best practice guide compressed air

7/27/2019 Best Practice Guide Compressed Air

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Energy Efficiency

Best Practice Guide

Compressed Air Systems

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Best Practice GuideCompressed Air Systems

Table of Contents i

1 Introduction 4

2 What are the business benefits of compressed air efficiency? 5

3 What is your opportunity? 6

4 Solution 1 Improve the efficiency of your existing system 7

4.1 Step 1: Review air demand 74.2 Step 2: Reduce leakage 104.3 Step 3: Fix pressure drop 114.4 Step 4: Review air receivers 124.5 Step 5: Maintain separators, ilters, dryers and valves 134.6 Step 6: Select a compressor 134.7 Step 7: Measure the improvement 17

5 Solution 2 Design a new system 18

5.1 Establish air demand (quantity and quality) 185.2 Design your piping and ittings 185.3 Select and locate air receivers 185.4 Select dryers, separators and ilters 195.5 Locate inlet and discharge air outlet 205.6 Select a compressor and control system 20

6 Selecting a service provider 21

6.1 Questions to ask service providers 216.2 Database o compressed air service providers 21

Appendix A Compressed air system overview 22

Appendix B Methods for estimating compressor energy consumption9 23

Appendix C Measuring leaks 24

Appendix D Cost savings from the installation of a DDS system 25

Appendix E Glossary 26

Appendix F Further reading/references 27

Contents


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Table of Contents 3

Figure 1: Compressor costs over a ten-year liecycle 5Figure 2: Compressed air usage and potential savings or the typical compressed air user 5Figure 3: Compressed air usage and potential savings or the typical compressed air user 9

Figure 4: Single main pipe layout with branch lines 11Figure 5: Example ring main with take-o points 11Figure 6: Power losses in various diameter pipes 12Figure 7: Graph o a load proile suitable or a ixed speed and variable compressor setup 15Figure 8: Typical power curve o a compressor using a load/unload control system 15Figure 9: Typical perormance o rotary oil lubricated compressors with dierent control systems 16Figure 10: Typical compressor perormance graph 23

List of Figures

Table 1: Compressed air use and substitution 7Table 2: Air quality classiications 8Table 3: Air leakage, wasted energy and cost or equivalent hole diameter 10Table 4: Advantages and disadvantages o air compressor types 14Table 5: Annual energy and cost savings with reduced compressor inlet temperature 20Table 6: Cost savings rom the installation o a DDS system. 25

List of Tables


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Introduction 4

This document is a step-by-step guide to improvingenergy eiciency in compressed air systems andachieving best practice. By ollowing this guide, you

will be able to determine what changes can be madein order to reduce operating costs, improve theoperation and perormance o equipment and improveenvironmental outcomes.

The guide has been developed to lead decision makersand service providers through system changes; it is notintended to be a thorough technical guide. Reerencesor more detailed technical inormation are provided.

1 Introduction


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What are the business benefits of compressed air efficiency? 5

Despite the act that they are essential or manybusinesses, compressed air systems are otenignored until something goes wrong with them, or the

compressors ail to keep up with rising air demand.Compressed air systems use up to 10% o totalindustrial electricity use in Australia, so it makes senseto look at their energy cost. Figure 1 illustrates the costo a typical compressor system over a 10-year liecycle,showing how important energy costs are to the overallcost o a system.

Figure 1: Compressor costs over a ten-year liecycle1

With 73% o the cost o a compressor due to energy

use, signiicant cost savings will be made by improvingenergy eiciency, as well as the added beneits oimproving the perormance o your system and reducingyour organisations carbon ootprint.

Energy eiciency will also increase the proportiono compressed air that is used or production andminimise unnecessary wastage, again resulting in

signiicant cost savings. An example o just how muchdemand on the compressed air system can be wastedis shown in Figure 2 below.

Figure 2: Compressed Air Usage and Potential Savingsor the Typical Compressed Air User.2

2 What are the business benefits

of compressed air efficiency?

Energy cost

73%Capital cost

18%

Maintenancecost 7%

Installationcost 2%

Production

demand 73%

Leaks 19%

Artificial

demand 16%

Artificial

demand 6%

System

inefficiencies 8%


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What is your opportunity? 6

Delivering the best outcome or your business requiresa whole systems approach to the design, installation,operation and maintenance o your compressed

air system.(Reer to Appendix A or a compressed airsystem overview).

Deining the limitations o your current compressedair system is the key to inding the best solution toachieving energy eiciency or your business:

CanImakemysystemmoreefficient?

DoIneedanewcompressor?

HowdoIexpandmyexistingsystem?

WhatdoIneedtoknowtoinstallanewsystem?

This guide oers step-by-step solutions to help youidentiy opportunities to implement best practice toachieve energy eiciency o your compressed airsystem.

Solution1:Improvetheefficiencyofyour

existing system

Do you have a compressed air system that is ulilling

needsbutcouldrunmoreefficiently?Thisprocessmay only involve a small investment but can providesignificantenergysavingsandcosts.Isyourexisting

systemstrugglingwiththedemand?Doyouneedto

upgradeyouraircompressor?Thisprocesswillalso

help in selecting the appropriate compressor or yourneeds, which could well be smaller and cost less thanyou originally thought.

Solution2:Designanewsystem

Are you planning a brand new compressed airsystem?Thisprocessoutlinesthestepsrequiredto

ensure you achieve excellent design and to help youunderstand where to spend your valuable capital.

Are you expanding your plant, workshop or actoryand need to ensure that your compressed air systemwillworkeffectively?Thiswillinvolveelementsof

both solutions. Firstly, ensure your existing systemis running eiciently (Solution 1) and secondly, iyour system needs to be expanded, design the newcomponents (Solution 3). Following this process willensure that you are not wasting money purchasingmore than you actually need. Additionally, inormationgained rom reviewing eiciency may guide the

selection and design o the new components othe system.

3 What is your opportunity?


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Solution 1 Improve the efficiency of your existing system 7

This solution irstly ocuses on improving the eiciencyo usage, distribution, storage and treatment ocompressed air beore considering the compressor

itsel.

