What is an Air Compressor?

Internals of an air compressor

What is an air compressor?  This may seem like a simple question, but it is the heartbeat for most industries.  So, let’s dive into the requirements, myths, and types of air compressors that are commonly used.  Like the name states, air compressors are designed to compress air.  Unlike liquid, air is compressible which means that it can be “squished” into a smaller volume by pressure.  With this stored energy, it can do work for your pneumatic system.

There are two types of air compressors, positive displacement and dynamic.  The core component for most air compressors is an electric motor that spins a shaft.  Positive displacement uses the energy from the motor and the shaft to change volume in an area, like a piston in a reciprocating air compressor or like rotors in a rotary air 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 types of air compressors HERE).

Compressed air is a clean utility that is used in many different ways, and it is much safer than electrical or hydraulic systems.  But most people think that compressed air is free, and it is most certainly not.  Because of the expense, compressed air is considered to be a fourth utility in manufacturing plants.  For an electrical motor to reduce a volume of air by compressing it.  It takes roughly 1 horsepower (746 watts) of power to compress 4 cubic feet (113L) of air every minute to 125 PSI (8.5 bar).  With almost every manufacturing plant in the world utilizing air compressors much larger than 1 horsepower, the amount of energy needed to compress air is extraordinary.

Let’s determine the energy cost to operate an air compressor to make compressed air by Equation 1:

Equation 1:

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


Cost – US$

hp – horsepower of motor

0.746 – conversion KW/hp

hours – running time

rate – cost for electricity, US$/KWh

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

As an example, a manufacturing plant operates a 100 HP air compressor in their facility.  The cycle time for the air compressor is roughly 60%.  To calculate the hours of running time per year, I used 250 days/year at 16 hours/day for shifts.  So operating hours equal 250 * 16 * 0.60 = 2,400 hours per year.  The electrical rate at this facility is $0.10/KWh. With these factors, the annual cost to operate the air compressor can be calculated by Equation 1:

Cost = 100hp * 0.746 KW/hp * 2,400hr * $0.10/KWh / 0.95 = $18,846 per year in just electrical costs.

So, what is an air compressor?  The answer is an expensive system to compress air to operate pneumatic systems.  So, efficiency in using compressed air is very important.  EXAIR has been manufacturing Intelligent Compressed Air Products since 1983.  If you need alternative ways to save money when you are using your air compressor, an Application Engineer at EXAIR will be happy to help you.

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


Compressor internals image courtesy of h080, Creative Commons License.

What is the USB Data Logger for Digital Flow Meters? How Can It Help Me?

USB Data Logger
The USB data logger works with all of EXAIR’s Digital Flow Meters and provides valuable feedback for optimizing your compressed air system.

EXAIR’s Model 9147 USB Data Logger has become one of the most valuable tools that we sell to help customers get a “view” of their compressed air usage over time. One of the important tenets we promote at EXAIR is energy savings by prudent use of compressed air through our engineered solutions (Air Knife, Air Nozzles, Air Amplifier, etc.). But how does a person in charge of such systems really “know” whether they are helping or hurting their compressed air system?

The first step is to have an appropriate flow meter which can give an indication of how much air volume is being used. EXAIR’s line of Digital Flow Meters are perfect for getting to that point with instant and direct readings that don’t need to be calculated any further. What you see on the meter is the flow in either SCFM or m3/hr calibrations.

The second step is to attach the USB Data Logger to the Digital Flow Meter so that readings can be kept over time. It is like setting up a security camera for your compressed air system. Nothing gets by without being recorded.

The USB Data Logger can be connected to just about any type of monitoring system that has a 4 – 20 mA output to which the 2-wire harness can be installed. A quick and easy initialization to choose the unit of measure, to select the frequency of measurement and some optional alarms is all that is necessary. The software package is included with the USB Data Logger and is convenient to run on a typical desktop or laptop computer. You simply, set it and forget it (at least until you want to do some reporting).

The reporting is how the USB Data Logger can help you as the person concerned with monitoring the compressed air use in your facility. Once the defined monitoring period of time has passed, the USB Data Logger can be removed from its socket, stopped from recording and the data is then downloaded into a suitable format that can be imported into EXCEL or other spreadsheet program for creating charts to analyze what is happening, when it is happening and how much compressed air is being used. In the analysis, you can compare the flow data and times with certain problems in a production line that might cause low pressure condition which shuts machinery down. You might also be able to determine where additional, point of use compressed air storage might be needed close to certain processes.

Ultimately, the USB Data Logger allows you to “see” your compressed air system in a way that allows you to sleuth out problems seen that might have no other explanation. It can also help you to justify your air savings when you apply the other air saving compressed air products that EXAIR produces by monitoring a base line for “before” performance and “after” performance. After all, it if is important to your organization, it should be measured. And compressed air is certainly a utility that should be measured.

Neal Raker, Application Engineer