Imagine you're in your car, stopped at a red light. There's nobody in front of you, and you're easing your toes off of the brake peddle ever-so-slightly, waiting for the light to turn green.
The light turns green, and your foot immediately slams the gas peddle to the floor. You hold the peddle to the metal until you reach another red light, then slam the brake.
If you drove that way all the time, you can imagine what would happen to your gas mileage. However, it's also not good for the vehicle. The same idea applies air compressors.
If your air compressor runs full-speed only, and simply shuts off and turns on as needed, you're not getting the most efficiency out of your air compressor. You could say, the speed with which your air compressor motor runs could use some variance.
With variable speed drive air compressors, you get that variance. The motor runs only at the speed you need, giving you the right amount of compressed air at the right pressure, and at the right time.
By converting incoming AC power to DC power, and back again as needed using an inverter circuit, variable speed compressors can control the current and voltage to speed up and slow down the motor in order to provide exactly the right amount of power to provide exactly the right amount of pressurized air to serve your individual needs.
This technology enables variable speed rotary screw air compressors to maintain an ideal amount of pressure at the least amount of output necessary, saving you energy costs and improving performance.
While variable speed compressors are more energy-efficient for most applications, there are some exceptions to the rule. If your compressed air needs are constant, or even mostly constant with only occasional slight variations, a variable speed compressor may not be necessary.
You may argue that, even though variable speed drive is not necessary, it can't hurt to have should there be any fluctuations in demand. However, if your compressed air application is to run assembly line machinery for 10 hours per day, you may be able to save the extra up-front cost of investing in a variable speed compressor and just continue to produce the same consistent compressed air supply to meet your consistent compressed air needs.
To determine whether or not your compressed air demands could benefit from a variable speed compressor, consider data logging. A data log is a reading and analysis of your compressed air system's loads over a period of time.
Data logs can be created in different ways, and you should choose the method that's right for your system. If your compressed air system is a major utility, used regularly for several important applications, you should implement a data logging system within your compressed air system that can log data over time and provide a highly-accurate load profile for your compressed air demands.
If you don't have the means to invest in such an elaborate system, or perhaps it's not as crucial to your compressed air demands, you can instead choose to have a field specialist set up and conduct a load data survey to determine the demands of your system. This means of collecting data will only provide you with data for a select period of time it's collected by the field specialist, but will give you some decent insight into your system's needs.
But if you're looking for the most cost-effective means of analyzing your compressed air demands, you can simply measure the time of a few load cycles and unload cycles will help you to roughly determine what the demands are so you can make a relatively informed decision about what kind of compressor would best serve your system's needs.