IOM 1206-1
37
Unit Controller Operation
Current software has a delay of 150 seconds after bootup is
complete before the first circuit can start. The software will be
changed to use the 110 second delay discussed above only
when the chiller is performing the RapidRestore operation.
Fast Loading
Fast loading will be performed when the following conditions
are met after the unit power up:
• Chiller enters RapidRestore operation
• Current LWT > Start Up Temperature
For reference, Start Up Temperature is Stage Up Temperature
+ Start Up Delta T. Stage Up Temperature is calculated based
on the Full Capacity Evaporator Delta T set point and the
number of compressors on the chiller.
Fast loading should end if any of the following conditions
occur:
• LWT < Stage Up Temperature
• Unit capacity = 100%
• All circuits become disabled for any reason
• Unit becomes disabled for any reason
• 10 minutes have passed since unit powered up
When fast loading ends, the RapidRestore operation is
considered complete.
Capacity Changes
Normally the delay between compressors staging on is
determined by the Stage Up Delay setting. That setting
defaults to 240 seconds and has a range of 120 to 480 seconds.
During fast loading, a delay of 60 seconds between
compressor starts within a circuit should be used. In addition, a
delay of 30 seconds between compressor starts on different
circuits should be used.
This change during RapidRestore operation will allow for a
faster time to full capacity while maintaining stable operation
within each circuit. Assuming both circuits are able to run, the
effective unit stage up delay will be 30 to 35 seconds, so it will
load about four times faster during RapidRestore than the
fastest it possibly can during normal operation.
Max Pulldown Rate
Max pulldown rate will be ignored during fast loading to avoid
having it interfere in the chiller getting loaded up as fast as
possible.
Backup Chiller Operation
If DI2 on the RapidRestore module has a signal and the unit
has RapidRestore enabled, then the chiller is considered a
‘backup chiller’. When a ‘backup chiller’ is enabled, it will
use an evaporator recirculation time of 13 seconds regardless
of what the evaporator recirculation time set point is. Then,
fast loading will be used as outlined above in the fast loading
section.
This backup chiller sequence is safe for the unit if it has had
power applied for the minimum time stated in the operation
manual. Since this sequence does not have to wait on the
compressor motor protection module delay, the unit can
achieve full capacity even faster than during a power loss
scenario.
Compressor Starts Per Hour
Since the compressor cycle timers are not maintained through
power cycling, a limitation on the number of starts per hour
will be added. Each compressor will be allowed six starts in an
hour.
If a compressor start is being delayed due to this limitation, it
can be cleared by using the existing Clear Cycle Timers
setting.
The following charts show the approximate best case scenario
for start time and loading time with the RapidRestore
operation.
