variable speed vs fixed speed air compressors
- Mar 24, 2023
The decision to choose a fixed or variable-speed air compressor is critical for any industrial business. You probably have an idea of the overall air compressor requirements needed for peak production in your plant. However, it’s worth considering your options when evaluating the cost differences and benefits of fixed versus variable speed compressors.
fixed-speed air compressor
What is a fixed-speed air compressor?
True to their name, fixed-speed air compressors operate by sending a constant or fixed voltage to a motor, which drives a rotating screw at a consistent speed to draw in and pressurize the air. In a fixed-speed compressor, your machine is always running at full speed, even with light loads.
As the compressed air is used up in this kind of compressor, the pressure in the tank drops. When this pressure reaches the set point, the motor runs again to drive more air into the tank. The motor’s frequent stopping and starting uses a lot of energy.
Advantages of fixed-speed air compressors
- Lower capital costs
- Easier parts availability
- Reduced maintenance and repair costs
- Most efficient in applications with consistent requirements
When to use a fixed-speed air compressor
Fixed-speed air compressors have a lower initial cost, so they can be a good option for companies with limited capital funding. Maintenance and parts are also less expensive for fixed-speed compressors.
Fixed speed compressors may also be more efficient where CFM changes are minimal, and the system will always operate near its maximum CFM rating. Fixed-speed air compressors are best for:
- Companies with little variation in compressed air needs, such as robotic applications that run 24/7/365.
- A company with inconsistent power supply. VSD compressors are highly sensitive to input power inconsistencies.
- A facility with extremely dirty, dusty, or wet ambient conditions. A VSD compressor’s electronics are more susceptible to moisture and contamination than a fixed-speed compressor’s parts are.
However, it’s important to remember that the energy savings of a VSD, coupled with utility company incentives, may largely eliminate the cost difference between fixed-speed and variable-speed drive air compressors over time.
variable speed air compressor
What is a variable speed air compressor?
Variable-speed air compressors, also known as variable-speed drive compressors, use an intelligent drive system to continuously change motor speed to match air demand. The speed of the unit will fluctuate with the output required by the system.
When the pressure is low, the air compressor will run at full speed to refill the air tank. When the pressure reaches the set point, the motor will run at a lower speed to maintain a constant air pressure. It can increase the motor speed as the output requirement increases.
Advantages of Variable Speed Air Compressors
Traditional air compressors are fixed speed, which means they run at a constant speed regardless of the desired output. This puts a lot of load and stress on your motor. If you don’t use that much compressed air, there may be better options. The following are some benefits of selecting a variable-speed air compressor.
Lower starting current
Variable-speed air compressors have lower starting current. When the fixed-speed compressor kicks in, you’ll see a massive spike in energy demand. In fact, you can see surge currents up to 600% of the normal operating current.
In contrast, VSD compressors use “soft” start/stop to reduce or eliminate these energy surges. Acceleration and declaration of power is reduced, thereby reducing current peaks. Some power companies are penalizing large current surges, so startup surges are a critical consideration.
Energy saving
The amount of energy saved is one of the most significant advantages of choosing a variable-speed air compressor. Not only does a fixed-speed compressor have a larger startup surge, but it consumes the same amount of energy regardless of compressed air output demand.
A variable speed machine revs down when less output is needed and up when more output is required. This will significantly reduce energy consumption and thus increase savings. In some cases, factories have seen their energy costs drop by more than 50% by changing the type of compressor they use.
Consistent factory pressure
Variable-speed air compressors provide more consistent pressure for factory operations. A fixed-speed compressor has a fairly wide operating range because its airflow is controlled using an intake valve. This allows for variation between 10-30 PSI.
But variable speed air compressors use electronic controls, so operating tolerances are tighter. These only allow about 1.5 PSI variation, giving your plant a more consistent pressure.
When to use a variable-speed air compressor
Most compressed air users can benefit from upgrading to VSD. VSD air compressors provide maximum energy savings for facilities with highly variable CFM requirements. E.g.:
- Companies with multiple shifts with different CFM demands.
- Applications where demand fluctuates widely between shifts or jobs (e.g., machine shops with air power tools, whose usage depends on their job).
- VSDs are also ideal for applications operating within very tight working pressure tolerances.
Variable Speed Vs Fixed Speed Air Compressors
| Aspect | Fixed Speed Compressors | Variable Speed Compressors |
|---|---|---|
| Energy Efficiency | Less energy efficient as they run continuously at full speed, even when not needed | More energy efficient as they adjust their speed to match the required output, reducing energy consumption |
| Cost | Lower upfront cost | Higher upfront cost |
| Maintenance | Simple maintenance, as there are fewer moving parts | More complex maintenance, as there are more moving parts and electronics |
| Noise Level | Higher noise level, as they run continuously at full speed | Lower noise level, as they adjust their speed to match the required output |
| Flexibility | Limited flexibility, as they operate at a fixed speed | More flexibility, as they can adjust their speed to match the required output |
| Suitable Applications | Best for applications with a consistent demand for compressed air | Best for applications with varying demand for compressed air |
Contact BISON for all your industrial compressor needs
Whether you’ve decided you need a variable-speed compressor, a fixed-speed compressor or are still unsure, BISON can meet all your industrial compressor needs.
BISON offer fixed speed air compressors as well as several models of variable speed air compressors. Our team understands compressors and is happy to discuss your needs and how to match them with the right product
frequently asked questions about variable speed vs fixed speed air compressors
Why are variable speed compressors more efficient?
- They have no unloading required - are able to start and stop at full system pressure
- reduced electricity costs - no-load operation results in no energy loss.
- Reduce power surges - Avoid peak currents that start the air compressor motor.
What speed should the air compressor run?
Most motors on compressors will run at about 1,725 or 3,400 rpm. Slower rpm units are generally a better value because they run quieter, generate less heat, and produce less wear than faster motors.
