designing your compressed air system

8/3/2019 Designing Your Compressed Air System

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Compressed Air System Guide

Provided as a Service by Kaeser Compressors, Inc.

Designing Your CompressedAir SystemHow to Determine the System You Need



Your compressed air system is acritical plant utility. To functionproperly and cost effectively, it

must be carefully designed to fill thespecial needs of your applications. Six

basic elements—demand, compressedair quality, supply, storage, distribution,and control/management—must beevaluated and factored into final layoutconsiderations to give you optimumresults at maximum efficiency. All sixelements must work together for thesystem to reach top performance levels.

What Is Your CompressedAir Demand?Determining the true demand in yourcompressed air system can be difficultbut is a critical first step. Air demandoften fluctuates significantly; however, ifactual flow demand at any given time isknown, storage and distribution systemscan be designed to meet demandwithout installing additionalcompressors.

The most accurate method ofestablishing demand over time in anexisting system is to monitor the air flowusing a flow meter ( see chart, pg. 3).Flow meters can be installed at variouspoints in the system, but are typicallyinstalled in the main headers. Recordeddata, such as air flow and pressure, canbe evaluated to determine the flow

pattern. It is especially important to notethe peaks and valleys in demand andtheir duration.

Electronic data loggers offer aneffective means to track compressor

activity over time. While they don’t direct-ly measure as many system parametersas flow meters, they provide substantialinformation to make an accurate assess-ment of system dynamics.

For smaller, less complex systems,the ratio between loaded and unloadedcompressor running time (on-line/off-lineor start/stop times) can indicate averagedemand over a long period of time.

When establishing compressed airdemand for a new system, you must

consider operating pressure require-ments and the duty cycle of individualequipment.

Equipment using compressed air israted by the manufacturer for optimumperformance at a certain pressure andair flow. To design a compressed airsystem that delivers uniform pressure, itis necessary to ensure that all tools andequipment work efficiently within anarrow pressure range. If this cannot bedone, you have the option of operatingthe entire system at the higher pressureand regulating pressure down asrequired, adding a booster compressorto increase pressure for a particularapplication, or installing two independent

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Designing Your Compressed Air System

Air Flow MeasurementKaeser’s air flow measurement system uses mass flow meters to record the actual amount of compressed air being used at any given time. Flow meters can be inserted into compressed air piping without interrupting system production,and output standard signals to a recording device that collects the data for review.Your local Kaeser representative can establish an accurate air demand profile and start improving system efficiency with a few simple steps.

Air Demand AnalysisKaeser’s exclusive Air Demand Analysis (ADA) provides a complete picture of a compressed air system’s operation and performance. Highly accurate sensors and data loggers record flow, power consump- tion and pressure during normal operating conditions. Once the information is chart- ed and analyzed, Kaeser engineers make recommendations for optimizing the system.



air systems working at differentpressures.

Leakage and artificial demand oftenrepresent a significant portion of youroverall demand. All systems have leaks.Leakage can be measured in severalways while no pneumatic equipment isrunning: measuring the loaded runningtime of a compressor, timing thepressure drop of the receiver tank whileall compressors are stopped, or measur-

ing leakage at the point of use. Yourexisting compressed air demand willalso include artificial demand caused byexcess system pressure that does notincrease productivity. Artificial demandcan be reduced significantly by installinga regulator at the point of use or a flowcontroller at the beginning of thedistribution network.

Kaeser Compressed Air System Guide 3

What Air Quality Do You Need?Different applications require different levels of compressed air quality. Because the cost of producing compressed air goes up with each level, it is important to meet but not exceed the required air quality level. If different sections of your plant require different levels of compressed air quality, it is more economical to treat smaller amounts of compressed air for a particular application rather than the entire air supply.

This is a typical flow chart reading which can be used to determine actual demand and flow pattern in existing systems. Flow and pressure are inversely related, as can be seen at Points 1 and 2. Pressure drops below the desired low pressure set points of 100 psig to 90 psig at Point 3 because the system cannot deliver the needed flow at Point 4. This can be remedied by adding compressor capacity to supply the needed flow (hatched area), or more efficiently, by adding adequate storage capacity, or eliminating the peak demand.

Flow Chart: Existing Systempsig

Flow (scfm)

Maximum sustainable flow

System pressure (psig) 110 psig100 psig

90 psig

TIME

2

4

5

3

1

Average flow demand in new systems can be determined by examining operating pressure requirements, compressed air requirements, and the duty cycle of existing equipment.

