1. Compressed Air Systems
Workgroup Meeting July 2014
Energy Efficient
Compressed Air Systems
Abdul Qayyum “Q” Mohammed
Engineer

2. Why is this important ?
Almost all Manufacturing Facilities use Compressed Air (CA)
These are large systems
Smaller systems draw about 40 kW (50-hp)
X 40

3. Expensive Resource Only 9% !
Compressed Air (CA) is a very expensive resource
The most expensive in many cases
About 90% of the input energy is lost through the system
Energy In
Heat
Conversion
Purges
And Drains
Only 9% !
Work Out
Source: David Vanderbeek, 2011 Power Smart Forum

4. Why use Compressed Air ? Simple : Its easy to use
Can be used for a wide variety of applications
All you need is a new hose for a new application
In many cases it is the economically feasible option

5. Well what’s the problem then?
Its ease of use makes it …….
…..the most misused resource

6. CA Fundamentals
Before we get into energy savings opportunities lets briefly look at
Types of air compressors
Reciprocating
Screw
Centrifugal
Different control strategies for the compressors
Pros and Cons

7. Reciprocating Compressors
Simplest and oldest compressor type
Size: 1 – 600 hp

8. Recips: Part Load Good part-load performance
Very close to ideal compressor
Ideal

9. Recips: Pros and Cons Pros: Simplest and oldest compressor type
Comparable full load efficiency
Very good part load efficiency
Cons:
Higher maintenance costs compared to the new compressor types (for larger compressors)

10. Screw Compressors Currently the most commonly
used compressor in industry
Sizes 5 – 700 hp

11. Screws: Part Load Multiple control options
Combinations of controls available with each compressor
Gives large scope for optimization
*VFDs have lower full-load efficiency
They are very efficient between
45% to 80% capacity

12. Screw: Pros and Cons Pros: Low maintenance
Different control options work well within different systems
Proper sizing is critical
Large cost range depending on
Control options
Other additional options (oil free, integrated dryers etc.)
Cons:
Optimization is often neglected (or done poorly) which degrades system part-load performance

13. Centrifugal Compressors
Larger compressors (these are dynamic)
Sizes 125 – 6,000 hp

14. Centrifugal: Part Load
Can be the most inefficient compressors at part loads
Combination of controls are available
Control optimization is necessary for efficiency

15. Centrifugal: Pros and Cons
Very high full-load efficiency
Very good for systems that have a high base load
Low maintenance if operated properly
Customizable
Can be built to match client needs
Oil free
Cons:
Slightly higher cost
Can be the worst at part-loads
Blow-off should be minimized
Dynamic nature limits turn down ratio (to avoid surge)

16. Energy Saving Opportunities
There can be endless opportunities in a system.
It can take couple of hours to go through them all.
So, Let’s just look at the BIG hitters
Inappropriate uses
Leaks
Pressure
Staging
Other opportunities
Air Drying
Storage
Filters
Heat Reclaim
These are things we look for when we have limited time with the client.

17. Let’s look at some examples.
Inappropriate Uses
Questions to ask..
Is CA even necessary ?
It is a VERY Expensive resource
Is there an alternative that can eliminate CA use?
Is CA being used effectively ?
Can CA use be reduced ?
Pressure
Timing
Let’s look at some examples.

18. In-appropriate use Examples
To blow off a product. Good idea?
Air Saver nozzles use about
70% less CA

19. In-appropriate use Examples
CA to cool off product. …. Good Idea?
200x more expensive than cooling towers
Energy Efficient Process Cooling – Dr. Kissock, University of Dayton

20. In-appropriate use Examples
Personal Cooling (We just saw cooling costs)
Occupational Safety and Health Administration (OSHA) safety violation

21. In-appropriate use Examples
Drains are used to remove condensate from the system
But do we need to lose air?
No-loss Drain: Zero air loss
Open valve: Always loosing air.
Timed Drain: Timing set for peak, often results in air loss

22. In-appropriate use Examples
Need low pressure air (20 psig) ? => Use Blowers !
Blowers use about
5x less energy

23. List of Common Inappropriate Uses
Blow-Off Applications
Air knives
Dust collector purges
Cleaning with CA
Personal cooling
Process cooling
Continuous CA Use Applications
Aeration
Agitation
Atomization (mixing)
Transport of material
Air motors /hoists
Diaphragm pumps
Air vibrators
Electrical cabinet cooling
Vacuum generation
Vortex coolers
Air Cylinders
Air Operated vacuum cleaners

24. Energy Saving Opportunities
There can be endless opportunities in a system.
It can take couple of hours to go through them all.
So, Let’s just look at the BIG hitters
In appropriate uses
Leaks
Pressure
Staging
Other opportunities
Air Drying
Storage
Filters
Heat Reclaim
These are things we look for when we have limited time with the client.

