NGER criterion AAA for gaseous fuels is the most prescriptive measurement criterion in the NGER (Measurement) Determination 2008. It sets out how gas must be measured and what the metering equipment must achieve.
Key points
- Measurement at standard conditions using a flow computer
- Continuous recording and integration of flow
- Four equipment categories by maximum daily gas combusted
- Categories 3 and 4 add flow device, flow computer and chromatograph rules
- Point-of-combustion measurement locks in for later years
Volumetric measurement
Gas must be measured volumetrically in cubic metres at standard conditions of 101.325 kilopascals and 15.0 degrees Celsius. Section 2.32 requires a flow computer that measures and analyses flow, relative density and gas composition at the delivery location. The flow rate must be continuously recorded and continuously integrated, with the integration device isolated so it keeps the last reading if the flow computer fails. Super-compressed gas is corrected under section 2.33.
Equipment categories
| Category | Maximum daily gas combusted | Transmitter accuracy |
|---|---|---|
| 1 | 0 to 1,750 GJ a day | Pressure and differential pressure within 0.25%, temperature within 0.50% |
| 2 | 1,751 to 3,500 GJ a day | As for category 1 |
| 3 | 3,501 to 17,500 GJ a day | Smart transmitters: pressure and differential pressure within 0.10%, temperature within 0.25% |
| 4 | 17,501 GJ a day or more | As for category 3 |
Additional rules for categories 3 and 4
- Flow devices must have an uncertainty of not more than 1.5% (section 2.35).
- Flow computers must record primary inputs and corrected and uncorrected volumetric flow (section 2.36).
- Gas chromatographs must be factory tested and calibrated, with accuracy of 0.15% for gross calorific value and 0.25% for relative density, and a way to re-calibrate against a certified reference gas (section 2.37).
Where the measurement is taken
Measurement is at the point of combustion, or at the point of sale if the stockpile conditions in section 2.31(5) are met. Measurement at the point of combustion locks in for later years.
If the equipment falls short
Where gas is acquired through a commercial transaction and metering does not meet these requirements, the reporter uses criterion A or AA. Where there is no commercial transaction, criterion BBB applies when the equipment does not meet criterion AAA.
References & sources
Primary regulatory documents and authoritative references underpinning this answer.