Report Open Access
de Laat, Hans
The suitability of measurement principles for standard gas meters for domestic consumers capable of measuring hydrogen was investigated based on gas characteristics, the measurement technology and availability. The availability of the meters was investigated through interviews with meter suppliers. Based on the results, ultrasonic meters and thermal mass flow meters were the two preferred options for selecting hydrogen meters for household pilot projects.
Due to the low density and viscosity of hydrogen, it is possible for the flow in a hydrogen meter to change between laminar and turbulent. At present, it is not known how the meters derive the correct flow pattern when calculating the quantity of gas. In addition, there are major differences in gas properties between hydrogen and air, the gas that is used for field testing the meter. This can cause a widely varying pressure difference across the meter. For the time being, it is assumed that the recently completed first European Type Approval according to MID has verified these two aspects.
Hydrogen of distribution quality may contain gaseous impurities. The thermal conductivity of these impurities differs from that of hydrogen to such an extent that even the permissible quantities result in a change that is within the order of magnitude of the accuracy class of the thermal mass flow meter. Here too, it is tentatively assumed that this aspect has been verified during the European type approval according to the MID of this type of meter. When hydrogen meters are evaluated by network operators, it is useful to examine the three aspects mentioned above in more detail.
The distribution network operators work together within the Meter Pool Small Consumers (Meter Pool KV) to monitor the quality of gas meters. Hydrogen is not yet considered in the Meter Pool KV. Proposals for expanding the scope for the purpose of adapting the KV Metering Regulations and the related Implementing Provisions and Work Instructions on hydrogen have been included in this report. In addition, it is also necessary to adapt control installations in order to be able to inspect hydrogen meters.
In Europe, there is not yet a traceable chain for measuring hydrogen flow. Traceability refers to a continuous series of comparative measurements that use a known national or international standard as a reference for the measurement results of an instrument. Some important steps for traceability have been taken, for example the establishment of a control installation for hydrogen meters at TÜV in Glasgow that can add gaseous impurities. A specification from this kind of an installation has been included in this report. Making hydrogen meters in the Netherlands traceable is expected to increase confidence in the quantity measurement of hydrogen.
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