43
Table 24 — Alarms Mode and Sub-Mode Directory
Table 25 — Example of Reading and Clearing Alarms
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 OAT and SPT reset (HH79NZ073 for
OAT and HH51BX006 for SPT). The Energy Management
Module (EMM) must be used for temperature reset using a 4 to
20 mA signal.
To use the return reset, four variables must be configured. In
the Configuration mode under the sub-mode RSET, items
CRST, CRT1, CRT2, and DGRC must be set properly. See Ta-
ble 26 on page 44 for correct configuration. See Fig. 2-4 for
wiring details.
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 was allowed to increase at part load,
the efficiency of the machine would increase.
Return temperature reset allows for the leaving temperature
set point to be reset upward as a function of the return fluid
temperature or, in effect, the building load.
SUB-MODE KEYPAD ENTRY ITEM ITEM EXPANSION COMMENT
CRNT
AXXX or TXXX CURRENTLY ACTIVE ALARMS
Alarms are shown as AXXX.
Alerts are shown as TXXX.
RCRN
YES/NO RESET ALL CURRENT ALARMS
HIST
AXXX or TXXX ALARM HISTORY
Alarms are shown as AXXX.
Alerts are shown as TXXX.
RHIS
YES/NO RESET ALARM HISTORY
ENTER
ENTER
ENTER
ENTER
SUB-MODE
KEYPAD
ENTRY
ITEM ITEM EXPANSION COMMENT
CRNT
AXXX or TXXX CURRENTLY ACTIVE ALARMS ACTIVE ALARMS (AXXX) OR
ALERTS (TXXX) DISPLAYED.
CRNT
RCRN
NO Use to clear active alarms/alerts
NO NO Flashes
YES Select YES
NO Alarms/alerts clear, YES changes to NO
ENTER
ESCAPE
ENTER
ENTER
LEGEND
Fig. 21 — Standard Chilled Fluid
Temperature Control — No Reset
EWT —
Entering Water (Fluid) Temperature
LWT —
Leaving Water (Fluid) Temperature
