Rockwell-automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE Manual de usuario descargar pdf (Pagina 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)

0.90

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

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