The total required air delivery in this example is 16.82 scfm (11.6 scfm + 1.16 scfm + 1.74 scfm + 2.32 scfm). Since the optimum duty cycle of a screw compressor is 100% (although this may vary for other compressor types), the required screw compressor must have a free air delivery of at least 16.82 scfm at a gauge pressure of 110 psig to account for pressure differential in the compressor controls and other pressure losses.

Establishing Flow Demand In New Systems

Air Demand 5 scfm 12 scfm 8 scfm 14 scfmWorking Pressure 40 psig 90 psig 90 psig 90 psigNumber 2 1 1 1Utilization Factor 50% 25% 10% 20%Effective Air 2 x 5 x 0.5= 12 x 0.25 8 x 0.1= 14 x 0.2=Demand 5 scfm 3 scfm 0.8 scfm 2.8 scfm

Pneumatic Paint Spraygun Paint Spraygun Blowgun ScrewdriverEquipment @ 1.5mm flat jet @ 3mm flat jet @ 2mm

Total Demand: 5 scfm + 3 scfm + .8 scfm + 2.8 scfm = 11.60 scfmThe following should be added to Total Demand: for leakages +10% = 1.16 scfm

for errors +15% = 1.74 scfmas a reserve +20% = 2.32 scfm

Total Delivery: = 16.82 scfm

QualityClasses

0123456

SOLIDSMaximum Particle Size

(microns)

as specified0.115

1540—

QualityClasses

01234

56

MOISTUREDew Point

°C °F

as specified-70 -94-40 -40-20 -43 38

7 4510 50

OILLiquid and Gas

mg/m3 ppmw/w

as specified0.01 0.0080.1 0.081 0.85 425 21— —

QualityClasses

0123456


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What Are Your SupplyRequirements?Compressed air supply is provided byair compressors. Your compressed airsupply, utilizing sufficient storage andproper distribution, must meet your com-pressed air demand. If supply, storage,and distribution are not in tune,excessive pressure fluctuation will occur,resulting in increased operating cost andreduced productivity.

Most compressors are controlled byline pressure. Typically, a drop inpressure signals an increase in demand,which is corrected by increasedcompressor output. Rising pressure,indicating a drop in demand, causes a

reduction in compressor output.Compressors use various capacity con-trol systems to monitor these changes inpressure and adapt the air supply to thechanging air demand. One of the moreefficient is a load/no load control whichruns the compressor at full load or idle,accommodating the demand variations.

Total plant supply can be providedby either a single compressor or a multi-ple compressor installation which can becentralized or decentralized. Single

compressor installations are best suitedto smaller systems or systems whichoperate almost exclusively at full output.Multiple compressor installations offernumerous advantages including:application flexibility (the ability toefficiently adjust to shift demandvariations); maintenance flexibility; theoption of centralized or decentralizedoperation; floor space flexibility; andbackup capability.

How Much Storage Do YouNeed?Your compressed air storage systemconsists of all the compressed-aircontaining vessels in your compressedair system. Sufficient storage is criticaland represents available energy that canbe released or replenished at any timeas required.

The air receiver tank typicallymakes up the bulk of total storage

capacity. Because some compressorcontrols (start/stop and on-line/off-line)depend on storage to limit maximumcycling frequency at demands less than100% of supply, a properly sized receiv-er tank prevents excessive cycling.

A properly sized receiver tank alsoprovides sufficient storage capacity forany peaks in demands. During peakdemand periods, a poorly designedsystem will experience a drop inpressure as air in excess of systemcapacity is taken from the system.Because not all compressors in a multi-ple compressor system remain on-line atall times, the actual air supply at anygiven time can be less than the totalsystem capacity. During the timerequired to bring additional compressorcapacity on line, stored compressed aircan be used to prevent any pressuredrop in the system. The amount of stor-age capacity needed depends on theamount of excess demand in cubic feet,available pressure differential betweenthe compressor station and point of use,compressor start-up time, as well as thetime available to replenish storedcompressed air.

Flow controllers are also extremelyimportant. Installation of a flow controllerafter the receiver tank is essential forproviding additional compressed airwhen needed without downstream pres-sure fluctuations.The flow controllerbasically works like a precisionregulator, increasing or reducing flow tomaintain constant line pressure. It alsoprovides the necessary pressuredifferential between the receiver tankand the system to create storage without

changing system pressure downstream.

How To Determine The BestDistribution System?Your compressed air distribution pipingis your means for transportingcompressed air and represents your linkbetween supply, storage, and demand.

