35
Table 31 — Dual Slave Chiller Control Parameters for Series Applications with Navigator Display
DUAL CHILLER PUMP CONTROL FOR SERIES
CHILLER APPLICATIONS — Pump control for series chill-
er applications is controlled by the master chiller only. The
control of the slave chiller is directed through commands emit-
ted by the master chiller. The slave chiller has no action in
master/slave operations. The slave chiller only verifies that
CCN communication with the master chiller is present. See the
Dual Chiller Sequence of Operation section on page 54.
Ramp Loading —
Ramp Loading limits the rate of
change of the leaving fluid temperature. If the unit is in a Cool-
ing mode and configured for Ramp Loading Select (
Ramp
Loading Select
, RL.S
), the control makes two comparisons
before deciding to increase capacity. First, the control calcu-
lates the temperature difference between the control point and
leaving fluid temperature. If the difference is greater than 4° F
(2.2° C) and the rate of change (°F or °C per minute) is more
than the configured Cool Ramp Loading rate (
Cooling Ramp
Loading
, CRMP
), then the control does not allow any increase
of capacity.
To configure this option with the Touch Pilot display:
To configure this option with the Navigator display:
Temperature Reset —
Temperature reset is a value
added to the basic leaving fluid temperature set point and the
resulting sum of these values is the new control point. When a
non-zero temperature reset is applied, the chiller controls to the
new control point, not the set point. The type of temperature re-
set is configured with the Cooling Reset Type (
Cooling Reset
Select
, CRST
) variable. Types of temperature reset are avail-
able: Return Water Reset, Space Temperature Reset, and 4-20
mA Temperature Reset.
Under normal operation, the chiller will maintain a constant
entering or leaving fluid temperature, based on the configura-
tion, approximately equal to the chilled fluid set point. As the
cooler load varies, the cooler fluid temperature difference will
change in proportion to the load. For example, if the chiller was
selected for a Entering to Leaving Water Temperature
difference of 10 F (5.5 C) at full load, at 50% load the tempera-
ture difference would be 5 F (2.2 C). See Fig. 19. Because the
change in temperature through the cooler is a measure of the
building load, the temperature difference reset is the average
building load. Usually the chiller size and fluid temperature set
point are selected based on a full-load condition. At part load,
the fluid temperature set point may be lower than required. If
the fluid temperature were allowed to increase at part load, the
efficiency of the machine would increase. The chiller can also
be set for return water temperature control. See Fig. 20.
Other indirect means of estimating building load and con-
trolling temperature reset are also available and are discussed
below.
To verify that reset is functioning correctly, subtract the Set-
point Select (
Current Setpoint,
SETP
) from the Control Point
(
Control Point,
CTPT
) to determine the degrees reset.
RETURN WATER RESET — The control system is capable
of performing fluid temperature reset based on cooler fluid
temperature difference. Because the change in temperature
through the cooler is a measure of the building load, the tem-
perature difference reset is, in effect, an average building load
reset method.
Return Water Temperature Reset allows for the chilled
water temperature set point to be reset upward as a function of
the fluid temperature difference (building load).
NOTE: Return Water Temperature Reset should not be used
with variable cooler flow rate systems.
To use Return Water Temperature Reset, four variables
must be configured. Cooling Reset Type (
Cooling Reset
Select
, CRST
) must be enabled. The variable Delta T No Reset
Temp (
Delta T No Reset Value
, CRT1
)
should be set to the
cooler temperature difference (T) where no chilled water tem-
perature reset should occur. The variable Delta T Full Reset
Temp (
Delta T Full Reset Value
, CRT2
)
should be set to the
cooler temperature difference where the maximum chilled
water temperature reset should occur. The variable Degrees
Cool Reset (
Cooling Reset Deg. Value
, DGRC
)
should be set
to the maximum amount of reset desired.
ITEM
ITEM EXPANSION
PATH
VALUE
MSSL
Master/Slave Select
Configuration
RSET
Slave
Default: Disable
SLVA
Slave Address
Configuration
RSET
Must be set to the Slave Chiller’s address.
The master and slave chiller must have
different addresses and be on the same
Bus Number
Default: 2
LLBL
Master Lead Lag Select
Configuration
RSET
Range: Always Lead, Lag if Fail,
Runtime Sel
Default: Always Lead
LLBD
Lead/Lag Balance Delta
Configuration
RSET
Range: 40 to 400 hours
Default: 168 hours
LLDY
Lag Start Delay
Configuration
RSET
Range: 2 to 30 minutes
Default: 10 minutes
LL.ER
Start If Error Higher
Configuration
RSET
Range: 3.0 to 18
F (1.7 to 10.0
C)
Default: 4.0
F (2.2
C)
LAG.M
Lag Unit Pump Select
Configuration
RSET
Range: Off If U Stp, On If U Stop
Default: Off If U Stp
LPUL
Lead Pulldown Time
Configuration
RSET
Range: 0 to 60 minutes
Default: 0 minutes
SERI
Chillers in Series
Configuration
RSET
YES
Default: NO
OPER
Operating Control Type
Operating Modes
SLCT
CCN Control
DISPLAY NAME
PATH
LINE NO.
VALUE
Ramp Loading
Select
Main Menu
Config
USER
5
Yes
Cooling Ramp
Loading
Main Menu
Setpoint
14
Range: 0.2 to 2.0 °F
(0.1 to 1.1 °C)
Default: 1.0 °F (0.5 °C)
ITEM
ITEM
EXPANSION
PATH
VALUE
RL.S
Ramp Load
Select
Configuration
OPTN
Yes
CRMP
Cool Ramp
Loading
Setpoints
COOL
Range: 0.2 to 2.0 °F
(0.1 to 1.1 °C)
Default: 1.0 °F (0.5 °C)
