Source of Emission Factors

The emission factors used in our ACE calculator are sourced from the New Zealand Ministry for the Environment (MfE). MfE factors are released annually and are based on calculated greenhouse gas emissions of an energy and/or emission  source within New Zealand for a particular calendar year. In May 2019, the latest MfE emission factors were released based on 2014 data.

Additional emission factors are sourced from the UK Department for Environment, Food and Rural Affairs (DEFRA). 

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 2019.

Emission Factors and reporting 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. 2017 emissions should be calculated using 2017 emission factors. However as emission factors are derived retrospectively, the time lag means that for any current year e.g. 2019, period specific emission factors do not exist. In their absence the most recently published factors should be used i.e. those in ACE 2019.

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. 

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 and resulting emissions will be calculated.

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

Waste

This function is 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%).

Users are to specify if the landfill used captures emitted gases or not.

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  MfE waste review strategy report, for uncompacted municipal solid waste.

Air travel

The emission factors used for air travel in ACE now apply an airlift factor to take into account non-direct routes and delays/circling, which adds 8 - 9%. The user also has the option to include a radiative forcing factor (ACE NZ only). Radiative forcing (RF) is a measure of the additional environmental impact of aviation.  These include emissions of nitrous oxides and water vapour when emitted at high altitude. Inclusion of RF multiplies flight emissions by 1.89. No specific recommendation is provided by the MfE for the use or not of RF. The UK Governement recommends that 'Organisations should include the influence of radiative forcing (RF) in air travel emissions to capture the maximum climate impact of organisations’ travel habits. However, it should be noted that there is very significant scientific uncertainty around the magnitude of the additional environmental impacts of aviation.'

If require  more information on the radiative forcing factor contact us.

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 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 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 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.

ACE updates

ACE was first launched in 2006 and has been updated on the following dates to incorporate new emission factors and added functionality: May 2008, April 2009, March 2010, July 2011, April 2012, May 2013, June 2014, May 2015, July 2016, February 2017 and now August 2019.