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CTV-PRC007-EN38
A demand for chilled water is
determined by a temperature differential
between the evaporator fluid setpoint
and the supply fluid temperature.
Start is inhibited and the condition
enunciated if high condenser pressure or
low oil temperature or high motor
winding temperature is detected. Restart
(defined as successive, unsuccessful
attempts to start — also called short-
cycling) Inhibit and the time remaining
before restart can be attempted will be
enunciated if this condition exists.
The next step issues a command to start
the condenser water pump, to confirm
that the guide vanes are closed and to
start the oil pump motor. When flow is
proven, after confirmation that the guide
vanes are closed, and after establishing
oil pressure, a 15 second start signal is
sent to the motor starter. A successful
start and acceleration of the motor is
followed by the “UNIT IS RUNNING”
message.
Any failure to complete a successful start
causes the sequence to abort and the
CenTraVac
™
to coast to a stop. A
diagnostic describing the reason for
failure, time and date of failure, a help
message and reset action required will
tell the operator that the micro- controller
has detected a problem during the
attempted start. As soon as the fail
condition is corrected and reset (either
manual or automatic) is accomplished,
the chiller can go through the start-up
sequence again.
Normal operation messages will include
information about limit modes when the
micro-controller identifies potential fail
conditions. This allows the CenTraVac to
continue safe operation even though
some other part of the system is not
operating properly.
“UNIT IS RUNNING CAPACITY LIMITED
BY HIGH CURRENT;”
This condition means that a motor
current limitation prevents further
opening of the compressor inlet guide
vanes in response to the temperature
controller.
“UNIT IS RUNNING CAPACITY LIMITED
BY HIGH COND PRES;”
The condenser high pressure limit has
been approached that further loading of
the compressor may result in a trip out.
(optional)
“UNIT IS RUNNING CAPACITY LIMITED
BY LOW EVAP TEMP;”
The evaporator low temperature limit
has been approached that further
loading of the compressor may result in
a trip out.
This Adaptive Control
™
prevents a
nuisance trip, alerts the operator to the
condition, and takes the following
corrective action:
1
the control will limit the rate of inlet vane
opening. If the condition worsens,
then…
2
the control will hold the inlet vane
position. If the condition worsens,
then…
3
the control will close the inlet vanes at a
controlled rate until the condition
stabilizes. If, however, the condition
worsens, the final step will be to close
the vanes even further.
Therefore, even though operating in a
controlled limit mode, the chiller may be
opening or closing the guide vanes to
keep the chiller on line as long as
possible.
When UCP2 detects that the chiller is
entering surge the message “UNIT IS
RUNNING SURGE DETECTED” is
enunciated. (Optional surge protection
energizes the head relief request relay. If
corrective action is not taken and surge
continues for 15 minutes, a latching
shutdown will occur with a diagnostic
message.)
Under normal conditions and when the
control source maintains an Auto signal,
a stop signal originates from the chiller
module which senses no further cooling
demand. At this time a “UNIT IS
PREPARING TO SHUT DOWN” message
appears as the guide vanes close. Then
the compressor motor starter and
condenser pump starter are de-
energized while the oil pump continues
to run for approximately
two minutes. The CenTraVac can be
manually stopped at any time by
pushing the Stop key once for a
“friendly” stop (coastdown) and
twice within five seconds for an
emergency stop.
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