Table 23 — Alarms Mode and Sub-Mode Directory
SUB-MODE KEYPAD ENTRY ITEM ITEM EXPANSION COMMENT
CRNT
ENTER
AXXX or TXXX CURRENTLY ACTIVE ALARMS
Alarms are shown as AXXX.
Alerts are shown as TXXX.
RCRN
ENTER
YES/NO RESET ALL CURRENT ALARMS
HIST
ENTER
AXXX or TXXX ALARM HISTORY
Alarms are shown as AXXX.
Alerts are shown as TXXX.
RHIS
ENTER
YES/NO RESET ALARM HISTORY
Table 24 — Example of Reading and Clearing Alarms
SUB-MODE KEYPAD ENTRY ITEM ITEM EXPANSION COMMENT
CRNT
ENTER
AXXX or TXXX CURRENTLY ACTIVE ALARMS
ACTIVE ALARMS (AXXX) OR
ALERTS (TXXX) DISPLAYED.
CRNT
ESCAPE
RCRN
NO Use to clear active alarms/alerts
ENTER
NO NO Flashes
YES Select YES
ENTER
NO Alarms/alerts clear, YES changes to NO
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 re-
turn temperature reset is in effect an average building load
reset method. The control system is also capable of tempera-
ture reset based on outdoor-air temperature (OAT), space tem-
perature (SPT), or from an externally powered 4 to 20 mA
signal. Accessory sensors must be used for OAT and SPT
reset (HH79NZ014 for OAT and HH51BX006 for SPT). The
Energy Management Module (EMM) must be used for tem-
perature reset usinga4to20mAsignal.
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
Table 25 on page 42 for correct configuration. See Fig. 2-4
for wiring details.
Under normal operation, the chiller will maintain a con-
stant 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. 20. Usually the chiller size and leaving-fluid tem-
perature set point are selected based on a full-load condi-
tion.At part load, the fluid 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 tempera-
ture set point to be reset upward as a function of the return
fluid temperature or, in effect, the building load.
LEGEND
EWT — Entering Water (Fluid) Temperature
LWT — Leaving Water (Fluid) Temperature
Fig. 20 — Standard Chilled Fluid Temperature
Control — No Reset
43
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