When complex calculations have to be made, and when LCIs of other databases have to be applied, it is important to understand the structure of the LCIs.
In practice, the lists of LCIs (Life Cycle Inventories) are never "from cradle to grave", since that is not practical because of the many variations of the total chain of one product. LCA practitioners compile a life cycle chain by combining the LCIs of the subsystems.
A LCI of a subsystem comprises a list of "inputs"
and a list of "outputs".
The outputs are emissions to air, water and ground. It is obvious that the product of the subsystem is also listed under output (with the quantity and the dimension)
The inputs are materials energy and transport which is required in the subsystem.
When electricity and/or heat is generated as a by-product (output) of the system, it is often given as an negative input.
|The are two types of LCIs:
- the LCI of the subsystem only (the Unit, U), i.e. from "gate to gate"
- the LCI of the system, including the subsystems of all inputs (the System, S), i.e. from "cradle to gate"
The meaning of Units ("gate to gate") and System ("cradle to gate") is depicted in Figure 8.3 .
It is obvious that the Use Phase and the End of Life Phase are often compiled by means of Unit LCIs( from gate to gate or from gate to grave) to be able to create the right life cycle chain for each individual case.
For the inputs of the Production Phase (materials, energy and transport), however, it is more practical to apply System LCIs (from cradle to gate).
Most data on "inputs" in the Ecocosts 2007 LCA databases are "from cradle to gate", unless it is obvious that it is otherwise (for Processing in the Production Phase, the Use Phase and the End of Life Phase).
Fig. 8.3 (click for details)
The compilation of LCIs to build the total chain is a matter
of common sense: one has to be careful that all subsystems are in the total
system (within the boundary limits), without double counting.
For an example see (an example will follow in due coarse)..
More information on this subject, as well as practical examples, can be found in the Simapro manuals.
A total system has always its boundary limits. That means that subsystems outside the boundary limits are neglected. An example of transport by truck:
- the fuel and its related emissions are always within the system
- the emissions related with the production of the truck ("indirect emissions") and the materials depletion, are sometimes within the system
- the emissions related with the construction of the roads are normally not within the system
- the emissions related with the construction of the plant where the truck is build are normally not within the system
- the office of the transport company is normally not within the system
LCIs have also Geographical boundaries.
The following abbreviations are used: DE = Germany; OCE = Oceanic; UCTE = Union for the Co-ordination of Transmission of Electricity; RER = Europe; NL = Netherlands; GLO: = Global; CH = Switzerland