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Guidance for humidity measurements of hydrogen vehicle fuel published

Hydrogen refuelling station

EMPIR MetroHyVe project highlights potential issue with hygrometers commonly used in hydrogen refuelling stations

Hydrogen is one of the most promising alternative fuels for future energy and transport applications, offering to increase energy security and reduce greenhouse gas emissions. To support its use as a low carbon transport fuel, an extensive infrastructure for hydrogen-powered vehicles is currently in development across Europe. However, until recently the hydrogen industry struggled to meet the measurement requirements of legislation surrounding the use of hydrogen fuel, due to a lack of methods and standards.

The project

EMPIR project Metrology for hydrogen vehicles (16ENG01, MetroHyVe) developed methods, standards and calibration facilities to ensure accurate flow metering and fair pricing for customers at refuelling stations, and methods, reference gases and online analysers to provide quality assurance and control of the hydrogen dispensed. This will support the uptake of low-emission hydrogen vehicles and the growth of Europe’s hydrogen economy by increasing confidence among both manufacturers and consumers.

Online monitoring of water content is required at hydrogen vehicle refuelling stations to ensure quality requirements are being met. The ISO 14687 standard specifies the limit for maximum water vapour content in hydrogen for fuel-cell vehicle use, together with concentration limits of other contaminants.  

Whilst EMPIR MetroHyVe has now finished, a follow on project EMPIR MetroHyVe 2 is now underway which focuses on metrology challenges for larger vehicles.

Challenges with water measurements

Good practice guide Calibration and use of humidity sensors for hydrogen refuelling station applications gives recommendations for the calibration and use of hygrometers for the measurement of the humidity of hydrogen fuel at hydrogen refuelling stations.

Hydrogen refuelling station operators using hygrometers for monitoring the quality of hydrogen in their stations will find the guidance helpful to consider when understanding the potential errors and measurement uncertainty of online water content measurement. Guidance includes recommended methods of calibration for the common hygrometer types used, including comparison against standards that can replicate the industrial conditions of use.

Project Coordinator Arul Murugan from NPL said

‘The work performed in EMPIR MetroHyVe highlighted an issue with water content measurements made using a hygrometer type commonly used at hydrogen refuelling stations. If unaddressed, hygrometers of this type may be drifting over time leading to incorrect measurements. The new good practice guide provides crucial guidance on ensuring hygrometers are appropriately calibrated for hydrogen refuelling station applications, reducing the uncertainty of water content measurement.’

The results of this project will be further advanced with new EMPIR project Metrology for hydrogen vehicles 2 (19ENG04, MetroHyVe 2) which will develop a metrological, traceable framework for testing hydrogen dispensing meters at hydrogen refueling stations and has recently started.


This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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