30
between the master and the slave remains less than the Lead/
Lag Balance Delta, the chiller designated as the lead will
remain the lead chiller. The Lead/Lag changeover between the
master and the slave chiller due to hour balance will occur dur-
ing chiller operating odd days, such as day 1, day 3, and day 5
of the month, at 12:00 a.m. If a lead chiller is not designated,
the master chiller will always be designated the lead chiller.
The dual chiller control algorithm has the ability to delay
the start of the lag chiller in two ways. The Lead Pulldown
Time parameter (
Lead Pulldown Type
, LPUL
) is a one-time
time delay initiated after starting the lead chiller, before
checking whether to start an additional chiller. This time delay
gives the lead chiller a chance to remove the heat that the
chilled water loop picked up while being inactive during an un-
occupied period. The second time delay, Lead/Lag Delay (
Lag
Start Timer
, LLDY
) is a time delay imposed between the last
stage of the lead chiller and the start of the lag chiller. This pre-
vents enabling the lag chiller until the lead/lag delay timer has
expired.
A quicker start of the lag chiller can be accomplished by
configuring the Start if Error Higher parameter (
Start if Error
Higher
, LL.ER
). If the difference between the common leav-
ing water temperature and the set point is greater than the con-
figured value, then the lag chiller will start.
A minimum on time for the lag chiller can be programmed
with the Lag Minimum Running Time configuration (
Lag
Minimum Running Time
, LAG.M
). This parameter causes
the control to run the lag chiller for the programmed minimum
on time. The Lag Unit Pump Select (
Lag Unit Pump Control
,
LAGP
) can be configured such that the pump can be on or off
while the chiller is off. This parameter is only active in Parallel
Chiller Operation.
For units with a Touch Pilot display, two additional steps
must be completed to start the machine. On the master chiller,
the Master Control Type must be configured for the start con-
trol defined in the Machine Control configuration. To start the
machines, the master chiller must be started with the Start/Stop
button and Master Mode selected. The slave chiller must be
started with the CCN Mode selected.
Each application, Parallel and Series, are described sepa-
rately below.
DUAL CHILLER CONTROL FOR PARALLEL APPLI-
CATIONS — To configure the master chiller for parallel
applications using the Touch Pilot display, see Table 24. To
configure the master chiller for parallel applications using the
Navigator display, see Table 25. A power cycle is required for
the values to take effect.
To configure the slave chiller for parallel applications using
the Touch Pilot display, see Table 26. To configure the slave
chiller for parallel applications using the Navigator display, see
Table 27.
