Energy efficiency of the production process – how to analyse and modernise a production line?

Energy efficiency in a production process starts not with the question “how much energy did the plant consume?”, but with “how much energy was needed to produce this specific output, and why exactly that much?”. A plant may consume fewer MWh in one month and still operate less efficiently if production falls by more than energy consumption does.

This is why a production line should be analysed alongside production data: number of units, tonnes, batches or cycles, operating time, downtime, changeovers, quality, temperature, pressure and equipment load. Only this combined view shows whether energy is actually being used more effectively and where modernisation makes the most sense.

In brief

• Do not assess a process solely by its total energy consumption. Compare energy use with the volume and type of production.
• Define the process boundary and allocate both direct energy use and the relevant share of common utilities: compressed air, cooling, steam, heat or vacuum.
• Separate production from start-up, idling, waiting, changeovers, washing, downtime and shutdowns.
• Use specific energy indicators such as kWh/t, kWh/unit, kWh/batch or kWh/cycle, but choose the denominator to match the actual function of the process.
• Assess modernisation at system level. Replacing a single motor or machine may not deliver the best result if the real issue is a bottleneck, poor control, pressure, temperature or cycle organisation.

Energy efficiency of a production process – what are we actually measuring?

At plant level, the energy bill shows how much energy was purchased. It does not show which batch, line or operation was responsible for the consumption, or what share of that energy was actually required to make the product.

At process level, the key issue is the relationship between energy and the technological output. That output may be a tonne of material, a finished unit, a batch, a metre of product, a processing cycle or another unit that reflects what the line actually produces.

The simplest specific indicator can be expressed as: specific energy consumption = energy consumed by the defined process / production output.

In practice, the formula itself is simple. The harder part is defining the numerator and denominator correctly: which consumers belong within the process, what period is being compared, whether good output or gross output is used, and how centrally generated utilities are allocated.

ISO 50006:2023 describes the use of energy performance indicators (EnPIs) and energy baselines to evaluate energy performance improvement. In industrial practice, this means the indicator must reflect how the process actually operates and, where consumption depends materially on production volume or other variables, the comparison should take those relationships into account.

From total plant consumption to energy per product, batch or cycle

1. Start by defining the process boundary

The boundary should be narrow enough to identify the cause of a change in consumption, but broad enough not to omit equipment that is necessary for the line to operate.

For a production line, this may include:

• main process machines,
• drives, pumps, fans and internal transport,
• local heating or cooling systems,
• extraction systems, vacuum and auxiliary equipment,
• compressed air consumed by the line,
• the relevant share of centrally generated utilities where they are required by the process.

There is no point including office energy or car-park lighting in a process indicator simply because they appear on the same bill. If the objective is a plant-wide indicator, the boundary will be broader. If the analysis concerns the energy intensity of a specific product, the boundary should match its actual production process.

2. Build the balance from the top down

The starting point is total plant consumption by energy carrier: electricity, gas, heat, fuels, steam or other utilities. The next step is to move down one level to departments, lines, major auxiliary systems and individual consumers.

A good energy balance should reconcile. The sum of measured and reasonably estimated consumption should match the upstream meter within an acceptable uncertainty range. If half of consumption remains in an “other” category, it becomes difficult to assess the effect of modernising a specific line with confidence.

This does not mean every motor has to be metered. It is often better to measure a few key points that explain most of the load profile and then add measurement points where a specific savings hypothesis emerges.

3. Link energy measurement to process time

Energy data need to be synchronised with what was happening on the line. A power profile is far less useful if it is not known when a batch started, when downtime occurred, when the recipe changed or when the machine was waiting for material.

Tags from PLC, SCADA or MES systems are useful, but the analysis can just as well begin with a simple event log. The important point is to be able to relate consumption to:

• the start and end of a cycle,
• the batch number or production order,
• the product type,
• the line speed or throughput,
• planned and unplanned downtime,
• changeovers,
• start-up and shutdown,
• temperature, pressure and other relevant setpoints.

The measurement resolution must match the process. If a cycle lasts only a few minutes, 15-minute data can hide start-up, idling and short stops. In a continuous process, a stable hourly profile combined with production throughput may be more informative.

4. Divide the cycle into operating states

On many lines, a significant share of energy is consumed not during production itself but between production periods. It is therefore useful to identify separately:

1. steady-state production,
2. start-up and warm-up,
3. idling or waiting for material,
4. changeover,
5. washing, cleaning or preparation,
6. planned downtime,
7. unplanned downtime,
8. standby mode and full shutdown.

