Compressor Operating Limit Protection - Mitsubishi Electric i-BX-N Technical Manual

TM_i-BX(-N)_NC05_00_06_20_EN
4.4.3

COMPRESSOR OPERATING LIMIT PROTECTION

There is a control of the compressor operating limits (hereinafter envelope). In order to prevent the compressor from working outside the safety limits
set by the manufacturer, this control cannot be disabled. Therefore, all unit compressors include the envelope data.
Below are the working zones of a generic envelope:
Zone Description
1 Zone inside the operating limits (prevent is in
any case active to prevent the limits from being
exceeded)
2 Max compression ratio
3 Max condensation pressure
3 Custom Max condensation pressure custom threshold
4 Max motor current
5 Max evaporation pressure
6 Min compression ratio
7 Min differential pressure
8 Min condensation pressure
9 Min evaporation pressure
The threshold of custom zone 3 is defined by parameter 131I.
When the work point moves outside the envelope, alarm delay count starts: if the work point remains outside the envelope, when the delay time
expires the specific alarm activates, shutting down the compressor. If on the other hand the work point moves back within the limits of the envelope,
the alarm delay count resets itself.
The high condensation pressure limit is determined by the minimum between:
•
the compressor nominal threshold;
•
the threshold that may be modified by Service (131l).
The high evaporation pressure limit is determined by the minimum between:
•
the compressor nominal threshold;
•
the set MOP threshold.
The suction and discharge pressures define a work point. Depending on the control zone, corrective actions take place to keep or return the
compressor within the operating limits and therefore prevent compressor alarms.
Zone Description
1 Zone inside the operating limits (prevent is in
any case active to prevent the limits from being
exceeded)
2 Prevention due to high compression ratio
3 Prevention due to high condensation pressure
4 Prevention due to high motor current
5 Prevention due to high evaporation pressure
6 Prevention due to low compression ratio
7 Prevention due to low differential pressure
8 Prevention due to low condensation pressure
9 Prevention due to low evaporation pressure
In order to allow the compressor to operate within the envelope, specific preventive actions are performed which affect the power of the circuit, the
setpoint of the source fans and the opening of the ExV.
In specific, the actions affecting the circuit power are:
· Decreasing the increase/decrease speed of the power request from heat adjustment during the approach to the envelope limit (BLDC
compressors only).
· Limiting/increasing the circuit power.
The action on the ExV valve is exercised by changing the MOP threshold (maximum evaporation temperature): the algorithm follows the setpoint,
decreasing the opening of the valve, and reducing the maximum refrigerant flow rate, therefore decreasing the evaporation temperature value. This
action is performed both with BLDC compressors and fixed speed compressors.
The actions for the control of the power variation speed start when the duty point is at a preset distance from the operating limits of the compressor.
MEHITS S.p.A. ● TECHNICAL MANUAL
Condensation
temperature [°C]
3 Custom
2
9
Condensation
temperature [°C]
2
9
36
Version NC05 - Translation of the Original Instructions
3
4
5
1
6
7
8
Evaporation
temperature [°C]
3
4
5
1
6
7
8
Evaporation
temperature [°C]