Proposal of a novel approach to reference instrument and procedure definition to measure hydrogen volume and volumetric flow in a legal metrology framework

International standards concerning hydrogen measurement in legal frameworks are still lacking. This study proposes a novel approach to instrument and procedure definition for the legal measurement of pure hydrogen volume and volumetric flow rate according to main international standards of metrology. A wet drum meter filled with water is chosen as reference meter. The selected reference instrumentation and procedures are replicable in other laboratories. Simulations and calculations demonstrate that hydrogen diffusivity in water have no influence on error estimations, while water evaporation is considered because it affects the volumetric flow rate measurement. The expanded uncertainty of the total metrological chain is less than 0.25%. This reference procedure allows to perform tests for error of indication of new meters both using hydrogen and other flowing gases with the same measurement principle, instrumentation and procedures, helping the development and certification processes of new products useful for the upcoming energy transition.