Andy Godley. Senior Consultant – Flow Measurement and Metering, Water Research Centre
Flow data underpins many of the critical activities undertaken by the water industry including managing water resources, leakage and customer service. This means that metering is one of the most important tools the industry can use to meet future challenges. This article explores the implications of those challenges on meters and metering, and how technology is evolving. It also delves into the work going on to understand the characteristics of existing and novel metering technologies which is required if we are to get an appropriate quality of data, and use that data most effectively.
Absolutely critical to the water balance are the meters that measure distribution input – often very large, but few in number. One UK company estimates that 65% of its water into supply passes through just 44 meters, all of which are 500 mm in diameter or larger. Despite their importance, we have relatively little understanding of how very large meter performance is influenced by real-world conditions and how it changes over time. The latter is important as many of these assets are aging due to the costs and disruption of replacement.
At WRc we have tested meters 300 mm diameter but most experimental work has been conducted on meters 250 mm or smaller. It has long been assumed that this can simply be extrapolated onto larger meters. However, there is evidence(1) that flows behave differently in larger pipes, with flow distortions and swirl from upstream fittings, which cause measurement errors, requiring longer distances to decay. A report from UKWIR in 2020(2) highlighted the need to improve confidence in large DI meters.
An international collaboration led by Severn Trent Water, in conjunction with TUV-NEL, WRc, Arup and the University of Utah is launching a ground-breaking project using the unique facilities at Utah to conduct tests on very large meters, combining these with the capabilities of the other partners in computational fluid dynamics and uncertainty modelling. The project will deliver new installation standards for meters to optimise accuracy and tools to better assess uncertainty in installed meters and thereby increase confidence in the input side of the water balance.
Moving into the distribution network, Ofwat’s challenge to reduce leakage significantly is driving a need to detect ever smaller leaks more quickly and control networks to minimise leakage. Minimum night-flows are a key tool in this. Many companies now use rapid logging to provide better discrimination between underlying leakage and usage events. Sophisticated data analytics which help understand network behaviour and artificial intelligence to control networks are very powerful tools but these require high quality data to fulfil their promise. Previously, it has often been sufficient to look at trends in individual meters where an offset, for example, did not matter. However, the amalgamation of data by intelligent systems means that absolute meter accuracy becomes more important.
The response to the Covid pandemic changed household and non-household consumption patterns significantly. This has been a dynamic situation and is continuing to evolve as we return to more stability. There is no doubt, however, that some changes will become embedded as people enjoy greater flexibility in where and when they work. Covid therefore has led a discontinuity in those historic data trends that are often relied on for network management. The industry quickly needs to understand the “new normal” in its networks and adapt to these changes.
All these point to the need for network meters for DMAs and small areas to be accurate, sensitive to low flows and stable. They also need to interface with new options for data logging and comms to provide data swiftly.
In response, a number of new mid-sized meters (50-300mm) are entering the market, both from established and new suppliers. Typically, these are battery powered electromagnetic or ultrasonic meters, with advanced functionality including comms, that challenge the former dominance of mechanical meters. Novel designs of flow tube claim to have good sensitive to low flow rates whilst requiring zero diameters up and downstream of straight pipe increasing installation flexibility.
Battery powered meters are desirable as they can be located anywhere in the network and at customer premises without needing mains power. However, battery life is finite and with pressure on operational budgets, long battery life is required to avoid frequent maintenance or replacement. A variety of sophisticated power management techniques are used to prolong battery life which can manifest themselves in the flow data or have implications on meter installation. This is illustrated by the following real-world examples.
Some meters conserve power by sampling the flow at intervals ranging from a few times per second to once every several seconds. This can apply to both household and network meters. Work originally carried out in the Czech Republic showed very significant errors in the consumption recorded by solid state household meters when flows were switched on and off suddenly, as might occur with a modern washing machine that has a solenoid valve injecting short spurts of water. Currently tests for meter approvals, such as those in ISO 4064, are carried out under steady flow conditions. The European MetroWaMet project (https://www.ptb.de/empir2018/metrowamet/the-project/), reporting later this year, is investigating this further and developing tests for approval of meters under varying flow conditions.
Other meters limit instantaneous power consumption by inhibiting certain functions when others are occurring. This has been observed to result in an uneven pulse train under steady flow conditions. The meter gives the correct number of pulses over time but the spacing of the pulses is irregular. This has implications when using data from fast loggers for night flow analysis.
Some electromagnetic meter manufacturers have reduced the power consumption by reducing the current supplied to the magnetic coils. This reduces the strength of the field generated and consequently the signal voltage. This makes the meter more susceptible to interference and offsets caused by stray voltages or nearby electrical fields. To counter this, much greater care is required with the electrical grounding.
As metering assets typically have a life of 10 – 15 years getting the right meter installed, and installed correctly, for these critical duties is more important than ever. Water companies need to be innovative in their approach to metering, considering what benefits the new meters have, but also being aware that they may behave differently to their conventional meters and seeking independent evidence to support the claims made by suppliers.
So far, we haven’t considered customer metering, but this is another area where meter technology is advancing – again with solid state meters challenging traditional mechanical devices and hybrid meters combining mechanical measurement with electronic registers, all offering a high level of functionality. These meters are opening new opportunities for tackling customer-side leakage and improving customer service.
The developments in metering technology link to another challenge – that of sustainability and zero carbon. We are installing more, and more sophisticated, meters. These are often sealed units with large proportion of plastic parts and non-replaceable batteries. This is a step change from traditional metal bodied mechanical meters visually read or linked to standalone loggers. The end-of-life management for these new meter assets needs to be planned for now. The waste and recycling industry is not yet familiar with these devices and, with a typical 10 year lifespan there could be 2 million plus meters being replaced per year. WRc’s unique mix of experts in metering and waste resources are developing work to explore this further and finding the solutions the industry needs in the near future.
In conclusion, the requirement for both more, and more accurate, meter data from source to tap has never been greater if the industry is to meet the challenges it faces. The industry needs to get confidence in the new products the suppliers are offering, learn how to get the best out of them whilst also improving its understanding of its installed meter base.
www.wrcplc.co.uk
References
1. Furness R, Phatnani S. Experimental and Theoretical Studies in Large Water Supply Lines. Flowday 2003
2. Best Practice For Trunk Main Flow Monitoring Areas. UKWIR ref 20/WM/08/74.
