De-aggregating ecoinvent processes in Brightway2 - brightway

Question

Let's say I want use an ecoinvent process for an automobile, and that the process model includes impacts for producing the car, maintenance, road maintenance, fuel, etc. And let's assume that I want to model the automobile without the fuel, because I want to model the use of a different fuel. Can I tell Brightway to calculate impacts for the automobile minus the fuel?

Answer 1

There are at least two ways to get the results you want. Let's say your inventory datasets look like this:
[
{
'code': 'car',
'database': 'example',
'exchanges': [{
'input': ('database', 'fuel'),
'amount': 1
}]
}, {
'code': 'fuel',
'database': 'example',
}
]
Then you can either construct a new data set and subtract the fuel:
{
'code': 'car w/out fuel',
'database': 'example',
'exchanges': [{
'input': ('example', 'car'),
'amount': 1
}, {
'input': ('example', 'fuel'),
'amount': -1
}
}]
}
And then use this dataset as your functional unit. Alternatively, you could subtract the fuel input directly in your functional unit passed to the LCA class:
LCA({('example', 'car'): 1, ('example', 'fuel'): -1)})
You could also save this modified functional unit in a calculation setup.
Responding to a comment about the ease of manipulating datasets, there isn't really a simple way. It is very difficult to define generic rules for working with inventory datasets, as inputs are structured very differently from industry sector to sector. To answer the specific comment, you could do something like:
from brightway2 import *
db = Database("ecoinvent 3.2 cutoff")
car = db.search('transport, passenger car, large size, diesel')[0]
new_car = car.copy()
for exc in new_car.exchanges():
if 'diesel, low-sulfur' in exc.input['name']:
exc.delete()
But this would require that you examine the search terms manually to make sure you get the behaviour that you want. In an ideal world, we would have a domain-specific language for manipulating datasets in simple ways, but I don't know what that would look like yet.