Equivalent units

[l-emele]

Description of the issue

In an e-mail correspondence in the SIROP team we opened the question "How to express ontology the unit kt CO2e (kiloton CO2 equivalents)?

I thought a bit about that and noticed that we also have other mass equivalent units:

• ton of coal equivalent: A ton of coal equivalent is an energy unit which is equal to the amount of energy released by burning one metric ton of coal with a certain net calorific value. That is defined as 0.7 tons of oil equivalent (toe) and thus equals 29.3076 gigajoules or 8.141 megawatt-hours.
• kilo ton of oil equivalent: A kilo ton of oil equivalent is an energy unit which is equal to 1,000 tons of oil equivalent.
• Multiples of those: kiloton of coal equivalent, megaton of coal equivalent, kiloton of oil equivalent, megaton of oil equivalent

And now we want to add ton of CO2 equivalent. So there seems to be a common pattern: on expresses another unit with an equivalent mass unit. So it seems that a mass unit (and potentially also other units) can have a role.

Ideas of solution

Add roles

• equivalent unit role: An equivalent unit role is a role of a unit to express an equivalent quantity.
  • energy equivalent unit role: An energy equivalent unit role is an equivalent unit role that has the purpose to be used as energy unit.
  • mass equivalent unit role: An energy equivalent unit role is an equivalent unit role that has the purpose to be used as mass unit.

Redefine existing classes

ton of coal equivalent: A ton of coal equivalent is a mass unit but has the purpose to be used as an energy unit. It ~which~ is equal to the amount of energy released by burning one metric ton of coal with a certain net calorific value. That is defined as 0.7 tons of oil equivalent (toe) and thus equals 29.3076 gigajoules or 8.141 megawatt-hours. Axiom:

'ton of coal equivalent'
    SubClassOf:
        'mass unit'
        'has role' some 'energy equivalent unit role'

ton of coal equivalent: A ton of oil equivalent is an energy unit which is equal to the amount of energy released by burning one metric ton of crude oil with a certain net calorific value. That is defined as 41.868 gigajoules or 11.63 megawatt-hours.

'ton of oil equivalent'
    SubClassOf:
        'mass unit'
        'has role' some 'energy equivalent unit role'

Likewise the other toe/tce based units.

Add ton CO2 equivalent

• ton of CO2 equivalent: A ton of CO2 equivalents (t CO2e) is a mass unit which is equal to the emission of 1 metric tonne of CO2. Axiom: 'has role' some 'mass equivalent unit role'
• kiloton of CO2 equivalent: A kiloton of CO2 equivalents (kt CO2e) is a mass unit which is equal to the emission of 10^3 metric tons of CO2. Axiom: 'has role' some 'mass equivalent unit role'
• megaton of CO2 equivalent: A megaton of CO2 equivalents (Mt CO2e) is a mass unit which is equal to the emission of 10^6 metric tons of CO2. Axiom: 'has role' some 'mass equivalent unit role'
• gigaton of CO2 equivalent: A gigaton of CO2 equivalents (Gt CO2e) is a mass unit which is equal to the emission of 10^9 metric tons of CO2. Axiom: 'has role' some 'mass equivalent unit role'

Add equivalent class

• unit with energy role: A unit with an energy role is an energy unit that is a unit that is used to express an energy unit. Axiom:

  'unit with energy role'
  EquivalentTo:
      'unit' and 'has role' some energy equivalent unit role'
  SubClassOf:
      'energy unit'

This should make ton of coal equivalent and ton of coal equivalent and so on to be inferred as subclasses of unit with energy role and hence as subclasses of energy unit.

Workflow checklist

• [ ] I discussed the issue with someone else than me before working on a solution
• [ ] I already read the latest version of the workflow for this repository
• [ ] The goal of this ontology is clear to me

I am aware that

• [ ] every entry in the ontology should have a definition
• [ ] classes should arise from concepts rather than from words

[l-emele]

@stap-m : Have you any thoughts on my proposals?

[stap-m]

In priciple, I like the idea. unit is hierarchically on the same level as information content entity, which may get the reference role. Therefore, I think it is ok to go with roles for units, too.

The energy equivalent unit is only interesting when it comes to burning fuels, and measures the energy content. Here, energy equivalent unit makes sense. The CO2e units are only interesting when it comes to emitting greenhouse gases. What extactly does it measure? The emission factor? Greenhouse gas acitivity? Therefore, I am wondering whether mass equivalent unit is really correct.

[l-emele]

The CO2e units are only interesting when it comes to emitting greenhouse gases. What extactly does it measure? The emission factor? Greenhouse gas acitivity? Therefore, I am wondering whether mass equivalent unit is really correct.

In our conversions paper I wrote the following example:

So in this metric, a mass of 0.5 Mt CH4 has the same effect as 14 Mt CO2 if released to the atmosphere, hence the 0.5 Mt CH4 can be expressed as 14 Mt CO2 equivalents.

[stap-m]

So in this metric, a mass of 0.5 Mt CH4 has the same effect as 14 Mt CO2 if released to the atmosphere, hence the 0.5 Mt CH4 can be expressed as 14 Mt CO2 equivalents.

Yes. Then let's call it greenhouse effect equivalent unit?

[stap-m]

Can we solve this issue before the next release?