How fuel factors are converted

A fuel factor is served in the unit its publisher printed it in, rescaled only by a fixed ratio such as 1 GJ = 277.78 kWh. Turning a cubic metre or a tonne of fuel into kilowatt-hours needs a heating value, and that is never applied to the factor itself: where the publisher's own data gives one, it is recorded beside the factor as a separate conversion. This page applies the general rules of units and unit conversions to fuels, with worked examples.

The printed unit is kept#

Publishers price the same fuel in different units: per GJ, per tonne, per litre, per cubic metre, per mmBtu, per kWh of net or of gross energy. Each unit the publisher printed becomes its own factor. DESNZ prints UK natural gas four ways, per tonne, per cubic metre, per kWh (net) and per kWh (gross), so factor search holds four natural gas combustion factors from DESNZ, not one converted four times.

Pick the factor whose unit is the unit on your invoice or meter. Then nothing stands between your quantity and the publisher's own number, and none of the rest of this page applies to you.

The publisher's unit label and the multiplier used to serve it are kept with every value, so the original number can always be read back.

Fixed ratios#

A factor is rescaled at import only when the two units measure the same thing and the ratio between them is a definition, not a property of the fuel. The general list is on the units page, under the conversions that are made. The ones that matter for fuels:

The ratio scales the number and nothing else: the fuel, the year, the boundary and the heating value basis stay those of the publisher.

Note. ADEME prints its natural gas mix both per GJ and per kWh, so its 0.20088 per kWh, converted from 55.8 per GJ, sits beside ADEME's own 0.201 per kWh as a second factor. The two differ only by ADEME's rounding. Both are kept, because each is a number ADEME printed.

Net and gross are never folded#

A fuel's energy can be counted two ways. The net (lower) heating value leaves out the heat held in the water vapour of the exhaust; the gross (higher) value counts it. The same cubic metre of natural gas is about 11 % more kWh gross than net, so the factor per gross kWh is about 10 % smaller. DESNZ shows it on one fuel:

Net-basis factors carry kwh, gross-basis factors carry kwh_hhv, and nothing converts one into the other: the gap depends on how much hydrogen the fuel holds, so it is a property of the fuel, not a constant. A factor printed per GJ or per mmBtu takes the basis its publisher states. ADEME's GJ is net (its label says ICV), EPA's mmBtu is gross, as US heat content conventions are.

Read the basis off your invoice before you pick a factor. Many gas bills, in the UK and France among them, state kWh on the gross basis. Applying a net factor to gross kWh overstates emissions by the gap, about 11 % for natural gas.

Gas volumes to energy and mass#

A cubic metre of gas is served per litre by the exact 1,000 ratio. The temperature and pressure it was metered at are a separate question, covered in gas volumes and metering conditions. Turning that volume into kWh needs the gas's heating value, and into kg its density. Neither is a constant: both depend on where the gas comes from, and they move year to year.

So the factor per litre is never converted. Where the publisher prints the same gas per cubic metre and per kWh or per kg, the ratio of its own two numbers is its own heating value or density, and that ratio is recorded beside the factor as a conversion:

DESNZ's 36.1 is its 2.02633 kg CO2e per cubic metre divided by its 0.20199 per kWh (net): 10.03 kWh, or 36.1 MJ, in each cubic metre. A "none" means the publisher prints no sibling factor that would give the number, so no conversion is recorded. EPA's figure comes from the ratio of its own per-scf and per-mmBtu factors, not from its separate heat content table.

Watch out. The three gases are not the same gas at the same conditions. ADEME's cubic metre states no metering conditions, and neither do DESNZ's or EPA's. Two heating values per cubic metre are only comparable when the metering conditions match.

A publisher's own heating values#

A conversion marked as the publisher's is recorded only from a number the publisher itself published. There are three ways it can arrive, from the most direct to the least:

• Printed on the row. The factor's own table prints the heating value next to it, as some statutory fuel tables do, giving GJ per thousand cubic metres beside the CO2 coefficient.
• A sibling ratio. The publisher prints the same fuel in two units, and the ratio of its own two numbers is the heating value or density. DESNZ, ADEME and EPA above are this case.
• A companion publication of the same publisher. Some publishers print emission factors per tonne of fuel in one document and the net heating value of each fuel in another, such as the energy balance a national statistics office publishes. The heating value is read from that document only where it names the same fuel and gives it one number. A printed range, a value marked company-specific, or a residual "other fuels" line is refused, and the reason is stored.

