C.A. BASICS
C.A. Basics• Compressed air is simply a medium to transmit
power, similar to electricity or steam to transmit heat
• Often referred to as the ‘fourth utility’ • Compressed air can be used for a multitude of
applications– Simple: Pumping up tires and blow-off nozzles– More Complex: Instrumentation, Vacuum generation,
Pneumatic tools, cylinders and valves• Ex: flow controllers, pumps, impact wrenches, nail guns, etc
– End-use equipment is cheap, lightweight, compact & powerful
– Explosive environments– Easy to control (solenoid valves, pressure
proportional to force)
Why Compressed Air?
C.A. Basics Basic Compressor
Specialized Bicycles/Popular Mechanics
C.A. Basics
$$$Typically the most expensive utility at a plantRule of Thumb: It takes 7 units of compressor
horsepower to provide one horsepower of useful work!Why is compressed air so expensive???
Ex: Cost of operating a 10hp motor for 1 year (8,760hrs) 10hp Electric Motor 10hp Pneumatic Motor
Why NOT Compressed Air?
$5,388
$32,818
C.A. Basics• Surely if it’s the most expensive utility at a
plant it’s being continuously managed…• Example:
– Foundry Sand Transport System– 350 hp of compressor power– Energy consumption reduced by 36%– $16,300 in annual savings– 1.3 year simple payback
• Substantial opportunity throughout industry to reduce compressed air usage and cost
• Plant personnel often think compressed air is free
Why Manage Compressed Air?
Compressed Air Challenge, www.compressedairchallenge.org
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
COMP
Greg Harrell, Energy Management Services (EMS)
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
# kW of loss??
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
98-99% Efficient
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
98-99% Efficient
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
98-99% Efficient
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
98-99% Efficient*
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
# kW of thermal energy loss??
98-99% Efficient*
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
90 kW of thermal energy loss
98-99% Efficient*
COMP
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
90 kW of thermal energy loss
98-99% Efficient*
COMP C.A.MTR
#kW of shaft
energy from comp. air motor??
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
90 kW of thermal energy loss
98-99% Efficient*
COMP C.A.MTR
10 to 20 kW of shaft
energy from comp. air motor
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
90 kW of thermal energy loss
98-99% Efficient*
COMP C.A.MTR
10 to 20 kW of shaft
energy from comp. air motor
What about the 1st Law of Thermo??
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
90 kW of thermal energy loss
98-99% Efficient*
COMP C.A.MTR
10 to 20 kW of shaft
energy from comp. air motor
The 1st Law of Thermo is not
violated because the air discharged is
very cold
Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
90 kW of thermal energy loss
98-99% Efficient*
COMP C.A.MTR
10 to 20 kW of shaft
energy from comp. air motor
The 1st Law of Thermo is not
violated because the air discharged is
very cold
COMPRESSION EFF:10-20%Greg Harrell, EMS
C.A. Basics Compression Thermodynamics
MOTOR
100 kW of electrical
energy input
5-8 kW of thermal energy
loss
We want high-pressure air from the compressor…
What we get is high-pressure,
high-temperature air
90 kW of thermal energy loss
98-99% Efficient*
COMP C.A.MTR
10 to 20 kW of shaft
energy from comp. air motor
The 1st Law of Thermo is not
violated because the air discharged is
very cold
COMPRESSION EFF:10-20%Greg Harrell, EMS
C.A. Basics Compression ThermodynamicsPROVE IT
THE C.A. SYSTEM
The C.A. System Typical System
Compressed Air Challenge
Supply Side Demand
Side
The C.A. System Supply Side
Types of Compressors
Compressed Air Challenge
The C.A. System• Analogy: Car IC
Engine• How it works:• Oil and Oil-free• Single-acting and
double-acting• Single or multi-
stage, depending on pressure/size
• Typically smaller units (less than 30hp*)
Supply SideReciprocating
Compressed Air Challenge (pg. 129)
The C.A. System
• Originally THE compressor technology
• Many vintage reciprocating compressors operating today, some in excess of 1,000 hp
• THE most efficient compressor technology (double-acting)
• Not used much today in industry
• 22-24 kW/100 cfm (single-acting), 15-16 kW/100 cfm (double-acting)
Supply SideReciprocating
Belliss and Morcom
The C.A. System
• Analogy: Car turbocharger
• How it works:– Impeller spinning at
10,000+ rpm• Typically larger units
(300 hp to >4,500 hp)• All Oil Free• Multi-stage, typically 2-
4 depending on size/pressure
• Centrifugal Compressor Animation
Supply SideCentrifugal
The C.A. System
