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This section describes the editable elements of openLCA as you can find them in the category tree.

The openLCA reference database

When you create a new database, this one is not empty. It has been established, based on ecoinvent, NREL US-LCI and ELCD databases. It contains all elementary flows, unit and compartments already contained in these databases. A mapping table included in the software ensures that there are no double flows created during imports.

Also, the language of the database (flow name, units, compartments) depends on the language of the software. This has been established during the installation, but it can be changed if you would like a database with another language. Simply change a setting (explained here) before creating a new database.

Actors

An actor is someone who either adds and modifies data, or models. An actor can also be author of a report or a research study, etc. An actor can be a person or an organisation.

Sources

Sources are references to books and other literature as well as to databases.

Unit groups

Units are measurement units (like m, s, kg, and so on). They are further grouped into unit groups. A unit group comprises units of a similar type (length-related units; mass-related units, and so on).

You can open unit groups by double-clicking. In the editor you can make changes. If you add or delete units in the unit group use the plus or cross symbol. You can also change the reference unit set the check mark at a different unit.

Creating a new unit group

If you want to create a new unit group, the wizard looks like the following screenshot.

Lets enter a "test unit group" and a "test reference unit" as reference unit. Note that the entries are validated and missing entries are highlighted.

A reference unit is used in the process system calculation: All units within a unit group are transformed, prior to calculating the system, to the reference unit. Therefore, every unit group needs a reference unit.

The conversion factor expresses the relation to the reference unit. Here, as always, a decimal must be a point (and not a comma as in e.g. German). This is also checked.

Note that once you have changed anything on an element, it is marked with a * and you need to save it in order to let the changes take effect.

Flow properties

Flow properties are characteristics of flows, both extensive and intensive ones, such as mass, radioactivity, length, and so forth. You can distinguish flow properties into chemical composition, economic, and technical flow properties. You can modify the categories of flow properties as described in the working with the GUI page .

Creating a new flow property

For a new flow property, open the wizard, select "Flow property", and click on "Next".

You need to assign a unit group in order to specify the type of the property (e.g., length-related, mass-related, and the like). This assignment can be changed later on. Click on "Finish".

Flows

Flows are streams of substances. Every flow has a flow type. There are three flow types in openLCA:

Elementary flows: Material or energy entering the system that has been drawn from the environment without prior treatment, or material or energy leaving the system that is released into the environment without subsequent treatment
Product flows: Products entering or leaving to another process
Waste flows: Products leaving the product system

Note that you cannot change the flow type later on, as this could create several problems (as: product systems without product if you change a product flow type to an elementary flow type; products in LCIA methods if you change a flow type form elementary flow to product flow). Therefore, if you really need to change the type of a flow, it is required to create a new flow with the different type then.

Moreover, every flow has flow properties as e.g. mass, volume or amount. Flows have at least one flow property, but can also have several ones. The reference flow property is highlighted in bold and can be easily changed by checking "Is reference".

Creating a new flow

If you want to create a new flow, open the wizard and assign a reference flow property and a flow type. These assignments can also be changed later on. If there is no appropriate flow property, you have to create one first.

The reference flow property is used in the calculation: All flow properties are expressed in relation to the reference flow property.

At the bottom of the Flow editor, you find two tabs. On the flow properties tab, you see (evidently) the flow properties of the flow. You can add new properties by dragging flow properties from the left category tree into the flow property table (see screenshot).

The reference flow property is printed in bold.

By default, the conversion factor is 1.0; it expresses the conversion between the reference unit of the reference flow property and the reference unit of the other flow property.

Processes

A process illustrates the production or a modification of a substance or product. It comprises flows as inputs and outputs. There are unit processes and LCI systems, i.e. aggregated processes. If you open a process by double-clicking on it, it looks like this:

At the bottom of the editor, you find several tabs with different functions. For example, if you go to the tab "Inputs/Outputs", you can add or delete input and output flows with the plus and the minus symbol which are located at the top right. As advanced features you can label input flows as avoided products, add allocation, define parameters, or assign probability distributions to the different flows (see Advanced functions).

Creating a new process

The input and output list of all flows for a process is probably the most important part of the process. In order to create this list, the flows first need to exist, and if they don’t, need to be created (see in the Flows sheet). In Life Cycle Assessments, each process has one flow as quantitative reference. All other flows are scaled according to this quantitative reference. You "declare" one of the input or output flows in the tab "General information" of the process, see below.

