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If the lag chiller's water pump was not started when the ma-
chines went into occupied mode, then the lag chiller water
pump will be started. The lag chiller will start when the master
chiller forcing the lag chiller demand limit value (LAG_LIM)
to the master's demand limit value. If lead/lag capacity balance
is selected, once the lag chiller has started, the master chiller
will try to keep the difference in capacity between lead and lag
to less than 20%. The master chiller will then be responsible for
water loop capacity calculation, and will determine which
chiller, the lead or lag, will increase or decrease capacity. When
the load reduces, the lag chiller will unload first. To accomplish
this, the lead chiller set point is decreased by 4° F (–2.2° C)
until the lag chiller unloads.
To configure the two chillers for dual chiller operation,
the master chiller must have the Control Method variable (Op-
erating Mode
SLCT
OPER) set to meet the job require-
ments. The slave chiller must be set to Control Method variable
(Operating Mode
SLCT
the remote-off-enable switch must be in the enable position.
The master chiller and the slave chiller CCN addresses (Con-
figuration
OPTN
CCNA) must be configured. The master
and slave chillers can be addressed from 1 to 239. Each device
connected to the network must have its own unique address.
Both chillers must have the same CCN Bus Number (Configu-
ration
OPTN
CCNB). Lead/Lag Chiller Enable must be
set for both chillers by configuring Master/Slave Select (Con-
figuration
RSET
MSSL) to 1 (Master) for the master
chiller. The slave chiller Master/Slave Select must be set to 2
(Slave). The master chiller can be configured to use Lead/Lag
Balance (Configuration
RSET
and lag chillers after a configured number of hours of opera-
tion. The Lag Start Delay (Configuration
can be configured. This prevents the Lag chiller from starting
until the lead chiller is fully loaded and the delay has elapsed.
Operating Modes
MODE 1 (Operating Mode
Delay in Effect
Criteria for Mode — Tested when the unit is started. This
mode is active when the Minutes Off Time (Configuration
OPTN
DELY) timer is active.
Action Taken — The unit will not start until the timer has
expired.
Termination — The mode will terminate when the timer
expires.
Possible Causes — This mode is in effect only due to the Min-
utes Off Time timer.
MODE 2 (Operating Mode
Setpoint in Use
Criteria for Mode — Tested when the unit is ON. This mode
is active when Cooling Setpoint 2 (Setpoints
CSP.2) or Ice Setpoint (Setpoints
use. While in this mode, the Active Setpoint (Run Status
VIEW
SETP) will show the CSP.2 or CSP.3 value.
Action Taken — The unit will operate to the Cooling Setpoint
2 (CSP.2) or Ice Setpoint (CSP.3).
Termination — This mode will terminate when the Cooling
Setpoint 2 (CSP.2) or Ice Setpoint (CSP.3) is no longer in use.
Possible Causes — This mode is in effect only due to pro-
gramming options.
MODE 3 (Operating Mode
Effect
Criteria for Mode — Tested when the unit is ON. This mode
is active when Temperature Reset (Configuration
CRST) is enabled either by CRST=1 (Outside Air Tempera-
ture), CRST=2 (Return Water), CRST=3 (4-20 mA Input), or
CRST=4 (Space Temperature) and is active.
OPER) = 2 (CCN Control) and
LLBL) to rotate the lead
RSET
LLBD)
MODE
MD01) — Startup
MODE
MD02) — Second
COOL
COOL
CSP.3) is in
MODE
MD03) — Reset
RSET
Action Taken — The Active Setpoint (Run Status
SETP) will be modified according to the programmed
information and will be displayed as the Control Point (Run
Status
VIEW
Termination — This mode will terminate when the Tempera-
ture Reset is not modifying the active leaving water set point,
so SETP is the same as CTPT.
Possible Causes — This mode is in effect only due to pro-
gramming options.
MODE 4 (Operating Mode
Limit Active
Criteria for Mode — Tested when the unit is ON. This mode
is active when Demand Limit (Configuration
DMDC) is enabled either by DMDC=1 (Switch), DMDC=2
(4-20 mA Input) or the Night Time Low Sound Capacity Limit
(Configuration
Action Taken — The Active Demand Limit Value (Run
Status
VIEW
according to the programmed information and the unit's capac-
ity will be reduced to the amount shown or lower.
Termination — This mode will terminate when the Demand
Limit command has been removed.
Possible Causes — This mode is in effect when capacity is be-
ing limited by the demand limit function.
MODE 5 (Operating Mode
Loading Active
Criteria for Mode — Tested when the unit is ON. This mode
is active when Ramp Loading (Configuration
RL.S) is enabled and the following conditions are met:
1. The leaving water temperature is more than 4° F (2.2° C)
from the Control Point (Run Status
and
2. The rate of change of the leaving water temperature is
greater
than
Points
COOL
Action Taken — The control will limit the capacity step
increase until one of the two conditions in Mode 5 is no longer
true.
Termination — This mode will terminate once both conditions
in Mode 5 are no longer true.
Possible Causes — This mode is in effect only when capacity
is being limited by the ramp loading function.
MODE 6 (Operating Mode
Heater Active
Criteria for Mode — Tested when unit is ON or OFF. This
mode is active when the cooler heater is energized, if the
Outdoor Air Temperature (Temperature
less than the calculated value (Freeze Setpoint + Cooler Heater
Delta T Setpoint [Configuration
– 2° F [1.1° C]), and either the Leaving Water Temperature
(Temperature
ature (Temperature
the Freeze Setpoint + Cooler Heater Delta T Setpoint (HTR).
The Freeze Setpoint is 34 F (1.1 C) for fresh water systems
(Configuration
the Brine Freeze Setpoint (Configuration
for Medium Temperature Brine systems (Configuration
SERV
FLUD=2).
in
Action Taken — The cooler heater will be energized.
Termination — The cooler heater will be deenergized when
both the Entering Water Temperature (EWT) and Leaving
Water Temperature (LWT) are above the Freeze Setpoint +
Cooler Heater Delta T Setpoint (HTR).
Possible Causes — This mode will be enabled for freeze pro-
tection. If the temperatures are not as described above, check
46
CTPT).
MODE
MD04) — Demand
OPTN
LS.LT).
LIM) will display the current demand limit
MODE
MD05) —
the
Cool
Ramp
CRMP).
MODE
MD06) — Cooler
SERV
UNIT
LWT) or the Entering Water Temper-
UNIT
EWT) are less than or equal to
SERV
FLUD=1). The Freeze Setpoint is
VIEW
RSET
Ramp
OPTN
VIEW
CTPT),
Loading
(Set
UNIT
OAT) is
HTR] default
SERV
LOSP)
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