A-Z of Compressed Air Systems & Maintenance

To fully appreciate how impactful a properly functioning air compressor system is to your bottom line, it is foremost important to fully understand how much your compressed air costs. Compressed air is a self generated utility within your facility that is a top 3-4 utility expense for your company. This fact is often overlooked or misunderstood, because the expense is primarily linked to the electric and or gas bill. This can be a costly oversite. You will see an example below where a single common maintenance issue causes a 4psi reduction in performance and resulted in \$1265 in additional annual cost to that company. Imagine when/if there are multiple issues…

In order to calculate the compressed air cost, some companies use an educated guess of @\$0.25 per 1000 cubic feet of compressed air consumed, and others are more precise. The U.S. department of Energy performed an energy saving study in 2004 and they show a precise way to calculate your compressed air cost. Here is their sample calculation:

“Compressed air is one of the most expensive sources of energy in a plant. The overall efficiency of a typical compressed air system can be as low as 10%-15%. For example, to operate a 1-horsepower (hp) air motor at 100 pounds per square inch gauge (psig), approximately 7-8 hp of electrical power is supplied to the air compressor. To calculate the cost of compressed air in your facility, use the formula shown below:

Cost (\$) = (bhp) x (0.746) x (# of operating hours) x (\$/kWh) x (% time) x (% full-load bhp) ÷ Motor Efficiency
Where:
bhp = Motor full-load horsepower (frequently higher than the motor nameplate horsepower—check equipment specification)
0.746 = conversion between hp and kW
Percent time = percentage of time running at this operating level
Percent full-load bhp = bhp as percentage of full-load bhp at this operating level
Motor efficiency = motor efficiency at this operating level
Example:
A typical manufacturing facility has a 200-hp compressor (which requires 215 bhp) that operates for 6800 hours annually. It is fully loaded 85% of the time (motor efficiency = .95) and unloaded the rest of the time (25% full-load bhp and motor efficiency = .90). The aggregate electric rate is 0.05/kWh.
(215 bhp) x (0.746) x (6800 hrs) x (\$0.05/kWh) x (0.85) x (1.0) = \$48,792
.95
(215 bhp) x (0.746) x (6800 hrs) x (\$0.05/kWh) x (0.15) x (0.25) = \$2,272
.90
Annual energy cost = \$48,792 + \$2,272 = \$51,064″

I encourage you to calculate this self generated utility cost for your facility. Also keep in mind that this example is using \$0.05/kWh, this example was form 2004, today the average industrial sector cost in the US is \$0.0747 (see more here). This annual cost puts so many things into perspective. First and foremost the importance of Maintenance. Even more specific, the preventative maintenance costs become much lower than the impact of even one small oversite. Here is an example from the Department of Energy that discusses a specific and common maintenance issue and it’s annual impact.

“A compressed air system that is served by a 100-horsepower (hp) compressor operating continuously at a cost of \$0.08/kWh has annual energy costs of \$63,232. With a dirty coalescing filter (not changed at regular intervals), the pressure drop across the filter could increase to as much as 6 psi, vs. 2 psi when clean. The pressure drop of 4 psi accounts for 2% of the system’s annual compressed air energy costs. (or an increase of \$1,265 per year)”

The realization of the dollars spent for compressed air certainly pushes the priority of maintenance. If we extrapolate from the above filter example, we can see that a 4 psi pressure drop in that system increased the cost by \$1265 per year. We need to then ask ourselves, what other areas could be causing a pressure drop or stressing the motor? And if there is an issue upstream to this issue, will it cause even more issues, or more pressure drops?

There are many tips, tools, websites, YouTube videos and more, out there that address the recommended maintenance of your compressor and system. Many of you already have specific guidelines for your precise system, and set maintenance schedules in place. Below is a sample checklist (not all-inclusive) of maintenance items to watch for with your compressor in case you need a starting point. If left unchecked and or uncorrected, any of these (if an issue) will cost your company money – over time, lots of money.

• Visually Inspect Air Compressor
• Check moisture traps
• Change Air Filters
• Change Oil Filters
• Change Oil/Water Separators – could (should) be many of these on the lines
• Change Oil Separator O-Ring if necessary
• Inspect Couplers, Hubs and Shaft Seals
• Check Drive Belts condition if applicable
• Check and Log Drive Motor Bearing Temps
• Check and Log Fan Motor Bearing Temps
• Change Oil if necessary
• Check and Log Oil Cooler Temps
• Check and Log After Cooler Temps
• Blow Out Coolers

I would be amiss if I finished this blog without mentioning the perils of pressure leaks. The Compressed Air and Gas Institute stated that a single 1/4″ leak, can cost you between \$2500 and \$8000 per year (CAGI article). Imagine the impact of several leaks!!!

How do I find leaks? I’m glad you asked. The first step is to walk your lines and check any or all of the following areas for leaks or damage.

• Couplings
• Hoses
• Tubes
• Fittings
• Point-Of-Use Devices
• Pipe Joints
• Quick Disconnects
• Filters
• Regulators
• Lubricators
• Condensate Traps
• Valves

A great way to identify leaks is to use our Ultrasonic Leak Detector to listen for leaks. Look for and ask the technicians if there seems to be a change in productivity. Install Pressure Regulators and gauges at each point of use in your facility – monitor and log these pressures often. Once you find an issue, no matter how small, correct it. A small leak adds up \$\$\$ over the hours, weeks, and months.

In addition to leaks, there are many times that air is wasted by being blown on empty space (i.e. the space between items on your conveyor). you, please look at our Electronic Flow Control (EFC) product, this device gives you an out of the box automation solution that can be set up in minutes and save thousands. There are so many clogged and leaking pipes, bad hoses inside many plants, this coupled with using an poor performing Air Gun, or Air Nozzle all have large dollar impacts for your company. EXAIR has products that can help in all of these areas…

In parting, please keep in mind that many Utility companies offer incentives to companies that take an initiative to reduce their energy footprint. In our current time of inflation this is a real way to reduce costs, many times significantly. We are here to help. Please contact us for assistance in dramatically reducing both your utility costs, and your environmental impact.