The ideal distribution system providesa sufficient supply of compressed air atthe required pressure to all locations

Sigma Air ManagerKaeser’s Sigma Air Manager is the ultimate in compressed air system sequencing, monitoring, and management. Combining the benefits of modern industrial PC technology with

Internet technology to provide unparalleled system control with real-time monitoring and HTML reporting. Optional software provides enhanced historical charting and reporting as well as remote access capabilities from virtually any location.



where compressed air is needed. A net-work of pipelines is used to supplydifferent locations with compressed air.The flow of compressed air in pipelines,however, creates friction and results inpressure drop. Pressure drop in thepipelines should, ideally, be no morethan 1 to 2 psi.

The following steps can be taken toreduce pressure drop:reduce the distance the air must betransportedreduce the friction through the pipesby increasing pipe size andeliminating unnecessary elbows,valves, and other flow restrictionsreduce the flow rate of air through thesystemselect smooth bore piping

minimize the drop in pressure acrossthe system componentseliminate leaks.

Friction loss is higher in longer pipesand in pipes with a smaller diameter. Aneffective way to reduce pressure drop isto use a loop system that provides two-way flow at any point in the system, cut-

ting the flow in each pipe path in halfand reducing compressed air velocity.

Even more important than pressuredrop caused by fr iction, however, is thatresulting from the system componentsthemselves.This drop typically rangesfrom 5 to 25 psid and can be controlled,through careful equipment selection andproper maintenance.


Single vs. Multiple Compressors

Multiple compressor systems offer several advantages over single compressor systems. Among these are the ability to adjust to variations in shift demand, and to apply computer-based air system management, providing proper flow and pressure with the highest overall efficiency.

Figure 1 shows the optimized response to fluctuating demand. Five compressors are operated by a computer-based air system controller which selects the minimum number of compressors needed to satisfy demand. This set-up offers significant operating cost savings as com- pared to a single compressor installation (Figure 2), while also increasing system reliability by providing back-up in case of malfunc- tion or compressor maintenance requirements.

Computer BasedAir System

Management

1000

900

800

700

600

500

400

300

200

100

$100,000

$75,000

$50,000

$25,000

Air Flow in cfm

12:00 am 4:00 am 8:00 am 12:00 pm 4:00 pm 8:00 pm 12:00 am

12:00 4:00 8:00 12:00 4:00 8:00 12:00am am am pm pm pm am

1

2

3

Figure 1. Optimized Response to Fluctuating Demand Figure 2. Operating Cost* Savings

1) Blue line represents five 200 cfm compressors

controlled by a sequence controller2) Orange line represents one 1000 cfm compressor with

modulation control3) Area in between represents savings potential

*$0.30 / 1000 cfm

Compressor 5Off

Compressor 5Off

Compressor 4Partially loaded

Compressor 4Off

Compressor 5Off

Compressor 4Off

Compressor 3Off

Compressor 2Off

Compressor 1

Loaded

Compressor 1

Loaded

Compressor 1

Loaded

Compressor 2Loaded

Compressor 2Loaded

Compressor 3Loaded

Compressor 3Off


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Optimized Compressed Air System This diagram depicts multiple compressors controlled by a system controller, followed by clean air treatment and a storage air receiver with a flow controller. This setup ensures optimal use of energy.

What Are Some ImportantLayout Considerations?The exact layout of your compressed airsystem will depend on the interplay ofthe system elements discussedpreviously: air demand, air quality, airsupply and storage requirements, anddistribution considerations.

Although information on com-pressed air generation and use is widelyavailable, most compressed air usersdesign and install the distribution system

themselves. Only experienced compres-sor professionals can provide theinformation necessary to design a trulyeffective system because of thecomplexity and the number of designcriteria involved. Any customer wantingto make full use of the compressed airthat is available should consult with oneof these companies.

Important installation considerationsare: adequate ventilation, foundationrequirements, compressor room require-

ments, and piping materials.There are five basic methods of

ventilation: natural ventilation; forcedventilation with an exhaust fan; ductedventilation to the outside without adamper for air recirculation (suitable forambient temperatures above 32°F); duct-ed ventilation with circulating air damperfor winter operation, mixing warm air withcold intake air (suitable for intaketemperatures below 32°F), or an exhaust

air duct vented to the outside during

summer, and space heating duringwinter.

There are two ways to ventilate aroom with multiple compressors. Oneway is to add the horsepower of all thecompressors and ventilate the room as ifa single compressor of that horsepowerwere in the room. A better way, is to pro-vide each compressor with a separateintake air opening. To determine the sizeof the intake opening, add up the drivepower of all the compressors and deter-mine the cooling air flow and therequired intake air opening for the totaldrive power. Divide the area of this open-ing into smaller intakes, proportional tothe relative size of the compressors.Note that in general, no intake ducting isrequired.

