Show Me the Money

Going Green and Treatment Optimization can save you money. Ironically, these two topics are subjects for continuing education classes that DCA offers this year. A lot of times instructors offer operators alternatives and solutions that are viable but operators often see as only textbook theory. I’ll give you an example of how a simple change can make a big difference. Let’s say that you have a pump with a 100-horsepower motor and runs 12 hours out of the day.

Cost to run pump yearly at $0.11 per kW*hr

Kilowatts used by the pump       .746 *100 = 74.6 kW

Kilowatt*hrs for pump                  74.6 kW * 12 hrs = 895.2 kW* hrs

Yearly Kilowatt*hrs for pump    895.2 kW*hrs * 365 days = 326,748.00 kW*hrs

Yearly cost to use the pump      326,748.00 kW*hrs * $.11 = $35,942.28

You would like to see how purchasing a variable frequency drive will affect your power consumption and the electric bill.

Motor speed (rpm) Motor torque (ft-lb) Motor power (hp) Input power (kW) Input current (A)
0 0 0 0 0
0 100 0 0 0
900 0 0 0 0
900 295 50 39.3 55
1800 0 0 0 0
1800 295 100 78.8 111
*Motor is rated for 100 hp with a rated torque of 295 ft-lb.
This chart and the following information is from How VFDs Save Energy “Analysis and examples of power conversion by variable-frequency drives” by Edward Tom, Yaskawa America, Inc.

A VFD is merely a power conversion device that converts the fixed voltage and frequency of incoming power to a variable voltage and frequency output to provide the variable speed capabilities––input current lower than the output current.

If the motor is operating at half the speed and producing full torque, the motor is outputting half of its rated power. Consequently, if the motor is running at full speed and producing half torque, the motor is also outputting half of its rated power.

Let’s say that a 100-hp VFD motor runs 6 hours at half speed and 6 hours at full speed daily.

Cost to run pump yearly at $0.11 per kW*hr

Kilowatts used by the pump at full speed            .746 *100 = 78.8 kW

Kilowatts used by the pump at half speed           .746 *50 = 39.3kW

Kilowatt*hrs for pump at full speed                       78.8 kW * 6 hrs = 472.8 kW* hrs

Kilowatt*hrs for pump at half speed                      39.3 kW *6 hrs = 235.8 kW* hrs

Yearly Kilowatt*hrs for pump                  708.6 kW*hrs * 365 days =   258,639 kW*hrs

Yearly cost to use the pump                                  258,639 kW*hrs * $.11 = $28,450.29

The yearly savings on this pump alone will be $35,942.28–$28,450.29 = $7,491.99

Now imagine doing this for each pump that you use in your system. The savings would be substantial. So now that I have shown you the money, you can do more reading about VFDs and or attend the Treatment Optimization class at Blue Licks State Resort Park April 17-18 for a more in-depth look.

http://www.plantservices.com/articles/2010/06vfdssaveenergy/?show=all

VFD Estimated Savings Calculator http://www.cerusind.com/VFDEstSavingsCalc.asp

DCA does not endorse Franklin Control Systems, but are merely showing that estimated savings using VFDs can be found online and can be very useful tools. They can also be product-specific instead of hypothetical as the above example.

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