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Adaptive
Frequency Drives
Figure O-4 — CVHE500 Part Load Efficiencies with/without AFD
Benefits
Trane Adaptive Frequency drives*
provide motor control, but they are
much more than just starters. They also
control the operating speed of the chiller
compressor motor by regulating output
voltage in proportion to output
frequency. Varying the speed of the
compressor motor can translate into
significant energy cost savings.
Reliable, Optimized Compressor
Efficiency for Energy Savings
Conventional chillers use inlet vanes to
provide stable operation at part-load
conditions. Capacity is reduced by
closing the vanes while maintaining a
constant motor speed. The drive can be
used to significantly reduce power
consumption by reducing motor speed
at low load conditions. Trane patented
AFD Adaptive Control
™
logic safely
allows inlet guide vane and speed
control combinations that optimize part-
load performance.
To Avoid Mechanical Stress
Controlled “soft” start with linear
acceleration results in limited starting
current to eliminate motor stress, reduce
power line disturbance and provide a
lower power demand on start. Reduced
motor speed as a result of reduced
chiller load means less current drawn,
less heat generated, increased motor
winding life. This translates into longer
time between compressor maintenance
and less downtime throughout the life of
the machine.
Application
Certain system characteristics favor
installation of an AFD because of energy
cost savings and shorter payback.
Among them are:
A large number of part-load operating
hours annually
Figure O-4, based on a CVHE500, 500-ton
load at standard ARI conditions, shows
that major kW savings occur at part-load
conditions, typically below 90 percent
load.