Handling multi-product processes

To take multi-product processes into account you have two options: Either you use allocation or system expansion.

Allocation

For using allocation, open the multi-product process, go to the „Inputs/Outputs” tab, and select an allocation method. You can choose between physical and causal allocation.

The physical allocation calculates the factors automatically from the share of the product in the reference flow property. Typical examples are the mass or the heating value of the product. This share represents the allocation factor, and is used for each flow of the process. In order to work, products need to have the same flow property. The default (reference) flow property is used to calculate the shares between the product.

The causal allocation method allows to specify individual percentage shares (i.e. allocation factors) for each of the flows. Via „set causal allocation factors” a default causal factor for all flows of the process can be set. This default setting can be changed for each individual flows in the flow properties section. All allocation factors need to sum up to 100%, otherwise an error is thrown.

In the example we have a cogeneration unit that produces 1 MJ heat and 2 MJ electricity. If we apply causal allocation, we can enter percentage shares for every flow in the properties field. You can also use the same factors for all exchanges, if you click on the button „Set causal allocation factors for all exchanges”.

If you select the physical allocation method, these steps are not necessary. In our example all flows will be divided by three: Electricity is responsible for 2 thirds of the emissions and heat causes 1 third of the emissions. Because the example has not inputs, only outputs are considered.

System expansion

If you want to apply system expansion, open the multi-output process and go to the „Inputs/Outputs” tab. If your product system is open, you can click in the graph on the process with the right mouse button and say „Open in editor”.

Now, add an input flow which corresponds to the output that is not needed as a product. In this example we join the flow „Heat” to our input table and set a check mark for „Avoided product”. It is important that no allocation method is selected, otherwise you cannot define avoided products. Save changes.

Then go back to the graph of your product system and add one process which has heat as output. Note that here you can only use system processes.

The avoided product is accentuated in grey, the link between the multi-output process and the help process is dashed.
As a result of our modeling, the system will credit the production of the heat.