Frequency converters (website: http://www.frequencyinverter.org ) are often proposed as a means of energy reduction. In systems with widely varying flow rate requirements, and where system friction is a significant component of the system head, frequency converters offer a viable solution for reducing life circle cost. In some applications frequency converters also can eliminate the need for control valves and their associated maintenance expense. Unfortunately, frequency converters often involve significant installation and set-up costs that may offset any impact on savings. Other costs associated with frequency converters should be considered.

For example, conditioning of the power supply may be required to ameliorate high frequency harmonics. The type of process control is important. There are differences between a flow rate-regulated system and a flow quantity-regulated system. Most pumps are flow rate-regulated with a control valve or frequency converter. Some pumps are quantity-regulated by means of timers or level. Examples of these systems are municipal potable water systems that supply stand tanks and waste treatment lift pumps. In a quantity regulated system energy consumption is primarily affected by pump and motor efficiency; piping system changes to existing installations are usually impractical.