Dunham-Bush ACDX, Installation, Operation And Maintenance Instructions

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12. To change the days for this schedule, 10. High pressure safety
press one or more of the following number
keys: 0 - Clear all current days; 1 -
Sunday(S); 2 - Monday(M); 3 -
Tuesday(T); 4 - Wednesday(W); 5 -
Thursday(R); 6 - Friday(F); 7 -
Saturday(A); 8 - *** ALL DAYS***.
13. Press ENTER. The revised schedule
number is now stored.
14. To add another schedule, press the right
arrow key and repeat steps 7-13.
15. To delete a schedule, clear all of the days
by pressing 0 at Step 12.
The schedule group turns on when any of the
individual schedules turns on. The turn-on time does
not have to be earlier than the turn off time.
Schedules turn on by time and day, but turn off by
time alone. For example, a schedule from 1900 to
0700 Saturdays would turn on at 7:00 PM Saturday
(time and day) and turn off at 7:00 AM Sunday (time
only).
Example: If a unit is to operate at all times except
between the hours of 1:00 AM and 6:00 AM, the
following schedule would be entered:
CP 17 SCHEDULE GRP:1 SCH:1 0600 0100 DAYS:
*** ALL DAYS ***
Another example: A typical building may require
cooling from 6:00 AM to 7:00 PM Monday - Friday and
from 7:00 AM -3:00 PM on Saturdays. The schedules
would be entered as follows:
CP 17 SCHEDULE GRP:1 SCH:1 0600 1900 DAYS:
MTWRF
CP 17 SCHEDULE GRP:1 SCH:2 0700 1500 DAYS:
A
4. ACDX/AUDX Package Control
In order to start a unit, the following conditions
must be met:
S
chilled water pump running
S
chilled water flow switch made
S
customer control contact closed
S
control switch and compressor switch on
S
main unit power on
S
all safety conditions satisfied
S
reset pressed on microcomputer keypad
S
the compressor has not started within the last
15 minutes
S
leaving chilled water temperature 2
E
F or more
above set point
The NC25 computer system performs the following
functions on small screw compressor packages :
1. Capacity control of compressors
2. Staging of compressors
3. Compressor current limiting
4. Ramp control
5. Manual lead/lag
6. Compressor start delay
7. Power loss reset
8. Anti-recycle timing
9. Low pressure safety
19
11. Freeze safety
12. High Oil Temp Safety
13. Alarm Output
14. Fan control
15. Chilled water reset and customer control
interlock
16. Hot Gas Bypass option control
17. Compressor power control (No-stop
alarm)
18. Sensor alarm shutdown
19. External shutdown indication (No-run
alarm)
20. Fast Unload Solenoid Control (ACDX040-
185B)
21. Low suction / discharge differential
pressure alarm
22. High Motor temperature safety
23. Low chiller flow alarm
24. High discharge pressure unload
25. Low suction pressure unload
A description of each of the functions follows.
4.1. Capacity Control of Screw Compressors
The capacity of a compressor can be
controlled manually or automatically.
The status of a compressor can be observed
by displaying the compressor control point
(1/CP, 4/CP, 7/CP or 10/CP). One of the
following messages will be displayed where
# is 1, 4, 7 or 10 for compressors 1, 2, 3 or
4:
CP# COMP LOAD COM Computer load
CP# COMP CURRENT STATUS: LOAD Manual load
CP# COMP HOLD COM Computer hold
CP# COMP CURRENT STATUS: HOLD Manual hold
CP# COMP UNLD COM Computer
unload
CP# COMP CURRENT STATUS: UNLD Manual unload
CP# COMP OFF COM Off on a normal
control
shutdown
CP# COMP COFF COM Off on timer
(clock off)
CP# COMP LOFF MAN Manual off or
safety
shutdown
4.1.1 Automatic Control
The computer calculates the operating
percent capacity of a compressor by
measuring discharge pressure and amps.
This operating percent capacity is then
compared to a target percent capacity. If
the operating capacity is outside of a + 3%
deadband, the load or unload solenoids
are pulsed to match the operating and
target percent capacities. Since all
compressors have the same target, their
percent capacities are balanced.
The target percent capacity is given a fixed
value when a compressor starts or stops.
This value is then increased or decreased
based on how far the leaving water
temperature (TLW) is from setpoint and
also on how fast the TLW is approaching
setpoint. The target percent capacity will
not change if the temperature is within a
temperature deadband around the
setpoint.