IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY

Improving 

Compressed Air

System Performance

A Sourcebook for Industry 

Third Edition 

U.S. DEPARTMENT OF 

ENERGY Energy Efficiency &

Renewable Energy ADVANCED MANUFACTURING OFFICE
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY

ACKNOWLEDGEMENTS

Improving Compressed Air System Performance: A Sourcebook for Industry is a cooperative effort of the U.S. 

Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) Advanced Manufacturing Office 

and the Compressed Air Challenge®. EERE originally undertook this project as part of a series of sourcebook 

publications on industrial systems. Other topics in this series include: pump systems; fan systems; motors; process 

heating; and steam systems. As work on the first edition progressed, the Compressed Air Challenge® was formed, 

bringing together the extraordinary combined talents of compressed air system auditors, trade associations, 

equipment manufacturers and distributors, utilities, and government agencies in a collaborative effort to improve 

the performance of industrial compressed air systems. The two programs joined forces in preparing the second and 

this third edition. For more information about EERE and the Compressed Air Challenge®, see Section 3: Where to 

Find Help.

The Compressed Air Challenge®, EERE’sAdvanced Manufacturing Office, Lawrence BerkeleyNational Laboratory, and

Resource Dynamics Corporation wish to thank the staff at the many organizations who so generously assisted inthe

collectionofdataforthissourcebook. Thecontributionsofthefollowingparticipants are appreciated:

Ron Marshall, Manitoba Hydro

William Scales, Scales Industrial Technologies, Inc.

Gary Shafer, Shafer Consulting Services, Inc.

Paul Shaw, Scales Industrial Technologies, Inc.

Paul Sheaffer, Lawrence Berkeley National Lab

Rick Stasyshan, Compressed Air and Gas Institute

H.P.VanOrmer,Air PowerUSA

The review and comment from the following participants is also appreciated: Niff Ambrosino, Scales Industrial 

Technologies, Inc.; Joseph Ghislain, Ford Motor Company; Thomas Hyde, Alcoa, Inc.; Tracey Kohler, Compressed 

Air Challenge; Doug Peace, Shaw Industries Group, Inc.; David Prator, Atlas Copco; Tom Osborn, Bonneville 

Power Administration; Bill Orthwein, U.S. Department of Energy, Dean Smith, Air Science Engineering, Inc.; 

Dusty Smith, Pneu-Logic Corp.; Jody Sutter, Ingersoll Rand; Tony Yanessa, Tennessee Valley Authority; Jeff 

Yarnall, Rogers Machinery Co.

Finally,aspecialthankstoWilliamScalesforhis extraordinary assistance in developing this third edition and previous 

editions.

Prepared for: Compressed Air Challenge and the

United States Department of Energy

Prepared by: Lawrence Berkeley National Laboratory

Berkeley, CA

Resource Dynamics Corporation

McLean, VA

U.S. Department of Energy

Energy Efficiency and Renewable Energy

Bringing you a prosperous future where energy is clean, 

abundant, reliable, and affordable
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY

CONTENTS

QUICK START GUIDE

SECTION 1. INTRODUCTION TO INDUSTRIAL COMPRESSED AIR SYSTEMS

SECTION 2. PERFORMANCE IMPROVEMENT OPPORTUNITY ROADMAP

FACT SHEET 1: ANALYZING COMPRESSED AIR NEEDS .....................................................................................................................20

FACT SHEET 2: POTENTIALLY INAPPROPRIATE USES OF COMPRESSED AIR .....................................................................................24

FACT SHEET 3: COMPRESSED AIR SYSTEM LEAKS.............................................................................................................................28

FACT SHEET 4: PRESSURE DROP AND CONTROLLING SYSTEM PRESSURE.........................................................................................31

FACT SHEET 5: COMPRESSED AIR SYSTEM CONTROLS .....................................................................................................................34

FACT SHEET 6: COMPRESSED AIR STORAGE.....................................................................................................................................43

FACT SHEET 7: PROVEN OPPORTUNITIES AT THE COMPONENT LEVEL.............................................................................................45

FACT SHEET 8: MAINTENANCE OF COMPRESSED AIR SYSTEMS FOR PEAK PERFORMANCE..............................................................51

FACT SHEET 9: HEAT RECOVERY AND COMPRESSED AIR SYSTEMS...................................................................................................58

FACT SHEET 10: BASELINING COMPRESSED AIR SYSTEMS................................................................................................................60

FACT SHEET 11: DETERMINING YOUR COMPRESSED AIR SYSTEM ANALYSIS NEEDS ........................................................................62

FACT SHEET 12: COMPRESSED AIR SYSTEM ECONOMICS AND SELLING PROJECTS TO MANAGEMENT.............................................65

SECTION 3. WHERE TO FIND HELP

ADVANCED MANUFACTURING OFFICE ............................................................................................................................................70

THE COMPRESSED AIR CHALLENGE..................................................................................................................................................71

DIRECTORY OF CONTACTS ...............................................................................................................................................................73

RESOURCES AND TOOLS ..................................................................................................................................................................74

BOOKS AND REPORTS ................................................................................................................................................................................74

EDUCATIONAL BROCHURES.........................................................................................................................................................................77

ONLINE RESOURCES ..................................................................................................................................................................................78

DOE TIP SHEETS ......................................................................................................................................................................................79

DOE CASE STUDIES ..................................................................................................................................................................................79

PERIODICALS............................................................................................................................................................................................79

SOFTWARE ..............................................................................................................................................................................................79

VIDEOS...................................................................................................................................................................................................80

WORKSHOPS AND TRAINING COURSES..........................................................................................................................................................80

APPENDIX A: GLOSSARY OF BASIC COMPRESSED AIR SYSTEM TERMINOLOGY................................................................................83

APPENDIX B: PACKAGED COMPRESSOR EFFICIENCY RATINGS .........................................................................................................89

APPENDIX C: CAGI COMPRESSOR AND DRYER DATA SHEETS...........................................................................................................91

ROTARY COMPRESSOR...............................................................................................................................................................................92

REFRIGERANT DRYERS ...............................................................................................................................................................................93

ROTARY VARIABLE FREQUENCY DRIVE COMPRESSOR.......................................................................................................................................94

CENTRIFUGAL COMPRESSORS......................................................................................................................................................................95
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY

APPENDIX D: THE COMPRESSED AIR SYSTEM MARKETPLACE ..........................................................................................................96

MARKET SIZE AND ENERGY CONSUMPTION ...................................................................................................................................................96

COMPRESSED AIR SYSTEM MARKETPLACE .....................................................................................................................................................96

THE MARKET FOR COMPRESSED AIR SYSTEM EFFICIENCY SERVICES ..................................................................................................................100

APPENDIX E: GUIDELINES FOR SELECTING A COMPRESSED AIR SYSTEM PROVIDER.......................................................................103

WHAT TO LOOK FOR WHEN SELECTING A SERVICE PROVIDER...........................................................................................................103

COMPRESSED AIR CHALLENGE®.........................................................................................................................................................104

LEVELS OF ANALYSIS OF COMPRESSED AIR SYSTEMS.........................................................................................................................104

LEVELS OF ANALYSIS ..........................................................................................................................................................................105
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY

FIGURES

Figure 1.1 Components of a Typical Industrial Compressed Air System..............................................................................................................4

Figure 1.2 Compressor Family Tree...........................................................................................................................................................................6

Figure 2.1 Performance Opportunities...................................................................................................................................................................19

Figure 2.2 Simplified Compressed Air System Block Diagram.............................................................................................................................22

Figure 2.3 Pressure Profile at Single Point in Time................................................................................................................................................22

Figure 2.4 Pressure Profile over a Defined Time Period...................................................................................................................................... 23

Figure 2.5 Effect of Receiver Capacity on Lubricant-Injected, Rotary Compressor with Load/Unload Capacity Control...........................40

Figure 2.6 Lubricant-Injected Compressor with Inlet Valve Modulation...........................................................................................................41

Figure 2.7 Lubricant-Injected Rotary Compressor Performance with Variable Displacement.......................................................................41

Figure 2.8 Lubricant-Injected Rotary Compressor Performance with Variable Speed Control......................................................................42

Figure D-1. The Compressed Air System Marketplace.........................................................................................................................................97

TABLES

Table 1.1 Industrial Sector Uses of Compressed Air.............................................................................................................................................16

Table 1.2 Non-Manufacturing Sector Uses of Compressed Air...........................................................................................................................17
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 1

QUICK START GUIDE

Thissourcebook is designed to provide compressed air

system users with a reference that outlines opportunities for

system performance improvements. It is not intendedto

be a comprehensive technicaltexton improving

compressed airsystems, but rather a documentthatmakes

compressed airsystemusers aware of the performance

improvement potential, details some of the significant

opportunities, and directs users toadditionalsourcesof

assistance.Thesourcebook is dividedintothethreemain

sectionsoutlinedbelow.

Section 1. Introduction to Industrial 

Compressed Air Systems

This sectionisintendedforreaderswhowantto gainan

understandingofthebasicsofindustrial compressed air

systems. The components of an industrial compressed air

system are described and applications of compressed air

systems in different industries are characterized.

Compressed airsystem users already familiar with

compressed airfundamentals maywantto skipthissection.

Section 2. Performance Improvement 

Opportunity Roadmap

This section consists of a series of fact sheets that 

outline specific opportunities for enhancing the 

performance of a compressed air system. The fact 

sheets address system-level opportunities such as using 

heat recovery and fixing leaks as well as individual 

component-level opportunities. The following fact 

sheets are included.

2.1—Analyzing Compressed Air Needs

2.2—Potentially Inappropriate Uses of Compressed Air

2.3—Compressed Air System Leaks

2.4—Pressure Drop and Controlling System Pressure

2.5—Compressed Air System Controls

2.6—Compressed Air Storage

2.7—Proven Opportunities at the Component Level

2.8—Maintenance of Compressed Air Systems for Peak

Performance

2.9—Heat Recovery and Compressed Air Systems

2.10—Baselining Compressed Air Systems

2.11—Compressed Air System Assessments and Audits and

Selecting a Service Provider

2.12—Compressed Air System Economics and Selling

Projectsto Management

Section 3. Where to Find Help

The third section of this sourcebook is a directory of 

resources, tools, and information that are available to 

compressed air systems users to help them improve 

their systems. It includes:

• A description of EERE’s Advanced Manufacturing 

Office, a division of the U.S. Department of Energy 

aimed at improving the performance of industrial 

systems

• A description of the Compressed Air Challenge®, a

nationaleffortinvolvingallcompressedair market

stakeholders aimed at increasing the demand for high

performance compressed air systems, primarily

through awareness building, education, and training

• Adirectoryofassociationandotherorganization

contacts involved in the compressed air system

market

• A listing and description of compressed airsystemrelated resources and tools, including books,

brochures, periodicals,software, videos,workshops,

and training courses.

• Electric utility companies may be able to provide 

some assistance or referrals

• Financial assistance may be available from utility 

rebates, energy efficiency grants and loans. A listing 

of available assistance by state is available at 

www.dsireusa.org. 

Appendices

The sourcebook also contains five appendices:

A. A glossary defining terms used in the 

compressed air industry

B. Information on the Compressed Air and Gas 

Institute’s (CAGI) Packaged Compressor 

Efficiency Ratings

C. Data sheets outlining a common format and 

style for reporting compressor and dryer 

performance

D. Overview of the compressed air systems 

marketplace
QUICK START GUIDE

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 2

E. Guidelines for Selecting a Compressed Air 

System Service Provider, a document that offers 

guidance for selecting a firm to provide 

integrated services to improve compressed air 

system performance.

The Systems Approach

Improving and maintaining peak compressed air system 

performance requires not only addressing individual 

components, but also analyzing both the supply and 

demand sides of the system and how they interact. This 

practice is often referred to as taking a “systems 

approach” because the focus is shifted away from 

individual components to total system performance. 

Applying the systems approach usually involves the 

following types of interrelated actions:

• Establishing current conditions and operating 

parameters, including baselining of inefficiencies

• Determining present and future process 

production needs

• Gathering and analyzing operating data and 

developing load duty cycles

• Assessing alternative system designs and 

improvements

• Determining the most technically and 

economically sound options, taking into 

consideration all of the sub-systems

• Implementing those options

• Assessing operations and energy consumption 

and analyzing economics

• Continuing to monitor and optimize the system

• Continuing to operate and maintain the system 

for peak performance.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 3

SECTION 1: INTRODUCTION TO COMPRESSED AIR SYSTEMS

This section of the sourcebook is intended for readers 

who want to gain an understanding of the basics of 

industrial compressed air systems. A glossary of basic 

terminology is included in Appendix A for users 

unfamiliar with the terms used in this chapter.

Compressed air is widely used throughout 

manufacturing industries and is often considered the 

“fourth utility” at many facilities. Almost every 

industrial plant, from a small machine shop to an 

immense pulp and paper mill, has some type of 

compressed air system. In many cases, the compressed 

air system is so vital that the facility cannot operate 

without it. Plant air compressor systems can vary in size 

from a small unit of 5 horsepower (hp) to huge systems 

with more than 50,000 hp.

In many industrial facilities, air compressors use more 

electricity than any other type of equipment. 

Inefficiencies in compressed air systems can be 

significant. Energy savings from system improvements 

can be substantial, resulting in thousands, or even 

hundreds of thousands of dollars of potential annual 

savings, depending on use. A properly managed 

compressed air system can save energy, reduce 

maintenance, decrease downtime, increase production 

throughput, and improve product quality

Compressed air systems consist of a supply side and a 

demand side. The supply side includes compressors and 

air treatment (dryers and filters). The demand side 

includes distribution and end-use equipment. A 

properly managed supply side will result in clean, 

appropriately dried, stable air being delivered at the 

appropriate pressure in a dependable, cost-effective 

manner. A properly managed demand side minimizes 

wasted air and uses compressed air for appropriate 

applications. Improving and maintaining peak 

compressed air system performance requires 

addressing both the supply and demand sides of the 

system and how the two interact.

Components of an Industrial 

Compressed Air System

A compressor is a machine that is used to increase the 

pressure of a gas. The earliest compressors were

bellows, used by blacksmiths to intensify the heat in 

their furnaces. The first industrial compressors were 

simple, reciprocating piston-driven machines powered 

by a water wheel.

A modern industrial compressed air system is composed 

of several major sub-systems. Major sub-systems 

include the compressor, prime mover, controls, 

treatment equipment and accessories, and the 

distribution system. The compressor is the mechanical 

device that takes in ambient air and increases its 

pressure. The prime mover powers the compressor. 

Controls serve to regulate the amount of compressed 

air being produced. The treatment equipment removes 

contaminants from the compressed air, and accessories 

keep the system operating properly. Distribution 

systems are analogous to wiring in the electrical 

world—they transport compressed air to where it is 

needed. Compressed air storage can also serve to 

improve system performance and efficiency. Figure 1.1 

shows a representative industrial compressed air 

system and its components.

Compressor Types

Many modern industrial air compressors are sold 

“packaged” with the compressor, drive motor, and 

many of the accessories mounted on a frame for ease of 

installation. Provision for movement by forklift is 

common. Larger packages may require the use of an 

overhead crane. An enclosure may be included for 

sound attenuation and aesthetics.
INTRODUCTION TO COMPRESSED AIR SYSTEMS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 4

Compressor

Package

Enclosure

Moisture 

Separator

Condensate 

Drain

Figure 1.1 Components of a Typical Industrial Compressed Air System

Air Inlet 

Filter

Aftercooler 

and Lubricant 

Cooler

Control 

Panel

Motor

Compressor 

Air End

Lubricant/Air 

Separator

Filter, Regulator 

Lubricator

Pneumatic 

Tool

Distribution 

System

Pressure-Flow 

Controller

Dryer Air Filter Air 

Receiver
INTRODUCTION TO COMPRESSED AIR SYSTEMS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 5

As shown in Figure 1.2, there are two basic compressor 

types: positive-displacement and dynamic. In the 

positive-displacement type, a given quantity of air or 

gas is trapped in a compression chamber and the 

volume which it occupies is mechanically reduced, 

causing a corresponding rise in pressure prior to 

discharge. At constant speed, the air flow remains 

essentially constant with variations in discharge 

pressure. Dynamic compressors impart velocity energy 

to continuously flowing air or gas by means of impellers 

rotating at very high speeds. The velocity energy is 

changed into pressure energy both by the impellers and 

the discharge volutes or diffusers. In the centrifugaltype dynamic compressors, the shape of the impeller 

blades determines the relationship between air flow 

and the pressure (or head) generated.

Positive Displacement Compressors

These compressors are available in two types: 

reciprocating and rotary. Reciprocating compressors 

work like bicycle pumps with the exception that an 

electric motor replaces the human energy source. A 

piston, driven through a crankshaft and connecting rod 

by an electric motor, reduces the volume in the cylinder 

occupied by the air or gas, compressing it to a higher 

pressure. Single- acting compressors have a 

compression stroke in only one direction, while doubleacting units provide a compression stroke as the piston 

moves in each direction. Large, industrial reciprocating 

air compressors are double-acting and water-cooled. 

Multi-stage, double- acting compressors are the most 

efficient compressors available, and are typically larger, 

noisier, and more costly than comparable rotary units. 

Reciprocating compressors are available in sizes from 

less than 1 hp to more than 600 hp.

Rotary compressors have gained popularity and are 

now the “workhorse” of American industry. They are 

most commonly used in sizes from about 10 to 500 hp. 

The most common type of rotary compressor is the 

helical-twin, screw-type (also known as rotary screw or 

helical-lobe). Male and female rotors mesh, trapping 

air, and reducing the volume of the air along the rotors 

to the air discharge point. Rotary screw compressors 

have low initial cost, compact size, low weight, and are 

easy to maintain. Rotary screw compressors may be airor water-cooled. Less common rotary compressors 

include sliding-vane, liquid-ring, and scroll-type.

Single-Acting, Reciprocating Air Compressors

This type of compressor is characterized by its 

“automotive” type piston driven through a connecting 

rod from the crankshaft. Compression takes place on 

the top side of the piston on each revolution of the 

crankshaft. Single-acting, reciprocating air compressors 

are generally air-cooled. These may be single- stage, 

usually rated at discharge pressures from 25 to 125 

pounds per square inch gauge (psig), or two-stage, 

usually rated at discharge pressures from 125 psig to 

175 psig or higher.

The most common air compressor in the fractional and 

single-digit hp sizes is the air-cooled, reciprocating air 

compressor. Single-acting reciprocating compressors 

above 30 hp are much less common. Two-stage and 

multi-stage designs include inter-stage air-cooling to 

reduce air temperatures to the second stage for 

improved efficiency and durability.

Pistons used in single-acting compressors are of the 

“automotive” or “full skirt” design, the underside of the 

piston being exposed to the crankcase. Lubricated 

versions have a combination of compression and 

lubricant-control piston rings, which seal the 

compression chamber, control the lubricant to the 

compression chamber, and act (in some designs) as 

support for piston movement on the cylinder walls.

Lubricant-free, or non-lube designs, do not allow 

lubricant in the compression chamber and use pistons 

of self-lubricating materials or use heat resistant, nonmetallic guides and piston rings that are selflubricating. Some designs incorporate a distance piece 

or crosshead to isolate the crankcase from the 

compression chamber.

Lubricant-less (or oil-less) designs have piston 

arrangements similar to lubricant-free versions, but do 

not have lubricant in the crankcase. Generally these 

have greased pre-packed crankshafts and connecting 

rod bearings.
INTRODUCTION TO COMPRESSED AIR SYSTEMS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 6

 Figure 1.2 Compressor Family Tree

Cooling. Single-acting air compressors have different 

arrangements for removing the heat of compression. 

Air-cooled versions have external finning for heat 

dissipation on the cylinder, cylinder head, and in some 

cases, the external heat exchanger. Air is drawn or 

blown across the fins and the compressor crankcase by 

a fan, which may be the spokes of the drive 

pulley/flywheel.

Liquid-cooled compressors have jacketed cylinders, 

heads and heat exchangers, through which liquid 

coolant is circulated to dissipate the heat of 

compression. Water, or an ethylene glycol mixture to 

prevent freezing, may be employed.

Drives. The most common drive arrangement is a belt 

drive from an electric motor. The compressor sheave 

also acts as a flywheel to limit torque pulsations and its 

spokes often are used for cooling air circulation. Belt 

drives allow a great degree of flexibility in obtaining the 

desired speed of rotation.

Flange-mounted, or direct-coupled motor drives 

provide compactness and minimum drive maintenance. 

Belts and couplings must be properly shielded for safety 

and to meet Occupational Safety & Health 

Administration (OSHA) requirements.

Double-Acting, Reciprocating Air Compressors

Double-acting reciprocating compressors use both sides 

of the piston for air compression, almost doubling the 

capacity for a given cylinder size. A piston rod is 

attached to the piston at one end and to a crosshead at 

the other end. The crosshead ensures that the piston 

travels concentrically within the cylinder. These 

compressors may be single- or multi-stage, depending 

on discharge pressure and hp size. These are generally 

available in larger horsepower sizes.

Cooling. Double-acting air compressors generally have 

cooling water jackets around the cylinder body and in 

the cylinder head. This, combined with their relatively 

slow speed of operation and water-cooled intercooling, 

results in excellent compression efficiency.

Lubrication. Cylinder lubrication is generally by means 

of a pressure or vacuum-feed cylinder lubricator, with a 

feed rate of several drops per minute, depending on 

cylinder size and piston speed and as specified by the 

manufacturer. Lubricant-free versions also are available 

with polytetrafluorethylene (PTFE) or similar materials 

for pistons, riders, and compression rings. A distance 

piece is provided between the crankcase and the 

cylinder(s) to ensure that no part of the piston rod, 
INTRODUCTION TO COMPRESSED AIR SYSTEMS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 7

which enters the lubricated crankcase, can enter the 

lubricant-free cylinder area.

Balance. Single- and two-cylinder compressors of this 

type generally require a substantial foundation due to 

unbalanced reciprocating forces.

Drives. Below 200 hp, belt drives and flange-mounted 

induction motors are normally used. For motors larger 

than 300 hp, flange-mounted, synchronous motors are 

sometimes used with a 1.0 power factor or 0.8 leading 

power factor to provide power factor correction to offset other induction-type electrical loads.

Lubricant-Injected Rotary Screw Compressors

The lubricant-injected rotary screw compressor 

powered by an electric motor has become a dominant

type of industrial compressor for a wide variety of 

applications.

Compression Principle. The lubricant-injected, rotaryscrew compressor consists of two intermeshing rotors 

in a machined housing (Rotor Housing) having an inlet 

port at one end and a discharge port at the other. The 

male rotor has lobes formed helically along its length 

while the female rotor has corresponding helical 

grooves or flutes. The number of helical lobes and 

grooves may vary in otherwise similar designs.

Air flowing in through the inlet port fills the spaces 

between the lobes on each rotor. Rotation then causes 

the air to be trapped between the lobes and the rotor 

housing as the inter-lobe spaces pass beyond the inlet 

port. As rotation continues, a lobe on one rotor rolls

into a groove on the other rotor and the point of 

intermeshing moves progressively along the axial length 

of the rotors. This reduces the space occupied by the 

air, resulting in increased pressure. Compression 

continues until the inter-lobe spaces are exposed to the 

discharge port when the compressed air is discharged.

Lubricant is injected into the compression chamber 

during compression and serves three basic functions:

1) lubrication for the intermeshing rotors and 

associated bearings; 2) removal of the heat caused by 

compression; and 3) seals the clearances between the 

meshing rotors and between rotors and rotor housing.

Lubrication. The generic term “lubricant” has been 

used instead of oil. The lubricant may be a hydrocarbon 

product, but most compressors now use cleaner and 

longer life synthetic lubricants, including diesters, 

polyglycols, polyalphaolefins, polyol esters, and siliconebased lubricants. These newer products are suitable for 

a wider range of temperatures.

A mixture of compressed air and injected lubricant 

leaves the air end and is passed to a sump/separator 

where the lubricant is removed from the compressed 

air. Directional and velocity changes are used to 

separate most of the liquid. The remaining aerosols in 

the compressed air, then are separated by means of an 

air/lubricant separator or a coalescing filter, resulting in 

only a few parts per million (ppm) of lubricant carryover (usually in the range of 2 to 5 ppm). A minimum 

pressure device, often combined with a discharge check 

valve, prevents excessive velocities through the 

separator element until a normal system pressure is 

achieved at start-up. Most lubricant-injected rotary 

screw compressor packages use the air pressure in the 

lubricant sump/separator, after the discharge of the air 

end, to circulate the lubricant through a filter and 

cooler prior to reinjection to the compression chamber. 

Some designs may use a lubricant pump.

Multi-stage compressors. Multi-stage compressors 

have different manufacturing designs. Multiple stages

are used either for improved efficiency at a given 

pressure or to achieve higher pressures.

Cooling. The temperature of the lubricant injected into 

the compression chamber is generally controlled 

directly or indirectly to a minimum temperature by

controlling the discharge temperature. A thermostatic 

bypass valve allows some or all of the lubricant being 

circulated to bypass the lubricant cooler to maintain the 

desired temperature over a wide range of ambient 

temperatures.

Generally, suitable lubricant temperature and viscosity 

are required for proper lubrication, sealing, and to avoid 

condensation in the lubricant sump. It also is necessary 

to avoid excessive temperatures, which could result in a 

breakdown of the lubricant and reduced life.

In addition to lubricant cooling, an aftercooler is used to 

cool the discharged air and a moisture separator with 

an automatic drain trap removes the condensate. In the 
INTRODUCTION TO COMPRESSED AIR SYSTEMS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 8

majority of applications, air-cooled, radiator-type 

lubricants and air coolers are employed and provide the 

opportunity for heat recovery from the compression 

process for facility heating. In water-cooled designs, 

water-cooled heat exchangers with water control valves 

also are available on most rotary screw compressor 

packages.

Single-stage, lubricant-injected, rotary screw 

compressor packages are available from 3 to 900 hp, or 

8 to 5000 cubic feet per minute (cfm), with discharge 

pressures from 50 to 250 psig. Two-stage versions can 

reduce specific power and some can achieve discharge 

pressures up to 500 psig. Lubricant-injected, rotary 

screw vacuum pumps also are available from 80 to 

3,100 inlet cfm and vacuum to 29.7 inches Hg. 

Lubricant-injected, rotary-vane compressors are a less 

common type of rotary compressor and are available in 

a limited size range.

Air/Lubricant Separators. The air/lubricant separator in 

a lubricant-cooled, rotary screw compressor generally 

starts with a 2 to 3 psid pressure drop at full-load when 

new. Higher pressure differentials cause the 

compressor motor to consume more energy and 

possibly exceed the service factor. Maintenance 

manuals usually suggest changing them when there is a 

10 to 12 psid pressure drop across the separator. In 

many cases it may make sense to make an earlier 

separator replacement, especially if electricity prices 

are high.

Lubricant-Free Rotary Screw Compressors

The principle of compression in lubricant-free rotary 

screw compressors is similar to that of the lubricantinjected rotary screw compressors but, without 

lubricant being introduced into the compression 

chamber. Two distinct types are available: the dry type 

and the water-injected type.

In the dry type, the intermeshing rotors are not allowed 

to touch and their relative positions are maintained by 

means of lubricated timing gears external to the 

compression chamber. Since there is no injected fluid to 

remove the heat of compression, most designs use two 

stages of compression with an intercooler between the 

stages and an aftercooler after the second stage. The 

lack of a sealing fluid also requires higher rotation 

speeds than for the lubricant-injected type. Dry-type, 

lubricant-free rotary screw compressors have a range 

from 25 to 4,000 hp or 90 to 20,000 cfm. Single-stage 

units operate up to 50 psig, while two-stage can 

generally achieve up to 150 psig.

In the water-injected type, similar timing gear 

construction may sometimes be used, but water is 

injected into the compression chamber to act as a seal 

in internal clearances and to remove the heat of 

compression. This may allow pressures in the 100 to 

150 psig range to be accomplished with only one stage. 

The injected water, together with condensed moisture 

from the atmosphere, is removed from the discharged 

compressed air by a conventional moisture separation 

device. Similar to the lubricant-injected type, lubricantfree rotary screw compressors generally are packaged 

with all necessary accessories.

Lubrication. Lubricant-free rotary screw compressors 

utilize lubricant for bearings and gears, which are 

isolated from the compression chamber. The lubricant 

also may be used for stator jacket cooling in air-cooled 

units. Typically, a lubricant pump is directly driven from 

a shaft in the gearbox, assuring lubricant flow 

immediately at start-up and during run-down in the 

event of power failure. A lubricant filter, typically with 

10 micron rating, protects bearings, gears, and the 

lubricant pump from damage.

Cooling. The cooling system for the dry-type, lubricantfree rotary screw compressor normally consists of an air 

cooler after each stage and a lubricant cooler. These 

may be water-cooled or air-cooled, radiator-type. Some 

older two-stage designs also employ an additional heat 

exchanger to cool a small portion of the compressed air 

for recycling to the compressor inlet during the 

unloaded period.

Dynamic Compressors

Dynamic compressors can be categorized as centrifugal 

or axial. The centrifugal-type is the most common and is 

widely used for industrial compressed air. Each 

impeller, rotating at high speed, imparts radial flow to 

the air or gas, which then passes through a volute or 

diffuser. Some large manufacturing plants use 

centrifugal compressors for both base loading and 

trimming, while in other facilities, plants use other 

compressor types to accommodate demand load swings 
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while the dynamic centrifugal compressors handle the 

base load.

Axial compressors consist of a rotor with multiple rows 

of blades and a matching rotor housing with rows of 

stationary vanes. The rotating blades impart energy to 

the air, primarily in an axial plane. The stationary vanes 

then act as a diffuser to convert the residual kinetic 

energy into potential energy by increasing the pressure. 

This type of compressor is restricted to very high flow 

capacities. Mixed flow compressors have impellers and 

rotors which combine the characteristics of both axial 

and centrifugal compressors.

Centrifugal Air Compressors

A centrifugal air compressor has a continuously flowing 

air stream which has kinetic energy, imparted to it by an 

impeller, or impellers, which rotate at speeds that can 

exceed 50,000 revolutions per minute (rpm). 

Approximately one half of the energy is developed in 

the impeller with the other half achieved by converting 

the velocity energy to pressure energy as the air 

velocity is reduced in a diffuser and volute. 

The most common centrifugal air compressor is one 

with two to four stages for pressures in the 100 to 150 

psig range. A water-cooled intercooler and separator 

between each stage returns the air temperature to 

approximately ambient temperature and removes 

condensed moisture before entering the next stage. An 

aftercooler cools the air from the final stage and a 

moisture separator with an automatic drain removes 

the moisture prior to air delivery to distribution. Aircooled centrifugal compressors are available within a 

limited size range.

The inherent characteristic of centrifugal air 

compressors is that as system pressure decreases, the 

compressor’s flow capacity increases. The steepness of 

the pressure head/capacity curve is dependent upon 

the design of the impellers and diffusers. 

Most standard industrial centrifugal air compressor 

packages are designed for an ambient temperature of 

95°F and near sea level barometer pressure. The 

dynamic nature of the centrifugal compressor results in 

the pressure head generated by each impeller 

increasing as the air density increases. The compressor 

mass flow and actual cubic feet per minute capacity at a 

given discharge pressure increases as the ambient 

temperature decreases, provided the motor can 

support the increased power requirements. 

Typically, a capacity control system is provided with the 

compressor to maintain the desired capacity and to 

operate within the motor horsepower limits. The 

control system regulates the air flow by means of an 

inlet throttle valve or inlet guide vanes. The minimal 

throttle point is established to prevent flow reversal 

thru an impeller/diffuser stage, which is also known as

surge. Control systems either unload the compressor or 

blow off the excess air to atmosphere to avoid surge, 

which could result in excessive vibration and potential 

damage to the compressor. Given adequate storage, 

some manufacturers will operate the compressor 

controls in a load/unload mode at lower flow 

conditions.

Centrifugal air compressors range from around 200 to 

more than 100,000 cfm, but the more common air 

compressors are from 1,200 to 5,000 cfm and with 

discharge pressures up to 125 psig. These may have 

several impellers in line on a single shaft or with 

separate impellers integrally geared.

Centrifugal air compressors provide lubricant-free air 

delivery as there is no lubricant in the compression 

chambers. Lubrication for speed increasing gears and 

the special high-speed shaft bearings is kept away from 

the compression chambers by means of shaft seals, 

which may also have air purge and vent connections.

Centrifugal air compressors are high-speed rotating 

machines and as such, shaft vibration monitoring is 

mandated to record operational trends and protect the 

equipment. Automatic control of the compressors is 

typical and has been greatly improved by the use of 

microprocessors, which monitor the pressure, capacity,

temperature characteristics and main-drive motor 

current draw. It is important that the manufacturer’s 

recommended maintenance procedures be followed 

and that certain maintenance procedures be carried out

by qualified staff. This is particularly true of attempts to 

remove an impeller from its shaft, since special 

procedures and tools may be involved.

Lubrication and Lubrication Systems. Centrifugal 

compressors use a pressure lubrication system for 

bearings and drive gears. The main lubricant pump may 
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IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 10

be driven from the gearbox input shaft with an electric 

motor-driven auxiliary lubricant pump for prelubrication prior to start-up and for post-lubrication 

during a cool down period. A water-cooled lubricant 

cooler is also included.

Because of the high rotation speeds, some designs use a 

high-pressure lubricant supply to the special bearings 

involved. The manufacturer’s recommended lubricant

should be used and changed at the specified intervals.

Compressor Prime Movers

The prime mover is the main power source providing 

energy to drive the compressor. The prime mover must 

provide enough torque and power to start the 

compressor, accelerate it to full speed, and keep the 

unit operating under various design conditions. This 

power can be provided by any one of the following 

sources: electric motors, diesel or natural gas engines, 

steam turbines and combustion turbines. Electric 

motors are by far the most common type of prime 

mover.

Electric motors are a widely available and economical 

means of providing reliable and efficient power to 

compressors. Most compressors use standard, 

polyphase induction motors. In many cases, either a 

standard- or a premium-efficient motor can be specified 

when purchasing a compressor or replacement motor. 

The incremental cost of the premium efficient motor is 

typically recovered in a very short time from the 

resulting energy savings. When replacing a standard 

motor with a premium-efficient version, careful 

attention should be paid to performance parameters, 

such as full-load speed and torque. A replacement 

motor with performance as close as possible to the 

original motor should be used. Most new motors are 

suitable for inverter duty applications.

Diesel or natural gas engines are common compressor 

power sources in the oil and gas industries. 

Considerations such as convenience, cost, and the 

availability of liquid fuel and natural gas play a role in 

selecting an engine to power a compressor. Although 

the majority of industrial compressed air systems use 

electric motors for prime movers, in recent years there 

has been renewed interest in using non-electric drives, 

such as reciprocating engines powered by natural gas, 

particularly in regions with high electricity rates. 

Standby or emergency compressors may also be enginedriven to allow operation in the event of a loss of 

electrical power. Maintenance costs for engine-driven 

systems are significantly higher than those that use 

electric motors.

The oldest method of driving compressors is through 

the use of a steam engine or turbine. In general, however, it is not economical to use a steam engine or 

turbine unless the steam is inexpensively and readily 

available within the plant for use as a power source.

Compressed Air System Controls

Compressed air system controls serve to regulate the 

pressure by matching compressor supply with system 

demand. Proper compressor control is essential to 

efficient operation and high performance. Because 

compressor systems are typically sized to meet a 

system’s maximum demand, a control system is almost 

always needed to reduce the output of the compressor 

during times of lower demand. Compressor controls are 

typically included in the compressor package, and many 

manufacturers offer more than one type of control 

technology. Systems with multiple compressors use 

more sophisticated controls (network or system master 

controls) to orchestrate compressor operation and air 

delivery to the system.

Network controls use the on-board compressor 

controls’ microprocessors linked together to form a 

chain of communication that makes decisions to 

stop/start, load/unload, modulate, vary displacement, 

and vary speed. Usually, one compressor assumes the 

lead with the others being subordinate to the 

commands from this compressor.

System master controls coordinate all of the functions 

necessary to optimize compressed air as a utility. 

System master controls have many functional 

capabilities, including the ability to monitor and control 

all components in the system, as well as trending data, 

to enhance maintenance functions and minimize costs 

of operation. Other types of controllers, such as 

pressure/flow controllers, may also improve the 

performance of some systems.

The type of control system specified for a given system 

is largely determined by the types of compressors being 

used and the facility’s demand profile. If a system has a 
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IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 11

single compressor with a very steady demand, a simple 

control system may be appropriate. On the other hand, 

a complex system with multiple compressors, varying 

demand, and many types of end uses will require a 

more sophisticated control strategy. In any case, careful 

consideration should be given to compressor system 

control selection because it can be the most important 

single factor affecting system performance and 

efficiency. For information about efficiency and 

compressor controls, see the fact sheet titled 

Compressed Air System Controls in Section 2.

Accessories

Accessories are the various types of equipment used to 

treat compressed air by removing contaminants such as 

dirt, lubricant, and water; to keep compressed air 

systems running smoothly; and to deliver the proper 

pressure and quantity of air throughout the system. 

