Estimating the Total Cost of Compressed Air

It is important to know the cost of compressed air at your facility.  Most people think that compressed air is free, but it is most certainly not.  Because of the expense, compressed air is considered to be a fourth utility in manufacturing plants.  In this blog, I will show you how to calculate the cost to make compressed air.  Then you can use this information to determine the need for Intelligent Compressed Air® products.

There are two types of air compressors, positive displacement and dynamic.  The core construction for both is an electric motor that spins a shaft.  Positive displacement types use the energy from the motor and the shaft to change the volume in an area, like a piston in a reciprocating compressor or like rotors in a rotary compressor.  The dynamic types use the energy from the motor and the shaft to create a velocity energy with an impeller.  (You can read more about air compressors HERE).  For electric motors, the power is described either in kilowatts (KW) or horsepower (hp).  As a unit of conversion, there are 0.746 KW in 1 hp.  The electric companies charge at a rate of kilowatt-hour (KWh).  So, we can determine the energy cost to spin the electric motors.  If your air compressor has a unit of horsepower, or hp, you can use Equation 1:

Equation 1:

hp * 0.746 * hours * rate / (motor efficiency)

where:

hp – horsepower of motor

0.746 – conversion to KW

hours – running time

rate – cost for electricity, KWh

motor efficiency – average for an electric motor is 95%.

If the air compressor motor is rated in kilowatts, or KW, then the above equation can become a little simpler, as seen in Equation 2:

Equation 2:

KW * hours * rate / (motor efficiency)

where:

KW – Kilowatts of motor

hours – running time

rate – cost for electricity, KWh

motor efficiency – average for an electric motor is 95%.

As an example, a manufacturing plant operates 250 day a year with 8-hour shifts.  The cycle time for the air compressor is roughly 50% on and off.  To calculate the hours of running time, we have 250 days at 8 hours/day with a 50% duty cycle, or 250 * 8 * 0.50 = 1,000 hours of running per year.  The air compressor that they have is a 100 hp rotary screw.  The electrical rate for this facility is at $0.08/KWh. With these factors, the annual cost can be calculated by Equation 1:

100hp * 0.746 KW/hp * 1,000hr * $0.08/KWh / 0.95 = $6,282 per year.

In both equations, you can substitute your information to see what you actually pay to make compressed air each year at your facility.

The type of air compressor can help in the amount of compressed air that can be produced by the electric motor.  Generally, the production rate can be expressed in different ways, but I like to use cubic feet per minute per horsepower, or CFM/hp.

The positive displacement types have different values depending on how efficient the design.  For a single-acting piston type air compressor, the amount of air is between 3.1 to 3.3 CFM/hp.  So, if you have a 10 hp single-acting piston, you can produce between 31 to 33 CFM of compressed air.  For a 10 hp double-acting piston type, it can produce roughly 4.7 to 5.0 CFM/hp.  As you can see, the double-acting air compressor can produce more compressed air at the same horsepower.

The rotary screws are roughly 3.4 to 4.1 CFM/hp.  While the dynamic type of air compressor is roughly 3.7 – 4.7 CFM/hr.  If you know the type of air compressor that you have, you can calculate the amount of compressed air that you can produce per horsepower.  As an average, EXAIR uses 4 CFM/hp of air compressor when speaking with customers who would like to know the general output of their compressor.

With this information, we can estimate the total cost to make compressed air as shown in Equation 3:

Equation 3:

C = 1000 * Rate * 0.746 / (PR * 60)

where:

C – Cost of compressed air ($ per 1000 cubic feet)

1000 – Scalar

Rate – cost of electricity (KWh)

0.746 – conversion hp to KW

PR – Production Rate (CFM/hp)

60 – conversion from minutes to hour

So, if we look at the average of 4 CFM/hp and an average electrical rate of $0.08/KWh, we can use Equation 3 to determine the average cost to make 1000 cubic feet of air.

C = 1000 * $0.08/KWh * 0.746 / (4 CFM/hp * 60) = $0.25/1000ft3.

Once you have established a cost for compressed air, then you can determine which areas to start saving money.  One of the worst culprits for inefficient air use is open pipe blow-offs.  This would include cheap air guns, drilled holes in pipes, and tubes.  These are very inefficient for compressed air and can cost you a lot of money.  I will share a comparison to a 1/8” NPT pipe to an EXAIR Mini Super Air Nozzle.  (Reference below).  As you can see, by just adding the EXAIR nozzle to the end of the pipe, the company was able to save $1,872 per year.  That is some real savings.

