FARM ENERGY INNOVATION PROGRAM - ENERGY IN SHEDS
Compressed-air systems: air leak reduction
Leakage accounts for nearly one third of compressed-air energy
consumption. A proactive leak repair and maintenance program
should be followed for compressed-air systems. Applying repair
and maintenance measures in a sustainable manner requires
regular inspection and assessment of your system and
engagement with equipment operators. The upside is that
energy savings of up to 80 percent can be achieved.
Why does air leakage matter?
Leakage is usually the largest source of energy wastage
associated with compressed air usage. Leaks typically waste
around 20 to 30 percent of a compressor’s output, but some
systems can lose 50 percent or more of their air through leaks.
Not only do leaks increase energy costs; they also contribute
to operating losses and reduced productivity because the
pressure drops they create affect the performance of air-using
equipment.
Leaks typically occur in pipe fittings and joints, hoses, valves,
flanges, couplings and point-of-use equipment. Systems that
operate at a higher pressure than is actually required can
promote leaks and can also increase the risk of damage to the
equipment.
A well-maintained system – which means having a leakage
detection and repair program in place – should have a leakage
rate of less than 10 percent.
In terms of energy savings, a general rule says that an effective
air-leakage reduction program can reduce energy wastage by
up to 80 percent.
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Run the compressed-air system during a non-production
period (i.e. when there is no immediate demand for
compressed air).
Make sure that no equipment is operating at the time
(Note: You can isolate selected parts of the system to
determine the main sources of leakage).
Measure the load and unload cycles and calculate the
average power consumed. The compressor will load and
unload because the air leaks will cause it to cycle on and
off as the pressure drops due to air escaping through the
leaks.
Plot power usage on the compressor performance graph
(below), which represents the air leak rate of the system.
Compressor Performance Graph
Power Input (kW)
Full Load
Condition
Measured
Full Load
160
Average Load
Condition
Measured
Average
140
Load
120
Technical explanation
Leakage rates are a function of the supply pressure in an
uncontrolled system and they tend to increase with higher
system pressures. Leakage rates (expressed as flow rate) are
also proportional to the square of the orifice diameter. An
example of air losses for different equivalent orifice sizes is
shown below.
IMAGE FOR SHEET
100
Air Leakage
Condition
Load during non-80
production periods
Measured60 No Load
Condition
No Load
40
20
0
20
40
60
80
Measured Air
Leakage Rate
100 120
140 160 180 200 220
Average Air
Demand
Max Rated
Air Delivery
Free Air Delivery (litres per second)
Read the corresponding air leak rate in Free Air Delivery (FAD)
or use the following equation:
Leakage (%) = [(T x 100)/(T + t)]
Where:
T = on-load time (minutes)
Figure 1: Leakage rates for different supply pressures and approximately
equivalent orifice sizes. Source: (1).
t = off-load time (minutes)
The leakage rate, expressed as percentage of compressor
capacity lost, can be determined by measuring the compressor
performance during non-production periods.
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FARM ENERGY INNOVATION PROGRAM - ENERGY IN SHEDS
Compressed air systems: air leak reduction
The best method for identifying leaks is to use an ultrasonic
acoustic detector. Contact your supplier to arrange a leak
survey to detect and tag leaks. Fixing leaks can be as simple as
tightening a connection or as complex as replacing faulty
equipment; therefore it is convenient to prioritise repairs so
that the largest leaks are fixed first (as this will be where most
of your energy savings are concentrated).
Wherever feasible (i.e. without affecting or disrupting the
operation of air-using equipment), try to reduce the pressure
of the system so as to minimise the leakage rate.
976%20F4%20Compressed%20air.pdf
[Accessed 2013].
US DOE; EERE, 2004. Compressed Air Tip Sheet #3: Minimize
Compressed Air Leaks. [Online]
Available at:
www1.eere.energy.gov/manufacturing/tech_assistance/comp
ressed_air.html
[Accessed 2013].
Other methods of reducing air leaks
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Install air isolation valves to individual production areas
with shorter operating hours and close these valves
when these areas are not being used.
Install solenoid valves on equipment so that the air
supply to that equipment gets switched off whenever
the power is turned off.
Implement a leak prevention program that incorporates
identification (including tagging), tracking, repair,
verification and employee involvement.
Evaluating quotes
Estimate the leakage rate using the method described, and
once the survey has been conducted and leaks detected,
compare quotes by looking at the cost-benefit of each repair
option, i.e. cost of repair versus improvement in leakage rate
(energy savings).
Further information
The Energy Efficiency Exchange (eex.gov.au)
‘Opportunities – Compressed Air’
eex.gov.au/technologies/compressed-air2/opportunities/#Detect_and_eliminate_leaks
References
Queensland Government, n.d. Eco-Efficiency for Queensland
Manufacturers, Stage 3 – Opportunities for Improvement,
Foundry Factsheets. [Online]
Available at:
www.ecoefficiency.com.au/Portals/56/factsheets/foundry/00
NSW Farm Energy Innovation Program © NSW Farmers Association 2013
NSW Farmers gives no warranty regarding this publication’s accuracy, completeness, currency or suitability for any particular purpose and to the extent
permitted by law, does not accept any liability for loss or damages incurred as a result of reliance placed upon the content of this publication. This publication
is provided on the basis that all persons accessing it undertake responsibility for assessing the relevance and accuracy of its content. The mention of any
specific product in this paper is for example only and is not intended as an endorsement. This activity received funding from the Department of Industry as
part of the Energy Efficiency Information Grants Program. The views expressed herein are not necessarily the views of the Commonwealth of Australia, and
the Commonwealth does not accept responsibility for any information or advice contained herein.
Head Office: 02 9478 1000
Energy Info Line: 02 9478 1013
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