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Many of us hear the term VFD and automatically think of “constant pressure device”. But the reality is constant pressure is just one benefit available through use of a VFD (Variable Frequency Drive) in a water supply system.

 

By using a pressure sensor, a VFD can sense pressure and change speed by adjusting the frequency of the power supply, varying the speed at which the motor turns. In addition to pressure sensors, a VFD can also work with level sensors, flow sensors or simply control other pumps with input and output relays.

 

A chicken farm, for instance, cannot get enough flow from one well to provide the needs of a chicken growers operation. Two additional wells were added as the operation added growing houses. When the birds are small and the weather cool, water demand is low. The primary well operates to provide constant pressure with modest flow. As the maximum of the well is exceeded, relays within the drive are turned on to activate the smaller wells to assist with the flow and the primary well adjusts speed to the new demand. During this time constant pressure is delivered to the growing houses.

 

We often overlook the fact that when the VFD is reacting to demand, it is only producing the pressure at the necessary flow. A typical pump without a VFD runs at full speed whenever energized. If it produces more than required, either some flow is vented to waste, or pressure regulating valves restrict to hold a higher pressure before the point of use.

 

This is wasted energy. By slowing a motor from 3600 rpm to 3000 rpm can reduce energy usage by 40%. That is 40% of the electric bill as well. Even slowing to just 3300 rpm can save 8% of the electric bill.

 

Some municipal wells use the VFD ramp up and ramp down features in place of “Soft Start Controls” that power companies often require on large motors to prevent dimming lights on the power grid when the motor starts. The VFD can then adjust the speed of the pump to operate at the most efficient point on the pump curve as opposed to full speed and fill the towers at a little slower rate. A change of 2% in efficiency running a 100hp motor 15 to 18 hours a day is a very significant savings in energy costs over the period of one year.

 

A food production plant was operating 7 to 10 pumps within the plant. Each system had different flow needs but all needed a constant pressure. Flows within the plant also varied with the time of day.

 

All of this was replaced with a skid of 3 pumps networked together by VFD’s to operate on- or up to 3 at a time. This not only provided the flow, but sensed the best efficiency points so that any number of pumps can run together at the most efficient point.

 

In addition, the drives kept track of the run times of each unit and always started with the pump of least run time. In this case, maintenance and energy efficiency combined to drastically reduce the cost of operation over the lifetime of the pumps.

 

These are only a few examples of how a VFD can optimize a pump system. Along with this are several pump protection features that normally are expensive add-ons included in the VFD software. Loss of prime, low water level, overload protection, and detection from external sensors are included in the features typically available.

 

Energy savings, maintenance costs, motor protection are just a few of the benefits that can be achieved along with operating the pump to the optimum of the conditions.

 

The Yaskawa iQpump1000 is a quality variable frequency drive. iQpump1000 features an integrated pump-specific software and setup parameters that allow the operator to set up specific control values for a wide range of applications. It automatically adjusts pump operating conditions as the process variables change while still maintaining optimum pump performance and protection.

 

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