Compressed-air audit reports and verification

Why the report matters as much as the measurement

An audit can involve days of logging, leak surveys and pressure measurements. If the report then gives only a headline figure and a list of products to buy, the plant cannot judge whether the advice is sound. Worse, nobody can later prove whether the changes worked.

A useful report is an engineering document, not a sales brochure. It should let a maintenance manager defend a decision to management, let a finance team see where the numbers come from, and let a future auditor repeat the measurements and compare.

What a complete audit report contains

1. Scope and objective. Which compressors, dryers and distribution areas were included, what was excluded, and what question the audit set out to answer.
2. System description. Asset list with make, model, rating, control mode and condition; a layout or schematic of the supply side and main distribution.
3. Measurement plan. Instruments used, their range and calibration status, where they were installed, sampling interval, start and end of logging.
4. Production context. Shifts, holidays, batch processes and anything unusual during logging, so the data can be judged as representative or not.
5. Results. Power, flow, pressure, dew point and air quality as measured, with charts and the derived figures such as specific power.
6. Findings. Leaks, pressure losses, control problems, artificial demand, inappropriate uses, treatment issues, each with its evidence.
7. Recommended actions, ranked, with estimated effect and the assumptions behind it.
8. Measurement and verification plan for each significant action.
9. Limitations. What could not be measured, data gaps and uncertainties.

Separating facts, calculations and estimates

The most important discipline in an audit report is to label where every number comes from. We use a simple classification.

Mixing these without labels is how audits overpromise. A leak-loss figure from an ultrasonic survey is an estimate; a reduction in compressor energy after leak repair, logged under similar production, is a verified result.

How actions should be ranked

A report should not simply list everything that could be done. It should put actions in a logical order, because many depend on each other. A sound sequence usually looks like this:

1. Safety and reliability first. Unsafe receivers, missing safety valves, overheating compressors.
2. Reduce waste on the demand side. Leak repair, removing inappropriate uses such as open blowing, fixing drains that waste air.
3. Remove pressure losses. Filters, dryers, piping and point-of-use restrictions.
4. Lower the setpoint once the losses are removed – about 7% less power for each bar reduced.
5. Improve control and storage. Sequencing, base and trim arrangement, receiver capacity.
6. Only then consider supply changes such as a variable-speed machine or replacing an inefficient compressor, sized to the reduced demand.
7. Heat recovery where there is a genuine heat user.

Buying a new compressor first, before fixing leaks and pressure, often leaves a plant with an oversized machine that runs inefficiently at part load.

Each action should show the estimated effect, the basis of that estimate, the approximate effort or cost category, and any dependency on other actions.

Key performance figures in a report

• Specific power in kW per m³/min of delivered air (or kW per 100 cfm), at the actual pressure, for each compressor and for the whole system.
• Average and peak demand, and the demand profile across shifts and non-production periods.
• Non-production demand as a pointer to leaks.
• Pressure at the compressor and at critical users, and the drop between them.
• Load/unload or speed profile for each machine, showing time spent unloaded.
• Dew point and air-quality results where measured.

Always quote specific power with the pressure at which it was measured, and say whether flow was measured or taken from data sheets.

Measurement and verification: proving the result

Measurement and verification (M&V) is how you show that an action actually delivered. A practical M&V plan defines:

• The baseline: measured performance before the change, with the production conditions it represents.
• The adjustment method: how to correct for changes in production, shifts or weather between the before and after periods.
• The post-change measurement: same parameters, same points, same or equivalent instruments, similar duration.
• The result: the change in energy, pressure, demand or air quality, with its uncertainty stated honestly.
• Persistence checks: leaks return and setpoints drift, so a later re-check shows whether the gain is being held.

Common weaknesses in audit reports

• Savings quoted without stating the electricity tariff, running hours or method.
• Logging over a day or two that misses the plant’s real demand pattern.
• Data-sheet flow used as if it were measured.
• Recommendations that all point to one brand of equipment.
• No way of checking results after implementation.
• No mention of limitations or data gaps.

We write our reports to avoid these. Our framework follows the logic of recognised assessment practice such as ISO 11011 for scope, measurement and reporting, applied to the realities of Indian plants.

