ISO 50001 energy review: how to analyse energy use and select significant energy uses (clause 6.3)

What does the ISO 50001 energy review require?

The ISO 50001 energy review is a structured analysis of how an organisation uses energy, carried out on measured data, that identifies its significant energy uses (SEUs) and the opportunities to improve energy performance. It sits in clause 6.3 of ISO 50001:2018 and feeds the objectives, indicators, baseline, operating criteria and data collection plan.

The 2018 edition reads as a sequence: you look at all the energy first, narrow down to the uses that count, understand each of those in detail, then turn what you learned into ranked opportunities and a view of what consumption will look like next year. A tidy SEU list with no analysis behind it is a finding waiting to happen.

What the review does not do is set the indicators or the baseline. Those belong to clauses 6.4 and 6.5, covered in EnPIs, energy baselines and normalisation; the review supplies the data and the relevant variables they are built on.

The five parts of the energy review

How do you analyse energy use and consumption?

Start with the invoices: twelve months or more of invoices for electricity, gas, fuel oil, steam, LPG, diesel for vehicles and any other energy type inside the boundary give totals by carrier. Scope matters here: ISO 50001 does not allow an energy type inside the scope and boundaries to be left out, so a fleet or a standby generator counts if it sits inside them.

Next, split the totals by use. Main meters and existing sub-meters do some of the work; the rest comes from engineering estimates, such as rated power multiplied by run hours and a load factor, or a short logging campaign on a compressor or a chiller. What an auditor will question is a breakdown that adds up to more, or less, than the invoices say.

The output is a consumption map: for each site and energy type, the main uses and their approximate share. Keep the arithmetic visible, so next year's questions are answered by the workbook rather than one engineer's memory. Metering gaps are closed by the data collection plan, explained in The energy data collection plan and metering.

How are significant energy uses selected?

ISO 50001 defines a significant energy use as one that accounts for substantial energy consumption, offers considerable potential for improvement, or both. The standard sets no percentage. You decide the criteria, write them down and apply them the same way every time the review is updated.

Good criteria combine both tests. A consumption threshold catches the big loads; an opportunity test catches a badly controlled smaller use. A useful practical rule is that every SEU must be something a named person can influence through operation, maintenance or purchasing, because clause 6.3 asks you to identify the people whose work affects each one.

Profiling each SEU

For every SEU, record three things. The relevant variables are the factors that genuinely drive consumption, such as tonnes produced, degree days, occupied rooms or operating hours; they are tested later with data, not assumed. Current energy performance is today's position, often a specific consumption per unit of output. The people are the operators, maintenance technicians, shift leaders or contractors whose decisions change the result, and they become the audience for competence and awareness under clause 7.

A worked example: a single-site food factory

Consider a factory that uses electricity and natural gas. The figures below are illustrative, to show the method, and are not benchmarks for any sector. The energy team agreed two criteria: any use above ten per cent of total site energy is an SEU, and any smaller use with a clear, low-cost improvement is added on the opportunity test.

Four SEUs now carry about 79% of site energy. The opportunities register ranks a leak survey on compressed air first (low cost, quick), then condensate return on the boilers, then scheduling of the HVAC. The future estimate uses next year's production plan and a normal weather year, and it becomes the reference for comparing actual with expected consumption under clause 9.1.

When must the energy review be updated, and what is the record?

Two triggers apply. The first is a defined interval that you set; annually is a practical choice because it lines up with the management review. The second is a major change in facilities, equipment, systems or energy-using processes: a new production line, a building extension, a switch from gas to electric heating, or a site closure. Define what counts as major in advance.

The record has two layers. One is the method: the data sources, the estimating rules, the SEU criteria and how opportunities are ranked. The other is the result of each review: the consumption breakdown, the SEU list with variables, current performance and people, the ranked opportunities and the forecast. Keep earlier versions. At recertification the auditor will ask how the picture changed.

When an update changes the SEUs or their variables, check the knock-on effects the same day: indicators and baselines, operating criteria, the data collection plan and training needs may all move with it.

Common mistakes in the energy review

• SEUs chosen by convenience. The uses that already have meters are picked, while the unmetered boiler house is left out. Criteria first, metering second.
• Variables assumed, never tested. Production is named as the driver of every SEU without checking the data. Some loads follow the weather or the calendar instead.
• No names against SEUs. The clause requires the people whose work affects each one; a blank column shows up in competence and awareness later.
• A one-off exercise. The review was done for the certification project and never updated after the new line was installed.

For the full set of ISO 50001 requirements around the review, see the ISO 50001 requirements guide.

ISO 50001 energy review: questions buyers ask