Only then can you see whether the problem is equipment efficiency during production or the number of hours in which equipment consumes energy without producing good product.

5. Allocate shared utilities

Centrally generated utilities are usually the most difficult to allocate. A compressor room, chiller, boiler house or vacuum system may serve several lines, so its energy cannot simply be divided equally between them.

The best approach is to meter the utility at the point of use or process branch while also measuring the energy consumed by the generating system. If full metering is not possible, use a transparent allocation key based on actual use, such as flow, operating time or load. The resulting value should be identified as an estimate rather than a direct measurement.

For compressed air, the analysis should cover not only compressor operation but also pressure, flow, leaks, inappropriate uses and network behaviour. For cooling, load, temperatures, setpoints and operating conditions of the whole system are relevant. In both cases, analysing a single machine without considering the system can lead to incorrect conclusions.

6. Choose the production output you actually want to reward

If 1000 units leave the machine but 80 need rework or are rejected, the energy used to make those 80 units does not disappear. Where scrap is significant, the number or mass of conforming products is often a better denominator than gross production.

Where multiple recipes are used, products with completely different energy requirements should not be mixed in one indicator either. It is better to track product groups separately or apply normalisation where the impact of product mix can be described reliably.

7. Finally, reconcile the result with the plant balance

The detailed analysis still has to agree with the upstream measurement. If the sum of energy allocated to lines, auxiliary utilities and other consumers differs significantly from the main meter, revisit the boundaries, operating times or utility-allocation method.

This is particularly important before evaluating an investment. A modernisation project may look very good on one meter while shifting consumption to another system. One example is reducing a machine’s electricity demand at the cost of higher cooling or compressed-air demand.

What data should be collected on a production line?

Not every process requires all of these parameters. From an auditor’s perspective, I would first select the variables that could explain a change in consumption. Collecting hundreds of signals without a hypothesis often produces plenty of data but few answers.

Specific energy indicators: kWh/t, kWh/unit, kWh/batch or kWh/cycle?

The most useful indicator is one that reflects the physical output of the process.

• kWh/t – suitable for bulk production, mixing, drying, grinding, extrusion or material-processing operations.
• kWh/unit – clear and practical for repeatable products with similar characteristics.
• kWh/batch – useful in batch processes where the complete cycle is important.
• kWh/cycle – useful for machines that perform a repeatable operation.
• kWh per good unit or per tonne of conforming product – appropriate where scrap and rework have a noticeable impact.

A specific energy indicator should not always be the only KPI. If a line has a large fixed load independent of production, it is also worth monitoring idle power, non-production time and throughput. If quality constrains performance, the share of good product should also be tracked.

For more complex processes, a simple “energy / production” ratio may not be sufficient. DOE Better Plants notes that performance can be normalised for variables that affect consumption, such as production, weather or facility utilisation. On a production line, analogous variables may include product mix, line speed, process temperature or the length of a production campaign – provided their influence is genuinely material and can be documented.

Why a reduction in total energy consumption does not necessarily mean an improvement

Suppose we compare two months of the same production process:

Total consumption fell from 120 to 100 MWh, i.e. by 16.7%. Production, however, fell by 30%. As a result, specific consumption increased from 1.20 to 1.43 MWh/t, i.e. by approximately 19%.

The plant purchased less energy, but the process used it less efficiently per tonne of product. Possible causes include a higher share of idling, shorter production runs, more frequent start-ups, a different product mix, lower line utilisation or auxiliary systems operating largely independently of production.

From an auditor’s perspective, this is often where the real analysis begins. The bill shows the change in MWh, but only by linking energy use with production and operating states can you determine whether the process itself has improved.

The opposite situation is also possible. After modernisation, total consumption may increase because the plant produces significantly more, while kWh/t or kWh/unit falls at the same time. Looking only at total energy would then lead to the incorrect conclusion that the modernisation had worsened performance.

Cycle time, idling, start-ups and changeovers

In cyclic processes, it is worth calculating not only the energy used by the entire cycle but also the duration of individual operating states. A machine may draw less power when stopped than during production, but if the stop lasts a long time, that energy accounts for a larger share per unit produced.

Particularly important are:

• start-ups and warm-up – frequent short production runs can increase the share of energy used solely to reach process conditions;
• idling – drives, fans, heaters, pumps and utilities may continue operating even when no product is being made;
• changeovers – parts of the system may remain at production settings throughout the entire product-change period;
• waiting for material or an operator – the process produces nothing, but some consumers remain active;
• washing and cleaning – in some industries this is an integral, energy-intensive part of the cycle and should be allocated consistently to the batch or production campaign.

