Nitrogen oxides emissions standards for domestic gas appliances

Background study
Mr Bob Joynt, Environmental Consultant and Mr Stephen Wu, Combustion Engineering Consultant
Environment Australia, February 2000


1.1 Background of the Study

The Clear the Air program represents the Commonwealth Government's initial response to the recommendations of the Inquiry into Urban Air Pollution in Australia. The development of Standards for Emissions of Nitrogen Oxides (NOx) from domestic appliances is one of the projects identified. As part of its program, Environment Australia is working with the gas industry to develop voluntary industry standards for emissions of NOx from domestic gas appliances. The appliances considered are water heaters, flued and unflued space heaters, and cookers.

Initial discussions between Environment Australia and the gas industry identified the need for a background study outlining relevant existing standards, technologies for achieving reductions in NOx emissions and methods and costs of implementing standards that reduce NOx emissions. The authors present this report in fulfillment of a contract to Environment Australia with objectives as set out in Section 2.1.

1.2 Fuel gas consumption in Australia

In 1996-97 Australia's consumption of LPG was 108 PJ, compared with 637 PJ of natural gas and towns gas. Residential sales of natural gas amounted to 30.7% of total sales, excluding Western Australia (AGA, 1998). It is assumed that NOx emissions from LPG and natural gas are similar. Due to the preponderance of natural gas and LPG used in Australia, the study has not focused on tempered LPG and towns gas which may amount to around 1% of total domestic use of fuel gas (C. Blogg, personal communication).

1.3 NOx emissions from Australian domestic gas appliances

Natural gas and liquid petroleum gas (LPG) are widely used throughout Australia. Gas is suitable for domestic use because it burns relatively cleanly and can be reticulated. It is used in dwellings for cooking, water heating and space heating. The most significant pollutant emitted to the atmosphere from domestic gas use is NOx. Domestic gas appliances contribute a small but significant proportion of urban NOx emissions. In Australia, gas space heaters use approximately as much energy as gas water heaters and cookers combined. (Todd et al, 1997).

There are two main types of gas water heaters: storage and instantaneous (continuous). Air heaters have been sold in forms such as wall furnace, space heaters and gas logs. They may be radiant or convective according to the means of heat transfer. Gas cooking appliances include ranges, cooktops, ovens and grills. The gas appliances may be flued to bring the combustion exhaust gases outside the building, or unflued to discharge the combustion exhaust indoors.

Bavaro et al (1995) quote appliance efficiencies of 0.65 for a high efficiency storage water heater, 0.8 for a gas space heater and 0.5 for gas cooking appliances.

The Inquiry into Urban Air Pollution in Australia (Todd et al, 1997) estimated the annual NOx emissions from major domestic gas appliances in Australia. The results are summarised and reproduced in Table 1.

Table 1: NOx emissions from major domestic gas appliances in Australia
  Sydney t/a Melbourne t/a Brisbane t/a Adelaide t/a Perth t/a Hobart t/a Darwin t/a Canberra t/a Total* t/a
Gas Hot Water Heaters 259 794 76 194 139 0 0.3 28 1489
Gas Space Heating 23 567 0.1 25 12 0.5 0.1 36 664
Gas Cooking 20 42 7 13 10 0 0 0.2 92
Total 302 1403 83 232 160 1 0.4 64 2245

Note: * Added from the figures given in the original table tabulated by Todd et al (1997).

Over 66% of the NOx were emitted from water heaters. Another 30% of NOx were emitted from space heaters, with the balance emitted from gas cooking. Victoria, represented by Melbourne, accounted for 62% of the total emission.

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