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) calculators  are sourced from:

• the New Zealand Ministry for the Environment (MfE) for ACE 2011 (NZ). MfE factors are released annually and are based on calculated greenhouse gas emissions of an energy source within New Zealand for a particular calendar year. In May 2011, the latest MfE emission factors were released based on 2009 data.
• the Australian Government Department of Climate Change and Energy Efficiency (DCCEE) for ACE 2010 (Aus). These factors, termed National Greenhouse Account (NGA) factors are also released annually and like MfE factors are country specific. The factors used in ACE 2010 (Aus) were released by the DCCEE in mid 2010.

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 emission factors used in ACE 2011 (NZ) and ACE 2010 (Aus).

Table 1. General emission factors used in ACE

[1] released in June 2011 and used in ACE 2011 (NZ)
[2] released in mid 2010 and used in ACE 2010 (Aus)

Australian electricity emission factors vary with state due to different generation profiles. For this reason users of ACE 2010 (Aus) must select their state when using ACE. Australian electricity emission factors are listed in Table 2.

Table 2. State-specific electricity emission factors used in ACE 2010 (Aus)

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. In their absence the most recently published factors should be used i.e. those in ACE 2010.

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 2010/2011 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 travelled 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 the UK Department for Environment, Food and Rural Affairs (DEFRA) and are listed in the Vehicle Efficiency tab. 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 nationwide average taxi fare per km of $2.50 to calculate emissions based on fare.

Waste

This function simple with two options to select from:

• 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%).

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). Emission factors for waste are based on weight so 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 landfills 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.

A stand alone tab has been created for refrigerant 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 emission factors for electricity used in both versions of ACE have 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 factors account for the emissions from fuel combustion at thermal power stations which are associated with the consumption of purchased electricity from the grid. They also include a relatively small proportion of fugitive emissions from geothermal generation. As national and state grid averages they do 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 this. For more information contact us.

Electricity line and distribution losses

Not all electricity that is generated makes it to the end user, a percentage (9-18%) 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.