Advanced functions
From Documentation
In this section advanced functions as allocation, system expansion, parameters, and uncertainty are described. You will learn how you can handle multi-output processes, apply parameters, and calculate uncertainty.
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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, economic, 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 economic allocation method calculates the allocation factors also automatically based on the economic value of the flows. In order to apply economic allocation you need to add first an economic flow property to every flow and enter then the economic value of each flow in the process.
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% (i.e. 1.0), 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.
If you select the physical or economic allocation, these steps are not necessary.
NB:
- All allocation factors must sum up 1. This is mandatory for each flow.
- Also, no parameter or formula can be used in this field.
- Waste flows are considered for allocation calculations like product flows. This is understood as a co-product. To disable this, one must apply 0 to this flow as allocation factor.
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.
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.
Parameters
In openLCA it is possible to assign processes and product systems different parameters, for example to handle with preliminary values. Parameters can easily be changed later in the modeling of product systems. A parameterised process can substitute hundreds of black-box processes.
openLCA distinguishes local and global parameters. Local and global parameters can overwrite each other; the direction can be defined under File > Preferences >Parameter settings (see Settings).
Notation for parameters
Only letters and numbers can be used in the name field (no capital letter, space, dash, underscore...).
Simple mathematical calculations can be entered directly, e.g. a=6; b=2*5 + 4.
Many more complicated formulas can be used, but then need to be specified according to the Java Math specification. A list of all provided functions is available here: http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Math.html.
Local Parameters
If you open a process or a product system you find a tab "Parameters" at the bottom. If you click on it a table occurs where you can define parameters. For adding a new parameter, click on the plus symbol top right and fill in a name, a formula or a value, and a description (optional). The formula can refer to other parameters, but loops for parameters should be avoided (example: P1 uses P2, P2 uses P3, and P3 uses P1). Please make sure that you do not use commas for point numbers. Make also sure that you have specified arithmetic operators before bracket terms.
To delete parameters, mark one and click on the red cross top right.
Global Parameters
To define global parameters go to File/Preferences/Global parameters". Select a database and click on the plus symbol to add a new global parameter. Fill in a name, enter a formula or a value for the parameter, and describe the parameter (optional). The formula can include other parameters, but loops for parameters should be avoided (example: P1 uses P2, P2 uses P3, and P3 uses P1), because of discontinuity. Please do not use commas for point numbers and specify arithmetic operators before bracket terms. Finally click "Apply" to save the changes. If you mark a parameter and click on the red cross you can delete it.
If you define both types of parameters, with identical names, be careful with overwriting! Under preferences, you can define whether global parameters overwrite local ones or vice versa.
Content assistant
If you edit a parameters formula, you can press CTRL+SPACE and a popup window will appear containing all local defined and database wide parameters. Just select on and it will be added to your formula.
Uncertainty
The modeling of LCAs is related to many different types of uncertainties.
First, open a process by double-clicking it and go to the tab "Inputs/Outputs". Click once in the field "Uncertainty distribution type" of every flow where you want to add a distribution (If you click twice you will open the flow in the editor). In the field "Properties" at the bottom of the process editor you can indicate geometric or arithmetic mean value, (geometric) standard deviation, Max or Min value depending on the selected probability distribution and save the changes.
If you now calculate your product system with the sequential method you can see the approximation under the "Standard deviation" column in the Inventory tab
Approximation
For an estimation of the uncertainty for flows openLCA provides another faster calculation option, by using Gaussian error propagation formulas. The approximation formulas assume normally distributed random errors for these flows. According to literature, Gaussian approximation formulas provide the same results as Monte Carlo Simulation provided that the relative error (i.e. the variation coefficient, standard deviation divided by the mean) is below 20% (Ciroth 2001). This condition is checked during the calculation; if the variation coefficient is found to be higher during the calculation, a warning message is issued together with the calculation results.
To use approximation for uncertainty calculation, you can edit settings for the calculation in the "Preferences" under "Settings for calculation methods", and change the default entry use uncertainty calculation to true. Note that you can use only the sequential methods for the calculation. As default uncertainty approximation is inactive.
Handle waste management processes
openLCA considers waste management processes as input. This allows a process to bear the whole waste burden. On the other side, if you plan to calculate a mass balance, this may lead you to false results.
The following example comes from the case study Remodelling of a park. The deforestation is composed of tree growing, the chopping of wood and its incineration. Instead of sending the cut wood to burn, it is considered here, just as other processes, as an input ("disposal, wood untreated, 20% water, to municipal incineration").
If the waste management process were considered as an output of a process, it would not be part of the upstream chain that leads to the functional unit. To rectify this, one could instead add a service flow, looping back to the deforestation.
Change the language of openLCA
If you have installed openLCA in English and you wish to use it in German (or the contrary), it is possible to do so with the following method.
- Close openLCA
- Go to the installation folder (ex for Windows users : C:\Program Files\openLCA)
- Open the file "openLCA.ini", which can look like this:
-nl
en
-data
@noDefault
-vmargs
-Xmx512M
- Change the value from "en" to "de" (or the contrary)
- Save the file and restart openLCA. Windows users require an administrator access! An alternative is to first copy the file somewhere else and overwrite the original file.
NB: This will affect the language settings of the software menu, but also the language (of flows, compartments, units...) of each future database created!
Uninstall openLCA
If ever you want to uninstall openLCA (for example, to install a newer version), please follow these simple steps:
- Go to the installation directory (for example "C:\Program Files\openLCA")
- Double clic on "uninstall.exe" (Windows users can also access this option from the start menu)
- Clic on "uninstall" and it is done within a second!
NB: the databases you created (and also preferences) are retained on your computer. Windows users can find the databases kept in their local folder "C:\Users\xxx\openLCA-data\data".
