PCF Allocation Methods: How to Split Factory Energy Across Products

A factory may use one electricity meter to supply multiple production lines, yet manufacture dozens of products. A customer, meanwhile, wants a product-level figure: kilograms of CO₂e for the item they are buying. Turning shared electricity consumption into a defensible per-product figure is an important methodological challenge in many Product Carbon Footprint (PCF) studies. The result can depend on the allocation method, the available data, and the relationship between energy use and production.

This blog explains PCF allocation methods in plain English. It covers what relevant standards say, how each method works, where its limitations arise, and how to document your choice so a reviewer can understand and assess the approach.

PCF allocation is the process of assigning the inputs, outputs and associated environmental burdens of a shared process to the different products that process helps make. It may be needed when a plant produces multiple products or outputs using shared equipment, utilities or production processes and the relevant environmental flows cannot be directly attributed to individual products or allocation cannot otherwise be avoided.

ISO 14044 defines allocation in terms of partitioning the input or output flows of a process between the product system under study and one or more other product systems. In a PCF, shared energy consumption is one common input that may require allocation. Examples include electricity, natural gas, steam and other shared utility services.

Allocation does not change the factory's measured total energy consumption. It determines how the relevant shared inputs and associated environmental burdens are attributed to individual products. That is why the choice of method matters. The same plant data can produce different per-unit results depending on the allocation basis you apply.

Raw material inputs can often be traced through bills of materials and production records. A bill of materials (BOM) lists the specified materials and quantities required for a product or assembly. Actual material consumption may differ because of scrap, yield losses and rework. Energy presents a different challenge for three reasons.

A practical way to group factory energy before choosing an allocation method is into three categories:

Each category may call for a different allocation approach. Applying the same allocation basis to all three without considering their differences can make PCF results harder to justify.

Before choosing an allocation formula, follow the allocation procedures established in ISO 14044. Product carbon footprint (PCF) studies under ISO 14067 follow the life cycle assessment principles and framework of ISO 14040 and ISO 14044, alongside the specific requirements of ISO 14067.

The ISO 14044 allocation hierarchy can be summarized in three main stages:

The practical message is that economic allocation should not be the automatic starting point when following the ISO 14044 procedure. Before using economic allocation, assess whether allocation can be avoided through subdivision or system expansion, and whether a relevant physical relationship provides a suitable basis. Document the chosen method and explain why it is appropriate for the process being assessed.

Applying this hierarchy requires judgment. Different allocation methods can produce different product-level environmental results from the same underlying process data. A clear rationale, consistent application and transparent documentation help reviewers understand how the results were calculated and assess whether the chosen approach is appropriate.

Here is a side-by-side comparison of common approaches for attributing factory energy consumption to products.

No single method is suitable for every situation. The objective is to choose an approach that reflects the underlying physical or other relevant relationship, follows the applicable methodology, and can be justified using available data.

Direct measurement helps establish how much energy a machine, production line or process consumes. When the measured energy can be attributed to a specific product or process, it reduces the need for estimation and allocation.

For example, if a furnace processes only one product during a defined production run and its energy consumption is measured reliably, that consumption can be attributed to the relevant production activity. If the furnace processes several products together, further attribution may be necessary.

Process subdivision is a separate concept. It involves separating a multifunctional process into smaller processes so that their inputs and outputs can be attributed more directly. Where subdivision or another permitted approach avoids allocation, it should be considered before selecting an allocation basis.

In practice, shared utilities such as compressed air, chillers and boilers may supply several production activities. Their energy consumption may still need to be allocated using an appropriate basis.

Machine hours provide a practical allocation basis when reliable operating-time records are available. The method distributes shared energy according to the time each product uses the relevant equipment.

For example, if Product A uses a press for 600 hours and Product B uses it for 300 hours, allocating energy in proportion to machine hours gives Product A twice the share assigned to Product B.

This relationship is reasonable when the press draws approximately the same power under both products' operating conditions. It becomes less representative when products require different speeds, loads, temperatures or machine settings. In those cases, measured energy consumption or estimates based on actual operating conditions may provide a better basis.

Mass and volume are possible physical allocation bases. They are relatively straightforward to apply when the selected measure reflects the factors driving energy consumption.

For example, mass may provide a reasonable basis for allocating certain process burdens among similar products manufactured under comparable conditions. However, a heavier product does not necessarily consume more energy, and a larger product does not necessarily require more processing time.

When products differ substantially in material composition, geometry, processing requirements or production routes, a mass- or volume-based allocation may misrepresent their relative energy demands. The suitability of the method should therefore be assessed for the specific process rather than assumed.

When equipment-level measurements or reliable process data are available, energy can be attributed using actual consumption or estimates based on equipment power, operating time and load.

For example, a curing process may require more energy than a drying process, depending on the equipment, operating temperature, cycle duration, load and efficiency. Reliable measurements or estimates of process-specific energy consumption may provide a more representative basis than machine hours when energy demand differs across operating conditions.

Rated power alone is not enough to establish actual energy use. The calculation also needs to account for how long the equipment operates and, where relevant, its actual load. The quality of the result depends on the accuracy and representativeness of the supporting data.

Floor area may be useful for allocating certain types of general facility energy when the area occupied by a production line or activity reasonably reflects its share of the relevant energy demand.

For example, floor area may provide an initial basis for allocating some lighting loads when lighting intensity and operating conditions are sufficiently comparable across the relevant areas. Heating, cooling and ventilation may require additional consideration because consumption can depend on operating hours, occupancy, insulation, ventilation requirements and the characteristics of each space.

Floor area is therefore a proxy, not a direct measurement of product-level energy use. Its suitability depends on the type of facility energy being allocated and the relationship between floor area and the factors driving consumption.

Economic allocation distributes relevant inputs or associated environmental burdens according to the relative economic values of the products. Under the ISO 14044 allocation procedure, other relationships, including economic value, are considered when allocation cannot be avoided and a suitable physical relationship cannot be established or used.

Economic allocation requires a clearly defined value basis, such as sales revenue or another appropriate measure, applied consistently to the products being assessed. The choice of value basis and the period used to determine it should be documented.

One limitation is sensitivity to changes in relative prices. If one product's price rises relative to another's while total factory energy consumption and production conditions remain unchanged, its allocated share may change even though its physical energy demand has not. This does not automatically make economic allocation invalid, but it means that the method's assumptions and sensitivity to market conditions should be considered when interpreting the results.

Use these questions to move from theory to a practical decision.

As a starting point, consider direct measurement for process energy where attribution is possible, an appropriate physical basis for shared process energy, and a relevant allocation basis for general facility energy. These are practical guidelines, not fixed rules: the chosen method must reflect the process, the available evidence and the applicable PCF methodology.

Allocating factory energy across products is not about finding one perfect formula. It is about choosing an approach that reflects how energy is consumed, following the applicable standards and methodology, and documenting the reasoning behind each decision.

Choosing the right PCF allocation methods means combining appropriate energy data, a justified allocation basis and consistent documentation. These practices make product-level results easier to review, explain and update, while helping manufacturers identify where better measurement or more representative allocation methods may improve their assessments.