Let’s look at one example: We create a process that builds a compost plant.

Open the wizard and create a flow with the name "Compost plant, open", the property "Number of items", and the type "Product flow" (see flows). Save the flow.
Open the wizard and build a process with the name "Compost plant, open" and select the flow "Compost plant, open" as reference flow. Click on "Finish".

The process editor of the new process will be opened. In the first tab you can add general information about the process. Under the tab "Inputs/Outputs" add input and output flows you need for your process. You can change the mass/amount of the flows by clicking once in the resulting amount field (If you click twice the flow will be opened in another editor window.).

If you have a multi-output process you most likely need to apply allocation or system expansion (see advanced functions).

Product systems

Product systems are one of the more complex elements in openLCA. Main purpose of a product system is to model and calculate case studies.

Basically, a product system is a network of processes. The processes are connected to the reference process, which has the required product as output.

Creating a new product system

To build a new product system, open the wizard. Enter a name and specify a reference process. As an example we will create a case study of a compost plant.

If you check the marked box, the program will automatically build a whole product system, following up all the different connections in the database, starting from the reference process. Depending on the database, this function can lead to a very complex product system. If you need a small and clear system, you can build it manually; you can of course also modify a system that is created automatically, by adding and deleting processes manually.

If you click on "Finish", the product system editor will be opened. At the bottom of the editor you find several tabs, for main elements of a product system

Elements in a product system

As you see from the screenshot above, each product system contains, beside general information, a graph and parameters.

Working with the outline

An element that is not in the tab band but belongs to a product system is the Outline. The outline lists all processes that are part of a product system. The outline window is opened by default when you open a product system. If you have closed it, you can re-open it via the menu by selecting Window/Show views/Outline.

The outline is convenient to locate processes in large product systems. You can filter and search for processes in the outline via entries in the top edit box of the outline...

...or highlight a process by clicking it or via the context menu (right mouse click):

openLCA tries to link a process to the existing visible process in the graphical editor. If this is not possible, because connected processes are not visible at present, the to-be-shown process is placed below the other processes as separate box.

Working with the graphical editor

If you go to the tab Graph at the bottom of the product system editor, the product system will be shown as a network. If you start modeling a product system, only one process might be visible; if you have already connected several processes, the graph can look like this:

The graph editor is the central point to model product systems in openLCA.

Each process in the product system is represented as one box. You can move these boxes around by pressing the left mouse button and holding it while moving the object to the target location. This process is known also in other applications, as dragging. If you double-click on a process-box, the inputs and outputs are shown. Double-clicking again hides the inputs and outputs. You can also change the size of the process-boxes by dragging the frame. With the small minus and plus symbols in the processes you can expand or collapse the next "layer" of processes connected to the specific process.

Adding or deleting processes in the graph

The graph is the visual structure of a product system. It is possible to add or delete processes of a product system in the graph. If you want to add a process drag and drop it from the navigation tree and it will be located top left. Now you can set links to other processes in the network by clicking with the left mouse button on an input/output and hold it pressed while dragging it to the corresponding input/output of another process. All possible connections are highlighted in blue.

If you want to delete a process in the graph you have to delete its connections to other processes first. Just right-click on the process and say "Remove connections"; then you can select "Delete".

If you decided to build the system automatically, you will initially see the process that provides the quantitative reference for the product system, plus the next layer of processes. If not, you will only see the reference process. By double-clicking on it, the process inputs and outputs are shown.

In order to find the processes that either provide a product of a process or receive products of the selected process, openLCA has an implemented search function. It is accessable via the context menu. If you right-click on a process you can search providers and recipients for all inputs and outputs of the selected process.

All suitable processes are then displayed in a new list window. It is also indicated, on the right, whether the process is already part of the product system and whether it is already connected to the selected process (but not shown at present). If the process is not yet contained in the product system, it can be linked (check: "add to product system")to the selected process.

The miniature view

A small miniature view window is available after a click on this icon in the menu bar:

It always shows the compete graph of all processes, in a miniature view.

The window is useful for:

getting an overview of your process network
navigating to a specific location of your process graph by moving the blue area in the window (which represents the part of the graph that is displayed in the large graph window) with your mouse
changing the zoom factor of the graph window by moving the slider

Changing the layout

Processes can be moved around freely in the graphical editor. If you have expanded processes or minimised them, or added processes, it may be wise to let openLCA re-arrange the process boxes. Two layouts are available, one that creates a vertically oriented tree, and one that creates a more horizontal tree structure. The vertically oriented tree is called minimal tree. Both layouts are available via the layout icons:

Hints for working with very large product systems

Product systems, especially if they are automatically connected from large databases, can become very large. In these cases, the overview of the system structure may not be useful for modeling.

