Identifying Significant Energy Uses: From Pareto Analysis to Documentation

A Significant Energy Use (SEU) is a portion of an organisation's energy consumption that either accounts for a substantial share of total consumption or holds meaningful potential for improving energy performance. Correctly identifying SEUs shapes how resources are allocated, how EnPIs are defined, and how improvement actions are prioritised across the whole energy management system.

Criteria for identifying significant energy uses

ISO 50001 doesn't set a fixed threshold for what counts as 'significant' — each organisation has to document its own. In practice, though, four criteria are most commonly used, usually together. For an organisation with multiple sites, this threshold can even differ from site to site; what counts as significant at a small facility may be a negligible share of total consumption at a much larger one.

• Share of the organisation's total energy consumption (a threshold of roughly 5-10% is commonly used)
• Real potential for improving energy performance, even if the consumption share is only moderate
• Availability of data and the ability to measure that use independently
• Strategic importance or operational risk tied to that equipment or process

Pareto analysis by consumption

The first step is usually ranking all major equipment or processes by annual energy consumption and plotting a Pareto chart. In most industries, roughly 20% of the equipment accounts for close to 80% of total consumption — that small group becomes the primary initial candidate list for SEUs.

Pareto analysis by improvement potential

Relying purely on the consumption ranking can be misleading; some high-consumption equipment is already well optimised with little room to improve, while a moderate-consumption unit might hold high savings potential due to wear or inefficient operation. That's why a second Pareto pass, based on an estimate of improvement potential (such as the gap between current performance and best comparable performance), is run and combined with the first. A practical way to combine the two is a two-dimensional matrix: consumption rank on one axis and improvement-potential rank on the other. Equipment that ranks high on both axes becomes the top priority for defining an SEU; high-consumption equipment with low potential is still monitored, but doesn't get priority for improvement projects. It's also worth noting that distributed consumption — such as compressed-air leaks at multiple points, or lighting across several halls — can look insignificant at each individual point but add up to a substantial share of total consumption; Pareto analysis needs to aggregate this kind of consumption into a single category before ranking, so its real importance isn't overlooked.

• Equipment age and time since the last major overhaul
• Maintenance history and frequency of failures
• Gap between current performance and the manufacturer's efficiency specification
• Whether a comparable benchmark exists within the same industry

Documenting the decision

Every SEU needs to be documented with the reasoning behind its selection, the data source used, and who is responsible for monitoring it. This documentation matters both for internal audits and for justifying future investment in metering or improvement actions.

• Name and physical boundary of the significant energy use (equipment, line, or process)
• Share of total energy consumption and the energy carrier involved (electricity, gas, steam)
• The selection criteria applied
• Current measurement status and whether a dedicated EnPI exists
• Responsible owner and date of the last review

Periodically reviewing significant energy uses

The list of significant energy uses isn't static. Changes in production volume, equipment replacement, a new line, or even internal audit findings can shift priorities. An annual review, aligned with management review, is the recommended minimum interval; industries with fast-changing processes should review more frequently. The outcome of every review should be logged in the energy management system's records, even if the final SEU list stays unchanged — that record is what shows an auditor the review actually happened, rather than being copied from the previous year.

Without correctly identifying significant energy uses, improvement resources get spent where they have the least effect.

For example, in a steel plant, the electric arc furnace typically accounts for more than half of the plant's electricity consumption on its own and is clearly an SEU; the office building's HVAC system, despite constant consumption, usually has limited improvement potential and ranks lower in priority.