What does ISO 11011 cover?
ISO 11011:2013, Compressed air – Energy efficiency – Assessment, sets out requirements for conducting and reporting an assessment of a compressed-air system’s energy use. Its key idea is the system view: most of the energy that a compressor turns into compressed air is lost before it does useful work, through treatment pressure drop, piping losses, leaks, poor controls and users running at higher pressure than they need. Looking only at the compressor misses most of the opportunity.
The standard divides the system into three parts and expects the assessment to address each, together with how they interact. It also describes the roles of the people involved, the information to be collected and what the final report should contain. Check the current edition with ISO; any contract that calls for an ISO 11011 assessment should name the edition that applies.
It is an assessment framework, not a product or company certification. A plant can use its structure to run a better audit; claiming formal conformity requires working from the authorised text of the standard with suitably competent people. Below we explain the practical approach we follow, informed by that system view. It is not a reproduction of the standard or a clause-by-clause checklist.
Supply, transmission and demand: the three boundaries
| Part of the system | What it includes | Typical questions | Typical evidence |
|---|---|---|---|
| Supply | Compressors, drives, controls, coolers, dryers, filters, receivers at the station | How much electrical energy is used per unit of air? How well do controls match output to demand? | Real-power logging, flow at station outlet, load/unload states, specific power in kW per m³/min |
| Transmission | Headers, branches, drops, hoses, regulators, isolation valves | How much pressure is lost between station and user? Are there restrictions or undersized pipes? | Simultaneous pressure logging at several points, pipe sizes, layout survey |
| Demand | Production users, open blowing, leaks, drains, idle equipment | What pressure do users actually need? How much air is wasted on leaks and artificial demand? | Demand profile, leak survey, point-of-use pressure checks, non-production flow |
The interaction between the parts is where the biggest gains often hide. If header pressure is raised to overcome a blocked filter, the compressors use more power and every leak and unregulated user consumes more air. As a working rule, each extra bar of generation pressure costs about 7% more compressor power, before counting the extra leakage.
How a system assessment is organised
- Agree the purpose. Write a short statement of the decisions the assessment must support, such as cutting energy use, fixing unstable pressure, planning an expansion or setting a baseline before new controls.
- Define scope and exclusions. List the compressor houses, buildings and production areas included. State plainly what is not covered, such as pressure-vessel inspection, breathing or medical air qualification and electrical protection.
- Collect pre-visit information. Equipment lists, nameplates, layout drawings, energy bills, shift patterns and known problems.
- Walk the system. Trace the air from intake to user, noting controls, treatment, receivers, piping, drains, regulators and obvious waste.
- Measure. Log power, flow, pressure and machine states over a representative period, at the boundaries agreed in step 2.
- Analyse. Build the energy-to-air relationship, the pressure profile and the demand profile, and quantify losses with stated methods.
- Identify and rank measures. For each improvement, estimate the effect, implementation effort and any risk to production or air quality.
- Report and plan verification. Present findings with their evidence and limits, and agree how the result of each action will be checked later.
Roles and responsibilities on site
An assessment works best when responsibilities are agreed at the start. The plant owner provides access, safety rules, production information and a person who can take decisions. The assessor plans the measurement, runs it, analyses the data and writes the report. Maintenance, production and electrical staff each hold knowledge the data alone cannot supply: why a valve is left open, which machine is critical, when a shift changes.
Agree who installs electrical measuring equipment and under which permit, who may change compressor settings during the study (normally nobody, unless a controlled test is planned), and who receives the report. Independence matters too. An assessor who also sells compressors should say so and present measures that do not involve new equipment alongside those that do.
What gets measured, and how
- Electrical input: true power (kW) at each compressor or at the station, not current alone. Include or exclude dryers, fans and pumps consistently.
- Delivered air: flow at a defined point, with its reference basis stated (actual, normalised or FAD-equivalent).
- Pressure: at the compressor discharge, after treatment, at main headers and at critical users, logged together so drops can be calculated.
- Machine state: loaded, unloaded, stopped, modulating or VSD speed, from the controller or from logged current.
- Conditions: inlet and room temperature, cooling water where relevant and dew point where treatment is in scope.
- Production context: a diary of shifts, batches, breaks, maintenance and unusual events.
Specific power, expressed in kW per m³/min of delivered air, is the main indicator for the supply side. It is only meaningful when power and flow cover the same boundary over the same time and the flow basis is declared. Our power and flow logging and specific-power pages explain the method.
