Cradle to Grave Carbon Footprints

Cradle -to-grave carbon footprints include the contributions downstream of the production. The upstream part is handled as described in the previous section. Downstream contributions can be very diverse and typically come from logistics

■ Raw Materials. transportation. other

□ Power

base case CHP model base case CHP model

1.11

1.04

0.61

□ Raw materials, transport, other

1.09

20.8

1.09

0.91

mass molar mass H2 credit mass molar mass H2 credit mass molar base case

Chlorine

NaOH 50%

-Hydrogen -

Figure 1.7 Cradle-to-gate footprints (electrolysis example) with different allocation methods.

and packaging, additional production or finishing, purchasing (mostly a logistic effort), product application and disposal. Most of them can be treated similarly to the methodology described in the previous section. The process of calculating the contributions from application will not be discussed here in detail as it varies significantly case-by-case. Conceptually it is similar to the other contributions.

For the majority of cradle-to-gate footprints the functional unit is naturally the product itself expressed in unit mass, volume, or as packaged or delivered (barrel, bottle, blister, ...). The definition of the functional unit for a cradle-to-grave footprint is often more tricky and determines the downstream scope of the assessment. Let's consider an example for an insulation of a building. We want to compare a building without insulation to one with insulation made of different materials (e.g., rock wool, polystyrene foam, polyurethane foam). A cradle-to-gate footprint would compare the production chain and an obvious functional unit is kg or m3 of insulation material. Alternatively we can use a reference on the material property. For this application it is more meaningful to use the heat transfer resistance of the material as a functional unit. However, this still does not take into account the effort to install the insulation, the energy savings caused by it and the effort for removal and disposal. A reasonable functional unit is the life cycle of the wall to be insulated. This includes considerations on insulation thickness, lifetime of the insulation or the building, building conditions, mode of use (indoor temperatures), type of heating device, location of the building (climate, transport distances), and so on. It is also plausible to extend the scope and use the life cycle of an entire building as the functional unit. However, this scope would be so broad that we loose the close link to the product insulation material. A PCF for wall insulation compared to no insulation can be found quantitatively in [11] (Neopor from BASF). The results are given in Table 1.5 The heat loss through the wall is included in the use phase and hence dominates the result.

Another example is shown in Figure 1.8 for a washing detergent (Persil Meg-aperls from Henkel). The selected functional unit is a washing cycle. We can see from the graph that again the application dominates the carbon footprint and that the influence of washing temperature is greater than that of raw materials and manufacturing.

The use phase of products is often very vague and ambiguous. It raises the question to which amount the emissions are attributable to the existence or the characteristics of the product. The use phase contributions will dominate for most products that are applied in conjunction with energy consumption. Cradle-to-grave PCFs are frequently prepared to canvass consumers or inform about the climate impact of certain products. Some of these should be regarded critically as a single

Table 1.5 Contributions to the PCF for a building wall in kg CO2e/life cycle.

Contribution Wall with insulation Wall without insulation

Raw materials, production, distribution 17609

Product use 469166 754505

Disposal 3 804

Cradle Grave Waste Management

■ distribution

□ shopping tour

□ product manufacturing

□ waste treatment

■ raw materials

Figure 1.8 Cradle-to-grave footprint of a detergent at three different washing temperatures [21].

■ distribution

□ shopping tour

□ product manufacturing

□ waste treatment

■ raw materials

Figure 1.8 Cradle-to-grave footprint of a detergent at three different washing temperatures [21].

CO2e-number (like on a can of beans in a supermarket) usually does not have a relevant meaning without a comparison against an alternative and additional information on scope, assumption on use phase and so on.

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