Motor Savings Example

According to an article from Plant Services, "Motor-driven equipment accounts for 64% of the electricity consumed in the U.S. manufacturing sector". This is a tremendous amount of energy consumed by electric motors

Even in the commercial world, motors consume a large amount of energy in refrigeration and air handling machinery. The calculation below demonstrates how much can be saved by changing the operation parameters on a single 5HP motor. The motor could be an air handling motor or a small refrigeration unit.

Assumptions:

  • The energy cost is assumed to be $0.09 per kWh. This is average to low for energy cost today including demand charges.
  • Demand reduction was not taken into account because it is assumed that the motor will be required at peak times.
  • The motor is 93% efficient in all cases and is run at 100% loading. Therefore, the kW load for the motor calculates to about 4kW.

For the first example, the motor runs from the time Joe comes in in the morning at 6:00AM until Jack the security guard turns it off at midnight. Jack does not turn it off on Friday evening because it is needed for cooling for part of the weekend. Therefore, the motor runs from 6:00AM Friday morning until midnight Tuesday morning for a total of 90 hours plus 18 hours Tuesday through Thursday. This is a total of 144 hours per week. The energy costs would calculate as:

  • 4kW (motor load) x 144 hours per week x 52 weeks = 29,952kWh

At our assumed price of $0.09 per kWh, this calculates out to $2,695.68 in operating costs for the year.

Next, let us assume that the operating parameters are changed for the motor to only run 14 hours per day for 5 days per week. Joe still turns on the motor at 6AM but Jack now turns off the motor at 8PM just before his lunch break. Furthermore, a timer switch is installed for use on weekends that only runs the motor for 8 hours on Saturday and Sunday. This is a total of 86 hours. The energy costs would calculate as:

  • 4kW (motor load) x 86 hours per week x 52 weeks = 17,888kWh

At our assumed price of $0.09 per kWh, this calculates out to $1609.92 in operating costs for the year.

The total savings are $1,085.76 just from this change in procedures. This does not include reduced maintenance on the motor, belts, or machinery from running fewer hours. Furthermore, few motors run at 100% loading which reduces their efficiency considerably.

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