Air Compressors: Savings Found on the Supply and Demand Side

Producing compressed air can be expensive, but it is necessary for pneumatic systems.  And a large part of that expense is wasted energy, in the form of heat.  Waste will add to your overhead and affect your bottom line.  EXAIR has a line of products to help reduce air consumption at the point-of-use to save you money.  This would include replacing open-pipes and tubes with EXAIR Super Air Nozzles and Super Air Knives.  But, let’s look at the supply side inside your compressor room.  The air compressor operates at about 10% efficiency where most of that loss is in a form of heat. 

Wouldn’t it be nice to recover some of that expense?  You can.  By equipping your air compressor with a heat recovery system.  These systems are designed to recover the loss of heat for other uses.  Today, they can recover somewhere between 50% for liquid-cooled compressors to 80% for air-cooled compressors.  The heat can come from the after-coolers, the electric motor, the “heat of compression”, and the oil cooler.  This reclaimed heat can be used to heat water, warm rooms, pre-heat steam systems, and dry parts. 

Let’s create an example.  A company has a 100 HP air-cooled compressor that is running 8 hours per day for 250 days per year.  The heat recovery system will be able to reclaim 60% of the heat to warm city water in the plant.  If the electrical cost is $0.10 per KWh, we can calculate the savings.

Annual Savings:

100 HP * 0.746 KW/HP * 0.6 (reclaim) * 8 hours/day * 250 days/yr * $0.10/KWh = $8,952.00 savings per year.

In practice, reclaiming the maximum percentage may not be cost effective.  Your company can determine the best percentage for heat recovery by calculating the Return on Investment (ROI).  I wrote a blog post that can help you estimate (Click Here)

As mentioned above, EXAIR saves you money and increase efficiency on the demand side.  EXAIR has engineered nozzles to help reduce compressed air usage.  The following is a quick calculation by replacing an open-end blow-off with an EXAIR Super Air Nozzle.  If you have a ¼” (6mm) copper tube, it will use 33 SCFM (935 SLPM) of compressed air at 80 PSIG (5.5 bar).  As a common replacement, EXAIR uses a model 1100 Super Air Nozzle which will use 14 SCFM (396 SLPM) at 80 PSIG (5.5 bar).  With a simple tube fitting, you can mount the ¼” NPT Super Air Nozzle to the end of the ¼” copper tube.  If we use the same pretext as above, we can find the annual cost savings.  With an air compressor that produces 5 SCFM/hp, we can get a cost savings with the Super Air Nozzle.  The difference in air flow at 80 PSIG (5.5 bar) is:

33 SCFM (copper tube) – 14 SCFM (Model 1100) = 19 SCFM savings

Annual Savings:

19 SCFM * 1 HP/ 5 SCFM * 0.746 KW/HP * 8 hr/day * 250 days/yr * $0.10/KWh = $566.96 savings per year per nozzle.

Whether it is on the supply side or the demand side, companies are looking to reduce or reuse the wasted energy to have a more efficient compressed air system.  The heat recovery system is a bit more complex, but should be considered.  The EXAIR engineered nozzles are more simplistic, and they can give you a return on your investment in a short period of time.  If you would like to discuss how to improve your compressed air system from the supply side to the demand side, an Application Engineer at EXAIR will be happy to assist you. 

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo: Idea by Saydung89Pixabay License.

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.
Cost when fully loaded =
(215 bhp) x (0.746) x (6800 hrs) x ($0.05/kWh) x (0.85) x (1.0) = $48,792
.95
Cost when unloaded =
(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″

Pic courtesy of Gunjan2021 Pixaby License

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.

Pic courtesy of PIRO4D Pixaby License

Thank you for stopping by. Please reach out if you have any questions about this Blog, or any of EXAIR’s amazing products.

Brian Wages
Application Engineer
E-mail: BrianWages@EXAIR.com
Follow me on Twitter

Maintenance for your Air Compressor

In one of my previous jobs, I was responsible for the operation of the facility, and one of my biggest jobs was the operation of our air compressor.  Like with many industries, the compressor system is the life blood of the company.  If the compressor fails, the whole facility will stop.  In this blog, I will share some maintenance items and schedules for air compressors. 

Because the cost to make compressed air is expensive, the compressed air system is considered to be a fourth utility.  With such an important investment, you would like to keep it operating as long and efficiently as possible.  To do this, it is recommended to get your air compressor a “checkup” every so often.  I will cover some important items to check.  Depending on the size and type of air compressor, some items may or may not apply.  It is always best to check with the manufacturer. 

Intake filter:  The intake filter is used to clean the air that is being drawn into the air compressor.  The better the filtration, the less debris that will get into your system.  Particles can damage the air pump mechanisms over time as well as plug filters and heat exchangers downstream.  If they are not properly monitored and cleaned, the air flow can be restricted.  This will cause the motor to operate harder and hotter. 

Compressor Oil:  This would be for flooded screws and reciprocating compressor that use oil to lubricate the bearings and sleeves in the air pump.  Most systems have an oil sight gage to verify levels.  The oil can also be checked for acidity which will tell the degree at which the oil is breaking down.  Just like the motor oil in your car, you will have to replace it out after so many hours of operation. 

Belts & couplings:  These items transmit the power from the motor to the air pump.  Check their alignment, condition, and tension (belts only) as specified by the manufacturer.  You should have spares on hand in case of any failures.

