What Am I Comparing?

Priscilla’s next thought was: “more sustainable than what?”

Designers who want to decrease a product’s environmental impact need to have some way of evaluating what difference their choices make. The only way to evaluate whether a design is more sustainable is to see how its impacts compare with other options, such as an alternative design, a previous version, a benchmark, or an impact goal.

Throughout this guide, the term product has been used to describe the object of the designer’s work. When it comes to determining environmental impact, it’s important to specify a unit of analysis. Relative comparisons only work if there is a common basis. In some cases this might be quite straightforward, such as when it’s two generations of the same design or when faced with a simple material substitution. However, in most redesign opportunities, it’s necessary to specify a common “product unit” for the analysis.

An often-used way of handling this is to identify a functional unit. Instead of looking at a product as an item, it can be seen as a way for a certain function to be performed. In order to compare two different product systems, it’s necessary to choose a measure of the function of the systems that is consistent between the two. For instance, for a coffee maker it might be cups brewed, for laundry detergent it could be washing cycles, for paint it could be surface protection over time. This way, it’s possible to assess the impact of various ways to perform a specific function, without being constrained by differences in the forms of the designs.

“Well, that’s easy,” thought Priscilla. “My cup’s purpose is to hold liquid.” But when she thought about all the products designed to hold liquid -- detergent bottles, soda cans, mop buckets -- Priscilla realized she had to narrow down this purpose to define the functional unit. She decided that her cup’s functional unit was sixteen ounces or about 500 mL of (cool) liquid that could be poured in or out—or even better, 1600 ounces, equaling the volume of a pack of 100 cups. Now she could compare her bag of cups with all the other products imaginable that could hold this amount of cool liquid (and pour it in and out) and find the most sustainable option.

 

 

 

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