If the manufacturing site produces multiple products, how should I allocate the energy consumption and inputs per product?
When a manufacturing site or production line delivers several products, it becomes necessary to allocate shared energy consumption and material inputs across these outputs. The choice of allocation method can significantly influence the results of a Life Cycle Assessment (LCA). The goal is to ensure that each product carries its fair share of the environmental burden associated with its production.
1. Basic Principle
Allocation is needed when several products share the same process, machine, or infrastructure. Since most plants do not measure electricity, gas, or raw material consumption per product, it is necessary to distribute total resource use across all outputs. This step ensures that the LCA reflects a realistic share of environmental impact for each product.
ISO 14044 recommends avoiding allocation whenever possible—by subdividing processes or expanding system boundaries—but in practice, allocation is often unavoidable in multi-product sites.
2. Macro-Level Allocation (Simplified Approach)
A practical first step is to allocate consumption based on the relative production volume of each product over a representative period (usually one year).
If your factory produces three products—A, B, and C—and product A represents 30% of total annual production (by mass, units, or sales volume), then approximately 30% of the total energy and input flows can be allocated to product A.
This proportional approach is not perfectly accurate, but it provides a consistent and transparent assumption for building an initial LCA with limited data. It works well for early-stage assessments, especially when the production mix remains relatively stable.
3. Detailed Allocation (Machine or Process Level)
For higher precision, allocation can be refined by focusing on specific equipment or production stages.
For example, if a given machine operates 50% of the time on product A and 50% on product B, then half of the machine’s energy consumption should be attributed to each product. This approach is appropriate when equipment-level data are available—either from machine specifications, monitoring systems, or energy meters.
Where detailed operational data exist, allocation can also be based on:
Machine run time per product,
Batch size or frequency of production per product,
Specific process parameters (e.g., heating time, temperature, cycle duration) that drive energy use.
Such refined allocation requires more granular data but provides a more realistic representation of each product’s contribution to total resource use.
4. Alternative Allocation Bases
Depending on the context and available data, several allocation criteria can be used:
Physical allocation (mass, volume, energy content): recommended when physical properties directly influence resource use.
Economic allocation (market value): used when products differ strongly in value but share identical production processes.
Functional or energetic allocation (e.g., exergy): suitable for energy-related products (fuels, heat, etc.).
The general hierarchy, following ISO guidance, is:
Avoid allocation if possible (by subdividing processes or using system expansion).
If unavoidable, prefer physical relationships (mass, energy).
If not applicable, use economic allocation.
5. Practical Recommendation
For a multi-product manufacturing site:
Start simple: use annual production shares (by weight or units) for an initial, transparent LCA.
Refine progressively: where data allow, move to machine-level or batch-based allocation.
Document clearly: always state the allocation assumption and, if possible, perform a sensitivity analysis showing how results change with another method.
This structured approach ensures both practicality and methodological rigor, balancing data availability with the need for credible, reproducible LCA results.