Variable Frequency Drive (VFD) for Pumps

Like fans, using a variable frequency drive (VFD) to control the flow rate from a pump rather than using simple throttle control can result in large power – and therefore cost savings. This is illustrated in following Figure, where the broken line indicates the power input to a fixed-speed motor and the solid line indicates the power input to a variable frequency drive. The shaded area represents the power saved by using a variable frequency drive for a given flow.
Pump power saving of using VFD vs throttle valve

Pump power saving of using VFD vs throttle valve

Note: When operating at near full speed there is a crossover point where variable frequency drive control can use more energy than fixed speed control with a throttle. This is due to the losses in the variable frequency drive exceeding the savings from the speed reduction.

In a similar way to using damper control in fan applications, using throttle control for pumping applications results in a drop in pump efficiency, whereas the efficiency remains higher when the output is regulated by speed control. This is illustrated in Figure.
Pump efficiency of using VFD vs throttle valve

Pump efficiency of using VFD vs throttle valve

The original fixed speed operating point (1480rpm) of the pump is at (Point 1) where the system curve intersects the head-flow profile at a flow rate of 700m³/hr, the efficiency is circa. 85.1%. If the output is regulated by a throttle the system curve effectively moves to the left (Point 2) where the pump efficiency has declined to 78%. Conversely if the output is regulated by speed control the operating point moves down the system curve (Point 3) whilst the pump efficiency declines marginally.

On systems with a high static head, in particular pumping applications for example, boiler feed-water pumps or high lift applications, where the pump must overcome the resistance to lifting the water before any flow starts, the benefits of using variable frequency drives will be reduced. This is because higher speeds need to be maintained in order to overcome the additional resistance due to the high static head. Factor this into any calculations (including Affinity Laws) and consult your pump supplier for further information on how to take account of static head.

Typical examples of pump applications that will benefit from variable frequency drives include circulating water in HVAC systems, boiler feed-water pumps, process pumps and other applications where flow demands vary.

Other Applications:

AC inverter drive in agitator Built-in slip compensation function realizes high efficiency.
Advanced motor parameter auto tuning function.
Built-in PID regulator in the frequency inverter.
Friendly user interface, large screen LCD. Realize parameter online monitoring, online regulation, and parameter copy function to make operation more convenient.
Torque control function enables the motor be able to run with a constant torque.

Variable frequency drive in fans system 1. Achieve soft start and stop smoothly with little impact to the power grid and mechanical equipment.
2. Precise control and smooth speed adjusting, wide speed adjustment range and can realize stepless speed regulation.
3. Easy operation, decrease maintenance requirement and lower maintenance costs.
4. Strong protection function for the system, the variable frequency drives built-in overvoltage, overcurrent, undervoltage, overload, overheating and phase-loss protection, etc.

Variable frequency drive for Chinaware ball mill It is commonly said that it is hard to perform energy saving reconstruction to the Chinaware ball mill. However, this machine always contributes at least 80% of the factory's total power consumption. To respond to the government's appeal, Gozuk launched a new series variable frequency drive - that can be used in the Chinaware ball mill. Field operation from a famous ceramic plant in Foshan, Guangdong province, shows that Gozuk AC drive has high performance and high reliability, which can help the factory secure about 10% production cost.