Accessories include remote aftercoolers, filters, 

separators, dryers, heat recovery equipment, 

lubricators, pressure regulators, air receivers, and 

condensate drain traps.

Air Inlet Filters. An air inlet filter protects the 

compressor from atmospheric airborne particles. 

Further filtration is typically needed to protect 

equipment downstream of the compressor.

Compressor Cooling. Air or gas compression generates 

heat. As a result, industrial air compressors that operate 

continuously generate substantial amounts of heat.

Compressor units are cooled with air, water, and/or 

lubricant. Single-acting reciprocating compressors are 

typically air-cooled using a fan, which is an integral part 

of the belt-drive flywheel. Cooling air blows across 

finned surfaces on the outside of the compressor 

cylinder’s cooling fins. Larger, water-cooled, doubleacting reciprocating air compressors have built-in 

cooling water jackets around the cylinders and in the 

cylinder heads. The temperature of the inlet water and 

the design and cleanliness of the cooler can affect 

overall system performance and efficiency. Centrifugal 

compressors are generally water-cooled.

Lubricant-injected rotary compressors use the injected 

lubricant to remove most of the heat of compression. In 

air-cooled compressors, a radiator-type lubricant cooler 

is used to cool the lubricant before it is reinjected. The 

cooling fan may be driven from the main motor-drive 

shaft or by a small auxiliary electric motor. In plants 

where good quality water is available, shell and tube 

heat exchangers generally are used. Sometimes this 

heat can be recovered and used for other purposes.

Intercooling. Most multi-stage compressors use 

intercoolers, which are heat exchangers that remove 

the heat of compression between the stages of 

compression. Intercooling affects the overall efficiency 

of the machine.

Aftercoolers. As mechanical energy is applied to a gas 

for compression, the temperature of the gas increases. 

Aftercoolers are installed after the final stage of 

compression to reduce the air temperature. As the air 

temperature is reduced, water vapor in the air is 

condensed, separated, collected, and drained from the 

system. With cooler water temperatures, most of the 

condensate from a compressor with intercooling is 

removed in the intercooler(s), and the remainder in the 

aftercooler. Almost all industrial systems, except those 

that supply heated process air require aftercooling. In 

some systems, aftercoolers are an integral part of the 

compressor package, while in other systems the 

aftercooler is a separate piece of equipment. Some 

systems have both.

Moisture Separators. Moisture separators are devices 

that remove liquids entrained in the air or gas. A 

separator generally is installed following each 

intercooler or aftercooler to remove the condensed 

moisture. This involves changes in direction and velocity 

and may include impingement baffles. Lubricantinjected rotary compressors have an air/lubricant 

coalescing separator immediately after the compressor 

discharge to separate the injected lubricant before it is 

cooled and recirculated to the compressor. This 

separation must take place before cooling to prevent 

condensed moisture from being entrained in the 

lubricant.

Dryers. When air leaves an aftercooler and moisture 

separator, it is typically saturated. Any further radiant 

cooling as it passes through the distribution piping, 

which may be exposed to colder temperatures, will 

cause further condensation of moisture with 

detrimental effects, such as corrosion and 

contamination of point- of-use processes. This problem 

can be avoided by the proper use of compressed air 

dryers.
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Atmospheric air contains moisture. The higher the air 

temperature, the more moisture the air is capable of 

holding. The term “relative humidity” is commonly used 

to describe the moisture content. When the air contains 

all the moisture possible under the prevailing 

conditions, it is called “saturated.” Air at 80 percent 

relative humidity would contain 80 percent of the 

maximum possible moisture content.

When air is cooled, it will reach a temperature at which 

the amount of moisture present can no longer be 

contained in a vapor state and some of the moisture 

will condense and drop out. The temperature at which 

the moisture condenses is called the dew point. In 

general, reducing the temperature of saturated 

compressed air by 20°F will reduce the moisture 

content by approximately 50 percent.

When air is compressed and occupies a smaller volume, 

it can no longer contain all of the moisture possible at 

atmospheric conditions. Again, some of the moisture 

will drop out as liquid condensate. The result of both of 

these situations is a difference between the dew point 

at atmospheric conditions and the dew point at higher 

pressures. Drying compressed air beyond the required 

pressure dew point will result in unnecessary energy 

and costs.

Different types of compressed air dryers have different 

operating characteristics and degrees of dew point 

suppression. Dryer ratings usually are based on 

standard dryer inlet conditions, commonly referred to 

as “the three 100s.” That is, 100 psig, 100°F (inlet 

compressed air temperature), and 100°F ambient 

temperature. Deviations from these conditions will 

affect the capacity of a dryer. An increase in inlet 

temperature or a decrease in inlet pressure will reduce

the dryer’s rated capacity. Most manufacturers provide 

correction factors for this.

The most common types of dryers are discussed below.

• The refrigerant dryer is the most commonly used 

dryer in the industry, having relatively low initial 

and operating costs. Refrigerant-type air dryers 

(cycling and non-cycling) are not recommended for 

operation in sub-freezing ambient temperatures. 

The moisture in the compressed air can freeze and 

damage the dryer. Most refrigerated dryers are 

equipped with a pre-cooler/reheater that reheats 

the dried compressed air with an air-to-air heat 

exchanger using the hot incoming air. This lowers 

the temperature of the incoming air before it 

passes through the refrigerant or thermal mass-toair heat exchanger, reducing the heat load on the 

refrigerant system. Reheating the dried air 

prevents condensation on the outside of the 

compressed air piping in warm humid 

environments. The refrigerated dryer lowers the 

dew point of the air to the approximate 

temperature of the air exiting the refrigerant 

evaporator. To avoid freezing, the evaporator 

temperature should not go below 32°F. Allowing 

for separator efficiency, a pressure dew point of 

between 35 and 40°F can usually be obtained.

• Cycling dryers cool compressed air indirectly 

through a thermal storage medium (heat sink, 

thermal mass, chilled media, etc.) while non-cycling 

dryers directly cool compressed air in a refrigerant 

to air heat exchanger. Refrigerant-type cycling 

dryers are controlled with one or two thermostats 

to shut off the refrigerant compressor, saving 

energy when it is not needed, and a thermal 

storage medium (sometimes referred to as heat 

sink, chilled media or thermal mass) prevents rapid 

cycling of the refrigerant compressor(s). Powdered 

metal, glycol and water, sand, steel, and aluminum 

have all been used as this thermal storage medium. 

The ideal characteristics of this medium would be 

high specific heat (effective storage), high 

coefficient of heat transfer (easy transfer of stored 

cooling), corrosion protected, and low cost. The 

quantity of medium required is determined by the 

temperature band of the controlling thermostat(s) 

and the refrigerant capacity to be stored.

• Refrigerant-type, non-cycling dryers cool the air in 

a refrigerant-to-air heat exchanger. The cooling 

effect is from the evaporation of a liquid 

refrigerant causing moisture in the air to condense. 

The moisture then is removed and drained by a 

separator and drain. The temperature of the air 

leaving the refrigerant evaporator is controlled by a 

hot gas bypass valve

• Regenerative-desiccant-type dryers use a porous 

desiccant that adsorbs the moisture by collecting it 

in its myriad pores, allowing large quantities of 

water to be retained by a relatively small quantity
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of desiccant. Desiccant types include silica gel, 

activated alumina, and molecular sieves. Use only 

the type specified by the manufacturer. In some 

cases, more than one desiccant type can be used 

for special drying applications. In most of these 

cases, a larger particle size (1/4 inch or more) is 

used as a buffer zone at the inlet, while a smaller 

particle size desiccant (1/8 to 1/4 inch) is used for 

final drying. Where very low dewpoints are 

required, molecular sieve desiccant is added as the 

final drying agent.

Normally, the desiccant is contained in two 

separate towers. Compressed air to be dried flows 

through one tower, while the desiccant in the 

other is being regenerated. Regeneration is 

accomplished by reducing the pressure in the 

tower and passing previously dried purge air 

through the desiccant bed. The purge air may also 

be heated, either within the dryer or externally, to 

reduce the amount of purge air required. Purge air 

may also be supplied by a blower. Dryers of this 

type normally have a built-in regeneration cycle, 

which can be based upon time, dew point, or a 

combination of the two.

• Deliquescent-type dryers use a drying medium that 

absorbs, rather than adsorbs, the moisture in the 

compressed air. This means that the desiccant 

medium is used up as it changes from solid to liquid 

and cannot be regenerated. The most common 

deliquescent chemicals for compressed air drying 

are salts of sodium, potassium, calcium, and those 

with a urea base. Various compounds of these have 

been developed and sold under a variety of trade 

names.

• Heat-of-compression dryers are regenerativedesiccant dryers that use the heat generated 

during compression to accomplish desiccant 

regeneration, so they can be considered as heat 

reactivated. There are two types: the single-vessel 

and the twin-tower.

The single-vessel, heat-of-compression dryer 

provides continuous drying with no cycling or 

switching of towers. This is accomplished with a 

rotating desiccant drum in a single pressure vessel 

divided into two separate air streams. One air 

stream is a portion of the hot air taken directly 

from the air compressor at its discharge, prior to 

the aftercooler, and is the source of heated purge 

air for regeneration of the desiccant bed. The 

second air stream is the remainder of the air 

discharged from the air compressor after it passes 

through the air aftercooler. This air passes through 

the drying section of the dryer’s rotating desiccant 

bed, where it is dried. The hot air, after being used 

for regeneration, passes through a regeneration 

cooler before being combined with the main air 

stream by means of an ejector nozzle before 

entering the dryer.

The twin-tower, heat-of-compression dryer 

operation is similar to other twin-tower, heatactivated, regenerative-desiccant dryers. The 

difference is that the desiccant in the saturated 

tower is regenerated by means of the heat of 

compression in all of the hot air leaving the 

discharge of the air compressor. The total air flow 

then passes through the air aftercooler before 

entering the drying tower. Towers are cycled as for 

other regenerative-desiccant dryers.

The heat-of-compression dryers require air from 

the compressor at a sufficiently high temperature 

to accomplish regeneration. For this reason, it is 

used almost exclusively with centrifugal or 

lubricant-free rotary screw compressors.

• Membrane technology dryers have advanced 

considerably in recent years. Membranes 

commonly are used for gas separation, such as in 

nitrogen production for food storage and other 

applications. The structure of the membrane allows 

molecules of certain gases (such as oxygen) to pass 

through (permeate) a semi-permeable membrane 

faster than others (such as nitrogen), leaving a 

concentration of the desired gas (nitrogen) at the 

outlet of the generator. When used as a dryer in a 

compressed air system, specially designed 

membranes allow water vapor (a gas) to pass 

through the membrane pores faster than the other 

gases (air) reducing the amount of water vapor in 

the air stream at the outlet of the membrane dryer, 

suppressing the dew point. The dew point achieved 

is usually 40°F, but lower dew points to –40°F can 

be achieved at the expense of additional purge air 

loss.

Compressed Air Filters. Depending on the level of air 

purity required, different levels of filtration and types of 

filters are used. These include particulate filters to 

remove solid particles, coalescing filters to remove 
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lubricant and moisture, and adsorbent filters for tastes 

and odors. A particulate filter is recommended after a 

desiccant-type dryer to remove desiccant “fines.” A 

coalescing-type filter is recommended before a 

desiccant- type dryer to prevent fouling of the desiccant 

bed. Additional filtration may also be needed to meet 

requirements for specific end uses.

Compressed air filters downstream of the air 

compressor are generally required for the removal of 

contaminants, such as particulates, condensate, and 

lubricant. Filtration only to the level required by each 

compressed air application will minimize pressure drop 

and resultant energy consumption. Elements should 

also be replaced, as indicated by pressure differential,

to minimize pressure drop and energy consumption, 

and should be checked at least annually.

Heat Recovery. As noted earlier, compressing air 

generates heat. In fact, industrial-sized air compressors 

generate a substantial amount of heat that can be 

recovered and put to useful work. More than 80 

percent of the electrical energy going to a compressor 

becomes available heat. Heat can be recovered and 

used for producing hot water or hot air. See the fact 

sheet in Section 2 titled Heat Recovery and Compressed 

Air Systems for more information on this energy-saving 

opportunity.

Lubrication. In lubricant-injected rotary screw 

compressors, lubricants are designed to cool, seal, and 

lubricate moving parts for enhanced performance and 

longer wear. Important considerations for compressor 

lubricants include proper application and compatibility 

with downstream equipment, including piping, hoses, 

and seals. A lubricator may be installed near a point- ofuse to lubricate items such as pneumatic tools. The 

lubricator may be combined with a filter and a pressure 

regulator to make up what is commonly called a FRL 

(filter-regulator-lubricator). The lubricant should be that 

specified by the point-of-use equipment manufacturer.

Pressure/Flow Controllers. Pressure/flow controllers are 

system pressure controls used in conjunction with the 

individual compressor or system controls described 

previously. Their primary function is to regulate system 

pressure more precisely than multiple individual 

compressor controls and Master system controllers. A 

pressure/flow controller does not directly control a 

compressor, and it is generally not included as part of a 

compressor package. A pressure/flow controller is a 

device that serves to separate the supply side of a 

compressed air system from the demand side. Properly 

sized storage receiver capacity is needed for adequate 

pressure/flow control. Not all systems would benefit 

from this type of controller.

Air Receivers. Receivers are used to provide 

compressed air storage capacity to meet peak demand 

events and help control system pressure by controlling 

the rate of pressure change in a system. Receivers are 

especially effective for systems with widely varying 

compressed air flow requirements. Where peaks are 

intermittent, a large air receiver may allow a smaller air

compressor to be used and can allow the capacity 

control system to operate more effectively and improve 

system efficiency. An air receiver after a reciprocating 

air compressor can provide dampening of pressure 

pulsations, radiant cooling, and collection of 

condensate. Demand-side control will optimize the 

benefit of the air receiver storage volume by stabilizing 

system header pressure and “flattening” the load peaks. 

Properly sized air receivers also play a crucial role in 

orchestrating system controls, providing the time 

needed to start, or avoid starting, standby air 

compressors. Of course proper application and design 

is required to optimize the utilization of air receivers.

Traps. Traps (sometimes called drains) allow the 

removal of moisture from the compressed air system. 

Automatic condensate traps are used to conserve 

energy by preventing the loss of air through open 

petcocks and valves. Poorly maintained traps can waste 

a lot of compressed air.

There are four methods to drain condensate.

1. Manual. Operators will manually open valves to 

discharge condensate. However, this is not 

automatic, and unfortunately, too often, manual 

valves are left open to drain condensate from 

moisture separators, intercoolers, refrigerated 

dryers, and filters, allowing compressed air to 

continually escape into the atmosphere.

2. Level-operated mechanical traps. Float-type 

traps do not waste air when operating properly, 

but they often require a great deal of 

maintenance and are prone to blockage from 

sediment in the condensate. Inverted bucket 
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traps may require less maintenance but will waste 

compressed air if the condensate rate is 

inadequate to maintain the liquid level (or prime) 

in the trap.

3. Electrically operated solenoid valves. The 

solenoid-operated drain valve has a timing device 

that can be set to open for a specified time and at 

preset adjustable intervals. There are two issues 

with using these valves.

• The period during which the valve is open may 

not be long enough for adequate drainage of 

accumulated condensate.

• The valve will operate even if little or no 

condensate is present, resulting in the loss of 

valuable compressed air. Level-operated and 

electrically operated solenoid valves should 

have strainers installed to reduce 

contaminants, which block the inlet and 

discharge ports of these automatic devices.

Motorized ball valves are also used with 

programmable timers. However, while fairly 

reliable, these valves can be even more wasteful 

as the duration of the valve opening is dependent 

on the valve actuator and is not adjustable.

4. Zero air-loss traps with reservoirs. There are 

various types of zero air-loss traps.

• A float or level sensor operates an electric 

solenoid or ball valve and maintains the 

condensate level in the reservoir below the 

high-level point.

• A float activates a pneumatic signal to an air 

cylinder to open a ball valve through a linkage 

to expel the condensate in the reservoir to the 

low-level point.

Be sure to drain and clean the reservoir often to 

prevent the accumulation of contaminants, which could 

foul the mechanisms of these traps.

The potential for freezing must be considered and 

provision made for heated drains where necessary. The 

relatively common practice of leaving a manual drain 

valve cracked open should not be tolerated because it 

wastes costly compressed air.

Contaminated condensate requires removal of lubricant 

before the condensate is discharged to a sewer system. 

It is recommended that the local sewage authority be 

consulted for allowable contamination levels. 

Condensate treatment should meet local codes.

Air Distribution Systems. The air distribution system 

links the various components of the compressed air 

system to deliver air to the points-of-use with minimal 

pressure loss. The specific configuration of a 

distribution system depends on the needs of the 

individual plant, but frequently consists of an extended 

network of main lines, branch lines, valves, and air 

hoses. The length of the network should be kept to a 

minimum to reduce pressure drop. Air distribution 

piping should be large enough in diameter to minimize 

pressure drop. A loop system is generally 

recommended, with all piping sloped to accessible drop 

legs and drain points.

When designing an air distribution system layout, it is 

best to place the air compressor and its related 

accessories where temperature inside the plant is the 

lowest (but not below freezing). A projection of future 

demands and tie-ins to the existing distribution system 

should also be considered. Air leaks are an important 

issue with distribution system and are addressed in the 

fact sheet in Section 2 titled Compressed Air System 

Leaks. It is important to note that the majority of 

system leakage will be at the point of use and not in the 

distribution piping.

Headers should have a slight slope to allow drainage of 

condensate and drop legs from the bottom side of the 

header should be provided to allow collection and 

drainage of the condensate. The direction of the slope 

should be away from the compressor.

Piping from each compressor to the header, and the 

header to points-of-use should connect to the top or 

side of the header to avoid being filled with condensate. 

Drainage-drop legs from the bottom of the header 

should be installed to collect the condensate.

Uses of Compressed Air

Industrial facilities use compressed air for a multitude of 

operations. Almost every industrial facility has at least 

two compressors, and in a medium-sized plant there 

may be hundreds of different uses of compressed air.

Uses include powering pneumatic tools, packaging and 

automation equipment, and conveyors. Pneumatic tools 
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IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 16

tend to be smaller, lighter, and more maneuverable 

than electric motor-driven tools. They also deliver 

smooth power and are not damaged by overloading.

Air-powered tools have the capability for infinitely 

variable speed and torque control, and can reach a 

desired speed and torque very quickly. In addition, they 

are often selected for safety reasons because they do 

not produce sparks and have low heat build-up. 

Although they have many advantages, pneumatic tools 

are much less energy-efficient than electric tools. It 

generally costs 7 to 8 times more energy for pneumatic 

tools to produce the same mechanical output as electric 

tools.

Many manufacturing industries also use compressed air 

and gas for combustion and process operations such as 

oxidation, fractionation, cryogenics, refrigeration, 

filtration, dehydration, and aeration. Table 1.1 lists 

some major manufacturing industries and the tools, 

conveying, and process operations requiring 

compressed air. For some of these applications, 

however, other sources of power may be more cost 

effective (see the fact sheet titled Potentially 

Inappropriate Uses of Compressed Air in Section 2).

Compressed air also plays a vital role in many nonmanufacturing sectors, including the transportation, 

construction, mining, agriculture, recreation, and 

service industries. Examples of some of these 

applications are shown in Table 1.2.

 Table 1.1 Industrial Sector Uses of Compressed Air

Industry ExampleCompressedAirUses

Apparel Conveying, clamping, tool powering, controls and actuators, automated equipment

Automotive Tool powering, stamping, control and actuators, forming, conveying

Chemicals Conveying, controls and actuators

Food Dehydration, bottling, controls and actuators, conveying, spraying coatings, cleaning, vacuum packing

Furniture Air piston powering, tool powering, clamping, spraying, controls and actuators

General Clamping, stamping, tool powering and cleaning, control and actuators

Manufacturing

LumberandWood Sawing, hoisting, clamping, pressure treatment, controls and actuators

MetalsFabrication Assembly station powering, tool powering, controls and actuators, injection molding, spraying

Petroleum Process gas compressing, controls and actuators

PrimaryMetals Vacuum melting, controls and actuators, hoisting

PulpandPaper Conveying, controls and actuators

Rubber and Plastics Tool powering, clamping, controls and actuators, forming, mold press powering, injection molding

Stone, Clay, Conveying, blending, mixing, controls and actuators, glass blowing and molding, cooling

and Glass

Textiles Agitating liquids, clamping, conveying, automated equipment, controls and actuators, loom jet weaving,

spinning, texturizing
INTRODUCTION TO COMPRESSED AIR SYSTEMS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 17

 Table 1.2 Non-Manufacturing Sector Uses of Compressed Air
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 18

SECTION 2: THE PERFORMANCE OPPORTUNITY ROADMAP

Improving and maintaining peak compressed air system 

performance requires not only addressing individual 

components, but also analyzing both the supply and 

demand sides of the system and how they interact. This 

practice is often referred to as taking a “systems 

approach” because the focus is shifted away from 

components to total system performance.

Applying the systems approach usually involves the 

following types of interrelated actions:

• Establishing current conditions and operating 

parameters

• Determining present and future process 

production needs

• Gathering and analyzing operating data and 

developing load duty cycles

• Analyzing alternative system designs and 

improvements

• Determining the most technically and 

economically sound options, taking into 

consideration all of the sub-systems

• Implementing those options

• Analyzing operations and energy consumption 

and analyzing economics (i.e., validating 

performance)

• Continuing to monitor and optimize the system

• Continuing to operate and maintain the system 

for peak performance.

Most compressed air systems use considerably more 

energy than is needed to support the demand. 

Compressed air systems usually have a wire-to-work 

efficiency of around 10 percent, which is very low. In 

many cases, after a thorough review of a compressed

air system and after corrective actions are taken, one or 

more of the compressors may be shut off and the 

overall system efficiency improved.

System performance improvement opportunities and 

component efficiency improvement opportunities are 

addressed in the series of fact sheets that follow.

The Fact Sheets

The remainder of the Performance Opportunity 

Roadmap section of the sourcebook is a collection of 12 

fact sheets that address both component and system 

issues. Each fact sheet details a specific opportunity for 

improving compressed air system performance. Topics 

include:

1. Analyzing Compressed Air Needs

2. Potentially Inappropriate Uses of Compressed Air

3. Compressed Air System Leaks

4. Pressure Drop and Controlling System Pressure

5. Compressed Air System Controls

6. Compressed Air Storage

7. Proven Opportunities at the Component Level

8. Maintenance of Compressed Air Systems for 

Peak Performance

9. Heat Recovery and Compressed Air Systems

10. Baselining Compressed Air Systems

11. Compressed Air System Assessments and Audits

and Selecting a Service Provider

12. Compressed Air System Economics and Selling 

Projects to Management

The compressed air system diagram shown in Figure 2.1 

shows the performance improvement opportunities 

described in the fact sheets.
THE PERFORMANCE OPPORTUNITY ROADMAP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 19

Pressure Levels

see Pressure Drop and 

Controlling System Pressure

Use of Recoverable Heat

see Heat Recovery with 

Compressed Air Systems

Operator Experiencing 

Low Pressure

see Pressure Drop and 

Controlling System Pressure

Type of Control System

see Compressed Air 

System Controls

Baselining Your System

see Baselining Compressed 

Air Systems

Life Cycle Cost

see Compressed Air System 

Economics and Selling 

Projects to Management

How Much Air, At What Quality 

and Pressure?

see Analyzing Compressed Air 

Needs

End Uses

see Potentially 

Inappropriate Uses of 

Compressed Air

Air Leaks

see Compressed 

Air System Leaks

Keeping Equipment in Top 

Condition

see Maintenance of Compressed Air 

Systems for Peak Performance

Moisture Control and Air Treatment

see Proven Opportunities at the 

Component Level and Assessing 

Compressed Air Needs

Sizing of Receiver

see Compressed Air 

Storage

Pressure/Flow Controller

see Compressed Air 

System Controls

System-Wide Problems

see Determining Your 

Compressed Air System 

Analysis Needs

Figure 2.1 Performance Opportunities
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 20

Fact Sheet 1: Analyzing Compressed Air Needs

Compressed air needs are defined by the air quality, 

quantity, and level of pressure required by the end uses 

in your plant. Analyzing needs carefully will ensure that 

a compressed air system is configured properly so that a 

clean, dry and stable supply of compressed air can be 

delivered at minimal cost. This analysis should be done 

in conjunction with the measurements described Fact 

Sheet 10: Baselining Compressed Air Systems.

Air Quality

As illustrated in the table, compressed air quality ranges 

from plant air to breathing air.

Industrial applications typically use one of the first three 

air quality levels. Quality is determined by the dryness 

and contaminant level required by the end uses, and is 

accomplished with filtering and drying equipment. The 

higher the quality, the more the air costs to produce. 

Higher quality air usually requires additional equipment, 

which not only increases initial capital investment, but

also makes the overall system more expensive to 

operate in terms of energy consumption and 

maintenance costs.

One of the main factors in determining air quality is 

whether or not lubricant-free air is required. Lubricantfree air can be produced with either lubricant-free 

compressors, or with lubricant-injected compressors 

that have additional separation and filtration 

equipment. Lubricant-free rotary screw and 

reciprocating compressors usually have higher first 

costs, lower efficiency, and higher maintenance costs 

than lubricant-injected compressors. However, the 

additional separation and filtration equipment required 

by lubricant-injected compressors will cause some 

reduction in efficiency, particularly if systems are not 

properly maintained. Before selecting a lubricant-free 

or lubricant-injected compressor, careful consideration 

should be given to the specific end use for the lubricantfree air, including the risk and cost associated with 

product contamination.

Air Quantity – Capacity

Required compressed air system capacity for new 

systems can be determined by summing the 

requirements of the tools and process operations 

(taking into account load factors) at the site. For existing 

system the peak flow can be directly measured using 

flow meters or estimated by analyzing the response of 

the compressors in logged data. The total air 

requirement is not the sum of the maximum 

requirements for each tool and process, but the sum of 

the average air consumption of each. High short-term 

demands should be met by air stored in an air receiver. 

Systems may need more than one air receiver. 

Strategically locating air receivers near sources of high 

demand can also be effective. In most cases, a thorough 

evaluation of system demand may result in a control 

strategy that will meet system demand with reduced 

overall compressor capacity.

Oversized air compressors are extremely inefficient 

because most compressors use more energy per unit 

volume of air produced when operating at part-load. In 

many cases, it makes sense to use multiple, smaller 

compressors with sequencing controls to allow for 

efficient operation at times when demand is less than 

peak.

If a system is properly designed and maintained but is 

still experiencing capacity problems, an alternative to 

adding another compressor is to re-examine the use of 

compressed air for certain applications. For some tasks, 

blowers or electric tools may be more effective or 

appropriate. See Fact Sheet 2: Potentially Inappropriate 

Uses of Compressed Air for more information on this 

system improvement opportunity.
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Load Profile

Another key to properly designing and operating a 

compressed air system is analyzing a plant’s 

compressed air requirements over time, or load profile. 

The variation of demand for air over time is a major 

consideration in system design. Plants with wide 

variations in air demand need a system that operates 

efficiently under part-load. Multiple compressors with 

sequencing controls may provide more economical

operation in such a case. Plants with a flatter load 

profile can use simpler control strategies.

Artificial Demand

Artificial demand is defined as the excess volume of air 

that is consumed when supplying higher pressure than 

necessary for applications – unregulated and/or 

regulated to higher than necessary. Pressure/flow 

controllers (see Fact Sheet 5: Compressed Air System 

Controls) can help to minimize artificial demand.

Pressure

Different tools and process operations require different 

pressures. Pneumatic tool manufacturers rate tools at 

various pressures, and process operation pressure 

requirements vary widely as specified by the process 

engineers. Required pressure levels are set to satisfy 

the highest of all these requirements.

Required pressure levels must take into account system 

pressure losses from flowing thru dryers, separators, 

filters, and piping. This forces compressor discharge 

pressures higher. A rule of thumb for systems in the 100 

pounds per square inch gauge (psig) range is: for every 

2 pounds per square inch (psi) increase in discharge 

pressure, energy consumption will increase by 

approximately 1 percent at full output flow (check 

performance curves for centrifugal and two-stage, 

lubricant-injected, rotary screw compressors). There is 

also another penalty for higher-than-needed pressure. 

Raising the compressor discharge pressure increases 

the consumption of every unregulated usage, including 

leaks, open blowing, etc. Although it varies by plant, 

unregulated usage is commonly as high as 30 to 50 

percent of air demand. For systems in the 100 psig 

range with 30 to 50 percent unregulated usage, a 2 psi 

increase in header pressure will increase energy 

consumption by about another

0.6 to 1.0 percent because of the additional 

unregulated air being consumed. The combined effect 

results in a total increase in energy consumption of 

about 1.6 to 2 percent for every 2 psi increase in 

discharge pressure for a system in the 100 psig range 

with 30 to 50 percent unregulated usage.

See the Fact Sheet 4: Pressure Drop and Controlling 

System Pressure for information on ways to reduce 

system pressure and save energy while maintaining high 

performance.

Using Block Diagrams, Pressure Profiles, 

and Demand Profiles

Two simple tools that are available to help analyze 

compressed air systems are block diagrams and 

pressure profiles. Block diagrams identify all the 

components in the system. A sample diagram is shown 

in Figure 2.2 on the following page.

Another way to analyze a compressed air system is to 

draw a pressure profile. A pressure profile shows the 

pressure drops through a system. These pressure 

measurements give feedback for control adjustments, 

determine pressure drops across components, and help

determine system operating pressures. The tools 

required for measurement are matched, calibrated 

pressure gauges or differential pressure gauges. The 

following pressure measurements should be taken:

• Inlet to compressor (to monitor inlet air filter) 

versus atmospheric pressure

• Differential across air/lubricant separator (if 

applicable)

• Inter-stage on multi-stage compressors Consider 

pressure differentials, including:

• Aftercooler

• Treatment equipment (dryers, filters, etc.)

• Various points of the distribution system

• Check pressure differentials against 

manufacturers’ specifications, if available (highpressure drops indicate service is required).

Figure 2.3 shows an example of a pressure profile (in a 

system with excessive pressure drop).
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IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 22

Figure 2.2 Simplified Compressed Air System Block Diagram

Figure 2.3 Pressure Profile at a Single Point in Time
THE PERFORMANCE OPPORTUNITY ROADMAP 1 - ANALYZING COMPRESSED AIR NEEDS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 23

This method gives the pressure profile at a single point 

in time. Taking data at a single point, or even during 

various shifts, can provide some answers, but not the 

complete picture. The use of data loggers is important 

in determining how a system operates over time. Data 

logging system pressures and flow can indicate 

intermittent loads, system disruptions and general 

system conditions. It can also indicate system changes 

(e.g. production process changes or air leaks) that can 

affect the compressed air system operation and 

efficiency. These variations in pressure and flow can be 

managed through system control strategies and storage 

to minimize their impact on production. See Fact 

Sheet 5: Compressed Air System Controls. An example of 

pressure and demand (airflow) over a period of 30 

minutes is shown in Figure 2.4.

Figure 2.4 Pressure Profile over a Defined Time Period
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 24

Fact Sheet 2: Potentially Inappropriate Uses of Compressed Air

Compressed air is probably the most expensive form of 

energy available in a plant. Compressed air is also clean, 

readily available, and simple to use. As a result, 

compressed air is often chosen for applications for 

which other energy sources are more economical. 

Users should always consider more cost-effective forms 

of power before considering compressed air.

Many operations can be accomplished more 

economically using alternative energy sources. 

Inappropriate uses of compressed air include any 

application that can be done more effectively or more 

efficiently by a method other than compressed air. 

Examples of potentially inappropriate uses of 

compressed air include:

• Open blowing

• Sparging

• Aspirating

• Atomizing

• Padding

• Dilute-phase transport

• Dense-phase transport

• Vacuum generation

• Personnel cooling

• Open hand-held blowguns or lances

• Diaphragm pumps

• Cabinet cooling

• Vacuum venturis.

• Air motors

Each potentially inappropriate use and a suggested 

alternative is described below. Engineering assistance 

may be required for some of the suggestions.

Open Blowing

Open blowing is using compressed air applied with an 

open, unregulated tube, hose, or pipe for one of these 

applications:

• Cooling and bearing cooling

• Drying

• Clean-up

• Draining compressed air lines

• Clearing jams on conveyors

The alternatives to open blowing are vast. Some 

include:

• Brushes

• Brooms

• Dust collection systems

• Zero-air-loss auto drains

• Blowers

• Blowers with knives

• Electric fans

• Electric barrel pumps

• Mixers

• Engineered Nozzles.

Sparging

Sparging is aerating, agitating, oxygenating, or 

percolating liquid with compressed air. Alternatives to 

sparging include low-pressure blowers and mixers.

Aspirating

Aspirating is using compressed air to induce the flow of 

another gas with compressed air such as flue gas. An 

alternative is a low-pressure blower.

Atomizing

Atomizing is the use of compressed air to disperse or 

deliver a liquid to a process as an aerosol. An example is 

atomizing fuel into a boiler. Fluctuating pressure can 

affect combustion efficiency. An alternative is a lowpressure blower.

Padding

Padding is using compressed air to transport liquids and 

light solids. Air is dispensed over the material to be 

moved. The expansion of the air moves the material. 

The material is usually only moved short distances. An 

example is unloading tanks or tank cars. Molecular 

diffusion and wicking are typical problems with padding. 

An alternative is slow-to-medium pressure blowers.

Dilute-Phase Transport

Dilute-phase transport is used in transporting solids, 

such as powdery material, in a diluted format with 

compressed air. Molecular diffusion and wicking are 
THE PERFORMANCE OPPORTUNITY ROADMAP 2 - POTENTIALLY INAPPROPRIATE USES OF COMPRESSED AIR

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 25

typical problems with dilute phase transport. An 

alternative is a low- or high-pressure blower or a lowpressure air compressor designed for 35 psig. The 

pressure required depends upon the moisture content 

and size of the material being transported.

Dense-Phase Transport

Dense-phase transport is used to transport solids in a 

batch format. This usually involves weighing a batch in a 

transport vessel, padding the vessel with compressed 

air, forcing the batch into a transport line, and moving it 

in an initial plug with a boost of compressed air at the 

beginning of the transport pipe. Once the material is 

moving in a plug, the operation may fluidize the 

material in a semi-dense or moderate dilute-phase 

using fluidizers or booster nozzles along the transport 

path. The material is typically transported to a holding 

vessel that dispenses it on an as-needed basis using pad 

air from the secondary transport vessel to move it to 

the use location. A typical application would be the 

dense-phase transport of carbon black.

There are typically four compressed air elements to the 

transport. These elements are control air for the 

equipment, pad air for the initial transporter, transport 

air to move it in the piping, and fluidizers or booster 

nozzles along the transport piping. Most dense-phase 

manufacturers specify 80 to 90 psig with one single line 

supporting the entire process. The control air and 

booster nozzles typically use pressures in the 60 to 70 

psig range. The actual pressure required for the pad air 

and the transport air is typically 30 to 45 psig. Because 

of the lack of storage in most of these applications and 

the high-volume, short-cycle transport times, the 

original equipment manufacturers request 80 to 90 psig 

and use of the entire supply system as the storage tank. 

As this usually has a negative impact on the plant air 

system, separate compressors, filters, and dryers are 

often applied to this process at the elevated pressure.

Alternatives include supporting the control air, pad air, 

and boosters with regulated plant air plus metered 

storage, and using a two-stage, positive displacement 

blower (28 psig) or single-stage compressor (40 to 50 

psig) for the transport air. Another alternative is to use 

metered storage for both the pad air and transport 

cycle. This necessitates providing the entire 

requirement from storage and metered recovery per 

cycle, with a metering adjustment to refill the vessel 

just before the next transport cycle. The storage should 

be sized to displace the required air first for the pad and 

then for the transport cycles within an allowable 

pressure drop to terminate the transport cycle pressure 

at the required pressure. This will flatten the volumetric 

load on the system, eliminate any impact on other 

users, and reduce the peak energy required to support 

the process.

Vacuum Generation

The term vacuum generation describes applications 

where compressed air is used in conjunction with a 

venturi, eductor, or ejector to generate a negativepressure mass flow. Typical applications are hold-downs 

or 55-gallon, drum-mounted, compressed air vacuum 

cleaners. This is an inefficient application although for 

very intermittent use (less than 30 percent load factor), 

compressed air can be a reasonable solution. An 

alternative is a vacuum pump. If a compressed-airgenerated vacuum is required, install a solenoid valve 

on the compressed air supply line to shut this 

application off when it is not needed.

Vacuum generators are used throughout industry. Some 

applications for vacuum generators include:

• Shop vacuums

• Drum pumps

• Palletizers

• De-palletizers

• Box makers

• Packaging equipment

• Automatic die-cutting equipment.

Vacuum generators are selected for safety, ease of 

installation, physical size of the generator, the fact that 

no electricity is required at the point-of-use, and low 

first cost. Vacuum generators are usually less 

economical to operate than central vacuum systems.

