Specifications
22
Temperature Reset — The control system is capable of
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 13 and 14.
To use outdoor air or space temperature reset, four variables
must be configured. In the Configuration mode under the sub-
mode RSET, items (Configuration
RSET
CRST),
(Configuration
RSET
RM.NO), (Configuration
RSET
RM.F), and (Configuration
RSET
RT.DG)
must be properly set. See Table 15 — 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
maximum reset is to occur. The variable RM.DG should be set
to the maximum amount of reset desired. Figures 15 and 16 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 16
— 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 Set-
point (Run Status
VIEW
SETP) from the Control Point
(Run Status
VIEW
CTPT) to determine the degrees reset.
Table 13 — Menu Configuration of 4 to 20 mA Cooling Set Point Control
Table 14 — 4 to 20 mA Reset
NOTE: The example above shows how to configure the chiller for
4 to 20 mA reset. No reset will occur at 4.0 mA input, and a 5.0 F
reset will occur at 20.0 mA. An EMM (energy management module)
is required.
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.
MODE
(RED LED)
KEYPAD
ENTRY
SUB-MODE
KEYPAD
ENTRY
ITEM DISPLAY
ITEM
EXPANSION
COMMENT
CONFIGURATION
DISP
UNIT
OPT1
OPT2
CCN
RSET
SLCT CLSP 0 COOLING SETPOINT SELECT
0 Scrolling Stops
0 Flashing ‘0’
3Select ‘3’
3 Change Accepted
SUB-MODE
KEYPAD
ENTRY
ITEM DISPLAY
ITEM
EXPANSION
COMMENT
RSET
CRST 1
COOLING RESET
TYPE
0 = no reset
1 = 4 to 20 mA input
2 = Outdoor air temp
3 = Return Fluid
4 = Space Temperature
MA.DG
5.0 F
(2.8 C)
DEGREES COOL
RESET
Default: 0° F (0° C) Reset at 20 mA
Range: –30 to 30 F (–16.7 to 16.7 C)
ENTER
ENTER
ENTER
ENTER
ENTER
ENTER