Compressed-air system audit, assessment and benchmarking

What is a compressed-air audit, and what should it tell you?

Most plants know what their compressors are rated for. Very few know what the system actually delivers. An audit closes that gap. It looks at the whole chain: intake, compressors, controls, aftercoolers, dryers, filters, receivers, piping, drains, regulators, hoses and the machines that finally use the air.

The output should not be an equipment list or a brochure for a new compressor. It should explain why the system behaves as it does. Why does pressure sag on the second shift? Why does the plant run three compressors when the demand looks like two? Why is there water at the paint booth when the dryer shows a healthy dew point? Every finding should be backed by a measurement or a clearly stated observation, and every recommendation should say what it is expected to change.

The internationally recognised reference for this work is ISO 11011, which sets out how a compressed-air energy assessment should be planned, carried out and reported. We follow its logic of defined boundaries, measured data and documented assumptions, explained in more detail on our ISO 11011 assessment framework page. Our audits follow the ISO 11011 method; they are not a certification and we do not issue certificates.

Which type of audit do you need?

Audits differ in depth. Choosing the right depth at the start saves money and avoids a report that cannot support the decision you have to make.

If you only have a pressure complaint, a diagnostic audit is usually enough. If you are about to buy a new compressor, a detailed audit first is almost always worth it, because buying capacity to cover leaks and pressure losses is the most common mistake we see.

How a compressed-air audit is carried out

1. Agree the objective and boundary. Energy, capacity, reliability, air quality or all of them. Which compressor rooms, which production areas, which shifts.
2. Collect what already exists. Compressor list with make, model and serial number, single-line piping layout, dryer and filter details, electricity data, production schedule, service history and controller settings.
3. Inspect the installation. Compressor room ventilation and intake, cooler condition, drains, dryer operation, receiver arrangement, header layout and point-of-use connections.
4. Log data. Pressure at the compressor discharge, after treatment and at critical users; power or current on each compressor; load/unload or speed states; flow where a meter can be fitted; dew point where air quality matters. Logging should cover weekdays, weekends and night shifts, because non-production demand often reveals leakage.
5. Survey leaks. An ultrasonic survey of headers, drops, hoses, fittings, drains and machine panels, with each leak tagged and recorded. See our leak detection page for the method.
6. Map pressure drop. Measure differential pressure across dryers, filters, long headers and branch lines to find where pressure is lost.
7. Analyse. Build the demand profile, compare compressor states against demand, calculate specific power and identify waste.
8. Report and rank. Present findings, root causes and actions in order of benefit, cost and risk, with a plan to verify each result.

What we measure and why it matters

Power and flow logging is the backbone of any energy audit. We explain the equipment and sampling approach on our power and flow logging page, and how demand curves are built on the air demand profiling page.

Benchmarking: specific power done properly

The single most useful efficiency number in compressed air is specific power: electrical input in kW divided by delivered free air in m³/min (or kW per 100 cfm). It tells you how much power the station uses to make a unit of air at a given pressure.

Benchmarking only works when the numbers being compared are on the same basis. A specific-power figure means little unless you also state:

• the discharge pressure it was measured at, since each extra bar of pressure typically needs about 7% more power;
• whether flow is free air delivery (FAD) at stated reference conditions or something else;
• whether dryers, cooling fans, purge air and other auxiliaries are inside the boundary;
• the load pattern, because a fixed-speed machine at part load is far less efficient than at full load;
• the measurement period and how representative it was.

Comparing your station with a manufacturer’s datasheet figure, or with another plant, without matching these conditions produces misleading conclusions. A better benchmark is your own station over time: measure specific power now, fix the problems, and measure again on the same basis. Our specific-power assessment page covers the method in detail.

The findings audits usually uncover

Every plant is different, but some findings appear again and again across Indian factories:

• Leakage running all day and night. Weekend and night logging often shows compressors loading when nothing is in production.
• Pressure set higher than any user needs. Often raised years ago to overcome a pressure drop that nobody fixed.
• High unload hours. Fixed-speed machines spending long periods unloaded, still drawing a significant share of full-load power.
• Poor sequencing. Two or more machines trimming at the same time, or a VSD machine running at full speed while a fixed-speed machine unloads.
• Clogged filters and undersized dryers. High differential pressure and poor dew point, especially in summer when intake and cooling-air temperatures exceed 40 °C.
• Failed drains. Timer drains blowing air constantly or float drains stuck shut, flooding filters and pipework.
• Inappropriate uses. Open blowing, cooling with compressed air, or vacuum generators that could be replaced by lower-cost alternatives.
• Hot compressor rooms. Hot discharge air recirculating to the intake, raising discharge temperature and reducing capacity.

