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Energy


Accuracy Class 1 Low Flow


Meter Accuracy / MPE MPES


Volume Convertor accuracy Uncertainty Calculation


√(MPE2 + 1MPES2 Tier Threshold (EUETS Level attained) ) 3 4 1 2


0-20% ±2% ±2% ±1% 2.24


High Flow 20-100%


±1% ±1% ±1% 1.41


Accuracy Class 1.5 Low Flow


0-20% ±3% ±6% ±1% 6.08


High Flow 20-100%


±1.5% ±3% ±1% 3.16


conversion). The volume convertor accuracy impacts the overall accuracy in terms of an uncertainty value (%). There are four tiers of accuracy under the EU ETS legislation. Each tier has different uncertainty value, with the highest level of accuracy being tier 4 at <1.5%. As can be seen from the table below, this is difficult to achieve with a typical rotary or turbine meter with or without a volume converter. The updated guidance showed for a class 1 meter the MPES is equal to MPE. Under this criteria a standard class 1 meter and volume converter would meet tier 4 requirements under high flow conditions but would fail under low flow The table above compares the tier thresholds


achieved utilising class 1 or 1.5 standard meters. Therefore achieving the tier 4 threshold is not


achievable at the low flow rate without further improving the accuracy of either the gas meter or the converter. Following the re-issue of the EA guidance in February 2014, further clarification was given on the lower flow rates as follows: ‘It is inevitable that the low flow rate will be less than 20% of the maximum flow rate at some point. However, if the meter operates above 20% of the maximum flow rate during normal operation, the overall uncertainty is assumed to be within the higher flow.’ This clarification has allowed businesses to utilise the high flow rate metering accuracy of 1% to calculate the uncertainty value (unless normal flow runs at <20% of the maximum flow rate). However this clarification failed to resolve a key point on


how to validate that the meter in service was still working within its defined accuracy levels. The responsibility for ensuring a meter is within calibration under EU ETS lies with the end consumer. The only way to validate the accuracy of a rotary or turbine meter is to remove it and send it away to an approved test facility for calibration. Typically carrying out such an activity can cost up to £12,000 per annum. Therefore, an annual calibration is a very costly exercise and means that many sites cannot meet Tier 4 requirements. An additional problem caused by annual calibration is the disruption to supply and the amount of time a meter may be offline whilst being away calibrated.


Future proofing gas installations for EU ETS Trials have recently been run utilising SICK© ultrasonic meters. The capabilities of such an ultrasonic meter


24 FACILITIES


currently leads the way for the future of gas installations and EU ETS in that it can be calibrated to a much higher level of accuracy and can be self-calibrating. The meter’s built-in computer can automatically alarm if the meter deviates from its calibration range, ensuring the installation meets the requirements of the EU ETS. The alarm can be picked up as part of either a maintenance activity or through remote monitoring. This new range of ultrasonic meters also allows for increased accuracy having a standard accuracy of 0.5%, which can be further calibrated down to 0.2%. The 1.41% uncertainty figure from a standard meter is very close to the current Tier 4 EUETS <1.5% uncertainty requirement. Improving the meter accuracy further gives protection from future changes in the EUETS requirements. (Further improvements with volume converters combined with an ultrasonic meter would be capable of delivering an uncertainty value of less than1%). If further levels of accuracy are required, then it is possible to install a flow computer, which in essence does the same as a volume converter, but it measures much more accurately by increasing the number of sample points and by possibly measuring the calorific value at the meter point through a chromatograph. Typically the SICK flow computer with a flow computer can reach an uncertainty value of 0.20%. The changing requirements to help meet and tackle climate change will continue to be challenging, but by working with manufacturers, the Environmental Agency and end consumers, it is possible to meet EU ETS requirements.


Further information


No other company operating in our field, both MAP and MAM, is able to demonstrate the same depth and breadth of knowledge and experience as National Grid Metering. Through our long experience of running large-scale programmes of metering deployment and operation, we know what works. We also understand the critical importance of programme planning and risk management and we are continually looking for ways in which to improve our services. The key capability of National Grid Metering is our ability to provide a complete range of services. This gives us the ability to address all of our customers’ needs promptly and accurately, whether as part of on-going contract work or in an emergency. Feel free to get in touch at I&CSales@nationalgrid.com


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