4.1 Step 1: Review air demand

Beore any improvements to your compressed airsystem can be made, you should irst determine howit will be used and which aspects need improving byreviewing the air demand on the system.

4.1.1 Inappropriate uses

Compressed air is oten used or jobs because o itsavailability and because an alternative would require

higher capital cost. Compressed air is a very expensiveorm o energy and the associated running costsoten mean the overall cost is more expensive thanalternatives. Consider using alternative equipmentwithlowerrunningcosts.However,thereareoften

very good reasons or using compressed air poweredequipment. Careully consider the advantages anddisadvantages when making these substitutions, suchas the weight o tools or the saety risks o electric tools.Table 1 illustrates some examples o inappropriate useso compressed air, along with some solutions.

Table1:CompressedAirUseandSubstitution3

Compressed Equipment SolutionsAir Use Used

Blowing Nozzle/gun Airknife,Inductionor Cleaning nozzle, low

pressure blower,broom/brush

Cooling Cooling Air conditioninginduction systems,system chilled water, resh

air ventilation, ans

Drying o water Nozzle/gun Solenoid control,on product air knie, induction

nozzle

4.1.2 Current and future uses

Compile a list o (i) all the equipment that currently usescompressed air and (ii) equipment that is planned to

beinstalledthatwillusecompressedair.Includethetotal number o all tools or equipment o the same type.Determine the requirements or each pieceo equipment:

Maximumairpressure(inkPa)

Identifythehighestmaximumpressurerequired

by your system. This is the pressure that shouldbe available as your supply pressure. Any less andyour equipment may not unction properly; any moreand the system is running at a higher pressure thanrequired and costing you money.

Averageflow(inL/s)

Add the average lows o all equipment on yoursystem. This value indicates the average lowrequired o your air compressor. Although the actualdemand luctuates above and below this value, anyrapid increases in this demand can be met by thestored capacity in the air receivers. Thereore, this isthe low that your compressor should be capable oproducing continuously.

Airquality(pressuredewpointformoisture,

concentrationlimitsfordirtandoil)

Depending on your business, you may have allequipment needing the same air quality or havea range o air-quality requirements. A simpleclassiication o air-quality levels is provided inTable 2.

4 Solution 1 Improve the efficiency

of your existing system


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Table2:AirQualityClassifications4

Air Quality Applications

Plant Air Air tools, general plant air.

InstrumentAir Laboratories,paintspraying,powder

coating, climate control

Process Air Food and pharmaceutical processair, electronics

BreathingAir Hospitalairsystems,divingtankrefill

stations, respirators or cleaning and/

or grit blasting

Ifmostofyourequipmentuseslow-qualityairwhileyou

have a ew pieces o equipment that require high-qualityair, such as breathing air, then consider moving thatequipment on to a point o use system with a muchsmaller compressor and dryer. This will save on energycosts, as you will be using less energy in treating the airor your entire system.

4.1.3 How much energy is your compressor using?

Estimating how much energy your compressor is

using is relatively easy. Two methods are described inAppendix B.

4.1.4 System load profile

A system load proile shows the demand on thecompressed air system over time (load is another termfordemand).Itisimportanttomeasureandanalyse

the system load proile i you are to eectively improvethe perormance and eiciency o any compressedair system.

Measuring the profile

To obtain the load proile, the airlow rom thecompressor must be measured at various pointsovera periodoftime.Itisalsopossibletomeasure

the system pressure and the power drawn by thecompressor and dryer at the same points in timein order to see how the low, pressure and powerconsumed by the system changes over time. Thisproile should be obtained over a typical productioncycle so that demand on the compressed air systemcan be seen at all stages o the production cycle.For example, a seven-day period that is not part oa holiday season might be a typical production cycle.

Ideally,theloadprofileshouldbemeasuredbyusing

low meters on the main compressed air branch linesand the low recorded at regular intervals by a datalogger. Electronic pressure metering on the mainsystem lines and power metering or the compressorand dryer will enable you to look at all aspects oyour systems perormance and better diagnose anyproblems.However,settingupthisextentofmetering

is a time-consuming process that requires technicalknowhow.Ifyoudonothavetheseresources,you

could use a compressed air service provider to assistby conducting an air audit (reer to Section 6 Selectinga service provider) or you could use a less vigorousmethod o determining the load proile.


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There are a number o ways to determine how yoursystem is using compressed air. Power metering orthe compressor will indicate the demand over time.The control system or your compressor may be start/stop, load/unload or it might run on a variable speeddrive.Inallcases,bylookingatthepowerusageover

time and identiying when the compressor loads andunloads, you can get a rough idea o when the peakdemand times are.

Additionally, i you can obtain a pressure-low curveor your compressor (these are usually available romthe manuacturer) and your compressor has an outletpressure gauge, you can determine the low. Recordingthe pressure at various times will enable you to developa plot o low over time, just as low metering wouldhave done. You can also gain an understanding odemand by looking at the demand side rather than thesupplyside.Ifthedemandcyclesoftheequipment

that account or the largest use o compressed air arerelatively short, it might even be possible to observethem yoursel, noting how long and at what times theyareusingcompressedair.Inthisway,youcanbuilda

rough plot o the largest uses o compressed

air in the load proile.

Analysing the profile

Once you have obtained some inormation or a loadproile, you can identiy how your compressed airsystem is being used. Figure 3 illustrates a typicalair demand proile, showing the air demand in m3/hr(normal temperature and pressure) over time. The redlines indicate that, while the peak demand is 980 m3/hr, the average demand is only 190 m3/hr. The act thatthe average demand is only a small raction o the peakdemand is a sign that the compressor is oversized, not

running at its highest eiciency point and most likelywasting energy. A smaller compressor could be usedwith a larger air receiver and the peak demand couldstill be supplied to the system. For added beneit, tryto improve the demand spikes as well.

With a proile such as this, you can identiy whichequipment is responsible or various eatures o theproile. You can also determine the maximum demandor each piece o equipment and how this comparesto the maximum total load as a percentage. This is aneective method o ranking your equipment in terms otheir compressed air consumption, or signiicance tothe compressor system.