Foundation requirements depend onthe size and type of air compressor.Packaged rotary and small reciprocatingcompressors (25 hp or less) can beinstalled without any special foundation.For larger reciprocating compressorsextensive foundations are required.

Special foundations are not requiredfor base mounted rotary screw compres-sors as long as the compressor featuresvibration insolation mounts.

Engineering ExpertiseWith decades of combined experience in compressed air systems and design,Kaeser’s highly trained engineers provide expert applications assistance. From complex installations and challenging environ- ments to facilities with limited space,Kaeser can design and lay out a system to meet the specified requirements for performance and reliability.

Kaeser uses state-of-the-art CAD systems to lay out the proposed system .Plus, our three-dimensional, virtual walk- through tour of the proposed system allows the end user to experience the complete installation. Virtual modeling allows all options to be considered.Variables such as distance, diameters,equipment arrangement, location,accessories and connections can be reviewed and modified, if necessary, prior to installation.



What are the InstallationConsiderations?Compressors, especially medium orlarge compressors, should be installedin a special compressor room that isclean, dust-free, dry, and cool. Ifpossible, the compressor room shouldbe located in the north side of the build-ing, with all heat-dissipating pipes andmachinery being well insulated. To avoidfrost and corrosion from condensateaccumulation, the temperature in theroom should not fall below 40°F.Compressor units should be easilyaccessible and lighting should beadequate for maintenance andinspections. Because air-cooled

compressors require sufficient coolingair flow, the temperature in these roomsshould not exceed 95°F. Forcompressors with drives up to 25 hp,natural ventilation is generally sufficient,but larger compressors and smallercompressor rooms will require forcedventilation. Dryers are another item oftenoverlooked. Proper placement and/orcooling ducts/fans may be required forproper operation and long service life.

There are several ways to install

compressed air lines. They can beinstalled in channels and shafts, whichwill avoid any construction obstacles.

However, this arrangement is more com-plicated and expensive than othersolutions and may make access topiping difficult. Burying the air linesunderground has the advantage of lowcost, but makes repairs and

maintenance extremely difficult and alsorequires rust-proof material. Anotheroption is installing compressed air linesabove the ground with supports andsuspensions. This relatively low-costoption can present constructionobstacles. For outdoor installations, pipefreezing can only be avoided if thecompressed air has been dried to apressure dew point below the lowestoutside temperature.

Piping is critical to a compressed airsystem’s reliability and efficiency. Beforelaying the pipes, material choice, dimen-sions, layout, conditions on-site, andfuture needs must all be considered.Piping must be rugged enough for theexisting work conditions, provideminimum possible pressure loss andleakage, and be easy to maintain.Compressed air lines can be eitherblack piping, galvanized, copper, orstainless steel. Each has advantagesand disadvantages which should becarefully evaluated.


Rules of Thumb• Every 2 psi pressure drop costs 1% of

compressor horsepower in efficiency

• Compressors and dryers should belocated in a dry, clean, cool (40 to100°F), and well ventilated area. Allowenough room around the compressorand air treatment equipment for proper

air flow and maintenance accessibility.• Locate one air receiver near the com-

pressor to provide a steady source ofcontrol air, additional air cooling, andmoisture separation. A large storagereceiver should be located down-stream of the dryer and filters to actas a buffer for demand surges andcontrolled by a flow controller

• Air distribution piping should be ofsufficient size to minimize pressuredrop and allow for expansion.

• Piping in a loop system isrecommended with all piping sloped toaccessible drain points. Air outletsshould be taken from the top of themain line so that possible moisturewill not enter the outlet.

• The minimum amount of storage rec-ommended is one gallon per cfm ofcapacity. This should be increased to4-10 gallons per cfm of capacity forsystems with sharp changes indemand.

• Under average conditions, every 100cfm of air compressed to 100 psigproduces 20 gallons of condensate perday which needs to be treated.

Pressure DropTypical Initial Pressure

DropsInitial Replace at :

Separator 1 psid N/A

Filter 1 psid 10 psid

Refrigerator air 2 to 6 psid *dryer

Desiccant air 2 to 5 psid *dryer

*Some dryers have built-in filtration sys-tems. These filter elements must bereplaced when the pressure differentialreaches 10 psid, or earlier to save energy.

