Determining the functional unit

The functional unit is the basic quantity for the LCA process. In defiiiing the functional unit, it is important to understand the utility of the object under 

A more general definition of the functional unit would thus be the service delivered to a customer or a process by one or several sub-systems, or a measure of the performance which the system delivers. Generally, the functional unit consists of a unit and a quantity (Table 4.1) such as person-transport kilometres, listening to the radio for one hour, or consuming 200 grams of biscuits. 

There are, however, cases where the functional unit does not possess both a unit and a quantity. Heijungs et al. [8] take up flowers as a good example of a functional unit that has more to do with a gesture than a quantity. In general a customer asks for a bunch of flowers , not for flowers for ten days or 500 grams of flowers . 

Many products have several functions, and it can be difficult to determine which one of tiien is central to the product. A warm sweater, for example, is not on ) bought to keep a person warm, since its appearance also plays a role in the decision to purchase. The main utility of the sweater being to keep its owner wami, however, appearance can be considered to be secondary in this context. Wliea comparisons between different product alternatives are being made in LCA, they should always be made on the basis of equal functionality. In cases wiicre products provide the same main function but have different subsidiary functions these functions must be clearly defined to allow judgement of their relevance for the final selection. 

Once a rigorous functional unit has been defined, the systems delivering the defined functional unit can be evaluated in terms of their environmental efficiency in bringing their service to the user. 

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