You may also be able to obtain a graph o the powerconsumption o your compressor and/or dryer overthe same period o time as the load proile above.By combining these two graphs, you could see howthe eiciency o the system changes over time.

A key perormance indicator that can be used tomonitor the ongoing eiciency o the system is kWper L/s. The lower the kW/L/s, the more eicient thesystem is. This proile is valuable in identiying the timesat which your compressor may be running at part loadand so increasing your costs per unit o air demand.Taking an average value o this graph will give you youraverage eiciency in kW/L/s.

Figure 3: Compressed Air Usage and Potential Savingsor the Typical Compressed Air User. 2

Optimising the profile

The compressed air system may be more eectivei the proile is lattened or, in other words, i the largeswitching loads can be operated at dierent timessothatthedemandismorestable.If,forexample,

a purging unction can be run while a major line orpiece o plant is not running, the load proile will bemore constant.

Insomecases,itmaybemoreefficienttoplacecertain

loads on a separate system. For example, i thereis one load that only operates ater hours while allothers operate during the day, it could be placed ona separate (point o use) compressor so that the maincompressor system can be shut down and not have torun ineiciently at part-load. Although there are now twocompressors, the overall eiciency o your two systemswill be greatly improved.


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Solution 1Improvetheefficiencyofyourexistingsystem 10

4.2 Step 2: Reduce leakage

Leaks can waste up to 50% o the compressed airproduced by your compressor. Reducing leakage isa key measure that can be used to improve energyeiciency. Table 3 provides an indication o the cost oleaks.

4.2.1 Measuring leakage

Ifthereisaflowmeterinstalledimmediatelyafteryour

air compressor or receiver, measuring leakage is assimple as reading this low meter when all compressedair equipment is turned o and all outlet valves areclosed. Similarly, i you obtained data or the load proileas outlined in the previous step, then you simply needto ensure that you record data or the system load whileall equipment uses o compressed air are turned o.Ifflowmeteringisnotavailabletoyou,therearetwo

methods that may be used to determine systemleakage. These methods are detailed in Appendix C.

4.2.2 Finding leaks

Leaks can occur in any number o places, such as:hosesandcouplings

pipesandpipejoints

pressureregulators

valvesleftopen

equipmentleftrunningornotisolated

threadedfittingsnotproperlysealedwiththread

sealant or dirty.

Apart rom listening or leaks, which can be deceptivelyunreliable in a noisy environment, there are two keyways to ind compressed air leaks. The simplest is tobrush soapy water over areas suspected o leaking andlook or bubbling. Although cheap and simple, this canbe a very time-consuming process. The second isultrasonic leak detection. Ultrasonic detectors canpinpoint leaks very accurately and quickly by detectingthe signature ultrasound signals o high-pressure leaks.They can operate in noisy plant environments, so

equipment does not have to be turned o. While sometraining is required in their use, operators can becomecompetent ater less than an hour.

Some compressed air service providers will be able toperorm ultrasonic leak detection programs or you iyou do not have the resources yoursel. Once leaks areound, it is very important that you keep track o themeectively. The best way is to tag the leaks with brightcolours as soon as you ind them. Use a site map torecord the location o the leak. Give each leak a gradingor the amount o air loss through it, perhaps betweenone and ten. Record this grading on the tag itsel andon the site map. The leaks with the highest prioritygrading should be ixed irst.

One Australian company successfully implementeda leak management program with a compressed airparts supplier.

The supplier attended site on a monthly basis duringregular shut downs, reviewing and repairing simpleleaks on the spot. Larger leaks were tagged andrepaired at a later date.

Table3:AirLeakage,WastedEnergyandCostforHoleDiameter5

EquivalentHole Quantityofair Annualenergy Annualcost

Diameter (mm) lost in leaks (L/s) waste (kWh) of leaks ($)

0.4 0.2 133 13

0.8 0.8 532 53

1.6 3.2 2128 213

3.2 12.8 8512 851

6.4 51.2 34040 3404

12.7 204.8 136192 13619


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4.2.3 Fixing leaks

Fixing leaks oten involves tightening or replacingconnections, ixing holes in pipes or repairingdamaged equipment such as pressure regulators.Oten, simply cleaning and applying thread sealantto ittings will help. Replacing equipment will benecessary in some situations.

4.2.4Leakmanagementprogram

Once leaks are regularly being repaired, theimplementation o practices to avoid leaks gettingout o control will ensure that the compressed airsystem remains eicient. These practices can include:regularinspectionandmaintenanceofcompressed

air equipmentregularinspectionofairpipes,bendsandvalves

ensuringthatallairlinesareproperlysupportedsoas

not to cause leaks through excess stressremovingorproperlyisolatinganyunusedpartsof

the pipe distribution network or unused pressureregulators

implementingaleakreportingprogramamongstaff.

Making sta aware o the cost to the business rom

leaks and encouraging them to actively report leaks isan important step, as they are always present on theshop loor and are best placed to notice any changes.

4.3 Step 3: Fix pressure drop

Pressure drop is another major cause o ineiciency incompressed air systems. Pressure drop is the decreasein pressure between the compressor and the point ouseofthesystem.Itoccursduetothelossofenergy

rom the compressed air as it lows through the system.

A certain amount o loss is inevitable rom somecomponents such as ilters, dryers and separators.However,therearewaystoensureaminimalpressure

drop is obtained. A compressed air system that isperorming well should have a pressure drop o lessthan 10% between the compressor outlet and allpoints o use.

4.3.1 Measuring pressure drop

Using a calibrated pressure gauge, measurethe pressure at the compressor outlet and ateach pressure regulator, with the regulators set to

maximum pressure. Determine the lowest pressurerecorded ater measuring at all the regulators.

Pressure drop = compressor discharge lowestavailable pressure at regulatorsThe larger your pressure drop, the more ineicientyour system is, as the compressor must work harderto obtain a higher pressure while only a lower pressureis being utilised.

