Every renewable natural gas (RNG) credit, whether under a state clean fuel standard or the federal Renewable Fuel Standard (RFS), starts as a metered volume of biogas and a measured methane content. The flow meter on the digester or landfill gas line is the first number in the chain.
What Gets Measured
- California LCFS: CARB's Tier 2 pathway calculator asks for the monthly metered quantity of raw biogas in standard cubic feet and the methane concentration in the raw biogas.
- Federal RFS: parties required to measure biogas, RNG or renewable CNG/LNG volume must measure continuously using meters that meet specified requirements, including in-line gas chromatographs to ASTM D7164 and flow meters to listed API standards.
Projects that sell into both markets need measurements that satisfy both.
Flow Meter Types EPA Lists as Accepted
EPA publishes alternative measurement protocols for biogas and RNG that name accepted flow meter types and the standards they must meet:
| Meter type | Standard listed by EPA |
|---|---|
| Thermal dispersion | ASME MFC-21.2-2010 |
| Thermal mass | EN 17526 |
| Coriolis | AGA Report No. 11 / ASME MFC-11 |
| Turbine | AGA Report No. 7 |
| Ultrasonic | ISO 17089-2 |
| Rotary | ANSI B109.3 |
| Venturi | ISO 5167-4:2022 |
Where a flow meter is calibrated with a fluid other than RNG, EPA requires that equivalency to RNG flow be demonstrated.
Why Thermal Mass Meters Are Common on Biogas
Thermal mass meters read mass flow directly, without separate pressure and temperature transmitters, and have no moving parts. The Sage Model 51 thermal mass flow meter measures natural gas and biogas with NIST-traceable calibration, in insertion or inline configurations.
What the Meter Does Not Do
Meeting a measurement standard is one part of a fuel pathway. Pathway applications, registration, quality assurance plans and verification belong to the producer and its consultants. Confirm which standard your registration requires before ordering a meter.
Emergent Metering supplies flow meters and related hardware. It does not prepare pathway applications or verify measurements. For how clean fuel programs differ by state, see LCFS and Clean Fuel Standard Metering Requirements by State. Browse natural gas and biogas meters.
Frequently Asked Questions
What does CARB need to know about biogas for an LCFS pathway?
CARB's Tier 2 calculator uses the monthly metered quantity of raw biogas in standard cubic feet and its methane concentration.
Does the federal RFS require continuous biogas metering?
Yes. Parties required to measure biogas or RNG volume must measure continuously with meters that meet the requirements in 40 CFR 80.155.
Are thermal mass flow meters accepted for biogas?
EPA's alternative measurement protocols list thermal mass meters under EN 17526 and thermal dispersion meters under ASME MFC-21.2 among accepted options.