ACS HE Series, Operation And Instruction Manual

Page: 49 / 83

HE Series Central Chillers Chapter 6: 49 of 83
If the circuit is active when communication is lost, it will immediately switch to local
staging. If the circuit is inactive when communication is lost, the switch to local staging
is delayed by the communications loss control delay. While local staging is active the hot
gas valve is controlled by temperature as well as the configured PID loops.
The first stage activates when the circuit’s chiller out temperature is greater than the
circuit’s SP + 2.0°F. It stages off when the second stage has been off for the stage off
delay and the hot gas percent is at 100% OR the chiller out temperature is less than or
equal to the circuit’s SP - 2.0°F.
The second stage activates when the first stage has been active for the stage on delay
and the hot gas temp loop’s output is at 0.0%. It stages off when the hot gas is at 100% or
the chiller out temperature is less than or equal to the circuit’s SP - 2.0°F.
Each refrigeration module has a cooling enable/disable. If the module is disabled, a
display message pops up that states “When disabling a module on a chiller with multiple
modules, the fluid flow to that module must be shut off”. The flow switch status will
determine if this was done and a reminder will display every five minutes. The module
enable/disable will determine if that module will be allowed to start in the sequence.
If any module is in an alarm condition, that module will be taken out of the sequence.
Once the alarm is cleared, it will be brought back in the sequence based on its run time
hours. In other words, a module that is in an alarm condition will not prevent the other
modules from staging on. All alarms including the flow alarm will be disabled when the
module is disabled.
Compressor Anticycle
When a compressor turns on, the compressor anticycle delay is activated. It remains
active until the timer expires or the chiller is taken offline.
If the compressor anticycle delay is active when a compressor turns off, the
compressor inhibit bit is set. While set, the compressor ready bit is forced off, this
prevents the compressor from staging on. The bit remains set until the compressor
anticycle delay expires.
Compressors Staging
Circuits are staged based on the runtime hours of their compressor(s).
Compressors on a circuit are staged based on the Lead Lag setting. A PID loop based on
the tank temperature determines how many stages are requested. The loop’s output range
will be equally divided by the number of enabled compressors. Three sets of
parameters/defaults for the PID loop are present. The ambient / condenser in temperature
determines which set is used.
Staging On