ACS HE Series, Operation And Instruction Manual

Page: 51 / 83

HE Series Central Chillers Chapter 6: 51 of 83
• SUCT - The saturated suction temperature loop is used.
• DISC - The discharge pressure loops is used.
• SUCT/DISC - The saturated suction temperature and discharge pressure loops are used.
Note: When local staging control is enabled (
communication loss ) a chiller out
temperature based hot gas PID loop is activated in addition to the configured loops. The
loop with the highest output percent is used.
Discharge Pressure Control
Pre-Start and Hold
When the discharge pressure pre-start setpoint is greater than 0, the discharge pre-start bit
is set.
When the bit is active and the staging logic determines another circuit is required, the
following occurs:
• The discharge pre-start timer starts.
• The compressor activation is delayed (
until the pre-start timer expires ).
• The discharge analog output ( fan speed/WRV ) is enabled.
When the discharge pressure pre-start setpoint is 0, the discharge PID loop is enabled
when the Compressor activates. The PID loop controls the discharge analog output.
When the discharge pressure hold time is greater than 0, the discharge analog output is
set to the discharge pressure start percent and the discharge hold timer starts. When the
timer expires, the discharge PID loop is enabled and it then controls the discharge analog
output.
If the discharge pressure hold time is 0, the discharge PID loop controls the discharge
analog output as soon as the discharge analog output is enabled.
Three sets of PID parameters as well as pre-start time, hold time and start percent
variables are present. The ambient temperature determines which set of parameters is
used.
The discharge setpoint in °C’s maximum is 48.9°C (120°F) and its minimum is 21.1°C (70°F)
when one compressor is active and 32.2°C (90°F) when both compressors are active.
PID Loop
When the PID Loop activates, its output will match the discharge pressure start percent. It will
control from their based on the discharge pressure and the discharge pressure SP. The minimum
and maximum for the output are set by the discharge pressure minimum and discharge pressure
maximum setpoints.