Q&A: Pump Performance Monitoring

Oct. 10, 2008

Chris ThomasChris Thomas is a pumping application engineer for Schneider Electric in the company’s OEM Technology and Solution Center. He graduated from North Carolina State University with degrees in

Chris Thomas

Chris Thomas is a pumping application engineer for Schneider Electric in the company’s OEM Technology and Solution Center. He graduated from North Carolina State University with degrees in computer and electrical engineering. Mr. Thomas started his career in low-voltage circuit design for Powerware, then moved to building automation and controls where he designed, programmed and installed energy management systems for TAC Americas. His career eventually led him to variable frequency drive product engineering, and then on to pumping application and solution design for Schneider Electric. Mr. Thomas can be reached at [email protected] or 919 266-8604.

Q: In your experience, what are the most common reasons for poor pump performance in modern-day plant environments?

A: There are a variety of factors that contribute to poor pump performance. A few of the more common reasons for poor pump performance include:
• Pump Wear & Tear: Over time impellers wear down, reducing operating efficiency and requiring regular replacement.
• Over Sizing: Frequently pumps are over sized to meet anticipated, future demands, rather than current requirements, resulting in decreased efficiency and higher energy costs. Also, pumps are many times sized for completely filling a system, which can require much more volume than is pumped under actual operating conditions, again leading to higher energy costs.
• Antiquated Control Systems: Pumps are most frequently started using across-the-line starting methods. Newer technologies allow pumps to be operated at speeds more closely matching pumping needs, offering significant energy savings potential. These technologies include soft starters and variable frequency drives.

Q: In your estimation, how much energy could the typical plant save by implementing proper pump monitoring and optimization techniques?

A: Depending on the specific industry — for energy consumption attributed to rotating equipment (motors) — anywhere from 20 percent to 60 percent of a plant’s energy can be consumed by pumping applications. On average, close to 50% of total energy savings potential is attributable to pumps.

Q: What are some key best practices pump users should be employing to ensure the long-term efficiency of their pumps and pumping systems?

A: I recommend three primary best practices
• Proper and routine maintenance
• Proper application/sizing
• Use of VFDs or soft starters to maximize system efficiency

Q: What role does monitoring software play in the modern-day pumping application? Is monitoring software always necessary? Are there any application scenarios where monitoring software wouldn’t necessarily be beneficial to the long-term health of the pumping application?

A: I think that monitoring software is useful for applications where it is important to track changes in your system or maintain proper efficiency. Today, as our systems become more integrated with the building of monitoring and control networks and remote monitoring, the extraction and collection of data becomes easier and less expensive for the average user — meaning that more and more of our equipment can be monitored with software. Using the data collected, we can look for trends to determine wear, usage, and power consumption in our pumping system. And, we can then determine when maintenance is needed or how to better balance the system for maximum efficiency.

To fully utilize the monitoring software, you need the hardware required to collect and store data, which adds to the initial cost of a pumping system. For systems where (a) the pump is very small, (b) duty cycle is at or close to 100 percent, or (c) the application is non-critical, then using monitoring software is not recommended. This is because the payback for monitoring such a system does not warrant the cost of installing the necessary monitoring software and hardware.

Q: What role do variable-frequency drives play in the modern-day pumping application? Are VFDs always necessary? Are there any application scenarios where VFDs would not necessarily be a good fit?

A: Variable-frequency drives open the door for a wide range of benefits varying from energy savings to advanced control of a specific process loop. Today, with the prevalence of VFDs in the market, a VFD can be selected to provide a low-cost solution for a simple application. Or, it can provide a complex solution in which the VFD offers many of the features that the control system would provide, such as timed pumping, PID control (pressure and flow), as well as monitoring and feedback of critical data points. Also, the VFD provides advanced features, such as curved (S and U shaped) acceleration and deceleration ramps to tailor the starting and stopping of the pump to the needs of the system and to prevent water hammer.

The user now has the option of having precise control over their system. Now, instead of having a system of control valves and balancing valves, the VFD can be used to control the system using direct digital control that can be directly tied-in to the user’s system. The other benefit of having VFDs on the system is that now the operator can access data about each motor and pump in real time, so they can determine how the system is operating and make changes to the system on the fly.

The advances in VFD technology have also brought about improvements in communications options. Using the network technologies available in most VFDs, a user can monitor the pump from a remote location by tying the VFD into their management system, or by providing an HMI as an intuitive interface for system operators to use. As such, pumps can now be scheduled to run, stop, and provide feedback to the operator at a control center or from the comforts of their own home.

With all of the benefits of a VFD, a user still needs to consider their specific application before selecting it over a soft starter or contactor for their control needs. On loads that are sized for the motor and are not expected to change, then a VFD would be a bad choice, because the system will always be running at a fixed speed. In this case a soft starter would be a better choice to gain the benefit of the decreased wear and in-rush current on the pump and motor. Another example would be a primary/secondary pump system where in-flow on the primary loop is fixed. Again, this is a poor choice for a VFD, as the speed will never vary and the user will receive little benefit.

Q: Some pump experts I have spoken to have suggested that in some cases VFDs only serve to mask a larger problem of improper mating of the pump to the pumping system and/or application. How can users be sure that a VFD is the proper solution for their application environment? What are some of the common application scenarios where VFDs are a good fit? What are some of the common application scenarios where VFDs might not be a good fit?

A: It’s fair to say that the use of VFDs is not necessarily the only solution to improving pump system efficiency, but it is certainly a key factor. In mating the pump to the pumping system and/or application, please remember the three best practices for proper pump system efficiency:
• Proper and routine maintenance
• Proper application/sizing
• Use of VFDs or soft-starters to maximize system efficiency

We believe this is why Pump OEMs refer to a "much larger" problem. It’s the question of, "Is the pump oversized?" If yes, then a VFD is a perfect fit. However, there is one other major item to consider, and that is a pump’s "minimum speed." If a pump’s minimum speed is greater than the required demand, the pump should be replaced with one that matches the application.

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