A good modernisation project therefore does not always mean improving equipment efficiency. Sometimes a greater effect comes from shortening warm-up time, switching automatically to standby, shutting off utilities after a batch is completed or planning the sequence of production orders more effectively.

Line throughput and bottlenecks – energy follows the flow of production

A line runs only as fast as its bottleneck allows. If one stage limits throughput, speeding up other machines may not increase production. It may instead increase buffering, the number of stops and the energy consumed while waiting.

For this reason, the analysis should place the following on a common time axis:

• the throughput of the entire line,
• operating and downtime periods of successive machines,
• buffer levels,
• energy consumption,
• causes of blocking and starvation,
• product quality.

If removing a bottleneck allows the line to produce more in the same period, total energy consumption may increase. At the same time, energy per tonne or per unit may decrease because fixed loads are spread over a larger production volume.

Production-only indicators also require caution. High availability or OEE does not automatically mean high energy efficiency. However, these indicators can help explain changes in energy intensity when they are analysed together with energy use.

Where should modernisation opportunities be sought?

Drives: analyse the system, not just the motor

For motors and drives, I would not start with rated power. First, check what function the drive performs, its actual load, how speed, flow or pressure changes, and whether the equipment operates at the required operating point.

An oversized motor, an incorrectly selected pump, a throttled system or a fan running continuously at full speed can create a system-level problem. A variable-frequency drive is not an energy-saving measure in itself either – the effect depends on the load characteristics and the control strategy.

Process heating: temperature, time and losses

In thermal processes, the required product temperature should be compared with actual temperatures, heating time, holding time, furnace or dryer load and losses during interruptions.

DOE highlights, among other factors, the importance of controls, heat transfer, limiting infiltration and heat recovery in industrial process-heating systems. From the production-line perspective, however, the key point is that any change in parameters must remain consistent with the process technology and product-quality requirements.

Cooling: do not cool more than the process requires

In refrigeration systems, performance has to be assessed at system level. Setpoint temperature, load, condensing conditions, pump and fan operation, and the control strategy all influence one another.

If the process requires a specific temperature, lowering it “just in case” can increase consumption without improving production. Conversely, stabilising the load and controlling the system correctly may be more important than replacing a single component.

See also: energy efficiency in refrigeration.

Compressed air: look at line demand and the operation of the entire network

Compressed air is often a shared utility, so both the compressor room and the line-side consumers need to be analysed. DOE identifies key improvement measures including reducing inappropriate uses, lowering pressure to the level required by the process, improving control and storage, and reducing leaks.

At line level, measuring flow and pressure during production and downtime is particularly valuable. If flow remains high after the process stops, technological demand can quickly be separated from losses.

Automation and monitoring: energy use should respond to process status

Automation can improve repeatability, throughput and quality, but its energy effect must be measured. The most useful functions are those that link the operation of energy consumers to the actual production state.

For example, the control system can:

• reduce the operation of fans, pumps or drives while waiting,
• switch equipment to standby after the line stops,
• prevent unnecessary utilities from being left on after a batch is completed,
• run recipes with temperature and pressure control,
• record energy allocated to a production order or batch,
• issue an alarm when specific consumption increases under similar production conditions.

If the plant already has PLC, SCADA or MES systems, it is often worth checking what data are already available before adding another independent platform.

Does replacing an old machine always improve energy efficiency?

No. A new machine may be more efficient, but process performance also depends on utilisation, cycle time, availability, quality, auxiliary utilities and how well the machine fits the rest of the line.

Before replacement, compare at least:

1. energy per unit of good product,
2. throughput and cycle time,
3. power demand during and outside production,
4. demand for cooling, compressed air, vacuum and other utilities,
5. the number of start-ups and changeovers,
6. quality and scrap,
7. the machine’s impact on the bottleneck.

Only then is it possible to separate the effect of higher equipment efficiency from the effect of greater throughput, a shorter cycle or changes in production organisation.

Financing production-line modernisation – first define the technical option, then the financing instrument

Questions about financing production-line modernisation are common, but the sequence matters. First define the baseline, the modernisation option, expected energy consumption and the impact on production. Only then can you assess whether the investment fits a specific support mechanism.

