It’s Not Just About Energy: The Sins of Over-sizing, Continued

By: Kaeser Compressors, Inc.

We’re picking up on the thread of our last post about over-sized compressed air systems, where we showed that the further away from full load a fixed speed compressor operates, the higher the energy cost is per cfm of compressed air. Energy may be the easiest cost per unit of air to recognize and measure, but it’s not the only component of cost, and it may not be the most significant cost in your operation. 

Increased cycling associated with under-utilization has several negative effects on compressors, and we’ve found that for under-loaded systems, maintenance and repair costs increase as a portion of total operating cost.  A review of service records showed that units with duty cycles had a significantly shorter mean time between failure (MTBF). Because compressors are usually serviced based on total run time rather than actual load time, a machine that idles a lot costs more in parts and labor per loaded (i.e. productive) hour.  If you calculate the service costs based on cfm produced rather than hours of run time, you’ll find that PM and repair costs per cfm rises also.

Like highway miles vs city miles

Think of your car. Cost per mile for gas and maintenance goes down if most miles are highway miles. But highway miles are also gentler on your car (fewer starts and stops, etc.). City miles are notoriously inefficient with fuel, but they also accelerate wear on the motor, the brakes, steering and suspension.  

Likewise, low-loaded compressors are more likely to show wear at an accelerated rate. Inlet valves, vent valves, and others, cycle many more times at low load. Motors starts are more frequent which can affect bearing and winding life. On direct drive units with polymer couplings, frequent cycling can reduce coupler life. Frequent starts and stops put more wear on thrust bearings in the airend.   

Further, if the unit doesn’t run enough, it may not reach proper operating temperature, which results in moisture accumulation in the lubricant. This is a common cause of premature airend failures. Frequent changes in temperature can also cause metal fatigue on aluminum coolers. These conditions call for increased frequency of preventive maintenance and the likelihood of downtime for repairs.   

Downtime and Scrap

Another downside to poorly sized systems is pressure fluctuation. Swings in pressure may result in defective products, and more sophisticated production machinery have sensors that will shut down the equipment if pressure is outside of design specifications. Depending on the cost of raw materials and value of finished product, the costs of downtime and scrap may far exceed the losses in energy efficiency and service costs.  

Meeting the Challenge

If you are planning a compressed air system for a new plant or expansion, you may only be able to estimate your compressed air demands. So the smart money is spent splitting the estimated demand among multiple compressors and having good controls (and ample storage). Using variable output compressors as trim machines is part of a good strategy. 

For existing systems, the first step is an accurate air system assessment to determine how well your system is sized and controlled. If your budget allows for replacing compressors, the ROI from lower energy consumption, lower service expenses and reduced downtime may justify replacing over-sized compressors and adding controls. In some cases, just adding one smaller machine can make the difference.   

If your budget cannot accommodate new compressors, there are lower cost investments that can help mitigate over-sized compressors. Adding storage often reduces compressor cycling and can stabilize pressure. In some cases, flow controls may further improve the effect of storage. For systems with multiple compressors, adding a modern multi-unit controller will definitely help reduce starts/stops while stabilizing pressure and provide additional benefits such as remote monitoring and energy consumption information.  

Downtime and scrap caused by pressure fluctuations, high service and repair costs, and high energy costs, are problems that many plants simply live with as expected costs of operating compressors. But they don’t have to be. The first step is an honest assessment of how well your compressed air system is working. 

Read our white paper titled “Using Master Controls to Improve the Performance and Efficiency of Industrial Air Compressors” to learn more about how to minimize equipment run times, maintain stable air pressures, and deliver rapid payback in operational and energy savings.

That’s Classified

Cost effective options for compressed air in classified areas

By: Michael Camber

A few posts back, we wrote about removing compressors from a bad environment for their health (away from excess heat, dust, etc.). This time we’ll talk about moving them for the safety of people. Specifically, we are talking about hazardous areas where the presence of flammable gases or liquids, combustible dusts or easily ignited fibers exist in sufficient concentrations to cause a fire or explosion, given a source of ignition (such as electricity running through a compressor).   

