Flow Control A
Older encoded meters working side by side with new radio-enabled versions

Flow is the most important parameter measured by the water industry to manage and control the clean and wastewater networks from source to tap and drain to river. This article looks at three areas of flow metering which have changed significantly and which will see further expansion in the next few years: leakage monitoring, domestic metering and wastewater.

Significant milestones are an opportunity to pause and reflect on where we have been and where we are going. So when I was asked to write about flow technology for this anniversary edition of Water & Sewerage Journal, it made me think back on my 30 years in flow and metering. Not surprisingly, the methods used have evolved significantly as user requirements have changed driven by regulation, environmental pressures and public concerns.

WRc has remained at the forefront of testing and evaluating flow technologies against those changing needs.

Monitoring leakage

The influential Managing Leakage series of reports, which came out in the early 1990s, led to the widespread adoption of district metered areas (DMAs). Flow meters were required to monitor flows into these discrete areas. Initially, mechanical turbine meters were the only usable option. Electromagnetic meters had largely taken over from traditional differential pressure devices (Venturi and Dall tubes) for many measurements on abstractions, works outlets and trunk mains. However, they required mains power, making installation in the network expensive.

The electromagnetic meter manufacturers saw an opportunity and begun to develop battery-powered meters. Early versions suffered from poor battery life and other problems. Today though, battery-powered network meters are the preferred choice for many new installations, enabled by developments such as low power, digital electronics and battery technology.

With traditional DMA leakage management, treating DMAs as discrete entities and looking at trends in flow and pressure, it could be argued that the absolute accuracy of the meters has not been a key requirement. However, as drives to further reduce leakage lead to the development of smart networks and water companies begin to understand the benefits that they can bring, this will change. A smart network essentially means aggregating data from different sources and looking at the network more holistically. This means that (flow) data from many meters will need to be brought together on a common basis – absolute accuracy will become more important to facilitate this. The drive for greater sensitivity will also be there as the industry looks to find ever smaller leaks or detect developing leaks sooner.

The long-term stability of electromagnetic meters with on-board diagnostics to detect and report fault conditions (providing greater data confidence – essential for effective smart networks), integrated comms and the ability to integrate other sensors (eg pressure and temperature) are likely to mean that the use of electromagnetic meters in the network will continue to grow.

Domestic metering

The National Metering Trials final report on household customer metering was published in 1993. Household water meters were then exclusively mechanical devices read by eye at most twice a year. Indeed this is still the case in many places. However today, household meter penetration across England and Wales is over 50 per cent and growing, with most water companies planning to expand their use of customer meters in the next AMP.

Network
Mechanical meters (top) are being superseded by electromagnetic meters (bottom) for network applications

As cost pressures increase on the industry, more efficient meter reading methods are required. The need to better understand customer use, again driven by the need to reduce leakage, requires more detailed and frequent data on consumption. Most water companies are looking therefore at remote read meters, whether using fixed radio networks or short-range walk-by/drive-by solutions.

The basic design of a rotary piston measurement mechanism with a mechanical register has been around for over 100 years. The solid state fluidic meter posed a brief challenge in the ‘90’s but did not achieve a wide take up. However, the traditional design is being challenged on two fronts – both enabled by the addition of electronics. In hybrid designs, the meter mechanism remains mechanical but the register is electronic. Most manufacturers also now provide a solid state meter, based on electromagnetic or ultrasonic measurement sensors. What both hybrid and solid state meters offer is integration of remote reading and smart capabilities. This has been possible with wholly mechanical meters for a number of years but relies on clip-on units attached to the top of the meter which complicates installation.

Whilst hybrid meters are being installed in increasing numbers, the industry at the moment seems undecided as to whether to adopt completely solid state meters. These offer the potential of greater long term measurement stability, with no moving parts to wear, but clearly some reassurance is still required. At WRc we are developing projects to address user concerns.

So whilst it is likely that several million household meters will be installed in the next AMP, there is unlikely to be a wholesale change to completely solid state meters yet. However, an ever increasing number of new meters will include comms capability to provide more frequent or more detailed data.

Wastewater

Historically there has been far less monitoring of wastewater than clean. Weirs and flumes have dominated in open channel flows though the water level measurement has moved from floats to, almost exclusively, non-contact, ultrasonic sensors.

The Environment Agency’s MCERTS scheme has driven great improvements in wastewater measurement since 2000, particularly for environmental discharges. The MCERTS standards are widely recognised as good practice and their influence has spread to other domestic applications and internationally.

Wastewater
Non-contact area velocity instruments (right) are replacing traditional structures (left)

Traditional structures are now being challenged by the latest sophisticated area-velocity meters, both those submerged in the water (contact methods) or mounted above it (non-contact methods). These offer significant benefits in terms of costs of installation though tests, including those carried out at WRc, have shown that there are a number of factors that can influence installed performance. Discussions are ongoing as to how guidance can be provided, through MCERTS, as to how they should be deployed.

Another interesting development is the wastewater meter. This enables measurement in drains from sites, for example to separate surface water drainage charges for some commercial customers, or detect developing blockages. Trial deployments are underway and initial results look promising.

Flow will remain the most important measurement made by the water industry for both clean and wastewater. The demands on flow measurement technology will continue to evolve and no doubt become ever more challenging. It is this continuous change that has retained my interest over the years and I am looking forward to testing and evaluating more new technologies, as well as continuing to better understand established technologies, particularly with respect to installed (as compared to ideal) and long-term performance.

www.wrcplc.co.uk