1

UNIT 2

Function and functional unit

2

The aim of this unit is to achieve the following points:

– to be able to set the problem and define the objectives and scope of the study;

– to know how to determine the function of the system and the functional unit.

1.1 Objectives of lesson 21.1 Objectives of lesson 2

What should be assimilated:

At the end of this lesson, you should be able to answer the following questions:

– At the very beginning of an LCA, what are the points that have to be clarified?

– What is the use of the screening approach?

– How is a functional unit defined?

– Can we reasonably compare bread with an umbrella? Why?

– What is a reference flow?

– How is product life time linked to reference flow?

3

1.2 LCA phases, where are we ?1.2 LCA phases, where are we ?

The goal definition enables to set the problem, to define the objectives and the scope of the study. The aim of this lesson is to get a deeper understanding of the first part of the goal definition. The points that are going to be treated here are:

– problem setting,

– system function and functional unit.

First of all, let’s situate ourselves in the overall LCA process. Remember the chart of lesson 1:

LCA is a cyclical process in which every phase is closely linked to the others. All results hang on the problem setting, system function and functional unit. Usually, it is recommended to carry out the LCA in two steps:

– A first screening phase covering the whole LCA andassessing order of magnitude of emissions inventory and impacts

– A detailed analysis to improve the assessment for most significant impacts

Goaldefinition

Inventory of extractions and

emissions

Impact assessment

Interpretation

4

1.31.3aa Scope definition and actors Scope definition and actors

In the first phase of an LCA, problem setting enables to clarify the following points:

•Overall objective,

Is it a way to gain information about an existing product? Are we developing a new product?

• Target public,

Who will benefit from these information? Is it for internal benchmarking, for consumers or for a governmental body?

• Actors

Who are the concerned actors? The different stakehoders and NGOs should be involved from the start of the study within the steering committee.

Four stakeholders’ group are important to determine.

5

1.31.3bb Scope definition and actors Scope definition and actors

These groups are the following:

- the peer reviewers…

- the steering committee and stakeholders,

- the mandate giver,

The role of the steering committee is to guide the study and validate the choices made in the goal definition (scenarios, functional unit, basic hypothesis…).

Peer reviewers are required for a publically available LCA. Their role is to check the quality of the study and the consistency between final results and conclusions. It can be interesting to involve peer reviewers from the beginning in order to enable the LCA executants to take into account these remarks.

About 5 to 10% of the LCA cost should be kept for the peer reviewers

- the LCA executants,

6

2.1.a System function2.1.a System function

Now that the goal and scope are defined and the stakeholders gathered, the system function has to be determined. The system function allows the comparison of various products/services which fulfill the same function.

For example:

Washing

In your opinion, what could be the system function of “soap”?

– portable phones have a function of communication,

– paintings share a covering function.

7

2.1.b System function2.1.b System function

LCA relates the environmental impacts to a specific product function. Products or systems can only be compared on the basis of a similar function.

One should not forget that the studied systems may have multiple functions. If their secondary functions differs too much, the validity of the comparison becomes questionable. It is therefore essential to care about the secondary functions as well.

– In the phone secondary function could be “to look cool”…

– Painting is intended to cover and protect,it also has to look nice.

Perfuming, moisturing skin, relaxing…at least according to advertisements!

Let’s come back to soap. Do enumerate its secondary functions.

8

2.2 Functional unit2.2 Functional unitBased on the system function, it is possible to define the functional unit (FU) common to all scenarios. It represents the system function which will serve as a basis for scenario comparison: in the inventory (second step of the LCA, lesson 4), inputs and outputs are calculated per FU.

The FU stands for what is offered. It is a quantified and additive value (not a ratio!):

– FU for phones could be 1000 hours timespan of conversation,

– a FU of painting is one square meter covered during.

In the soap example, what could be a valid FU?

Remark: if a component is studied (e.g. phone batteries), FU generally refers to the overall function (number of batteries required for 1000 hours of communication).

A definite number of shower.Let’s take 50 “standard” showers

9

2.3 Reference flows2.3 Reference flows

Next step of the LCA is the determination of the reference flows (what is bought). They provide for each scenario the basic products quantities needed per FU. In our previous examples:

– a phone and electricity for charging the battery,

– the quantity of painting and the brushes necessary to cover 1m2.

Back to the soap: what would you see as being the major references flows?

The life time and the number of reuse are linked with the reference flow. For example, two 500h communication life time phones are needed to catch up with a good quality 1000h life time phone. Thus, greater reference flows.

Reference flows, product life time or number of reuse can be key parameters for environmental optimization.

the mass of soap and the volume of hot water required to take 50 showers

10

3.1 Light bulbs3.1 Light bulbs

As an illustration, let’s have a closer look to light bulbs. Their main function is lighting. Secondary functions could be aesthetics, heating, providing a nice atmosphere…

The chosen FU is 600 lumen of light intensity. As usual, emission will be calculated for the above mentioned FU. We are going to compare a 60W, 1000 hours lifetime incandescent bulb weighting 35g, with an 11W, 6000 hours lifetime low energy fluorescent bulb of 160g.

