Fix prefix abbrevs

[angularsen]

Fixes several wrong abbreviations.
Removes redundant prefix abbreviations (k, M etc is prefixed by default for kilo, mega etc.)

Breaking changes

GigabritishThermalUnit: mmBTU => GBTU
MegabritishThermalUnit: mBTU => MBTU
Kilopound: KLbs => klb (neither is commonly used)
Megapound: MLbs => Mlb (neither is commonly used)

[angularsen]

Nuget is out https://github.com/angularsen/UnitsNet/releases/tag/UnitsNet%2F3.94.0

[d-barker]

Interesting change. What is a GBTU?

[Wikipedia](https://en.wikipedia.org/wiki/British_thermal_unit#:~:text=The%20British%20thermal%20unit%20(Btu,water%20by%20one%20degree%20Fahrenheit)
The British thermal unit (Btu or BTU) is a unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

My understanding is that mmBTU is one million BTU's. This is often used as the energy of a large volume of gas for example has a very large BTU value and for us humans to better relate we need to divide by one million so that it makes comparison much easier (is this now a mix between metric and imperial?)

For example, 1 tonne of LNG gas is 51.7 mmBTU or 51,700,000 BTU.

I would like to use this library however my users will not be typing GBTU they will be using mmBTU, is there a way to extend the acronyms?

p.s. congratulations on a very interesting library

[angularsen]

@d-barker
I believe this change was made after adding kilo/mega/giga prefix support. I'm not familiar with this energy domain myself, so I'll have to lean on what the wiki says.

At least MBTU (1,000 BTUs) is problematic, because it is ambiguous with the metric Mega (1,000,000 BTUs) and kBTU (1,000 BTUs) is also used in some domains.
I can only assume this change was meant for all these to consistently use metric prefixes for kBTU, MBTU and GBTU.

From wiki:

Units kBtu are used in building energy use tracking and heating system sizing. Energy Use Index (EUI) represents kBtu per square foot of conditioned floor area. "k" stands for 1,000.
The units MBtu and MMBtu are used in the natural gas and other industries to indicate 1,000 and 1,000,000 BTUs, respectively.[11][12] However, there is an ambiguity in that the metric system uses the prefix "M" to indicate one million (1,000,000), and consequently "MBtu" is often used to indicate one million BTUs.[13] Some authors have deprecated the use of MBtu, and avoided its use to reduce confusion. [12]

Back to your question, yes, we should be able to add back support for mmBTU given that there are no existing Energy units with the same abbrevation. I did a quick check, and it seems available:

If you would be interested in doing a pull request, I see two ways of adding it:

Option 1 - Add an extra abbreviation to the unit

Add mmBTU to the array of abbreviations for the GigabritishThermalUnit
https://github.com/angularsen/UnitsNet/blob/master/Common/UnitDefinitions/Energy.json#L43-L54

, by adding this override:

      "Localization": [
        {
          "Culture": "en-US",
          "Abbreviations": [ "BTU" ],
          "AbbreviationsForPrefixes": { "Giga": ["GBTU", "mmBTU"] }
        }

ToString() would then default to GBTU as before, no breaking change, but it would also support

var myEnergy = Energy.Parse("1 mmBTU");
Console.WriteLine($"{myEnergy:v} {myEnergy:a1}"); // "1 mmBTU", a1 specifies index of a specific unit abbreviation

Option 2 - Add an entirely new unit for mmBTU

We could add a new unit MillionBritishThermalUnit.
The advantage is that Energy.Parse("1 mmBTU").ToString() would return "1 mmBTU", no need to specify the abbreviation index etc. But I generally want to avoid duplicating the GigabritishThermalUnit just to get a different name and different primary unit abbreviation. We can make exceptions if someone familiar with the domain can argue that it makes a lot more sense in the energy domain to have a different naming of the unit or the abbreviation than we already have.

[d-barker]

Thanks for the detailed reply, I will have a look at your suggested changes. I am away on leave for a couple of weeks so will have a look when I am back.