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O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
Figure 53. Duplex™ chiller sequence of operation:
ready to serve
Evap LWT Falls
Below
Differential to
Stop
Running
(Single Circuit)
Chiller Capacity
Greater than
Staging Off
Boundary
Setpoint
Running
(Both Circuits)
Simultaneous Compressor Start/Stop
Both compressors will start in close succession to
minimize the time it takes for the chiller to reach full
load. Some process applications need the chiller to
start and generate capacity as fast as possible. This
method will start both compressors, slightly staggered
to prevent doubling of the current inrush, but will
generally control the chiller as if there were only one
compressor. If the chiller is in the Auto mode and all
interlocks have been satisfied, Compressor 1 will be
started based on the leaving water temperature rising
above the "Differential to Start" setting. When
Compressor 1 is at speed, Compressor 2 will start. Both
compressors will run until water temperature falls
below the differential to stop, at that time both
compressors will be shut down.
70
Auto
Evap LWT Rises
Above
Differential to
Stop
On Start, if Initial
Capacity Command
Greater than Staging
On Boundary, then
Start First
Compressor, and
Immediately Start
Second Compressor
Chiller Capacity
Greater than
Staging On
Boundary
Setpoint
Figure 54. Duplex™ chiller sequence of operation:
combined start
Evap LWT Falls
Below
Differential to
Stop
Running
(Circuit 1)
Running
(Circuit
1 and 2)
Compressor Load Balancing
Duplex™ CenTraVac™ chillers with Tracer®
AdaptiView™ UC800 control will balance the
compressor load by giving each compressor the same
load command. The load command will be converted
to inlet guide vane (IGV) position that will be the same
on each compressor. Balancing compressor load
results in the best overall efficiency and with both
circuits operating with nearly the same refrigerant
pressures. When both compressors are running, the
overall chiller load command will be split evenly
between the two compressors unless limit control
overrides balancing. When transitioning between one-
compressor operation and two-compressor operation,
the load commands will be actively balanced at a rate
slow enough to minimize capacity control
disturbances.
R R e e s s t t a a r r t t I I n n h h i i b b i i t t . . The purpose of restart inhibit feature is
to provide short cycling protection for the motor and
starter. The operation of the restart inhibit function is
dependent upon two setpoints.
R R e e s s t t a a r r t t I I n n h h i i b b i i t t F F r r e e e e S S t t a a r r t t s s . . The Restart Inhibit Free
Starts (default = 3, range from 1 to 5) is adjustable via
the service tool and will allow a number of rapid
restarts equal to its value. If the number of free starts is
set to "1", this will allow only one start within the time
period set by the Start to Start Time Setting. The next
start will be allowed only after the start to start timer
has expired. If the number of free starts is programmed
to "3", the control will allow three starts in rapid
succession but thereafter, it would hold off on a
compressor start until the Start to Start timer expired.
R R e e s s t t a a r r t t I I n n h h i i b b i i t t S S t t a a r r t t t t o o S S t t a a r r t t T T i i m m e e S S e e t t t t i i n n g g . . The
Restart Inhibit Start to Start Timer (default = 20
minutes, range from 10 to 30 minutes) is adjustable via
the service tool and defines the shortest chiller cycle
period possible after the free starts have been used. If
Auto
Evap LWT Rises
Above
Differential to
Start
Confirm
Compressor A
Start, then
Immediately Start
Compressor B
CDHF-SVX01N-EN
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