Course LCA no. 3c - Purpose and Objective: Definition of functional unit

It is important to define from the beginning a reference measurement unit for the study, which we will call the "functional unit," with which to handle and present the data and information of an LCA. In particular, the UNI EN ISO 14040 standard states that: "A functional unit represents a measure of the performance of the functional output flow of the product system. Its purpose is to provide a reference to which to link the input and output flows. This reference is necessary to allow the comparability of the results of an LCA study. The comparability of the results of an LCA is particularly critical when evaluating different systems, as it must be ensured that such comparisons are made on a similar basis. A system may have a large number of possible functions and the function chosen for the study depends solely on the objective and the field of application. The functional unit must be defined and measurable."

The choice of the functional unit is arbitrary and essentially depends on the purpose for which the subsystems and the global system have been designed; it can be understood as an index of the performance carried out by the system. This unit was also created because the units of measurement normally used such as mass, number of pieces, or volume are often not always adequate to represent the energy or environmental performance of a production process, but also because equal results of a study expressed in different functional units can lead to completely different conclusions. Let's make some examples:

If the function of a process is the production of packaging, the unit of measurement to refer to the study will be the quantity of packaging needed to contain a certain volume of product and not the kg of glass or cardboard. Or, if the function of a process is painting a wall, the functional unit will be the square meters of surface protected by the paint for a guaranteed minimum duration and not, for example, the kg of paint.

To further clarify things, alongside the functional unit, the ISO 14041 standard (dedicated to this phase of the LCA) introduces the concept of "reference flow". This flow represents the amount of goods or services necessary to obtain the chosen functional unit. For example, in the case of a comparison analysis between two hand drying systems in public places, the functional unit will consist of "a number of hands" that can be dried using the two systems, while the reference flow will be in the case of the electric system, the amount of hot air needed to obtain the chosen functional unit and in the case of the paper system, the amount of paper used.