Automation: the key to unlock energy efficiency
Huge energy savings can be made by controlling pumps and other equipment using variable speed drives and automation, writes Martin Richardson
The trends of the 3Es - Efficiency, Environment and Expansion - focus on looking at things that drive growth within the water industry. These drivers include water reuse, reduction of non-revenue water, improving utility performance, prioritising investments in industrial and municipal wastewater treatment and how to meet the rising demand for safe and convenient water services.
As such, focus on energy saving has never been higher on the agenda than today. People have become increasingly aware of the correlation between wasting energy and environmental damage and acknowledge the benefits of conserving energy by technical solutions.
The biggest consumer of energy in water is the centrifugal pump such as intake, transfer, booster, sludge, submersible and progressive cavity pumps. Positive displacement pumps like screw pumps are also used. In addition to pumps there are fans, aeration blowers and compressors. Wastewater water applications include decanters, mixers and centrifuges.
Since water pumps typically run at partial load, huge energy savings can be achieved by controlling their speed with variable speed drives (VSDs). The power required to run a water pump is roughly proportional to the cube of the speed, i.e. a small reduction in speed can make a big reduction in the energy consumption. A water or wastewater pump running at half speed consumes as little as one eighth of the energy compared to one running at full speed. By employing VSDs on pumps instead of throttling, the energy bill can be reduced by as much as 60 percent. Consequently, VSDs also help to reduce CO2 emissions.
A good way to understand the installed base and to identify areas to improve energy efficiency is to undertake an energy assessment. Rather than assess every single application, a cost and time effective approach is to examine up to five motor-driven applications, which usually takes half a day. An executive summary will give an instant feedback as to the potential kWhrs (or MWhrs) that can be saved by switching from direct-on-line control of motors to variable speed. While it is not possible to provide a definitive payback period, as it will vary from project to project depending on the specific application and motor size, normally a return on investment can be achieved from six months to two years.
Similarly, productivity and reliability assessments can help use VSDs and motors to tackle issues such as water hammer, improve productivity of existing pumping systems and prolong the lifetime of the existing water utilities by carrying out life cycle assessments and manage harmonic mitigations.
For instance, when starting a pump, the VSD progressively increases the motor speed and smoothly accelerates the load to its rated speed. This soft starting and stopping approach is proven to reduce burst rates on booster sets by around 90 percent, meaning leakage and disruption to customers are greatly reduced. By soft starting, maintenance costs are reduced and the lifetime of the equipment extended.
In the water industry a growing number of embedded devices are now working together wirelessly either directly or via either the Internet ‘cloud’. The availability of real-time information enables operators to know how critical equipment such as drives and motors are performing. It also provides the basis for predictive maintenance.
Innovations like the ABB Ability Smart Sensor, a condition monitoring solution that simply attaches to the frame of a low voltage IEC motor, can provide critical condition monitoring data either over the Internet or via a smartphone app. This enables service teams to use mobile devices to check motor health and operating parameters like vibration, temperature and energy use.
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