In Poland, one such mechanism is Poland’s white certificate system (energy efficiency certificates). Not every modernisation project qualifies automatically. Article 24(3) of the Polish Energy Efficiency Act provides for refusal to forward information concerning the certificate, among other cases, where work commenced before the date on which the application referred to in Article 20(3) was filed. The statutory definition of “commencement of works” may cover not only the start of construction works but also the first legally binding commitment to order equipment or another commitment that makes the project irreversible. Eligibility for the scheme should therefore be checked before such an event occurs.

The conditions of grants, financing and other support instruments change over time, so their current rules should always be verified in the up-to-date documentation of the relevant programme or instrument.

Documenting the planned energy savings for a specific project is a separate issue and may require an energy efficiency audit.

How should the process analysis be structured before a modernisation decision?

A practical sequence is as follows:

1. select the product, line or process stage and define the analysis boundary;
2. collect energy and utility consumption within that boundary;
3. synchronise the data with production, cycles and operating states;
4. calculate a specific energy indicator for representative periods;
5. separate production, start-up, idling, changeovers and downtime;
6. check process parameters: temperatures, pressures, flows, speeds and loads;
7. identify the bottleneck and equipment operating without producing useful output;
8. compare operational, control, system-modernisation and equipment-replacement options;
9. calculate the impact of each option on energy use, throughput and quality;
10. only then assess economics, financing and the implementation method.

This sequence reduces the risk of selecting a modernisation measure that looks good on a datasheet but changes very little in the real process.

What should remain after the analysis?

A good production-line analysis does not end with a list of equipment. It should leave behind a data set that can later be used to verify the effect of modernisation:

• the process boundary and list of assigned consumers,
• an energy and utilities balance,
• a baseline indicator, e.g. kWh/t or kWh/unit,
• the conditions for which the indicator is representative,
• the cycle profile and share of non-production states,
• the key process parameters,
• a list of bottlenecks,
• modernisation options with their impact on energy, production and quality,
• the method for measuring performance after implementation.

This makes it possible to compare the process on the same basis after modernisation. Without such a baseline, it is easy to attribute savings from an investment to a change in production volume, or vice versa.

What if energy per product cannot be calculated today?

Do not start by buying another system or replacing a machine. First define the process boundary, choose the production unit and check what data already exist in meters, PLC, SCADA or MES systems. Only the gaps in that picture should determine where additional measurement points are needed.

If permanent metering and integration of energy and production data are required, the next step may be continuous energy monitoring linked to production data. The platform itself, however, cannot replace a correctly defined indicator and process boundary.

Frequently asked questions

Which indicator best describes the energy efficiency of a production line?

Most often it is energy per physical unit of product: kWh/t, kWh/unit, kWh/batch or kWh/cycle. The indicator should reflect the function of the process, and where scrap is significant it is better to relate energy to good product rather than gross production.

Does lower monthly energy consumption mean that the line is operating more efficiently?

No. If production falls more than consumption, specific energy consumption may increase. At a minimum, total energy, production volume and the specific energy indicator should therefore be compared.

How should compressed-air or cooling energy be allocated to a line?

The best approach is to measure utility consumption on the line branch and the energy consumed by the generating system. If direct measurement is unavailable, a transparent allocation key based on flow, operating time or load can be used, but the result should be treated as an estimate.

How long should a line be measured before modernisation?

There is no single correct period for every technology. The measurement period should cover representative operating states, products, loads, start-ups and downtime. For a repeatable process, a few well-recorded cycles may be sufficient to diagnose a specific phenomenon, while a baseline used to evaluate savings should represent normal process variability.

Does modernisation have to mean replacing the machine?

No. Some opportunities come from control, setpoint changes, reducing idling, optimising utilities, production sequencing or removing a bottleneck. Replacing the machine makes sense when the analysis shows that the existing equipment genuinely limits energy or production performance.

Sources

• ISO, ISO 50006:2023 – Energy management systems — Evaluating energy performance using energy performance indicators and energy baselines.
• ISO, ISO 50001:2018 – Energy management systems — Requirements with guidance for use.
• U.S. Department of Energy, Better Plants – Frequently Asked Questions – approach to energy intensity and normalisation.
• U.S. Department of Energy, Compressed Air Systems.
• U.S. Department of Energy, Motor Systems.
• U.S. Department of Energy, Process Heating Systems.
• U.S. Department of Energy, Industrial Refrigeration.
• European Commission JRC / EU-BRITE, Energy Efficiency BREF.
• Polish Electronic Journal of Laws / ELI, Energy Efficiency Act – consolidated text, Journal of Laws 2025, item 711.