4.3.2 Valves

The two common types o valves that are used incompressed air systems are ball valves and gatevalves. Both types have their place depending ontheir application. Ball valves are useul or isolatinglow and have the lowest pressure drop o the two,while gate valves are useul or controlling low.

4.3.3Pipinglayout

There are two common air distribution layouts asingle main system as illustrated in Figure 4 and a ringsystem as illustrated in Figure 5. A ring main setup isconsidered best practice, however, a single main setupmay also be useul in many applications. Try to restrictyour compressed air system to these layouts to ensurethat they maintain eiciency. The more bends you have inyour piping network, the higher the pressure drop will be.

Figure 4: Single Main Pipe layout with Branch Lines.6

Figure 5: Example ring main with take-o points.7

Compressed

air source

Additional take off points

Additional take off points Main point

of use

Compressorhouse

Processring main

Workshopring main

Paint shopring main


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4.5 Step 5: Maintain separators,ilters, dryers and valves

Nearly all compressed air systems have some level oair treatment to remove oil, water vapour and particulatematter rom the compressed air stream.

A compressed air system will usually contain:Aseparatortoextractlubricantoilfromtheairstream.

A separator is oten part o a packaged compressor.Adryertocondenseandextractwatervapourfrom

the air.Afiltertoremovecontaminants.Often,thereisafilter

itted to the inlet o the air compressor.

The level o quality required by your system dependsupon the application. For example, ood-processingapplications will require a very high air quality, whilea mechanics workshop will require a lower standard.Treating your compressed air to a higher quality thanis required wastes energy and may also result in highermaintenance costs.

4.5.1 FiltersRegularly check and replace ilters. Blocked ilters willcause a signiicant pressure drop and so waste energy.Gauges can be installed that measure the pressuredrop across the ilter and indicate when a new ilteris required.

4.5.2 Dryers

Dryers are oten an essential part o the system.There are three main types o dryers: rerigerant,membrane and desiccant. Fitting rerigerant anddesiccant dryers with control systems makes it possible

or the dryer to match its energy use to the air demandat that time, thereore reducing energy usage. Whilstdesiccant systems use no direct electricity, unlikererigerant systems, they use compressed air to purgethe desiccant, thus still using energy to operate.This needs to be included in any comparison o energycosts between dryer systems. Dessicant dryers willoten purge a set volume o air on a regular requency,despite the actual low through the dryer at that time.It ispossibletoretrofitdessicantdryerswithdependent

dewpoint switching (DDS) controls.

This system will measure the dewpoint within thedryer and only purge when it is required, thereorereducing the amount o wasted compressed air. For atypical system using a 55kW screw compressor and adessicant dryer, the installation o a DDS system couldsave up to 60% o annual operating costs o the dryer.Reer to Appendix D or a breakdown o this example.

4.5.3 Drain valves

Replace manual, disc and timed drains with newelectronic level sensing drains to reduce the amounto waste. Drain valves are itted on equipment in whichwater condenses, such as ater-coolers, receivers,dryers and ilters. There are various types, but they allrelease condensed water rom the equipment. Thelonger these drains remain open, even partly open, themore compressed air is lost rom the system. Electroniclevel sensing drains help to optimise the time that drainsare open or.

4.6 Step 6: Select a compressor

Optimising and upgrading your compressor should be

the last consideration when looking at improving theeiciency o your existing compressed air system. Makesure that you have ollowed Steps 15 irst to maximiseusage, distribution, storage and treatment ocompressed air.

4.6.1 Compressor types

Reciprocating compressors

Reciprocating compressors work through the actiono a piston in a cylinder. Pressure can be developedon one or both sides o the piston. They are usually themost expensive to buy, install and maintain, and require

large oundations due to their size and the vibrationsthey cause. Despite these disadvantages, reciprocatingcompressors have their uses. They are good or high-pressure applications (13 bar pressure and above) andor high air quality applications. They are also the mosteicient or quite small applications (in the 14 kW range).

Screw compressors

Screw, or rotary, compressors use two meshing helicalscrews, rotating in opposite directions at high speed,to compress air. These compressors are usually thelowest cost to purchase and install. They lose eiciencyrapidly at part load unless variable output compressorsare used.


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Vane compressors

Vane compressors have a rotor with steel sliding vaneswithin an eccentric housing. The vanes orm pocketso air that are compressed as the rotor turns until anexhaust port is exposed. Vane compressors havesimilar energy eiciency to screw compressors, butoten have better air quality.

Centrifugal compressors

Centriugal compressors use high-speed rotatingimpellors to accelerate air. To reach operatingpressures, several impellor stages are required.They have relatively low installation costs, but areexpensive to buy because they are precision machines,however, they are generally economical in large sizes,in the 200 kW and above range. They are eicient downto around 60% o their design output, below which theyhave little turndown in their energy consumption.

Table4:AdvantagesandDisadvantagesofAirCompressorTypes2

Compressor Advantages Disadvantages

Reciprocating Suitableforhighpressures Highnoiselevels

Efficiency: Canberelativelysmallsize Highmaintenancecosts

7.8 8.5 and weight Suitable or smaller systemskW/m3/min Smaller initial cost Requires strong oundation Simplemaintenance Highoilcarryoverwhenworn

proceduresEicient multi-stagecompression available

Screw Simpleoperation HighenergyuseEiciency: Lower temperatures Low air quality6.4 -7.8 Low maintenancekw/m3/min Quiet

CompacVibration reeCommercially availablevariable speed units withrelatively good turndown.

Vane Simple operation Limited range o capacity.Lower temperatures Low air qualityQuiet

Low maintenanceCentrifugal EnergyEfficient Highinitialcost

Efficiency: LargeCapacity Inefficientatlowcapacity

5.8 7 Quiet Specialised maintenancekW/m3/min Highairquality Onlywater-cooledmodels

available


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4.6.2 Using multiple compressors

Depending on your load proile, the addition o another(dierently sized) compressor may deliver a moreeicient outcome than replacement. For example,i your load proile contains a certain level o constantdemand with a small amount o luctuating demand andyou currently have one, ixed-speed screw compressor,you could add a variable screw or vane compressor toprovide or the luctuating demand while the ixed speedscrew compressor provides or the base load.