How audit findings become engineering actions

A finding is only useful if it leads to a decision. We rank actions by three questions: how much energy or risk does it remove, how much does it cost and disrupt, and how sure are we of the benefit?

Operating and maintenance fixes should normally come first. Only after demand, leaks and pressure losses are reduced can the right size of any new compressor be known. Savings should be reported in kWh and hours, verified by repeat measurement on the same basis, not assumed. We describe this on our audit reporting and verification page.

Audits in Indian plant conditions

Conditions in Telangana and Andhra Pradesh affect how an audit should be planned. Summer ambient temperatures of 40–45 °C, and above 45 °C on open sites, raise compressor discharge temperatures, load refrigerated dryers harder and reduce the dew point margin. Dust raises intake-filter differential pressure. Voltage variation can affect motor and drive behaviour. A survey done only in the cool months may understate the summer problem, so we ask about seasonal history and, where practical, recommend logging in the hot season or correcting the analysis for it.

Plants in pharma clusters, food parks and engineering estates also differ in air-quality requirements. An audit for a pharma plant must include dew point and contamination checks, not just energy.

How Reddy Compressors helps

Reddy Compressors has worked with compressed-air users since 2002 from our office at Tarnaka, Secunderabad. As an independent multi-brand specialist, we audit systems built around ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar and other makes without any interest in pushing one brand.

• Walk-through, diagnostic and detailed audits for plants across Telangana and Andhra Pradesh, with project-based support elsewhere in India where feasible.
• Pressure, power, state and dew-point logging, leak surveys with tagged registers, and pressure-drop mapping.
• Clear, ranked recommendations in plain English, with kWh and operating-hour estimates and a verification plan.
• Follow-through: leak repair, service and AMC work, dryer and filter correction, controls and sequencing changes, and new, used or rental compressors when the audit shows they are genuinely needed.
• Over 20 service engineers and technicians, and our own rental fleet to cover capacity during changeovers.

What to send us

• List of compressors and dryers with make, model, serial number and rated pressure (nameplate photos are ideal).
• A simple sketch or drawing of the compressor room and main piping.
• Production shifts, working days and any seasonal changes.
• The main problem you want solved: energy, pressure, moisture, reliability or expansion.
• Monthly electricity consumption for the compressor house if separately metered.
• Recent service reports and controller fault history.

Frequently asked questions

What is a compressed air audit?

A compressed-air audit is a structured study of how a plant generates, treats, distributes and uses compressed air. It combines inspection with logged measurements of pressure, power, compressor states and often flow and dew point. The result is a set of findings, such as leaks, excess pressure, poor control or treatment problems, with ranked actions that reduce energy use, improve pressure stability or protect air quality, and a plan to verify the outcome.

How long does a compressed air audit take?

It depends on the depth and size of the plant. A walk-through can be done in a day. A detailed audit normally involves a site visit to fit loggers, a logging period long enough to capture weekdays, weekends and different shifts, often around a week, then a leak survey and analysis. Investment-grade studies take longer because data must be reconciled and checked. We agree the scope and timeline before starting.

What is a good specific power for an air compressor?

There is no single good figure, because specific power depends on pressure, compressor type, size, load pattern and what auxiliaries are included. A meaningful comparison needs the same pressure, the same flow basis and the same boundary. The most reliable benchmark is your own station measured before and after improvements on an identical basis. Manufacturer datasheet values are tested under specific conditions and are rarely matched in a real plant at part load.

Will an audit tell me whether I need a new compressor?

Yes, and very often the answer is that you need less capacity than you think. An audit shows real demand, including peaks and leakage, so you can see whether pressure problems are caused by insufficient capacity or by losses, poor controls and leaks. If a new or additional machine is needed, the demand profile tells you what size and type, such as a VSD trim compressor, will match your load best.

Does a compressed air audit require a plant shutdown?

Usually not. Most loggers clamp onto cables or fit to existing pressure test points while the plant runs normally, and leak surveys are done in production because leaks are easier to hear under pressure. Some flow meters need a tapping point or short isolation, which can be planned during a scheduled stop. Normal production is actually what we need to measure, so the audit should disturb operations as little as possible.

Can you audit compressors of any brand?

Yes. We are an independent multi-brand specialist, not an authorised dealer of any manufacturer, so we audit stations with ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar and other machines, including mixed fleets. We have tie-ups with all major and reputed brands. Brand neutrality matters in an audit, because recommendations should follow the measurements rather than a sales target. Brand names and trademarks belong to their respective owners.

Related pages

• Compressed air audit and measurement hub
• Leak detection surveys
• Specific-power assessment
• Compressed-air energy and efficiency
• Working pressure and pressure budget
• Compressor controls and sequencing