Improving and maintaining peak compressed air system
performance requires addressing both the supply and the
demand sides of a system and understanding how the two
interact. Chris Dee, executive director of the British
Compressed Air Society, explains

The systems approach to energy and
economic efficiency involves more
than just fixing leaks. If you don’t
consider the rest of the system, then you will
continue to waste a lot of money every hour
you run your system.

Over the years BCAS has found that one
of the biggest issues that prevents companies
from maximising their compressed air
system’s efficiency is understanding that it is
a system – not just compressors and some
piping. In many cases when we ask to be
shown a company’s compressed air system
we are taken only to the compressor room,
an important part but just one part – the
supply side.

Few are able to identify their largest or
most critical end uses – the demand side.

Fewer still know the end uses’ actual
requirements – pressure, flow and air quality.

The BCAS Installation Guide introduces these
concepts by providing some basic knowledge
on components and then builds on them to
get participants thinking not just about how
they produce air, but how they actually use it.

The investigation of the demand side
involves breaking the system down into end
uses and assessing the characteristics of these
elements. In this way, proper planning of
efficiency and other system improvement
measures can be done without negatively
affecting the system. Too often companies buy
a new compressor thinking that it will solve
all their energy efficiency difficulties. If you
step back and take a systems approach and
start analysing the compressed air system as a
whole, you start to see what is reasonable and
efficient for the whole plant and not just one
component or one use. Often a company will
specify and spend more money on a
compressor just because it is 1 to 2% more
efficient at some rated full load condition. But
that same plant may be adding up to 20% to
their annual costs because of unnecessarily
elevated pressures or wasting over 30% of their
compressed air in leaks or driving equipment
that should not be powered by compressed air.

How much air do you need?
What is your current compressed air usage?
Each industry is different and each plant
within any given industry is unique. A new
plant will have specific initial requirements;
these will change over time and anticipated
growth should be considered in the initial
design. Identify and tabulate anticipated end
uses and quantify rate of flow compressed air
requirements.Machinery and processes
requiring compressed air should be identified
by type and the manufacturer’s specified air
flow requirements noted. General use plant
air also should be identified and quantified.

What is your actual compressed air
requirement? List each by type, identify
alternatives to any potentially inappropriate
uses, identify steady or intermittent demand
and check number of shifts and resulting
variations. Use equipment manufacturer’s
specifications for: Average flow rate
requirement, maximum flow rate
requirement, minimum pressure requirement
(challenge the stated requirement), maximum
pressure requirement (Is there a built-in
pressure regulator?), and air quality
requirement, (for example oil free, degree of
dryness and filtration). Note the locations –
groupings or scattered. Estimate potential
future additions, estimate total air flow and
best and worst case scenarios. (Include
provision for leaks). Develop a Demand
Profile Chart, shut off air to any application
not in use. Determine the range of pressure
requirements. Should some be segregated?
Determine if oil free applications should be
segregated or should all be oil free? Determine
maintenance needs. Each end use should be
compared with alternatives and justified.

Why are you using compressed air? Not all
uses of compressed air are appropriate and
in some cases BCAS may be able to suggest a
better alternative.We prefer to be open and
ensure that you are only using compressed
air in the appropriate applications.

How to develop a Demand Profile Chart:
Misapplication of compressed air at the end
use is very common and results in the system
operating inefficiently. A demand profile chart
can assist in identifying applications that lead
to poor system performance, excessive
energy costs, and increasing maintenance
expenses.Minimum, average and peak rates
of flow, combined with on-off cycle times,
are important criteria. The demand profile
chart will provide the information for an
overview of the system to determine the
actual end-use requirements. For a new plant
the chart is a compilation of the data
required to select the total compressor
capacity and the system operating pressure.

This data should be provided by the
manufacturers of the end-use equipment.

For an existing plant, an analysis of data
can assist in determining where inefficiencies
exist or where there may be opportunities for
improvement. For example, an end use with
small air consumption can cause the entire
system to operate at elevated pressure.

Determine if the application can be modified
to operate at a lower pressure or if it should
be segregated to allow the main system to
operate at a lower pressure. For intermittent
high volume use, additional storage may
avoid the need to continually operate
compressors inefficiently at partial load
merely to meet an occasional peak
requirement. End use equipment is often
added or modified, so you should update the
chart periodically so that it remains current.

With a systems approach the focus and
effort must be balanced between the supply
and demand sides. For peak efficiency, you
must produce compressed air efficiently, but
you must also conserve and use it efficiently.

Imagine your system as a child’s see-saw and
that you want to achieve a level balance; if you
move the fulcrum or focus point too far to
one side, it requires significantly more effort
on that side to reach a balance. If you focus
all your efforts on only one side (supply or
demand), at first you may achieve reasonably
good results, but it will become more and
more difficult and will require expending
more capital and human resources to keep
improving. A smaller effort and investment
on the other side may result in huge savings.