Cast your mind back to the summer and, alongside the excessively high temperatures of August, England also had the driest July since 2011. As reservoirs started revealing previously-hidden villages, thoughts turned to water supplies and how resilient they were.
The talk in the media was about the three million litres of water lost through leaks every day – around a trillion litres a year. Particularly severe leaks can also attract negative publicity and consumer outrage.
The industry is however making great efforts to rectify this. In fact, Ofwat requires water companies to cut the number of supply interruptions and reduce water leakage by at least 15 percent over five years.
But are we using the most effective methods? There are many ways to find leaks, some more inventive than others, including using sniffer dogs, ultrasound and detecting the thermal signature of leaking water from space. However, many of these methods tend to focus on resolving the symptoms of leaks rather than the underlying cause.
Prevention is always better than cure. A constant round of find and fix is no substitute for taking measures to prevent leaks and bursts from occurring in the first place.
One technique that is often overlooked is to employ variable speed drives (VSDs). By controlling the rate of change and the speed of a pump, and hence the pressure of the water in the supply network, we can reduce the severity of many of the problems that lead to leaks.
Think of a pump that is connected direct-on-line – every time the pump starts or stops, there will be a sudden change in pressure. The danger is that joints are put under stress and any cracks could open and turn into major leaks. A VSD allows the motor speed to be softly ramped up to help prevent pressure spikes.
The other major benefit of using a drive is precise pressure control using PID control, which allows pressure and flow to be reduced during non-peak times. If the pressure is reduced by half, for instance during the night, the leakage flow rate will also be reduced by approximately half during this period. If a leak is present, and many systems will have undetected leaks, then this reduced pressure means less water escapes from the pipe, reducing both the amount of water wasted, and energy usage.
Utilities with experience of these benefits include Scottish Water, which was, on average, suffering nine pipe bursts a year at its Castle Road pumping station. Each burst was costing the company an estimated £1,400 through a combination of leakage detection, repair materials and labour.
Again, the bursts were caused by pumps being started direct-on-line, which created pressure waves, causing pipes to fracture and leak.
To solve the problem, Scottish Water installed two 5.5 kW ABB water and wastewater drives at the site, one for each of the two booster pumps. The drives provide a soft ramp up and a controlled slow down to maintain supply pressure in the pipe network.
Before the ABB drives were installed, data loggers revealed that when using direct-on-line starting, pressures were peaking at 13.7 bar. Following installation of the drives, it was found that starting and stopping the pumps using the VSDs reduced maximum pressures to 8.1 bar.
Since the installation was commissioned in 2016, the site has seen no pipe bursts at all, saving £12,000 in reduced maintenance costs per year. The VSDs have also reduced the energy consumption of the pumps, saving an additional £200 per year.
We clearly need innovative ways to cure the perennial leakage problem. Yet, we don’t necessarily need to focus on completely novel techniques or experimental new technologies – with VSDs, an easy, cost-effective and widely available solution already exists.
To find out more about how variable speed drives can help to reduce leaks and save money, sign up for ABB’s webinar entitled “Reducing energy costs: How to maximise asset efficiency and resilience using VSDs and motors” on Friday 18th November at 10.30am. Click here to register your attendance: https://campaign.abb.com/GB_WaterEfficiencyResilience_UW