Rockwell Automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE - Manual (Page 142)

5-18 SMC Dialog Plus Controller Special Application Considerations
Energy Saver (cont.)
Figure 5.14 Sample Calculation
If this calculation looks favorable, then additional detailed
calculations must be made to get a more exact figure on the dollars
saved. Precise duty cycle and loading cycles must be more accurately
estimated. Points can then be selected from the theoretical maximum
savings curve. Savings for each increment of loading must then be
calculated.
Note that a motor running unloaded and not connected to equipment
is not the same as when the motor is connected to the equipment.
Motor manufacturers should be contacted to determine the actual no
load characteristics.
These calculations have been done on the basis that a solid-stat
controller was required for reasons other than energy savings. I
energy savings is the main reason for purchasing this type of device,
the savings would decrease, because there is approximately a 1 to
1-1/2 volt drop across each solid-state power pole. There ar
additional losses associated with solid-state devices.
For example, a solid-state controller for a three-phase motor drawing
50 amperes will have a loss ranging from 150 to 225 watts above an
equivalent electromechanical device. Therefore, if the energy saver
were replacing an electromechanical device, these losses are deducted
from the total energy savings.
Motor efficiency: 90%
Motor loading duty cycle: 50% (On 15 min., Off 15 min.).
Motor horsepower and run time: 50 HP, 8 hours per day, 2,080 hours per year
Use the above data and the following procedure for theoretical maximum energy savings
1. kW = 0.746(50)
kW = 37.3
2. kW
total
= (37.3) ³ 0.90
kW
total
= 41.4 kW
3. Losses = 41.4 - 37.3
Losses = 4.1 kW
4. Maximum theoretical savings - (4.1 kW) ¥ (0.50)
Maximum theoretical savings = 2.05 kW
5. (2.05) ¥ (0.5) ¥ (2,080) = 2,132 kWh per year
Finally at a typical cost of $0.08 per kWh, the estimated savings is:
6. (0.08) ¥ (2,132), for $170.56 per yea
Note: Calculations assume that the normal load is equal to the full load rating of the
motor, and that the loading level is a no-load condition