A: As with a water distribution plant, water treatment plants have periods of high and low demand. During periods of low demand, VFDs can be used to slow down blowers to generate savings. Please refer to figure given below for additional details on a typical water treatment plant operation. As is evident below, water treatment plants have varying demands placed upon them throughout the day. In addition to this hourly variation of influent water in relation to the daily maximum flow rate for a given day, there is also variation of maximum flow rate experienced by water treatment plants.

A: While further opportunities are limited for agricultural or golf course type of customers, water districts have other potential areas where operational efficiencies can be improved. One of the biggest areas of improvement is in water treatment plants. Traditional water treatments plants use energy intensive mechanical aeration plants in aerobic digesters for water treatment. Newer plants make use of VFD controlled blowers used in conjunction with dissolved oxygen sensors. On a per million gallons per day (MGD) basis, blowers use much less power and hence energy when compared to mechanical aerators.

A: Installing VFD on pumps feeding water distribution lines allows tighter control of line pressure. Usually, amount of water pumped into a water distribution line is controlled based on line pressure. Using a feedback system with pressure sensors, VFD set points can be controlled to maintain required line pressure.

A: Sometimes, pumps are designed to operate in a wide range of flow rates. Therefore, the pump should be able to ramp up and down depending upon flow requirements.  Motors powering these pumping plants are usually single speed, which means that pumps are also restricted to a single speed  and cannot ramp up or down depending upon flow requirements. In such situations, the pump discharge is throttled to reduce pump discharge rate. Throttling is a very inefficient means of controlling flow rate.

Motors can be retrofitted with Variable Frequency Drives (VFD) to vary motor speed. By changing motor speed, pump speed can be varied. Pump discharge rate is directly proportional to the operational speed.

A: Having individual pumps in a system operating at good efficiency is only the first step in reducing overall plant consumption. Reducing total consumption can also be done by properly sequencing and staging pumps in your system. Usually a control strategy can help you realize more savings.

A: Pump test is the best way to gauge pump performance. Pump output is usually a function of it’s efficiency. By diligent record keeping of flow and pressure developed by pumps, pump performance can be gauged on a real time basis. This is not a substitute for a pump test, however, it is usually an indication of pump performance at a very high level. It is always a good idea to keep track of flow rate and pressure developed by pumps using properly calibrated meters. SCADA systems can automatically track this and many other variables encountered in a pumping system.

A: It is recommended that pump efficiency be checked with a pump test every two years

Q: Why do pumps lose efficiency?

A: Pump operational efficiency can decrease overtime due to pump wear or the pump operating out of its design parameters. In some situations, decrease in efficiency is due to both reasons. Therefore, it is always a good idea to periodically check pump efficiency.

Q: What is the cost of pump overhaul?

A: Cost of pump overhaul can vary depending on your unique situation. It can be as little as $100/hp and as much as $1,000/hp. Local utilities work with

Q: Who should be proactive about pump efficiency?

A: If you have a big pump (> 15hp) and the unit runs for more than 1,000 hours/year, then being proactive about pump operational efficiency will reduce operational costs significantly.