Turning findings into ranked measures
A good assessment ends with a short list of actions a plant can take, ranked by effect and effort. Typical measures fall into a few groups:
| Area | Typical measures | How the effect is estimated |
|---|---|---|
| Demand | Leak repair, isolating idle zones, replacing open blowing with nozzles or blowers, lowering point-of-use pressure | Non-production flow, leak survey estimates, user pressure requirements |
| Transmission | Removing restrictions, re-sizing pipes, changing clogged filters, loop mains | Measured pressure drop and the set-point reduction it allows |
| Supply controls | Narrowing the pressure band, sequencing, base/trim strategy, VSD trim | Logged load/unload patterns and part-load power |
| Supply equipment | Replacing an inefficient machine, adding storage, dryer type change, heat recovery | Specific power comparison at the measured duty |
Estimates should be in kWh per year and in air volume, with the assumptions written beside them. A plant can then apply its own tariff. Measures that reduce demand and pressure normally come first, because they shrink the duty that any later equipment change must meet.
What a credible assessment report contains
- Purpose, scope, boundaries and exclusions.
- Equipment list with nameplate data and condition notes.
- Measurement plan: instruments, locations, dates, logging interval and any data gaps.
- Supply analysis: power, flow, specific power and control behaviour.
- Transmission analysis: pressure profile and losses by section.
- Demand analysis: profile, base load, peaks, leakage and artificial demand.
- Ranked measures with estimated effect, assumptions and implementation notes.
- A verification plan describing how results will be checked after work is done.
- Limits: what was not measured, uncertainties and what would improve confidence.
Common gaps in assessments that claim a system approach
- Spot readings over an hour presented as a plant profile.
- Specific power calculated from nameplate motor rating and rated FAD rather than measured values.
- No transmission data, so pressure losses and artificial demand are invisible.
- Leakage stated as a percentage with no method behind it.
- Recommendations limited to new compressors from one brand.
- No statement of what was excluded or how savings will be verified.
How Reddy Compressors helps
We run compressed-air system assessments that follow the supply, transmission and demand structure described above, for plants with any make of compressor. Our engineers log power, flow, pressure and machine states, walk the distribution and users with your team, and report ranked measures in kWh, air volume and pressure, each with its evidence and assumptions.
We are an independent multi-brand specialist that sells, rents and services ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and many other makes, and we are not an authorised dealer of any of them. We have tie-ups with all major and reputed brands. We do not issue certificates of conformity to ISO 11011. Where your contract or energy programme requires formal conformity, we will work with your appointed assessor and the authorised text of the standard. After the report we can carry out the work as well: leak repair, controls set-up, servicing, AMC, spare parts or a change of compressor.
Our office is at Srinilayam, 12-13-200, First Floor, Street No. 1, Tarnaka, Secunderabad 500017, and our service teams cover all of Telangana and Andhra Pradesh. Call +91 99590 60718 or +91 92468 88812.
What to send us
- The reason for the assessment and any contract or programme requirement, including the ISO 11011 edition if specified.
- List of compressors, dryers and receivers with nameplate photos.
- A layout sketch of the compressor house and main distribution.
- Recent electricity bills or sub-meter readings for the compressor house.
- Shift pattern, production days and known pressure or capacity problems.
- Site safety rules and permit requirements for installing loggers.
Frequently asked questions
What is ISO 11011 used for?
ISO 11011 sets out how to assess and report the energy efficiency of a whole compressed-air system. It divides the system into supply, transmission and demand, and expects the assessment to cover each and how they interact. Plants and energy programmes use it to make audits consistent and to avoid studies that only look at the compressor while ignoring leaks, pressure loss and wasteful users.
Is an ISO 11011 audit the same as an ISO 50001 certification?
No. ISO 50001 is a management-system standard for energy management across an organisation and can be certified. ISO 11011 describes how to assess a compressed-air system’s energy efficiency. A compressed-air assessment can provide evidence and actions that feed an ISO 50001 programme, but completing an assessment does not make the site or the assessor certified to either standard.
How long does a compressed-air system assessment take?
It depends on plant size and the questions being asked. Most assessments involve a site walk, installation of loggers, a measurement period of around a working week including non-production time, and then analysis and reporting. Larger sites with several compressor houses may need a longer campaign. The measurement period should cover every operating pattern that matters to the decision.
What is specific power in a compressed-air audit?
Specific power is the electrical power used per unit of delivered air, usually stated in kW per m³/min. It shows how efficiently the supply side turns electricity into compressed air. It is only valid when power and flow cover the same boundary and period, and when the flow basis and pressure are stated. Comparing machines at different pressures without adjustment gives misleading results.
Do I need to stop production for an ISO 11011 assessment?
Usually not. Most measurements are made during normal operation, because the aim is to understand the system as it really runs. Some flow meters need a short shutdown or a hot-tap point for installation, and a leak test is often best done during a planned non-production period. These needs are agreed in the measurement plan before work starts.
Can a compressor supplier carry out an independent assessment?
Yes, provided the supplier declares any commercial interest and presents measures fairly. Many of the best savings involve no new equipment: fixing leaks, lowering pressure, improving controls and removing restrictions. A multi-brand assessor has less reason to favour one manufacturer. Ask to see the measurement data and assumptions behind every recommendation.
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Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.