Instead, use the outline to look up processes, and to connect processes. Clicking on the minus icon in the menu will bring the expanded system to its origin state (the process that provides the quantitative reference and the next layer of connected processes). By adding processes via the outline, and connecting them as required, even extremely large product system with several thousand processes remain manageable in openLCA.

Calculating results

Inventory

To calculate the life cycle inventory or LCI results, click on "Calculate" to open the calculation properties wizard, where you can define which calculation method, allocation, LCIA method and normalization/weighting set you want to use. You can select between two different calculation methods, matrix and sequential calculation. Especially for large product systems with loops, the matrix method is recommended.

The sequential calculation method uses two different thresholds. These are important if the product system contains loops, i.e. if a process references itself (also indirectly, via other processes: heavy fuel oil that is used in a tanker that transports crude oil to a refinery that produces, among other things, heavy fuel oil).

These two thresholds are:

the lower limit of the (additional) scaling factor; this limit considers the scaling factor calculated for the "next-to-consider" process, and does not follow this process if the threshold is below the specified value.
the maximum number of iterations that are performed in a loop

Both these thresholds can be specified in preference page for calculation method settings. They are relevant only for the sequential calculation.

In the preference page you can also specify whether an uncertainty calculation shall be performed. The uncertainty calculation here is always performed by approximation formulas, using Gaussian first order error propagation.

These approximation formulas work best if the relative error is small. It has been found ¹ that the approximation works well if the relative errors is below specific thresholds (for the calculation of process scaling factors, 20%) - this is checked during calculation.

Impact Assessment

In openLCA, impacts can be calculated only for product systems (and projects as comparisons of product systems). Processes are used within product systems, and not in itself available for impact calculation. It is however possible to create a product system with only one process and calculate the impacts then for this system.

If you want to analyse the impact assessment, select an LCIA method while specifiying the calculation settings.

The diagram

Under the tab "Diagram" you can look up the impacts of the supply chain of a process displayed in a pie chart. Therefore, select a flow or an impact category you want to consider. You can double-click on a pie slice (or it’s legend item) to zoom into a process and display his supply chain.

The Sankey diagram

openLCA draws a Sankey diagram of the product system. This diagram is a graphical illustration of the impacts of different flows in the product system.

By clicking on the left corner of the diagram or the menu item "Set sankey diagram options" you can edit the Sankey diagram. You can select a flow or/and an LCIA category to be displayed in the sankey diagram. The first layer is affecting the line width of the connections and the second layer is affecting the box colour of each process.

Saving LCIA results

A calculated LCIA result can be saved as an LCIA result clicking the "save as..." icon in the result editor

The so created LCIA result will be put in the category tree under LCIA results

Projects

If you want to compare different product systems regarding LCI or LCIA, you need a project.

Open the wizard for creating a new project, and add a name.

Add the product systems you want to consider to the project by clicking on the green plus or via drag and drop from the category tree in the left. Theoretically you can compare as many systems as you want, practically the amount is determined by the size of the systems and the available main memory.

To compare the systems you have to select an impact assessment method under the tab "Comparison". Note that the product system you want to compare have to be calculated before comparing.

You have then the choice to display all or only some of the categories of the selected method...

Clicking on "draw chart" creates a bar chart, for the selected categories, where each bar is scaled to 100% in order to avoid visual comparison between different categories.

LCIA methods

LCIA (Life Cycle Impact Assessment) methods are needed for the impact calculation. openLCA has no default LCIA methods in the application (different from units, for example), so that the LCIA methods need either be created or imported from other sources. Nowadays many databases contain LCIA methods.

A typical LCIA method consists mainly of different categories with units and of an assignment of these categories to flows. These assignments can be found on the LCIA factors sheet, where they can be edited.

You can also define normalization/weighting sets. You can assign a normalization and/or weighting factor to each LCIA category.

Notes

¹ Ciroth, A., Fleischer, G., Steinbach, J.: Uncertainty Calculation in Life Cycle Assessments – A Combined Model of Simulation and Approximation, Int J LCA 9 (4) 216 – 226 (2004)

Elements in the application