UFC 3-520-01
June 10, 2002
B-11
Figure B-5. Typical Motor Load Profile With Motor Operating at Half of Rated Load
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B-7.3
Table B-1 provides a sample economic evaluation for an ASD installation for
a continuously operating HVAC system motor. This evaluation was for a hospital
application in which higher initial ASD costs were expected in order to address
harmonic distortion concerns as part of the design. Even so, a payback period of less
than 2 years was estimated. As can be seen in Table B-1, an ASD economic evaluation
is most sensitive to the following assumptions:
·
Total motor operating time per year--unless it is fully loaded, a continuously
energized motor will show a faster payback than an intermittently energized motor.
·
Estimated actual motor load/speed--for a typical centrifugal fan motor, energy
usage is proportional to the (speed)
3
. For example, if the motor speed can be
reduced to 90 percent of rated speed, the energy usage can be reduced to almost
70 percent of its nominal value.
·
Cost per kilowatt hour--the local average energy cost should be used.
·
ASD equipment and installation cost--for critical locations, the added cost of
ensuring acceptable power quality can double the total initial cost.
Summary :
Typical Motor Load Profile With Motor Operating at Half of Rated Load 21 22 23 24 25 14-Jun 15-Jun 16-Jun 17-Jun 18-Jun 19-Jun 20-Jun 21-Jun Date 3 - P h a s e P o w e r ( k w ) B-7.3 Table B-1 provides a sample economic evaluation for an ASD installation for a continuously operating HVAC system motor.
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