Electric Motors:  A mechanical device that turns electric energy into rotational energy.  It is the main component that uses much energy to make compressed air.  So, some checks are required to foresee any potential issues and major shutdowns.  For the windings inside, the resistance should be measured with a multimeter, and it should fall within the motor’s specifications.  Another check should be on the start capacitor.  The start capacitor stores energy to give the motor a powerful boost to get it turning.  One other item is the centrifugal switch.  Just like the name states, it will disconnect the start capacitor when the motor starts spinning.  One other item for large electric motors is the phase convertor.  These are typically capacitors, and they are designed to keep the direction of a three-phase motors going in the correct rotation.  Both types of capacitors can be checked with a multimeter. 

Air/Oil Separators:  This filter removes as much oil from the compressed air before it travels downstream.  It returns the oil back to the sump of the air compressor.  If the Air/Oil Separator builds too much pressure drop, excess oil can travel downstream.  Not only will the air pump loose the required oil level, but it will affect the performance of downstream parts like your air dryer and after cooler.  Also, the pressure drop is a waste and can rob your air system of workable energy.  

Internal filters:  Many air compressors will come with an attached refrigerated air dryer.   With this type of air compressor, they will place coalescing filters to remove any residual oil.  These filters should be checked for pressure drop.  If the pressure drop gets too high, then it will rob your compressed air system of pressure, and you will not get the required performance.  Some filters come with a pressure drop indicator which can help you to determine the time to change the element.    

Unloader valve:  When the air compressor unloads, this valve helps to remove any of the compressed air that is trapped in the cavity.  When the air compressor restarts, it does not have to “work” against this air pressure.  If they do not fully unload, the air compressor will have to work harder to start, wasting energy.

Preventative maintenance is very important.  As for a schedule, I created a rough sequence to check, change, or clean certain items that are important to your air compressor.  You should also check with your local compressor representative for a more detailed maintenance schedule. 

Daily:

  • After stopping, remove any condensate from the receiver tank.
  • Check oil level. 

Monthly:

  • Inspect cooling fins on air pump.  Clean if necessary
  • Inspect oil cooler. Clean if necessary

Quarterly:

  • Inspect the inlet air filter.  Clean or replace if necessary. 
  • Check the belt for tension and cracks.  Tighten or replace.
  • Check differential pressure indicators on outlet compressed air filters.
  • Ohm check on the electric motor

Yearly:

  • Replace Air Inlet Filter
  • Replace the air-oil separator
  • Test safety valves and unloader valve
  • Replace compressed air filters
  • Change oil
  • Grease bearings if required

Keeping your air compressor running optimal is very important for pneumatic operations and energy savings.  To help your air compressor, you should also check your pneumatic system for optimization.  EXAIR manufactures engineered products that can blow, coat, clean, and cool at reduced air consumption rates; saving you money.  As an example, the model 1102 Mini Super Air Nozzle can save your company $1,872.00 per year for one blow-off device by replacing a 1/8” NPT open pipe.  You can contact an Application Engineer to determine how much EXAIR products can save your company and your air compressor.   

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Image courtesy of Compressor1Creative commons license

Air Compressors: Air Intake and Altitude

Flow rate is the quantity of material that is moved per unit of time.  Generally, the quantity of material can be expressed as a mass or a volume.  For example, mass flow rates are in units of pounds per minute or kilograms per hour.  Volumetric flow rates are stated in cubic feet per minute or liters per hour.  The trick begins when volumetric flow rates are used for a compressible gas in different altitudes.

From the history of air compressors, they could calculate the volume of air being drawn into the air compressor by the size of the cylinder.  With the volume of the compression chamber and the rotations per minute of the motor, RPM, they could calculate the volumetric air flows.  As conditions change like air density, temperatures, and relative humidity; the values of the volumetric flowrate changes.

Since we are looking at the intake flow rates of an air compressor, what happens when they run at different altitudes?  I remember that when I was in Denver, I got easily winded.  Now, this could be that I was out of shape, but it was also because the air is less dense.  That means for a volume of air, the mass of air was less.  This is called the specific volume.  Air compressors work the same way.  So, let’s look at the Ideal Gas Law; Equation 1.

Equation 1:

P * v = R * T

v – Specific Volume

R – Universal Gas Constant

T – Absolute Temperature

P – Absolute Pressure

In a comparative relationship, we can show the changes that can occur with an air compressor at different altitudes.  Since we are looking at altitude, the air density and pressure will change at different elevations above sea level.  If we keep the temperature the same, we can derive a formula from Equation 1.

Equation 2:

P1 * v1 = P2 * v2

P1 – Absolute Pressure at Sea Level

P2 – Absolute Pressure at elevation

v1 – Specific Volume of air at P1

v2 – Specific Volume of air at P2

Specific volume is the inverse of density, so it has the units of ft3/lb or M3/Kg.  If we use an example of a 40 CFM air compressor at sea level, it will produce 40 cubic feet per minute.  We can calculate the flow rate of air that it can produce at 5,000 feet of elevation.  The absolute air pressure at sea level is 14.7 PSIA, and at 5,000 feet, the air pressure is at 12.2 PSIA.  So, if we look at Equation 2, we can rearrange the values to find the change in specific volume from sea level (position 1) to 5,000 feet (position 2):

v2 / v1 = P2 / P1 = 12.2 PSIA / 14.7 PSIA = 0.83

With the 40 CFM air compressor, it will now only produce 40 * 0.83 = 33.2 CFM of compressed air at 5,000 feet.

When sizing an air compressor, it is important to know the conditions.  In this blog, I discussed the effects of altitude as it applies to the intake of an air compressor.  But, no matter the size, elevation, or type of air compressor, EXAIR blow-off products like Super Air Knives, Super Air Nozzles, and Safety Air Guns will help you to save energy and increase safety.  You can speak to an Application Engineer to see how.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb