McQuay WSC Operating Manual page 55

Figure 31, Pressure Control Dropout
LEAVING
CHILLED
WATER
TEMP
Set Compressor Setpoints
SET COMP#N SPs (1)
Demand Limit = OFF
Minimum Amps =XXX%
Maximum Amps =XXX%
Demand Limit settings can be OFF or ON as determined from the Demand Limit setpoint.
SET COMP#N SPs (2)
StageMode = NORMAL
StageSequence# =XX
Max Comprs ON = XX
StageMode settings can be NORMAL, HI EFF, PUMP, and STANDBY as determined by the Stage
Mode setpoint.
NORMAL has the auto-balance sequence that starts compressors with least starts and stops
compressors with most hours, in sequence, providing all compressors have the same sequence
number. If they have different sequence numbers, say 1, 2, 3, 4, they will always start in that
sequence. That is, sequence number will take precedence over auto-balance sequencing.
HI EFF is used with multiple chillers and runs one compressor per chiller when ever possible.
PUMP starts all compressors on the same chiller first, starting with the chiller with the compressor
with the least starts (or by sequence number if they are different).
STANDBY is used in multi-compressor systems and reserves a compressor to come on only if
there is a failure of another compressor in the system and the standby compressor capacity is
required to maintain chilled water temperature.
StageSequence is set for each compressor:
In NORMAL or STANDBY Mode, all compressors can have the same number or a number from 1
up to the total number of compressors. Sequence number has priority over other considerations. If
four compressors in a system are given the sequence numbers 1 through 4, they will always start in
that order. With the same number they will auto-sequence.
In HI EFF or PUMP, all compressors must have the same sequence number.
Max Comprs ON limits the number of compressors allowed to run in multi-compressor systems. It
provides a "floating standby" compressor. All compressor controllers must have the same setting
for this setpoint.
OM Centrif Micro ΙΙ-5
80° F
40° F
TIME
PRESSURE CONTROL MODE
DROP OUT TEMP
PROGRAM CONTROL MODE
LWT SETPOINT
(PULLDOWN)
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