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VSD versus fixed speed

Compressing air can account for more than 40% of a plant’s total electricity bill. See more on how our VSD technology compares to fixed speed
Discover our VSD compressors

Variable speed drive versus fixed speed

As the name suggests, a fixed speed air compressor operates at the same speed whenever it’s running. By design, it always draws the amount of power needed to meet the maximum compressed air demand, even if demand is less than maximum. Because the speed of the motor can’t change, whenever the demand for air changes, an air inlet valve adjusts to allow either more or less air to flow out.

In contrast, a Variable Speed Drive (VSD) air compressor can operate anywhere in the range between its minimum and maximum speed, and it automatically adjusts the speed so production of compressed air matches demand in real time. When demand increases, the motor speeds up. When demand decreases, the motor slows down. This capability saves energy because the compressor doesn’t have to run flat out whenever it’s on. You can think of VSD like the accelerator in a car, which allows you to vary the car’s speed according to road conditions, level of traffic and whether you’re in a hurry!

VSD advantages

GA VSD+
Atlas Copco offers both VSD and fixed speed compressors because each type offers advantages in specific circumstances. For example, a fixed speed compressor is a smart choice when the demand for air is essentially constant. A factory running 24/7 with automated equipment that consumes compressed air at a predictable and uniform rate is a good application for a fixed-speed compressor. A VSD compressor is a smart choice when demand for air varies by process, time of day, shift or time of the year. When demand fluctuates, a VSD compressor that varies its speed is much more energy efficient than a fixed-speed compressor that can only run flat out. While VSD compressors cost more up front, they pay back the added investment through energy savings. The greater the variation in demand, the greater the potential savings. A VSD compressor can operate within a much tighter pressure band than a fixed-speed compressor can attain. A VSD compressor can operate at lower delivery pressures and still maintain the air system’s required minimum working pressure. VSD also delivers more consistent discharge pressure for all the compressed air applications throughout your facility. The net pressure on a VSD compressor can be set lower than the unloaded pressure on fixed speed compressor. Without no overpressure, each 1 bar results in 7 percent savings in energy.

VSD technology

where does the energy saving come from?

VSD versus fixed speed
Examples where VSD makes sense
Examples where VSD makes sense
  • Demand fluctuates significantly between jobs
  • Demand varies by shift, on weekends or seasonally
  • Manufacturing processes require tight tolerances for operating pressure
 
  • Demand fluctuates significantly between jobs
  • Demand varies by shift, on weekends or seasonally
  • Manufacturing processes require tight tolerances for operating pressure
Examples where fixed speed makes sense
Examples where fixed speed makes sense
  • Demand for compressed air fluctuates little
  • Up front cost is a significant consideration

 
  • Demand for compressed air fluctuates little
  • Up front cost is a significant consideration

Using VSD and fixed speed compressors together

Sometimes, the most efficient compressed air solution combines one or more fixed speed compressors to provide a base load with one VSD compressor that “trims” to meet changes in demand. A system with multiple smaller compressors instead of one big compressor also provides redundancy that allows you to keep part of your facility operational when a compressor is offline for service or repair. 

Energy incentives

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Variable Speed Drive reduces the overall load on the power grid and minimizes sudden spikes in demand that can overload the grid and cause an outage. As a result, governments and power companies may provide incentives for manufacturers to upgrade to energy-saving systems such as a VSD air compressor. These incentives can significantly offset the costs of upgrading to a new VSD air compressor and accelerate the payback period.

The optimal design of a compressed air system will reflect the specific needs of your processes, your facility and your approach to capital projects. To learn more about how Variable Speed Drive can address your needs, talk to an air system professional.

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VSD versus fixed speed

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