25. Reduce Leaks !
Leaks are lost $$$$$
Air Power Usa

26. Leaks Example Misconception “We do not have a large leak load..”
On average 30%* of a facility’s compressed air is lost to leaks
Example Facility
Weekend
Avg. Leak Load = 50% !!
In a two compressor system
100 kW in Non-production ~ 100 Homes
*U.S. DOE, Compressed Air Fact Sheet #7

27. Strategy to Reduce Leaks
Strategies we have observed:
Leak reduction programs
Other Methods
Use of Isolation Valves to valve off unused areas
Reduced pressure during non production
Turning off CA system on weekends

28. Goals for Leaks Can I have Zero Leak Load ? What should I aim for ?
Unfortunately, NO
What should I aim for ?
Good rule of thumb is to reduce it by 50%
We have observed facilities with leak loads
As high as 60% and
As low as 7-10% - this was accomplished overtime by reducing leaks and isolating unused areas

29. Energy Saving Opportunities
There can be endless opportunities in a system.
It can take couple of hours to go through them all.
So, Let’s just look at the BIG hitters
In appropriate uses
Leaks
Pressure
Staging
Other opportunities
Air Drying
Storage
Filters
Heat Reclaim
These are things we look for when we have limited time with the client.

30. Reduce Pressure at End Use
Did we adjust pressures at end use ? Do you need line pressure ?
We recently observed a large manufacturing facility with efficient compressors…..
Almost all end uses were unregulated !!!
Unregulated tool
~ 120 acfm
95 psig
~ 20% reduction !
Regulated tool
~ 95 acfm
70 psig

31. Reduce Pressure at Compressor
Why is a compressor used?
To pressurize the incoming air stream
A compressor has to Work harder for higher Pressure
Air Compressor
Air P2
Power kW
Air P1
Heat out

32. Reduce Pressure at Compressor
Common Misconception
“Raising the pressure increases capacity”
Reality – It decreases compressor capacity and increases operating costs
Often times other issues are compensated with pressure,
Lack of storage
Improper piping

33. Reduced Pressure - Energy Savings
Rules of Thumb
Compressor Efficiency Increases by 1% for every 2 psi reduction in operation pressure

34. Reduced Pressure - Benefits
Energy savings
Improves compressor efficiency
Reduced leak load
Reduces CA use at applications
Reduced pneumatic equipment fatigue
Increases equipment life

35. Goals for Reducing Pressure
How low should my system pressure be?
Rough rule of thumb, System Press = Min Press + 10
We have observed a large MFG facility with CA system at 75 psig.
This was done overtime by addressing system constraints such as adding storage, increasing pipe diameters etc.

36. Energy Saving Opportunities
There can be endless opportunities in a system.
It can take couple of hours to go through them all.
So, Let’s just look at the BIG hitters
In appropriate uses
Leaks
Pressure
Staging
Other opportunities
Air Drying
Storage
Filters
Heat Reclaim
These are things we look for when we have limited time with the client.

37. Staging This is one of THE most important opportunities Why?
Lets look at an example (worst case)
Compressor – Centrifugal with blow-off only
We just reduced compressed air demand by 50%
How much do we save ?

38. Staging
Centrifugal part load
How much do we save ? ZERO !

39. Staging System Part-Load with Multiple Compressors
Very Well staged multiple compressor system
Poorly staged multiple compressor system

40. Staging Fundamentals Points to remember
Constant speed compressors are only efficient at full loads
Operation at part loads should be minimized.
You NEVER* want multiple compressors at part-load
*Does not apply in special circumstances with centrifugal and VFD compressors
Eliminate (or minimize) blow-off in Centrifugal compressors

41. Complexities in Optimizing Staging
Need to understand
System air flow requirements
Compressor – full load efficiencies
Compressor – individual part-load performance
Effect of combination of different compressors within a system
How one staging sequence is different from the other
How ?
Metering the equipment is a start
Analysis of metered data
Need to apply knowledge to obtain
action items
Okay, Let’s not worry about complexities.
** This is where you may want to reach out for technical assistance.
Let’s look at a few case studies to understand the potential.

