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Optimising water supply network performance the smart way

Water network management is complex but accurate flow measurement plays across the spectrum of activities, says NEL's Alick MacGillivray.

In the UK, water network management is a complex undertaking. In England and Wales alone, water companies manage a network of 335,000km of pipes, with around 24 million connections to homes and industrial properties. As a consequence, water and sewerage companies face a large range of challenges in the effective maintenance of their delivery networks.

Every day in England and Wales, 3.3 billion litres of water are lost through leakage in the delivery networks. The scale of this problem is set to get worse since the UK population is projected to increase by nearly 15% over the next 25 years. This increase is predicted to be greater in areas that are already classed as water stressed such as London and the South-east. In addition to this, Environment Agency (EA) predictions show that water levels could drop by between 10% and 15% over the next few decades due to climate change. This represents a growing gap between what the industry can supply and what is required by customers.

There are a range of other challenges facing the water industry in the UK. Many of the water pipes were installed many years ago and are now old and more prone to leakage. In response to this, over the years the industry has invested vast amounts of capital into its assets and infrastructure.

A number of global trends are also having an effect on the water industry. Climate change is one of the most important of these. Water is currently perceived by the public as an inexhaustible resource that is cheap and always plentiful. The water industry must alter that perception as soon as possible because changes in rainfall patterns are likely to result in more regular infrastructure failure.

Water companies have also got to manage changing customer expectations. It is a fact that customers are only aware of their water supply when something goes wrong. For example, if there is a hosepipe ban due to a water shortage, or when the supply is temporarily cut off. Customers’ perceptions are also impacted when they are sent a substantially increased water bill caused by necessary ongoing investment in infrastructure, such as pipes and water meters.

The industry has to manage customer behaviours to assist in driving innovation, which will particularly be the case in the future when there will be more elderly and potentially vulnerable customers. Like many sectors within engineering, there is pressure brought to bear by an ageing workforce, resulting in a shortage of key skills. This may mean a substantial investment in re-training to ensure that they have the skills required in the future.

Along with all of this, water companies still have to meet the demands of the regulator. Water companies are obligated to perform an annual water balance calculation, which compares the water volume from sources of supply to that of the demand. There is also the SIM (Service Incentive Mechanism) score (out of 100) which is part of the regulatory process for setting the price and service package that each of the companies must deliver. Companies must publish these scores independently alongside other information about their performance.

With this range of array of challenges facing it, the industry is being driven to adopt new technologies and protocols to make the most of the resources that they have at their disposal. Principal amongst these are smart metering and the application data reconciliation techniques.

Smart metering
Smart meters measure and transmit a customer’s water usage data to supply companies. They can operate on their own or as part of a wireless network, transferring readings periodically from pipes connected to an individual property using a range of different technologies, so that both the customer and the provider can monitor the amount of water being used by the household.

They are often referred to as AMI (Advanced Metering Infrastructure) in that the meter can transmit data to the water company and also receive data from it. This removes the need for staff to have to physically check, or to inspect the meter, reducing the cost of maintenance.

There are several types of meters available from different companies falling into several categories such as mechanical meters, simple digital meters and upgraded mechanical meters. These meters cost in the region of £250 to install and are paid for by the customer.

It is anticipated that smart meters will reduce bills in most households by assisting in the identification of leaks. Some companies are also considering the introduction of “seasonal tariffs” which is expected to help with demand management. Practically, this means that customers would be charged more during periods of water scarcity. These meters are much cheaper to read than existing equipment and are generally more accurate. Because they can transmit a large volume of data they allow the company to manage their network much more efficiently.

Data reconciliation
In the past, water companies have used mass balance techniques to estimate the amount of leakage and other unmetered abstraction in their distribution and waste treatment flow networks. Data reconciliation (DR) takes this a stage further by identifying the instruments most likely to be responsible for imbalances, and allowing water companies to target maintenance to where it is most required.

DR is a calculation technique that is increasingly being used by water companies to monitor the quality and reliability of flow measurement data acquired from trunk mains. It performs a network self-check to ensure that all of the measuring devices are consistent with each other. Using this technique, engineers may quickly identify which meters are reading outside their uncertainty bands and take appropriate remedial action. It can also be used to determine the level of leakage in a network.

The basic premise behind data reconciliation is that it uses a mathematical technique known as ‘least squares’ to adjust the values of the measured flows so that they all exactly obey the balance equations in the network. The magnitudes of the numerical adjustments required to do this are compared with the uncertainty of the measurement (to 95% confidence) and a “quality index” is calculated for each measurement point in the network. If the value of this index is less than unity then the measurement is deemed acceptable; if greater, then there is an issue with the measurement that should be investigated.

The calculations are normally performed using DR software installed as part of the water company’s data historian. It is common that the calculations are triggered along with others during the minimum nightline period, usually on a daily basis. In this way, it can act as an “early warning” system for instruments drifting out of calibration or the development of leaks in the trunk mains.

Companies using this technique have much more confidence in their trunk main flow data, as it is continuously being checked for consistency against the rest of the network. It also can substantially reduce Opex due to reduction in the level of maintenance required.

Smart metering and data reconciliation used together will give water companies much more confidence in the reliability of their data and the resilience of their networks from trunk main level, down to the supply to individual properties. These techniques, along with recent advances in electronics and computing will go a long way to meeting the challenges facing water companies in the 21st century.

Alick MacGillivray is senior consultant at NEL.

 

This article first appeared in the March 2017 edition of WET News.

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