Temperature Reset; Dual Chiller Thermistor Location; Dual Leaving Water Thermistor Well; Brass Well Thermistor - Carrier AquaSnap 30MPA Series Controls, Start-Up, Operation, Service, And Troubleshooting

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 Emergency 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

Control Mode (Run Status
ing setpoint or Control Point (Run Status
RETURN MASTER
CHILLER
FLUID
SLAVE
CHILLER
*See Fig. 18 for thermistor and well part numbers.
Fig. 17 — Dual Chiller Thermistor Location
A
B
1/4 N.P.T.
10HB50106801 and 10HB50106802
B
A
Brass Well Thermistor — 00PPG000008000A
PART
NUMBER
10HB50106801
10HB50106802
00PPG000008000A
Fig. 18 — Dual Leaving Water Thermistor Well
Temperature Reset —
handling leaving-fluid temperature reset based on return cooler
fluid temperature. Because the change in temperature through
the cooler is a measure of the building load, the return tempera-
ture reset is in effect an average building load reset method.
The control system is also capable of temperature reset based
on outdoor-air temperature (OAT), space temperature (SPT), or
from an externally powered 4 to 20 mA signal. Accessory sen-
sors must be used for SPT reset (33ZCT55SPT) and for OAT
reset (HH79NZ014). The energy management module (EMM)
must be used for temperature reset using a 4 to 20 mA signal.
See Tables 27 and 28.

VIEW STAT) and its operat-
 
VIEW CT.PT).
THERMISTOR
WIRING
LEAVING
FLUID
INSTALL DUAL CHILLER LWT
LEAVING FLUID TEMPERATURE
THERMISTOR (T10) HERE*
0.505/0.495
6" MINIMUM
CLEARANCE FOR
THERMISTOR
REMOVAL
DIMENSIONS in. (mm)
A B
3.10 (78.7) 1.55 (39.4)
4.10 (104.1) 1.28 (32.5)
2.32 (58.86) 1.31 (33.28)
The control system is capable of
IMPORTANT: Care should be taken when interfacing with
other control systems due to possible power supply differ-
ences: full wave bridge versus half wave rectification. Con-
nection of control devices with different power supplies
may result in permanent damage. ComfortLink controls
incorporate power supplies with half wave rectification. A
signal isolation device should be utilized if the signal gen-
erator incorporates a full wave bridge rectifier.
To use outdoor air or space temperature reset, four variables
must be configured. In the Configuration mode under the sub-
mode RSET,
(Configuration

RSET RM.F),
must be properly set. See Table 29 — Configuring Outdoor Air
and Space Temperature Reset. The outdoor air reset example
provides 0° F (0° C) chilled water set point reset at 85.0 F
(29.4 C) outdoor-air temperature and 15.0 F (8.3 C) reset at
55.0 F (12.8 C) outdoor-air temperature. The space tempera-
ture reset example provides 0° F (0° C) chilled water set point
reset at 72.0 F (22.2 C) space temperature and 6.0 F (3.3 C) re-
set at 68.0 F (20.0 C) space temperature. The variable CRST
should be configured for the type of reset desired. The variable
RM.NO should be set to the temperature that no reset should
occur. The variable RM.F should be set to the temperature that
0.61 maximum reset is to occur. The variable RM.DG should be set
DIA
to the maximum amount of reset desired. Figures 19 and 20 are
examples of outdoor air and space temperature resets.
To use return reset, four variables must be configured. In the
Configuration mode under the sub-mode RSET, items CRST,
RT.NO, RT.F and RT.DG must be properly set. See Table 30
— Configuring Return Temperature Reset. This example pro-
vides 5.0 F (2.8 C) chilled water set point reset at 2.0 F (1.1 C)
cooler T and 0° F (0° C) reset at 10.0 F (5.6 C) cooler T. The
variable RT.NO should be set to the cooler temperature differ-
ence (T) where no chilled water temperature reset should oc-
cur. The variable RT.F should be set to the cooler temperature
difference where the maximum chilled water temperature reset
should occur. The variable RM.DG should be set to the maxi-
mum amount of reset desired.
To verify that reset is functioning correctly proceed to Run
Status mode, sub-mode VIEW, and subtract the Active
Setpoint (Run Status
Point (Run Status
reset.
Under normal operation, the chiller will maintain a constant
leaving fluid temperature approximately equal to the chilled
fluid set point. As the cooler load varies, the entering cooler
fluid will change in proportion to the load as shown in Fig. 21.
Usually the chiller size and leaving-fluid temperature set point
are selected based on a full-load condition. At part load, the flu-
id temperature set point may be colder than required. If the
leaving fluid temperature were allowed to increase at part load,
the efficiency of the machine would increase.
Return fluid reset allows for the leaving temperature set
point to be reset upward as a function of the return fluid tem-
perature or, in effect, the building load (See Fig. 22).
31

items (Configuration
 
RSET RM.NO), (Configuration

and (Configuration
 
VIEW SETP) from the Control
 
VIEW CTPT) to determine the degrees

RSET CRST),


RSET RT.DG)