PyGREET Terminology

This page provides definitions and explanations of key terms used throughout PyGREET.

Entity Colors and Icons

The following table shows the color coding used for different entity types in the PyGREET library:

Folder Name	Subfolder	Color	Entity Icon
Flows	Elementary Flow	Purple
Flows	Non-elementary Flow	Light Gray
Processes	Stationary Processes	Light Blue
Processes	Transportation Processes	Orange
Conversions	-	Pink
Transportation Modes	Tanker	Yellow
Transportation Modes	Barge	Yellow
Transportation Modes	Truck	Yellow
Transportation Modes	Pipeline	Yellow
Transportation Modes	Rail	Yellow
Transportation Modes	MagicMove	Yellow
Transportation Modes	Generic	Yellow
Operational Mode		Orange
Vehicles	-	Red
Pathways	-	Green
Pathway Mixes	-	Dark Blue
Global Parameters	-	Dark Gray
Locations	-	Light Blue
Impact Methods	-	Dark Teal
Impact Categories	-	Purple

Glossary of Terms

Term	Synonyms	Definition
Canonical Form		Form of LCA data/pathways stored in matrix-suitable format, akin to OpenLCA.
C2G		Cradle-to-Gate system boundary
Data Editors	Library	Part of application with interfaces to edit all entities in GREET – Pathways, Processes, Conversions, Vehicles, etc.
Flows	Resource, Emissions	Material substance (Gasoline, Gypsum, Sand, Alcohol, etc.) or certain quantity of energy (electricity, thermal energy, etc.). Flow is also used collectively to designate a collective summary of all movements of a particular substance/energy type in a given system (Pathway). A flow's role as a resource or emission is determined by its usage context, not stored on the flow itself; elementary flows may be used as either. Difference between resource and emission in a process is: resource can be used in the processes downstream, emission cannot as it ended up in the environment.
Flow Groups	Resource Groups	Entity holding association of flows (resources) to a group. Example: Fuels = Gasolines (Gasoline 87, Gasoline 91…) + Diesels (Military diesel, Biodiesel, …)
Formula/Time Series Editor	Formulas and Parameters	The Formula Editor is an interface (frontend) and backend functions to handle/process formulas in PyGREET. For the Time Series - each parameter may have different values for different target simulation years. Collection of all values for all years is called time series. For example, take the amount of diesel used in a conversion. This could be a time series value - say 1 mmBtu in 2020, 0.9 mmBtu in 2025, 0.8 mmBtu in 2030. Each of those values could be a formula. For example, it could be "A+B" in 2040, where A and B are variables.
Formula Parser	Formula Evaluator	Backend function to turn text representation of formula to a computable/runnable function
Global Variables	Simulation Parameters	Used to change input parameters that are reused in multiple locations. For example, users can select whether to use higher heating values or lower heating values, or which year to use for the simulations.
Impact Category		Impact Categories hold one or more impact factors used to calculate impacts during LCIA calculations.
Impact Method		Impact Methods hold groups of one or more Impact Categories. One Impact Method is chosen to run during calculations
Impact Factor		An Individual Impact, associated with a flow and impact value, contained within an Impact Category.
Pathway Mix	Mix	User defined combination/mix of pathways. Given we have pathways for electricity: US average and Diesel 10MW generator – we could create a mix: 30% US average + 70% Diesel generator to fulfill energy needs for pathway we're building.
Parameters		A description of a particular numerical value of a particular entity. Example: Density (parameter) of the Gasoline (flow). For most common gasoline it's currently about 0.710 g/mL. This is essentially numeric + unit. All numerical values in GREET can contain different values for different simulation years.
Pathway		A directed graph of transformation of resources (substances/flows). Represented by stationary and transportation processes connected by directed arrows. Result of a pathway is usually one or a few flows.
Processes		Stationary and transportation processes
Product		Designated outputs of a Pathway
Products Menu		Browse, select and drill down from Categories > Mixes > Products > Pathways
Resources		Inputs and outputs of the GREET processes and are organized in groups (or Categories, 11 in total to date). Resources can be defined physical properties and a member of more than 1 group.
Stationary Process		Description of a substance transformation process to be used in building pathways. Example: oil → Gasoline refinery. Also contains definitions of emissions, coproducts and byproducts created during such technological process
Conversions		An abstraction used to model emissions as a result of a combustion process or a chemical reaction.
Transportation Mode	Mode	Definition of a mode of transport. Usually means formula and schema of attributes necessary to characterize such mode of transport. Example: airplane, helicopter, heavy truck, barge, ocean tanker, pipe. Formulas to calculate and attributes required to do so vary wildly between them. Each mode is defined by three parameters: energy intensity, process fuel, emissions factors for each process fuel. A User can define more than one process fuel for a transportation step. When doing so, each process fuel needs to be assigned a weighted percentage value.
Transportation Process		Description/definition of a particular multi-step transportation process. Like Location 1 → Tanker → Truck → Location 2
Transportation Step	Step	An individual portion of a transportation process. A step represents one instance of transportation from one location to another.
Variables	Local variables, Local Parameters	A fixed value or a reference to a particular parameter-year value/formula accessible inside of a particular formula inside of a particular parameter.
WTP		Well to Pump or Product System Boundary
WTW		Well to Wheel System Boundary