• Low vibration, don’t need a heavy concrete pad like reciprocating
• Still very efficient
• Favored by industry today for large applications
• Operating range limited• 16-20 kW/100 cfm
Supply SideCentrifugal
The C.A. System Supply Side
Rotary Screw• Analogy: Car supercharger• How it works:
– Two screws meshed together which squeeze air
• Typically medium sized units (20 hp to 300 hp) but can be as large as 600 hp
• Oil and Oil Free• Typically single stage, some
larger units 2 stage
The C.A. System Supply Side
Rotary Screw
Ingersoll Rand
• By far, most common industrial air compressor today
• Low first cost, good efficiency, large operating range
• Variety of control techniques and manufacturers
• 17-22 kW/100 cfm (single stage)
The C.A. System
Supply SideRotary Screw (Lubricant-
Injected)
Credit: Ponna Pneumatic
Compressed Air/Oil MixtureOil (Lubricant)“Oil-Free” Compressed Air(2-3 ppm)
The C.A. System Supply SideDryers
Compressed Air Challenge
• Air dryers condense water out of compressed air• Air at 80°F and 50% = 60°F dewpoint and 0.01092 lbw/lba
• Compressed to 100 psig and 185°F, how much water in air?– Same! 0.01092 lbw/lba Squeeze water into space 8 times smaller (114.7/14.7=7.8)
• What is new dewpoint?– 125°F (Rule of Thumb: Double pressure, increase dewpoint by 20°F
• What happens if we send that air into a industrial plant that is 80°F ambient?– Rain inside compressed air pipes
The C.A. System
• Refrigerated dryers utilize a refrigerant circuit to condense moisture from the air stream
• Typical leaving dewpoint of 40°F• Cycling, non-cycling and head-unloading designs• 0.80 kW/100 cfm
Supply SideRefrigerated Dryers
The C.A. System
• Desiccant dryers use a desiccant to dry the air (via adsorption)
• Typical leaving dewpoint of -40°F to -100°F, depending on desiccant type
• Heatless, heat-assisted and blower-heat assisted designs• 2-3 kW/100 cfm
Supply SideDesiccant
Regenerative Dryers
The C.A. System• Storage (Air Receivers, piping, etc)• Pressure/Flow Controllers• After-coolers• Air/Lubricant Separators• Filters
– Particulate: Removes dirt/debris– Coalescing: Removes vapors (typically oil/lubricant
vapors)– Adsorption: Additional hydrocarbons and other
impurities• Traps and Drains
– Level operated– Timer operated– Zero-air loss
Supply SideAdditional
Components
The C.A. System• In a typical compressed air system,
how much air is used “appropriately” by production?
Demand SideUsage Breakdown
Compressed Air Challenge
• Leaks: Compressed air which leaks from distribution• Inappropriate Uses: Anything that compressed air is
used for which could be replaced via a more efficient process
• Increased Demand from Excessive System Pressure: Better known as artificial demand
The C.A. System• Pneumatic tools, cylinders, valves• Automation equipment• Instrumentation Air• Baghouses• Blow-off (special cases)• Motors/Pumps (where appropriate)• Etc.
Demand SideEnd-Users (Normal
Production)
The C.A. System
• Higher the system pressure, higher the leak rate– <2 cfm leak: can’t feel, can’t hear– 3-4 cfm leak: can feel, can’t hear– >5 cfm leak: can feel, can hear
• Leaks do more than waste energy– Shortens life of supply equipment because of increased
runtime– Buy/add new compressor capacity that is not needed
• Leak Table for a ‘perfect’ orifice (values are cfm)
Demand SideLeaks
Compressed Air Challenge
1/64” 1/32” 1/16” 1/8” 1/4” 3/8”70 psig 0.300 1.20 4.79 19.2 76.7 17380 psig 0.335 1.34 5.36 21.4 85.7 193
90 psig 0.370 1.48 5.92 23.8 94.8 213 100 psig 0.406 1.62 6.49 26.0 104 234
125 psig 0.494 1.98 7.90 31.6 126 284
The C.A. System
• An inappropriate use is anything that compressed air is currently used for, but has a more efficient alternative
Demand SideInappropriate Uses
DOE Tip Sheets
Potentially Inappropriate Uses
Suggested Alternatives/Actions
Clean-up, Drying, Process Cooling Low-pressure blowers, electric fans, brooms, nozzles
Sparging Low-pressure blowers and mixers
Aspirating, Atomizing Low-pressure blowers
Padding Low to medium-pressure blowers
Vacuum generator Dedicated vacuum pump or central vacuum system
Personnel cooling Electric fans
Open-tube, compressed air-operated vortex coolers without thermostats
Air-to-air heat exchanger or air conditioner, add thermostats to vortex cooler
Air motor-driven mixer Electric motor-driven mixer
Air-operated diaphragm pumps Proper regulator and speed control; electric pump
Idle equipment Put an air-stop valve at the compressed air inlet
Abandoned equipment Disconnect air supply to equipment
The C.A. System• If the pressure of the system is too
high, uncontrolled uses consume more air– For example, a system that is at 100 psig
has a leak load of 100 cfm. If the pressure is decreased, the leak rate is also decreased.