To ensure a service of 6000 hours at 600 lumen, what do you need to buy? (your reference flows)

One economic light bulb or 6 incandescent bulbs and:

6 * 60W * 1000h = 360kWh for incandescent bulbs

11W * 6000h = 66kWh for low energy bulb

11

3.2 Light bulbs3.2 Light bulbsenvironmental key parametersenvironmental key parameters

Some of the key environmental parameters can be identified without any further calculation:

– the number of lumen per watt (performance of the bulb),

– the life time.

The former has to be maximized for the use phase. The latter directly influences the environmental load for the raw material extraction and the manufacturing stage.

Further analysis is however required to assess the relative importance of these different development stages.

12

3.3 Light bulbs3.3 Light bulbseconomical considerationseconomical considerations

What is your main objection for purchasing fluorescent bulbs?

But the purchasing cost is not the only one that has to be considered. The whole economic costs can easily be calculated and compared on the basis of the same FU, applying a life cycle costing approach:

– an incandescent bulb is about 1$,

– low energy fluorescent bulbs cost 10$ each,

– electricity is about 0.1$/kWh (use phase).

Please feel free to calculate the corresponding investment costs…

Price is often raised as a main objection, since the low energy bulbs are more expensive.

13

Product or system

Functional unit=offered

service

Reference flow= what you buy

Key parameters Costs

Scenario 1

Scenario 2

Products Main function Secondary function/performances Scenario 1

Scenario 2

Alternative scenarios

3.3 LCA and design for environment:3.3 LCA and design for environment:

Contrary to apparent purchasing costs, fluorescent bulbs therefore lead to significant economic savings of 25.4$ per bulb for a 6000 h service.

All the results can be gathered the following way:

6000 hours at 600 lumen of light intensity.

60W * 6000h/FU

= 360kWh/FU

6 bulbs = 6 * 35g

= 210g

11W * 6000h/FU

= 66kWh/FU

1 bulb = 160g

The number of lumen per Watt.

The life time.

The manufacturing stage.

360kWh/FU * 0.1$/kWh = 36$/FU

6 * 1$ = 6$/FU

66kWh/FU * 0.1$/kWh = 6.6$/FU

1 * 10$ = 10$/FU

Incandescent bulb

Fluorescent bulb

Lighting Aesthetics

Heating

Providing a nice atmosphere

14

3.4 Light efficiency for different sorts of 3.4 Light efficiency for different sorts of bulbsbulbs

Beware comparing an emerging technology which has not yet been optimized with a well established one which has been improved over years.

On the second graph, you can see that efficiency of light bulbs has improved of a factor 1000 over 100 years. Turning a new technology into an efficient one requires time.

To go further in the study of light bulbs, we can consider more kinds of bulbs. In the following figures you can see the evolution of the light bulbs and of the improvement in their efficiency through the last two centuries.

15

4.1 Example : shoes4.1 Example : shoes

Now you are going to do an exercise to check if you understood the notions explained during this lesson.

Let ’s compare 2 different type of shoes:

– high quality (Swiss? ;-)) shoes with a life time of 2 years,

– lower quality shoes with a life time of 6 months.

Now it is your turn to fill in the following form… Answers are given in the second next slide.

16

4.2 Example: shoes4.2 Example: shoes

… ...

...

... ......

...

... ...

Product orsystem

Functionalunit=offered

service

Reference flow=what you buy

key parameters Costs

Scenario 1

Scenario 2

Products Main function Secondary function/performances Scenario 1

Scenario 2

Alternative scenarios

17

4.3a Example: shoes4.3a Example: shoesProducts Main function Secondary function/performances Scenario 1

Scenario 2

Alternative scenarios

Product or system

Functional unit=offered

service

Reference flow= what you buy

key parameters Life Cycle Costs

Scenario 1

Scenario 2

A pair of shoes protecting the feet during a definite timespan of "standard" use.

(2 years)

To protect the feet To be fashionable

To be comfortable

…

1 pair of 2-years lifetime shoes

4 pairs of 6-months lifetime shoes

Quantity of materials used,

Type of materials,

lifetime.

Let’s say HQS are 150 US$ and LQS are only 45 US$:

HQS: 1150=150US$

LQS:

445=180US$

High quality city shoes (HQS)

Low quality city shoes (LQS)

18

4.3b Example: shoes4.3b Example: shoes

Note: the shoes we are comparing are of the same kind, city shoes. It would not be possible to compare summer sandals with boots, since they have too different functions (protection against heat or snow).

We can see in our example that LQS are more expensive than HQS. Depending on your assumptions you may have a different result.

Moreover the environmental burden of producing four pair of LQS has proved to be higher than for one HQS. This is because of the materials used, for LQS mostly plastic derivates, for HQS mostly leather.

This is clearly a win-win situation where sparing money goes with lower environmental burden.

In addition to the shoes, the shoe shine should be taken into account if its amount is not the same for all the scenarios. This topic will be discussed in more details in Unit 3 (System boundaries).

19

5. Questions of understanding5. Questions of understanding

–At the very beginning of an LCA, what are the points that have to be clarified?

–What is the use of the screening approach?

–How is a functional unit defined?

–Can we reasonably compare bread with an umbrella? Why?

–What is a reference flow?

–How is life time linked to reference flow?

20

6. Group exercise6. Group exercise

The end of this session is dedicated to the group exercise.

Three by three, you now have to solve the case you subscribed for.

Thank you and see you soon...