saving system in water supply system, by using frequency conversion technology changing the pump speed to control fluid flow in pipes, to replace the valve adjustment mode, can achieve remarkable energy saving effect, general energy – saving rate is above 30%. In addition, inverter characteristics of the soft start function and smooth speed control can achieve the smooth flow regulation, while reducing the impact of starting and prolonging the service life of the machine set and tube group.

3. Characteristics of energy – saving system

1)Inverter interface is LED display; parameters are abundant of information; keyboard layout simple and easy to operate ;
2)Inverter has various electronic protective devices overcurrent, overvoltage, overtemperature, lack of equal, etc. And has a fault alarm output function, which can effectively protect the normal operation of the water supply system ;
3)Dedicated digital PID regulator for LED dual – screen display, parameter setting more convenient and easy to control.
4)After retrofit of frequency conversion energy saving device, pump motor has soft start and frequency conversion speed adjustment function, can effectively reduce the system’s mechanical wear, while reducing the burden of the pipeline ;
5) There are two working modes “Manual” and “Automatic”, in the case the inverter fail, the machine can continue to run in original mode.