HYDROGEN INDUSTRY TESTING


TIMES FOR GAS METERS


T


he UK is committed to drastically reducing emissions of carbon dioxide and other


greenhouse gases to achieve Net Zero emissions by 2050. This will require substantial changes to the ways in which energy is generated, stored, transported and consumed. One route to achieving the goal that is currently being pursued is through the decarbonisation of heat, since approximately 32% of total UK emissions are attributed to heating in buildings and industry. To ensure support for decarbonisation plans, it


is crucial to consider the needs and expectations of the public. Consumers will want a gas network infrastructure which is safe and reliable, and appliances which are intuitive and familiar. Crucially, there must be assurance that the billing is accurate, fair and well-regulated.


METERING GAS Two flow meter types are well established for domestic metering of natural gas. Diaphragm gas meters are installed in around 70% of homes with a gas grid connection and use the positive displacement principle first developed in the 19th century. Most smart meter installations are ultrasonic meters based on the transit-time measuring principle. Both are inexpensive and designed to operate accurately for a decade or more without maintenance. Accuracy is demonstrated during type approval,


where samples must meet the accuracy requirements of the UK Measuring Instruments Regulations. For a Class 1.5 meter, the maximum permissible error is ±1.5%, increasing to ±3.0% at low flow rates (less than 20% of the maximum). If a customer disputes the accuracy of their gas meter, it is sent to an approved lab for testing by an independent examiner.


Figure 1: TÜV SÜD’s traceable hydrogen calibration facility for domestic gas meters


Marc MacDonald, head of Clean Fuels at TÜV SÜD National


Engineering Laboratory, takes a look at accuracy testing of domestic gas flow meters operated with hydrogen and hydrogen blends


CHALLENGES While many of the existing metrological approaches remain applicable, the distinct physical properties of hydrogen present new challenges for instruments optimised for natural gas. Hydrogen has a low viscosity


and a smaller molecule size than any other gas, which leads to the well-known tendency of hydrogen to leak from systems that are leak-tight with other gases. In a diaphragm meter, these properties are expected to cause increased ‘slippage’ through internal clearances, resulting in increased errors, particularly at low flow rates. With ultrasonic meters, the


concern is that the acoustic properties of hydrogen are significantly different from natural gas. The speed of sound of hydrogen is 1300m/s, around three times higher than natural gas, meaning that greater precision is needed in the transit time measurements. Also, the density of hydrogen is 0.08 kg/m3, this is eight times lower than natural gas which leads to a lower acoustic impedance and poorer signal-to-noise ratio. As the UK’s Designated Institute


100% Methane


4 3


1 2


0 0 13 4 2


-4 -3 -2 -1


Reference Flow Rate (m3 /hr) Figure 2: Calibration of diaphragm meter with pure methane and 20% hydrogen Nitrogen


4 3


1 2


0 0 26 8 4


-4 -3 -2 -1


Reference Flow Rate (m3


for Flow Measurement, TÜV SÜD National Engineering Laboratory was a partner in the joint-research project ‘Flow metering of renewable gases’ (NEWGASMET) and worked with European metrology institutes, flow meter manufacturers and members of the CEN/TC 237 standardisation committee to determine how the existing type testing methods should be updated for domestic meters operated with hydrogen. This project deemed it was necessary to collect new data on accuracy with hydrogen and other gases. However, the existing laboratories for natural gas were considered unsuitable. Firstly, there is a safety issue, since hydrogen


has a wider flammability range than natural gas and is in the stricter ATEX gas group IIC. If the safety challenges were overcome, the laboratories would then need to prove that their reference measurements were accurate with hydrogen, which for many laboratories would be difficult or completely impractical. TÜV SÜD has addressed this need by building


the UK’s first independent, traceable, hydrogen calibration facility for domestic gas meters, with a measurement uncertainty of ±0.3% (k = 2) in the reference hydrogen flow rate.


RESEARCH The first test programme for the facility was


www.essmag.co.uk /hr) Figure 3: Calibration of diaphragm meter with pure nitrogen and pure hydrogen


devised to support the UK HyDeploy project, which aims to show that hydrogen can be safely blended into the existing gas networks with minimal disruption to gas network equipment and consumer appliances. TÜV SÜD tested 21 domestic gas meters with pure methane and a 20% hydrogen / 80% methane mixture. For most meters tested, the addition of 20% hydrogen had no discernible influence on accuracy. In the NEWGASMET project, TÜV SÜD and the


German National Metrology Institute, PTB, tested six diaphragm meters with 100% nitrogen and 100% hydrogen. Whilst there were noticeable differences in the error curves for both gases, the hydrogen results were not consistently worse than nitrogen, and most test meters still met the Class 1.5 Accuracy requirements. Since construction in 2020, the TÜV SÜD facility


has been used in numerous research projects, including projects for gas network operators and flow meter manufacturers. The overall aim is to support the transition to a decarbonised gas network by ensuring that billing remains accurate, fair and well-regulated.


TÜV SÜD National Engineering Laboratory www.tuvsud.com/en-gb/industries/ clean-energy


ENERGY & SUSTAINABILITY SOLUTIONS - Summer 2023 13 10 12 Hydrogen MID Accuracy Class 1.5 5 6 7 80% Methane / 20% Hydrogen MID Accuracy Class 1.5


Error (%)


Error (%)


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