Allocation in Life Cycle Assessment (LCA) addresses the challenge of how to distribute the environmental inputs and outputs when a process yields multiple valuable products, known as multifunctionality. Understanding this concept and its application is important for accurately assessing the environmental impact of products that share common production processes or resources. This article covers the following topics:
What is allocation in LCA?
When to use allocation?
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What is allocation in LCA?
When a process yields multiple functions or co-products, allocation becomes relevant (Figure 1). Put differently, multifunctionality occurs when a process yields more than one valuable product. When this happens, there is a question of how to allocate the inputs (e.g., electricity) between the two (or more) products. Allocation solves the issue of multifunctionality in LCA. It involves splitting up the amounts of the individual inputs and outputs between the co-functions according to some allocation criterion (mass, physical properties, economic cost/value, or production amount). Allocation methods vary based on the LCA standard you’re following or the specific context. Whether allocating process inputs and utilities or managing multifunctional systems, you must carefully select allocation methods to ensure accuracy and transparency in the assessment.
Figure 1: A multifunctional system.
When to use allocation?
Below we outline two examples to help you understand when to employ allocation in your model:
Example 1: Allocation of process inputs and utilities measured over more than one product
Let’s say energy use data is not measured per single product, but, for example, over multiple of the same products for a certain time. How do you deal with this?
You need data for two values: 1) energy usage over a specific time period, and 2) production amount/weight over the same respective period. If these two variables are known, you must divide this energy usage over your products.
Different ways to divide the energy:
Based on the production amount
Based on the produced weight
In this example, allocating by production amount will suffice if you believe that the electricity consumption is relatively equally distributed over all products. If, however, you know that certain products require more electricity to be produced, it would be more accurate to use an alternative method to distribute the total electricity consumption over all products. If heavier products need more electricity, allocate the total electricity consumption based on the total produced weight to account for such variations.
Note - Data and allocation: Sometimes you are limited by the amount or quality of data. In the example above, if you don’t know the total produced weight (option 2), you will initially be ‘forced’ to use option 1. LCAs are an iterative process - it could be beneficial to go back to your supplier and attempt to get better data and refine your LCA later.
Example 2: Allocation of multifunctional systems
Let’s assume Figure 2 represents the baking process of two pies (two co-products): an apple pie (product A) and a pecan pie (product B). To allocate the impact related to the baking process, all inputs (energy or electricity) must be allocated over the two co-products. Consider allocating the baking based on the following criteria:
Based on mass (e.g. weight)
Based on physical properties (e.g. energy content)
Based on economic value
Table 1 presents the results calculated using each method - notice the variation in results.
Table 1: Impact results using different allocation methods
Product Name | Amount | Mass | Baking time [Energy Content ] | Economic Value |
Apple pie | 1 (50%) | 1.0 kg (39%) | 15 minutes (30%) | €2.40 (12%) |
Pecan pie | 1 (50%) | 1.56 kg (61%) | 35 minutes (70%) | €17.60 (88%) |
In this case, the difference between allocating based on mass versus allocating on economic value is 27 percentage points. A huge difference!
Caution - Selecting an allocation method: As the example above shows, different allocation methods can lead to very different results. How you should allocate the impact of your products depends on the standard you’re following. Where relevant, standards should be consulted ahead of selecting an allocation method.
If, however, no information is provided on allocation, typically some form of ‘physical allocation’ takes precedence to ‘economic allocation’. Allocation based on some physical attribute is more robust over time, while economic properties (prices & value) can change, which is undesirable for creating a future-proof LCA.
Video Tutorial
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Next steps
Understanding and implementing allocation in LCA is necessary for accurately capturing the environmental impact of processes that produce multiple valuable products. By carefully selecting appropriate allocation methods based on the context and standards relevant to your LCA, you can ensure the accuracy and transparency of your assessment.
For more detailed guidance and examples, explore our other resources on LCA methodologies and best practices. If you have specific questions or need further assistance, our support team is always here to help. Good luck with your LCA projects!