Controls |
Unit
Control Panel Sequence of Operation |
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. |
