26
OMM 1008-1
Configuration Rules
1.
Each standby compressor must have a sequence number greater than or equal to all non-standby
compressors for which it is in standby.
2.
All compressors in an “efficiency priority” or “pump priority” group must be set to the same sequence
number.
Compressor State Control (Comp State)
Operation of the compressor is controlled by the state-transition diagram shown below. A state variable
(Comp State) shall be used to maintain the current state (OFF, START, INTLOK, RUN, UNLOAD, or STOP).
Transitions from one state to another are controlled by the condition statements in the
TEST
boxes.
TASK
boxes indicate actions that must be performed.
Figure 6,Compressor State
Compressor Capacity Control
Leaving Water Control Mode
Compressor capacity is determined by the status of the leaving chilled water temperature (LWT), which is a
direct indicator of whether the chiller is producing enough cooling to satisfy the cooling load. The LWT is
compared to the active chilled water setpoint, and compressor loading or unloading ensues, considering any
capacity overrides that may be in effect.
Capacity Overrides
The conditions described in the following subparagraphs override normal capacity control when the chiller is
in the COOL mode. These overrides are not in effect for loading and unloading when the Vane Mode is set to
OFF
InterLock
RUN
UNLOAD
VaneCloseDelay
TEST:
Unit State=AUTO
&
Evap State=RUN
&
Next On = Yes
&
Stage Up Now = YES
&
(Unit Mode NOT= HEAT
OR
EvLWT Temperature > Source No Start SP)
&
Start-Start Timer Expired
&
Stop-Start Timer Expired
&
No Safety Alarms
START
TASK:
Start Interlok Timer (10sec)
TEST:
Unit State= AUTO
&
Evap State=RUN
&
Cond State = RUN
&
Vanes Closed
&
I
nterLok Timer Expired
TEST:
Unit State = SHUTDOWN
OR
[Next Off = Yes
&
Stage Down Now = Yes]
TASK:
Start Unload Timer
TASK:
Start STOP Timer
Start Stop-Start Timer & Update Run Hours
TEST:
Manual OFF DI = OFF
OR
Vanes Closed
OR
Unit State = OFF
OR
Unload Timer Expired
OR
Safety Alarm
TEST:
Motor Current < Motor Current Threshold SP
&
STOP Timer Expired
TEST:
Manual OFF DI = OFF
OR
Unit State = OFF
OR
Safety Alarm
TEST:
Manual OFF DI = OFF
OR
Unit State = (OFF
OR
SHUTDOWN)
OR
Safety Alarm
Power ON
TASK:
Increment # of starts
TEST:
Unit State = AUTO
&
Next Off = No
TASK:
Restart Start-Start Timer
