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Functions
k.air +030220981 rel. 1.2 - 01.12.2020
9.10.6 C ompressor alarm prevention
The suction and discharge pressure determine a working point, and depending on the zone, the controller applies corrective
actions to maintain or return compressor operation within the limits.
9.10.7 P revention actions
Below is the description of the working zones in a generic envelope:
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Condensing
temperature
Evaporation
temperature
3
2
9
8
7
1
4
5
6
Fig. 9.v
To allow the compressor to work inside the envelope, specifi c prevention actions are adopted that adjust circuit capacity and the
opening of the electronic expansion valve (ExV).
In particular, the actions involving circuit capacity are:
• decrease the rate at which the capacity request from the temperature controller increases/decreases when approaching the
limit of the envelope;
• limit/increase circuit capacity
The action on the ExV valve is applied by varying the MOP threshold (maximum evaporation temperature): the algorithm
follows the set point, decreasing valve opening, and therefore reducing the mass fl ow of refrigerant, which in turn lowers the
evaporation temperature.
The actions involving the rate of capacity variation start when the working point is a set distance from the compressor operating
limits. Below are details of the various actions to prevent the operating limits from being exceeded; action 1 refers to the control
action (before exiting the envelope); action 2 to the limiting action (working point already outside of the envelope).
High compression ratio prevention (zone 2)
D evice D escription
BLDC compressor 1. Decrease the rate of capacity increase.
2. Reduce capacity
EXV -
A high compression ratio is a thermal limit of compressor operation: normally control is activated at the limit of the envelope,
reducing capacity when the limit is exceeded; if a probe is fi tted to measure discharge temperature and if the temperature ap-
proaches the limits, as the critical condition involves high compressor discharge temperature, compressor capacity control will
be based directly on the corresponding probe reading.
To control discharge temperature, a specifi c algorithm is activated, which initially slows down the increase in capacity, until
reaching zero when at the set point (5°C below the maximum limit); if the temperature increases further, the control algorithm
gradually and slowly reduces capacity, mimicking compressor thermal inertia.
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Discharge
temperature
5.0°C
Alarm threshold
Alarm
3. Power reduction
1. Normal functioning
2. Power increasing speed
reduction (gradual)
Limitthreshold
Action distance
Fig. 9.w
High condensing pressure prevention (zone 3)
D evice D escription
BLDC compressor 1. Decrease the rate of capacity increase.
2. Reduce capacity
EXV -
High motor current prevention (zone 4)
D evice D escription
BLDC compressor 1. Decrease the rate of capacity increase.
2. Reduce capacity
EXV MOP with specifi c algorithm