As a rule, in a base load situation, if the vacuum 

generator is operating less than 30 percent of the time, 

it will be more economical to operate than a central 

vacuum system. Otherwise, vacuum generators are, in 

general, less effective at pulling a vacuum and cost as 

much as five times more to operate than a dedicated 

vacuum pump. Using vacuum generators for shop 

vacuums and drum pumps, which are typically peak 

load applications, could cause another compressor to 
THE PERFORMANCE OPPORTUNITY ROADMAP 2 - POTENTIALLY INAPPROPRIATE USES OF COMPRESSED AIR

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 26

turn on and stay on until it times out. Having to operate 

a second compressor because of the added demand 

associated with vacuum generators eliminates any 

apparent savings even if operated only once a day for a 

short period of time.

A dedicated vacuum pump or the use of central vacuum 

system will provide more suction force at a fraction of 

the cost of vacuum produced by compressed air. In this 

case, it is significantly more cost effective to provide a 

system that is designed into the machine from the 

beginning than to retrofit a piece of equipment. This 

can be accomplished by being proactive at the time the 

machine specifications are prepared and the purchase 

orders issued. Vacuum generators must be applied 

properly and only after taking life cycle costs into 

consideration.

Vacuum venturis are a common form for vacuum 

generation with compressed air systems. In a venturi 

system, compressed air is forced through a conical 

nozzle. Its velocity increases and a decrease in pressure 

occurs. This principle, discovered by 18th century 

physicist G. B. Venturi, can be used to generate vacuum 

without a single moving part.

Multi-stage venturi devices generally provide a more 

efficient ratio of vacuum flow to compressed air 

consumed than single-stage venturi devices. Where 

vacuum requirements vary significantly, or are cyclical 

with a duty cycle of less than 30 percent, multi-stage, 

venturi-type vacuum generators with pressure 

regulators and automatic shut-off controls on the 

compressed air supply may be more efficient than 

continuously operating mechanical-vacuum pump 

systems. These devices also can be equipped with a 

vacuum switch that signals a solenoid valve to shut off 

the air supply when a set vacuum level is attained, thus 

reducing air consumption in non-porous applications. 

They may also be suitable where it is impractical to have 

a central vacuum system, particularly where the uses 

may not be confined to one area.

Personnel Cooling

Personnel cooling is when operators direct compressed 

air onto themselves for ventilation. This is dangerous 

because it can shoot particulates into the skin. A 1/4-

inch tube continually blowing air on an operator can 

consume 15 to 25 horsepower of compressed air. An 

alternative is fractional horsepower fans of 1/4 hp or 

less.

Open Hand-Held Blowguns or Lances

Unregulated hand-held blowing is not only a violation of 

most health and safety codes, but is also very 

dangerous. Hand-held blowguns that conform to all 

occupational health and safety standards should be 

used.

There are different styles of blowguns that can deliver 

various airflows, velocities, and concentrations. The 

proper gun must be selected for each application. Care 

must be taken to ensure optimized nozzles that 

consume more than the original nozzles are not 

inadvertently selected. Pipes installed in the end of 

hose and unregulated non-approved guns must not be 

used. Blowguns must have no more than 30 psig 

discharge nozzle pressure. The nozzle should be 

constructed to relieve backpressure if the nozzle is 

plugged or blocked. The blowgun must also have a 

spring-operated throttle mechanism so it shuts off 

automatically if it is dropped.

Diaphragm Pumps

A common error is to not size diaphragm pumps for the 

maximum viscosity, highest pressure, and highest 

volume required. The result is poor performance and an 

increased supply pressure requirement.

Diaphragm pumps are commonly found installed 

without regulators and speed control valves. Those 

diaphragm pumps that are installed with regulators are 

found with the regulators adjusted higher than 

necessary. This is often because of undersized 

regulators and supply piping or hose. The higher-thannecessary setting of the regulator increases the demand 

on the compressed air system and increases operating 

costs.

With a higher pressure setting, the amount of 

compressed air admitted into the diaphragm chamber is 

increased above that which is actually required to move 

the product. The amount of product actually transferred 

remains the same, but the amount of air used increases 

with the increased pressure.
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The regulator should be adjusted to equal the maximum 

head that the pump is required to provide. A flow 

control valve installed up stream of the regulator will 

accomplish the required speed control. Operating the 

diaphragm pump without speed control increases the 

rate of compressed air consumption by increasing the 

strokes per minute of the diaphragm pump. The speed 

control should be adjusted to pump product in the 

maximum allowable time. As a general rule, the 

regulator and flow control valve are not included with 

the standard pump package. Also, when the pump has 

no liquid or slurry to pump, it will rapid cycle, wearing 

out the diaphragm and wasting air. The pump controls 

must be configured to turn the pump off when there is 

nothing to pump.

Cabinet Cooling

Cabinet cooling should not be confused with panel 

purging. The following are typical applications where 

cabinet cooling is found.

• Programmable controllers

• Line control cabinets

• Motor control centers

• Relay panels

• Numerical control systems

• Modular control centers

• Computer cabinets.

When first cost is the driving factor, open tubes, air bars 

(copper tube with holes drilled long the length of the 

tube) and vortex tube coolers are often used to cool 

cabinets. When life-cycle costs are taken into 

consideration, these choices prove to be expensive. It is 

not uncommon to find an open tube or air bar 

consuming 7-1/2 horsepower (hp) of compressed air to 

cool a cabinet. Vortex tube coolers can be an 

improvement over open tubes and air bars because 

they are often cycled with a thermostat control, which 

reduces air consumption. However, air to air, air to 

water and refrigerated cabinet coolers are available 

that only use 1/3 hp to accomplish the same task. 

Air Motors

Compressed air driven vane or piston motors are used 

in a wide variety of tools and equipment, often used 

where light weight, or sparkless explosion proof 

operation is required. Since it requires a minimum of 7 

to 8 hp of equivalent compressor power for each hp of 

air motor shaft output it is worthwhile to consider 

converting applications that do not require special 

treatment to direct drive electric source.

Other Potentially Inappropriate Uses

Other improper uses of compressed air are unregulated 

end uses and those that supply air to abandoned 

equipment, both of which are described below.

Unregulated End Uses

A pressure regulator is used to limit maximum end- use 

pressure and is placed in the distribution system just 

prior to the end use. If an end use operates without a 

regulator, it uses full- system pressure. This results in 

increased system air demand and energy use, since the 

end use is using air at this higher pressure. High 

pressure levels can also increase equipment wear, 

resulting in higher maintenance costs and shorter end 

use equipment life.

Abandoned Equipment

Many plants undergo numerous equipment 

configuration changes over time. In some cases, plant 

equipment is no longer used. Air flow to this unused 

equipment should be stopped, preferably as far back in 

the distribution system as possible without affecting 

operating equipment.

Using Compressed Air

As a general rule, compressed air should only be used if 

safety enhancements, significant productivity gains, or 

labor reductions will result. Typical overall efficiency is 

10 to 15 percent. If compressed air is used for an 

application, the amount of air used should be the 

minimum necessary quantity and pressure and should 

be used for the shortest possible duration.

Compressed air use should also be constantly 

monitored and re-evaluated.
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Fact Sheet 3: Compressed Air System Leaks

Leaks can be a significant source of wasted energy in an 

industrial compressed air system, sometimes wasting 20 

to 30 percent of a compressor’s output. A typical plant 

that has not been well maintained will likely have a leak 

rate equal to 20 percent of total com- pressed air 

production capacity. On the other hand, proactive leak 

detection and repair can reduce leaks to less than 5 to 

10 percent of compressor output.

In addition to being a source of wasted energy, leaks 

can also contribute to other operating losses. Leaks 

cause a drop in system pressure, which can make air 

tools function less efficiently, adversely affecting 

production. In addition, by forcing the equipment to run 

longer, leaks shorten the life of almost all system 

equipment (including the compressor package itself). 

Increased running time can also lead to additional 

maintenance requirements and increased unscheduled 

downtime. Finally, leaks can lead to adding unnecessary 

compressor capacity.

While leakage can come from any part of the system, 

the most common problem areas are:

• Couplings, hoses, tubes, and fittings

• Pressure regulators

• Open condensate traps and shut-off valves

• Pipe joints, disconnects, and thread sealants

Estimating Amount of Leakage

For compressors that have start/stop or load/unload 

controls, there is an easy way to estimate the amount 

of leakage in the system. This method involves starting 

the compressor when there are no demands on the 

system (when all the air-operated, end-use equipment 

is turned off). A number of measurements are taken to 

determine the average time it takes to load and unload 

the compressor. The compressor will load and unload 

because the air leaks will cause the compressor to cycle 

on and off as the pressure drops from air escaping 

through the leaks. Total leakage (percentage) can be 

calculated as follows:

Leakage (%) = [(T x 100)/(T+t)]

where: T = on-load time (minutes)

t = off-load time (minutes)

Leakage will be expressed in terms of the percentage of 

compressor capacity lost. The percentage lost to 

leakage should be less than 5 to 10 percent in a wellmaintained system. Poorly maintained systems can 

have losses as high as 20 to 30 percent of air capacity 

and power. Note that this method may not account for 

idle end use equipment where the compressed air has 

been turned off.

Leakage can be estimated in systems with other control 

strategies if there is a pressure gauge installed on or 

after the air receiver. This method requires an estimate 

of total system volume, including any downstream 

secondary air receivers, air mains, and piping (V, in 

cubic feet). The system is started and brought to the 

normal operating pressure (P1). Measurements should 

then be taken of the time (T) it takes for the system to 

drop to a lower pressure (P2), which should be a point 

equal to about one-half the operating pressure.

Total leakage of free air can be calculated as follows:

Flow Rate (cfm)

6.5

26

104
THE PERFORMANCE OPPORTUNITY ROADMAP 3 - COMPRESSED AIR SYSTEM LEAKS

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Leakage (cfm) = (V x (P1-P2)/T x 14.7) x 1.25 

where: V is in cubic feet

P1 and P2 are in psig 

T is in minutes

The 1.25 multiplier corrects leakage to normal system 

pressure, allowing for reduced leakage with falling 

system pressure. Again, leakage of greater than 10 

percent indicates that the system can likely be 

improved. These tests should be carried out on a 

regular basis as part of a leak detection and repair 

program.

Leak Detection

Since air leaks are almost impossible to see, other 

methods must be used to locate them. The best way to 

detect leaks is to use an ultrasonic acoustic detector, 

which can recognize the high-frequency hissing sounds 

associated with air leaks. These portable units consist of 

directional microphones, amplifiers, and audio filters, 

and usually have either visual indicators or ear- phones 

to detect leaks. A simpler method is to apply soapy 

water with a paint brush to suspect areas. Although 

reliable, this method can be time consuming.

Ultrasonic Leak Detection

Ultrasonic leak detection is probably the most versatile 

form of leak detection. Because of its capabilities, it is 

readily adapted to a variety of leak detection situations. 

The principle behind ultrasonic leak detection is simple. 

In a pressure or vacuum leak, the leak flows from a 

high-pressure laminar flow to a low-pressure 

turbulence. The turbulence generates a white noise,

which contains a broad spectrum of sound ranging from 

audible to inaudible frequencies. An ultrasonic sensor 

focuses in on the ultrasonic elements in the noise. 

Because ultrasound is a short wave signal, the sound 

level will be loudest at the leak site. Ultrasonic

detectors are generally unaffected by back- ground 

noises in the audible range because these signals are 

filtered out.

Ultrasonic detectors can find mid- to large-sized leaks. 

The advantages of ultrasonic leak detection include 

versatility, speed, ease of use, the ability to perform 

tests while equipment is running, and the ability to find 

a wide variety of leaks. They require a minimum of 

training, and operators often become competent after 

15 minutes of training.

Because of its nature, ultrasound is directional in 

transmission. For this reason, the signal is loudest at its 

source. By generally scanning around a test area, it is 

possible to very quickly hone it on a leak site and pin 

point its location. For this reason, ultrasonic leak 

detection is not only fast, it is also very accurate.

How to Fix Leaks

Leaks occur most often at end-use joints and 

connections. Stopping leaks can be as simple as 

tightening a connection or as complex as replacing 

faulty equipment, such as couplings, fittings, pipe 

sections, hoses, joints, drains, and traps. In many cases, 

leaks are caused by failing to clean the threads or by 

bad or improperly applied thread sealant. Select high 

quality fittings, disconnects, hose, tubing, and install 

them properly with appropriate thread sealant.

Non-operating equipment can be an additional source 

of leaks. Equipment no longer in use should be isolated 

with a valve in the distribution system.

Another way to reduce leaks is to lower the air pressure 

of the system. The lower the pressure differential across 

an orifice or leak, the lower the rate of flow, so reduced 

system pressure will result in reduced leakage rates. 

Stabilizing the system header pressure at its lowest 

practical range will minimize the leakage rate for the 

system. Once leaks have been repaired, the compressor 

control system must be re-evaluated to realize the total 

savings potential.

Establishing a Leak Prevention Program

There are two basic types of leak repair programs, the 

leak tag program and the seek and repair program. The 

seek and repair program is the simplest. As it states, you 

simply find the leak and repair it immediately. With the 

leak tag program, the leak is identified with a tag and 

logged for repair at a later time. This is often a two-part 

tag; one part stays on the leak and the other part is 

turned into the maintenance department, identifying 

the location, size, and description of the leak to be 

repaired. The best approach depends on the type, size, 

and the culture/work practices of the facility. It is more 

likely that the best solution will be a combination of the 
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two. In any case, there are several key elements for a 

successful leak program.

• Baseline compressed air usage. Establish good 

grounds for comparison on the effectiveness of 

the compressed air leak repair program. (See Fact 

Sheet 10: Baselining Compressed Air Systems.)

• Establish leak loss. See the section on estimating 

leak loss in this fact sheet.

• Determine cost of air leaks. The cost of 

compressed air leaks is one of the most important 

aspects of the program. It should be used as a 

baseline, not only for the effectiveness and 

promotion of the program, but also to illustrate 

the amount of resources that can cost effectively 

be allocated to the program.

• Identify leaks. Survey the facility and identify the 

leaks. Leaks can be identified by many methods. 

The most common is using an ultrasonic acoustic 

leak detector. There are many types and price 

ranges, but for most applications, the inexpensive 

hand- held meter will identify leaks and give an 

indication of the size or intensity.

• Document the leaks. Document the location, 

type, size, and the estimated cost of the leak. Any 

documentation should be compatible with the 

facility’s predictive maintenance program. Leak 

tags can also be used but should not take the 

place of a master leak list. If you are using the 

seek and repair method, leaks should still be 

documented so the number and effectiveness of 

the program can be tracked.

• Prioritize leak repair. Fix the biggest leaks first to 

get the biggest savings. This will ensure a good 

start to the air leak program.

• Adjust controls. Once the leaks are fixed, adjust 

the compressor controls.

• Document repairs. Showing the fixed leaks and 

the cost savings shows the effectiveness of the 

program and strengthens support for it. 

Documenting the repairs and the type of leaks 

can also indicate equipment that is a recurring 

problem. When this occurs, look at the process 

for a root cause and develop a permanent 

solution to stop the recurring air leak.

• Compare baselines and publish results. By 

comparing before and after results, the 

effectiveness of the program and the savings can 

be determined. Then, tell “the world” about the 

program and the results that have been achieved. 

This is very important because showing the 

savings will solidify support for the program.

• Start over again. Air leaks continue to occur, so 

the program must be ongoing. Periodic reviews 

should be done on the system, and the process 

repeated as necessary to maintain system 

efficiency.

A good compressed air system leak repair program is 

very important to maintaining the efficiency, reliability, 

stability, and cost effectiveness of any compressed air 

system.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 31

Fact Sheet 4: Pressure Drop and Controlling System Pressure

Pressure drop is a term used to characterize the 

reduction in air pressure from the compressor discharge 

to the actual point-of-use. Pressure drop occurs in the 

piping as the compressed air travels through the 

treatment and distribution system. A properly designed 

system should have a pressure loss of much less than 10 

percent of the compressor’s discharge pressure, 

measured from compressor discharge output to the end 

point-of-use.

Excessive pressure drop will result in poor system 

performance and excessive energy consumption. 

Pressure drop upstream of the compressor signal 

requires higher compression pressures to achieve the 

control settings on the compressor. Control specialists 

should be consulted for these applications. Flow 

restrictions of any type require higher operating 

pressures than necessary, and minimizing differentials 

in all parts of the system is an important part of 

efficient operation. The most typical problem areas 

include the aftercooler, lubricant separators, air 

treatment equipment, and check valves. A rule of 

thumb for systems in the 100 psig range is: for every 2 

psi increase in discharge pressure, energy consumption 

will increase by approximately 1 percent at full output 

flow (check performance curves for centrifugal and twostage, lubricant-injected, rotary screw compressors).

There is an additional penalty for higher-than-needed 

pressure. Elevated system pressure increases 

unregulated uses, such as leaks, open blowing, and 

production applications. The added demand at elevated 

pressure is termed “artificial demand” and can 

substantially increase energy consumption. Although it 

varies by plant, unregulated usage is commonly as high 

as 30 to 50 percent of air demand. For systems in the 

100 psig range a 2 psi increase in header pressure will 

increase energy consumption another 0.6 to 1.0 

percent because of the additional unregulated air being 

consumed. The combined effect results in a total 

increase in energy consumption of about 1.6 to 2 

percent for every 2 psi increase in discharge pressure.

Pressure drop in the distribution system and in hoses 

and flexible connections at points-of-use results in 

lower operating pressure to the user. If the point-ofuse operating pressure has to be increased, try reducing 

the pressure drops by properly sizing components or 

adding secondary storage in the system before adding 

capacity or increasing the system pressure. Increasing 

the compressor discharge pressure or adding 

compressor capacity may result in significant increases 

in energy consumption and should be the last resort.

What Causes Pressure Drop?

Any type of obstruction, restriction, or roughness in the 

system will cause resistance to air flow and cause 

pressure drop. In the distribution system, the highest 

pressure drops usually are found at the points- of-use, 

including undersized or leaking hoses, tubes, 

disconnects, filters, regulators and lubricators (FRLs) 

usually within the last 30 feet of the system. On the 

supply side of the system, air/lubricant separators, 

aftercoolers, moisture separators, dryers and filters can 

be the main items causing significant pressure drops.

The maximum pressure drop from the supply side to 

the points-of-use will occur when the compressed air 

flow rate is highest. System components should be 

selected based upon these conditions and the 

manufacturer of each component should be requested 

to supply pressure drop information under these 

conditions. Filter elements should be changed when the 

pressure drop approaches the maximum recommended 

by the manufacturer. In many cases the element change 

is dictated by energy losses.

The distribution piping system is often diagnosed as 

having excess pressure drop because a point-of-use 

component cannot sustain the required down- stream 

pressure. If a regulator is set at 85 psig and an upstream 

filter has a pressure drop of 20 psi, the system upstream 

of the filter and regulator would have to maintain at 

least 105 psig. The 20 psi pressure drop may be blamed 

on the system piping rather than on the components at 

fault. The correct diagnosis requires pressure 

measurements at different points in the system to 

identify the component(s) causing the excess pressure 

drop. In this case the filter element or filter should be 

replaced, not the piping.
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Minimizing Pressure Drop

Minimizing pressure drop requires a systems approach 

in design and maintenance of the system. Air treatment 

components, such as aftercoolers, moisture separators, 

dryers, and filters, should be selected with the lowest 

possible pressure drop at specified maximum operating 

conditions. When installed, the recommended 

maintenance procedures should be followed and 

documented. Additional ways to minimize pressure 

drop are as follows:

• Properly design the distribution system. Size 

main lines for maximum flow with a 1-2% 

maximum pressure drop and be sure to allow for 

system growth.

• Operate and maintain air treatment equipment to 

reduce the effects of moisture, such as pipe 

corrosion.

• Consider pressure drop when selecting air 

treatment equipment. Install ∆P gauges across 

dryers and filters and pressure gauges at various 

points in the distribution system.

• Specify pressure regulators, lubricators, hoses, 

and connections having the best performance 

characteristics at the lowest pressure differential. 

These components must be sized based upon the 

actual rate of flow and not the average rate of 

flow. End use equipment should be specified and 

operated at the lowest efficient operating 

pressures.

Controlling System Pressure

Many plant air compressors operate with a full- load 

discharge pressure of 100 psig and an unload discharge 

pressure of 110 psig or higher. Many types of machinery 

and tools can operate efficiently with an air supply at 

the point-of-use of 80 psig or lower. If the air 

compressor discharge pressure can be reduced, 

significant savings can be achieved. Check with the 

compressor manufacturer for performance 

specifications at different discharge pressures.

An air compressor capacity control pressure signal is 

normally located at the discharge of the compressor 

package. In some systems it is possible to move the 

pressure signal location downstream of the compressed 

air dryers and filters to achieve a common signal 

pressure for all the compressors in the system. Some 

dangers must be recognized and precautionary 

measures taken. The control range pressure setting 

must be reduced to allow for actual and potentially 

increasing pressure drop across the dryers and filters. It 

is important to provide controls that prevent exceeding 

the maximum allowable compressor discharge pressure 

and drive motor amps of each compressor in the 

system.

Reducing system pressure also can have a cascading 

effect in improving overall system performance, 

reducing leakage rates, and helping with capacity and 

other problems. Reduced pressure also reduces stress 

on components and operating equipment. However, a 

reduced system operating pressure may require 

modifications to other components, including pressure 

regulators, filters, hoses, and the size and location of 

compressed air storage.

Lowering average system pressure requires caution 

because large changes in demand can cause the 

pressure at points-of-use to fall below minimum 

requirements, which can cause equipment to function 

improperly. These problems can be avoided with careful 

matching of system components, controls, and 

compressed air storage capacity and location. 

Pressure/flow controllers can also be used to control 

system pressure. (See Fact Sheet 5: Compressed Air 

System Controls.)

If an individual application requires higher pressure, it 

may be best to replace or modify this application, 

instead of raising the operating pressure of the whole 

system. It may be possible to have a larger diameter 

cylinder, gear ratios may be changed, mechanical 

advantage may be improved, or a larger air motor may 

be used. The cost of improvements probably will be 

insignificant compared to the energy reduction 

achieved from operating the system at the lower 

pressure.

It is also important to check if manufacturers are 

including pressure drops in filters, pressure regulators, 

and hoses in their pressure requirements for end-use 

equipment, or if the pressure requirements as stated 

are after those components. A typical pressure 

differential for a filter, pressure regulator, and hose is 

7 pounds per square inch differential (psid), but it could 

be much higher in poorly designed and maintained 

systems.
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When demand pressure has been successfully reduced 

and controlled, attention then should be turned to the 

compressor control set points to obtain more efficient 

operation, and also to possible unloading or shutting off 

a compressor to further reduce energy consumption.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 34

Fact Sheet 5: Compressed Air System Controls

Compressed air system controls regulate system 

pressure by matching the compressed air supply with 

system demand, and they are one of the most 

important determinants of overall system energy 

efficiency. Good control translates compressed air 

savings due to efficiency measures into proportionally 

lower input power. This fact sheet discusses both 

individual compressor control and overall system 

control of plants with multiple compressors. Proper 

control is essential to efficient system operation and 

high performance. The objective of any control strategy 

is also to shut off unneeded compressors or delay 

bringing on additional compressors until needed. 

Compressor systems are typically comprised of multiple 

compressors delivering air to a common plant air 

header. The combined capacity of these machines is 

generally sized to meet the maximum plant air demand. 

System controls are almost always needed to 

orchestrate a reduction in the output of the individual 

compressor(s) during times of lower demand. 

Compressed air systems are usually designed to operate 

within a fixed pressure range and to deliver a volume of 

air that varies with system demand. System pressure is 

monitored and the control system decreases 

compressor output when the pressure reaches a 

predetermined level. Compressor output is then 

increased again when the pressure drops to a lower 

predetermined level.

The difference between these two pressure levels is 

called the control range. Depending on air system 

demand, the control range can be anywhere from 2 to 

20 psi. In the past, individual compressor controls and 

non-supervised multiple machine systems were slow 

and imprecise. This resulted in wide control ranges and

large pressure swings. As a result of these large swings, 

individual compressor pressure control set points were 

established to maintain pressures higher than needed. 

This ensured that swings would not go below the 

minimum requirements for the system.

Today, faster and more accurate microprocessor-based 

system controls and variable speed compressors with 

tighter control ranges allow for a drop in the system 

pressure set points. Precise control systems are able to 

maintain lower average pressure without going below 

minimum system requirements.

A rule of thumb for systems in the 100 psig range is: for 

every 2 psi decrease in discharge pressure, energy 

consumption will decrease by approximately 1 percent 

at full output flow (check performance curves for 

centrifugal and two-stage, lubricant-injected, rotary 

screw compressors). There is also another benefit of 

lowering pressure. Reducing the compressor discharge 

pressure decreases the demand of every unregulated 

usage, including leaks, open blowing, etc. Although it 

varies by plant, unregulated usage is commonly as high 

as 30 to 50 percent of air demand. For systems in the 

100 psig range with 30 to 50 percent unregulated 

usage, a 2 psi decrease in header pressure will decrease 

energy consumption by about another 0.6 to 1.0 

percent because of the lower unregulated air being 

consumed. The combined effect results in a total 

decrease in energy consumption of about 1 to 1.6 

percent for every 2 psi decrease in discharge pressure 

for a system in the 100 psig range with 30 to 50 percent 

unregulated usage.

Caution must be taken when lowering average system 

header pressure, because large, sudden changes in 

demand can cause the pressure to drop below 

minimum requirements, which can lead to improper 

functioning of equipment. With careful matching of 

system controls and storage capacity, these problems 

can be avoided.

Controls and System Performance

Few air systems operate at full-load all of the time. Partload performance is therefore critical, and is primarily 

influenced by compressor type and control strategy. 

The type of control specified for a given system is 

largely determined by the type of compressor being 

used and the facility's demand profile. If a system has a 

single compressor with a very steady demand, a simple

control system may be appropriate. On the other hand, 

a complex system with multiple compressors, varying 

demand, and many types of end uses will require a 

more sophisticated strategy. In any case, careful 

consideration should be given to both compressor and 

system control selection because they can be the most 
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important factors affecting system performance and 

efficiency.

Individual Compressor Control Strategies

Over the years, compressor manufacturers have 

developed a number of different types of control 

strategies. Controls, such as start/stop and load/unload, 

respond to reductions in air demand, by monitoring 

increasing compressor discharge pressure and turning 

the compressor off or unloading it at a set unload point 

so that it does not deliver air for periods of time. 

Modulation, variable displacement, multi-step, and 

variable speed controls allow the compressor to 

operate at part-load and deliver a reduced amount of 

air during periods of reduced demand. Some 

compressors have more than one control mode and the 

manual selection of the mode is an operator function. 

The efficiency of these control modes varies widely 

depending on site conditions, so careful selection 

should be made to maintain good overall efficiency.

Start/Stop. Start/stop is the simplest control available 

and can be applied to either reciprocating or rotary 

screw compressors. The motor driving the compressor 

is turned on or off in response to the discharge pressure 

of the machine. Typically, a simple pressure switch 

provides the motor start/stop signal. This type of 

control should not be used in an application that has 

frequent cycling, because repeated starts will cause the 

motor to overheat and other compressor components 

to require more frequent maintenance. This control 

scheme is typically only used for applications with very 

low-duty cycles for compressors in the 30 horsepower 

(hp) and under range. Its advantage is that power is 

used only while the compressor is running, making it 

quite efficient, but this is offset by having to compress 

to a higher receiver pressure to allow air to be drawn 

from the receiver while the compressor is stopped. 

Some modern controls will allow larger compressors to 

start and stop, saving energy, if the control detects that 

the maximum motor starts will not be exceeded.

Load/Unload. Load/unload control, also known as 

online/offline control, allows the motor to run 

continuously, but unloads the compressor when the 

discharge pressure is adequate. Compressor 

manufacturers use different strategies for unloading a 

compressor, but in most cases, an unloaded rotary 

screw compressor will consume 15 to 35 percent of fullload horsepower while delivering no useful work. As a 

result, some load/unload control schemes can be 

inefficient. For lubricated screw compressors, the 

effective size of the system storage affects part load 

efficiency. Compressors with limited effective storage 

can experience short cycling, which will have an even 

greater negative effect on efficiency and reliability.

Most single acting reciprocating compressors pressure 

controls are designed as two-step, either start/stop or 

load/unload. Larger double acting reciprocating 

compressors can be two-step, three-step cylinder 

unloading (0, 50, 100 percent) or five-step (0, 25, 50, 75, 

100 percent) control. These control schemes generally 

exhibit an almost direct relationship between motor 

power consumption and loaded capacity.

Modulating Controls. Modulating (throttling) inlet 

control allows the output of a compressor to be varied 

to meet flow requirements. Throttling is usually 

accomplished by partially closing the inlet valve, 

thereby restricting inlet air to the compressor. This 

control scheme is applied to centrifugal and lubricantinjected rotary screw compressors. This control method 

cannot be used on reciprocating or lubricant-free rotary 

screw compressor and when applied to lubricantinjected rotary screw compressors, is an inefficient 

means of varying compressor output at the lower 

demand levels. 

When used on centrifugal compressors, more efficient 

results are obtained, particularly with the use of inlet 

guide vanes, which direct the air in the same direction 

as the impeller inlet. However, the amount of capacity 

reduction is limited by the potential for surge and 

minimum throttling capacity, which is in the basic 

design parameters of each specific unit.

Inlet-valve modulation used on lubricant-injected rotary 

air compressors allows compressor capacity to be 

adjusted to match demand. A regulating valve senses 

system or discharge pressure over a prescribed range 

(usually about 10 psi) and sends a proportional pressure 

to operate the inlet valve. Closing (or throttling) the 

inlet valve causes a pressure drop across it, reducing the 

inlet pressure at the compressor and, hence, the mass 

flow of air. Since the pressure at the compressor inlet is 

reduced while discharge pressure is rising, the 

compression ratios are increased so that energy savings 

are somewhat limited.
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Inlet valve modulation is normally limited to a range of 

from 100 percent to about 40 percent of rated capacity. 

When operating at 40 percent rated capacity and when 

discharge pressure reaches full load pressure plus 10 

psi, it is assumed demand is insufficient to require 

continued air discharge to the system. At this point the 

compressor will operate fully unloaded, like a 

compressor using load/unload controls.

Dual-Control/Auto-Dual. For lubricant-injected rotary 

screw compressors, auto-dual control provides the

addition of an overrun timer to stop the compressor 

after running unloaded for a pre-set time, thereby 

saving power.

Variable Displacement. Allows progressive reduction of 

the compressor displacement without reducing the inlet 

pressure. Manufacturers use turn valve, slide valve, 

spiral valve or poppet valves to control the compressor 

discharge pressure and reduce energy consumption at 

part load. 

Some lubricant-injected rotary screw compressors can 

vary their compression volumes (ratio) through the first 

50% of available capacity using turn valves, spiral valves 

or poppet valves. These are generally applied in 

conjunction with modulating inlet valves to provide 

more accurate pressure control with improved partload efficiency. This control scheme reduces the power 

and flow in a very similar manner as the reciprocating 

pocket valves, by keeping the compression ratios stable, 

which keeps the power consumption near optimal 

levels. For capacities below 50 percent, the compressor 

will typically operate in load/unload or modulation 

mode. 

There are sometimes separate manual control 

adjustments for the modulation valve, the variable 

displacement valve and the load/unload pressures. Each 

adjustment must be carefully coordinated with the 

other in order to benefit from this type of control. 

Adjustment of these settings should be done using 

trained personnel.

Variable Speed Drives. Variable speed is an efficient 

means of rotary compressor capacity control, using 

integrated variable frequency AC or switched reluctance 

and other DC drives. Compressor discharge pressure 

can be held to within 1or 2 psi over a wide range of 

capacity, allowing additional system energy savings. 

Some variable speed compressors also use variable 

displacement controls to enhance the machine turndown range.

Compressors equipped with variable speed drive 

controls continuously adjust the drive motor speed 

within a variable range to match variable demand 

requirements with an almost direct one to one 

relationship to full load power consumption. At or near 

full-output capacity, a variable speed drive compressor 

will use more input power than a comparable fixed 

speed unit due to the inherent drive losses. Also, at low 

speeds the package efficiency of variable speed 

compressors falls off. Therefore, continuous operation 

at full or minimum speeds should be avoided. Best 

efficiency occurs if the variable speed compressor 

operates between 30 and 80 percent speed for the 

majority of its operating hours.

Variable speed compressors typically load/unload or 

start/stop at output capacities below minimum speed. 

Long term operation of lubricated screw compressors at 

below minimum speed should be avoided to prevent 

condensate contamination of the compressor lubricant. 

Variable speed compressors require proper effective 

storage to avoid continuously ramping the speed up and 

down which may damage the driver.

Capacity Controls for Centrifugal Type Compressors.

Centrifugal compressors have complex characteristics 

affected by inlet air density and inter-stage cooling 

water temperature. 

Two potential occurrences must be avoided. The first is 

surge, caused by a flow reversal, which can occur at low 

flow rates and can cause damage to the compressor. 

Surge is avoided by limiting the amount of flow 

reduction generally controlled by preset minimum 

motor ampere limiters. The second is choke at 

increased flow rates below design pressure, when the 

velocity of the air at the impeller inlet approaches the 

speed of sound and flow and head cannot be sustained.

The flow rate can be reduced by an inlet throttle valve, 

which reduces the pressure at the inlet to the first-stage 

impeller. This “constant pressure control” reduces the 

mass flow in direct proportion to the absolute inlet 

pressure. The inlet air density also is reduced, resulting 

in reduced pressure head produced by the impeller. 
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A variation of this uses inlet guide vanes, which also 

reduce the mass flow and the inlet air density, but 

cause the air to be directed radially towards the 

impeller inlet in the same direction as the impeller 

rotation. This improves the efficiency compared with 

simple throttling. In some cases, discharge bypass or 

blow-off control is used to limit flow delivered to the 

compressed air system. “Capacity can typically be 

reduced from 100 percent capacity to about 70-80 

percent with reasonable energy reduction” At lower 

capacities compressed air is discharged to the 

atmosphere (“blowoff”) through a discharge silencer or 

cooled and returned to the compressor inlet. This is a 

waste of energy and should be used only where 

necessary to avoid surge.

Multiple Compressor Control

Systems with multiple compressors can be set up 

manually or use more sophisticated controls to 

orchestrate efficient compressor operation and 

constant air pressure delivery to the system. Network 

controls use the on-board compressor controls’ 

microprocessors linked together to form a chain of 

communication that makes decisions to stop/start, 

load/unload, modulate, vary displacement, and vary 

speed. Usually, one compressor assumes the lead with 

the others being subordinate to the commands from 

this compressor. 

System master controls coordinate all of the functions 

necessary to optimize compressed air as a utility. 

System master controls have many functional 

capabilities, including the ability to monitor and control 

all components in the system, as well as trending data 

to enhance maintenance functions and minimize costs 

of operation. Other system controllers, such as 

pressure/flow controllers, can also substantially 

improve the performance of some systems.

The objective of an effective automatic system control 

strategy is to match system demand with compressors 

operated at or near their maximum efficiency levels. 

This can be accomplished in a number of ways, 

depending on fluctuations in demand, available storage 

receiver capacity, and the characteristics of the 

equipment supplying and treating the compressed air.

Local Control. Systems within multiple compressors can 

be manually operated by coordinating the load and 

unload pressure settings of each individual compressor 

in a cascaded arrangement (provide graphic). This 

method needs to be carefully planned to compensate 

for pressure differentials across dryers and filters and to 

ensure pressures do not exceed the rated capacity of 

any system compressors. Special considerations may 

exist if one or more of the system compressors use 

variable speed control to avoid a condition called 

“control gap”. This can also be avoided with some 

system controllers.

Network Controls. Less sophisticated network controls 

use the cascade set point scheme to operate the system 

as a whole. Those systems are capable of avoiding part 

load compressors, but can still present the problem of 

approaching production’s minimum pressure 

requirement as more and more compressors are added 

and the range of compressor load and unload set points 

increases.

Some network control systems use single set-point logic 

to make their operational decisions to start/stop, etc. 

Use of a single set-point system should include a control 

specialist. The intent is to save energy by keeping 

compressor discharge pressures as low as possible. In 

systems with positive- displacement compressors 

(reciprocating, rotary screws, etc.) the best system 

efficiency occurs when all compressors are kept fully 

loaded except for one trim compressor that is operated 

in some part-load fashion specific to the design of the 

machine. The trim compressor is typically a unit with 

the best part load efficiency such as a variable speed 

compressor or a unit with low unloaded power 

consumption.

Three major disadvantages of network system controls 

are:

• They are capable of controlling only air 

compressors.

• They cannot easily be networked with remote 

compressor rooms.

• Typically they only work with compressors of the 

same brand and configuration because of microprocessor compatibility issues.

Expensive upgrades or retrofits may be required to 

make different brands of compressors, or older versions 

of the same brand, work in the system. In some cases, 

retrofits are not available and a different brand or 
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outdated compressors cannot be used in the control 

scheme.