Figure 7: Graph o a Load Proile suitable or a ixedspeed and variable compressor setup.

4.6.3 Compressor control systems

There are dierent types o control systems availableor compressors. Your current system may not beusing the most eicient method, or may have nocontrol system at all.

Start/Stop

This method o control will start the compressor

once the pressure drops below a certain level andstop it once the desired pressure has been reached.This method should not be used when there is arequent increase in demand, as continually startingand stopping the compressor can be detrimental to thelie o the compressor (increasing maintenance costs).

While energy is saved during the periods that thecompressor is not running, the compressor mustcharge the receiver to a higher pressure than isrequired by the end uses so that a minimum pressureis maintained until the compressor starts again.

Load/Unload

Using this method, the compressor will charge thesystem to the desired pressure, then the compressormotor will continue to run at constant speed while thecompressor action is disengaged. While this meansthat the compressor is using less power or a largeamount o the time, the motor can use between 15and 35% o ull load power, meaning this schemecan also be ineicient. Figure 8 below shows a typicalpower consumption proile or a compressor usinga load/unload control system. You can see that thecompressor still uses roughly 30% o peak powerwhile unloaded. During the time immediately ater thecompressor enters the unloaded stage, the oil separatorperorms a blow down to clean out accumulated oil.This leads to the compressor running at part load orsome time, meaning that quite a signiicant amount oenergy can still be used during unloaded operation.

Figure 8: Typical power curve o a compressor usinga load/unload control system2

Time

Flow(

L/s)

Base load

Fluctuating load

Time (seconds)Oil/Air separator

pressure blowingdown

Power

(kW)

00

25

50

75

100

125

150

175

200

30 60 90 120 150 180

UnloadedLoaded


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Throttling

Throttling control varies the degree to which the inletvalve is open, controlling the amount o air intake to thecompressor. This method is only eective with screw orvane compressors that run at 70% load or above.

Centrifugal compressor control

Centriugal compressor control systems are usuallymore complex and involve throttling and recirculatingair load, as well as venting o air to the outsideenvironment.

Variable-speed screw compressors

Variable-speed screw compressors control the motorspeed whilst keeping the slide valve to the compressorully open to meet luctuating air demand. Whencombined with a base load compressor providingconstant air supply at optimum eiciency, a variable-speed and ixed-speed combination can be the mosteicient or real-world, luctuating, air-demand patterns.

Figure 9: Typical perormance o rotary oil lubricatedcompressors with dierent control systems.2

Compressor power consumption with flow

The power drawn by compressors changes signiicantlywith changes in airlow. Figure 9 shows the power-lowcurves or a number o compressor control systems.This graph shows how the dierent control systemscan aect the compressors eiciency at low low levels.The curve shows the amount o power consumed(relative to maximum power) as the low capacitythrough the compressor changes. The steeper thecompressor curve, the more eiciently it perormsat part loads.

Performance comparisonrotary oil lubricated air compressors

Total kW Input -vs- Capacity

00

10

10

20

20

30

30

40

40

50

50

60

60

70

70

80

80

90

90

100

100Variable inlet controlledrotary oil injected aircompressors with modulationblowdown at 40 and 60%

Variable outlet controlledrotary oil injected aircompressors

Load/Unload controlledrotary oil injected aircompressors

Variable speed drivenrotary oil injected aircompressors

Flow capacity (%)

kWA

bso

rbedinput(%)


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4.6.4 Compressor maintenance

Ensuring regular maintenance is carried out on yourcompressor will also reduce energy costs. Ensure theinlet ilter is not blocked and keep coolers clean andproperly lubricated.

4.6.5 Variable speed drives

Variable speed drives can be itted to the motors oscrew and vane compressors, and most suppliersare now oering actory-itted, variable-speed units.These allow the motor to be run at the rate requiredin order to ulil demand at that time. This methodcansaveconsiderableamountsofenergy.However,

variable-speed drives should only be itted in caseswhere air demand varies. Using a variable-speed driveor a compressor that runs at ull load constantly willconsume more energy. Some companies have electedto install one variable speed unit, with two or more baseload units to save on capital cost.

4.6.6 Multi-stage compressors

Multiple stages can be used to improve the eiciencyo screw and centriugal compressors. Additional

cooling can be placed between the stages to urtherincrease the eiciency o the second stage.

4.6.7 Compressor operating conditions

Once you have selected the type o compressor systemthat you wish to install, you should ensure that the plantservices the new compressor will require are availableand that operating conditions are suitable.

4.6.8Location

When installing a new air compressor, the location oinstallation is important. There should be suicient room

or the equipment as well as access or maintenance.The compressor should also be as close as possible totheplant.Ifthecompressoristobelocatedoutsideor

in a compressor house that is detached rom the mainbuilding, it is best to place the compressor house in themost shaded area. This is usually on the south side othe main building.

4.6.9 Inlet air temperature

Lower air inlet temperatures allow your compressorto operate more eiciently. Section 5.5 (in Solution2) illustrates how important this is and what sort oenergysavingstoexpect.Inessence,compressors

producelargeamountsofheat.Ifthisisnotexhausted

to the atmosphere via cooling towers (water-cooling)or through exhaust stacks, you are wasting energy.

When selecting a new compressor, it is importantto locate the air inlet to use the lowest temperature airpractically available and to discharge the waste heatto the atmosphere i possible.

4.6.10Power

There should be suitable access to electrical poweror the compressor. The distribution board rom whichthe compressor is run should be well within its ratedpower limits and the cables supplying the compressorshould also be rated or the current required by thecompressor.

4.6.11 Water

Access to suitable water should be available or coolingthe compressor i required. This water should beas cool as possible, so a supply rom pipes that areexposed to the sun is not recommended.

4.6.12 Blowdown

Air compressors oten have blowdown mechanisms,which will blow any condensed water or iltered oilrom ilters or condensate traps. This waste should beconsidered as contaminated, so there should be access

at the compressor or disposal o this waste.