Obviously, this might apply to parts of (or entire) chemical, oil or gas processing plants.  But it could also apply in other industries we don’t think of as handling hazardous materials. Fine powders or fibers from grains, wood, etc. can create fire hazards. We’re not trying to raise the fear factor. This is not a common concern, and if it does apply in your plant, you are probably are already well aware.  

In the oil & gas and petrochemical markets, there are suppliers who specialize in engineering and modifying air compressor systems and other motor-driven equipment to be “explosion proof.” This gets very expensive, very fast. It also takes time for these systems to be designed, built, installed, and certified to operate. This is specialized work and these suppliers (rightfully) charge a premium for it.

A natural gas processing plant

In the case of a compressed air system, however, there may be an easy cost-saving alternative: Move it. Move it to another part of the plant that is not in the “classified area” and pipe the compressed air in. Usually, the air is not the source of risk. It’s the motor, starter and electrics. Sometimes it just takes a little out-of- the-box thinking to find another spot for the compressed air source. But sometimes there simply isn’t a safe place or enough space for the compressors somewhere else in the plant. In these cases, compressor system enclosures set outside at a safe distance are viable options. 

Compressed air production was moved a few hundred yards away

This solution presents the increased costs of packaging the air system up and of piping the air longer distances. But they may compare favorably to the engineered explosion-proof system. Further, they usually offer faster design, build, install, and commissioning. Not to mention lower maintenance costs by using standard compressed air equipment and less downtime when service is due (think about procedures to get outside personnel into restricted areas).

Weather-proof enclosure with complete compressed air system pre-installed.

Visit our website and download the white paper: Hazardous Area Classification Considerations for more on this subject and check out this ThingLink to see what one of these enclosures looks like on the inside.

Calculating the Value of Avoided Unplanned Downtime

By Matt McCorkle

In a recent article titled “Calculating the value of avoided unplanned downtime” from Plant Services magazine, Burt Hurlock poses the question “How much have the avoidable catastrophic events of the 21st century cost us, and how much would we have willingly spent to prevent them?”

He goes on to talk about how downtime events that were avoided still have value and sophisticated plant operators know exactly how much value. Understanding that downtime, of any length, has rippling effects on the entire organization is valuable in itself. One small event can cause unproductive labor hours, costly incident investigation, wasted raw materials, product spoilage, etc. and the bigger the event, the higher the risk and higher the cost is.

Knowing that your compressed air system is not only critical to your production but also affects the quality of your products, would you invest to avoid downtime from your compressed air system? We often encounter customers who tell us “If my compressor goes down, the facility stops.” But in the next breath tell us a back-up compressor isn’t worth the investment. Customers are frequently more concerned with purchasing a larger than necessary compressor that accommodates future growth than planning for the present with a redundant solution.

So, what’s the cost of unplanned downtime? Estimates of the average cost vary from $30,000/hr (Industry research by Stratus) to $260,000 (Aberdeen research). At that rate, any investment in back up quickly pays for itself.

Planning your compressed air system to have redundancy with a back-up compressor or using the 50-50-50 approach with three smaller compressors can help eliminate the risk of unplanned downtime in your compressed air supply. Not only will a multi-unit solution eliminate the compressed air system as a downtime risk for your production lines, it will also supply air more efficiently as your compressed air demands vary by shift and production level.

Ask yourself Burt’s initial question about your own company. “How much have the avoidable events of this year (or the past 2 years or 5 years) cost us, and how much would we have willingly spent to prevent them?”

As Burt Hurlock writes in the article, “all avoided unplanned downtime has value.” Knowing that your compressed air system is vital to your plant, realizing the value, and planning to have a back-up air supply will help you avoid downtime from an unplanned event or even downtime for scheduled maintenance. The value of a reliable second compressor may far outweigh the cost of the downtime it prevents.

Burt goes on to say “The single most important ingredient to the just-right balance between investment and risk is information. Companies that know the value of events that don’t happen also understand that reliability is nine-tenths information and only one-tenth perspiration. The opposite is true for companies that don’t know the value of events that don’t happen.”

When you have your next event, how much will you be sweating?

Your eyes are often bigger than your stomach

A report card on compressed air knowledge: Part 2

By Michael Camber

Missed part 1?

