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Kaishan USA | January 8, 2025| Uncategorized
VSD compressors perform best in environments that do not have excessive heat, dust, dirt or airborne contaminants.
By now, most facility managers are familiar with the benefits of equipping their air compressors with variable-speed drives.
You can save energy, lots of it. You can save money. You can get better performance from your compressor with less moisture and contaminants.
A few of these points are worth exploring in more detail.
Save Energy
A variable-speed drive compressor consumes almost no energy when no load is required. It simply shuts down. A fixed-speed compressor, on the other hand, consumes 30-70% of full-load energy in that no-load state.
As a result, a VSD enables an air compressor to operate more efficiently at part-load conditions. That can translate into real savings.
Save Money
You may even qualify for rebates through your local utility.
A rotary screw air compressor equipped with a variable-speed drive can operate more efficiently at part-load conditions. But they are not for everyone.
Get Better Performance
A variable-speed drive compressor can gradually ramp up to full speed, avoiding the high in-rush current (six times as high as standard operating current) that fixed-speed compressors draw during startup. Thus, they reduce peak amps, avoiding utility company penalties for increased demand on the power grid.
These soft starts also save energy and reduce the stress on your compressor’s components, extending equipment life. They help you control your compressed air system’s pressure band—the gap you set between load pressure and unload pressure.
Control Your Pressure Band
With a variable-speed air compressor, you can keep the pressure band to +/- 1.5 PSIG, according to CAGI.
That gives you better control of your system and saves a significant amount of energy (and money). For more on the benefits of paying attention to this critical performance measurement, read our blog post, “How Lowering the Pressure Band of Your Compressed Air System Can Save You Money.”
A VSD also allows you to produce air of higher quality. You’ll get a steady flow of compressed air and a reduction in moisture buildup and contamination, especially during periods of lower demand.
VSDs enable compressors to supply air of higher quality, reducing moisture buildup and contamination. That’s important for applications like this facility, which makes sterile medical bandages and masks.
Not only will you be able to have better control of your system, but you’ll also better match your compressor’s output to your facility’s demand for compressed air.
Match Your Demand Profile
Using a variable-speed drive, you can match the demand profile of your plant as efficiently as possible. Your compressor will only use enough energy to compress the air you need. You can encompass the different demand profiles you might see throughout the day, keeping your system operating as efficiently as possible.
It’s perfect for industrial plants that operate three shifts. For instance, you could use a 100-HP compressor for the day shift but could get by with a 75-HP model on the second shift and a 50-HP unit on the third. That would be an ideal application for a VSD.
But not every plant has that kind of ideal profile.
They’re Not for Everyone
A VSD can actually cost you money if it is not applied appropriately. Here’s why: A VSD compressor has a higher initial cost than a fixed-speed compressor. Plus, frequent breakdowns all too often occur when a variable-speed air compressor is not the right choice for the application, especially in facilities with heavy concentrations of dirt and dust in the air.
Facilities with heavy concentrations of dirt and particulates are not a good application for VSD compressors.
The biggest problem is that people try to use a VSD compressor to cover a capacity range that is too large. Both extremes—too high and too low—cause problems.
Too High
In a pharmaceutical plant, an air compressor could be running full bore 24/7/365. That’s good for a rotary screw compressor designed to operate at full capacity.
But that’s not the best use of a VSD-equipped compressor (even a rotary screw) because there are energy losses associated with the drive itself. And you’re wasting your money.
Running at a level that’s too low is even worse.
Too Low
We have seen plants where someone tried to anticipate future growth. Or they thought they’d get out in front of a planned expansion, just running their compressor at a lower level until the expansion happens. Good, in theory. However, it is a potential disaster for a VSD. Especially if the planned expansion is delayed or even cancelled.
Here’s why: If you operate a variable-speed air compressor consistently at less than 20% capacity, it will not get warm enough (more than 150∞F) to evaporate the moisture in the air. As a result, your compressor will fill with water, creating the potential for rust and corrosion that will quickly ruin your machine. And all those benefits go down the drain.