4.7 Step 7: Measure theimprovement

By ollowing these steps, you have done almosteverything possible to improve the energy eiciency oyour compressed air system. Repeat the measurementsyou made when determining the current old usage.By comparing the result, you can determine thereduction in energy used to run the system (kW/L/s)

and hence the reduction in energy costs o the system.


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Design a new system 18

5.1 Establish air demand(quantity and quality)

Using the techniques described in Section 4.1(in Solution 1), air demand quantity and quality canbe estimated or your new or extended acility.The key principles that should be adhered to are:

Designoutinappropriateuses

of compressed air.

Take the opportunity to consider substitution ocompressed air or other technologies (or example,electric drives instead o compressed air cylinders,low-pressure blowers or water removal).

Separateservicesusingdifferingairquality.Establishing air-quality requirements is critical, as itcan dictate the types o compressor and iltrationused.Higherqualityairismoreexpensivetoproduce

and you should consider multiple compressors withseparate duties.

Minimisecompressedairdemandspikes.

By considering how equipment operates together,you can minimise pressure spikes, which in turnaects how eiciently your compressors can operate.Bear in mind that you will also be using receivers,which can also help to minimise pressure spikes.

Separatelyitemisetheequipmentthatuses

high pressure.

Ifyourhigh-pressurerequirementsarearelatively

small proportion o your overall air demand, it may bepossible to supply them via a separate compressor.

Minimisepressurerequirementsfor

your system.

A compressors eiciency is linked to its pressuresetting. Less energy is required to compress air to alower pressure, so once you have itemised the air-quality requirements o your equipment, consider howyou can minimise that even urther through equipmentselection and substitution.

5.2 Design your piping and ittings

Pipes and ittings also aect the pressure set pointo your compressor. A compressed air system that isperorming well should have a pressure drop o lessthan 10% between the compressor outlet and all pointso use. There are ways to ensure a minimal pressuredrop is obtained, including:

Optimisepipediameter,lengthandthenumberof

bends. Pressure drop is a unction o a number othings importantly: the velocity o the air down thepipe (which is dictated by your air demand combinedwith pipe diameter); the distance o the pipingbetween the compressor and the end uses; and the

number and type o bends. By paying attention tothese things, total pressure drop can be minimised.

Selectvalvesandfittingswithlowpressuredrop.

Section 4.3.3 and Section 4.3.4 in Solution 1 havemore inormation on piping layout and pipe diameter.

5.3 Select and locate air receivers

Receivers have a key role in maximising the eiciencyo your compressor. They achieve this by storingcompressed air to meet rapid increases in demand,

which reduces the impact o air demand surges on thecompressor. This allows compressors to run at theiroptimum load position and minimises the number oload/unload cycles (i using ixed-speed compressors).Oten, a single main receiver is used, but secondaryreceivers should be considered i speciic equipmentor work areas can be identiied that induce intermittent,high, air demand.

5 Solution 2 Design a new system


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Design a new system 19

5.4 Select dryers, separatorsand ilters

Rerigerant dryers add electrical consumption, pressuredrop dessicant dryers waste compressed air throughpurging and increasing pressure and separators andincreasing pressure and separators and ilters alsointroduce pressure drop to your system. Careulselection can minimise the negative impact on energyeiciency. Section 4.5 (in Solution 1) explores details

o why and how dryers, separators and ilters are used,with the key points being:

Treatingyourcompressedairtoahigherqualitythan

is required wastes energy and may also result inhigher maintenance costs.

Althoughdesiccantdryersdonotuseenergytorun,

they require compressed air or purging. These energycosts should be included in any comparison betweendessicant and rerigerative dryer systems.

Regularlycheckingandreplacingfilterswillminimise

pressure drop across them (these can be monitored

to optimise the energy costs with ilter replacementcosts).Electroniclevelsensingdrainshelptooptimisethe

time that drains are open (drain valves are ittedon equipment in which water condenses, such asatercoolers, receivers, dryers and ilters).


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Solution 2 Design a new system 20

Table 5: Annual Energy and Cost Savings with Reduced Compressor Inlet Temperature8

Air Intake

temperature

reduction 3C 6C 10C 20CComp- kWh/yr $/yr kWh/yr $/yr kWh/yr $/yr kWh/yr $/yrarative savings savings savings savings savings savings savings savings

averageload (kW)

4 80 8 160 16 264 26 528 53

7.5 150 15 300 30 495 50 990 99

11 220 22 440 44 725 73 1450 145

15 300 30 600 60 990 99 1980 198

22 440 44 880 88 1450 145 2900 290

30 600 60 1200 120 1980 198 3960 396

37 740 74 1480 148 2440 244 4880 488

55 1100 110 2200 220 3625 363 7251 72575 1500 150 3000 300 4950 495 9900 990

110 2200 220 4400 440 7260 726 14520 1452

160 3200 320 6400 640 10550 1055 21100 2110

5.5 Locate inlet and dischargeair outlet

The eiciency o the compressor can be greatlyimproved by providing cooler air at its intake. Thiscan be as simple as ducting air rom outside thecompressor house or another location on-site. Anotherimportant consideration is where the waste heat romyourcompressorisdischargedto.Isitexhaustedinto

thecompressorhouse?Orintotheatmosphere?Best

practice would ensure that waste heat does not ind itsway back into heating the inlet air to the compressor.Table 5 illustrates energy savings arising rom reducingthe air inlet temperature to your compressor.

5.6 Select a compressorand control system

Selecting the control philosophy may be an iterativeprocess that includes:choosingacompressor,orrangeofcompressors

(dierent sizes, types and so on)selectinghoweachcompressorwilloperateinrelation

to the others given its range o operational options.Section 4.6 (in Solution 1) discusses actors to be

considered in selecting a compressor. Suice to saythat the aim is to meet air demand at the lowest totalcost, including the energy costs.


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Selecting a service provider 21

Upgrading and improving your compressed airsystem can take considerable time depending on yourcircumstances. While you may want to ollow the steps

in this guide, you may not have the time orresources available to do so. Compressed air serviceproviders can supply the services required to assess,upgrade or install your compressed air system. Youmay wish to ask them to assist you with some or all otheprocess.Ineithercase,therearesomequestions

you should ask beore you begin.

