Variable-speed VS. Fixed-speed Air Compressor

Variable-speed VS. Fixed-speed Air Compressor

(05/09/2021 - Lượt xem: 430)

More and more people choose or update a VSD (Variable speed drive) or VFD (Variable frequency drive) air compressor for their industry. What are the benefits of a VSD air compressor compared with a Fixed-speed air compressor? Is a VSD compressor the right choice for your facility?

What is a Variable Speed Drive Air Compressor?

A variable-speed compressor can adjust the airflow automatically according to the real-time demand for your facility, by controlling the frequency supplied to the motor.

That means when the facility needs more air, the VSD will increase the frequency and speed up the motor to produce more compressed air. When the compressed air needs are low, the VSD will slow down the motor, and the system costs less energy accordingly.

What is a Fixed Speed Drive Air Compressor?

A fixed-speed compressor supply a fixed or consistent frequency to the motor, which means the compressor operates at the same RPM all the time. To adjust the airflow, the fixed-speed air compressor needs to adjust the air inlet valve to let more or less air out. So the disadvantage is even when the air demand is low, the motor always operates at the same speed, so it is a waste of energy.

How does Variable Speed and Fixed Speed Air Compressor Work?

The motor drives the screw rotor to produce compressed air, and the compressed air enters the air storage tank. And what is the difference between variable-speed and fixed-speed air compressor during the consuming and producing process?

For the fixed-speed air compressor

When the pressure of the gas storage tank reaches the set value, the motor stops;

When the compressed air is partially used, the pressure of the air storage tank becomes smaller. When the pressure reaches a certain (set) value, the motor is started again to drive the air compressor to work;

When the compressed air is used a lot, the motor will start and stop frequently, and the motor will consume more electric energy when the electric current is larger during the starting process. When it stops, the energy of the motor cannot be used, so the energy consumed by the frequent start and stop of the motor is More.

For the variable-speed air compressor

When the air pressure is low, the motor of the air compressor rotates at full speed to inflate the air tank.

When the air pressure of the air storage tank reaches the set value, the inverter will reduce the frequency of the power supply to the motor, and the motor will run at a very low speed. At this time, the motor consumes very little power and the air compressor basically does not generate pressure;

When the compressed air is partially used, the pressure drops to the set value, and the power supply frequency to the motor rises to the power frequency state, and the motor runs at full speed under the power frequency, this saves a lot of power for starting and stopping the unit.

The Advantages of Variable Speed Drive Air Compressors

Why does Variable-speed SAVE ENERGY when compared to fixed speed? Why should we choose or update a VSD air compressor?


  • Compare to a car, fixed speed is either drives 100 km per hour or not at all. Fixed speed compressors run at one fixed speed, and are very efficient when operating fully on load 100%, but most applications don’t, they have a fluctuating air demand.
  • A variable speed drive (VSD) compressor can adjust its motor and elements speed to match the air demand, which saves considerable amounts of energy.
  • Generally, use VSD can save 10% ~ 35% energy, it depends on the working conditions of the air compressor. When the customer’s air consumption fluctuates greatly, the energy-saving effect is better.

More reliable

  • A stable soft-start reduces the impact on the power grid, extends the mechanical life of the motor and the whole unit. Make the air system more stable and reliable, reduce downtime and production losses.

Consistent Pressure

  • A fixed speed compressor operates within wide pressure range as much as +/- 10-30 PSIG, meaning PSI for the system may vary by this much during the course of operation.
  • A VSD compressor uses electronic controls and operates within a +/- 1.5 PSIG pressure range. No matter the air demands are high or low, it can adjust the motor speed with consistent pressure.

Reduces noise

  • When the amount of exhaust air decreases, the speed of the motor slows down, and the noise of the air compressor is much smaller than that at full speed. The time of unloading operation is reduced, and the noise of venting is also reduced.

The Advantages of Fixed Speed Drive Air Compressors

  • Lower purchase costs
  • Lower maintenance and repair costs
  • High efficient for consistent air demand

When to Use a Variable-Speed or Fixed-Speed Air Compressor?

Compared with the VSD air compressor, the fixed-speed air compressor spends lower capital costs, if the air compressor needs to be operated on a 7*24hours for your production line, and always near the maximum CFM, then your energy consumption may be fairly consistent, and a fixed-speed air compressor might be a good choice. Besides, as the electronics in a VSD air compressor are very sensitive to moisture and dirt, if the environment is very dirty, dusty, or wet, you can choose the fixed-speed air compressor.

However, if your air compressor will be operated goes with daily, weekly, or even seasonal changes and with different air demands, then a fixed-speed air compressor will use more energy and be somewhat wasteful over the course of its life cycle. So If there is fluctuation in flow demand, choosing the VSD air compressor will be a good option and offer great savings.

When to Use Both Variable and Fixed Speed Air Compressor?

In many facilities, the best proposal is to use both the fixed speed and variable speed air compressors in tandem. For example, you have one set of VSD air compressor and one set of fixed speed air compressor for your plant,

  • The variable-speed air compressor will be used as the primary air compressor, and it can adjust the airflow according to your actual needs to save energy.
  • When the compressed air demand is larger than the VSD air compressor, the fixes speed air compressor start work. Then the fixed speed compressor will work on full load and while the VSD will adjust its motor speed to meet the total demand.

So we suggest you calculating not only the total volume but also the most usual air demands for your production line. Then our engineers can provide the most energy-saving proposal of air compressor system for you.

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