Compressed Air Savings

Making compressed air is expensive, so why would you not use it as efficiently as you can. With the equations above, you can calculate how much you are paying.  You can use this information to make informed decisions and to find the “low hanging fruit” for cost savings.  As in the example above, targeting the blow-off systems in a facility is a fast and easy way to save money.  If you need any help to try and find a way to be more efficient with your compressed air system, please contact an Application Engineer at EXAIR.  We will be happy to assist you.

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

 

Air: What is it?

Air Balloons

What is Air? Air is an invisible gas that supports life on earth. Dry air is made from a mixture of 78% Nitrogen, 21% Oxygen, and 1% of remaining gases like carbon dioxide and other inert gases.  Ambient air contains an average of 1% water vapor, and it has a density of 0.0749 Lbs./cubic foot (1.22 Kg/cubic meter) at standard conditions.  Air that surrounds us does not have a smell, color, or taste, but it is considered a fluid as it follows the rules of fluid dynamics. But unlike liquids, gases like air are compressible.  Once we discovered the potential of compressing the surrounding air, we were able to advance many technologies.

Bellows

Guess when the earliest air compressor was used?  Believe it or not, it was when we started to breathe air.  Our diaphragms are like compressors.  It pulls and pushes the air in and out of our lungs.  We can generate up to 1.2 PSI (80 mbar) of air pressure.  During the iron age, hotter fires were required for smelting.  Around 1500 B.C., a new type of air compressor was created, called a bellows.  You probably seen them hanging by the fireplaces.  It is a hand-held device with a flexible bag that you squeeze together to compress the air.  The high stream of air was able to get higher temperature fires to melt metals.

Then we started to move into the industrial era.  Air compressors were used in mining industries to move air into deep caverns and shafts.  Then as the manufacturing technologies advanced, the requirements for higher air pressures were needed.  The stored energy created by compressing the air allowed us to develop better pneumatic systems for manufacturing, automation, and construction.  I do not know what the future holds in compressed air systems, but I am excited to find out.

Since air is a gas, it will follow the basic rules of the ideal gas law;

PV = nRT  (Equation 1)

P – Pressure

V – Volume

n – Amount of gas in moles

R – Universal Gas Constant

T – Temperature

If we express the equation in an isothermal process (same temperature), we can see how the volume and pressure are related.  The equation for two different states of a gas can be written as follows:

P1 * V1 = P2 * V2  (Equation 2)

P1 – Pressure at initial state 1

V1 – Volume at initial state 1

P2 – Pressure at changed state 2

V2 – Volume at changed state 2

If we solve for P2, we have:

P2 = (P1 * V1)/V2  (Equation 3)

In looking at Equation 3, if the volume, V2, gets smaller, the pressure, P2, gets higher.  This is the idea behind how air compressors work.  They decrease the volume inside a chamber to increase the pressure of the air.  Most industrial compressors will compress the air to about 125 PSI (8.5 bar).  A PSI is a pound of force over a square inch.  For metric pressure, a bar is a kg of force over a square centimeter.  So, at 125 PSI, there will be 125 pounds of force over a 1” X 1” square.  This amount of potential energy is very useful to do work for pneumatic equipment.  To simplify the system, the air gets compressed, stored as energy, released as work and is ready to be used again in the cycle.

Air Compressor

Compressed air is a clean utility that is used in many different applications.  It is much safer than electrical or hydraulic systems.  Since air is all around us, it is an abundant commodity for air compressors to use.  But because of the compressibility factor of air, much energy is required to create enough pressure in a typical system.  It takes roughly 1 horsepower (746 watts) of power to compress 4 cubic feet of air (113L) to 125 PSI (8.5 bar) every minute.  With almost every manufacturing plant in the world utilizing compressed air in one form or another, the amount of energy used to compress air is extraordinary.  So, utilizing compressed air as efficiently as possible is mandatory.  Air is free, but making compressed air is expensive

If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Products, you can contact an Application Engineer at EXAIR.

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

 

Picture: Hot Air Rises by Paul VanDerWerf. Creative Commons Attribution 2.0 Generic.

Picture: Bellows by Joanna Bourne. Creative Commons Attribution 2.0 Generic.

Picture: Air Compressor by Chris Bartle. Creative Commons Attribution 2.0 Generic.

FREE EXAIR Webinar – November 2nd, 2017 @ 2:00 PM EDT

On November 2, 2017 at 2 PM EDT, EXAIR Corporation will be hosting a FREE webinar titled “Optimizing Your Compressed Air System In 6 Simple Steps”.