6.1 Questions to ask serviceproviders

Will the provider take a systems approach?Itisimportantthatyourserviceproviderconsidershow

to optimise your entire compressed air system, not onlyone or two o its components. Ensure that the providerwill include the ollowing in their investigation:

airtreatmentlevelspecifications

leakmanagementassessment

pressurelevelsthroughoutthesystem

flowthroughoutthesystem

controlsystemoptimisation

heatrecoverypotential.

Will the provider examine the demand side

as well as the supply?

While the supply side o equipment such as thecompressor, dryer, receiver and ilters are importantconsiderations, the provider should also be investigatingthe demand side o your system, including thedistribution network, pressure regulators, the end usesand the proile o the demand.

What analysis services do they offer?

Inordertoensureyoursystemrunsasefficientlyas

possible, the provider must irst conduct a detailed

analysis o various aspects o your system. While leakdetection is important, your provider should also beable to measure and analyse the load proile o yoursystem, the pressure at various points around thesystem and the power consumption o the compressorand dryer. Other questions to ask o your providerinclude:

Whattrainingdothestaffhave?

Aretheyqualifiedtoworkonallcompressortypes?

Cantheyserviceandinstallequipmentsuchasfilters,

drainsandpiping?

Dotheyprovideemergencyserviceresponse?

Willtheytakecareofpartsshipping?

Willtheycontractoutanyoftheworkthemselves?

Dotheyhavethecapabilitytoremotelymonitoryour

system?

Cantheyprovideemergencyrentalcompressors?

6.2 Database o compressedair service providers

A database o proessional compressed airservice providers can be ound in the Sustainable

Manuacturing Directory provided by the SustainabilityVictoria. This directory can be oundat the Sustainability Victoria website:www.sustainability.vic.gov.au

6 Selecting a service provider


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Appendix ACompressed air system overview 22

A compressed air system consists o a number omain stages: compression the air is put underpressure; treatment the air quality is improved;

storage reservoirs o air to meet rises in demand; anddistribution piping o air to end uses. Each componentin a typical system helps to deliver clean, dry,compressed air that is ree o pressure luctuations at itspointofuse.Ifanycomponentisworkinginefficiently,

the systems perormance suers and operating costsrise. A brie description o each component ollows.

Inletfilter:removesparticlesfromtheairenteringthe

compressor. Usually part o the compressor package.Compressor:compressesairtoasmallvolume,

increasing the pressure.Motor:drivesthecompressoralsoknownasprime

mover.Compressorcontroller:directsthecompressors

output.Itmaybemicroprocessor,electromechanical

or pneumatically based. Advanced controllers includemachine protection and inormation management.

Aftercooler:compressionleavestheairhotand

wet. The atercooler lowers the temperature o theair leaving the compressor and removes water thatcondenses as the air cools.

Separator:removesliquidsfromthecompressedair.

Receiver:storesalargereserveofcompressedairto

maintain a smooth low to the plant, especially when

air demand rises.Airlinefilter:removessolidsandliquidsfromthe

compressed air stream. Can be placed throughoutthe system.

Dryer:helpstoeliminateanyremainingmoisturein

the compressed air by using either a rerigeratedcondenser or a desiccant. Rerigerated condenserscool the air to condense water vapours into a liquidthat is then drained rom the system. Desiccants arepowders or gels that remove water by absorbing it.

Condensatetrap:collectsanddischargesliquidthat

condensesoutoftheairstream.Itisanintegralpart

o atercoolers, dryers and separators.

Distributionpiping:linksthecomponents.Itdistributesthe air rom a main header to branch lines andsubheaders to drop points connected to individualtools.

Pressureregulator:controlsairpressureandflowat

individual points o use.

Appendix A Compressed

air system overview


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Appendix B Methods or estimating compressor energy consumption9 23

One o the two methods below can be used. Ensurethat all electrical meters are installed by qualiiedelectricians.

Method 1

A power demand analyser or a suitable meter canbe used to measure the average power (kW) o thecompressor system over a test period, or kWh usedover that period.

Method 2

Ifthecompressorisoperatingatasteadyload,

measurement o the compressor circuit three-phasecurrents can be used to determine compressor energyconsumption. A clip on ammeter can be used tomeasure the instantaneous currents o each phase andan average phase current can be calculated.Power or the three-phase circuit:

power (W) = 1.732 E Iav power factor, where

E = supply voltage (usually 415V)

Iav= average phase current (amps)

Power actor is usually about 0.85 at ull load reducingto 0.7 at hal load and to about 0.2 at no load.

monthly energy use (kWh) = power (kW) number

of operating

hours/month

An accurate assessment o compressor powerusage may require no load and ull load tests tobe conducted to determine power at ull and no-loadconditions. This can then be multiplied by the hours thecompressor runs in each load condition to obtain kWh/annum.

Alternatively, some modern compressors record totalkWh consumed in their control systems, which may

need to be read on regular basis to obtain annualconsumption.

Test type Description

NO LOAD test Shut the valve betweenthe compressor and the air

receiver. Measure the powerconsumed by the processor.

FULL LOAD test Expel some air rom the airreceiver. Measure powerconsumed by thecompressor as it buildsup air pressure.

On the basis o the above electrical measurements,an approximate compressor perormance graph canbe drawn, as indicated below, and used with theoperating hours to obtain kWh/annum.

Figure 10: Typical Compressor Perormance Graph9

Appendix B Methods for estimating

compressor energy consumption9

Free air delivery (L/s)

Measured

full load

Measured

average load

Measured

no load

No load

condition

Air leakage

condition

Average load

condition

Max rated

air

delivery

Average

air

demand

Full load

condition

Powerinput(kW)

Performance graph

0

0

10

20

30

40

50

60

70

80

20 40 60 80 100 120 140 160 180 200


24/28


Appendix C Measuring leaks 24

This section describes a method or measuring leaks inyour compressed air system.

