Carel uChiller UCHBD00001230, User Manual

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63
ENG
μc0300053EN rel. 2.2 - 14.12.2021
Functions
5.7
B
LD
C
comp. alarm prevention
The evaporation and condensation pressures determine a working point in a zone of the envelope, and depending on the zone,
the controller applies corrective actions to maintain or return BLDC compressor operation within the limits.
5.7.1 Prevention actions for
B
LD
C
compressors
Below is the description of the working zones in a generic envelope for BLDC compressors:
300053_059_R01
Tc
Te
1
2
3 4
5
6
7
8
9
10
Fig. 5.n
Zone Descrizione
1 Zone inside the operating limits
2 Prevention due to high compression ratio
3 Prevention due to high condensing 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 diff erential pressure
8 Prevention due to low condensing pressure
9 Prevention due to low evaporation pressure
Tab. 5.i
To allow the compressor to work inside the envelope, specifi c prevention actions are adopted that adjust circuit capacity, the
source fan set point and the opening of the ExV valve.
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. This action is applied with both BLDC compressors and fi xed-speed compressors.
The actions involving the rate of capacity variation start when the working point is a set distance from the compressor operating
limits. These actions are only possible with BLDC compressors.
In the event of fi xed-speed compressors, the only actions possible on the circuit are to limit capacity via the number of the
compressors on: this is implemented as soon as the working point exceeds the maximum condensing temperature (par. C017)
or minimum evaporation temperature (par. U050/S057) or minimum evaporation threshold (par. C018) - or the minimum of
the two.
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).
Low evaporation pressure prevention (zone 9)
The low evaporation pressure limit for the prevention action is determined by maximum between:
• the nominal compressor threshold (BLDC only);
• the threshold set by the "Manufacturer": par. C018/P000 for On-Off /BLDC compressor;
• the frost protection limit, depending on the operating mode: par. U050 in cooling mode and S057 in heating mode with
water/water units.
Device Description
BLDC compressor 1. Decrease the rate of capacity increase.
2. Limit
capacity
Tandem on-off compressors 1. -
2. Shutdown a compressor
ExV -
Fan -