During this short presentation, we will explain the average cost of compressed air and why it’s important to evaluate the current system. Compressed air can be expensive to produce and in many cases the compressor is the largest energy user in a plant, accounting for up to 1/3 of the total energy operating costs. In industrial settings, compressed air is often referred to as a “fourth utility” next to water, gas and electric.

Next we will show how artificial demand, through operating pressure and leaks, can account for roughly 30% of the air being lost in a system, negatively affecting a company’s bottom line. We will provide examples on how to estimate the amount of leakage in a system and ways to track the demand from point-of-use devices, to help identify areas where improvements can be made.

To close, we will demonstrate how following six simple steps can save you money by reducing compressed air use, increasing safety and making your process more efficient.

CLICK HERE TO REGISTER

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

Intelligent Compressed Air: How to Develop a Pressure Profile

An important part of operating and maintaining a compressed air system is taking accurate pressure measurements at various points in the compressed air distribution system, and establishing a baseline and monitoring with data logging.  A Pressure Profile is a useful tool to understand and analyze the compressed air system and how it is functioning.

Pressure Profile 1
Sample Pressure Profile

The profile is generated by taking pressure measurements at the various key locations in the system.  The graph begins with the compressor and its range of operating pressures, and continues through the system down to the regulated points of use, such as Air Knives or Safety Air Guns.  It is important to take the measurements simultaneously to get the most accurate data, and typically, the most valuable data is collected during peak usage periods.

By reviewing the Pressure Profile, the areas of greatest drop can be determined and the impact on any potential low pressure issues at the point of use.  As the above example shows, to get a reliable 75 PSIG supply pressure for a device or tool, 105-115 PSIG must be generated, (30-40 PSIG above the required point of use pressure.)  As a rule of thumb, for every 10 PSIG of compressed air generation increase the energy costs increase 5-7.5%

By developing a total understanding of the compressed air system, including the use of tools such as the Pressure Profile, steps to best maximize the performance while reducing costs can be performed.

If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

ROI – Return on Investment

Return on Investment (ROI) is a measure of the gain (preferably) or loss generated relative to the amount of money that was invested.  ROI is typically expressed as a percentage and is generally used for personal financial decisions, examining the profitability of a company, or comparing different investments.  It can also be used to evaluate a project or process improvement to decide whether spending money on a project makes sense.  The formula is shown below-

ROI

  • A negative ROI says the project would result in an overall loss of money
  • An ROI at zero is neither a loss or gain scenario
  • A positive ROI is a beneficial result, and the larger the value the greater the gain

Gain from investment could include many factors, such as energy savings, reduced scrap savings, cost per part due to increased throughput savings, and many more.  It is important to analyze the full impact and to truly understand all of the savings that can be realized.

Cost of investment also could have many factors, including the capital cost, installation costs, downtime cost for installation, and others.  The same care should be taken to fully capture the cost of the investment.

Example – installing a Super Air Nozzles (14 SCFM compressed air consumption) in place of 1/4″ open pipe (33 SCFM of air consumption consumption) .  Using the Cost Savings Calculator on the EXAIR website, model 1100 nozzle will save $1,710 in energy costs. The model 1100 nozzle costs $37, assuming a $5 compression fitting and $50 in labor to install, the result is a Cost of Investment of $92.00. The ROI calculation for Year 1 is-

ROI2

ROI = 1,759% – a very large and positive value.  Payback time is only 13 working days.

Armed with the knowledge of a high ROI, it should be easier to get projects approved and funded.  Not proceeding with the project costs more than implementing it.

If you have questions regarding ROI and need help in determining the gain and cost from invest values for a project that includes an EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

Many Ways to $ave on Compressed Air Costs

Using compressed air in the plant is common for many types of processes.  Typical uses are drying, cooling, cleaning and conveying. Compressed air does have a cost to consider, and there are many ways to keep the usage and the costs as low as possible.  The first step is to use an EXAIR Intelligent Compressed Air Product, which has been engineered to provide the most performance while using the least amount of compressed air. The next step is to control the use of the air, to only have it on when needed.

EXAIR offers the EFC – Electronic Flow Control.  It offers the most comprehensive method to maximize the efficiency of compressed air usage.  It combines a photoelectric sensor with a timing control that operates a solenoid valve to turn on and off the air as required. With 8 different program types, an on/off mode that works with any process can be programmed ensuring that the minimum amount of compressed air is used.  You can use the online EFC Savings Calculator to see how quickly the savings add up!