Click here for the results of a recent quiz of automotive service shops about compressed air.

The point least understood among the surveyed compressor users is how to size a system for the shop.  We presented a scenario with five techs, each using 15 cfm tools, and gave five different compressor size (hp) options. Less than 40% picked the most appropriate option, and most incorrect answers were heavily over-sized.  We see this in the field all the time.  Operators routinely overestimate the size of compressor needed.

Depending on the type and design efficiency, most commercial/industrial compressors produce between 3 and 4.5 cfm per horsepower.  The (simplistic) quiz scenario assumed all air users would need air simultaneously.  Using 4 cfm/hp, a 20 hp compressor with 100% duty cycle would supply air to all five users.  As mentioned above, 40% chose this option, but another 40% chose either the 30 or 50 hp options. 

The downsides to oversizing include:

  • spending more up-front for the equipment (compressors, dryers, etc)
  • paying more for parts and service
  • increased wear from over-cycling (starts and stops)
  • reduced energy efficiency (this applies more to rotary type machines than pistons, which mostly operate on start/stop controls)

Now factor in the reality that it is very rare for all techs to be operating air tools at the same time.  So let’s say only three of five people will be using air simultaneously (total of 45 cfm).  A 15 hp compressor would easily handle it.  If only two out of five were using air at the same time, an efficient 7.5 hp with 100% duty cycle might suffice.  Or bump it to 10 hp (40 cfm) and add 100-200 gallons of storage to be safe.  Far more cost effective than buying the 20 hp.

For energy efficiency, it would be better to get two smaller machines than one large one. This also give you back-up, but it does drive up the initial cost.

If you anticipate that you will need more air in the future,  arrange your compressor room/area to allow for additional machines, but only buy what you need in the short term.  The money you save on energy and service will help pay for the upgrade later.

Download our Compressed Air System Installation Guide E-book for more installation tips.

A Report Card On Compressed Air Knowledge

By: Michael Camber

One of our media partners recently quizzed their subscribers to assess users’ knowledge about compressed air systems.  The respondents were in the automotive service industry, but the questions were not industry or application specific and the answers are a fair reflection of compressed air knowledge of most businesses with compressors 25 hp and below.  We thought it would be useful to present the results and discuss areas where understanding of compressed air systems needs a boost.

Duty Cycle

A strong majority (84%) of respondents knew that reciprocating/piston type compressors operate at higher internal temperatures than rotary type compressors, but nearly 1/3 mistakenly thought that shop recips could safely run at 100% duty cycle.  Some recips are built to run at higher duty cycles than others, but all air-cooled units need at least some downtime to cool off.  The consequences of overrunning them include loss of lubrication, seizure, motor failure and higher oil carry-over into paint and equipment.

Check out our Piston vs. Rotary Screw Infographic for a quick comparison.

Piping Material Choices

Regarding piping, nearly 2/3 know that copper or aluminum are better choices– especially if air quality is important– but a full 20% picked PVC as top choice.  While PVC doesn’t accumulate or add contaminants, it presents one major problem:

Wait for it ….

Yes, PVC is less safe than any metal pipe and is subject to rupturing and fragmenting.

Solving Pressure Problems

When presented with five possible solutions for solving a low pressure problem, everyone recognized that buying another (or larger) air compressor to get more flow is not the first step to address the problem.  Checking for leaks, checking pipe size, adding storage and doing a pump-up test to check compressor function were all known to be better first steps.  We were pleased to see that over 80% recommended doing all of these things before buying another compressor to get more flow (cfm).

Filters Are Not Dryers

Likewise, we were pleased to see that everyone knew that a compressed air dryer is a simple solution to address the common summertime problem of increased water in compressed air lines and tools.  It’s apparent though that not everyone understands the difference between dryers and other devices that remove some moisture. Filter style moisture separators (with drain valves) are effective at removing liquid water.  Storage tanks do the same and can allow some moisture vapor to cool and condense to liquid, but the key to effective drying is reducing the compressed air pressure dew point below the ambient temperature.  Tanks and filters cannot do it. A dryer can.

The last quiz question was about compressor sizing. Since this topic is a bit more complex it deserves its own post. Stay tuned…