– An unregulated air cylinder• Reducing the pressure not only saves
energy because the compressor doesn’t have to work as hard, it also reduces the amount of air it has to generate
Demand SideArtificial Demand
The C.A. System• Compressed air systems are dynamic,
meaning that a spot check is not sufficient to determine how well it is operating
• Determining how a compressor is operating requires logging equipment
Measurements and Baselining
C.A. CONTROL STRATEGIES
C.A. Control Strategies• The simplest and most efficient control method• Turn compressor on and low pressure setpoint and
turn off at high pressure setpoint• Only practical for small motors
On/Off Control
C.A. Control Strategies• Compressor operates in a pressure dead-
band, similar to on/off• At upper band, instead of shutting off,
compressor “unloads”• Bleed off air/oil separator (~40 seconds)
– Only bleed down to ~40 psi– Why does it take 40 second to bleed sump?
• Wait for pressure to reach lower setpoint• Compress air/oil separator back to
operating pressure (~6 seconds)• Resume operation
Load/Unload Control
C.A. Control Strategies Lubricant-Injected Rotary Screw
Load/Unload Control
Credit: Ponna Pneumatic
Compressed Air/Oil MixtureOil (Lubricant)“Oil-Free” Compressed Air(2-3 ppm)
LoadedUnloadingUnloaded
C.A. Control Strategies Lubricant-Injected Rotary Screw
Load/Unload Control
Credit: Ponna Pneumatic
Compressed Air/Oil MixtureOil (Lubricant)“Oil-Free” Compressed Air(2-3 ppm)
LoadedLoadingUnloaded
C.A. Control Strategies• Storage plays a huge role in
load/unload power consumption
Lubricant-Injected Rotary ScrewLoad/Unload Control
C.A. Control Strategies Load/Unload Control
Compressed Air Challenge
Capacity of
TRIM
compressor!
C.A. Control Strategies• A low and high pressure limit as with
load/unload• Inlet valve modulates flow rate into
compressor– System pressure increases, inlet valve
closes– System pressure decreases, inlet valve
opens– No blowdown valve, sump always
pressurized• Pressure drop across inlet valve
– inlet pressure at screws decreases– increases pressure ratio, increases work
• Results in competition between savings and costs
Modulating Control
C.A. Control Strategies Modulating Control
Compressed Air Challenge
C.A. Control Strategies• Add variable speed drive to motor• Speed is proportional to capacity
– So at 80% speed, you produce roughly 80% of the rated capacity
• Less efficient than other types at 100% capacity– VFD drive consumes some power– Screws on constant speed machines can be
designed for a single speed. Screws on variable speed machines must pick a design point, typically about 80% of full speed.
Variable Speed Control
Compressed Air Challenge
C.A. Control Strategies Variable Speed Control
Compressed Air Challenge
C.A. ENERGY SAVINGS
55
C.A. Energy Savings• Compressed air leaks can be between 5
and 30% of system energy usage– Typically 20-30% for ‘unmanaged’ systems– Poorly maintained plants can be even more!