There are no network controls available that can 

coordinate the control of rotary screw, reciprocating, 

and centrifugal compressors as one system. To do this, 

system master controls are required, particularly if 

there is a desire to monitor and operate compressors, 

cooling systems, dryers, filters, automatic drain traps, 

storage, pressure/ flow controllers, and any other part 

of a compressed air system that a facility might want 

included in the control scheme.

System Master Controls. If complexity outpaces the 

capabilities of local and network controls, a system 

master control is required to coordinate all of the 

functions necessary to optimize compressed air as a 

utility. System master controls have many functional 

capabilities, including the ability to monitor and control 

all components in the system, as well as to trend data 

and provide performance reports to enhance 

maintenance functions and help system operators 

minimize costs of operation. System master controls 

interface with all brands and types of air compressors, 

and can coordinate the operation of satellite 

compressor rooms spread around the facility, or in 

different buildings across an industrial campus. The 

primary function of these controls, as with the network 

controls, is to operate a multiple compressor system in 

harmony.

The least sophisticated have few, if any, of the features 

mentioned above and use cascading set-point logic to 

control compressors. The most sophisticated, state-ofthe-art system master controls use rate-of-change 

dynamic analysis to make decisions regarding how the 

compressed air system responds to changes. These 

changes can occur on the demand side, supply side, or 

in the ambient conditions. All affect the performance of 

the system and have a role in how the system should 

respond. Some of these require short duration support, 

such as additional storage. Others require additional 

compressor power to be brought online, and some will 

require a combination of both.

A properly configured system master control can 

determine the best and most energy-efficient response 

to events that occur in a system. The number of 

components a system master control can interface with 

is governed by practicality and cost limitations. System 

master control layout has the capability of performing 

many other complex functions, such as effective 

monitoring and reporting of key performance indicators 

so proactive actions can be initiated to maintain system 

efficiency and reliability.

Multiple Compressor Control with VSD

If one or more variable speed compressors operate with 

multiple fixed speed compressors some special 

considerations apply. In this case the control strategy 

should be arranged so that the variable speed 

compressor is always the trim compressor, regardless of 

how many fixed speed compressors are running.

Integration of variable compressors in systems with 

multiple compressors should be done in consultation 

with the manufacturer or a compressed air system 

expert. Care should be taken in sizing variable speed 

compressors as some models may have limited ranges.

Pressure/Flow Controllers

Pressure/flow controllers are precision pilot-operated 

system pressure regulators used in conjunction with the 

individual compressor or system controls described 

previously. A pressure/flow controller does not directly 

control a compressor and is generally not included as 

part of a compressor package. This is a device that 

serves to separate the supply side of a compressor 

system from the demand side. This requires 

compressors to be operated at an elevated pressure 

and therefore, increased horsepower (but possibly 

fewer compressors and/or shorter periods of 

operation), while pressure on the demand side can be 

reduced to a stable level to minimize actual compressed 

air consumption caused by artificial demand.

Storage, sized to meet anticipated fluctuations in 

demand, is an essential part of the control strategy. 

Higher pressure supply air enters the primary storage 

tanks from the air compressors and is available to 

reliably meet fluctuations in demand at a constant 

lower pressure level.

To function properly, pressure/flow controllers require 

a properly sized primary air receiver located upstream. 

The pressure swing caused by the multiple compressor 

control band is relegated to the primary receiver, while 

the pressure/flow controller controls the plant header 

pressure in a lower, much narrower pressure range. The 
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primary air receiver shields the compressors from 

severe load swings, which may avoid the need to start 

another compressor. Lowering and controlling system 

pressure downstream of the primary receiver can result 

in reducing energy consumption by 10 percent or more, 

if most of the end uses had not been properly pressure 

regulated. This also presumes that compressor controls 

efficiently handle the decrease in demand.

A well designed and managed master control system 

could include a pressure/flow controller in its strategy 

where it is deemed beneficial. The goal is to deliver 

compressed air at the lowest stable pressure to the 

main plant distribution system and to support transient 

events, as much as possible, with stored higher pressure 

compressed air. When stored air is at the lowest 

acceptable pressure, care should be taken to utilize the 

minimum compressor horsepower to restore the 

primary pressure to the required level.

Pressure/flow controllers are not always appropriate for 

every system. Each compressed air system differs in 

supply, distribution, and demand aspects, which require 

proper evaluation of the benefits to the system of a 

pressure/flow controller. Rather than installing a 

pressure/flow controller the proper sizing and 

placement of primary and/or secondary air receivers 

may also address intermittent loads, which can affect 

system pressure and reliability, and may allow 

operating the compressor at the lowest possible 

discharge pressure and input power. 

Some lubricant-injected rotary-screw compressors are 

sold with load/unload capacity control, which is claimed 

to be the most efficient. This can also be misleading, 

because an adequate receiver volume is essential to 

obtain any real savings in energy.

One solution sometimes proposed is to eliminate 

modulation and have the compressors operate in a 

load/unload mode. Certain factors must be recognized 

before making such a change. The standard fullcapacity, full-load pressure, often has the compressor 

running at around 110 percent of motor nameplate 

rating, or using 10 percent of the available 15 percent 

continuous overload service factor. The remaining

5 percent is meant to cover tolerances and items such 

as increased pressure drop through the air/lubricant 

separator before it is required to be changed.

If the discharge pressure is allowed to rise by an 

additional 10 psi without the capacity being reduced by 

inlet valve modulation, the bhp will increase by 5 

percent and the motor could be overloaded. A 

reduction in discharge pressure may be necessary to 

operate in this mode.

In addition, for lubricant-injected rotary screw 

compressors it is falsely assumed that a straight line, 

from full-load bhp to unloaded bhp, represents the 

actual power requirement in this mode of operation. 

This presumes, for example, that if the average capacity 

is 50 percent, the compressor would run fully loaded 50 

percent of the time and fully unloaded 50 percent of 

the time. Unfortunately, the compressor is not fully 

unloaded 50 percent of the time 

When the compressor discharge pressure reaches the 

unload set point, the inlet valve is closed to reduce the 

mass flow through the compressor. Simultaneously, the 

lubricant sump/separator vessel pressure is gradually 

relieved. Typically, this takes about 40 seconds to 

prevent foaming of the lubricant with the potential of 

excessive lubricant carryover. The rate at which blowdown occurs gradually slows as the pressure is reduced. 

The fully unloaded power is not realized until the 

pressure in the lubricant sump/separator is fully 

relieved. In addition, a period of about 3 seconds is 

required to repressurize the air/lubricant 

sump/separator vessel when the system calls for the 

compressor to reload.

In many cases, the system pressure will fall and the

compressor will reload before the fully unloaded power 

is realized. To overcome this, an adequately sized air 

receiver and/or system volume is essential. Taking the 

above factors into account, Figure 2.5 shows the effect 

of different sizes of air receiver/system volume. Some 

rules of thumb established many years ago for 

reciprocating air compressors are not adequate for a 

lubricant-injected rotary screw compressor.

Most lubricant-injected rotary screw compressors are 

equipped with capacity control by inlet valve 

modulation designed to match the output from the air 

compressor with the demand from the points-of-use. 

On this basis, it has been stated that an air receiver is 

not needed. At best, this is misleading. An air receiver 

near the discharge of a rotary screw compressor will 

shield the compressor control system from pressure 
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fluctuations from the demand side downstream of the 

receiver, and can allow the compressor to be unloaded 

for a longer period of time, during periods of light

demand. The addition of an over-run timer (automatic 

dual control) can stop the compressor if it runs 

unloaded for a preset time, saving additional energy.

The top line in Figure 2.6 on the following page shows 

what would happen if inlet valve modulation was used 

without unloading the compressor.

Approximately 70 percent of full-load power would still 

be used when modulation had reduced compressor 

output to zero. The second line shows inlet valve 

throttling to 40 percent capacity and unloading at that 

point. Figure 2.7, also on the following page, shows 

variable displacement (slide/turn/spiral/poppet valve)

capacity reduction to 50 percent capacity followed by 

throttling to 40 percent capacity and unloading at that 

point.

Variable speed may be achieved by variable frequency 

AC drives, or by switched reluctance DC drives. Each of 

these has its specific electrical characteristics, including 

inverter and other losses.

Percent kW Input

Figure 2.5 Effect of Receiver Capacity on Lubricant-Injected, Rotary Compressor with Load/Unload 

Capacity Control
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On the next page, Figure 2.8 shows how input power 

varies by percent capacity output for a lubricantinjected rotary screw compressor with variable speed 

control.

Percent kW Input

Figure 2.6 Lubricant-Injected Rotary Compressor with Inlet Valve Modulation

Figure 2.7 Lubricant-Injected Rotary Compressor Performance with Variable Displacement

Percent kW Input Power
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Air-end displacement is directly proportional to rotor 

speed, but air-end efficiency depends upon male rotor 

tip speed. Most variable speed drive (VSD) pack- age 

designs involve full capacity operation above the 

optimum rotor tip speed, at reduced air-end efficiency 

and increased input power, when compared with a 

constant speed compressor of the same capacity, 

operating at or near its optimum rotor tip speed.

Efficiency with VSD is generally improved at reduced 

capacities. The best energy savings are realized in 

applications where the running hours are long, with a 

high proportion in the mid- to low-capacity range.

Some designs stop the compressor when a lower speed 

of around 20 percent is reached, while others may 

unload at 40 to 50 percent, with an unloaded power of 

10 to 15 percent. The appropriate amount of storage 

volume should be considered for each of these 

scenarios.

Field conversion of an existing compressor to variable 

speed drive must consider many factors, including the 

electric motor, the proposed male rotor tip speed at 

100 percent capacity and the reduction of air-end 

efficiency at reduced speeds and capacity. The potential 

impacts of harmonics on other end-use equipment 

must also be considered.

It should be noted that in systems with multiple 

compressors and sequencing controls, it is possible to 

have most of the compressors running fully loaded on 

base load with only one compressor modulating 

(operating as the “trim” compressor), providing the 

most efficient mode for the system. In addition, it is not 

necessary to have the air receiver/system storage 

capacity based upon the total capacity of all the 

compressors, provided they are not all on the same load 

and unload pressure settings.

The capacity of the one compressor is either modulated 

or operated in load/unload control. This is also a good 

application for variable displacement, or compressors 

with variable displacement or VSD control to match 

system demand.

Percent kW Input Power

Figure 2.8 Lubricant-Injected Rotary Compressor Performance with Variable Speed Control
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Fact Sheet 6: Compressed Air Storage

The basic purpose of an air receiver is to store a volume 

of compressed air for use when needed. As shown in 

Fact Sheet 5, for load/ unload compressors, adequate 

storage acts to effectively increase efficiency. Storage 

can also be used to: 

• control demand events (peak demand periods) in 

a compressed air system by reducing both the 

amount of pressure drop and the rate of decay, 

• protect critical pressure applications from other 

events in the system, and 

• control the rate of pressure drop to end uses. 

Many systems have an extra compressor operating 

inefficiently in modulation to support occasional 

demand events, and sometimes strategic storage 

solutions can allow for this compressor to be turned off. 

Controls and System Performance

The most common example of using storage for control 

is a small, air-cooled, piston- type compressor, mounted 

on a “tank” or air receiver. The compressor operates on 

a start/stop control system, usually controlled by a 

pressure switch having a fixed differential. For 

automotive applications, the compressor is normally 

stopped at a pressure of 175 psig. The compressor is 

restarted when the regulated pressures for the end uses 

of the compressed air causes the pressure to fall to 

about 145 psig (a differential of 30 psi). The wide 

pressure band combined with the storage reduces the 

frequency of motor starts, thereby protecting the 

motor.

In industrial compressed air systems, the supply side is 

generally considered to be the air compressors, dryers,

related filters and a primary air receiver. There are two 

differing points of view on the optimal location of a 

primary air receiver in a plant air system. If the receiver 

is located soon after the compressor discharge and the 

compressor(s) is a piston-type, the receiver acts as a 

dampener for pressure pulsations. If the receiver is 

located before the compressed air dryer, the receiver 

may provide additional radiant cooling and drop out 

some of the condensate and entrained oil, benefiting 

the dryer. However, the receiver will be filled with 

saturated air, and if there is a sudden demand that 

exceeds the capacity rating of the compressor and 

matching dryer, the dryer can be overloaded, resulting 

in a higher pressure dew point.

If the air receiver is located after the compressed air 

dryer, some of the above advantages are lost. However, 

the receiver is filled with compressed air (which has 

been dried), and a sudden demand in excess of the 

compressor and dryer capacity rating will be met with 

dried air. The dryer is not overloaded, since it is seeing 

only the output of the compressor, so the pressure dew 

point is not affected. One way to resolve this dilemma is 

to install storage both upstream and downstream of 

the dryer, remembering that the storage downstream 

of the dryer should be equal to or larger than the 

storage upstream of the dryer. In any case, it should be 

recognized that the compressed air dryer and 

associated filters will add pressure drop. This must be 

taken into account when determining the compressor 

discharge pressure to achieve the desired pressure that 

leaves the primary air receiver to the system.

The size of an air receiver can be calculated as follows:

V = T x C x Pa

P1 - P2

where:

V = Receiver volume, cubic feet

T = Time allowed (minutes) for pressure drop to occur

C = Air demand, cubic feet per minute (cfm) of free air

Pa = Absolute atmospheric pressure, psia 

P1 = Initial receiver pressure, psig

P2 = Final receiver pressure, psig

The formula assumes the receiver volume to be at 

ambient temperature and that no air is being supplied 

to the air receiver by the compressor(s). If the 

compressor(s) is running while air is being drawn from 

the receiver, the formula should be modified so that C is 

replaced by C - S, where S is the surplus compressor 

capacity, cfm of free air. The formula also can be 

revised with a known receiver size, to determine the 

time (T) to pump up an air receiver if the input flow is 

known. In this case, C is replaced by S, which is the 

compressor capacity, cfm of free air.
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In the past, mainly with reciprocating compressors, the 

rule of thumb for sizing a primary air receiver has been 

from 1 gallon per cfm to 3 gallons per cfm of

compressor capacity. This is no longer regarded as good

practice, and the recommended primary receiver size

will vary with the type of compressor and capacity

control used.

Secondary Air Receivers

In many industrial plants, there will be one or more 

applications with an intermittent demand of relatively 

high volume. This can cause severe dynamic pressure 

fluctuations in the whole system, with some essential 

points-of-use being intermittently starved, impacting 

the operation of pressure critical compressed air 

powered equipment. In most cases the system pressure 

will be artificially raised, increasing energy 

consumption. One strategy to address this is correctly 

sizing and locating a secondary air receiver close to the 

point of high intermittent demand. Such demand is 

often of short duration, and the time between the 

demand events is such that there is ample time to 

replenish the secondary receiver pressure with- out 

adding compressor capacity. A check valve before the 

secondary air receiver will prevent back flow to the 

rest of the system and ensure that the required volume 

is stored to meet the anticipated event(s).

A strategy called high pressure offline storage can be 

used to reduce the size of the required storage that 

might be required to feed a high volume intermittent 

use. A high pressure source such as a booster or standalone compressor pumps up the storage to a pressure 

much higher than system pressure, utilizing a much 

larger storage differential. For example a 500 gallon 

storage receiver with a 100 psi storage differential 

contains the same amount of air as a 5,000 gallon 

receiver with a 10 psi differential. The effectiveness of 

this strategy varies as it take more energy to produce 

the high pressure air, but this might enable a spare 

running compressor to shut off, saving more energy and 

reducing electrical peak demand charges.

Correctly sized and located air receivers can provide 

major stability and reliability advantages in a 

compressed air system and require little maintenance. 

All pressure vessels should meet pressure vessel safety 

requirements and have appropriate pressure relief 

valves. An automatic drain device, with manual bypass 

for service, should also be included. Condensate 

removed should be decontaminated to meet 

appropriate federal, state and local codes.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 45

Fact Sheet 7: Proven Opportunities at the Component Level

In some cases, taking a systems approach to analyzing 

compressed air systems can require more detailed 

analysis of an individual components as well as 

investigation of performance issues. In general, 

compressed air systems contain five major sub-systems: 

1) compressors; 2) prime mover; 3) controls; 4) air 

treatment equipment and other accessories; and 5) the 

air distribution sub-system. Important performance 

aspects of each of these sub-systems are discussed in 

detail below.

Compressors

While there are many different types of compressors, 

all compressor types generally operate more efficiently 

for 80-150 psig systems if they are designed to include 

multiple stages. With multiple stages, the final 

discharge pressure is generated over several steps, 

thereby saving energy.

Many multi-stage compressors save energy by cooling 

the air between stages, reducing the volume and work 

required to compress the air. In spite of this, many 

industrial compressors only have a single stage because 

equipment manufacturing costs are lower. Performance 

and efficiency issues of the three most common types 

of compressors—single- and double-acting 

reciprocating compressors, rotary compressors, and 

centrifugal compressors—are discussed below.

Single- and Double-Acting Reciprocating Compressors.

In the past, reciprocating air compressors were the 

most widely used in industrial plant air systems. Singleacting reciprocating compressors are generally aircooled, in the smaller hp sizes, and do not require 

substantial foundations. These compressors are less 

efficient than other types at full load, but operate quite 

efficiently at part load. Double-acting reciprocating air 

compressors are generally water- cooled and require 

substantial foundations. Multi-stage versions are usually 

considered to be the most efficient air compressors, but 

have high initial and installation costs and higher 

maintenance requirements. Other than for specialty 

applications double-acting reciprocating compressors 

are increasingly being replaced by other compressors 

due to obsolescence, maintenance issues and lack of 

parts. 

Rotary Compressors. Today, lubricant-injected rotary 

screw compressors are used in most industrial plant air 

applications and for large applications in the service 

industries. They have some advantages over 

reciprocating compressors, including lower initial 

installation and maintenance costs; smaller size; 

reduced vibration and noise; reduced floor space 

requirements. Rotary screw compressors provide 

continuous flow and do not have the type of pressure 

pulsations typically associated with reciprocating 

compressors. 

Lubricant-injected rotary screw compressors are 

typically less efficient than two-stage, double-acting 

reciprocating compressors or three-stage centrifugal 

compressors. Two-stage rotary screw compressors are 

generally more efficient than single-stage units. In 

general, rotary screw compressors are also less efficient 

at part-load than reciprocating compressors.

A wide range of models is usually available from 

different manufacturers for any given application. A 

good efficiency measure is to select the most efficient 

model available at full output capacity. The selection of 

the compressor with the best part load power 

consumption characteristics for units that are not base 

loaded can also be an important consideration. 

Published Compressed Air and Gas Institute (CAGI) data 

sheets can be used to compare brands and types of 

screw compressors. (See Appendix B titled Packaged 

Compressor Efficiency Ratings.)

Centrifugal Compressors. The use of centrifugal 

compressors is usually limited to higher volume 

industrial plant applications, such as chemical, textile 

plants, petroleum refining, or general plant air systems 

in larger manufacturing facilities. The compressors 

operate at high speeds and therefore use smaller, more 

compact equipment. In larger sizes, three-stage 

centrifugal compressors are often more efficient than 

rotary screw compressors and can approach the 

efficiency levels of double-acting reciprocating 

compressors. 

Centrifugal air compressors typically have 100 to 125 

psig discharge pressures for industrial applications and

are generally available from 150 hp to above 10,000 hp, 
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generally with improving efficiency as the size increases.

Centrifugal compressors are sometimes best suited to 

applications where demand is relatively constant or in 

industrial plants where they can be used primarily for 

base-load operation, allowing other compressor types 

to be as used as trim machines to meet peak demands. 

Best efficiency occurs if centrifugal compressors are 

operated at their best efficiency point and blow-off 

control is kept to a minimum.

Lubricant-Free Compressors. Lubricant-free versions of 

reciprocating and rotary air compressors are available. 

Centrifugal air compressors are inherently lubricantfree. Lubricant-free compressors may be appropriate 

for specific applications or to meet specific air quality 

requirements. Lubricant-free rotary screw and 

reciprocating compressors are generally less efficient 

than lubricant-injected machines.

Advantages and Disadvantages of Each 

Compressor Type

Advantages and disadvantages of any compressor are 

based on its characteristics and application. Advantages 

and disadvantages listed below are for a typical 

compressed air system in an industrial plant. 

Single-Acting, Air-Cooled Reciprocating Air 

Compressors

Advantages include:

• Good part load efficiency

• Small size and weight

• Generally can be located close to point-of-use 

avoiding lengthy piping runs and pressure drops

• Do not require separate cooling systems

• Simple maintenance procedures

Disadvantages include:

• Lubricant carryover as piston rings wear, which 

should be avoided

• Relatively high noise

• Less efficient at full load 

• Generally are designed to run not more than

50% of the time, although some can be at 80%

• Generally compress and store the air in a receiver 

at a pressure higher than required at the point-ofuse. The pressure then is reduced to the required 

operating pressure, but without recovery of the 

energy used to compress to the higher pressure.

Operating Efficiency: 22 to 24 kW/100 cfm*

Double-Acting, Water-Cooled Reciprocating Air 

Compressors

Advantages include:

• Efficient compression, particularly with multistage compressors

• Three-step (0-50-100 percent) or five-step (0-25-

50- 75-100 percent) capacity controls, allowing 

efficient part-load operation

• Relatively routine maintenance procedures

Disadvantages include:

• Obsolescence and lack of parts

• Relatively high first cost compared with 

equivalent rotary air compressors

• Relatively high space requirements

• Lubricant carryover, except on oil-free models

• Relatively high vibrations require high foundation 

costs

• Repair procedures require some training and skills

Operating Efficiency: 15 to 16 kW/100 cfm*

Lubricant-Injected Rotary Screw Compressors

Advantages include:

• Compact size and complete package

• Economic first cost

• Vibration-free operation does not require special 

foundation

• Part-load capacity control systems can match 

system demand

• Suitable for variable speed control with improved 

performance at part load)

• Routine maintenance includes lubricant and filter 

changes.

Disadvantages include:

• Part- load (efficiency can vary depending on 

control mode

• Lubricant carryover into delivered air requires 

proper maintenance of air/lubricant separator 

and the lubricant itself.

Operating Efficiency at 100 psig:

• 16 to 19 kW/100 cfm, single-stage*

• 15 to 17 kW/100 cfm, two-stage*
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Lubricant-Free Rotary Screw Air Compressors

Advantages include:

• Completely packaged

• Designed to deliver lubricant-free air

• Do not require any special foundations.

Disadvantages include:

• Significant premium over lubricant-injected type

• Less efficient than lubricant-injected type

• Limited to load/unload capacity control and VSD

• Higher maintenance costs than lubricant-injected 

type over the life of the machine.

Operating Efficiency: 17 to 22 kW/100 cfm*

Centrifugal Air Compressors

Advantages include:

• Completely packaged for plant or instrument air 

through tens of thousands of horsepower sizes

• Relative first cost improves as size increases

• Designed to deliver lubricant-free air

• Do not require any special foundations.

Disadvantages include:

• Operation below 70-80 percent of capacity may 

require blow off to avoid surge, resulting in 

wasted energy. (Note: Load/unload may be 

possible)

• High rotational speeds require special bearings, 

sophisticated monitoring of vibrations and 

clearances

• Specialized maintenance considerations. 

Operating Efficiency: 16 to 20 kW/100 cfm*

*By taking the estimated full-load bhp requirement of each 

compressor type at 100 psig discharge pressure at the compressor, a 

main-drive motor with a typical efficiency of 92 percent and 0.746 

kW/bhp, the approximate efficiencies are obtained.

Prime Movers

The majority of industrial compressed air systems use 

electric motors as the prime mover. Most major 

manufacturers of industrial packaged compressed air 

systems now offer energy-efficient motors. There is a 

range of efficiencies available for any given application, 

and manufacturers will likely offer lines of premiumefficiency motors that have higher efficiencies than 

standard-efficiency motors.

Motors can be flange-mounted, connected with a Vbelt, or direct-coupled. Proper alignment is critical for 

all applications. Direct coupling or flange mounting 

results in the least loss of efficiency, while V-belt 

applications may allow for more compact packaging. Vbelts should always be inspected and tensioned per 

manufacturer’s specification to avoid increased power 

transmission losses.

Because of the heavy-duty and load cycles on most 

compressors, it almost always makes sense to buy the 

most efficient motor available. The incremental cost for 

a more efficient motor is typically paid back in less than 

one year from the resulting energy savings. Users 

should be aware that new energy-efficient motors 

sometimes have lower available starting torque than 

standard motors and often have slightly higher 

operating speeds because of reduced slip. Match 

operating speeds and torque requirement as closely as 

possible when replacing a motor. 

Controls

Compressor control mechanisms are used to match the 

compressed air volume and pressure delivered by the 

compressor with facility demand. Compressor controls 

are often the most important factor determining a 

compressor’s ability to perform efficiently at part- load. 

Controls are frequently configured poorly, and proper 

control strategies can lead to substantial reductions in 

energy consumption.

For more information on controls and compressed air 

system performance, see Fact Sheet 5: Compressed Air 

System Controls.

Air Treatment Equipment and Other 

Accessories 

Air treatment equipment must provide for both 

contaminant removal and preparation of the air for

equipment use. The level of air treatment and 

accessories needed is often dependent on air quality 

requirements. For optimum performance, air treatment 

equipment should be operated as close to 

manufacturers’ design conditions as possible. Drying to 

unnecessarily low dew points or excessive filtration of 
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compressed air can waste significant energy and 

possibly increased maintenance costs. A discussion of 

important compressor system accessory equipment and 

performance follows.

Dryers. Compressed air system performance is typically 

enhanced by the use of dryers, but since they require 

added capital and operating costs (including energy), 

drying should only be performed to the degree that it is 

needed for the proper functioning of the equipment 

and the end use.

Single-tower, chemical deliquescent dryers use little 

energy, but provide pressure dew point suppression of 

15 to 50°F below the dryer inlet temperature, 

depending on the desiccant selected. The drying of the 

air consumes the desiccant which must be replaced at 

regular intervals. They are not suitable for most systems 

and are typically used only in specialty applications. The 

approximate power requirement, including pressure 

drop through the dryer and any associated filtration, 

but excluding the cost of replacement desiccant, is 

approximately 0.2 kW/100 cfm.

Refrigerant-type dryers are the most common and 

provide a pressure dew point of 35 to 39°F, which is 

acceptable for many applications. In addition to the 

pressure drop across the dryer (usually 3 to 5 psid), the 

energy to run the refrigerant compressor must be

considered. Some refrigerant-type dryers have the 

ability to efficiently cycle on and off at lower than rated 

flows, which may save energy. The full load power 

requirement, including the effect of pressure drop 

through the dryer, is 0.79 kW/100 cfm. Cylinder head 

unloading dryers are also available (single and two-step) 

in larger dryers and offer improved part-load 

performance over conventional refrigerated dryers.

Twin-tower, desiccant-type dryers are the most 

effective in the removal of moisture from the air and 

typically are rated at a pressure dew point of –40°F. In a 

pressure-swing regenerative dryer, the purge air 

requirement can range from 10 to 18 percent of the 

dryer’s rating, depending on the type of dryer. This

energy loss, in addition to the pressure drop across the 

dryer, must be considered. The heated-type requires 

less purge air for regeneration, as heaters are used to 

heat the desiccant bed or the purge air. 

Heated blower type dryers use no purge air and a small 

amount for cooling. Some heated blower types use 

secondary cooling and zero purge. The heater (and 

blower) energy must also be considered against the 

reduction in the amount of purge air, in addition to the 

pressure drop. Approximate full-load power 

requirement, including pressure drop through the 

dryer, is 2.0 to 3.0 kW/100 cfm. Energy efficiency can be 

improved at part loads using dew point controls.

Heat-of-compression dryers are regenerative- desiccant 

dryers, which use the heat generated during 

compression to accomplish desiccant regeneration. 

Common types use desiccant drum or twin tower 

configuration. This means that there is no loss of purge 

air. This type of dryer requires air from the compressor 

at sufficiently high temperature to accomplish 

regeneration. For this reason, heat-of-compression 

dryers are used almost exclusively with centrifugal or 

lubricant-free rotary screw compressors. There is often 

no reduction of air capacity with this type of dryer 

except a very small percentage due to cooling purge.

The twin-tower, heat-of-compression dryer operation is 

similar to other twin-tower, heat-activated, 

regenerative desiccant dryers. The difference is that the 

desiccant in the saturated tower is regenerated by 

means of the heat of compression in all of the hot air 

leaving the discharge of the air compressor (aftercooler 

bypassed). The total air flow then passes through a 

secondary aftercooler before entering the drying tower. 

Temperatures must be high enough to regenerate the 

desiccant and may require secondary heat.

The total power requirement, including pressure drop 

and compressor operating cost (not including cooling 

purge or secondary heat, is approximately

0.8 kW/100 cfm.

Membrane-type dryers can achieve dew points of 40°F,

but lower dew points to –40°F can be achieved at the 

expense of additional purge air loss. These dryers are 

suitable for small point-of-use applications where the 

air quality is greater than that of the general 

applications.

Advantages of membrane dryers include:

• Low installation cost

• No electrical consumption

• Can be installed outdoors
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• Can be used in hazardous atmospheres

• No moving parts.

Disadvantages of membrane dryers include:

• Limited to low-capacity systems

• High purge air loss (15 to 20 percent) to achieve 

required pressure dew points

• Membrane may be fouled by oil or other 

contaminants and a coalescing filter is 

recommended before the dryer.

The total full-load power requirement, including 

pressure drop and compressor operating cost is 

approximately 3 to 4 kW/100 cfm. Efficiency can drop 

off drastically if used with very light loads. Use of 

energy saving controls can improve part load efficiency.

Dryer Selection. The selection of a compressed air 

dryer for the rated conditions should be based upon the 

required pressure dew point and the estimated cost of 

operation. Where a pressure dew point of less than 

35°F is required, a refrigerant-type dryer cannot be 

used. The required pressure dew point for the 

application at each point- of-use eliminates certain 

types of dryers. Dryers must be sized by taking into 

account worst case operating inlet temperature, system 

pressure and ambient temperature. Where average 

loading conditions are less than the dryer rating, the 

selection of units with good part load efficiency through 

efficient control can save energy. Typically, the pressure 

drop through a compressed air dryer is 3 to 5 psi and 

should be taken into account in system requirements. 

Compressed air should be dried only where necessary 

and only to the pressure dew point required.

Compressed Air Filters. These include particulate filters 

to remove solid particles, coalescing filters to remove 

lubricant and moisture, and adsorbent filters for 

removal of odors and taste. A coalescing-type filter is 

recommended before a desiccant-type dryer to prevent 

fouling of the desiccant bed. A one micron after-filter is 

necessary to prevent desiccant “fines” from entering 

the distribution piping. Additional filtration may also be 

needed to meet requirements for specific end uses.

Compressed air filters downstream of the air 

compressor are generally required for the removal of 

contaminants, such as particulates, condensate, and 

lubricant. Filtration only to the level required by each 

compressed air application will minimize pressure drop 

and resultant energy consumption. Elements should 

also be replaced as indicated by pressure differential, 

and at least annually, to minimize pressure drop and 

energy consumption. Filters should be installed with 

efficient condensate drains.

Air Receivers. The storage of compressed air in air 

receivers is a critical component to any compressed air 

system. Air receivers are designed to provide a supply 

buffer to meet short-term demand spikes that can 

exceed the compressor capacity. They also serve to 

dampen reciprocating compressor pulsations, separate 

out particles and liquids, and make the compressed air 

system easier to control. In some cases, installing a 

larger receiver to meet occasional peak demands can 

even allow for the use of a smaller compressor.

In most systems, the receiver will be located just after 

the dryer. In some cases, it makes sense to use multiple 

receivers, one prior to the dryer and one closer to 

points of intermittent use. Refer to Fact Sheet 6: 

Compressed Air Storage for additional information.

Condensate/Lubricant Separators. It is no longer 

acceptable to discharge condensate from a compressed 

air system to sewer lines without treatment to remove 

contaminants such as entrained lubricants (except for 

condensate from some lubricant-free compressor 

systems). Condensate/lubricant separators are available 

in the marketplace to achieve separation by means of 

settling tanks and/or permeable membranes. This 

equipment helps to avoid the potentially high costs of 

contaminated waste disposal.

Air/Lubricant Separators. The air/lubricant separator in 

a lubricant-cooled, rotary screw compressor generally 

starts with a 2 to 3 psid pressure drop at full-load when 

new. Higher pressure differentials cause the 

compressor motor to consume more energy and 

possibly exceed the service factor. Maintenance 

manuals usually suggest changing them when there is a 

10 to 12 psid pressure drop across the separator. In 

many cases it may make sense to make an earlier 

separator replacement, especially if electricity prices 

are high.

Heat Recovery Systems. Most systems do not employ 

heat recovery, even though economics can be good, 

with typical paybacks of less than one year. Heat 

recovery systems require electricity for fans or pumps, 

but can decrease the need for fossil fuels usually used 
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for heating. See the Fact Sheet 9: Heat Recovery and 

Compressed Air Systems for more information on this 

energy saving opportunity.

The Air Distribution Sub-System

The air distribution sub-system, which connects the 

major components, is one of the most important parts 

of the compressed air system. It is made up of main 

trunk lines, hoses and valves, drops to specific usage 

points, pressure regulators and lubricators, additional 

filters and traps, and supplementary air treatment 

equipment. It is throughout this sub-system that most 

leaks occur, energy is lost, and maintenance is required. 

Equipment should be chosen to avoid excessive 

pressure drops and leakage.

In addition, consideration of appropriate sizing of 

equipment and layout will provide for proper air supply, 

good tool performance, and optimal production. The 

complete drying, filtration, and distribution system 

should be properly sized and arranged so that the total 

pressure drop from the air compressor to the points- ofuse is much less than 10 percent of the compressor 

discharge pressure.

Some users bypass automatic condensate traps and 

leave valves partially open at all times to allow for 

constant draining. This practice wastes substantial 

energy and should never be undertaken. If a floatoperated, automatic condensate drain is not 

functioning properly, it should be cleaned and repaired 

instead of bypassed. If maintenance of float-operated 

drain traps is a burden, consider replacing them with 

more reliable demand- type drain traps.

The efficiency of the entire system can be enhanced by 

the proper selection, application, installation, and 

maintenance of each component.
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Fact Sheet 8: Maintenance of Compressed Air Systems for Peak Performance

Like all electro-mechanical equipment, industrial 

compressed air systems require periodic maintenance 

to operate at peak efficiency and minimize unscheduled 

downtime. Inadequate maintenance can have a 

significant impact on energy consumption via lower 

compression efficiency, air leakage, or pressure 

variability. It can also lead to high operating 

temperatures, poor moisture control, and excessive 

contamination. Most problems are minor and can be 

corrected by simple adjustments, cleaning, part 

replacement, or the elimination of adverse conditions.

Compressed air system maintenance is similar to that 

performed on cars; filters and fluids are replaced, 

cooling water is inspected, belts are adjusted, and leaks 

are identified and repaired.

All equipment in the compressed air system should be 

maintained in accordance with manufacturers’ 

specifications. Manufacturers provide inspection, 

maintenance, and service schedules that should be 

strictly followed. In many cases, it makes sense, from 

efficiency and economic standpoints, to maintain 

equipment more frequently than the intervals 

recommended by manufacturers, which are primarily 

designed to protect equipment.

One way to tell if a system is well-maintained and 

operating properly is to periodically baseline the system 

by tracking power, pressure, flow, and temperature. If 

power use at a given pressure and flow rate increases, 

the system’s efficiency is degrading. This baselining will 

also indicate if the compressor is operating at full 

capacity, and if the capacity is decreasing over time. On 

new systems, specifications and operating data should 

be recorded when the system is first set up and 

operating properly. See Fact Sheet 10: Baselining 

Compressed Air Systems for more information.

Proper maintenance is essential to compressed air 

system efficiency and reliability. The key to success 

requires compressor operators to determine the 

requirements for each piece of equipment, the 

necessary resources, and trend analysis of recorded 

data. All observations and meter readings should be 

recorded for compressors, dryers, filters, and any 

components in the compressor plant. The combination 

of equipment control panel data, frequent inspections, 

and log sheets are required to avoid unscheduled 

system shutdowns, and to utilize the principles of 

preventive and predictive maintenance. Recording the 

dates of all maintenance and repairs, including a list of 

all parts that were replaced or serviced is 

recommended.

The maintenance schedules provided in this fact sheet 

are intended to be used only as a guide. For more exact 

procedures, always refer to the manufacturer’s manuals

and follow all safety precautions.

Stopping for Maintenance

The following procedures should be followed when 

stopping the compressor for maintenance or service.

Step 1. Per Occupational Safety & Health Administration 

(OSHA) regulation 1910.147: The Control of Hazardous 

Energy Source (Lockout/Tagout), disconnect and 

lockout the main power source. Display a sign in clear 

view at the main power disconnect switch stating that 

the compressor is being serviced.

Step 2. Isolate the compressor from the compressed air 

supply by closing a manual shutoff valve down- stream 

(and upstream, if applicable in booster service) from the 

compressor. Display a sign in clear view at the shutoff 

valve stating that the compressor is being serviced. Be 

certain that a pressure relief valve is installed upstream 

of any isolation valve.

