Mitsubishi Electric EMU4-CNT-MB User Manual page 79

■Lower limit value
While a pressure value is below the lower limit value, the following control operation is repeated.
*The adjustment operation time is a delay time when a compressor is switched from the stop mode to the loaded operating
mode.
(1) When a pressure value becomes below the lower limit value for the first time only, the following control operation is
executed.
Except for the first time, this control operation is not executed and the operation is moved to (2) below.
When the pressure value becomes the lower limit value or more once and then drops below the lower limit value or
less again, the control is executed as the first time.
・Check whether some compressors with the stop mode exist.
If any, a compressor with higher priority will be switched to the loaded operating mode at the next control period.
(2) Check whether some compressors with the stop mode exist.
If any, the control target compressor will be one with higher priority.
(3) When the set delay time (total of adjustment operation time and start delay time) passes with the control target
compressor keeping the stop mode, the control target is switched to the loaded operating mode.
If the pressure value becomes the lower limit value or more before the delay time (total of adjustment operation time
and start delay time) is over, the control will not be executed.
*The delay time is reset. When the control is resumed, it is in standby mode until the reconfigured delay time is over.
(4) Change the control target to a compressor with next higher priority.
<Example of action>
Adjustment operation time: 1 minute
Start delay time:
59 min
Control target at
the start of control
Pressure measured value
Lower limit
Priority
value
High
Compressor 1
Stop
Compressor 2
Stop
Compressor 3
Stop
Compressor 4
Operation (load)
Low
①A pressure value drops below the lower limit value. At the next control period (01 min), a compressor with the highest priority,
compressor 1, will be switched to the loaded operating mode.
②The compressor 1 is switched to the loaded operating mode.
A compressor with the highest priority in compressors with the stop mode, compressor 2, is targeted and it keeps standby
mode until the adjustment operation time is over.
③Since the adjustment operation time is over, the standby mode is kept until the start delay time is over.
④Since the start delay time is over, the compressor 2 is switched to the loaded operating mode.
A compressor with the highest priority in compressors with the stop mode, compressor 3, is targeted and it keeps standby
mode until the adjustment operation time is over.
However, since the pressure value becomes the lower limit value or more, the control will not be executed at the next control
period (04 min).
⑤Since the pressure value drops below the lower limit value, at the next control period (05 min), the compressor 3 with the
highest priority will be switched to the loaded operating mode.
⑥The compressor 3 is switched to the loaded operating mode.
Since no compressor with the stop mode exists, the control operation is ended.
1 minute
00 min 01 min 02 min
Operation (load)
②
①
04 min
03 min
Operation (load)
④ ⑤
③
78
Adjustment operation time
Start delay time
Measurement value for
determination
05 min 06 min
Operation (load)
⑥
⑦