From meter reading to tonnes
Each emission source has a calculation method with a version, a data quality tier and one or more data streams. When data changes (an import, a form, a mobile entry), EmitLedger recalculates the affected months automatically in the background. It calculates the quantity of each gas first (CO₂, CH₄, N₂O and others) and converts to CO₂-equivalent only for display. Units and gas reference conditions are converted by the engine.
After a commit the import job shows Recalculation queued and then the run status. Dashboards show the new numbers when the run has finished.
Methods
| Method | Used for |
|---|---|
| COMB_GAS_MB_V1 | Gaseous fuel in turbines, engines and heaters: carbon mass balance on the measured gas composition |
| COMB_LIQUID_NCV_V1 | Liquid fuel such as diesel, including mobile combustion |
| FLARE_COMP_V1 | Flaring, from the flared volume and the gas composition |
| VOLUME_COMP_V1 | Vented whole gas: tanks, glycol, rod packing, metered pneumatic supply gas, liquids unloading |
| ELEC_DUAL_V1 | Purchased electricity, location-based and market-based |
| BLOWDOWN_PVT_V1 | Depressurisation events from pressure, volume, temperature and Z-factor |
| AMINE_CO2_MB_V1 | Acid gas removal (amine) CO₂ vent: mass balance between inlet and sales gas |
| FUGITIVE_LDAR_V1 | Measured leaks from LDAR findings |
| COUNT_EF_V1 | Count × factor × hours for pneumatics, components and seals |
| MASS_TOPUP_V1 | Refrigerant, SF₆ and fire-suppression top-ups |
| LOADING_EF_V1 | Crude loading and offloading |
| HEAT_STEAM_V1 | Purchased heat, steam and cooling |
| THROUGHPUT_V1 | Methane per throughput, event or well-year: glycol dehydrators, tank flashing, produced water, well completions, workovers and liquids unloading (API Compendium 2021 Chapter 6 factors) |
THROUGHPUT_V1 sources need a data stream with the role throughput (gas processed, crude, condensate or water produced), events (completions, workovers or unloadings in the month) or wells (number of wells, for per well-year factors), and a Factor row in the source form that matches the source, for example tank size and control (crude_large_vru) or separator pressure and salt content (water_sep250_salt10). There is no default row: without one, the month shows factor missing. With a gas composition the method also estimates CO₂ from the methane; without one it reports methane only.
The method of each source is shown in the Source register of its asset setup.
GWP set, consolidation and Scope 2 method
- GWP set: results are stored per gas. The GWP set filter (AR4, AR5 or AR6) converts them to CO₂e when you view them, so changing it never requires data to be entered again. Your default is on Settings → General. Factors that a publisher gives only as CO₂e are the exception; see Emission factors.
- Consolidation: Operational control counts 100 % of the assets you operate; Equity share uses each asset’s equity share periods.
- Scope 2 method: Location-based and Market-based are both always calculated; the filter chooses which one is shown. Market-based uses your energy instruments.
When a number is missing
If a factor or an input needed for a gas is missing, the calculation reports a finding for that source and month instead of inventing a value. A month with error findings cannot be locked until the data is fixed and recalculated. See Emission factors and Reporting periods.
Warnings you may see
| Warning | Meaning |
|---|---|
| W-FACTOR-YEAR-FALLBACK | Your country’s factors are published by year, and none covers the reporting year of this month, so the factor of another year was used. Check that the right edition is loaded (see Emission factors) |
| W-PERIOD-LOCKED-SKIPPED | The run covered locked months and left them unchanged. Reopen them with a restatement if they must change |
Some details that affect the numbers:
- When a source has several data streams with the same role (for example two fuel-gas meters feeding one turbine), their values are added together.
- Purchased electricity, heat and steam use, for each month, the factors that apply to that month, also when an energy instrument covers several months.
- A source that has a calculation error in one of its items (for example one component of a count-based source) shows no total for that month rather than a partial one.
Calculation runs
Data → Calculation runs lists every calculation: when it was queued, what started it (an import, a data change, a library pin, a restatement or you), its status and its findings. Details shows the findings of one run with the asset and month they concern.
- Recalculate calculates months again for one asset or every asset, with the current data, factors and library pins. Use it when a lock asks for a calculation (Calculation required), or after you changed a factor or composition. Locked months keep their results.
- A failed calculation also appears under Waiting for you on the Overview.