Compressed Air Systems

3 steps to better compressed air system design

Spend some time and attention up front to prevent major headaches later.

During the live Q&A portion of the webinar, “Examine Key Design Considerations That Contribute to an Efficient Compressor System," (now available on demand) Neil Mehltretter, engineering manager at Kaeser Compressors, and Wayne Perry, senior technical director at Kaeser, tackled several attendee questions on common compressed air problems.

PS: How can I tell if my compressors are fighting each other?

NM: Usually, you will hear the sound of one machine loading while the other machine is turning off and vice versa. You can also see it in the operating pressure of your system. The pressure will be low, and then it will go up. You can also see it in the rapid cycling that we talked about (in the webinar).

Typically, if you have more than one compressor, and those machines are loaded, you want to take a look at what that pressure drop is in your air station. If you turn one compressor off and widen your pressure band, you can figure out if only one compressor is needed to operate that system.

WP: If you don't have an air assessment done, then you don't have the system instrumented up. One of the things that I always do is take a single pressure gauge and check the control pressures at each compressor that's in there to see if they're fighting each other. Oftentimes, the compressor gauge itself or display is going to be off by a few pounds.

So, take a single gauge and check the pressure at both compressors. Then you can tell whether the gauges match on the compressors. You can often find that they're fighting each other simply because you thought you had them set right, and they're not.

PS: What would you say are the most important design considerations within a compressor room?

NM: It really depends on what the most important thing for you is. I spent a lot of time talking about ventilation. For me, what you have in the room is going to make a huge difference in getting that heat out. You’ve already planned where the compressors are going to be. You already know what the demands are. Ventilation, for me, would be paramount. But I think Wayne probably has a different perspective on it.

WP: We've talked for years and years about viewing the compressed air system as a total system, and not as just a group of components. But if this is a greenfield plant, then I would take the whole plant as a system. Look and see if you have the opportunity for heat recovery. Locate the compressor station near that opportunity.

If it's a food plant, then you always do clean-in-place. You're using hot water. Use water-cooled machines. A100-horsepower compressor is basically a 75-kilowatt heater. You might as well use that heat: it's a BTU to BTU offset for whatever you're using to heat the water. That would be the first thing. Then ventilation and distribution piping.

Those are the two big areas that I see that are often neglected. They'll buy the compressors, the dryers, the filters, and then neglect to use the right size pipe to get the air to where they need it. I think that's really important in a system design.

PS: Are service intervals really necessary? Can I just have someone visit twice a year?

WP: If you only run the compressor for a few hours a day, you might be able to get somebody to come twice a year. But yes, service intervals are critical. Whether it's a dry running screw or a lubricated screw, whether it's a centrifugal machine or a piston machine, manufacturers have given you service intervals to say, "If you service the machine at these intervals, you're less likely to have a failure than if you don't." It's the unintended failures that cause the whole plant to go down. So, I would go by the service intervals and scheduled maintenance around that.

If you have a poorly designed system, then you have to remember that you're doing service intervals based on running hours, not necessarily loaded hours. You really want to make that system so the compressors run loaded or they're off. That way, you're maximizing your service dollar by doing the service on machines that have actually loaded time and not a lot of unloaded time.

Watch the on-demand webinar