Limiting pressure drop caused by system components is crucial for the efficiency of the whole system. Evaluate initial pressure drop carefully when selecting equipment and maintenance intervals.

Pressure drop results from the friction produced by the flow of compressed air in pipelines and from the system components themselves.

Main Pipe work 1.0 psi

Distribution Pipe work 0.5 psi

Connecting Lines 0.5 psi

Regulator Lubricator 5 to 8 psiand hose

Max 15 psi

Consumer pressure 85 psiCompressor controls 10 psiPressure at compressor 110 psi

1

1

22

3 3

4 44

3



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Corporate Headquarters: Kaeser Compressors, Inc.P.O. Box 946Fredericksburg, VA 22404(800) 777-7873Fax: (540) 898-5520www.kaeser.com

Mission Statement

We strive to earn our customers’ trust

by supplying high quality Kaeser aircompressors, related compressed air

equipment and premium blower

systems. Our products are designed for

reliable performance, easy

maintenance, and energy efficiency.

Prompt and dependable customer

service, quality assurance, training,

and engineering support contribute to

the value our customers have come to

expect from Kaeser. Our employees

are committed to implementing andmaintaining the highest standards of

quality to merit customer satisfaction.

We aim for excellence in everything we

do.

Our engineers continue to refine

manufacturing techniques and take full

advantage of the newest machining

innovations. Extensive commitment to

research and development keeps our

products on the leading edge of

technology to benefit our customers.

Compressed Air System Glossary

Air flow:Volume of free air in cfm.

Air receiver tank: Tank used for compressed airstorage.

Artificial demand: Additional air consumptioncaused by excessive system pressure.

Capacity: The amount of air flow delivered orrequired under some specific conditions. May bestated as acfm, scfm, or cfm FAD.

Cubic feet of air per minute (cfm): Volumedelivery rate of air flow.

Cubic feet of air per minute, free air (cfmFAD):cfm of air delivered to some specific pointand converted back to ambient air (free air)conditions.

Actual cubic feet per minute (acfm): Flowrate of air measured at some reference point andbased on actual conditions at that reference

point.Inlet cubic feet per minute (icfm): cfm flow-ing through the compressor inlet filter or inletvalve under rated conditions.

Standard cubic feet per minute (scfm):Flow of free air measured at a reference point andconverted to a standard set of referenceconditions (e.g., 14.5 psia, 68°F, and 0% relativehumidity).

Demand: Flow of air under specific conditionsrequired at a particular point.

Discharge pressure, rated: Air pressure

produced at a reference point.Discharge pressure, required: Air pressurerequired at the system inlet.

Dual control: Load/unload control system thatmaximizes compressor efficiency. Compressor isnormally operated at full load or idle, and isstopped and restarted automatically depending ondemand.

Duty cycle: Percentage of time a compressor unitcan operate at full load over a thirty minute period.

Flow meter: An instrument used to measure flowrate, pressure, vapor, or gas flowing through apipe.

Load factor: Ratio of the average compressorload to the maximum rated compressor loadduring a given period of time.

Modulating control: Control system which willrun the compressor at reduced output toaccommodate demand variations. Running a com-pressor at less than full load results in a drop incompressor efficiency and thus an increase inoperating costs.

Pressure: Force per unit area.

Pounds per square inch (psi): Force per unitarea exerted by compressed air.

Pounds per square inch absolute (psia):Absolute pressure above zero pressure.

Pounds per square inch gauge (psig):Pressure difference between absolute pressure(psia) and ambient pressure.

Pounds per square inch differential (psid):Pressure difference between two defined pointsin the system.

Pressure dew point: Temperature at whichwater will begin to condense out of air at a givenpressure. To ensure that no liquid water is present,the pressure dew point must be less than the low-est temperature to which the compressor air willbe exposed.

Pressure drop: Loss of pressure in acompressed air system due to friction or flowrestriction.

Conversion Formulas

Multiply by To Obtain

Volume: cubic feet/minute 0.472 liter/second

gallons 0.134 cubic feetliters/minute 0.2642 gallons/minutecubic meters 35.315 cubic feet

Pressure: inches mercury 0.4912 psiinches water 25.4 mm waterpsi 27.68 inches waterbar 14.504 psi

Density: pint water 1.042 pounds watergallon water 8.336 pounds waterpounds water 7000 grains water

Power: horsepower 0.7457 kilowattshorsepower 2544.43 Btu/hour

Temperature: degrees Fahrenheit (degrees-32) x 0.556 degrees Centigrade

designing your compressed air system

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