Testing hydrogen dispenser accuracy at refuelling stations

Testing the accuracy of the dispensing system at the Hydrogen Refuelling Station (HRS)

Utilising hydrogen to power the transport sector

Recent policies introduced by UK Government, such as the Ten Point Plan for a Green Industrial Revolution¹ triggered a shift towards zero emissions transport. Options being developed include hydrogen-powered vehicles which run on a hydrogen tank and fuel cell. A fuel cell hydrogen vehicle (FCEV) requires about 5 minutes to refuel, provides a driving range of around 300 miles with the only emission being water vapour.

The release of the UK Government’s ‘UK Hydrogen Strategy’ in 2021 identified hydrogen as likely to play a key role in decarbonising the transport sector with it being utilised across all modes of transport. As the use of hydrogen increases, so will the requirement for standardised and agreed weights and measurements regulations. Similar to refuelling with petrol, there is a need to ensure that stations are dispensing accurate quantities for billing and taxation purposes while operating safely for their employees, consumers and the surrounding environment.

The refuelling process for hydrogen vehicles is like the petrol pump: the driver parks at the dispenser, opens the refuelling flap, connects the nozzle to the receptacle in the vehicle and presses the refuelling button on the dispenser panel. The refuelling process stops automatically when the target pressure is reached. However, unlike liquid fuels, hydrogen is dispensed in mass units, and therefore requires a mass measurement system.

Developing a measurement system to quantify dispensed mass

TÜV SÜD National Engineering Laboratory developed the Light-Duty Hydrogen Refuelling Station Field Test Standard (LD HFTS). The concept behind the design was to be able to test dispensers in the field in such a way that the ’pump’ does not distinguish the test as different from a standard FCEV. Our system is composed of 153 L hydrogen tanks, balance, multiple control valves and monitoring sensors (pressure and temperature). The complete test unit is fully ATEX and pressure rated, which is required by UK and EU regulations and makes it safe to use at hydrogen dispensers.

The heart of the system is the balance which is used to compare the weight of the tanks before and after refuelling. The balance is high precision and high resolution, so to avoid the readings being affected by draughts or vibrations, the LD HFTS is transported in a trailer which reduces the impact of the environment during measurements.

How does the Light-Duty Hydrogen Refuelling Station Field Test Standard work in practice?

The mobile test standard is driven on site and the measurement process is fully managed by highly trained operators. The test matrix has been developed according to OIML R139 3.

Before the system is operational, the operators will secure and mark a 5-meter safety zone and perform a number of safety checks before levelling the balance and installing a venting stack. The field test standard is powered up and the balance is checked and calibrated within its working range. The initial weight with empty tanks is then taken.

Next, the hydrogen dispenser nozzle is connected to the LD HFTS and the refuelling process starts. When the target pressure is reached, the system stops, the nozzle is disconnected and the skid is now weighed with tanks full.

Figure 1 Schematic of the LD HFTS system setup at the dispenser during tests.

Figure 2 System deployed and ready for measurements at UK Hydrogen Refuelling Station

The difference in mass between the full and empty tanks is calculated, a buoyancy correction is applied, and this result is compared with the dispenser reading.

The LD HFTS uncertainty is less than ±0.3% (k=2), which has been verified by numerical approach (uncertainty budget), calibration of instruments following ISO 17025 and intercomparison within the EURAMET-funded project “Metrology for Hydrogen Vehicles 2” (MetroHyVe 2). Therefore, we can use the LD HFTS safely and with confidence to measure accuracy of the dispensed quantities at hydrogen refuelling stations following OIML R139 regulations. The system is designed to prove the accuracy of the dispenser, giving confidence to the operator and consumers that the correct quantity of fuel has been charged for. The LD HFTS also logs the pressure, temperature and flow profile of the dispenser during the refuelling process which may be used for optimising the dispensing system as well as troubleshooting should the test fail the 2% error requirement.

View further information including technical specification of the TÜV SÜD hydrogen refuelling station field test standard or contact us today about visiting your premises.

Guidance Note: Flow Measurement for Hydrogen Refuelling Stations

We have also produced a Guidance Note: Flow Measurement for Hydrogen Refuelling Stations which provides guidance on flow measurement for hydrogen dispensed at hydrogen refuelling stations (HRS) and verification for the quantity of hydrogen billed to the customer.

1 https://www.gov.uk/government/publications/the-ten-point-plan-for-a-green-industrial-revolution