Emission Factors

Emission factors are provided in terms of CO₂ equivalent (CO₂e) emissions. The emissions of different GHGs are calculated separately and converted to CO₂e on the basis of their global warming potential. For example:

• 1 unit of methane is equivalent to 21 units of CO₂e
• 1 unit of nitrous oxide is equivalent to 310 units of CO₂e.

Emissions for the consumption/combustion of fuel are then calculated based on the simple formula:

Emissions (tonnes CO₂e) = quantity of energy (unit) X emission factor (tonne CO₂e/unit)

Source

The emission factors used in our online Annual Carbon Emissions (ACE) calculator and in carbon inventory emission calculations are sourced from the Ministry for the Environment (MfE). These are released annually by MfE and are based on calculated greenhouse gas emissions of an energy source for a particular calendar year. In late 2009, the latest MfE emission factors were released based on 2008 data. These factors are used in the 2010 free ACE download.

Other online calculators may use emission factors different to those in ACE, either in source or in year. For this reason outputs may differ between calculators. It is important to understand the emission factors behind your calculations.

The table below lists the 2008 emission factors used in ACE 2010. [2007 emission factors are also listed. These were used in ACE 2009]

Emission source	Units	2008 emission factors (kg CO2e /unit) [1]	2007 emission factors (kg CO2e /unit) [2]
Electricity	kWh	0.195	0.165
Electricity distribution & line losses	kWh		0.0142
Natural Gas	GJ	54.0	54.0
Coal	kg	1.98	2.01
Petrol	L	2.34	2.33
Diesel	L	2.69	2.68
Flights - Domestic	km	0.1728	0.1753
Flights – International short haul <3700km	km	0.0946	0.0983
Flights - International long haul >3700km	km	0.0827	0.1106
Mixed waste	kg	1.06	0.947
Office waste	kg	1.55	1.55

[1] used in current version of ACE (ACE 2010)
[2] used in previous version of ACE (ACE 2009)

Period

Ideally, emission calculations should be performed using factors representing the year being assessed. This is possible for historic data and previous years e.g. 2006 emissions should be calculated using 2006 emission factors. However as emission factors are derived retrospectively, the time lag means that for any current year e.g. 2010, period specific emission factors do not exist. For this reason ACE 2010 uses 2008 emissions factors which were released at the end of 2009.

GHG reporting

When reporting your GHG emissions it is important to quote the source and year of the emission factors used in your calculations, and reasons for using them. An example can be found in our own 2009/2010 financial year GHG Inventory Report (click here to download, PDF; 285KB).

Other important information about ACE

The information below contains conversion factors, definitions, assumptions (where made), and further instruction pertinent to the use and understanding of ACE. We encourage you to read it.

Vehicle fuel

Emissions from the combustion of vehicle fuel are most accurately determined when actual fuel usage (L) is the input. Where vehicle fuel usage is not known the user can enter distance traveled and fuel usage will be calculated. This is based on default fuel conversion rates for a range of fuel types and vehicle sizes. These default values have been sourced from MfE (except for diesel and hybrid values which, in the absence of MfE data, are from the UK Department for Environment, Food and Rural Affairs (DEFRA)), are listed in the Vehicle Efficiency tab, and differ from those used in previous versions.

The impact of this will be that calculated emissions based on distance traveled may be different using ACE 2010 from those calculated with previous versions. If you have any queries regarding these changes please contact us.

If the user has alternative efficiency values these can be entered in the Vehicle Efficiency tab. In doing this the default values are overridden.

Taxi use

Users can enter either distance traveled or cost of fare. In instances where a combination of data exists (e.g. some fare data, some distance data) both can be entered.

Calculations are based on:

• fuel efficiency of a large petrol car (which most taxis are), and
• a 2008/2009 nationwide average taxi fare per km of $2.50 (source: Taxicharge NZ) to calculate emissions based on fare.

Waste

We have kept this function simple with only two waste options to select from: Mixed and Office. Use the Mixed option if you are a household, or a business that produces waste similar in composition to that of a household. Office based businesses should use the Office waste option which assumes some food and garden waste (21%) but a predominance of paper (54%).

If neither option fits your profile contact us for a customised version. Note that emissions from waste disposal are only generated by biodegradable material in the waste. If your waste is purely inorganic you can assume no emissions from disposal and therefore eliminate waste as a source of emissions in your analyses.

For mixed waste, users may enter data in either units of weight (kg) or units of volume (m³). As MfE emission factors for waste work on units of weight, we have incorporated a volume-to-weight conversion factor for mixed waste to accommodate this input option. The factor we have used is 0.200 tonnes/m³, and was sourced from a 2003 MfE waste review strategy report, for uncompacted municipal solid waste.

This calculator assumes no gas recovery at landfill. For the small number of landfills nationwide that do recover emitted gas, different emission factors apply. Contact us for more information.

Refrigerant losses

Refrigerants used in cooling appliances such as freezers, chillers and air conditioning units contain GHGs with extremely high global warming potentials (GPWs). Emissions of small amounts of these through leakage or overfilling can be significant when converted to CO₂e. For this reason we have added a new function to ACE to measure these emissions.

A stand alone tab has been created to capture input data. Data can be entered any time over the year. The calculation is based on either:

• Known annual losses for each appliance – data based on service record details: amount of refrigerant added to appliance at service equals refrigerant lost since the last service.
• Default annual losses for each type of appliance provided by MfE, based on an assumed leakage percentage (1 - 8% depending on the appliance) and refrigerant capacity.

Based on the refrigerant type (entered by user for each appliance) and its GWP, emissions in terms of CO₂e are calculated and carried through to the summary tab.

A note about electricity emissions

The MfE emission factor for electricity used in ACE has been calculated based on actual electricity generation in a calendar-year. This can vary due to changes in hydro and/or wind generation and therefore thermal generation. The emission factor accounts for the emissions from fuel combustion at thermal power stations which are associated with the consumption of purchased electricity from the grid. It also includes a relatively small proportion of fugitive emissions from geothermal generation. As a national grid average, it does not distinguish between thermally generated electricity and carbon neutral forms of electricity generation such as wind and hydro.

Where details of purchased electricity generation are known, users of ACE may like to make provision. For more information contact us.

Electricity line and distribution losses

Not all electricity that is generated makes it to the end user, a small percentage (just under 10%) is lost between the generator and the consumer. We have made provision for users of ACE to include emissions related to the generation of this “lost” electricity in their overall emission calculations. This is optional - measuring and reporting these emissions is not mandatory - so we have provided the user with the option.

Implications of changing methodologies and emission factors

If you are reporting your GHG emissions and intend to have them verified it is a requirement of the GHG Protocol and ISO standards that changes to the methodology used year on year be documented and explained.

If you have used different versions of ACE for your calculations you need to be aware of any changes. Across the 4 versions to date there have been changes to emission factors, vehicle efficiency rates and airline flight categories and these have been explained above. Contact us if you require further clarification.

Have ACE customised to your requirements

We recognize that "one size doesn't fit all" and that every business will have different circumstances. If you would like the calculator customised to your requirements we would be pleased to undertake this. For an estimate on cost contact us.