Configuring And Operating Dual Chiller Control; Temperature Reset - Carrier AquaSnap 30RAP011-060 Controls, Start-Up, Operation, Service, And Troubleshooting

pumps will be operated every other day for 2 seconds starting at
14:00 hours. If a pump has failed and has an active Alert condi-
tion, it will not be started that day.

Configuring and Operating Dual Chiller Control

The dual chiller routine is available for the control of two units
supplying chilled fluid on a common loop. This control algorithm
is designed for parallel fluid flow arrangement only. One chiller
must be configured as the master chiller, the other as the slave. An
additional leaving fluid temperature thermistor (Dual Chiller
LWT) must be installed as shown in Fig. 32 and 33 and connected
to the master chiller. Refer to Sensors section, page 29, for wiring.
The CCN communication bus must be connected between the two
chillers. Connections can be made to the CCN screw terminals on
LVT. Refer to Carrier Comfort Network
28, for wiring information. Configuration examples are shown in
Tables 22 and 23.
RETURN MASTER
CHILLER
FLUID
SLAVE
CHILLER
*Depending on piping sizes, use either:
• HH79NZ014 sensor/10HB50106801 well (3-in. sensor/well)
• HH79NZ029 sensor/10HB50106802 well (4-in. sensor/well)
Fig. 32 — Dual Chiller Thermistor Location
PART
NUMBER
10HB50106801
10HB50106802
A
B
1/4 N.P.T.
Fig. 33 — Dual Leaving Water Thermistor Well
Refer to Tables 22 and 23 for dual chiller configuration. In this ex-
ample the master chiller will be configured at address 1 and the
slave chiller at address 2. The master and slave chillers must reside
on the same CCN bus (Configuration  CCN  CCNB) but can-
not have the same CCN address (Configuration  CCN 
CCNA). Both master and slave chillers must have Lead/Lag
Chiller Enable (Configuration  RSET  LLEN) configured to
Interface section, page
®
THERMISTOR
WIRING
LEAVING
FLUID
INSTALL DUAL CHILLER LWT
LEAVING FLUID TEMPERATURE
THERMISTOR (T10) HERE*
DIMENSIONS IN. (MM)
A B
3.10 (78.7) 1.55 (39.4)
4.10 (104.1) 1.28 (32.5)
0.505/0.495
6" MINIMUM
CLEARANCE FOR
THERMISTOR
REMOVAL
ENBL. Master/Slave Select (Configuration  RSET  MSSL)
must be configured to MAST for the master chiller and SLVE for
the slave. Also in this example, the master chiller will be config-
ured to use
tion  RSET  LLBL) and Lead/Lag Balance Delta (Configura-
tion  RSET  LLBD) to even out the chiller run-times weekly.
The Lag Start Delay (Configuration  RSET  LLDY) feature
will be set to 10 minutes. This will prevent the lag chiller from
starting until the lead chiller has been at 100% capacity for the
length of the delay time. Parallel configuration (Configura-
tion  RSET  PARA) can only be configured to YES. The vari-
ables LLBL, LLBD, and LLDY are not used by the slave chiller.
Dual chiller start/stop control is determined by configuration of
Control Method (Configuration  OPT1  CTRL) of the Master
chiller. The Slave chiller should always be configured for
CTRL=0 (Switch). If the chillers are to be controlled by Remote
Controls, both Master and Slave chillers should be enabled togeth-
er. Two separate relays or one relay with two sets of contacts may
control the chillers. The Enable/Off/Remote Control switch
should be in the Remote Control position on both the Master and
Slave chillers. The Enable/Off/Remote Control switch should be
in the Enable position for CTRL=2 (Occupancy) or CTRL=3
(CCN Control).
Both chillers will stop if the Master chiller Enable/Off/Remote
Control switch is in the Off position. If the Emergency Stop switch
is turned off or an alarm is generated on the Master chiller the
Slave chiller will operate in a Stand-Alone mode. If the Emergen-
cy Stop switch is turned off or an alarm is generated on the Slave
chiller the Master chiller will operate in a Stand-Alone mode.
The master chiller controls the slave chiller by changing its Con-
trol Mode (Run Status  VIEW  STAT) and its operating set-
point or Control Point (Run Status  VIEW  CT.PT).

Temperature Reset

The control system is capable of handling leaving-fluid tempera-
ture reset based on return cooler fluid temperature. Because
change in temperature through the cooler is a measure of the
building load, the return temperature reset is in effect an average
building load reset method. The control system is also capable of
0.61
temperature reset based on outdoor-air temperature (OAT), on
DIA
space temperature (SPT), or from an externally powered 4 to
20 mA signal. Accessory sensors must be used for SPT reset
(33ZCT55SPT). The energy management module (EMM) must
be used for temperature reset using a 4 to 20 mA signal. See
Table 24.
IMPORTANT: Care should be taken when interfacing with
other control systems due to possible power supply differences:
full wave bridge versus half wave rectification. Connection of
control devices with different power supplies may result in per-
manent damage. ComfortLink controls incorporate power sup-
plies with half wave rectification. A signal isolation device
should be utilized if the signal generator incorporates a full
wave bridge rectifier.
43
Lead/Lag Balance Select (Configura-