Method 11. Let the compressor build up the system pressure

until it reaches the shuto point and the compressorstops.IfthecompressorNEVERreachestheshutoff

point,theairleakageratemustbeVERYHIGH.

2. For a period o hal an hour, record the time thecompressor runs and the time that it is o.

3. The quantity o air leaking rom the system can beestimated as ollows (F.A.D. = Free Air Delivery):

Method 2

1. Run the compressor until the pressure in the airreceiver builds up to its maximum operating pressure.

2. Switch o the compressor and measure the timetaken or the receiver pressure to drop by, say, 100kPa (The pressure should drop enough to allow thecompressor to restart or the second hal o the test).

3. Switch on the compressor and record the time takento build up the 100 kPA pressure loss.

4. The quantity o air leaking rom the system can beestimated as ollows:

5. Using Figure 10, a power use corresponding tothe measured air leakage level (kW) and a powerrequirements corresponding to the no load condition(kW2) can be established. From these graph readings,the actual net power use attributable to air leakagecan then be calculated as ollows:

Appendix C Measuring leaks

F

F


25/28


Appendix D Cost savings rom the installation o a DDS system 25

Table 6 outlines the potential savings with DDS

retrofitted to a typical heatless dessicant air dryer

installed with a 55kW rotary screw air compressor.

Adsorption dryers operating costs

Min.InletPressure: 7.0barg

Ambient Temperature (std re conditions): 21.0 C

InletTemperature(Aircompressordischtemp-+10deg.C) 31.0C

Outlet Pressure Dewpoint: -40 C

InletMoistureContent: 4.1385g/m3

Max inlet water content: 3.3751 kg/hr

Operating costs

Energy required to produce purge air: 12.64 kWh

Energy cost per kWh: $ 0.100

Operating hours per annum: 3840

Annual running cost: $4,853.76

Operating Costs with Dewpoint Dependent Switching System

AverageInletTemperature(atstdrefconditions): 21.0C

AverageInletPressure: 7.0barg

Average Flow rate (70% o Max low rate): 9.90 m3/min

InletMoistureContent: 2.2849g/m3

Average inlet water content: 1.3572 kg/hr

Cost savings: 59.78%

Estimated annual savings: $2,901.58

Estimated annual running costs: $,1952.18

Table 6: Cost savings rom the installation o a DDS system.2

Appendix D Cost savings from

the installation of a DDS system


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Appendix E Glossary 26

Air Compressor A machine that puts air under pressure by compressing a volume o air.

Artiicial Demand Air demand that is not actually used by the end uses o the compressed air,such as loss causeby pressure drop.

Control System The mechanism that controls how the compressor meets demandthrough switching on/o and by varying its operation.

Demand Proile A graph o the air demand rom the system over time.

Dessicant Dryer A dryer that uses two separate chambers to remove moisture rom the air.

Inlet Theairintakeforthecompressor.

Leak Management An action plan o how to check or and deal with leaks on a regular basisso that they do not cause signiicant loss.

Load The demand or air that the air compressor experiences.Piping Layout The arrangement o the compressed air piping network.

Rerigerant Dryer A dryer that removes moisture rom the air by coolingtheairsothatwatercondenses.Itusesa typical rerigeration principle and equipment.

Appendix E Glossary


27/28


Appendix F Further reading/reerences 27

Further reading

The ollowing manuals provide more detailed technicalinormation and exhaustive best practice methods or

improving compressed air eiciency:

Compressed Air Factsheets, published by theCompressed Air Association o Australasia, Australia.www.energyrating.gov.au/library/detailsaircomp-brochure.html

Good Practice Guide: Energy Efficient Compressed

Air Systems, published by the Carbon Trust,United Kingdom.www.bcas.org.uk/pd/carbontrust/GPG385.pd

Improving Compressed Air System Performance,published by the Compressed Air Challenge,United States.www.compressedairchallenge.org/content/library/pds/compressed_air_sourcebook.pd

Reerences

1 Energy eicient compressed air systems, p. 1,Carbon Trust, UK, February 2005

2 CompAir Australasia Limited.3ImprovingCompressedAirSystemPerformance,

p. 23, Compressed Air Challenge, US, November 20034ImprovingCompressedAirSystemPerformance,

p. 19, Compressed Air Challenge, US, November 20035 Energy Smart Compressed Air Systems, p. 48,

Sustainability Victoria, Australia.6 Energy eicient compressed air systems, p. 11,

Carbon Trust, UK, February 2005.7 Energy eicient compressed air systems, p. 12,

Carbon Trust, UK, February 2005.8 Energy Smart Compressed Air Systems, p. 49,

Sustainability Victoria, Australia.9 Compressed Air Savings Manual, p. 16-17State Electricity Commission o Victoria

Appendix F

Further reading/references


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For urther inormation and enquiries, please contact:

Sustainability Victoria

Urban WorkshopLevel 28, 50 Lonsdale StreetMelbourneVictoria 3000

Ph: +61 (03) 8626 8700Fax: +61 (03) 9663 1007

Email: [email protected]

Energy Efciency Best Practice Guide Compressed AirSystems Sustainability Victoria 2009.

Sustainability Victoria gives no warranty regardingthis publications accuracy, completeness, currencyor suitability or any particular purpose and to theextent permitted by law, does not accept anyliability or loss or damages incurred as a result oreliance placed upon the content o this publication.This publication is provided on the basis that allpersons accessing it undertake responsibility orassessing the relevance and accuracy o its content.

Energy Efciency Best Practice Guide Compressed AirSystems should be attributed to Sustainability Victoria.

Energy Efciency Best Practice Guide Compressed

Air Systems is licensed under a Creative CommonsAttribution-No Derivatives 3.0 Australia licence.In essence,youarefreetocopyand distribute

the work, as long as you attribute the work, do notadapt the work and abide by the other licence terms.To view a copy o this licence, visit:http://creativecommons.org/licenses/by-nd/3.0/au/

Acknowledgements

Sustainability Victoria would like to acknowledgeClimate Managers or preparing this report and

best practice guide compressed air

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