Pumping Systems: Variable-Duty Requirements Bring Savings

Many pumping applications with variable-duty requirements offer great potential for savings, which often go well beyond energy costs. These savings can include improved performance, increased reliability, and reduced life-cycle costs.

Most existing pumping systems that require flow control use bypass lines, throttling valves, or pump-speed adjustments. The most efficient of these strategies is pump-speed control, which managers can implement in a number of ways.

Most rotodynamic pumps in service today are oversized — many are more than 20 percent oversized. So retrofitting many of these systems with VSDs could help to match systems to actual load requirements more accurately and save energy.

VSDs offer several benefits for facilities. Some benefits are relatively easy to quantify, while others are less tangible. They include:

• Energy savings. Many rotodynamic pump installations incorporating VSDs have achieved savings of 30-50 percent.
• Improved process control. By matching pump-output flow or pressure directly to the application's requirements, managers can correct small variations more rapidly by using a VSD than by other control forms, which improves performance.
• Improved system reliability. Any reduction in speed achieved by using a VSD has major benefits in reducing pump wear, particularly in bearings and seals. Also, by using reliability indices, managers can accurately calculate the time between maintenance or breakdowns.

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