Step 3. Lock open a pressure relief valve within the 

pressurized system to allow the system to be 

completely depressurized. NEVER remove a plug to 

relieve the pressure!

Step 4. Shut off the water cooling supply (water- cooled 

compressors).

Step 5. Open all manual drain valves within the area to 

be serviced.

WARNING!

Never assume a compressor is safe to work on just because it

is not operating. It could restart at any time.
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Step 6. Wait for the unit to cool before starting to 

service. (Temperatures of 125°F can burn skin. Some 

surface temperatures exceed 350°F when the 

compressor is operating, and just after it is shut down).

Step 7. Refer and give preference to the manufacturer’s 

manuals over these typical maintenance procedures.

Maintenance Schedules

To assure maximum performance and service life of 

your compressor, a routine maintenance schedule 

should be developed. Sample schedules have been 

included here to help you to develop a maintenance 

schedule designed for your particular application.

Time frames may need to be shortened in harsher 

environments.

The documentation shipped with your compressor 

should contain a maintenance schedule checklist.

Make copies of this checklist and retain the master to 

make more copies as needed. On each copy of the 

checklist, enter dates and initials in the appropriate 

spaces. Keep the checklist and this fact sheet readily 

available near the compressor.

General Maintenance Discussion

All equipment in the compressed air system should be 

maintained in accordance with manufacturers’ 

specifications. Manufacturers provide inspection, 

maintenance, safety, service schedules and pressure 

relief valve testing that should be strictly followed.

Maintenance issues for specific system components are 

discussed below.

Lubricant-Injected Rotary Screw Compressor 

Package

The main areas of the compressor package that need 

maintenance are the compressor, heat exchangers airlubricant separator, lubricant, lubricant filter, and airinlet filter. The compressor and all coolers need to be 

kept clean and foul-free. If they are dirty, compressor 

efficiency will be adversely affected. Cooling fans and 

water supplies should also be inspected to ensure that 

they are operating at peak performance.

The air lubricant separator in a lubricant-cooled, rotary 

screw compressor generally starts with a 2 to 3 psid 

pressure drop at full-load when new. Maintenance 

manuals usually suggest changing them when there is 

about a 10 psid pressure drop across the separator. In 

many cases it may make sense to make an earlier 

separator replacement, particularly if electricity prices 

are high.

The compressor lubricant and lubricant filter should be 

changed per manufacturer’s specification. Lubricant can 

become corrosive and degrade both the equipment and 

system efficiency. Lubricant sampling and analysis is 

recommended.

For lubricant-injected rotary compressors, the 

lubrication is provided to bearings, gears, and intermeshing rotor surfaces. The lubricant also acts as a seal 

and removes most of the heat of compression. Only a 

lubricant meeting the manufacturer’s specifications 

should be used.

Inlet filters and inlet piping should also be kept clean. A 

dirty filter can reduce compressor capacity and 

efficiency. Filters should be maintained at least per 

manufacturer’s specifications, taking into account the 

level of contaminants in the facility’s air.

Compressor Drives 

If the electric motor driving a compressor is not 

properly maintained, it will not only consume more 

energy, but will be apt to fail before its expected lifetime. The two most important aspects of motor 

maintenance are lubrication and cleaning.

Lubrication. Too much lubrication can be just as 

harmful as too little and is a major cause of premature 

motor failure. Motors should be lubricated per the 

manufacturer’s specification, which can be anywhere 

from every 2 months to every 18 months, depending on 

annual hours of operation and motor speed. 

Cleaning. Since motors need to dissipate heat, it is 

important to keep all of the air passages clean and free 

of obstruction. For enclosed motors, it is vital that 

cooling fins are kept free of debris. Poor motor cooling 

can increase motor temperature which shortens motor 

life and increases energy consumption.
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Belts. Motor V-belt drives also require periodic 

maintenance. Tight belts can lead to excessive bearing 

wear, and loose belts can slip and waste energy. Under 

normal operation, belts stretch and wear and therefore, 

require adjustment. A typical rule of thumb is to 

examine and adjust belts after every 400 hours of 

operation. Follow manufacturers recommended tension 

requirements.

Air Treatment Equipment

Fouled compressed air treatment equipment can result 

in excessive energy consumption as well as poor-quality 

air that can damage other equipment. All filters should 

be kept clean. Dryers, aftercoolers, and separators 

should all be cleaned and maintained per 

manufacturer’s specifications.

Automatic Condensate Drain Traps. Most compressed 

air systems have numerous moisture traps located 

throughout the system. Traps need to be inspected 

periodically to ensure that they are not stuck in either 

the open or closed position. An automatic trap stuck in 

the open position will leak compressed air; a trap stuck 

in the closed position will cause condensate to back up 

and be carried downstream where it can damage other 

system components. Traps stuck in the open position 

can be a major source of wasted energy.

End-Use Filters, Regulators, and Lubricators. Point-ofuse filters, regulators, and lubricators are needed to 

ensure that a tool is receiving a clean, lubricated supply 

of air at the proper pressure. Filters should be inspected 

periodically because a clogged filter will increase 

pressure drop, which can either reduce pressure at the 

point-of-use or increase the pressure required from the 

compressor, thereby consuming excessive energy. A 

filter that is not operating properly will also allow 

contaminants into a tool, causing it to wear out 

prematurely. The lubricant level should also be checked 

often enough to ensure that it does not run dry. Tools 

that are not properly lubricated will wear prematurely 

and use excess energy. 

Leaks

Leak detection and repair is an important part of any 

maintenance program. For more information on finding 

and fixing leaks, see Fact Sheet 3: Compressed Air 

System Leaks.

Temperature

Temperature measurements help to indicate if 

equipment is operating at peak performance. Generally, 

equipment that runs hotter than specified parameters is 

not performing at peak efficiency and requires service. 

The following temperature measurements should be 

taken when baselining a system.

• Aftercooler and intercoolers cold temperature 

difference or approach temperature of cold water 

inlet to cooled air outlet. Because dryers are 

normally designed at 100°F maximum inlet air 

temperature, some remedial action may be 

required if aftercooler outlet temperatures 

exceed 100°F.

• For rotary-lubricated compressors, the air 

discharge temperatures must be maintained for 

reliable compressor performance. Normal 

operation requires temperatures below 200°F.

• Inlet air temperature.

Maintenance Schedules

Establishing a regular, well-organized maintenance 

program, and strictly following it, is critical to 

maintaining the performance of a compressed air 

system. One person should be given the responsibility 

of ensuring that all maintenance is performed properly, 

on schedule, and is adequately documented.

The following are typical recommended minimum 

maintenance procedures for air-cooled reciprocating 

compressors; water-cooled, double-acting reciprocating 

compressors; lubricant-injected rotary compressors; 

lubricant-free rotary compressors; and centrifugal 

compressors.

Air-Cooled Reciprocating Compressors

Every 8 Hours (or Daily)

• Maintain lubricant level between high- and lowlevel marks. (Discoloration or a higher lubricant 

level reading may indicate the presence of 

condensed liquids). If lubricant is contaminated, 

drain and replace.

• Drain receiver tank, drop legs and traps in the 

distribution system.

• Give compressor an overall visual inspection and be 

sure safety guards are in place.
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• Check for any unusual noise or vibration.

• Check lubricant pressure on pressure lubricated 

units. 

• Check for lubricant leaks.

Every 100 Hours (or Weekly)

• Be certain pressure relief valves are working. 

• Clean the cooling surfaces of the intercooler and 

compressor.

• Check the compressor for air leaks.

• Check the compressed air distribution system for 

leaks.

• Clean or replace the air intake filter. Check more 

often under dusty conditions.

• Check belt tension.

As required by manufacturer 

• Change lubricant in accordance with 

manufacturer’s instructions. (more frequently in 

harsher environments).

• Check lubricant filter on pressure lubricated units 

(more frequently in harsher environments).

• When synthetic lubricant is used, lubricant 

change intervals may be extended. 

• Inspect compressor valves for leakage and/or 

carbon build-up. The lubricant sump strainer 

screen inside the crankcase of pressure-lubricated 

models should be thoroughly cleaned with a 

safety solvent during every lubricant change. If 

excessive sludge build-up exists inside the 

crankcase, clean the inside of the crankcase as 

well as the screen. Never use a flammable or toxic 

solvent for cleaning. Always use a safety solvent 

and follow the directions provided.

Every 2,000 Hours (or 12 Months)

• Inspect the pressure switch contacts, diaphragm 

and motor starter contacts. 

Lubrication 

Compressors may be shipped without lubricant in the 

crankcase. Before starting the compressor, add enough 

lubricant to the crankcase to register between the high 

and low marks on the dipstick or on bull’s eye sight 

gauge. Use the specified lubricant or consult the 

manufacturer for recommendations.

Certain synthetic lubricants have proven under 

extensive testing to minimize friction and wear, limit 

lubricant carryover, and reduce carbon and varnish 

deposits. They will support the performance 

characteristics and life and are highly recommended. 

Refer to the manufacturer’s specifications to determine 

the correct amount of lubricant and viscosity to use for 

your model and application. Use the supplier’s lubricant 

analysis program.

Routine Maintenance for Water-Cooled, 

Double-Acting Reciprocating Compressors 

The following are typical minimum maintenance 

requirements for this type of compressor.

Every 8 Hours (or Daily)*

• Check compressor lubricant level in crankcase and 

cylinder lubricator and, if necessary, add to level 

indicated by sight gauge.

• Check cylinder lubrication feed rate and adjust, as 

necessary.

• Check lubricant pressure and adjust as necessary 

to meet specified operating pressure.

• Check cylinder jacket cooling water temperatures.

• Check capacity control operation. Observe 

discharge pressure gauge for proper load and 

unload pressures.

• Drain control line strainer.

• Check operation of automatic condensate drain 

trap (intercooler and aftercooler).

• Drain condensate from discharge piping as 

applicable (drop leg and receiver).

• Check intercooler pressure on multi-stage 

machines, and refer to manufacturer’s manual if 

pressure is not as specified.

Every 360 Hours (or Monthly)*

• Check piston rod packing for leaks and for blowby at gland. Repair or replace as necessary per 

manufacturer’s manual.

• Inspect lubricant scraper rings for leakage. 

Replace as necessary per manufacturer’s manual.

• Inspect air intake filter. Clean or replace as 

necessary.

• Drain lubricant strainer/filter sediment.

• Lubricate unloader mechanism per 

manufacturer’s manual.

• Check motor amperes (amps) at compressor fullcapacity and pressure.
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Every 3,000 Hours (or Semi-Annually)*

• Perform valve inspection per manufacturer’s 

manual.

• Inspect cylinder or cylinder liner, through valve 

port, for scoring.

• Change crankcase lubricant, if required.

• Clean crankcase breather, if provided.

• Change lubricant filter element.

• Remove and clean control air filter/strainer 

element.

• Check all safety devices for proper operation.

• Perform piston ring inspection on non-lubricated 

design. Replace as necessary per manufacturer’s 

manual.

Every 6,000 Hours (or Annually)*

• Remove and clean crankcase lubricant strainer.

• Check foundation bolts for tightness. Adjust as 

necessary.

• Perform piston ring inspection. Replace as 

necessary per manufacturer’s manual.

*Whichever interval is sooner. Experience gained from a well-kept 

maintenance log may allow the recommended times to be adjusted.

Routine Maintenance for LubricantInjected Rotary Compressor

The following are typical minimum maintenance 

requirements.

Periodically/Daily 

Monitor all gauges and indicators for normal operation.

• Check lubricant level and top off as necessary.

• Check for lubricant leaks.

• Check for unusual noise or vibration.

• Drain water from air/lubricant reservoir.

• Drain control line filter.

Monthly

• Service air filter as needed (more often if

extremely dusty conditions exist).

• Wipe down entire unit to maintain appearance.

• Check drive motor amps at compressor full 

capacity and design pressure.

• Check operation of all controls.

• Check operation of lubricant scavenger/return 

system. Clean, as necessary.

6 Months or Every 1,000-2000 Hours

• Take lubricant sample and have it analyzed.

• Change lubricant filter.*

Periodically/Annually

• Inspect the entire package and check all bolts for 

tightness.

• Change air/lubricant separator.

• Change lubricant per manufacturer’s instructions.

• Change air filter.

• Lubricate motors per manufacturer’s instructions.

• Check safety shutdown system. Contact 

authorized service person.

*Manufacturers may recommend changing the lubricant filter within 

the first week of operation to rid the system of foreign matter which 

may have collected during initial assembly and start-up.

Routine Maintenance for Lubricant-Free 

Rotary Screw Compressor

The following are typical minimum requirements for 

this type of compressor. Routine maintenance is 

relatively minimal. The microprocessor control panel 

monitors the status of the air and lubricant filters.

When maintenance to either device is required, the 

control panel may display the appropriate maintenance 

message and flash the location on the display as a visual 

remainder.

Do not remove caps, plugs, and/or other components 

when compressor is running or pressurized. Stop 

compressor and relieve all internal pressure before 

doing so.

Daily

Following a routine start, observe the various control 

panel displays and local gauges to check that normal 

readings are being displayed. Previous records are very 

helpful in determining the normalcy of the 

measurements. These observations should be made 

during all expected modes of operation (i.e., full-load, 

no-load, inter-stage and discharge pressures, motor 

amps and cooling water temperatures).
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After Initial 50 Hours of Operation

Upon completion of the first 50 hours of operation, 

essential readings of operating conditions should be 

verified and any necessary adjustments made.

Every 3,000 Hours of Operation

The following items should be checked every 3,000 

hours of operation, although service conditions, such as 

relative cleanliness of process air or quality of cooling 

water, may require shorter inspection intervals.

• Check/change lubricant charge and filter element.

• Check/change air filter element.

• Check/change sump-breather filter element.

• Check/clean control line filter element.

• Check/clean condensate drain valve.

• Check condition of shaft coupling element and 

tightness of fasteners.

• Measure and record vibration signatures on 

compressor, gearbox, and motor (optional).

• Annual rebuilding of the inlet valve is normally 

recommended.

Note: Please refer to the motor manufacturer’s 

documentation for recommended maintenance. Keep in 

mind that the specified type and quantity of lubricating 

grease for motor bearings is crucial.

Every 15,000 Hours of Operation

In addition to those items covered in the 3,000-hour 

maintenance interval, the following items must also be 

checked every 15,000 hours of operation, depending 

upon conditions of service.

• Operate/test all safety devices.

• Check/clean heat exchangers.

• Check/clean blowdown valve.

• Check operation of balancing switch/valve 

assembly.

• Check/clean water regulating valve.

• Check/clean check valve.

• Check/clean galvanized interstage pipe work.

• Check condition of isolation mounts under 

compressor unit and motor.

• Check/clean strainer and check valve included in 

lubricant pump suction line, inside lubricant 

sump.

Be aware that work on the compressor stages and 

gearbox must be conducted by manufacturer’s 

personnel only. Any work done by unauthorized 

personnel can render the manufacturer’s equipment 

warranty null and void.

Parts Replacement and Adjustment Procedures

Familiarize yourself with the safety guidelines offered in 

the safety section of the manufacturer’s manual before 

attempting any maintenance on the package.

Routine Maintenance for Centrifugal Air 

Compressors

The following are typical maintenance requirements for 

this type of compressor.

Daily

• Record operating air inlet, interstage and 

discharge pressures and temperatures.

• Record cooling water inlet and outlet pressures 

and temperatures.

• Record lubricant pressure and temperatures.

• Record all vibration levels.

• Check inlet air filter differential pressure.

• Check proper operation of drain traps.

• Drain control air filter.

• Check for leaks, air, water, and lubricant. Repair 

and clean as necessary.

• Check lubricant sump level and adjust as 

necessary.

• Check drive motor for smooth operation and 

record amps.

Every 3 Months

• Check lubricant filter differential pressure. 

Replace element as necessary.

• Check lubricant sump venting system. Replace 

filter elements as necessary.

• Check operation of capacity control system.

• Check operation of surge control system.

• Check main-drive motor amps at full-load 

operation.

• Check automatic drain traps and strainers. Clean 

and/or replace as necessary.

Every 6 Months

• Check inlet air filter and replace element as 

necessary.
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• Take oil sample for analysis. Replace lubricant as 

necessary.

Annually

• Inspect intercooler, aftercooler, and lubricant 

cooler. Clean and/or replace as necessary.

• Inspect main drive motor for loose mounting 

bolts, frayed or worn electrical cables, and 

accumulated dirt. Follow manufacturer’s 

recommendations, including lubrication.

• Inspect main drive coupling for alignment and 

required lubrication.

• Inspect gearbox for loose mounting bolts, 

vibration, unusual noise or wear and axial 

clearances per manufacturer’s manual.

• Check impeller inlets and diffusers for signs of 

wear, rubbing or cracking.

• Check control panel for complete and proper 

operation.

• Check all control valves for proper operation.

• Check all safety devices for proper settings and 

operation.

• Inspect check valve; replace worn parts.

Keep all components/accessories clean and follow all 

recommended safety procedures.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 58

Fact Sheet 9: Heat Recovery and Compressed Air Systems

As much as 80 to 93 percent of the electrical energy 

used by an industrial air compressor is converted into 

heat. In many cases, a properly designed heat recovery 

unit can recover anywhere from 50 to 90 percent of this 

available thermal energy and put it to useful work 

heating air or water.

Typical uses for recovered heat include supplemental 

space heating, industrial process heating, water heating, 

makeup air heating, and boiler makeup water 

preheating. Recoverable heat from a compressed air 

system however, is usually not hot enough to produce 

steam directly.

Heat recovery systems are available for both air- and 

water-cooled compressors.

Heat Recovery with Air-Cooled, Rotary Screw 

Compressors

Heating Air. Air-cooled, packaged, rotary screw 

compressors are very amenable to heat recovery for 

space heating or other hot air uses. Ambient 

atmospheric air is heated by passing it across the 

system’s aftercooler and lubricant cooler, where it 

extracts heat from both the compressed air and the 

lubricant that is used to lubricate and cool the 

compressor.

Because packaged compressors are typically enclosed in 

cabinets and already include heat exchangers and fans, 

the only system modifications needed are the addition 

of ducting and possibly another fan to handle the duct 

loading and to eliminate any back pressure on the 

compressor cooling fan. These heat recovery systems 

can be modulated with a simple, thermostatically 

controlled hinged vent. When heating is not required

—such as in the summer months—the hot air can be 

ducted outside the building. The vent can also be 

thermostatically regulated to provide a constant 

temperature for a heated area.

Hot air can be used for space heating, industrial drying, 

preheating aspirated air for oil burners, or any other 

application requiring warm air. As a rule, approximately 

50,000 British thermal units (Btu) per hour of energy is 

available for each 100 cfm of capacity (at full-load). Air 

temperatures of 20 to 40°F above the cooling air inlet 

temperature can be obtained. Recovery efficiencies of 

80 to 90 percent are common.

Caution should be applied if the supply air for the 

compressor and the recovered heat is used in another 

space, because this can cause a decrease in the static 

pressure in the cabinet and reduce the efficiency of the 

compressor. Under this scenario, the user may want to 

consult a ventilation expert.

Heating Water. Using a heat exchanger, it is also 

possible to extract waste heat from the lubricant 

coolers found in packaged water-cooled, reciprocating 

or rotary screw compressors and produce hot water. 

Depending on design, heat exchangers can heat nonpotable (gray) or potable water. When hot water is not 

required, the lubricant is routed to the standard 

lubricant cooler.

Hot water can be used in central heating or boiler 

systems, industrial cleaning processes, plating 

operations, heat pumps, laundries, or any other 

application where hot water is required. Heat 

exchangers also offer an opportunity to produce hot air 

and hot water, and allow the operator some ability to 

vary the hot air/hot water ratio.

Heat Recovery with Water-Cooled Compressors

Heat recovery for space heating is not as common with 

water-cooled compressors because an extra stage of 

heat exchange is required and the temperature of the 

available heat is lower. Because many water-cooled 

compressors are quite large, however, heat recovery for 

space heating can be an attractive opportunity. 

Recovery efficiencies of 50 to 60 percent are typical.

Calculating Energy Savings

When calculating energy savings and payback periods 

for heat recovery units, it is important to compare heat 

recovery with the current source of energy for 

generating thermal energy, which may be a low-price 

fossil fuel, such as natural gas. The equations in the text 

box on the next page illustrate the annual energy and 

costs savings available by recovering heat for space 

heating from an air-cooled, rotary screw compressor. 
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Applications where the existing heater is less than 85 

percent efficient will see proportionally higher savings.

* Cost of operating an additional fan for duct loading has not been included.

**$0.90/therm is the average natural gas cost for the 50 US states less 5% (from eia.gov 2014).

***Actual savings could be somewhat less, because of the inefficiencies of additional heat exchanger(s) potentially required.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 60

Fact Sheet 10: Baselining Compressed Air Systems

The purpose of baselining is to establish current energy 

performance levels and costs of a compressed air 

system, and to correlate the results with your plant’s 

present production levels. These measurements should 

be done at the same time as the pressure and flow 

measurements discussed in Section 1 “Analyzing 

Compressed Air Needs”. As you make improvements to 

your system, it will be possible to estimate the success 

by comparing the new measurements with the original 

baseline. Baselining a compressed air system and 

ongoing monitoring of energy performance may be part 

of an energy management system as specified by 

ISO50001 standard.

First, measurements of the system need to be taken. 

This requires the measurement of power, pressure, and 

flow. These measurements will be used in calculations 

to baseline system performance and energy 

consumption correlated to the plant production levels. 

Correlation to plant production levels is required to 

normalize data and perform an “apples-to-apples” 

comparison.

Energy saving measures implemented on both the 

supply and demand sides of the system, combined with 

proper compressor controls, will result in reduced 

energy consumption. This should be documented 

through continued measurements, again correlated to 

your plant’s production levels.

Some companies will also benchmark their compressed 

air systems against similar plants in their company, and 

sometimes even compare individual compressors.

Tools Needed

Properly baselining and monitoring a compressed air 

system requires the right tools. The following tools are 

required.

• Matched, calibrated pressure gauges or 

differential pressure gauges.

• Hook-on amp/volt meter (or preferably a kW 

meter).

• Data loggers—Data loggers are used in 

conjunction with other measurement devices to 

record multiple readings over a period of time. 

Data loggers are used to create plant pressure, 

flow, and energy consumption profiles, and can 

be important tools in developing a control 

strategy for a compressed air system.

• Flow meter—Factors to consider in selecting flow 

meters include type (in-line or insertion), air 

quality (wet or dry), ease of installation, life cycle 

cost (including possible pressure drop, such as 

orifice plates and maintenance), and accuracy 

(repeatability and turndown range).

What to Measure

Baselining a system requires measurement of power, 

pressure, flow, and temperature under different 

operating conditions, and also estimating leak load. 

Each is discussed below. Please refer to all operation 

and safety instructions provided with measurement 

equipment before using it.

Power

Power is measured in order to estimate the annual 

energy consumption of a compressed air system. Basic 

spot power rough estimation can be done using a hookon amp/volt meter or a wattmeter. The current and 

voltage into the compressor package should be 

measured. Full-load and no-load input power to the 

compressor should be measured.

For three-phase systems, power can be estimated by 

the following equation.

kW = 1.73 x volts x amps x power factor*

1,000

Volts = average line-to-line voltage of all three phases

Amps = average amps of all three phases

*Assume 0.85 power factor at full-load for 1,800 rpm motors, 

check with motor manufacturer for more accurate calculations. 

(The power factor at no load varies significantly) 

In general, spot measurement of amps and volts is only 

suitable for a basic rough estimation of annual energy 

consumption. Using a wattmeter in conjunction with 

data logging provides a more accurate direct reading of 

kW with no calculation or power factor adjustment.

Pressure
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Pressure is measured to give feedback for control 

adjustments, and to determine pressure drops across 

equipment. Measurement of pressure through all 

operating conditions can uncover system performance 

issues that can be corrected to improve energy 

performance and system pressure stability. Calibrated 

measuring instruments are required, preferably used 

with a data logging system. The following pressure 

measurements should be taken when baselining a 

system.

• Inlet to compressor (monitor inlet filter)

• Differential across air/lubricant separator for a 

lubricated rotary compressor

• Interstage on multistage machines

• Pressure differentials, including:

– Aftercooler

– Treatment equipment (dryers, filters, etc.)

– Various points in the distribution system.

Flow

Flow meters are necessary to measure total flow and to 

determine compressed air consumption. Flow, in 

conjunction with power or energy input, can be used to 

calculate the system specific power, or the amount of 

power consumed for a given flow output.

Flow should be measured:

• On the main compressor room output during all 

shifts

• At potential inappropriate uses to determine 

waste and as energy savings measures are 

implemented (for leaks during non-production 

periods)

Flow meters of the mass flow design will compensate 

for pressure and temperature variations and, if 

practical, should be suitable to measure the output of 

each individual compressor in the system. The mass 

flow is based upon standard reference conditions, 

which should be checked for the specific instrument 

used.

Using Power, Pressure, and Flow to Baseline 

System Performance and Energy Consumption 

Using the techniques described previously, determine 

both cfm at psig and energy consumption (kW x hours) 

per unit of production. Always correlate to production 

levels for a true measure of air compressor system 

performance.

Other parameters to monitor over time include:

• Specific Power (cfm per kW or kW per 100 cfm) at 

a given pressure

• Pressure (psig)

• Pressure drop across various components.

The expectation is that as efficiency measures are 

implemented, the total energy use will be reduced. This 

assumes, of course, that production does not increase

with a corresponding increase in the compressed air 

consumption. In general, improvements to compressor 

room efficiency through improved control reduce both 

the specific power and energy. Demand side flow 

reductions mostly affect the total energy with slight 

adjustment of the specific power. If flow reductions are 

made, and the pressure increases while energy 

consumption stays the same, adjust controls 

appropriately.

Estimating Leak Load

The ongoing measurement of leakage levels is an 

important part of baselining a compressed air system. 

Where appropriate, leakage levels can be tested during 

production downtime where compressed air consuming 

machines are turned off and all that remains is leakage 

flow. Leakage can be measured using flow meters, by 

observing the duty cycle of air compressors during nonproductive periods or by doing a receiver blow down 

test. Procedures for leak estimation are shown in Fact 

Sheet 3: Compressed Air System Leaks.
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Fact Sheet 11: Determining Your Compressed Air System Analysis Needs

A compressed air system analysis can highlight the true 

costs of compressed air and identify opportunities to 

improve efficiency and productivity.

Compressed air system users should consider using an 

auditor to analyze their compressed air system. A 

number of firms specialize in compressed air system 

analysis. System analysis is also performed by electric 

utilities, equipment distributors and manufacturers, 

energy service companies, and engineering firms. An 

informed consumer should be aware that the quality

and comprehensiveness of system analysis can vary.

Independent auditors should provide recommendations 

that are systems-neutral and commercially impartial. 

Independent auditors should neither specify nor 

recommend any particular manufacturer’s products.

A comprehensive compressed air system analysis 

should include an examination of both air supply and 

usage and the interaction between the supply and 

demand. Auditors typically measure the output of a 

compressed air system, calculate energy consumption 

in kilowatt-hours, and determine the annual cost of 

operating the system. The auditor may also measure 

total air losses caused by leaks and locate those that are 

significant. All components of the compressed air 

system are inspected individually and problem areas are 

identified. Losses and poor performance caused by 

system leaks, inappropriate uses, demand events, poor 

system design, system misuse, and total system 

dynamics are calculated, and a written report with a 

recommended course of action is provided.

The Compressed Air Challenge® (CAC) has developed 

guidelines to define three levels of system analysis 

services, independent of the type of firm offering these 

services. These three levels of service include: a walkthrough evaluation (1/2 to 2 days), a system assessment 

(2 to 5 days), and a fully-instrumented audit (3 to

10 days). More information on these services can be

found in the CAC’s Guidelines for Selecting a 

Compressed Air Service Provider. (See Appendix E.)

Selecting a Service Provider

In selecting a service provider, a compressed air user 

should consider the following outlined below.

This information is also taken from the CAC’s

Guidelines for Selecting a Compressed Air Service 

Provider.

Familiarity with the Systems Approach. The CAC 

provides Fundamentals of Compressed Air Systems and 

Advanced Management of Compressed Air Systems 

training to end users and service providers. One way to 

gauge a service provider’s commitment to the systems 

approach is whether they have staff who have received 

CAC training. If they do, ask whether these individuals 

will be providing or supervising services for your 

facility. Providers who are familiar with using a systems 

approach are much more likely to address situations, 

both inside and outside the compressor room, that 

affect the reliability of your compressed air supply.

Availability of Compressed Air System Analysis 

Services. Does the provider offer compressed air 

system analysis services? If yes, how well do these 

services fit your needs? If no, can the provider 

outsource these services to an experienced system 

specialist? How experienced are the individuals who will 

be providing these services? Once a walk-through, 

assessment, or audit is performed, what kind of followup services are available to ensure that the 

recommendations are properly implemented and 

produce the desired results? Ask for a sample of similar 

work that the provider has done for others, résumés of 

the personnel who will be performing the work, and 

client references. Please note that while leak detection 

is a useful element of a system assessment, a true 

system assessment should include much more. See 

www.compressedairchallenge.org for additional 

guidance.

Important Note: Recommendations resulting from 

system analysis activities should provide productneutral solutions to system problems and include, only 

if needed, performance-based rather than brand- based 

equipment recommendations.

Compressor Knowledge and Expertise. Does the 

service provider have the expertise to work on your 

equipment? Can the service provider work on all types 

of compressors in your facility? How much experience 

do the service technicians have? How are the service 
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technicians trained? Is formal schooling involved? 

Knowledgeable service technicians are worth the 

premium price they may demand because of their 

ability to troubleshoot and get equipment back on line 

efficiently and effectively.

System Components and Controls Knowledge and 

Expertise.

• Treatment, accessory, and ancillary equipment—

Does the service provider have the expertise to 

perform refrigeration and other work on dryers 

and related equipment? Is the service provider 

capable of servicing the types of filters, drains, 

distribution and point-of-use equipment found in 

your facility?

• System controls—Does the service provider have 

the diagnostic and technical controls capability to 

determine how to optimize your existing control 

configuration and make recommendations for 

improvements? Can they help network 

compressors together or remotely monitor, if 

necessary? Advanced controls can save energy as 

well as improve reliability through automatic start 

and stop, as well as turning compressors off that 

can then serve as back-ups. Advance warning 

through remote monitoring may help identify a 

problem before it turns into a major shutdown.

Company Capabilities. Ask about the standards of 

performance that the prospective service provider has 

established for:

• Emergency service response

• Parts shipments

• Other factors which may influence your decision, 

such as:

– Installation capabilities internally or through 

a mechanical contractor

– Emergency rental fleet availability—electric 

or portable diesel driven

• Your company may request information on the 

service provider’s:

– Financial stability

– Insurance coverage

– Compliance with specific government 

regulations or those of your company.

Service Facilities. Visit the facilities of two or three 

service providers under consideration to see first-hand

the type of repair shop and parts warehouse with which 

you will be dealing.

Important aspects of a basic compressed air system 

audit are discussed below.

System Issues

System issues go beyond examining the performance of 

an individual compressed air system component and, 

instead, examine how components on both the supply 

and demand sides of the system interact. Auditors 

typically address a number of systems issues. These are 

discussed below, and many are addressed in more 

detail in other compressed air systems fact sheets.

Level of Air Treatment. The auditor typically examines 

the compressed air applications and determines the 

appropriate level of air treatment required for proper 

operation of the equipment. Actual air quality levels are 

then measured. If the air is not being treated enough, 

alternative treatment strategies are recommended. If 

the air is being over-treated (an indication of energy 

being wasted), recommendations are made to modify 

the system. In some cases, only certain end-use 

equipment requires highly-treated air, and the auditor 

may recommend a system that allows for different 

treatment levels at different points in the system.

Leaks. The auditor should identify and quantify leaks in 

the system and recommend a leak management 

program.

Pressure Levels. An auditor also typically determines 

the lowest possible pressure level required to operate 

production equipment effectively. In many cases, 

system pressure can be lowered, thereby saving energy. 

Most systems have one or more critical applications 

that determine the minimum acceptable pressure in the 

system. In some cases, the application of dedicated 

storage or differential reduction on the critical 

applications will allow a reduction in overall system 

pressure.

Controls. The existing control system is evaluated to 

determine if it is appropriate for the system demand 

profile. Performance gains available from operating the 

system in a different mode or using an alternative 

control strategy should be estimated.
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Heat Recovery. Auditors will identify potential 

applications for the use of heat recovery, if it is not 

already being used.

Demand-Side Issues

The demand side of the system refers to how 

compressed air is actually used in the plant.

Distribution System. The overall layout of the 

distribution system (piping) is examined. Pressure drop 

and efficiency are measured or estimated, and the 

effectiveness of the condensate removal system is

evaluated. Simple changes that can enhance system 

performance are suggested if appropriate.

Load Profile. Auditors typically estimate the 

compressed air load profile in terms of how the demand 

in cfm changes over time. A facility with a varying load 

profile will likely benefit from advanced control 

strategies. A facility with short periods of heavy demand 

may benefit from implementing storage options.

To establish the load profile, an auditor will measure 

system flow and pressure across the system under 

different demand conditions, while observing the 

loading effect on the existing compressors. This may 

require a number of measurements over a 24-hour 

period (or even several days or a week) if demand 

varies significantly over time. Auditors may use data 

logging equipment to obtain both demand and power 

consumption profiles.

End-Use Equipment. The equipment and processes 

that use compressed air will also be examined. In some 

cases, recommendations, such as specifying equipment 

that operates at a lower pressure, will be made. An 

auditor may also recommend replacing existing 

compressed air-powered equipment with equipment 

that uses a source of energy other than compressed air. 

(See Fact Sheet 2: Potentially Inappropriate Uses of 

Compressed Air.) Critical pressure applications are 

examined in detail. Local storage and other 

modifications may be recommended.

Supply-Side Issues

The supply side refers to how the compressed air is 

generated and treated.

Compressor Package. The compressors are evaluated in 

terms of appropriateness for the application and 

general appearance and condition. Compressor 

efficiency is usually estimated based on manufacturersupplied data, corrected to site conditions. The 

installation is also evaluated in terms of its location, 

connection to cooling water, and ventilation. A general 

appraisal and any recommendations for alternative 

systems are also made.

Filters. Filters are examined for cleanliness and 

suitability for the application. Pressure drop across the 

filters is measured to estimate energy losses from the 

filter. A maintenance schedule for changing the filters, 

and possibly higher performance filters, may be 

recommended.

Aftercooler. Aftercooler and separator efficiency, 

cooling effectiveness, and condensate separation 

effectiveness are all measured and evaluated, and 

feasible modifications or alternative systems are 

recommended.

Dryer. Dryer appropriateness is assessed based on the 

facility’s end-use applications. Dryer size, pressure drop, 

and efficiency are measured and evaluated. 

Modifications and replacements are recommended if 

needed.

Automatic Drains. Location, application, and 

effectiveness of both supply-side and demand-side 

drains are evaluated and alternatives recommended if 

necessary.

Air Receiver/Storage. The effectiveness of the receiver 

tank is evaluated in terms of location and size, and the 

receiver drain trap is examined to see if it is operating 

properly. Storage solutions to control demand events 

should also be investigated.

More Comprehensive Evaluations

A comprehensive evaluation may also include extensive 

measurements and analysis of supply and demand 

interactions. Some auditors will also prepare a detailed 

systems flow diagram. A financial evaluation may also 

be performed, including current and proposed costs 

after retrofits are taken.
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Fact Sheet 12: Compressed Air System Economics and Selling Projects to 

Management

Delivering compressed air to a manufacturing facility is 

an expensive operation. Delivery requires costly 

equipment that consumes significant amounts of 

electricity and this equipment needs proper and 

sometimes frequent maintenance. In spite of this, many 

facilities have no idea how much their compressed air 

systems cost on an annual basis, or how much money 

they could save by improving the performance of these 

systems.

Electricity costs are by far the largest expense of owning 

and operating most compressed air systems. The initial 

cost for a 100-hp compressor is $30,000 to $50,000, 

depending on the type of compressor and 

manufacturer, while annual electricity charges for the 

same system can reach $74,000. Added to this are 

annual maintenance costs, which can be 10 percent or 

more of the initial cost of the system. In addition, 

reliability or air quality problems may be costing a 

significant amount in lost production.

This fact sheet shows a simple calculation to estimate 

annual electricity costs and a more accurate calculation 

requiring electrical measurements.

Calculating Electricity Costs

Full-Load Operation. Even if an air compressor is not 

separately metered, estimating annual electricity cost is 

simple. For more detailed analysis techniques, see the 

AIRMaster+ software referenced in the Resource and 

Tools section.

A Simple Calculation. The following data is needed for 

a quick rough calculation of electricity costs for a 

compressor operating at full-load and rated pressure.

• Compressor motor nameplate rating (bhp)

• Motor nameplate efficiency (or an estimate of 

efficiency)

• Annual hours of operation (hours/year)

• Cost of electricity in dollars per kilowatt-hour 

($/kWh).