• Savings depend on type of compressor and control type, but applicable for all compressed air systems
Fix Compressed Air Leaks
C.A. Energy Savings• At $0.10/kWh, 8,760 hrs/yr• For a variable speed compressor:
Fix Compressed Air Leaks
Leak Volumetric Power Loss Demand Energy CostDiameter,
DFlow Rate,
VfL Reduction,
DRSavings Savings
(in) (cfm) (hp) (kW) (kWh/yr) ($/yr) 1/32 1.0 0.22 0.16 727 $72 1/16 4.0 0.88 0.66 2,908 $291 1/8 16.1 3.53 2.63 11,634 $1,163 1/4 64.6 14.11 10.53 46,535 $4,654• For a modulating compressor:Leak Volumetric Power Loss Demand Energy Cost
Diameter, D
Flow Rate, Vf
L Reduction, DR
Savings Savings
(in) (cfm) (hp) (kW) (kWh/yr) ($/yr) 1/32 1.0 0.22 0.048 218 $22 1/16 4.0 0.88 0.198 872 $87 1/8 16.1 3.53 0.789 3,490 $349 1/4 64.6 14.11 3.16 13,961 $1,396 • Ex: Reduce air leaks by 160 cfm, save $3,458/yr
C.A. Energy Savings• Pressure typically set at whatever compressor is
rated • Plant rarely needs that high of a pressure• Pressure should be set based on highest pressure
need– If the highest pressure need is 65 psig for a process line,
then the compressor should be set at a pressure to provide that 65 psig
– <100 psi is a typical header pressure• Rule of Thumb: 1% for every 2 psi reduction• Recall discussion about artificial demand• Example: Can we decrease pressure with system “as-
is?”– No, already below critical pressure at high demand!– Then modify the system
Reduce Compressor Pressure
C.A. Energy Savings• Screw compressors can switch from modulating to
load/unload very easily*– *Many compressors can do it at the flip of a switch, not
all– Storage is important (next slide)
• Difficult to retrofit from single speed to variable speed– Typically have to buy new compressor, even more pricy
• Interlink multiple compressors with network controls– Typically only useful for many compressor systems– Not as helpful in our example
• Overlapping control bands– With pressure fixed, control bands can be separated
Change Control Type/Setpoint
C.A. Energy Savings• Only for load/unload• Adding storage allows for compressor to run
unloaded for longer periods of time, resulting in lower overall energy usage
• Storage is expensive– $20,000 or more for 7,000 gal of storage
• What does 7,000 gallons look like?• What does 20,000 gallons look like?
• Add 4,000 gal of storage to system– Switch to Load/Unload– Lower control bands to appropriate points (18 psi
improvement)– Savings of $22,226/yr (this includes load/unload savings,
pressure reduction savings and overlapping control band savings)
Add Storage
C.A. Energy Savings• Cooling the air at the compressor inlet
reduces energy consumption• Doesn’t work for flooded-oil screw
compressors• Works well for reciprocating,
centrifugal and oil-free rotary screw compressors
Cool Compressor Inlet
C.A. Energy Savings• Baghouse pulse causes severe pressure
drops in system• 6 cubic foot pulse for 0.25 seconds every 1
minute• Instantaneous Flow:
– (6 ft3)/(.25 sec)x(60 sec/min) = 1,440 cfm• Average Flow
– (6 ft3)/(2 minutes)=6 cfm• Add secondary storage• Savings are hard to figure, likely from
productivity increase
High Volume, Intermittent Needs
C.A. Energy Savings• Air Knifes can be replaced with low
pressure blowers• Think about an industrial-strength hair
blower without the heat• High flow, low pressure
Low Pressure Blowers
C.A. Energy Savings• Use the 80-85% of energy wasted as
heat– If air cooled, use to heat areas during
winter– If water cooled, might be able to utilize
for boiler makeup water or other sources• Piping can get very expensive
• Low-grade heat, makes it difficult to capture
Utilize Compressor Waste Heat
C.A. Energy Savings• Facility not operating, still need
compressed air• Typically a result of a “dry” sprinkler
system• Compressed air pressurizes and fills
pipes, if a sprinkler head bursts the compressed air escapes and the water follows behind
• Typically need <5 hp to keep system pressurized
• Many companies run one compressor off-shift to pressurize system
• Savings for our example are $14,400/yr!
Off-Hours Compressed Air Use
C.A. Energy Savings• Savings are intertwined; cannot add savings
from other slides all together because effects are cumulative
• Summary– Eliminate Compressed Air Leaks– Reduce Pressure and Fix Control Bands– Add storage and switch to Load/Unload– Add low pressure blower for air knifes– Add new 5 hp compressor for sprinkler system
• Total savings: $66,331 or 65%!• Implementation cost likely below $30,000• Doesn’t include Productivity Increase!
Total Savings from Example
QUESTIONS???
67