How can you choose the right functional unit for life cycle assessment?

A functional unit is a key concept that defines the quantified performance of a product system for use as a reference unit in a study. It provides a basis for comparison when evaluating the environmental impacts of products or systems. Examples: Car: Compare two cars based on the distance traveled by one person. Truck: Assess two trucks based on distance and cargo weight. Package: Compare two packages based on durability and contents. The functional unit is essential in LCA because it ensures that the systems being compared provide an equivalent function or service, making the comparison meaningful.

Defining a functional unit ensures we compare 'apples to apples' in LCAs. It allows us to measure the total environmental impact of a product or service across its life cycle – from raw material extraction, through manufacturing and use, to disposal or recycling – based on its *specific function*. The functional unit is pivotal in anchoring every stage of the LCA, from data gathering to result interpretation. Its careful selection greatly enhances the LCA's utility and relevance. Consider an LCA of a truck: - FU: traveling 100km. - FU: traveling 100km with 2.5 tons of goods. The latter functional unit captures the essential purpose of using a truck, making the comparison more meaningful.

Life Cycle Assessment of Disposable vs. Reusable Coffee Cups 1. Define the Purpose of the LCA: Compare disposable vs. reusable coffee cups. 2. Identify the Main Function of the Product/System: Holding a standard serving of coffee. 3. Determine Key Performance Indicators (KPIs): Volume of coffee held (e.g., 250 ml). 4. Consider the End-User's Perspective: Convenience and ease of use while drinking coffee. 5. Analyze Variability in Use: Differences in usage frequency (daily for reusable, single-use for disposable). 6. Evaluate Data Availability: Collect data on material composition and manufacturing processes for both cup types. 7. Test the Functional Unit: Conduct a preliminary LCA on both cup types for 250 ml coffee servings.

LCA of Laundry Detergents Well-Defined FU: Washing 100 standard laundry loads. Poor FU: One liter of detergent. (fails to specify the cleaning performance or number of uses.) LCA of Building Materials (e.g., Insulation) Well-Defined FU: Maintaining a specified indoor temperature in a 100 square meter area for one year. Poor FU: One square meter of insulation material. (This doesn’t account for performance or application context.) These examples demonstrate how a well-defined functional unit in LCA is specific and clearly tied to the product's or service's performance and purpose, while a poor functional unit is vague, lacking in performance context, and does not facilitate a meaningful comparison of environmental impacts.

Pour un service numérique, l'unité fonctionnelle est souvent caractérisée par une fonctionnalité "métier" du service. Par exemple, sur un site e-commerce, l'unité fonctionnelle peut être par exemple "Acheter un produit". Pour affiner l'ACV, il est possible de détailler l'Unité Fonctionnelle en sous-process: - Rechercher un produit sur le site. - Mettre le produit dans le panier.

In addition to the selection steps provided earlier, here are some best practices to consider for functional unit selection in LCA: Review Industry Standards: Examine existing LCAs and standards for commonly used functional units, ensuring consistency and relevance. Seek Expert Input: Consult with LCA experts or stakeholders familiar with your product or system to refine your functional unit choice. Test and Refine: Apply the functional unit in a preliminary LCA to evaluate its effectiveness, and be prepared to make adjustments based on the findings. These practices further ensure that your functional unit is appropriate, enhancing the accuracy and validity of your LCA results.