Annual electricity costs can be calculated by inserting 

this information into the equation as follows:

This equation assumes the electric motor driving the 

compressor is 90 percent efficient (the 90 in the 1/0.90 

factor). Newer energy-efficient motors generally have 

even higher efficiencies, which are typically shown on 

the motor nameplate. If the system uses an older motor 

that has been rewound several times, or has a smaller 

motor, a somewhat lower percent efficiency (or the 

motor nameplate efficiency rating) should be used. For 

a more accurate analysis, add the horsepower ratings 

for the parasitic loads from any auxiliary motors such as 

cooling fans to the compressor motor rating.

It should be noted that the common practice in the 

industry is to apply motors having a 15 percent 

continuous service factor and to use about two-thirds 

of this service factor. This means that a motor having a 

nominal nameplate rating of 100 hp may, in fact, be 

loaded to 110 bhp at compressor full capacity and 

pressure. This may not be expressed in the 

manufacturer’s sales literature, so engineering data 

sheets or a published CAGI sheet for the specific 

compressor should be consulted. If the motor is running 

into the service factor (some as high as 30 percent), the 

higher horsepower estimate should be used instead of 

the nameplate horsepower rating.

Simple Calculation

(100-hp Compressor)

Annual electricity costs =

(Motor full-load bhp) x (0.746 kW/hp) x (1/0.9 motor efficiency)

x (Annual hours of operation) x (Electricity cost in $/kWh)

For example:

Compressorfull-loadbhp=100hp

Annual hours of operation = 8,760 hours (3-shift,

continuous operation)

Costofelectricity=$0.10/kWh

Annual electricity costs =

(100hp)x(0.746hp/kW)x(1/0.9)x(8,760hours)x($0.10/kWh)

= $72,610
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A Calculation with Measurements. A more accurate 

way to determine electricity consumption and costs 

involves taking electrical measurements. The best 

option is to measure the kW directly; if this is not an 

option estimation can be done by measuring both fullload amps and volts. Motor full-load bhp and efficiency 

are not required for this calculation, although full-load 

power factor, which can be obtained from the motor 

nameplate or manufacturer’s data, is required. The 

calculation measures voltage and full-load amps, 

converts to full-load kW, and then multiplies by hours of 

operation and electricity costs. This calculation captures 

the lower power input due to lower than rated 

discharge pressure and accounts for ancillary loads. A 

calculation is shown below.

Part-Load Operation. If the compressed air system 

operates below full-load at times, and has a good 

control system, electricity costs will be less than if the 

compressor ran at full-load during all hours of 

operation. Estimate the percentage of time the 

compressor is running at full-load, and add the 

percentage as another multiplier in the equation shown 

previously. Compressor hour meters are a good source 

for this information. Repeat the calculation for the 

percentage of time the compressor is running unloaded 

(or at part- load) and include a factor to compensate for 

the reduced load on the motor (0.20 to 0.30 is a good 

estimate for fully unloaded operation for rotary screw 

compressors and 0.10 to 0.15 for reciprocating 

compressors—0.30 is used in the equation in the next 

text box). Add the two results for total energy costs. 

For a more accurate calculation of energy costs for 

compressors running at part-load, create a number of 

“tiers” with the percentage of time running at different 

percentages of load. Manufacturers’ data on energy 

consumption for the different percentages of load will 

be needed.

The text box below shows an example calculation taking 

into account unloaded operation.

Remember, the calculations shown will only provide a 

good estimate of energy consumption, not an exact 

number.

Energy and Demand Charges—Understanding Your 

Electricity Bill. The calculations shown previously use 

electricity rates stated in terms of $/kWh. Electric 

utilities bill industrial customers using more 

complicated rate structures that typically include both 

energy ($/kWh) and demand charges ($/kW), and may 

have different rates depending on the level of 

Calculation WithPart-Load Operation

(100-hp Load/Unload Compressor)

Annual electricity costs =

[(Motor full-load brake horsepower) x (0.746 kW/hp) x (1/0.90)

x (Annual hours of operation) x (Electricity cost in $/kWh)] x

[(Percentoftimerunningfullyloaded)+(Percent full load 

power running unloaded)x(Percentof time running fully

unloaded)]

For example:

Motor full-load bhp = 100 hp

Annual hours of operation = 8,760 hours (3-shift,

continuous operation)

Runs65%ofthetimefully loaded,35%ofthetimeunloaded

Fully unloaded operation consumes 30 percent of the

electricity of fully loaded operation

Costofelectricity=$0.10/kWh

Annual electricity costs =

[(100hp)x (0.746hp/kW) x (1/0.9) x(8,760hours)

x ($0.10/kWh)]x[0.65+(0.30) x(0.35)]

= $54,820

More Detailed Calculation

(100-hp Compressor)

Annual electricity costs =

[(Full-load amps) x (volts) x (1.732) x (power factor)]/1000) x

(Annual hours of operation) x (Electricity cost in $/kWh)

For example:

Full-loadamps=115amps

Voltage=460volts

Full-load powerfactor=0.85*

Annual hours of operation = 8,760 hours (3-shift, continuous

operation)

Costofelectricity=$0.10/kWh

Annual electricity costs =

[(115amps)x(460volts)x(1.732)x(0.85)]/1000)x

(8,760 hours) x ($0.10/kWh)

= $68,222

*from motor manufacturer (unloaded power factor may differ substantially)
THE PERFORMANCE OPPORTUNITY ROADMAP 12 - COMPRESSED AIR SYSTEM ECONOMICS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 67

consumption ,time of day or seasons. Demand charges 

are based on the peak demand for a given month or 

season and can have significant impacts on electricity 

costs for some customers. When the economic impacts 

of efficiency measures are calculated, the actual 

marginal cost of the electricity needs to be considered, 

taking into account energy and demand charges,

seasonal rates, and different rates for different levels of 

consumption.

Pressure and Electricity Cost. High-pressure air is more 

expensive to produce and deliver than low-pressure air. 

A rule of thumb for systems in the 100 psig range is: for 

every 2 psi increase in discharge pressure, energy 

consumption will increase by approximately 1 percent 

at full output flow (this may differ for centrifugal and 

two-stage, lubricant-injected, rotary screw 

compressors). 

There is also another penalty for higher-than-needed 

pressure. Raising the compressor discharge pressure 

increases the demand of every unregulated usage, 

including leaks, open blowing, etc. Although it varies by 

plant, unregulated usage is commonly as high as 30 to 

50 percent of air demand. For systems in the 100 psig 

range with 30 to 50 percent unregulated usage, a 2 psi 

increase in header pressure will increase energy 

consumption by about another 0.6 to 1.0 percent 

because of the additional unregulated air being 

consumed. The combined effect results in a total 

increase in energy consumption of about 1.6 to 2 

percent for every 2 psi increase in discharge pressure 

for a system in the 100 psig range with 30 to 50 percent 

unregulated usage.

Savings from Performance Improvements. Because of 

the relatively low initial cost of the compressor when 

compared to lifetime electricity expenses, users should 

utilize life-cycle cost analysis when making decisions 

about compressed air systems. In addition, a highly 

efficient compressed air system is not merely a system 

with an energy-efficient motor or efficient compressor 

design. Overall system efficiency is the key to maximum 

cost savings. Too often users are only concerned with 

initial cost and accept the lowest bid on a compressed 

air system, ignoring system efficiency.

Thorough analysis and design will be required to obtain 

an efficient system. Many compressed air system users 

neglect these areas, thinking they are saving money, but 

end up spending much more in energy and 

maintenance costs.

Following the steps outlined in this sourcebook can lead 

to substantial energy savings for most compressed air 

systems. A system that has undergone numerous 

modifications and has only been maintained enough to 

keep it running can frequently achieve energy savings of 

20 to 50 percent or more. For the 100-hp system 

described previously, this represents annual savings of 

$14,000 to $36,000. Larger systems will have 

correspondingly greater energy savings.

Too many decisions regarding compressed air systems 

are made on a first-cost basis, or with an “if it ain’t 

broke, don’t fix it” attitude. To achieve optimum 

compressed air system economics, compressed air 

system users should select equipment based on lifecycle economics, properly size components, operate 

equipment at the lowest possible pressure, turn off 

unneeded compressors, use appropriate control and 

storage strategies, and operate and maintain the 

equipment for peak performance.

Selling Projects to Management

Once you have defined your project and potential 

benefits and are ready to start work, what do you do 

next? If you are in the same situation as most plant 

engineering personnel, you need to request funding for 

the project from your management. Few individuals 

have the ability to make a major expenditure of funds 

without approval. All of the work done to create a block 

diagram, perform baselining, locate opportunities to 

save money, and organize a plan of action to reduce 

costs could be a waste of time if sufficient funding 

cannot be obtained from management to implement 

the change. Factors to consider securing funding will be 

discussed. Topics will be covered in general, rather than 

specifics, since each firm potentially requires a different 

approval process.

Financial management in any firm is focused on 

maximizing profit in that firm’s or that plant’s 

operation. Any money spent to improve a process or 

system in the plant is an expenditure that erodes the 

short-term profitability of that operation. This does not 

mean that management is opposed to spending money. 

It does mean that management will select to spend 

funds on projects that will increase profitability within a 
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period of time that they set. If you offer suggestions or 

recommendations for a project that will save more 

money than it costs, you will get attention from your 

management. For example, if you have a project in 

mind that will cost $100,000, and it will decrease energy 

consumption by $125,000 per year, you are helping to 

improve profitability.

The easiest way to look at a project is annual savings 

and simple payback. Simple payback is simply the cost 

of the project divided by the projected annual savings. 

Let’s look at this concept by using two examples.

Example 1

Cost of the project: $100,000

Projected annual savings: $125,000 per year 

Payback period: 9.6 months (100,000/125,000 x 12)

Example 2

Cost of the project: $100,000

Projected annual savings: $10,000 per year 

Payback period: 120 months (100,000/10,000 x 12)

Note that annual savings could include reduced 

maintenance costs due to new upgraded equipment or 

additional annual savings due to reduced production 

losses as a result of poor compressed air system 

reliability.

Available utility incentives may be available that could 

reduce capital costs and project paybacks for qualifying 

energy efficiency measures. To search for these 

opportunities see the DSIRE database at 

www.dsireusa.org. 

These simple calculations demonstrate two ways to

measure the projected return of the cost of an 

improvement, annual savings, and simple payback 

period. These are usually used for smaller expenditures 

or to determine if the project is feasible. In general, 

projects with short paybacks (such as Example 1 above) 

can easily be approved.

Your financial management team will use the financial 

data that you submit to calculate other financial views 

of the expense. They may calculate the projected 

savings based on the net present value of the 

investment. Similarly, they may calculate the internal 

rate of return on the investment in a project. We will 

not go into discussion of these financial calculations or 

tools, since each firm has a different view and different 

requirements. If you have a project that meets simple 

payback criteria, work with your financial management 

to determine the methodology and expected results 

that the firm utilizes.

If your proposed project passes one of the simple tests, 

read on. If not, go back and look for other opportunities 

to save money.

You are now to the point that you have determined that 

your project will add to the operation’s profitability, at 

least in simple terms. What do you do next? You will 

most likely want to create a written presentation to 

your management asking for the approval to spend the 

money you need. It must be concise, outline specific 

actions to be taken, list the expected return or cost 

saving, and provide documentation to support the 

conclusions you made.

Many firms have a set format to use in a Capital 

Expenditure Request, to answer questions and supply 

information. If your company uses this method, your 

job is easier. Simply complete the form, attach the 

requested information, and send it for approval. You 

would be wise to have additional information and 

possibly a PowerPoint presentation. This will include all 

of the information in the Expenditure Request, plus 

other information, such as photos and excerpts from 

articles and publications. If your firm does not use a 

standard format, you will have to create your written 

presentation from scratch.

Creating your own presentation/request can be done 

quite simply if you think and act logically. It most likely 

will include the following.

1. An “executive overview” that states the problem, 

the actions to be taken, the cost of the project, 

and the projected return. All of this should fit on 

one page of paper.

2. Detailed information on current operating data 

and costs. This is where you use your baseline 

information. You will want to describe the 

methodology that you used to establish your 

baseline.

3. A detailed list of the actions you plan to take, the 

equipment you need to buy, and a detailed cost 
THE PERFORMANCE OPPORTUNITY ROADMAP 12 - COMPRESSED AIR SYSTEM ECONOMICS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 69

summary. Make sure you include any internal 

costs for engineering, project management, and 

down- time. When possible, provide vendor 

quotes to back up your cost data.

4. A detailed summary of the projected savings. 

What will change in operating cost, how did you 

calculate it, and what you considered. The 

presentation needs to be based on facts, and with 

full calculations to support the projected savings.

5. A statement of risks that outlines what may not 

go exactly per the plan, and the contingencies you 

have included to quickly remove barriers that may 

affect the project as it progresses.

6. A time schedule listing the start and end date of 

all actions.

7. Photos, diagrams, and drawings to demonstrate 

the current state of operation, and what the end 

product will look like upon completion.

8. A statement of results verification. In this section, 

you will outline the process and procedure that 

you will use to measure and document the actual 

cost savings.

9. A list of references to articles, books, or 

presentations that support the action that you 

plan to take. Case studies of similar actions that 

achieved the planned results can be very useful.

10. A summary, which will include a request for 

action by your management.

11. A copy of the appropriate approval form that is 

fully completed except for management 

signatures.

12. This documentation should be high-quality and 

use color copies when and where appropriate, 

and should be bound per the normal system used 

by your firm. Anything less than first class will not 

get the first-class reply, which is the approval for 

the project.

13. Depending on your firm and the budget of the 

project, you may want to have a formal 

PowerPoint presentation if your management 

requests that.

14. Finally, maintain complete and detailed records 

on any action related to the project and plan to 

keep them for a number of years after completion 

of the project. Documentation of project results is 

important.

Energy Management Systems

Facilities that seek to maintain low energy consumption 

may implement energy management systems (EnMS) 

such as ISO 50001. ISO 50001 provides organizations 

with an internationally recognized framework for 

implementing an energy management system (EnMS). 

The standard addresses the following:

• Energy use and consumption

• Measurement, documentation, and reporting of 

energy use and consumption

• Design and procurement practices for energyusing equipment, systems, and processes

• All variables affecting energy performance that 

can be monitored and influenced by the 

organization

An EnMS helps an organization internalize the policies, 

procedures, and tools to systematically track, analyze, 

and improve energy efficiency. It considers 

maintenance practices, operational controls, and the 

design and procurement of renovated, modified, and 

new equipment, systems, processes, and facilities. With 

ISO 50001, energy management is integrated into 

normal business processes involving multiple types of 

employees across the organization.

ISO 50001 is based on the Plan-Do-Check-Act structure 

to continual improvement held in common with the ISO 

9001 (quality management), ISO 14001 (environmental 

management), and other management systems. ISO 

50001 is designed to be compatible with these 

management systems.

As part of an EnMS the compressed air system may be 

identified as a significant energy use (SEU) and subject 

to continuous monitoring. As part of this monitoring 

energy performance indicators (EnPIs) will be compared 

against an energy baseline (EnB) to ensure the 

compressed air system energy performance is 

maintained at expected levels.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 70

SECTION 3: WHERE TO FIND HELP

This section of the sourcebook is a directory of 

resources and information that can help compressed air 

system users improve the performance of their systems. 

It is organized into four sections. A brief summary of 

each section is provided below.

Advanced Manufacturing Office

This section describes the Advanced Manufacturing 

Office (AMO), a national effort sponsored by the U.S. 

Department of Energy (DOE) aimed at improving the 

performance of manufacturing systems. The AMO 

works closely with the Compressed Air Challenge (CAC) 

and the Compressed Air and Gas Institute (CAGI) on

issues pertaining to industrial compressed air systems.

Compressed Air Challenge®

This section describes a national effort involving all 

compressed air market stakeholders aimed at improving 

compressed air system performance.

Compressed Air and Gas Institute

This section provides information on the Compressed 

Air and Gas Institute, including projects of interest and 

available resources.

Directory of Contacts

This section provides lists of associations and other 

organizations involved in the compressed air system 

market.

Resources and Tools

This section provides information on books and reports, 

brochures, periodicals, software, videos, work- shops, 

and training courses that are currently available to help 

compressed air system users understand and improve 

the performance of their compressed air systems.

Advanced Manufacturing Office

The Department of Energy’s Advanced Manufacturing 

Office (http://energy.gov/eere/amo/advancedmanufacturing-office) partners with industry, small 

business, universities, and other stakeholders to 

identify and invest in emerging technologies with the 

potential to create high-quality domestic manufacturing 

jobs and enhance the global competitiveness of the 

United States. They partner with industry, small 

business, universities, regional entities, and other 

stakeholders to identify and invest in emerging clean 

energy technologies. The AMO establishes collaborative 

communities focused on developing and 

commercializing targeted technologies; play a 

leadership role in the national interagency Advanced 

Manufacturing Partnership; and encourage a culture of 

continuous improvement in corporate energy 

management. Their investments have high impact, use 

project diversity to spread risk, target nationally 

important innovation at critical decision points, and 

contribute to quantifiable energy savings. 

AMO Technical Assistance Activities

The AMO delivers solutions for industry that result in 

significant energy and cost savings, waste reduction, 

pollution prevention, and enhanced environmental 

performance. The AMO offers technical assistance to 

manufacturing facilities in a number of different ways, 

including Better Plants, Superior Energy Performance, 

Industrial Assessment Centers, and Combined Heat and 

Power Deployment. They also provide an Energy 

Resource Center with software tools, training, technical 

publications and case studies. Information on all of the 

AMO’s Technical Assistance Activities and resources can 

be found at http://energy.gov/eere/amo/ta.

Better Plants. The DOE’s Better Buildings, Better Plants 

Program is an important partnership which consists of 

approximately 150 industrial companies, representing 

about 2,300 facilities and close to 11% of the total U.S. 

manufacturing energy footprint as well as several water 

and wastewater treatment organizations. The 

companies sign a voluntary pledge to reduce their 

energy intensity by 25 percent over a ten-year period. 

In turn, partners achieve their own corporate, 

institutional, or plant goals and objectives by expanding 

services to customers and suppliers. Better Plants 

Partners benefit from DOE technical support and are 

able to implement cost-effective energy efficiency 

improvements that save energy and improve 

competitiveness.
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 71

Superior Energy Performance. Facilities certified to 

Superior Energy Performance (SEP) are leaders in 

energy management and productivity improvement. To 

become certified, facilities must implement an energy 

management system that meets the ISO 50001 

standard. The facilities in SEP have improved their 

energy performance up to 25% over three years or up 

to 40% over 10 years.

Industrial Assessment Centers. Small- and mediumsized manufacturers may be eligible to receive a no-cost 

assessment provided by DOE Industrial Assessment 

Centers (IACs). Teams located at 24 universities around 

the country conduct the energy audits to identify 

opportunities to improve productivity, reduce waste, 

and save energy. IACs typically identify more than 

$130,000 in potential annual savings opportunities for 

every manufacturer assessed, nearly $50,000 of which 

is implemented during the first year following the 

assessment. Over 16,000 IAC assessments have been 

conducted, with case studies available at 

https://iac.rutgers.edu/case_studies/.

Combined Heat and Power Deployment. Combined 

heat and power (CHP) provides a cost-effective, nearterm opportunity to reduce greenhouse gas emissions 

by efficiently generating on-site electric power and 

useful thermal energy from a single fuel source. The 

CHP Deployment Program provides stakeholders with 

the resources necessary to identify CHP market 

opportunities and support the implementation of CHP 

systems.

Energy Resource Center

The AMO’s Energy Resource Center provides system 

related software decision support tools, training, 

technical publications and case studies, as well as 

information on industrial assistance, state and utility 

engagement. Related publications available from the 

AMO’s Energy Resource Center are further discussed in 

the Resources and Tools section of this sourcebook.

Software Tools. For compressed air systems, 

AIRMaster+ helps users analyze energy use and savings 

opportunities in manufacturing compressed air systems. 

AIRMaster+ can be used to baseline existing and model 

future system operations improvements, and evaluate 

energy and dollar savings from many energy efficiency 

measures. Other software tools for industrial 

manufacturing are also available from AMO, including 

MotorMaster+, the Process Heating Modeler Tool 

(PHMT), the Pump System Assessment Tool (PSAT), and 

the Fan System Assessment Tool (FSAT). Descriptions 

and links to all of the downloadable software can be 

found at http://energy.gov/eere/amo/software-tools. 

Training. The Compressed Air Challenge and the 

Compressed Air and Gas Institute provide training for

compressed air systems tools, Fundamentals of 

Compressed Air Systems, Advanced Management of 

Compressed Air Systems, and the AIRMaster+ software. 

Information on available training for compressed air 

systems can be found at 

http://energy.gov/eere/amo/articles/trainingcompressed-air-systems. 

Technical Publications. Sourcebooks, handbooks, tip 

sheets, technical fact sheets, market assessments, case 

studies, and presentations are available through the 

AMO website. These publications cover a variety of 

industrial systems and topics, including compressed air

equipment. Technical publications by system type are 

available at http://energy.gov/eere/amo/technicalpublications-system. Case studies are covered 

separately, at http://energy.gov/eere/amo/casestudies-system.

All of the available technical publications specific to 

compressed air systems, including useful tip sheets and 

case studies can be found at 

http://energy.gov/eere/amo/compressed-air-systems.

The Compressed Air Challenge

A national collaborative, the CAC 

(www.compressedairchallenge.org) was formed in 

October of 1997 to assemble state-of-the-art 

information on compressed air system design, 

performance, and assessment procedures. This 

collaborative delivers compressed air system best 

practices information to the plant floor, creating a 

consistent national market message and providing a 

technically sound and professionally delivered training 

program for plant operating personnel. Participants 

include: large industrial users of compressed air, 

manufacturers and distributors of compressed air 

equipment and their associations, facility engineers and 

their associations, compressed air system consultants, 
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 72

state research and development agencies, energy 

efficiency organizations, and utilities.

The goals of the CAC are to:

• Increase the reliability and quality of industrial 

production processes

• Reduce plant operating costs

• Expand the market for high quality compressed 

air services

• Save energy: a 10 percent improvement over 

current usage, resulting in annual savings of 

approximately 3 billion kilowatt-hours of 

electricity nationwide.

The purpose of the CAC is to initiate a national 

collaborative that develops materials, a training 

curriculum, a certification program, and other 

information that can be used by the project sponsors in 

cooperation with others to:

• Raise awareness of the importance of efficient, 

effective plant air systems

• Train industrial plant operating personnel on best 

practices for plant air systems

• Expand the market for expert plant air 

assessment services

• Help build the local market infrastructure to 

deliver these services.

The CAC has developed several training workshops that 

are being taught across the United States and Canada.

• Fundamentals of Compressed Air Systems, (Level 

1), is a 1-day introductory course designed to 

teach facility engineers, operators and 

maintenance staff how to achieve 15 to 25 

percent cost savings through more effective 

production and use of compressed air.

• Advanced Management of Compressed Air 

Systems, (Level 2), is an intensive 2-day training 

that provides in-depth technical information on 

troubleshooting and making improvements to 

industrial compressed air systems.

• Qualified AIRMaster+ Specialist Training is a 31⁄2 

day program; those who successfully complete 

the workshop and exam are designated Qualified 

Specialists in the AIRMaster+ software tool. 

• “Compressed Air, It’s Not Free!” Shop Floor 

Training Package is a 1 hour awareness training 

program for operators with the flexibility to be 

customized to site specifications operations. 

See the Resources and Tools section for more 

information on these workshops and any additional 

offerings that may be developed. In addition to 

Improving Compressed Air System Performance: A 

Sourcebook for Industry, the CAC has a full offering of 

educational material; including: Guidelines for Selecting 

a Compressed Air System Service Provider (see 

Appendix E) and Best Practices for Compressed Air 

Systems. 

The Best Practices for Compressed Air Systems manual 

was developed to provide the tools needed to reduce 

the operating costs associated with the use of 

compressed air and improve the reliability of the entire 

system. This manual addresses the improvement 

opportunities from the air entering the compressor inlet 

filter to the end uses, including hoses, quick couplers, 

air tools, cylinders and other devices.

The CAC created the Best Practices for Compressed Air 

Systems manual to provide “how to” information to 

implement recommendations, which will achieve peak 

performance and reliability of the system at the lowest 

operating cost. 

In addition to the training and published documents, 

numerous case studies, fact sheets and tip sheets can 

be found online in the CAC library at:

www.compressedairchallenge.org/library.

Organizational Structure

The CAC includes:

• An Advisory Board comprised of the project 

sponsors

• A Project Development Committee, which 

includes a representative from each key 

stakeholder group and is responsible for overall 

project coordination

• Working Groups, provide essential technical input 

to the project.
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 73

CAC Sponsors 

• Airleader

• BC Hydro

• Compressed Air & Gas Institute 

• Efficiency Vermont

• Eversource

• Independent Compressor Partners, Inc.

• Iowa Energy Center 

• Manitoba Hydro

• National Grid USA

• New York State Energy Research & Development 

Authority

• Northwest Energy Efficiency Alliance 

• Pacific Gas & Electric

• Tennessee Valley Authority

• U.S. Department of Energy

Compressed Air and Gas Institute (CAGI)

CAGI has been active in development of standards and 

informational material regarding compressed air 

systems for 100 years. The institute is a founding 

sponsor of CAC and has contributed CAGI technical 

resources to CAC. 

CAGI became an Allied Partner of DOE and worked to 

improve the efficiency and effectiveness of compressed 

air systems and compressed air equipment, acting 

through its Energy Awareness Committee and System 

Assessment Section. 

Some CAGI projects of particular interest:

• Development, in many cases with the 

international standards community, of 

performance standards for compressed air system 

equipment.

• Standard formats, called CAGI Datasheets, which 

are used by manufacturers to state performance 

in uniform, consistent ways, making comparisons 

easier for purchasers, specifiers, and end users.

• Information on the CAGI website regarding the 

importance of performance standards and 

datasheets.

• Online access to datasheets produced by 

participating CAGI member manufacturers

• Development and maintenance of third party 

performance verification testing for rotary 

compressors and refrigerated dryers.

• Free online access to the CAGI Compressed Air 

Handbook.

• Eight online educational modules as part of the 

CAGI online training and education program. CAGI 

formed an Energy Awareness Committee and 

became an Allied Partner. Related projects being 

developed by CAGI include:

• Standard performance reporting forms (data 

sheets) that allow consumers to compare 

products more easily (see Appendix B)

• A consumer fact sheet explaining compressor 

testing methods and the importance of standard 

reporting forms

• An Internet-accessible database containing 

information from the standard performance data 

sheets, and participation in CAC.

Most CAGI resources are available on the CAGI website 

(www.cagi.org), which provides a wealth of general 

information about compressed air systems and 

compressed air systems equipment. The portion of the 

website titled "Working with Compressed Air" provides 

access to selection guides, useful calculations, 

maintenance and service advice, and much more. Many 

of the available Resources and Tools from CAGI are 

detailed later in this section.

Directory of Contacts

The following organizations can provide more 

information on improving the performance of 

compressed air systems.

Advanced Manufacturing Office

http://energy.gov/eere/amo/advanced-manufacturingoffice

The Advanced Manufacturing Office contains resources 

and information on improving electric motor systems, 

including compressed air systems.

The Compressed Air Challenge®

www.compressedairchallenge.org

The CAC is a national collaborative that assembles stateof-the-art information on compressed air system 

design, performance, and assessment procedures. For 

additional information, contact 

info@compressedairchallenge.org.
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 74

The Compressed Air and Gas Institute

Phone: (216) 241-7333

cagi@cagi.org

www.cagi.org

Since 1915, CAGI has been the leading organization 

representing manufacturers of compressed air system 

equipment, including air compressors, blowers, 

pneumatic tools and air and gas drying and filtration 

equipment. For more than 80 years, the Institute has 

been working to improve production and proper use of 

equipment used in compressed air and gas systems.

CAGI continues to strive to increase the satisfaction of 

compressed air system users. This is accomplished in a 

variety of ways, primarily through education and 

training of users so that they better understand 

compressed air systems and through development of 

improved equipment and related standards.

Compressed Air Equipment Distributor 

Associations

Compressed air equipment distributor associations 

represent the companies that sell compressed air 

equipment to end users. Compressor distributor 

associations usually focus around one compressor 

manufacturer. 

Resources and Tools

A wide range of information is available on the 

application and use of compressed air systems. This 

section of the sourcebook focuses on resources and 

tools in the following categories.

• Books and reports

• Educational Brochures

• Online Resources

• DOE tip sheets

• DOE case studies

• Periodicals

• Software

• Videos

• Workshops and training courses

The resources and tools presented here are not 

intended to represent all available information 

pertaining to compressed air systems. Instead, this list 

presents the reference material and tools that would be 

of interest to those involved in energy-efficient 

compressed air systems. Neither DOE nor the CAC imply 

any endorsement of the information included in this 

section.

Books and Reports

The books and reports listed are grouped into one of 

the following three categories.

• Documents on compressed air systems focusing 

on performance improvement

• Specialty books on compressors (e.g., compressor 

design)

• Information on the compressed air market.

Documents Focusing on Performance 

Improvement

Best Practices for Compressed Air Systems, Second 

Edition

Author: Compressed Air Challenge® with 

William Scales, P.E., and David M. 

McCulloch

Description: A ‘how to’ volume, comprised of more 

than 350 pages of original text and 

reference appendices, photos and 

performance data, for use to help 

compressed air end users and service 

providers to improve operating 

efficiencies and reliability of installed 

compressed air systems.

Available from: The Compressed Air Challenge®

https://www.compressedairchallenge.o

rg/bookstore/bpm/

Compressed Air and Gas Handbook, Sixth Edition

Author: Various Compressed Air and Gas 

Institute members with David 

McCulloch, editor

Description: A comprehensive reference work on all 

phases of compressed air and gas, this 

handbook covers reciprocating, rotary, 

and dynamic compressors; pneumatic 

tools; air quality and treatment; 

construction equipment; pneumatic 

controls; materials handling equipment; 

and many other topics.

Available from: Compressed Air & Gas Institute

1300 Sumner Avenue
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 75

Cleveland, OH 44115

Phone: (216) 241-7333

cagi@cagi.org

www.cagi.org

Compressor Engineering Data

Author: William Scales, P.E.

Description: A handbook of reference material on 

compressed air systems.

Available from: Scales Industrial Technologies

www.scalesair.com

Compressor Handbook

Author: Paul C. Hanlon (editor)

Description: Provides information on design

procedures, practical application, and 

maintenance of compressors—from top 

experts on these widely used machines. 

Details on everything from 

fundamentals and theory to advanced 

applications and techniques, including 

sought-after data on compressors that 

inflate tires, spray paint, and increase 

the density of natural gas.

Available from: McGraw-Hill Professional

http://www.mhprofessional.com/produ

ct.php?isbn=0071414665

Compressors: Selection and Sizing, Third Edition

Author: Royce N. Brown

Description: This reference text provides 

information on compression principles, 

equipment, applications, selection, 

sizing, installation, and maintenance, 

allowing proper estimation of 

compressor capabilities and selection of 

designs. Updated with new American 

Petroleum Institute standards and 

current technology in areas of 

efficiency, 3-D geometry, electronics, 

and plant computer use, this guide 

covers reciprocating, rotary, and 

centrifugal compressors and compares 

their reliability.

Available from: Gulf Publishing Company

Houston, Texas 

Phone: (713) 529-4301

www.gulfpub.com

Guidelines for Selecting a Compressed Air System 

Service Provider

Author: Compressed Air Challenge®

Description: This document offers guidance for 

selecting a firm that offers integrated 

services to improve compressed air 

system performance. It also explains 

the different levels of system analysis 

service.

Available from: Compressed Air Challenge®

www.compressedairchallenge.org

A Practical Guide to Compressor Technology

Author: Heinz P. Bloch

Description: This text offers a thorough overview of 

the operating characteristics, 

efficiencies, design features, 

troubleshooting, and maintenance of 

dynamic and positive displacement 

process gas compressors.

Available from: Gulf Publishing Company

Houston, Texas 

Phone: (713) 529-4301

www.gulfpub.com

Specialty Books

Centrifugal Compressor Design and Performance

Author: David Japikse

Description: This publication is both a state-of-theart review of the technology base of 

centrifugal compressors and a practical 

guide to designers.

Available from: Concepts NREC

www.concenptsnrec.com

Compressor Performance, Aerodynamics for the User 

Author: Pe Gresh and Theodore Gresh 

Description: This book covers the full spectrum of 

information needed for an individual to 

select, operate, test and maintain axial 

or centrifugal compressors. It includes 

some basic aerodynamic theory to 

provide the user with the “how’s” and 

“why’s” of compressor design. 

Maintenance Engineers especially will 

appreciate the troubleshooting 

guidelines offered.
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 76

Available from: Elsevier Store

www.store.elsevier.com

Compressor Performance: Selection, Operation, and 

Testing of Axial and Centrifugal Compressors

Author: Theodore Gresh

Description: This book is divided into two main 

sections. In the theory section of the 

book, the author introduces 

aerodynamics, thermodynamics, 

aerodynamic components, and 

compressor characteristics. In the 

application section, the author 

discusses equipment selection, 

operation, field performance testing, 

troubleshooting, and flow meters.

Available from: Butterworth Heinemann, an imprint of 

Elsevier

www.store.elsevier.com

Compressor Surge and Stall

Author: Ronald C. Pampreen

Description: This text discusses the stability, surge 

and stall of axial and centrifugal 

compressors. Both theory and 

applications are discussed. The book 

includes multi-stage compressor 

designs and various methods for 

extending stable operation.

Available from: Concepts NREC

www.conceptsnrec.com

Demand-Side Energy Savings in Compressed Air 

Systems

Author: H. P. Van Ormer, Air Power Staff

Description: Addresses the demand-side of air use in 

compressed air systems, including how 

to eliminate demand on the 

compressed air equipment and 

operating strategies. Heat recovery and 

compressed air savings opportunities 

are also covered.

Available from: Air Power USA, Inc.

11520 Woodbridge Lane

Baltimore, OH 43105

Phone: 740-862-4112

www.airpowerusainc.com

Leak-Free Pumps and Compressors, 1st Edition

Author: Gerhard Vetter

Description: As environmental regulations 

concerning leaks and emissions become 

more stringent, this practical reference 

manual targets those concerned with 

systems using leak-free pumps or 

compressors.

This handbook explains the various 

designs and properties of leak-free 

pumps and helps you select the right 

pump or compressor to ensure leakfree systems, whatever the application.

Available from: Elsevier Store

www.store.elsevier.com

Reciprocating Compressors: Operation and 

Maintenance 

Author: Heinz P. Bloch and John J. Hoefner 

Description: This book discusses the theory of 

operation and describes methods of 

proper installation, troubleshooting, 

overhauling, and repairing of all types 

of reciprocating compressors. Engineers 

and maintenance personnel in the 

process industries such as mining, food 

processing, pharmaceuticals, and 

petrochemicals will find this text useful.

Available from: Elsevier Store

www.store.elsevier.com

Rotary Screw Air Compressors

Author: H. P. Van Ormer

Description: This guide provides a close look at the 

lubricant-cooled rotary compressor and 

its role in construction and industrial 

applications. It discusses the history, 

development, basic technology, 

application, selection, installation, and 

general maintenance of rotary screw air 

compressors.

Available from: Air Power USA, Inc.

11520 Woodbridge Lane

Baltimore, OH 43105

Phone: 740-862-4112

www.airpowerusainc.com
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 77

Supply-Side Energy Savings in Compressed Air 

Systems, 16th Edition

Author: H. P. Van Ormer, Air Power Staff

Description: Provides a practical guide to the supplyside of compressed air systems 

including: centralized versus 

decentralized systems, basic piping, air 

compressor types, applications, 

selection, installation, operating costs, 

predictive maintenance and EPA issues.

Available from: Air Power USA, Inc.

11520 Woodbridge Lane

Baltimore, OH 43105

Phone: 740-862-4112

www.airpowerusainc.com

Information on the Compressor Marketplace

Assessment of the Market for Compressed Air 

Efficiency Services

Author: U.S. DOE

Description: The U.S. DOE, with technical support 

furnished by the CAC published the 

Assessment of the Market for 

Compressed Air Efficiency Services. The 

assessment provides a comprehensive 

view of the market for engineering and 

consulting services to improve the 

energy efficiency of plant compressed 

air systems. These services include 

plant assessments to identify 

improvement opportunities for 

compressed air systems, preventive 

maintenance services, and redesign of 

system components to reduce energy 

use.

Available from: U.S. Department of Energy, Advanced 

Manufacturing Office 

http://www.energy.gov/eere/amo/com

pressed-air-systems

Pumps and Compressors

Author: U.S. Department of Commerce, Bureau 

of the Census

Description: This annual Current Industrial Report 

provides statistics on the quantity and 

value of manufacturers’ shipments, 

number of producers by product type 

and industry, exports, and imports. 

These statistics reflect market trends in 

the pump and compressor industry.

Available from: U.S. Department of Commerce

Bureau of the Census Gaithersburg, MD 

Download from www.census.gov

Educational Brochures

The following educational brochures are available from 

CAGI at:

1300 Sumner Avenue

Cleveland, OH 44115-2851

Phone: (216) 241-7333

cagi@cagi.org

http://cagi.org/education/publications.aspx

ANSI/CAGI B19.1, Safety Standard for Compressor 

Systems

Description: This standard classifies and makes 

available general information on 

practices, specific requirements, and 

recommendations covering safety for 

air compressors, their drives, and 

auxiliaries.