42. Case Study 1
Pre:
Two new 900-hp centrifugal compressors are operated in base trim manner
Project cost ~ $800,000
Both of them can modulate and then blow-off
Post:
Compressors are operated in parallel so that
Only one compressor blows-off first

43. Case Study 1 (Cont)
Savings ~ $50,000/year

44. Case Study 2
A facility has two compressed air systems that were put in place for two different systems
Pre
As often seen
Both systems were oversized
What's interesting is both systems operate at 95 psig.
Post
Combine the two compressed air systems
Facts:
Engineers like factor of safety;
Vendors like to sell larger compressors

45. Compressor Optimization: Case Study 2
Savings ~ 20%
In the new case only one compressor is part-loaded instead of two.

46. Case Study 3 Manufacturing facility wanted to save energy Pre Post
They thought VFD compressor is a good idea (it is, but..)
Pre
They bought a Oversized (215 hp) VFD compressor
Why ? Sales person recommendation ? Lack of analysis ?
Issue: the VFD could not trim
Used a 250 hp load/unload as the trim instead
Not good
Post
Bought appropriately sized (125 hp) VFD compressor
Compressor Cost ~ $150,000
And changed the control sequence

47. * Could have been achieved the first time if the VFD was sized right.
Case Study 3
Savings ~ 24%
* Could have been achieved the first time if the VFD was sized right.
Big Savings

48. Case Study 4 Multiple facilities with multiple compressors
Are more compressors better ?
Is a control system better ?
Is a VFD better ?

49. Case Study 4 1. Poorly Staged (Manual) - 8 similar compressors
2. Staged with VFD
(Pressure based)
- 8 different compressors
Facility 1
Facility 2
3. Very well staged. (Demand Based)
No VFD
- 8 similar but different size compressors.
Facility 3

50. Case Study 4 Most of the savings can be achieved by effective staging
Control systems are vital for optimization in large systems
A VFD compressor can help improve your part-load performance
Typically only one effective VFD is required per system
If sized correctly

51. Its time for the Recommendations
Summary
We discussed
Importance of compressed air
Why its an expensive resource
Different types of compressors and their controls
Reciprocating
Screw
Centrifugal
Largest Energy savings opportunities
In-appropriate uses
Leaks
Pressure
Staging
We looked at a few case studies
Its time for the Recommendations

52. Recommendations Pursue all the low-cost no-cost opportunities
In-appropriate uses
Leaks
Reducing pressure
Staging with available control systems
Consult experts to evaluate best strategy with available controls
Consult technical experts before Investing Capital
The last thing you want is invested capital and no savings.
New compressor installation
Control system upgrade

53. Abdul Qayyum “Q” Mohammed
Questions ?
Thanks for Listening!
Abdul Qayyum “Q” Mohammed
Additional Slides are available at the End for Interested Parties
x308

54. End Use: CA Diaphragm Pumps
Facilities use CA Diaphragm Pumps.
Needed for extremely corrosive or volatile fluids
However, in many cases diaphragm pumps are used for fluids that can be moved with a regular centrifugal pump
Motor Operated pumps use about
4x less energy

55. End Use: Dust Collector Purges
CA is used in dust collector for purges.
These purges can use significant amount of air if not optimized properly.
Control CA with solenoids to appropriately time purges
Bag house uses ~ 40% of system capacity

56. Distribution: Storage
Used to eliminate (or dampen) the variation of pressure within the system.
Particularly important in systems with load/unload compressors
Storage improves part load performance of a system with load/unload compressors
“Improving Compressed Air System Performance: A Sourcebook for Industry.” – US D.O.E, Nov 2003

57. Distribution: Storage (Cont.)
How much storage should I have ?
Rule of thumb 3 to 5 gal/cfm of compressor output
Actual requirement depends on fluctuations in CA demand and types of compressors

58. Optimize Compressed Air Drying
Appropriate drying technologies should be used
Common drying technologies in order of decreasing efficiency
Refrigerant Dryers
Cycling
Non-Cycling
Desiccant Dryers
Heat of Compression* (HOC)
Heated desiccant
Heated with Blower purge
Heated with CA purge
Heatless desiccant
* HOC dryers are more efficient than refrigerated dryers

59. Generation: Reclaim Heat
~ 80% of input energy is lost as heat
Heat can be used for various purposes
For space heating during winter
For process use throughout the year

60. Generation: Reclaim Heat
Example Installation

61. Generation: Compress Outdoor Air
Outdoor air is typically cooler than a mechanical room
Cooler air is denser hence easier to compress
Fraction savings ~ 2% per 10 F reduction
Note:
Savings are realized in oil free compressors only
In oil lubricated compressors the air is mixed with hot oil before compression. This eliminates savings.
Considerations should be made to avoid freezing temperatures

62. What's the benefit of Energy Savings?
We reduce emissions
Helps slow down global warming
Helps Protect Out planet
What are we talking about ?
Lets rephrase “What is MY benefit ?”