AC drive in constant pressure water supply system

Constant pressure water supply system characteristics AC drive in constant pressure water supply system

Electricity saving ratio up to 20%-40% percent.
Small installation space, low cost with high efficiency.
Comprehensives function with flexible configuration.
Soft start/stop feature can eliminate water hammer impact, and reduce average torque and attrition on motor axis to lower maintenance cost and prolong water pump's service life.
Control the drive system through network communication to achieve automation management to save human source.

Energy saving principle
According to the water pump working principle: the water flow is direct ratio to the water pump's motor speed, the water pump's lift is direct ratio to the square of water pump motor's speed, and the shaft power is equal to the product of water flow and list, so the shaft power is direct ratio to the cube of motor speed. Therefore, the water pump's power can be changed by the pump motor's speed.

The flow formula: Q∝N H∝N2 KW=Q*H∝N3
Q means flow，N means speed，H means lift，KW means shaft power.
For example: the frequency reduce from 50HZ to 45HZ, then P45/P50=（45/50）3= 0.729, i.e. P45=0.729 P50;
The frequency reduce from 50HZ to 40HZ, then P40/P50=（40/50）3= 0.512, i.e. P40=0.512 P50.

Generally the water pump is determined according to the water supply system's maximum power requirement, but in practical experience, the water supply system doesn't need to work in its maximum power all the time. Normally it adopts throttle valve to control water flow, but the pump motor working in full load all the time, then it wastes electricity consumption. However, after install variable frequency drive to the system, it will work more smooth and stable, to control water supply by adjusting pump motor speed, and earn investment back by electricity saving in low speed running.

Here is the form to see the difference between 3 flow control modes by a 100kW water supply system electricity consumption:
flow control method comparison

Lots of motor driving systems have overmeasure, low working efficiency, high power consumption, high starting current and loud operation noise etc., which will affect company's efficiency. However, the variable frequency drive can solve these problems, generally we can expect earning investment back within 10 months by improve the system working conditions.

Main applications of variable frequency constant pressure water supply system
1. High-rise buildings, residential area domestic water supply;
2. The application needs constant water pressure control, cooling water circulation, thermal water circulation, boiler water supplement etc.;
3. Central air-conditioning system;
4. Irrigation, sewage treatment, artificial fountain;
5. And other liquid system needs constant pressure control.

Constant pressure water supply system composition
AC drive is core part of the whole system.
variable frequency drive system composition

variable frequency drive system composition

The pump motor is output link, the motor speed is controlled by variable frequency AC drive to achieve variable flow with constant pressure control. The AC drive receives signal from PID controller to control the pump motor speed, pressure sensor detects pipe network water pressure and sends signal to PID controller, and adjusts AC drive's output frequency by PID controller, to achieve a closed-loop control system.

GK3000 series AC drives in constant pressure water supply system
GK3000 series AC drives have integrated PID controller, with perfect dormancy feature to enable maximum energy saving rate.
The basic wiring diagram of GK3000 series AC drives in variable frequency constant water supply system.

AC drives in constant pressure water supply system

Other Applications:

VFD for Center Pivot Irrigation Pumping System In this application a methodology was developed for experimental evaluation of the potential for energy conservation in center pivot irrigation using variable speed pump controlled by variable frequency drive (VFD).

Variable frequency inverter drive for injection molding machines 1. Reduce at least 35% of electricity power consumption, and reduce production costs.
2. Smooth soft start to protect the electric motor and prolong service life.
3. Reduce impact of clamping/opening mold to extend the machinery and molds service life.
4. Comprehensive protection of electric motor's overvoltage, overcurrent and phase loss.
5. Switching variable frequency system and power frequency easily to ensure production continuously if the variable frequency system failures.

Variable speed drive in air compressor In some cases, the electric motor running power cannot lower even if air compressor don’t need to full load operation. But, the variable speed drive can control the electric motor in lower speed running in this case to achieve energy saving. Normally, a single motor driving system cannot adjust consecutively according to load capacity. However, we can easy adjust speed consecutively after adopting variable speed drives to the air compressor, and keep air pressure, flow and temperature stable, thus to improve the air compressor working performance greatly.