CAGI B186.1 Safety Code for Portable Air Tools

Description: This This code promotes the safe 

design, and use of air tools by 

prescribing safety requirements to 

guard against injury to workers, by 

providing guidance to tool 

manufacturers, owners, employers, 

supervisors, and others concerned with, 

or responsible for, worker safety, and 

by assisting in the promulgation of 

appropriate safety directives and safety 

training programs.

CAGI-PNEUROP PN2CPTC2 Acceptance Test Code for 

Electrically Driven Packaged 

Centrifugal Air Compressors 

Description: This code defines and describes 

acceptance tests for electrically driven 

packaged air compressors of standard 

types which are constructed to 

specifications determined by the 

manufacturer and which are sold 

against performance data published in 
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 78

the manufacturer's sales 

documentation.

CAGI / BL 100-2004 Mechanical Vibration – Evaluation 

of Machine Vibration by 

Measurements on Non Rotating Parts 

Description: This standard defines the basis for 

specifying the rules to be employed in 

evaluating the mechanical vibration of 

machines in the operating range of 600 

to 30,000 rpm in such a way that 

comparison is possible with similar 

measurements obtained from other like 

machines. 

CAGI / BL 300-2014 Simplified Acceptance Test of 

Electric Driven, Low Pressure Air 

Blower Packages

Description: This standard addresses all types of 

blowers for use in all applications, 

including wastewater treatment, 

general industry, process, chemical, etc. 

The standard contains three sections: a 

simplified performance test method for 

dynamic blowers based on ISO 5389, a 

simplified performance test method for 

positive displacement blowers based on 

ISO 1217, and a means of marrying the 

two methods by comparing 

performance between blowers 

regardless of the type of blower.

ANSI/CAGI 1217-2013, Displacement Compressors: 

Acceptance Tests 

Description: This standard provides standardized 

acceptance tests for all types of 

displacement compressors. It was 

adopted as an American National 

Standard.

Online Resources

There are several organizations and websites that 

contain valuable resources available to view or 

download via the internet. This section summarizes the 

organizations and resources that are currently available 

online.

Compressed Air Challenge

Description: The Compressed Air Challenge website 

has a number of downloadable fact 

sheets, tip sheets, guidelines, case 

studies, reports, articles, videos, and 

software covering industrial 

compressed air systems.

Website: www.compressedairchallenge.org

Compressed Air and Gas Institute

Description: The Compressed Air and Gas Institute’s 

website provides a number of 

downloadable publications, including 

the CAGI Handbook, videos, tech 

sheets, articles and selection guides.

Websites: www.cagi.org/education,

www.cagi.org/videos

Database of State Incentives for Renewable Energy 

and Efficiency (DSIRE)

Description: DSIRE is the most comprehensive 

source of information on local, state, 

and federal incentives and policies that 

support renewables and energy 

efficiency in the United States. Energy 

efficiency incentives may be applicable 

to new compressed air system 

installations.

Website: www.dsireusa.org

British Compressed Air Society

Description: This British organization has some 

valuable information available online, 

including information on energy savings 

and heat recovery, an installation guide, 

and a code of practice for pressure and 

leak testing.

Website: www.bcas.org.uk/compressed-airproduct-listing

LinkedIn

Description: Many professionals and organizations in 

the compressed air business, including 

the Compressed Air Challenge can be 

found on LinkedIn, with discussion 

groups for improving efficiency and 

finding solutions to common problems.

Website: www.linkedin.com
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 79

DOE Tip Sheets

These two-page tip sheets provide quick advice on how 

to keep your systems running at their maximum 

efficiency.

For a complete list of available tip sheets, see the 

publications section at 

www.energy.gov/eere/amo/compressed-air-systems. A 

number of additional tip sheets are under development.

DOE Case Studies

These case studies highlight projects where industrial 

plants have improved the performance of their 

compressed air systems. Case studies can be found at 

http://energy.gov/eere/amo/case-studies-system.

Periodicals

The following periodicals often contain articles about 

improving compressed air systems, and can be very 

good sources of state-of-the-art information.

AFE Facilities Engineering Journal

Description: This technical journal provides practical, 

in- depth information on key on-the-job 

issues, covering the topics of 

maintenance, management, safety, 

compliance, and professional 

development for facility operations.

Available from: Association for Facilities Engineering, 

McLean, VA

Phone: (571) 395-8777

www.afe.org

Compressed Air Best Practices

Description: Online magazine that provides the 

latest news and information on 

compressed air systems and the 

compressed air industry. Available at 

www.airbestpractices.com

Available from: Smith Onandia Communications, LLC

37 McMurray Rd, Suite 106

Pittsburgh, PA 15241

 www.airbestpractices.com

Energy Engineering Online Journal

Description: A professional journal that chronicles 

the latest advancements in energy 

engineering, published six times a year, 

and available online through 

www.aeecenter.org.

Available from: Association of Energy Engineers

Atlanta, GA

Phone: (770) 447-5083 ext. 210

www.aeecenter.org

Plant Services

Description: Information for successful plant 

systems and management, including 

equipment performance, maintenance, 

and operation. Plant Services also 

publishes a Buyer’s Guide for plant 

systems and equipment.

Available from: Plant Services

www.plantservices.com

Software

AIRMaster+: Compressed Air System Assessment 

Software

Description: AIRMaster+ is a Windows-based 

software tool used to analyze industrial 

compressed air systems. AIRMaster+ 

enables auditors to model existing and 

future improved system operation, and 

evaluate savings from energy efficiency 

measures with relatively short payback 

periods.

AIRMaster+ provides a systematic 

approach to assessing compressed air 

systems, analyzing collected data, and 

reporting results. Users include 

companies or distributors of 

compressed air equipment, compressor 

system auditors, industrial plant 

personnel, and utility representatives. 

Available from: DOE EERE Advanced Manufacturing 

Office

http://energy.gov/eere/amo/articles/airmaster

C-MAX Engineering Software

Description: C-MAXTM software’s compressor module 

is designed for systems analysis of 
WHERE TO FIND HELP

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 80

centrifugal compressors, reciprocating 

compressors, and rotary screw 

compressors. Multiple compressors and 

“what if” case studies can be modeled 

for pure gases or gaseous mixtures, 

such as dry or wet air, hydrogen, 

nitrogen, refinery gas mixture, fuel gas, 

and natural gas. The software allows 

users to perform “offline” modeling of 

compressor performance, energy, and 

flow capacity calculations, and to create 

case studies by changing process, 

mechanical, or load variables. 

Available from: www.appdig.com/adicon_new/cmax.htm

Videos

The following videos are available from CAGI at:

The Compressed Air and Gas Institute 

1300 Sumner Avenue

Cleveland, OH 44115-2851

Phone: (216) 241-7333

cagi@cagi.org

www.cagi.org/education/videos

Compressed Air: Industry’s Fourth Utility

Description: This video presents a broad overview of 

air compression, distribution, and 

treatment. It describes key 

considerations in designing and 

specifying a compressed air system, 

including compressor selection, 

distribution considerations, air dryers, 

and filters. (Running time: 13 minutes)

Performance Under Pressure

Description: This video discusses the role of 

compressed air and gas in various 

applications ranging from residential to 

industrial. (Running time: 16 minutes)

Principles of Air Compression

Description: This video explains in non-technical 

terms, the theory and principals 

involved in air compression. It 

illustrates the operation of both 

positive-displacement and dynamictype compressors and introduces key 

terms, such as PSIG, SCFM, relative 

humidity, and dew point. (Running 

time: 14 minutes)

How to Select an Air Compressor

Description: This video focuses beyond the 

compressor and encourages buyers to 

look at their complete air system. The 

video provides answers to some key 

questions that should be considered 

before making a compressor purchase. 

The video is accompanied by datasheets 

that provide a standardized format for 

manufacturers to use to provide basic 

information about compressor and 

dryer performance and efficiency. 

(Running time: 18 minutes)

Air Treatment

Description: This video provides an excellent 

overview of compressed air treatment. 

It introduces the viewer to the different 

ISO air quality classes. The video is 

divided into three major sections: 

cooling, drying and cleaning. 

Descriptions of the components and 

equipment used to treat the air are 

provided. (Running time: 17 minutes)

Workshops and Training Courses

Workshops focusing on energy efficiency and 

performance improvement in compressed air systems 

are developed and presented by independent 

consultants, equipment manufacturers, distributors, 

and others.

Many compressed air system consultants offer 

workshops and training courses on improving the 

performance of compressed air systems. In addition, 

some equipment manufacturers and distributors offer 

training to their customers. Workshops are sometimes 

sponsored by electric utilities, universities, and state 

energy offices.

Compressed Air Challenge

The CAC has developed several courses.

Fundamentals of Compressed Air Systems, (Level 1), is 

a 1-day introductory course designed to teach facility 
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IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 81

engineers, operators and maintenance staff how to 

achieve 15 to 25 percent cost savings through more 

effective production and use of compressed air.

Participants will learn how to:

• Calculate the energy cost of compressed air in 

their facility

• Improve compressed air system efficiency and 

reliability

• Identify inappropriate uses of compressed air

• Establish a baseline by which they can measure 

improvements in compressed air performance 

and efficiency

• Match system supply to actual production 

requirements for pressure and flow;

• Find and fix leaks

• Establish a leak prevention program

• Better control compressed air to improve 

productivity and profitability.

Advanced Management of Compressed Air Systems, 

(Level 2), is an intensive 2-day training seminar that 

provides in- depth technical information on troubleshooting and making improvements to industrial 

compressed air systems. This training is designed to 

help end users as well as industry solution providers 

learn how to:

• Collect and use data and tools to assess the 

efficiency and cost-effectiveness of compressed 

air systems

• Develop and use a system profile

• Implement a system maintenance program

• Address air quality, highest pressure 

requirements and high-volume intermittent 

applications

• Understand complex control system strategies

• Align the supply side to demand side operation

• Explain the value of heat recovery

• Successfully sell compressed air improvement 

projects to management

Qualified AIRMaster+ Specialist Training is a 31⁄2 day 

program for compressed air system specialists; those 

who successfully complete the workshop and exam are 

designated Qualified Specialists in the AIRMaster+ 

software tool. Participants learn how to:

• Use the AIRMaster+ and LogTool software

• Accurately acquire input data

• Develop a measurement plan

• Make measurements of hourly trends of typical 

daily data vs. dynamic measurements to 

characterize system events, pressure, and flow 

• Create operating scenarios

“Compressed Air, It’s Not Free!” Shop Floor Training is 

a 1 hour awareness training for the end users of 

compressed air. It has the flexibility to be customized 

for specific site operations. Operators learn basics,

including:

• Compressed air is expensive, good and bad uses,

and that operators are important in how it is used

• The cost of compressed air

• Supply and demand

• Air Leaks – cost 

• Air uses – appropriate and inappropriate

For more information on upcoming courses and training

events, see www.compressedairchallenge.org/calendar.

Compressed Air and Gas Institute

CAGI Online Education on the basics of compressed air

and compressed air systems is available from:

http://www.cagi.org/education/online-training.aspx

The eight modules include:

• Compressed Air Basics 

• Types of Compressors 

• Capacity Controls 

• Distribution Systems 

• Controlling Wastes 

• Air Treatment 

• Compressor Installation & Air System 

Maintenance 

• Integrally Geared Centrifugal Compressors
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 82

Appendices

The following five appendices have been included in the sourcebook:

Appendix A

This appendix is a glossary defining terms used in the compressed air industry.

Appendix B

This appendix contains information on packaged compressor efficiency ratings.

Appendix C

This appendix contains Data Sheets outlining a common format for reporting compressor and dryer performance.

Appendix D

This section presents an overview of the compressed air systems marketplace, including market size and dynamics, and 

a description of the stakeholders.

Appendix E

This section offers guidance for selecting a firm that offers integrated services to improve compressed air system 

performance. It also explains the different levels of system analysis service and standards related to efficiency 

assessments of compressed air systems.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 83

Appendix A: Glossary of Basic Compressed Air System Terminology

Absolute Pressure — Total pressure measured from 

zero.

Absolute Temperature — See Temperature, Absolute.

Absorption — The chemical process by which a 

hygroscopic desiccant, having a high affinity with water, 

melts and becomes a liquid by absorbing the condensed 

moisture.

Actual Capacity — Quantity of gas actually compressed 

and delivered to the discharge system at rated speed 

and under rated conditions. Also called Free Air 

Delivered (FAD).

Adiabatic Compression — See Compression, Adiabatic.

Adsorption — The process by which a desiccant with a 

highly porous surface attracts and removes the

moisture from compressed air. The desiccant is capable 

of being regenerated.

Air Receiver — See Receiver.

Air Bearings — See Gas Bearings.

Aftercooler — A heat exchanger used for cooling air 

discharged from a compressor. Resulting condensate 

may be removed by a moisture separator following the 

aftercooler.

Atmospheric Pressure — The measured ambient 

pressure for a specific location and altitude.

Automatic Sequencer — A device that operates 

compressors in sequence according to a programmed 

schedule.

Brake Horsepower (bhp) — See Horsepower, Brake.

Capacity — The amount of air flow delivered under 

specific conditions, usually expressed in cubic feet per 

minute (cfm).

Capacity, Actual — See Actual Capacity.

Capacity Gauge — A gauge that measures air flow as a 

percentage of capacity, used in rotary screw 

compressors

Check Valve — A valve which permits flow in only one 

direction.

Clearance — The maximum cylinder volume on the 

working side of the piston minus the displacement 

volume per stroke. Normally it is expressed as a 

percentage of the displacement volume.

Clearance Pocket — An auxiliary volume that may be 

opened to the clearance space, to increase the

clearance, usually temporarily, to reduce the volumetric 

efficiency of a reciprocating compressor.

Compressibility — A factor expressing the deviation of a 

gas from the laws of thermodynamics.

Compression, Adiabatic — Compression in which no 

heat is transferred to or from the gas during the 

compression process.

Compression, Isentropic – The isentropic efficiency is 

the amount of work needed by the ideal isentropic 

compression divided by the power input of the real 

compressor for the same compression task.

Compression, Isothermal — Compression is which the 

temperature of the gas remains constant.

Compression, Polytropic — Compression in which the 

relationship between the pressure and the volume is 

expressed by the equation PVn is a constant.

Compression Ratio — The ratio of the absolute 

discharge pressure to the absolute inlet pressure.

Constant Speed Control — A system in which the 

compressor is run continuously and matches air supply 

to air demand by varying compressor load.

Critical Pressure — The limiting value of saturation 

pressure as the saturation temperature approaches the 

critical temperature.
APPENDIX A: GLOSSARY

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 84

Critical Temperature — The highest temperature at 

which well-defined liquid and vapor states exist.

Sometimes it is defined as the highest temperature at 

which it is possible to liquefy a gas by pressure alone.

Cubic Feet Per Minute (cfm) — Volumetric air flow rate.

cfm, free air — cfm of air delivered to a certain point at 

a certain condition, converted back to ambient 

conditions.

Actual cfm (acfm) — Flow rate of air at a certain point 

at a certain condition at that point.

Inlet cfm (icfm) — cfm flowing through the compressor 

inlet filter or inlet valve under rated conditions.

Standard cfm — Flow of free air measured and 

converted to a standard set of reference conditions 

(14.5 psia, 68°F, and 0 percent relative humidity).

Cut-In/Cut-Out Pressure — Respectively, the minimum 

and maximum discharge pressures at which the 

compressor will switch from unload to load operation 

(cut-in) or from load to unload (cut-out).

Cycle — The series of steps that a compressor with 

unloading performs 1) fully loaded; 2) modulating (for 

compressors with modulating control); 3) unloaded; and 

4) idle.

Cycle Time — Amount of time for a compressor to 

complete one cycle.

Degree of Intercooling — The difference in air or gas 

temperature between the outlet of the intercooler and 

the inlet of the compressor.

Deliquescent — Melting and becoming a liquid by 

absorbing moisture.

Desiccant — A material having a large proportion of 

surface pores, capable of attracting and removing water 

vapor from the air.

Dew Point — The temperature at which moisture in the 

air will begin to condense if the air is cooled at constant 

pressure. At this point the relative humidity is 100 

percent.

Demand — Flow of air at specific conditions required at 

a point or by the overall facility.

Diaphragm — A stationary element between the stages 

of a multi-stage centrifugal compressor. It may include 

guide vanes for directing the flowing medium to the 

impeller of the succeeding stage. In conjunction with an 

adjacent diaphragm, it forms the diffuser surrounding 

the impeller.

Diaphragm Cooling — A method of removing heat from 

the flowing medium by circulation of a coolant in 

passages built into the diaphragm.

Diffuser — A stationary passage surrounding an 

impeller, in which velocity pressure imparted to the 

flowing medium by the impeller is converted into static 

pressure.

Digital Controls — See Logic Controls.

Discharge Pressure — Air pressure produced at a 

particular point in the system under specific conditions.

Discharge Temperature — The temperature at the 

discharge flange of the compressor.

Displacement — The volume swept out by the piston or 

rotor(s) per unit of time, normally expressed in cfm.

Droop — The drop in pressure at the outlet of a 

pressure regulator, when a demand for air occurs.

Dynamic Type Compressors — Compressors in which 

air or gas is compressed by the mechanical action of 

rotating impellers imparting velocity and pressure to a 

continuously flowing medium (can be centrifugal or 

axial design).

Efficiency — Any reference to efficiency must be 

accompanied by a qualifying statement which identifies 

the efficiency under consideration, as in the following 

definitions of efficiency:

Efficiency, Compression — Ratio of theoretical 

power to power actually imparted to the air or gas 

delivered by the compressor.
APPENDIX A: GLOSSARY

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 85

Efficiency, Isothermal — Ratio of the theoretical 

work (as calculated on an isothermal basis) to the 

actual work transferred to a gas during compression.

Efficiency, Mechanical — Ratio of power imparted to 

the air or gas to brake horsepower (bhp).

Efficiency, Polytropic — Ratio of the polytropic 

compression energy transferred to the gas, to the 

actual energy transferred to the gas.

Efficiency, Volumetric — Ratio of actual capacity to 

piston displacement.

Exhauster — A term sometimes applied to a 

compressor in which the inlet pressure is less than 

atmospheric pressure.

Expanders — Turbines or engines in which a gas 

expands, doing work, and undergoing a drop in 

temperature. Use of the term usually implies that the 

drop in temperature is the principle objective. The 

orifice in a refrigeration system also performs this 

function, but the expander performs it more nearly 

isentropically, and thus is more effective in cryogenic 

systems.

Filters — Devices for separating and removing 

particulate matter, moisture or entrained lubricant from 

air.

Flange Connection — The means of connecting

a compressor inlet or discharge connection to piping by 

means of bolted rims (flanges).

Fluidics — The general subject of instruments and 

controls dependent upon low rate of flow of air or gas 

at low pressure as the operating medium. These usually 

have no moving parts.

Free Air — Air at atmospheric conditions at any 

specified location, unaffected by the compressor.

Full-Load — Air compressor operation at full speed with 

a fully open inlet and discharge delivering maximum air 

flow.

Gas — One of the three basic phases of matter. While 

air is a gas, in pneumatics the term gas normally is 

applied to gases other than air.

Gas Bearings — Load carrying machine elements 

permitting some degree of motion in which the 

lubricant is air or some other gas.

Gauge Pressure — The pressure determined by most 

instruments and gauges, usually expressed in psig. 

Barometric pressure must be considered to obtain true 

or absolute pressure.

Guide Vane — A stationary element that may be 

adjustable and which directs the flowing medium 

approaching the inlet of an impeller.

Head, Adiabatic — The energy, in foot pounds, required 

to compress adiabatically to deliver one pound of a 

given gas from one pressure level to another.

Head, Polytropic — The energy, in foot pounds, 

required to compress polytropically to deliver one 

pound of a given gas from one pressure level to 

another.

Horsepower, Brake — Horsepower delivered to the 

output shaft of a motor or engine, or the horsepower 

required at the compressor shaft to perform work.

Horsepower, Indicated — The horsepower calculated 

from compressor indicator diagrams. The term applies 

only to displacement type compressors.

Horsepower, Theoretical or Ideal — The horsepower 

required to isothermally compress the air or gas 

delivered by the compressor at specified conditions.

Humidity, Relative — The relative humidity of a gas (or 

air) vapor mixture is the ratio of the partial pressure of 

the vapor to the vapor saturation pressure at the dry 

bulb temperature of the mixture.

Humidity, Specific — The weight of water vapor in an 

air vapor mixture per pound of dry air.

Hysteresis — The time lag in responding to a demand 

for air from a pressure regulator.

Impeller — The part of the rotating element of a 

dynamic compressor which imparts energy to the 

flowing medium by means of centrifugal force. It 

consists of a number of blades which rotate with the 

shaft.
APPENDIX A: GLOSSARY

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 86

Indicated Power — Power as calculated from 

compressor- indicator diagrams.

Indicator Card — A pressure-volume diagram for a 

compressor or engine cylinder, produced by direct 

measurement by a device called an indicator.

Inducer — A curved inlet section of an impeller.

Inlet Pressure — The actual pressure at the inlet flange 

of the compressor.

Intercooling — The removal of heat from air or gas 

between compressor stages.

Intercooling, Degree of — The difference in air or gas 

temperatures between the inlet of the compressor and 

the outlet of the intercooler.

Intercooling, Perfect — When the temperature of the 

air or gas leaving the intercooler is equal to the 

temperature of the air or gas entering the inlet of the 

compressor.

Isentropic Compression — See Compression, Isentropic.

Isothermal Compression — See Compression, 

Isothermal.

Leak — An unintended loss of compressed air to 

ambient conditions.

Liquid Piston Compressor — A compressor in which a 

vaned rotor revolves in an elliptical stator, with the 

spaces between the rotor and stator sealed by a ring of 

liquid rotating with the impeller.

Load Factor — Ratio of average compressor load to the 

maximum rated compressor load over a given period of 

time.

Load Time—Time period from when a compressor loads 

until it unloads.

Load/Unload Control—Control method that allows the 

compressor to run at full-load or at no-load while the 

driver remains at a constant speed.

Modulating Control—System which adapts to varying 

demand by throttling the compressor inlet 

proportionally to the demand.

Multi-Casing Compressor — Two or more compressors, 

each with a separate casing, driven by a single driver, 

forming a single unit.

Multi-Stage Axial Compressor — A dynamic 

compressor having two or more rows of rotating 

elements operating in series on a single rotor and in a 

single casing.

Multi-Stage Centrifugal Compressor — A dynamic 

compressor having two or more impellers operating in 

series in a single casing.

Multi-Stage Compressors — Compressors having two or 

more stages operating in series.

Perfect Intercooling — The condition when the 

temperature of air leaving the intercooler equals the 

temperature of air at the compressor intake.

Performance Curve — Usually a plot of discharge 

pressure versus inlet capacity and shaft horsepower 

versus inlet capacity.

Piston Displacement — The volume swept by the 

piston; for multistage compressors, the piston 

displacement of the first stage is the overall piston 

displacement of the entire unit.

Pneumatic Tools — Tools that operate by air pressure.

Polytropic Compression — See Compression, 

Polytropic. 

Polytropic Head — See Head, Polytropic.

Positive Displacement Compressors — Compressors in 

which successive volumes of air or gas are confined 

within a closed space and the space mechanically 

reduced, resulting in compression. These may be 

reciprocating or rotating.

Power, Theoretical (Polytropic) — The mechanical 

power required to compress polytropically and to 

deliver, through the specified range of pressures, the 

gas delivered by the compressor.
APPENDIX A: GLOSSARY

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 87

Pressure — Force per unit area, measured in pounds 

per square inch (psi).

Pressure, Absolute — The total pressure measured 

from absolute zero (i.e. from an absolute vacuum).

Pressure, Critical — See Critical Pressure.

Pressure Dew Point — For a given pressure, the 

temperature at which water will begin to condense out 

of air.

Pressure, Discharge — The pressure at the discharge 

connection of a compressor. (In the case of compressor 

packages, this should be at the discharge connection of 

the package.)

Pressure Drop — Loss of pressure in a compressed air 

system or component due to friction or restriction.

Pressure, Intake — The absolute total pressure at the 

inlet connection of a compressor.

Pressure Range — Difference between minimum and 

maximum pressures for an air compressor. Also called

cut-in/cut-out or load/no-load pressure range.

Pressure Ratio — See Compression Ratio.

Pressure Rise — The difference between discharge 

pressure and intake pressure.

Pressure, Static — The pressure measured in a flowing 

stream in such a manner that the velocity of the stream 

has no effect on the measurement.

Pressure, Total — The pressure that would be produced 

by stopping a moving stream of liquid or gas. It is the 

pressure measured by an impact tube.

Pressure, Velocity — The total pressure minus the static 

pressure in an air or gas stream.

Rated Capacity — Volume rate of air flow at rated 

pressure at a specific point.

Rated Pressure — The operating pressure at which 

compressor performance is measured.

Required Capacity — Cubic feet per minute (cfm) of air 

required at the inlet to the distribution system.

Receiver — A vessel or tank used for storage of gas 

under pressure. In a large compressed air system there 

may be primary and secondary receivers.

Reciprocating Compressor — Compressor in which the 

compressing element is a piston having a reciprocating 

motion in a cylinder.

Relative Humidity — see Humidity, Relative.

Reynolds Number — A dimensionless flow parameter 

(L x v x ρ / μ), in which ‘L’ is a significant dimension, 

often a diameter, ‘v’ is the fluid velocity, ‘ρ’ is the mass 

density, and μ is the dynamic viscosity, all in consistent 

units.

Rotor — The rotating element of a compressor. In a 

dynamic compressor, it is composed of the impeller(s) 

and shaft, and may include shaft sleeves and a thrust 

balancing device.

Seals — Devices used to separate and minimize leakage 

between areas of unequal pressure.

Sequence — The order in which compressors are 

brought online.

Shaft — The part by which energy is transmitted from 

the prime mover through the elements mounted on it, 

to the air or gas being compressed.

Sole Plate — A pad, usually metallic and embedded in 

concrete, on which the compressor and driver are 

mounted.

Specific Gravity — The ratio of the specific weight of air 

or gas to that of dry air at the same pressure and 

temperature.

Specific Humidity — The weight of water vapor in an 

air-vapor mixture per pound of dry air.

Specific Power — A measure of air compressor 

efficiency, usually in the form of bhp/100 acfm.
APPENDIX A: GLOSSARY

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 88

Specific Weight — Weight of air or gas per unit volume.

Speed — The speed of a compressor refers to the 

number of revolutions per minute (rpm) of the 

compressor drive shaft or rotor shaft.

Stages — A series of steps in the compression of air or a 

gas.

Standard Air — The Compressed Air & Gas Institute and 

PNEUROP have adopted the definition used in ISO 

standards. This is air at 14.5 psia (1 bar); 68°F (20°C) and 

dry (0 percent relative humidity).

Start/Stop Control — A system in which air supply is 

matched to demand by the starting and stopping of the 

unit.

Surge — A phenomenon in centrifugal compressors

where a reduced flow rate results in a flow reversal and 

unstable operation.

Surge Limit — The capacity in a dynamic compressor 

below which operation becomes unstable.

Temperature, Absolute — The temperature of air or 

gas measured from absolute zero. It is the Fahrenheit 

temperature plus 459.6 and is known as the Rankin 

temperature. In the metric system, the absolute 

temperature is the Centigrade temperature plus 273 

and is known as the Kelvin temperature.

Temperature, Critical — See Critical Temperature.

Temperature, Discharge — The total temperature at 

the discharge connection of the compressor.

Temperature, Inlet — The total temperature at the inlet 

connection of the compressor.

Temperature Rise Ratio — The ratio of the computed 

isentropic temperature rise to the measured total 

temperature rise during compression. For a perfect gas, 

this is equal to the ratio of the isentropic enthalpy rise 

to the actual enthalpy rise.

Temperature, Static — The actual temperature of a 

moving gas stream. It is the temperature indicated by a 

thermometer moving in the stream and at the same 

velocity.

Temperature, Total — The temperature which would 

be measured at the stagnation point if a gas stream 

were stopped, with adiabatic compression from the 

flow condition to the stagnation pressure.

Theoretical Power — The power required to compress 

a gas isothermally through a specified range of 

pressures.

Torque — A torsional moment or couple. This term 

typically refers to the driving couple of a machine or 

motor.

Total Package Input Power — The total electrical power 

input to a compressor, including drive motor, belt 

losses, cooling fan motors, VSD or other controls, etc.

Unit Type Compressors — Compressors of 30 bhp or 

less, generally combined with all components required 

for operation.

Unload — (No-load) compressor operation in which no 

air is delivered because the intake is closed or modified 

not to allow inlet air to be trapped.

Vacuum Pumps — Compressors which operate with an 

intake pressure below atmospheric pressure and which 

discharge to atmospheric pressure or slightly higher.

Valves — Devices with passages for directing flow into 

alternate paths or to prevent flow.

Volute — A stationary, spiral shaped passage which 

converts velocity head to pressure in a flowing stream 

of air or gas.

Water-Cooled Compressor — Compressors cooled by 

water circulated through jackets surrounding cylinders 

or casings and/or heat exchangers between and after 

stages.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 89

Appendix B: Packaged Compressor Efficiency Ratings

Evaluating and comparing industrial air compressor 

capacities and efficiencies can be a daunting task. 

Standards exist for testing the performance of a 

compressor, but they have not always been applied in a 

consistent manner, and performance test results and 

efficiency ratings are not always published in consistent, 

standard formats. The result is that purchasers of air 

compressors can find it difficult to compare the 

equipment performance. In recent years, end-user 

education efforts from compressor manufacturers and

trade associations have attempted to tackle this issue.

The Compressed Air and Gas Institute (CAGI), the 

primary compressed air industry trade association in 

the United States, has developed performance testing 

standards. CAGI, in conjunction with its European 

counterpart PNEUROP, has developed simplified 

performance testing standards which have been 

incorporated as addenda in International Standards 

Organization (ISO) Standard ISO 1217 for displacement 

compressors, ISO-7183 for refrigerant dryers and ISO

5389 for centrifugal compressors. These Simplified Test 

Codes were adopted by the membership of CAGI and 

will be reflected in performance data published in 

manufacturers’ literature, CAGI Data Sheets, and CAGI 

and member websites. Some CAGI members also have 

ISO 9001 Certification which requires documentation of 

compliance with published performance and 

procedures. Finally, the CAGI Rotary sections and the 

refrigerant dryer manufacturers have voluntarily agreed 

to embark on a third party performance verification to 

demonstrate performance to published data.

Compressed air system users should be aware that not 

all manufacturers marketing compressors in the United 

States are members of CAGI, and some may test their 

compressors using different standards, although an 

increasing number of companies in the marketplace are 

complying with these standards.

The following standards have been developed for 

measuring air compressor performance.

• CAGI/PNEUROP—Acceptance Test Code for Bare 

Displacement Air Compressors (PN2CPTC1)

• CAGI/PNEUROP—Acceptance Test Code for 

Electrically-Driven Packaged Displacement Air 

Compressors (PN2CPTC2)

• CAGI/PNEUROP—Acceptance Test Code for I.C. 

Engine-Driven Packaged Displacement Air 

Compressors (PN2CPTC3)

• American Society of Mechanical Engineers 

(ASME)— Power Test Code 9, Displacement 

Compressors, Vacuum Pumps, and Blowers

• International Standards Organization (ISO)—ISO 

1217, Displacement Compressors Acceptance 

Tests [distributed in the United States by the 

American National Standards Institute (ANSI)]

• International Standards Organization (ISO) ISO 

5389-2005 Dynamic Acceptance tests.

The revised ISO 1217 with Simplified Test Codes will 

likely be the most commonly used standard in the 

future. CAGI has also developed data sheets outlining a 

common format and style for reporting compressor 

performance, including efficiency. For more information 

on CAGI Data Sheets, see Appendix C.

The industry norm for comparison of compressor 

efficiency used to be given in terms of brake 

horsepower per actual cubic feet per minute (bhp/100 

acfm) at a compressor discharge pressure of 100 

pounds per square inch gauge (psig). Now, total specific 

package input power (in kW) at full load operating 

pressure is generally used. 

Even when accurate and consistent efficiency 

information is available, it may only be specified for fullload operation (i.e., full capacity and specified full-load 

discharge pressure). Since most systems operate at 

part-load much of the time, it is also important to 

compare part-load efficiencies when evaluating the 

performance of different compressors. The variety of 

control methods can, however, make this difficult.

CAGI members have developed data sheets 

demonstrating various performance levels of Variable 

Drive equipped rotary levels to enable users to evaluate 

the competitive offerings in such equipped models.

When gathering information on compressor 

performance and comparing different models, users 
APPENDIX B: PACKAGED COMPRESSOR EFFICIENCY RATINGS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 90

should make sure the compressors have been tested 

using the same standard, at the same conditions, and 

that the data is being reported in a consistent manner. 

Some situations can lead to “apples-and-oranges” 

comparisons. For example:

• Manufacturers may test their compressors under 

different “standard” conditions. Standard 

conditions should be at 14.5 psia (1 bar); 68°F 

(20°C) and dry (0 percent relative humidity).

• The actual full-load power required by a typical air 

compressor package might exceed the nominal 

nameplate rating of the main-drive electric 

motor. Such motors have a continuous service 

factor, usually 15 percent, which allows 

continuous operation at 15 percent above the 

nominal rating. Most manufacturers use up to 

two-thirds of the available service factor, so that 

full-load power will be 10 percent above the 

nominal motor rating. It is therefore important to 

use the bhp rating, not the motor nameplate 

horsepower (hp) rating, when comparing 

efficiency ratings in hp/acfm. To include the 

motor efficiency and all package accessories and 

losses, use a rating in total kilowatt input per 

acfm to provide more precise data.

• Manufacturers may use a flange-to-flange rating 

that does not include inlet, discharge, and other 

package losses. This can affect overall efficiency 

by 5 percent or more.

• Energy consumption for accessory components, 

such as cooling fan motors, may not be treated 

consistently.

• Manufacturers may apply ranges or tolerances to 

performance data.

• Performance is usually based on perfect 

intercooling, which may not be realized under 

actual operating conditions. Perfect intercooling 

requires the air inlet temperature at each stage to 

be the same, requiring a cooling water 

temperature approximately 15°F below the 

ambient air temperature. Poor intercooling will 

adversely affect compressor performance.

As the revised ISO standard and CAGI Compressor Data 

Sheets become more commonly used, these equipment 

comparison problems should become less significant.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 91

Appendix C: CAGI Compressor and Dryer Data Sheets

These data sheets have been developed by the 

Compressed Air & Gas Institute (CAGI) as an aid to the 

end user/customer in the selection of pneumatic 

equipment for the planned operating conditions. The 

data sheets can be used to compare like equipment 

under equal operating parameters. Data sheets for 

rotary compressors, refrigerant dryers, variable speed 

drive (VSD) compressors, and centrifugal compressors 

are included in this appendix.

The members of the Compressed Air & Gas Institute 

(CAGI) have long been involved in standards for the 

equipment manufactured by the industry. CAGI has 

worked closely with the European Committee of 

Compressors, Vacuum Pumps and Pneumatic Tools 

(PNEUROP), the International Organization for 

Standardization (ISO), and other standards 

development bodies to develop appropriate standards 

for compressed air and gas equipment.

For displacement type compressors, including rotary 

screw compressors, American Society of Mechanical 

Engineers (ASME) Power Test Code 9 has been the 

recognized performance standard in the United States 

and ISO 1217 in Europe. These are too complex for 

performance testing in volume production.

CAGI and PNEUROP developed Simplified Test Codes 

which have been incorporated as appendices to ISO 

1217. CAGI members agreed that published 

performance of their products would be based upon the 

Simplified Test Codes, and Performance Data Sheets 

were developed to provide a standardized method of 

presenting the performance data. 

For compressors, a useful tool to calculate energy 

consumption is the power cost formula. Power cost 

equals the brake horsepower that the compressor is 

using, times the conversion factor of point-seven-foursix, times the hours of operation, times the local cost of

electricity per kilowatt hour. The result is all divided by 

the motor efficiency rating. Here's an example:

The yearly electrical cost of operating a 100 hp (~75 kW) 

compressor that uses 109 brake horsepower (~81 kW) 

consistently over 8,000 hours, with a local electrical cost 

of 6 cents per kilowatt hour and a 93% efficient motor is 

$41,968.

The information necessary to plug into the power cost 

formula can be found on the data sheets, which are 

sources of basic information about compressor 

performance. This information will help you make 

comparisons and select the compressor that best meets 

your needs.

CAGI further engaged in participation in a voluntary 

performance verification program to demonstrate 

compliance to the data sheet information. The program

is open to all manufacturers, whether they are a CAGI 

member or not. The verification program covers rotary 

compressors from 5-200 HP, and stand-alone 

Refrigerated Compressed Air Dryers from 200-1000 

SCFM.