How results should be presented

Good presentation helps busy managers act. We start with a one-page summary: the main findings, the top actions in order, and the verification plan, with each figure tagged as measured or estimated. Charts follow: a weekly demand profile, pressure at compressor and at critical users, compressor loading, and power. Tables list leaks with location, size estimate and status; pressure-drop segments; and each compressor’s specific power at its working pressure. Technical appendices hold raw data, instrument details and calculation methods. Everything uses consistent units – m³/min with cfm alongside, bar with psig where helpful, kW and kWh – so figures can be compared with future audits.

Finally, the report should name who carried out the measurements, who reviewed the conclusions, and when the next check is due. That turns a one-off document into the start of a managed improvement programme.

Audit reports for Indian plants: practical points

Several local factors should be stated in any report written for a plant in Telangana, Andhra Pradesh or elsewhere in India. Power quality and voltage variation affect motor and compressor performance and should be noted where logged. Summer ambient temperatures of 40–45 °C and above reduce compressor and dryer capacity, so a report based only on winter logging may understate peak problems. Plants that run on DG sets during power cuts have a different cost of air at those times. Tariff structures vary, so the report should state the tariff used for any cost estimate. Recording these points makes the conclusions more robust and easier to defend.

How Reddy Compressors helps

Reddy Compressors, at Tarnaka in Secunderabad, carries out compressed-air audits across Telangana and Andhra Pradesh and supports projects elsewhere in India where feasible. Because we are an independent multi-brand specialist working with ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar and other makes, our recommendations are not tied to selling one brand.

• We plan and carry out measurement: power and flow logging, pressure profiling, pressure-drop, leak detection and dew-point checks.
• We deliver a clear report that separates measured, calculated and estimated values.
• We rank actions in a practical order and explain the reasoning.
• We can carry out the work: leak repair, service and AMC, piping changes, controls, new, used or rental compressors and dryers.
• We re-measure after implementation to verify the result.

What to send us

• List of compressors, dryers and receivers with makes, models and ratings.
• Recent electricity bills or meter readings for the compressor house, if separately metered.
• Shift pattern and production calendar.
• The main concern: energy, low pressure, wet air, reliability or expansion.
• Any earlier audit report you want reviewed or repeated.

Frequently asked questions

What should a compressed-air audit report include?

It should include the scope, an asset list, the measurement plan with instruments and logging period, production context, measured results such as power, flow, pressure and dew point, findings with evidence, ranked actions with their assumptions, a measurement and verification plan, and a clear statement of limitations. Measured, calculated and estimated values should be labelled separately so the conclusions can be checked.

How long should compressed-air logging last for an audit?

Long enough to capture the plant’s real pattern. For most plants that means at least a full week including weekend or non-production periods, because night and holiday demand reveal leaks and the weekly cycle shows peaks. Batch or seasonal processes may need longer. A short logging run on a quiet day can give misleading results and recommendations.

How do I know if audit savings are real?

Ask how each saving was calculated and whether it is measured or estimated. Real savings are confirmed by measuring after the change, using the same points and instruments, and adjusting for differences in production. A good report includes this verification plan. Be cautious of headline savings without a stated method, tariff, running hours or baseline.

What is specific power in a compressed-air system?

Specific power is the electrical power used per unit of compressed air delivered, usually in kW per m³/min or kW per 100 cfm, at a stated pressure. It lets you compare compressors and track system efficiency over time. It must be based on measured power and, ideally, measured flow, and is only comparable between machines at similar pressures.

Should I buy a new compressor based on an audit?

Only after the demand-side actions are done. Fixing leaks, removing inappropriate uses and reducing pressure losses usually lowers demand and the required pressure. A new compressor should then be sized to that reduced, measured demand. Buying first often results in an oversized machine. A neutral audit should show this order clearly.

What is measurement and verification (M&V)?

M&V is the method used to prove the effect of an energy or performance improvement. It sets a measured baseline, defines how to adjust for changes in production or conditions, repeats the measurement after the change and reports the difference with its uncertainty. Later persistence checks show whether the improvement is being held over time.

Related pages

• Compressed air audit and measurement hub
• ISO 11011 assessment framework
• Power and flow logging
• Specific-power assessment
• Measurement, verification and energy performance
• Leak repair register and verification