In all three cases the number is the publisher's own, for its own fuel. A default from another source, such as the IPCC's default heating values or a neighbouring country's table, is never used, even where it would fill a gap: the publisher's factor was computed with its own fuel's properties, and another source's number would describe a different fuel.

Conversions open-climate.ai states#

Search also has to match a fuel bill in litres to a factor per kilogram when the publisher prints no density. For that, open-climate.ai keeps conversions of its own in the same table as the publisher's, and each one says whose it is:

• origin names who stated the number. source_printed and source_sibling are the publisher's own; rule_curated and rule_generated are open-climate.ai's.
• tier says how firm the number is. deterministic for a constant with one accepted value, such as the density of diesel; heuristic for a typical value of a class of products. A publisher's conversion is always deterministic.
• Every open-climate.ai conversion cites its source, and a number outside the physical range of its kind (a density no liquid has) is refused rather than recorded.

Where the publisher states a conversion, search uses it before ours. Neither kind changes a factor's value, and neither is shown on a factor page yet.

What is never done#

• The published value is never replaced. A conversion is a separate record beside the factor. The factor keeps the publisher's number in the publisher's unit.
• Net is never turned into gross, nor gross into net.
• No default heating value or density is presented as the publisher's. No IPCC default, no textbook value; an open-climate.ai conversion is kept apart and flagged as ours (above).
• One gas metering condition is never restated as another. A normal cubic metre stays a normal cubic metre.
• No single number is picked from a range. Where the publisher prints a span of heating values for a class of fuels, no conversion is recorded.
• An estimated fuel leg is not a conversion. Where open-climate.ai adds the emissions of producing and transporting a fuel beside a combustion-only factor, that is a new factor marked as an estimate, with its own method: see estimated fuel legs.

How to see the conversion on a factor#

• On a factor page, the section that walks from the publisher's record to the served factor states the unit as published and, when it was rescaled, the multiplier: "multiplied by 0.0036 to serve it per kWh". A factor served in its printed unit says no conversion was needed.
• On a library page, the Canonical units card under Open data counts the factor values that carry a conversion to a related unit, for example on the DESNZ library page.
• The heating values themselves are not served in factor search, the exports or the read API. open-climate.ai uses them to compare factors across libraries. A SQL reader finds them in open_ef.unit_conversion, one row per value and target unit with an origin starting source_, with quantity_per_unit in kWh or kg per litre.

To apply one by hand, divide the factor per litre by the kWh per litre, or the factor per cubic metre by the kWh per cubic metre.

Worked examples#

A gas bill in kWh, against a factor per GJ#

A French site uses 100,000 kWh of natural gas, billed on the gross basis (kWh PCS). ADEME prints its 2022 natural gas mix, combustion, three ways that concern this bill:

The bill is gross, so the factor is ADEME's 0.181 per gross kWh: 18,100 kg CO2e. Taking either net factor would give about 20,100 kg, 11 % too high, from the basis alone.

Comparing two publishers' natural gas#

EPA prints US natural gas at 53.1171 kg CO2e per mmBtu, its CO2, methane and nitrous oxide combined. An mmBtu is gross energy, so it is served at 0.18124 per gross kWh. DESNZ's UK natural gas is 0.18231 per gross kWh: the two differ by 0.6 %. Set against DESNZ's net factor, 0.20199, EPA's would look 10 % lower, a gap that is the heating value basis and not the gas.

A meter in cubic metres#

A UK site's meter reads 1,000 cubic metres of natural gas. The DESNZ factor per cubic metre is 2.02633 kg CO2e, so the answer is 2,026 kg CO2e, with no conversion. The heating value only matters if you want the same quantity in kWh, for example to set it beside another library's per-kWh factor: 1,000 cubic metres at DESNZ's 36.1 MJ per m³ (net) is 10,032 kWh, and 10,032 kWh at 0.20199 per kWh is the same 2,026 kg.

Related#

• Units and unit conversions in emission factors
• Estimated fuel legs: the supply chain before the burn
• Calculate emissions for a quantity
• Glossary: unit basis