HomeFAQHow is a variable frequency drive saving energy?

How is a variable frequency drive saving energy?

Energy saving using variable frequency drive is always vary application to application. Following points you need to consider before using VFDs for energy saving.

1. How much process flow and pressure requirement through AC motors
2. Existing control methodology like control valve in pumps, Damper or guide vane for Fans & Blowers etc. and position of the valve or dampers
3. If you have process flow and pressure data and pump or fan design data, you can calculate energy saving using affinity law
4. Loading and Unloading cycle for compressor application. If the unloading time is higher for compressor application, you will get better energy saving
5. Using affinity law, you can calculate the energy saving with consideration of VFD losses. With this you can calculate the Pay back of VFDs.

Simply put, a variable frequency drive can save energy COMPARED to OTHER means of VARYING flow and/or pressure in centrifugal machines, like pumps and fans. If you are not VARYING the speed, you will not save energy, regardless of whether is full speed or not. There are more cost effective means of permanently CHANGING the output if it will run continuously at that output. But if VARYING the speed is a part of your process (the work that the machine does), then compared to OTHER methods of accomplishing that, a VFD will save significant energy. This is a very commonly misunderstood and overstated part of the picture.

The other time I have seen VFDs save energy in non-centrifugal machines is when mechanical vari-drives are used, such as variable pulley systems, hydraulic drives, particle clutches etc., but only IF it is only speed control you are after (as opposed to torque multiplication when using a vari-drive for instance). The losses in a VFD are slightly lower than the losses in most other non-electronic speed control methods.
There are different ways you can use VFD or soft starter to reduce your energy bill. Carefully analyse the possibilities of your plant.

For example, if you have a blower/ ID fan/ pump etc., you may run the motor full speed and adjust the suction or flow using a valve. But you run the motor full speed (consumes total energy) even you need less work from the motor. So for that application you can use a variable frequency drive where you can reduce the motor speed to reduce suction or flow instead of closing vale. This will help you to use only required amount of energy for your application. This will reduce the power consumption of the motor.

Also if you use soft starters with your motor it will start the motor with less starting current, where it will help to bring down your maximum demand of utility bill.

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