Retrotec USACE - Manual (Page 234)

D104 ENERGY & PROCESS ASSESSMENT PROTOCOL
air-handling units, and processes such as machining operations and stamping
presses. Electric motors are commonly constant-speed devices and will apply
the amount of torque needed to turn the shaft of the equipment to which they
are attached (Figure D162). As the motor becomes lightly loaded, its effi ciency
drops; while it will use less energy, the amount of energy required to overcome
internal losses becomes a higher percentage.
Another issue is how the loads are varied. The loads on a fl uid fl ow system
may be varied by valves or dampers that restrict the outgoing fl ow. These
devices provide little energy savings to the motor operation of the pump or
fan—even though the fl ow goes down, the pressure increases. An eddy cur-
rent coupling could also be used to connect the motor to a variable-speed
outlet shaft. As the unit operates, slippage in the coupling is used to vary
the output speed. This slippage creates a waste of energy, but not as great
as with fl ow-restricting devices. The optimum choice for a varying load is a
variable frequency drive (VFD) in which the alternating current frequency
is adjusted to provide a variable-speed motor. The input power on a VFD
operating motor system at 60% of the maximum fl ow will be approximately
half that of an eddy current coupling and a third of that when using valve or
dampers to restrict the fl ow.
D.6.1.7 Idling Equipment (Waste)
Figure D163. Timer used to turn off process equipment.
Turning off process equipment when not in use can provide signifi cant savings
for some applications. A signifi cant fraction of industrial process equipment
is designed to be turned off by the operator when not in use. Simple timer
switches (Figure D163) can reduce energy costs associated with operators’ for-
getting to turn off their equipment at the end of their shift.
By using a scheduling format to turn off the equipment during nonoper-
ating time intervals, electric energy usage will decrease. The cooling load on
the air conditioning equipment will also be reduced, and the longevity of the
equipment may be increased.