Energy review (ISO 50001)

The energy review is a systematic analysis of your energy use and the most important technical step in ISO 50001 . You map out in detail where your energy goes: which process uses how much, when, and why? The NEN (Netherlands Standardization Institute) publication of the standard calls this energiebeoordeling (energy review, clause 8.2). Without a good energy review, you cannot identify meaningful SEUs, set realistic objectives or plan effective measures.

The energy review is not a one-off exercise. You repeat it (or parts of it) every year at the management review, and whenever there are major changes to your processes, installations or buildings.

What exactly is an energy review under ISO 50001?

An energy review under ISO 50001 is a structured examination of your entire energy use. You answer four questions:

Which energy flows come into your organisation? (electricity, gas, heat, fuel, compressed air)
Where does that energy go? Per process, department, installation or building
How much does each part use? In kWh, m³, GJ or other units
Where is the savings potential? Which processes are inefficient, outdated or poorly controlled?

The result is a complete picture of your energy use. This forms the basis for everything that follows: determining SEUs, setting objectives and creating action plans.

Step by step: carrying out the energy review

Step 1: Invoice analysis

Start with what you already have: your energy bills. Collect invoices for at least 12 months (preferably 24 to 36 months for trend analysis).

What you collect:

Electricity use per month (kWh)
Gas use per month (m³)
Heat/cold supply (if you are connected to a heat network)
Fuel (if transport or emergency power falls within scope)
Costs per energy type

What you do with it:

Calculate total use per year
Recognise seasonal patterns (more gas in winter, more cooling in summer)
Spot deviations (was there a month with unexplained high use?)
Map the cost breakdown (what do you pay for what?)

Example: invoice analysis for a production company

Energy type	Use per year	Cost per year	Peak
Electricity	520 MWh	€78k	Summer (cooling)
Gas	80,000 m³	€48k	Winter (heating)
Total		€126k

This is your starting point. It is detailed enough to begin with, but not detailed enough for ISO 50001. For that, you need submetering.

Step 2: Map the energy flows

Make an overview of all energy flows in your organisation. Where does energy enter, how is it transformed, and where is it consumed?

Method: Walk through your company (a “walkthrough”) with your technical staff. Use the process diagram as a basis and note at each step which energy goes in.

Example: energy flows for a production company


Electricity (main meter) ──┬── Compressors (compressed air)
                           ├── HVAC (climate control)
                           ├── Production line A (presses, ovens)
                           ├── Production line B (assembly)
                           ├── Lighting
                           └── Office + IT

Gas (main meter) ──────────┬── Heating (boilers)
                           └── Production ovens

At this point, you do not yet know exactly how much each part uses. That comes in step 3.

Step 3: Submetering and data collection

This is where it becomes technical. You want to know how much each part uses, not just the total. For that, you need measurements.

Comparison of measurement methods:

Method	Cost per unit	Accuracy	Suitable for
Submeter cabinets (fixed in the panel)	€500 to €2,000	High (±1 to 2%)	Permanent monitoring of the biggest consumers
Wireless sensors (CT clamps)	€200 to €600	Good (±3 to 5%)	Quick insight into medium-sized consumers
Temporary loggers (2 to 4 weeks)	€100 to €300	Good	One-off analysis or validation
Estimate (power × operating hours)	€0	Moderate (±15 to 25%)	Starting point for small consumers

Example estimate: A 75 kW compressor that runs 4,000 hours per year at an average load of 70%: 75 × 4,000 × 0.7 = 210 MWh per year.

Advice: Combine methods. Use submeter cabinets for your top 3 to 5 consumers, wireless sensors for medium-sized items, and estimates for the rest. Make sure at least 70 to 80% of your total use is measurable.

Step 4: Calculate the breakdown

With the data from step 3, you make the breakdown: of the 100% of energy that comes in, where does it go?

Example: production company (520 MWh electricity per year)

Process/system	Use (MWh per year)	% of total
Compressors (compressed air)	182	35%
HVAC (climate control)	130	25%
Production line A	104	20%
Lighting	52	10%
Office + IT	36	7%
Other	16	3%

Check: Add up all the items. If the total deviates by more than 10% from your main meter, something is wrong. Go back to your measurements.

Step 5: Analyse variables and patterns

Look not only at totals but also at patterns. When is a lot of energy used? What influences use?

Relevant variables:

Production volume: More production means more use. But how much more, exactly?
Outdoor temperature: HVAC use peaks in summer and winter
Occupancy: Office use is linked to the number of people
Process settings: Does the oven run at 200°C or 250°C?

Example: Your compressors use 182 MWh per year, but you see that they also run at night and at weekends when no production takes place. Standby use: 30 MWh per year. That is 16% of compressor use that you can eliminate by switching them off outside working hours. How to trace that pattern systematically is covered on the page about weekend use.

You only find this kind of insight by analysing patterns, not by looking at annual totals.

Step 6: Visualise

Make your findings visual. This helps when communicating with management and staff.

Options:

Sankey diagram: Shows energy flows as a flow chart with widths proportional to use. Visually strong, and it immediately shows where the large flows are.
Pie chart: Simple breakdown per process. Works well for presentations.
Heatmap: Use per hour of the day, per day of the week. Shows patterns (night use, weekend use).

Tools such as Excel, Power BI or specialised software (Metrix, EnergyCAP) can do this.

What does the energy review deliver for ISO 50001?

After a completed energy review, you have:

Energy balance: An overview of all energy flows and use per process
Top consumers: The 5 to 10 processes that together account for 80% or more of your use
Savings opportunities: Where is inefficiency? (standby use, outdated equipment, poor control)
Data for SEU determination: Input for determining your significant energy aspects
Baseline data: Figures to base your energy baseline on
Communication material: Graphs and diagrams for management and the shop floor

Common mistakes in the ISO 50001 energy review

Too little detail in the analysis

“We use 500 MWh” is not an energy review. The auditor wants to know where that 500 MWh goes. Without submetering, you cannot steer, and your ISO 50001 audit becomes difficult.

Analysing only electricity and forgetting gas

Many companies focus on electricity and forget gas, heat, fuel or compressed air. If your scope covers all energy flows, your energy review must cover them too.

Carrying out the energy review once and forgetting it

The energy review under ISO 50001 is not a one-off report that disappears into a drawer. Update it every year (new installations, changed processes) and use it actively for decisions.

No involvement from operators

The facility manager knows the installations on paper. The operator knows them in practice. Involve operators in the walkthrough. They know which machine is always on, which leaks there are, and where energy is wasted.

Cost of an energy review for ISO 50001

The energy review is one part of the total implementation costs of ISO 50001. Below are the costs specific to the review itself.

Cost item	Small (10 to 50 FTE)	Medium-sized (50 to 250 FTE)	Large (250+ FTE)
Internal time	40 to 80 hours	80 to 150 hours	150 to 300 hours
External specialist	€3k to €6k	€5k to €12k	€10k to €25k
Measurements (meters, sensors)	€2k to €5k	€5k to €15k	€15k to €40k
Total	€5k to €15k	€12k to €30k	€30k to €75k
Lead time	4 to 6 weeks	6 to 10 weeks	8 to 16 weeks

Tip: If you already have ISO 14001, you probably already have some of the data (energy use as an environmental aspect). That saves 20 to 30% on the review costs.

Working on it in practice

Turn your data needs into a measurement plan for ISO 50001. In it, you record the source, unit, measurement interval, owner and checks for missing data.