EFCp4
EFC – Electronic Flow Control

Another method would be to use a solenoid valve with some other method of control. Depending on the process, the solenoid could be energized via a machine control output, or as simple as an electrical push button station. EXAIR offers solenoid valves in a variety of flow rates (from 40 to 350 SCFM) and voltages (24 VDC, 120 VAC and 240 VAC) to match the air flow requirements of the products we provide, while integrating into the facility and available supply voltages.

For control of the Cabinet Cooler Systems, the ETC – Electronic Temperature Control, uses a thermocouple to measure cabinet temperature and cycle the system on and off to maintain a precise cabinet temperature, and provides a digital readout of the internal temperatures and on the fly adjustment.  Also available is the Thermostat Control models, which utilize an adjustable bimetallic thermostat to control the solenoid valve, also cycling the unit on and off as needed to maintain a set cabinet temperature.

ETC CC
ETC – Electronic Temperature Control

There are several manual methods that can be used to control the compressed air.  A simple valve can be used to turn the air off when not needed, whether at the end of the work day, at break time, or whenever the air isn’t required.  We offer several options, from a foot controlled valve, to a magnetic base with on/off valve, to a simple quarter turn ball valve.

footpedalvalve (2)dualstand (2) manual_valves (2)

 

To discuss your processes and how an EXAIR Intelligent Compressed Air Product can control the air supply and save you money, feel free to contact EXAIR and myself or one of our other Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web
Like us on Facebook
Twitter: @EXAIR_BB

 

 

A Digital Flowmeter can Help Improve Your Monthly Electric Bill

No one likes paying their bills at the end of the month.  But, if you can save yourself some money, it helps to make it a little easier.  For this customer, he received a monthly bill for his compressed air.

Monthly Bill

An industrial facility consisting of four separate manufacturing plants and a power company that supplied all of them with utilities, i.e. hot water, natural gas, electricity, and compressed air.  The parent company decided to reorganize and sell the entities.  At the end of it, the power company was controlled by a different organization than the manufacturing plants.  The power plant was contracted to still supply the utilities to the individual plants, but now they would be charged individually on a monthly basis.

Being that compressed air is one of the most expensive utilities, the general manager of a solid-state electronic plant really noticed the charge on his bill.  He did an estimate on the amount of air that his equipment was using, and he compared it to the charges.  There was roughly a 20% difference in the figures.  Because of the excessive amount of money, he contacted EXAIR to see what we could offer.

In discussing their system, the compressed air was supplied through one 6” schedule 40 black pipe.  The pipe came into the facility in the ceiling and it branched off to supply the entire shop with compressed air.  He was looking for something to measure the compressed air flow with the ability to measure a cumulative amount.  He could use this amount to compare to his monthly usage.  He was also concerned about cutting into his compressed air line as this could cause him much downtime and additional costs.  He needed something easy to install, accurate, and versatile.

EXAIR Digital Flowmeter

I suggested our 6” Digital Flowmeter with the Model 9150 Summing Remote Display.  EXAIR Digital Flowmeters are designed to measure flow continuously and accurately.  You do not need to weld, cut, or disassemble pipe lines to install.  With a drill guide, the Digital Flowmeter can be easily mounted onto the 6” black pipe by drilling two small holes.  After that, they just had to insert the Digital Flowmeter into the holes, and tighten the clamp around the pipe.  The total procedure took less than 30 minutes, so downtime was minimal.  The EXAIR Digital Flowmeter measures flow by comparative analysis with thermal dispersion; so, the accuracy is very high and recalibration is not required.

EXAIR Summing Remote

With the option of the Summing Remote Display, they could attach it to the Digital Flowmeter and display the flow remotely up to 50 feet away.  They mounted it on the wall next to his office for the operational functions.  With a simple press of a button, it can show the current flow rates, daily flow rates, and cumulative flow rates.  So, during the billing cycle, he was able to get the cumulative measurement to compare the results, and reset the counter to zero for the next month.

Believe it or not, the power company was correct in their measurements.  But, not to waste an entire blog, I did have him turn the compressed air supply off after business hours to watch the flow rate.  He did find his 20% difference in compressed air leakage.  The Digital Flowmeter was able to measure low flows to target other problem areas in your compressed air system.  Now he had another chore in leak detecting and pipe fixing.

EXAIR Optimization line has different products that can help you to get the most out of your compressed air system.  With the customer above, he was able to measure his compressed air flow with the Digital Flowmeter, as well as detecting other issues.  I will now have to talk to him about our Ultrasonic Leak Detector.

 

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Picture: Calculator Calculation Insurance by stevepb.  Creative Commons CC0 Public Domain