Participating Manufacturers and the results of the 

verification tests will be posted on this website. 

Participating Manufacturers that pass the verification 

program test procedures will be allowed to utilize the 

CAGI Program Verification Seal on the models' 

specification sheets and in its product literature. This is 

the Participant's public representation that the stated 

Air Flow Capacities and Efficiencies have been verified 

by an independent laboratory.

For more information on CAGI data sheets, visit 

http://cagi.org/performance-verification/datasheets.aspx. 
APPENDIX C: CAGI DATA SHEETS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 92

Compressor Data Sheet:

Rotary Compressor
APPENDIX C: CAGI DATA SHEETS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 93

Dryer Data Sheet:

Refrigerant Dryers
APPENDIX C: CAGI DATA SHEETS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 94

Compressor Data Sheet:

Rotary Variable Frequency Drive Compressor
APPENDIX C: CAGI DATA SHEETS

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 95

Compressor Data Sheet:

Centrifugal Compressors
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 96

Appendix D: The Compressed Air System Marketplace

Compressed air is used in a wide variety of commercial 

and industrial applications. It is used to lift, hold, and 

position pneumatic and hydraulic devices; to operate air 

cylinder devices such as rivet guns and chipping 

hammers; to pressurize and atomize paint in spray 

guns; to operate air motors on grinders and drills; and 

to agitate liquids. In these applications, compressed air 

offers the advantages of being flexible, versatile, safe, 

and lightweight.

Market Size and Energy Consumption

More than 1 million air compressors are sold in the 

United States each year, the majority of which are 

powered by small motors of 5 horsepower (hp) or less. 

These small compressors are sold primarily to the 

commercial and residential markets to operate portable 

tools, air pumps, and pneumatic heating, ventilation, 

and air conditioning (HVAC) controls.

Although these small compressors account for 

approximately 98 percent of all air compressors sold, 

they account for only 12 percent of annual electricity 

consumption. Larger air compressors (25 hp or above) 

on the other hand, are sold primarily to the industrial 

and institutional sector. Although they account for less 

than 1 percent of annual sales, they represent an 

estimated 80 percent of the annual electricity 

consumption.

Industrial sector air compressors are typically plant air 

compressors in the range of 10 to 350 hp. Compressors 

larger than 350 hp are typically used to supply air for 

large process applications or plant air for very large 

manufacturing facilities. According to a recent analysis 

by Easton Consultants, Inc., energy consumption by 

these two populations of air compressors is 

approximately 27 to 32 terawatt hours per year, 

equivalent to about 6 percent of all motor- driven 

electricity consumption in the industrial sector.

There are two basic types of (plant) air compressors: 

Rotary Positive Compressors, which includes 

reciprocating, rotary screw, sliding vane, and scroll 

compressors, and Dynamic Compressors, which includes 

axial and centrifugal compressors. Within the 

compressor types, options such as lubricated and 

lubricant-free designs are available. For example, 

lubricant-free rotary screw compressors are used in 

applications that require clean air, such as food 

processing, pharmaceuticals, and electronics. Lubricantinjected, rotary screw air compressors are the dominant 

type used in applications above 25 hp, accounting for 75 

percent of unit sales. The popularity of the rotary screw 

air compressor is because of its low initial and 

maintenance costs and lower noise and vibration.

Although tools driven by compressed air can consume 

10 times as much energy as comparable electric tools, 

they are used because of their ability to provide high 

torque in a small, light, and safe package, and because 

they usually have significantly lower maintenance costs 

than electric tools in manufacturing environments. The 

primary benefits of using compressed air in applications 

instead of alternative approaches include flexibility, 

versatility, and safety.

Compressed Air System Marketplace

The air compressor marketplace (see Figure D-1) is 

somewhat complex, with at least five key players or 

stakeholders.

• Air compressor manufacturers

• Air compressor auxiliary equipment 

manufacturers

• Air compressor and auxiliary equipment 

distributors

• Contractors and architect-engineering (A&E) firms

• Compressed air system users.

In addition to influencing each other, these stakeholders are affected by trade associations, auditors, 

governmental entities, and electric utilities.

Each of the stakeholder groups is discussed below.

Air Compressor Manufacturers

Rotary compressor or “air-end” manufacturers play a 

primary role in the air compressor industry. Since they 

are involved in component design and manufacturing, 

packaging, and assembly, they determine the effort 

applied to compressor engineering and the overall level 
APPENDIX D: THE COMPRESSED AIR SYSTEM MARKETPLACE

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 97

 Figure D-1 The Compressed Air System Marketplace

of efficiency of compressor packages. A standard air 

compressor package consists of an electric motor, 

motor starter, compressor, controls, filter, lubricant and 

air coolers, and lubricant/air separator. An air-end 

accounts for a significant portion of a packaged air 

compressor’s initial cost.

The market structure for plant air compressors is a 

mature market that has, in recent years, made the 

transformation from reciprocating to rotary screw 

compressors. A number of factors led to this 

transformation, including the lower first cost, lower 

maintenance requirements, and ease of installation of 

rotary screw units compared with reciprocating 

compressors. The market is fairly well concentrated and 

competitive, and the number of companies that 

manufacture industrial compressors continues to 

decline. Single-stage, lubricant-injected, rotary screw 

type compressors account for about 70 percent of the 

market. Most global manufacturers are members of the 

Compressed Air and Gas Institute (CAGI). Since 

compressor equipment is perceived as a commodity, 

competition is high.

Taking inflation into account, industrial compressor 

prices have fallen over the past 5 years.

Auxiliary Equipment Manufacturers

Auxiliary equipment manufacturers produce 

components such as filters, dryers, aftercoolers, 

receiver tanks, pneumatic tools, lubricant separators, 

condensate treatment products and distribution system 

components. There are thousands of different 

equipment manufacturers, ranging in size from small, 

family-owned businesses to large, multinational 

corporations.

Air Compressor Distributors

A group of 500 to 600 distributors dominate the plant 

air compressor market, representing a major portion of 

the market. The remainder is sold directly from the 

manufacturer to the compressed air system user, 

specifying engineer, or design-build contractor. Sales to 

other original equipment manufacturers are rare.
APPENDIX D: THE COMPRESSED AIR SYSTEM MARKETPLACE

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 98

Distributors provide many useful services to 

compressed air system users and specifying engineers 

by offering information on new products, responding to 

requests for bids, supplying sample specifications, 

providing compressed air system design 

recommendations, and offering parts and service.

Although many distributors furnish detailed technical 

proposals with sound engineering design, they are often 

not able to convince the user to purchase a higher-cost 

compressed air system design based on energy 

efficiency, even though total life-cycle costs are lower 

on the energy efficient system. This is in part because of 

the way requests-for-proposals are issued by 

compressed air system users. Often decisions are made 

purely on the lowest initial cost. Depending on 

customer specifications, distributors may offer a highcost, energy-efficient compressed air system, along with 

a low-cost, less efficient system. CAGI and the CAC have 

been working to educate users to change this trend.

There are three types of distributors who provide 

different levels of service to the market: compressed air 

specialists, general industrial distributors, and 

warehouse distributors.

Compressed Air Specialists. Compressed air specialists 

work with complete compressed air systems, including 

the compressor and all ancillary components. These 

firms typically offer assistance with layout, specification, 

and sizing of components, storage, and controls. They 

offer a wide variety of maintenance programs, 

complete parts and service facilities, and locally stocked 

parts inventories. Compressed air specialists may also 

test, audit, and redesign systems, or install the 

complete system including the distribution network.

General Industrial Distributors. General industrial 

distributors offer limited assistance in system design; 

most of their business is responding to bids or 

specifications. These distributors also depend on parts 

and service business, but they do not generally service 

or install complete compressed air systems or offer 

consulting services on existing systems like distributors 

that specialize in compressed air systems or 

professional compressed air system auditors.

Warehouse Distributors. Warehouse distributors offer 

little or no technical support services, and do not 

provide repair, maintenance, or other services. Their 

sales tend to lean toward smaller equipment.

Contractors and Architect-Engineering Firms

Contractors and architect-engineering (A&E) firms are 

typically concerned with designing and specifying 

systems for reliability, ease of maintenance, and low 

noise, but don’t always take energy efficiency into 

account. Other than a small number of national firms, 

regional and local consulting engineering firms generally 

lack an air compressor system department or specialist. 

Contractors and A&E firms often do, however, play an 

important role in writing equipment bid specifications. 

Since it is often difficult to compare the performance of 

equipment offered by different manufacturers, 

consulting engineers may oversize equipment by using 

high-safety factors.

Compressed Air System Users

Industrial users of compressed air systems possess a 

wide range of expertise. While a small number of large, 

sophisticated firms have compressed air specialists inhouse and proactively manage and control their plant’s 

compressed air systems, many manufacturers do not, 

although the situation is improving.

Compressed air system users often misdiagnose 

problems in air systems and do not recognize the 

amount of energy wasted due to poor compressed air 

system design, equipment selection, and operation and 

maintenance (O&M) practices. In addition, users are not 

represented by an industry or professional organization 

that emphasizes compressed air system issues.

Compressed air system users often do not consider 

energy costs when buying new air compressors. 

Because of a focus on lowest first cost, which is driven 

by separate budgeting and accounting for operating and 

capital costs, energy-efficient options (such as premium 

efficiency motors, the best microprocessor and partload controls, and the most efficient equipment type or 

model for the applications) are usually not purchased.

Rebuilders

Compressor rebuilders are a rather minor force in the 

air compressor market with less than 5 percent of unit 

sales. Rebuilders were a larger influence 2 decades ago 

when reciprocating compressors dominated the plant 

air market and rebuilt equipment accounted for 25 

percent of sales. Today, users are more likely to replace 
APPENDIX D: THE COMPRESSED AIR SYSTEM MARKETPLACE

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 99

their defunct reciprocating compressor with a low-cost 

rotary compressor instead of rebuilding it.

Remanufacturing is performed by some manufacturers 

and distributors and by a few independent rebuilders.

Compressed Air System Audit Firms

Compressed air system audit firms audit, analyze and 

troubleshoot a plant’s compressed air systems and then 

recommend improvements to equipment, systems, and 

O&M practices. Audits can frequently decrease energy 

consumption by 20 to 50 percent or more with actions 

such as revised operation and maintenance plans, leak 

programs, equipment downsizing, and other efficiency 

upgrades. Auditors may be independent consultants or 

affiliated with manufacturers of controls, compressors, 

or auxiliary equipment.

Other Stakeholders

The other stakeholders that play a major role in the 

compressed air system marketplace by influencing it 

include trade associations, crosscutting organizations, 

government entities, and electric utilities. Each is 

discussed below.

Trade Associations.

CAGI—The most important trade association in the 

compressed air industry is the Compressed Air and Gas 

Institute (CAGI). CAGI is a nonprofit organization of 45 

companies that manufacture air and gas compressors, 

pneumatic machinery and air and gas drying 

equipment; products which have a myriad of 

applications worldwide in construction, manufacturing, 

mining, and the process and natural gas industries.

The principal objectives of CAGI are:

• To promote cooperation among its members for 

the improved production, proper use and 

increased distribution of air and gas compressors 

and related equipment

• To develop and publish standards and 

engineering data for air and gas compressors and 

related equipment

• To increase the amount, and improve the quality 

of service of air and gas compressors and related 

equipment to the general public

• To collect and distribute information of value to 

CAGI members and to the general public

• To engage in cooperative educational and 

research activities

• To cooperate with governmental departments 

and agencies and other bodies in matters 

affecting the industry.

Many of CAGI’s activities are carried out in its separate 

sections, which are categorized by product scope. 

Individual member companies may affiliate with one or 

more of these sections, depending upon their product 

lines.

In addition, important work of the Institute is carried 

out by committees, whose membership is composed of 

one representative from each section. These ongoing 

committees include the System Assessment, 

Educational and Promotional, Standards, Statistical 

Coordinating, and Technical.

More information on CAGI can be found in the sections 

of this sourcebook and the Compressed Air Challenge® 

(CAC), and in the fact sheet titled Packaged Compressor 

Efficiency Ratings.

CAGI contact information can be found in the section 

titled Directory of Contacts.

Compressor Distributor Associations—Another 

important group of trade associations serves 

compressed air equipment distributors. Compressor 

distributor associations usually focus around one 

compressor manufacturer. Distributor association 

contact information can be found in the section titled 

Directory of Contacts.

Crosscutting Organizations. The CAC is a national effort 

involving all compressed air system stakeholders aimed 

at improving compressed air system performance. This 

collaborative will: deliver best-practice compressed air 

system information to the plant floor; create a 

consistent national market message that supports the 

application of these best practices; provide a technically 

sound and professionally delivered training program for 

plant operating personnel; and through a certification 

program, recognize plant personnel’s skills in operating 

compressed air systems. Participants include large 

industrial users of compressed air; manufacturers and 

distributors of compressed air equipment and their 

associations; facility engineers and their associations; 

compressed air system consultants; state research and 
APPENDIX D: THE COMPRESSED AIR SYSTEM MARKETPLACE

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 100

development agencies; energy efficiency organizations; 

and utility companies. The CAC is described in detail in 

the Where To Find Help section of this sourcebook.

Government Entities. The major governmental 

influence on the compressed air systems marketplace is 

the U.S. Department of Energy’s (DOE) Advanced 

Manufacturing Office (AMO) which is designed to help 

industry improve the performance of their 

manufacturing systems (including compressed air 

systems).

AMO activities are described in the Where To Find Help

section of this sourcebook.

Electric Utilities. During the past 10 to 15 years, electric 

utilities have influenced the compressed air system 

marketplace primarily through their demand- side 

management programs, largely under the influence of 

state utility regulatory boards. Many electric utilities 

offered programs, such as compressor rebates that paid 

the incremental cost difference between a highperformance compressor and one of an average 

efficiency, or offered free or reduced-priced audits of 

compressed air systems. Most of these programs have 

now been discontinued, however.

As the electric utilities industry continues to deregulate 

and evolve, many utilities are interested in providing 

value-added energy services to their industrial 

customers. Compressed air systems offer a good 

opportunity for such services. Under the unregulated 

environment, utilities may offer anything from 

assistance with audits to complete outsourcing of a 

customer’s compressed air operations.

The Market for Compressed Air System 

Efficiency Services

The Assessment of the Market for Compressed Air 

Efficiency Services1 is a report commissioned by DOE 

with technical support provided by CAC. The objective 

of this report is to provide a comprehensive and 

balanced view of the market for engineering and 

 

1 XENERGY, Inc. (June 2001) Assessment of the Market 

for Compressed Air Efficiency Services, U.S. DOE in 

cooperation with Lawrence Berkeley National 

Laboratory and Oak Ridge National Laboratory.

consulting services to improve the energy efficiency of 

plant compressed air systems. These services include 

plant assessments or audits to identify opportunities to 

improve compressed air system operations, preventive 

maintenance services, such as leak detection and repair 

that are aimed at reducing energy use, and redesign of 

controls and other system components to reduce 

energy use. The report is intended for use by the CAC 

and other industrial energy efficiency program 

operators in developing strategies to encourage the 

growth of the compressed air system efficiency industry 

and enhance the quality of the services it offers. 

Compressed air system vendors and designers may also 

find it useful in charting their own approach to 

providing energy efficiency services.

The project was designed to answer a number of key 

questions concerning the demand and supply sides of 

the market for compressed air efficiency services. 

Among the key research questions to be addressed on 

the demand side of the market were:

• To what extent are customers in key end-use 

sectors aware of compressed air usage, costs, and 

savings opportunities?

• What practices do these customers follow to 

monitor, maintain, and enhance the efficiency of 

compressed air systems?

• What, if any, services do these customers 

purchase to maintain or enhance the efficiency of 

compressed air systems?

• What barriers do customers experience in 

purchasing such services?

The key research questions on the supply-side of the 

market were:

• What efficiency services do compressed air 

distributors, installers, and consultants currently 

offer?

• What is the current volume of sales for these 

services (number of customers, number of 

projects, dollar volumes)? How has volume 

changed over the past few years? What are 

vendors’ expectations regarding growth?

• What role do these services play in the overall 

business strategy of manufacturers, distributors, 

and consultants?
APPENDIX D: THE COMPRESSED AIR SYSTEM MARKETPLACE

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 101

• What barriers do these businesses face in 

developing and selling compressed air system 

efficiency services?

Key Findings

Demand-Side Findings

• Customer awareness of and concern for 

compressed air efficiency is low. Only 9 percent of 

customers interviewed for the program identified 

controlling energy costs as the primary objective 

in compressed air system maintenance and 

management. Only 17 percent mentioned 

efficiency at all as a system management 

objective. This low level of interest and 

knowledge was echoed in findings from the 

regional studies and interviews with compressed 

air system efficiency consultants.

• Maintenance of consistent, reliable compressed 

air supply is the principal objective of system 

management. Seventy-one percent of customers 

reported that ensuring adequate air supply is 

their primary objective in system management. 

According to consultants interviewed for this 

project, concern about operating consistency 

provides an effective route to selling efficiencyoriented services.

• A large portion of customers report serious 

problems in compressed air system operation and 

maintenance. Thirty-five percent of those 

interviewed reported that they had experienced 

unscheduled shutdowns of their compressed air 

systems during the previous 12 months. For 60 

percent of these establishments, or 21 percent of 

all establishments, the shutdown had lasted 2 

days or more. Two-thirds of the customers 

reported experiencing potentially serious 

operating problems in their compressed air 

systems. Excess moisture and inadequate air 

pressure were the most frequently reported 

problems.

• A significant portion of customers report having 

service contracts for their compressed air 

systems, but few of these contracts address 

system efficiency. Thirty percent of customers 

reported that they had service contracts for their 

compressed air systems. However, only one-third 

of these (or 10 percent of all participants) 

reported that efficiency-oriented services such as 

leak detection, energy-use monitoring, or 

assessment of control strategies were included in 

the service contract. There was no difference in 

the incidence of unscheduled system shutdowns 

or operating problems between customers with 

service contracts and those without such 

contracts.

• Thirty-five percent of customers interviewed 

reported that they conducted leak prevention 

programs.

• Reported implementation of compressed air 

efficiency measures is very low. The United States 

Industrial Electrical Motor Market Opportunities 

Assessment2 found that 57 percent of 

manufacturing plants had taken no action to 

improve compressed air system efficiency—

including repairing leaks— in the 2 years prior to 

the survey. A 1999 survey of 270 large industrial 

users served by Pacific Gas & Electric obtained a 

similar finding.

• Seventy-five percent of operators of the systems 

installed had had no formal training in 

compressed air system efficiency.

• Seventeen percent of customers reported that 

they had undertaken a compressed air system 

audit over the past 7 years. Most of the audits 

had been conducted in the past 6 years; and six 

audits were underway at the time of the 

interview. While most of the audits included 

estimates of energy use and identified potential 

energy-saving measures, fewer than half included 

estimated savings and costs for recommended 

measures. Two-thirds of the customers who 

conducted system audits reported that they had 

implemented at least one of the recommended 

measures.

• One-third of the customers reported that vendors 

selling “services specifically designed to reduce 

energy costs in compressed air systems” had 

approached them. The nature of these services 

varied widely. The most frequently mentioned 

were preventive maintenance for compressors, 

assessment of control strategies, and 

identification of energy-saving measures. No one 

service was mentioned by more than 46 percent 

 

2 XENERGY, Inc. (1998) United States Industrial Electrical 

Motor Market Opportunities Assessment, U.S. DOE and 

Oak Ridge National Laboratory.
APPENDIX D: THE COMPRESSED AIR SYSTEM MARKETPLACE

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 102

of those interviewed. This result reflects the 

formative state of the market for compressed air 

system efficiency services. Vendors have not 

defined the nature of such services consistently. 

Only 3 percent of customers reported that they 

had purchased compressed air efficiency services 

in response to these sales approaches. The most 

frequent objections to these services were high 

cost and the customers’ view that they could 

undertake such activities with in-house staff.

Supply-Side Findings

• A large portion of distributors report that they 

offer compressed air efficiency services. Over 

three-quarters offer system-efficiency measures, 

while over one-half offer end-use analyses and 

leak services.

• Over one-half of vendors feel that the demand for 

efficiency services has increased in the last year.

• Most distributors that offer efficiency-related 

services have entered the market within the past 

10 years; one-third have entered in the past 4 

years.

• Most distributors interviewed consider efficiency 

services essential to their competitive positions. 

Sixty-seven percent of distributors rate efficiency 

services as being important to their competitive 

position. Their major motivation to enter the 

market is customer retention. With the number of 

firms that offer efficiency services increasing, 

vendors believed that they needed to reply in 

kind to maintain satisfaction among their 

equipment purchasers. Access to additional 

revenue streams from consulting was not 

mentioned at all as a motivating factor.

• Most distributors identified customers’ lack of 

under- standing of the benefits of compressed air 

efficiency measures as the major barrier to their 

increased sale. These findings mirror the 

experience of compressed air efficiency 

consultants. Forty-five percent of the vendors 

identified customer perceptions that compressed 

air efficiency services were already being 

provided by in-house staff as an objection to sales 

efforts. This finding, combined with the reported 

low incidence of specific measure 

implementation, further reinforces the 

consultants’ observation that customers are 

largely in the dark about the nature of 

compressed air system efficiency measures and 

maintenance practices.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 103

Appendix E: Guidelines for Selecting a Compressed Air System Provider

Compressed air is one of the most important utility 

requirements of the typical industrial manufacturer. 

Compressed air is used throughout many processes, 

such as pneumatic tools, pneumatic controls,

compressed air operated cylinders for machine 

actuation, product cleansing, and blow-offs. Without a

consistent supply of quality compressed air, a 

manufacturing process can stop functioning.

The Compressed Air Challenge® (CAC) is a national 

collaboration that was created to assist industrial 

facilities in achieving greater reliability, improved 

quality control, and lower operating costs for their 

compressed air systems. The CAC encourages facilities 

to take a systems approach to optimizing compressed 

air operation. Taking a systems approach means looking 

beyond individual components to assess how well your 

compressed air system meets actual production needs. 

This is known as “matching supply with demand.” It also 

means identifying the root causes of system problems, 

rather than treating the symptoms.

For most industrial facilities, this approach will require 

specialized knowledge and equipment, both to assess 

system needs and to continue to service those needs 

over time. Outside assistance frequently is required. 

System assessment services and ongoing system 

maintenance may require the use of separate firms, 

although there is a growing market trend toward more 

fully integrated services. The process of selecting the 

right mix of services can be confusing.

The CAC is working with the compressed air industry to 

help industrial compressed air users become informed 

consumers. Guidelines for Selecting a Compressed Air 

System Service Provider offers guidance to assist you in 

selecting a firm that offers integrated services. 

Independent compressed air system specialists typically 

provide comprehensive system assessment services as 

their principal business; many are not involved in sales 

of equipment, other products, or maintenance.

The CAC also is developing guidelines to define three 

levels of system analysis services, independent of the 

type of firm offering these services. These three levels 

of service include: a walk-through evaluation, a system 

assessment, and a fully instrumented system audit. 

More information on analysis services guidelines can be 

found under the CAC Levels of Analysis of Compressed 

Air Systems in this Guidelines document, or you can visit 

the CAC Web site at www.compressedairchallenge.org. 

In selecting a service provider, a compressed air user 

should consider the guidelines that follow.

WHAT TO LOOK FOR WHEN SELECTING A 

SERVICE PROVIDER

In selecting a service provider, a compressed air user 

should consider the following guidelines.

I. Familiarity with the Systems Approach

The Compressed Air Challenge® (CAC) provides 

Fundamentals of Compressed Air Systems and 

Advanced Management of Compressed Air Systems 

training to end users and service providers. One way to 

gauge a service provider’s commitment to the systems 

approach is whether they have staff who have received 

CAC training. If they do, ask whether these individuals 

will be providing or supervising services for your 

facility. Providers who are familiar with using a systems 

approach are much more likely to address situations, 

both inside and outside the compressor room, that are 

having an effect on the reliability of your compressed 

air supply.

II. Availability of Compressed Air System 

Assessment Services

Does the provider offer compressed air system analysis 

services? If yes, how well do these services fit your 

needs? If no, can the provider outsource these services 

to an experienced system specialist? How experienced 

are the individuals who will be providing these services? 

Once a walk-through, assessment, or audit is 

performed, what kind of follow-up services are available 

to ensure that the recommendations are properly 

implemented and produce the desired results? Ask for a 

sample of similar work that the provider has done for 

others, résumés of the personnel who will be 

performing the work, and client references.

Please note that while leak detection is a useful 

element of a system assessment, a true system 

assessment should include much more. See 
APPENDIX E: GUIDELINES FOR SELECTING A COMPRESSED AIR SYSTEM PROVIDER

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 104

www.compressedairchallenge.org for additional 

guidance.

Important Note: recommendations resulting from 

system analysis activities should provide productneutral solutions to system problems and include, only 

if needed, performance- based rather than brand-based 

equipment recommendations.

III. Compressor Knowledge and Expertise

Does the service provider have the expertise to work on 

your equipment? Can the service provider work on all 

types of compressors in your facility? How much 

experience do the service technicians have? How are 

the service technicians trained? Is formal schooling 

involved? Knowledgeable service technicians are worth 

the premium price they may demand because of their 

ability to troubleshoot and get equipment back on line 

efficiently and effectively.

IV. System Components and Controls 

Knowledge and Expertise

Treatment, accessory, and ancillary equipment–Does 

the service provider have the expertise to perform 

refrigeration and other work on dryers and related 

equipment? Is the service provider capable of servicing 

the types of filters, drains, distribution and point of use 

equipment found in your facility?

System controls–Does the service provider have the 

diagnostic and technical controls capability to 

determine how to optimize your existing control 

configuration and make recommendations for 

improvements? Can they help network compressors 

together or remotely monitor, if necessary? Advanced 

controls can save energy and improve reliability through 

automatic start and stop, as well as turning 

compressors off that can then serve as back-ups.

Advance warning through remote monitoring may help 

identify a problem before it turns into a major 

shutdown.

V. Company Capabilities

Ask about the standards of performance that the 

prospective service provider has established for:

• Emergency service response

• Parts shipments

• Other factors which may influence your decision, 

such as:

– Installation capabilities internally or through a 

mechanical contractor

– Emergency rental fleet availability—electric or 

portable diesel-driven

• Your company may request information on the 

service provider’s

– Financial stability

– Insurance coverage

– Compliance with specific government regulations 

or those of your company.

VI. Service Facilities

Visit the facilities of two or three service providers 

under consideration to see first-hand the type of repair 

shop and parts warehouse with which you will be 

dealing.

CAC® LEVELS OF ANALYSIS OF

COMPRESSED AIR SYSTEMS

Overview

The Levels of Analysis of Compressed Air Systems listed 

below have been developed in an effort to provide 

commonality of terminology, methods, and procedures 

to be used by service providers and the results to be 

expected by end users. This overview is essentially brief. 

More detailed versions of these Levels of Analysis are 

under development, at this time, and will be available 

through the CAC Web site at 

www.compressedairchallenge.org. 

Energy utilities are actively involved in these efforts and 

some provide incentives to use these analyses to 

improve the energy efficiency of compressed air 

systems.

Conducting a walk-through evaluation is the first step in 

analyzing a compressed air system. Depending on 

individual needs, this can be conducted either by plant 

personnel or by an experienced compressed air system 

services provider. A walk-through evaluation is not 

intended to provide the level of detail found in a system 

assessment or a system audit but significant reductions 

in energy (25 percent or more) and lower maintenance 

costs frequently have resulted from a walk-through 

evaluation alone. Once initial opportunities have been 
APPENDIX E: GUIDELINES FOR SELECTING A COMPRESSED AIR SYSTEM PROVIDER

IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 105

identified, a decision should be made concerning 

whether additional analysis services are required to 

further define system dynamics and corresponding 

system improvement opportunities. This decision will 

depend, in part, on the size and complexity of the 

system being examined (both supply and demand) and 

whether critical issues surfaced during the Evaluation 

that require further investigation to understand the 

root cause and suggest potential remedies.

LEVELS OF ANALYSIS

Walkthrough Evaluation (1/2 to 2 days)

A walk-through evaluation is an overview of a plant 

compressed air system by identifying the types, needs, 

and appropriateness of end uses, pressures and air 

quality requirements.

• The distribution system is analyzed for any 

apparent problems of size, pressure drops, 

storage, leaks, and drains.

• The supply side is analyzed for types of 

compressors, and the types, suitability and 

settings of capacity controls.

• A simple block diagram of the system is drawn.

• Maintenance procedures and training are also 

analyzed.

• Written report of findings and proposed solutions 

is submitted.

• Solution and product neutrality should be 

maintained with any recommendations.

System Assessment (2 to 5 days)

A system assessment is more detailed than a walkthrough evaluation of a plant compressed air system.

• In addition to identifying the items and problems 

of the walk-through evaluation, readings are 

taken at appropriate locations to identify the 

dynamics of the system.

• A simple block diagram of the system is drawn, 

also a pressure profile and a demand profile, to 

help identify potential problems and how they 

could be resolved.

• Again, maintenance procedures and training are 

reviewed.

• A written report of findings and 

recommendations is submitted.

• Solution and product neutrality should be 

maintained with any recommendations.

System Audit (3 to 10 days)

A system audit is similar to a system assessment but in 

more depth and detail.

• Data logging of readings throughout the system is 

conducted for more in-depth analysis of the 

dynamics of the system and resulting problems.

• Again, maintenance procedures and training are 

reviewed.

• The objective is a proper alignment of the supply 

side and the demand side for optimum efficiency, 

energy savings, and reliability. A baseline is 

established, against which the results of any 

proposed changes are measured.

• A comprehensive written report of all findings, 

recommendations, and results is submitted.

• Solution and product neutrality should be 

maintained with any recommendations.

Standards Related to Compressed Air Efficiency 

Assessments

Two main standards are currently available: ISO 

11011:2013 Compressed Air Energy Efficiency 

Assessment sets requirements for conducting and 

reporting the results of a compressed air system 

assessment that considers the entire system, from 

energy inputs to the work performed as the result of 

these inputs. ISO 11011:2013 considers compressed air 

systems as three functional subsystems: supply which 

includes the conversion of primary energy resource to 

compressed air energy; transmission which includes 

movement of compressed air energy from where it is 

generated to where it is used; demand which includes 

the total of all compressed air consumers, including 

productive end-use applications and various forms of 

compressed air waste. ISO 11011 is based on ASME EA4-2010.

ASME EA-4-2010 sets requirements for conducting and 

reporting the results of a compressed air system energy 

assessment that considers the entire system, from 

energy inputs to the work performed as the result of 

these inputs. An assessment complying with this 

Standard does not need to address each individual 

system component or subsystem within an industrial 

facility with equal weight; however, it must be 

sufficiently comprehensive to identify the major energy 

efficiency opportunities for improving the overall 

energy performance of the system. A guidance 

document, EA-4G-2010, is also available.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 106

About Compressed Air Challenge®

The Compressed Air Challenge® was formed in 1997 as an independent, non-profit, voluntary collaboration of industrial 

users; manufacturers, distributors and their associations; consultants; state research and development agencies; energy 

efficiency organizations; and utilities. This group has one purpose in mind — helping you enjoy the benefits of improved 

performance of your compressed air system.

The CAC’s mission is to be the leading source of product-neutral compressed air system information and education, 

enabling end users to take a systems approach leading to improved efficiency and production and increased net profits. 

The vision of the CAC is to maintain a financially viable organization capable of fulfilling its mission by effectively using

fees from our sponsors and income from our products.

The CAC has developed a ready-to-use portfolio of product-neutral seminars that can immediately be put to work as the 

ideal enhancement to industrial incentive or rebate programs. These highly rated, self-funding, awareness seminars 

target compressed air systems where energy savings of between 30 and 60 percent can typically be achieved with 

affordable improvement projects.

The CAC offers several training programs: Fundamentals of Compressed Air Systems, Advanced Management of 

Compressed Air Systems, Qualified AIRMaster+ Specialist Training (developed with the U.S. Department of Energy) and 

the latest, “Compressed Air, It’s Not Free!” Shop Floor Training Package. The CAC has trained over 17,000 compressed 

air users since 1999. Evaluation of CAC training has shown fully 76 percent of seminar participants implement CAC 

training recommendations, such as replacing inefficient compressors, upgrading distribution systems and improving 

controls. The bottom line for compressed air users and energy efficiency related organizations alike is energy savings –

an average savings of 17 percent on compressed air energy use, with added benefits of increased compressed air system 

reliability and plant productivity. 

The Fundamentals of Compressed Air Systems is a one-day, 8-hour seminar designed to teach facility engineers, 

operators and maintenance staff how to achieve 15-25 percent cost savings through more effective production and use 

of compressed air. The Advanced Management of Compressed Air Systems is a two-day, 16-hour seminar that provide 

more in-depth technical information designed to help participants return to their facilities with skills and practical tools 

to further improve productivity and reduce energy costs. 

In addition to Improving Compressed Air System Performance: A Sourcebook for Industry, the CAC has a full offering of 

educational material; including: Guidelines for Selecting a Compressed Air System Service Provider (see Appendix E) and 

Best Practices for Compressed Air Systems. 

The 350-page Best Practices Manual was developed to provide you with the tools to reduce the operating costs 

associated with the use of compressed air and improve the reliability of the entire system. This one-source manual 

addresses the improvement opportunities from the air entering the compressor inlet filter to the end uses including 

hoses, quick couplers air tools, cylinders or other devices.

The Best Practices Manual provides the “how to” information to implement recommendations which will achieve peak 

performance and reliability of the system at the lowest operating cost. The use of the recommendations will:

• Reduce energy and repair costs

• Improve system reliability

• Increase productivity

• Reduce unscheduled downtime
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 107

The manual begins with the considerations for analyzing existing systems or designing new ones, and continues through 

the compressor supply to the auxiliary equipment and distribution system to the end uses. Learn how to use 

measurements to audit your own system, calculate the cost of compressed air and even how to interpret utility electric 

bills. Best practice recommendations for selection, installation, maintenance and operation of all the equipment and 

components within the compressed air system are in bold font and are easily selected from each section.

ORGANIZATIONAL STRUCTURE

The CAC includes:

• A Board of Directors comprised of CAC Sponsor representatives

• A Project Development Committee, which includes a representative from each key stakeholder group and is 

responsible for overall project coordination at the direction of the Board of Director

• Working Groups, which will provide essential technical input to specific projects

CAC SPONSORS

• Airleader

• BC Hydro

• Compressed Air & Gas Institute 

• Efficiency Vermont

• Eversource

• Independent Compressor Partners, Inc.

• Iowa Energy Center 

• Manitoba Hydro

• National Grid USA

• New York State Energy Research & Development Authority

• Northwest Energy Efficiency Alliance 

• Pacific Gas & Electric

• Tennessee Valley Authority

• U.S. Department of Energy

FOR MORE INFORMATION

The CAC is seeking additional participants interested in sponsorship or contributing to materials development. For 

general information, please contact that CAC at info@compressedairchallenge.org. If you would like more information, 

please visit, www.compressedairchallenge.org. 

About the U.S. Department of Energy’s Advanced Manufacturing Office

The Department of Energy’s Advanced Manufacturing Office (http://energy.gov/eere/amo/advanced-manufacturingoffice) partners with industry, small business, universities, and other stakeholders to identify and invest in emerging 

technologies with the potential to create high-quality domestic manufacturing jobs and enhance the global 

competitiveness of the United States. They partner with industry, small business, universities, regional entities, and 

other stakeholders to identify and invest in emerging clean energy technologies. The AMO establishes collaborative 

communities focused on developing and commercializing targeted technologies; play a leadership role in the national 

interagency Advanced Manufacturing Partnership; and encourage a culture of continuous improvement in corporate 

energy management. Their investments have high impact, use project diversity to spread risk, target nationally 

important innovation at critical decision points, and contribute to quantifiable energy savings. 
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 108

The AMO delivers solutions for industry that result in significant energy and cost savings, waste reduction, pollution 

prevention, and enhanced environmental performance. AMO's Industrial Technical Assistance supports the deployment 

of manufacturing technologies and practices, including their Better Plants Program and Industrial Assessment Centers, 

along with strategic energy management, and combined heat and power installation, across American industry to 

increase productivity and reduce water and energy use.
IMPROVING COMPRESSED AIR SYSTEM PERFORMANCE: A SOURCEBOOK FOR INDUSTRY | 109

Co-Sponsored by:

The Compressed Air Challenge

www.compressedairchallenge.org

U.S. DEPARTMENT OF 

ENERGY

Energy Efficiency &

Renewable Energy

For more information, visit: 

http://energy.gov/eere/amo/advanced-manufacturing-office DOE/Publication Number: DOE/EE-1340 

About the Office of Energy Efficiency and Renewable Energy

The Office of Energy Efficiency and Renewable Energy (EERE) invests in clean energy technologies 

that strengthen the economy, protect the environment, and reduce dependence on foreign oil.

Advanced Manufacturing Office

U.S. Department of Energy

Energy Efficiency and Renewable Energy

Washington, D.C. 20585-0121

Improving Compressed Air System Performance: 

A Sourcebook for Industry, Third Edition

One in a series of industrial energy efficiency 

sourcebooks.