Martin Richardson, Water Framework Manager at ABB, explains how variable speed drives (VSDs) can represent an easy and cost-effective way for the water industry to progress rapidly to Net Zero.
Electric motors account for a significant proportion of the water industry’s energy consumption. Many motors are run without any kind of speed control, while some use mechanical means such as valves and dampers to modulate flow and pressure. This is inherently inefficient, as the motor is still running at full speed, regardless of demand. A variable speed drive (VSD) instead controls the motor electronically, to always match motor output with actual demand. As such, the motor only uses the minimum amount of energy that it needs, which can save both energy and money.
Pumps, fans, and compressors, are centrifugal applications, and as such obey the cube law. This means that a small decrease in speed results in a proportionally higher decrease in energy use. In practice, running a motor at 80% speed requires 50% of the energy required to run at full speed.
HIDDEN FUNCTIONALITY
In most cases, installing a VSD will lead to improved energy efficiency almost overnight simply by reducing the motor’s speed. However, VSDs are highly complex, with modern devices boasting huge amounts of functionality, and so the real savings come when you start exploring what else a VSD can do for you.
For instance, energy tariffs are generally higher during peak demand and lower at night (depending on your supplier). A VSD provides the flexibility to operate intensive or non-critical processes at the right point in time to achieve the lowest cost. Reservoir controls, for example, can pump water into a reservoir overnight when tariffs are lower. And the more you get into this level of detail, the more you can gain control over processes to uncover other efficiency savings.
Pumping slower for longer can also make a big difference. Consider the example of using a pump to empty a tank. Pumping slower may take more time, but even a small change in pump speed can lead to a disproportionately higher energy saving.
At a basic level, a VSD will save energy on pumping applications. But it also provides the flexibility to rethink control philosophies for applications driven by motors in the water industry and helps to optimise processes so that they reflect varying changes in costs upstream and demand downstream. Modern VSDs are also packed with sophisticated application-specific features such as multi-pump control, which can make a big difference to the resilience of operations.
IMPROVING RESILIENCE
Reducing leakage and bursts will be crucial in working towards the industry’s Net Zero goals. Prevention clearly is better than cure when it comes to leakage; however, many leaks are only detected when roads start flooding with water. As well as wasting water and potentially causing damage to the surroundings, digging up roads to repair pipes uses enormous amounts of carbon. VSDs incorporate internal PID loops, which, in this context, can ensure that pressure is maintained at certain levels regardless of any other variables in play, as the VSD is able to constantly adjust motor speed depending on the circumstances. The VSD can also provide an early warning system for any potential leaks, as issues can be inferred from the behaviour of the motor and pump. For instance, if a booster pump is running with VSD control and is operating at full speed for more than, for example, one minute, then this usually suggests that there is an issue that needs resolving somewhere, and the VSD can flag this up. Running motors at lower speeds generally will also reduce strain on pipes and valves.
IN SUMMARY
When people think about how to save energy, often the first suggestions are to turn lights off and reduce the heating. However, the difference this makes can be negligible when compared to reducing the energy usage of, for instance, a pump at a pumping station by up to 50%. Moreover, turning off lights and reducing temperatures can end up compromising comfort. A VSD, on the other hand, allows required output to be maintained, at a much higher efficiency, and with no compromise on productivity and effectiveness. When looking for cost-effective ways to save energy, the VSD could be the key to unlocking significant progress on the water industry’s road to Net Zero.
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