Do You Need A Variable Speed Drive Compressor?

Compressed air is critical to a wide range of functions within manufacturing. Poorly designed and maintained compressed air systems account for significant energy losses and waste every year. You may require a variable speed drive compressor.

This makes sense not only in the economic world, but also when considering how to produce compressed air and use it in a manufacturing facility.

A wide range of manufacturing functions require compressed air. However, poorly designed and maintained compressed air systems account for significant energy losses and waste every year. It is in your best interest to ensure that your facility is not squandering energy in its compressed air production process. Simply consider the benefits a properly sized variable speed drive compressor provides you.

Some plants require round-the-clock operations every single day of the week. However, lulls present themselves, giving you opportunities for energy savings. For example, a week includes 168 hours. Many compressed air systems only require full capacity between 60 and 100 hours, or about half the time. When this partial demand load event occurs, you need to regulat or stop the air compressor output capacity. With units 15 HP or larger, it is not feasible to stop and start the air compressor motor several times an hour throughout the day. As a result, a form of inlet control regulation is the choice.

You may run the unit with a Load/No-load control (fully loaded or a closed inlet for unload and bleed-down) or Modulation (cutting back the inlet throttle plate). However, to accomplish a partial load run-time, these control systems may not be the most efficient.

Don’t Waste Energy

For example, imagine you are exiting the highway with your car. In this instance, you go from highway speed (optimally 55 MPH) to a stop at the bottom of the ramp. There, the car is idling and wasting energy as long as it sits at the stop sign. City driving is even worse or similar to a very fluctuating demand – starting and stopping, but idling at every stoplight. Now, think of your car sitting (idling) at stop signs and lights for 60 to 100 hours per week.

A compressed air energy audit determines if a VSD compressor is a good fit for you. This assessment will provide the energy efficiency that you desire. These audits include review of the demand profile, compressed air usage patterns, available air storage capacity and piping network, and the operating environment.

Variable Speed Drive Technology Supplies Power When Needed

Properly sized Variable Speed Drive compressors, offer the capability to fine-tune a compressor output precisely to fluctuating compressed air demands. Varying the speed of its drive motor decreases the air demand. The VSD then lowers the delivered air flow. In addition, a VSD lowers the electrical power consumption in a largely linear fashion. This reduces energy consumption to a minimum when fluctuating demand is the norm. In fact, the comparatively low in-rush currents in VSD motor designs causes VSD compressors to stop at lower air demands. Even with several starts per hour there is not an issue, so wasteful energy (idling time) is virtually eliminated.

The Business Case

Statistics compiled through compressed air system assessments and performance analysis show that many air compressor applications are ideal for VSD. Compared to a fixed speed drive compressor, a properly sized VSD compressor can yield significant power savings. In some cases, based on the demand profile, one-third costs of compressed air reduce. Also, due to economic cycles and shifting manufacturing to other countries, many facilities have reduced the compressed air amount needed. Therefore, the facilities are operating oversized air compressors. This highlights the need to review the facility compressed air needs when significant production and compressed air demand profiles change. In addition, many local municipalities and state utilities offer rebate incentives for energy savings compressed air solutions. Within these rebates, the VSD technology qualifies.

Energy costs, already on the rise in recent years, have garnered additional attention of late as facility managers are continually charged with finding new ways to cut costs. Many corporations have instituted “green” policies with aggressive annual energy reduction targets.

The Problem:

Let’s consider a situation where a manufacturer’s compressor system ran a single 200 horsepower air compressor. The operation has fluctuating compressed air demands 24 hours a day at 3 cents per kWh. These energy costs doubled in the last five years, increasing in some areas to 8 cents per kWh or more. The annual cost to operate that compressor at 3 cents per kWh was $41,273. Today, at 8 cents per kWh, that same compressor costs $110,062 to operate every year, or more than a half a million dollars over five years.

The Solution:

After a detailed compressed air demand assessment, it was determined that the fluctuations were within the control range and averaged 35% less than the full capacity of the compressor and the factory had inadequate storage. In this case, switching to a properly sized VSD compressor potentially saved this facility $38,521 annually or more than $192,000 in five years, if the current conditions remain similar over that time period.

If you combine these savings with the greater efficiency and more efficient machines, you often experience a return on investment within less than two years. Not every installation yields this kind of payback. That is the purpose of a professional air demand assessment and proper compressor selection. However, it is worth the consideration.

In summary, manufacturers who choose a properly sized VSD compressor as part of their infrastructure experience immediate energy savings that only compound over time.

So technically, how does it work?

The VSD concept simply measures the system pressure and maintains a constant delivery pressure within a narrow pressure band. In regulating the motor speed of the compressor with frequency conversion, a varying air flow is delivered. With today’s advanced VSD electronic controls the delivery pressure is kept within a + 1.5 psi band – this is another benefit of systems with a VSD compressor; systems with all fixed speed compressors typically have a minimum a 10-15psig pressure fluctuation.

Therefore, a lower air compressor delivery pressure maintains the required minimum working pressure of the system. Say hello to increased energy savings and profitability! Remember, every 2 psi reduction in pressure lowers 1 percent of power consumption. As a result, one VSD compressor gives a 6 percent energy savings in lowering operating pressure.

The inverter in the VSD system performs a “soft” start operation. A soft start ramps up motor speed, eliminating amperage draw peaks that are typical when a fixed speed motor is started. Power companies usually impose penalties for these amperage peaks in the form of higher rates. A VSD compressor soft start also helps protect electrical and mechanical components from the starting mechanical stresses that can shorten the life of an air compressor.

For more detailed information about VSD technology applications or answers to any of your compressed air questions, please contact JHFOSTER by phone (800.582.5162) or email.

Reminder that prescriptive rebates are available for integrated VSD Compressors. Click here to see if you qualify. 

Article supplied by CAGI. For more information, visit CAGI.

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