If you have excess water showing up when you draw and test an oil sample, you know you have a problem.
That’s why we shoot for a range of 30-80%. And definitely not below 20%. For more on the pros and cons of VSDs, see our blog post, “How Variable-Speed Drive Rotary Screw Air Compressors Save You Money.”
Does that mean you shouldn’t consider a VSD if your demand varies too much? Not necessarily.
What To Do If You Have Too Much Variation
If there are times when your usage is less than 20%, all is not lost. You may benefit from a different configuration of your compressed air system.
Rather than try to cover all your needs with one compressor, you might benefit from a multiple-compressor arrangement including:
- A base load compressor designed to meet your system’s minimum compressed air requirements. It will not fluctuate in output as demand changes. Instead, it should be run at 100% capacity or turned off. When you only need a small amount of capacity, significantly below the base load—like weekends, holidays or a minimal third shift—we recommend meeting that need with a trim compressor.
- A trim compressor is designed to handle fluctuations in demand above the base unit. Since the level of flow needed will rise and fall depending on the needs of your system, rotary screw compressors are a natural for this application. Equipping them with a variable-speed drive makes them more cost-effective and energy-efficient. Trim units are an excellent application for variable-speed drive compressors.
- A backup compressor is on standby if a base or trim unit goes offline. It should be the same size as the base load compressor to fill in appropriately.
Together, the three compressors have you covered in your most likely demand profiles. For more information on a three-compressor approach, read our blog post, “How Energy-Efficient Air Compressors Can Reduce Your Carbon Footprint.”
An alternative to VSDs may also be worthwhile in some applications.
Modulation As a VSD Alternative
Modulation, which adjusts the inlet valve to a partially open position, has traditionally been viewed as a waste of money and energy. But, considering the higher initial cost of a VSD, it may be a more cost-effective way to prevent rapid cycling for some users. The key is to balance the potential cost with the negatives of rapid cycling.
Neither modulation nor VSDs, however, take the place of an appropriately sized compressor and storage tank. It’s a best practice to have both wet and dry storage to remove moisture and maintain stable header pressure. For more on tank storage, see our post, “A Quick Guide to Accurately Size Air Compressor Tanks.”
Sorting out all the options for deploying VSDs is a significant challenge for most companies. That’s why we recommend that companies engage their local compressed air professional to conduct an audit.
If you are considering the purchase of a variable-speed drive compressor, an air audit by a compressed air professional will more than pay for itself.
Start with An Audit
Unfortunately, most companies do not have the technical resources or data to accurately assess their usage levels and configure a system to take full advantage of a VSD compressor.
We’ve proven that audits more than pay for themselves and that’s especially true when considering the addition of a variable-speed drive compressor. Our blog post, “How an Air Compressor Audit Can Reduce Operating Costs” documents actual customer accounts in which audits cut energy use and saved compressed air users tens or even hundreds of thousands of dollars. And, to see all our customer successes, visit our case studies page.
Our nationwide network of independent distributors, stands ready to provide the on-site expertise and consultation you need to make a good business decision about the use of a variable-speed air compressor. These factory-trained air compression experts can also assist you in many other ways, helping you operate and maintain your compressed air system.
Key Takeaways
- VSD compressors save money and energy and improve performance. With less moisture and contaminants.
- But variable-speed drives are not for everyone: They can cost you money if not applied appropriately.
- The biggest problem is that people try to use a VSD compressor to cover a capacity range that is too large. Both extremes—too high and too low—cause problems.
- An audit by a compressed air professional will more than pay for itself, ensuring a VSD compressor is right for your application.
Let Us Help
Deciding whether a variable-speed drive compressor is right for your application is critical to the operation of your compressed air system and all the processes that rely on it. If you need help sorting out the options, get in touch with the experts at Kaishan. Contact us today.
