Measuring hydrogen: which units?
The unit of measurement for hydrogen varies according to the context and use:
- When it is distributed at petrol stations, the fill-up is invoiced in kg
- When it is delivered in cylinders for industry or the tertiary sector, its volume is expressed in liters
- When it is used as fuel (industrial furnace or boiler), consumption is in MWh
- When it is transported by pipeline, the flow rate is expressed in m3/h
Mass and Volume
The mass – expressed in kg – is the unit of reference, as it is invariable and reflects the quantity of matter. To calculate the volume (cubic meter or m3 ), the pressure and temperature conditions must be specified. When it is gaseous, the volume occupied varies with temperature or pressure.
To avoid this constraint, the volume can be expressed under normal conditions, i.e. at atmospheric pressure (1.013 bar) and a temperature of 0°C or 15°C depending on the standards. This is referred to as normo-cubic meters, symbolized as Nm3 or m3(n).
At atmospheric pressure, hydrogen is gaseous. For it to become liquid, its temperature must be below -252.8°C. It then occupies a much smaller volume.
Influence of pressure – Volume occupied by 1 kg of hydrogen
Calorific value is a property that allows the energy contained in 1 kg of hydrogen to be measured and thus compared with other fuels. It is expressed in kWh.