Carel Hecu CO2, User Manual

Page: 23 / 64

23
ENG
Hecu
C O
2
+0300085EN rel. 2.2 - 07.05.2019
If the operating conditions are close to the envelope limit or outside
of this, the controller applies corrective actions in an attempt to keep
the operating point inside the limits specifi ed by the manufacturer. It
is therefore possible that in such cases, the actual compressor speed
does not correspond to the cooling capacity request of the temperature
controller, that superheat is not maintained at the set point, or that the
discharge pressure is not kept at the optimal value. If the operating
conditions remain outside of the envelope for a time exceeding the alarm
threshold (screen Cag55, default 60 s), the compressor is stopped and an
out-of-envelope alarm is signalled.
9
5
2
8
3
6
1
7
Suction pressure
D
ischar
ge pr
essur
e
Fig. 6.c
The following zones are defi ned (see Figure 6.e):
1. Inside the envelope 6. Low compression ratio
2. High compression ratio 7. Low diff erential pressure
3. High discharge pressure 8. Low discharge pressure
5. High evaporation pressure 9. Low evaporation pressure
Timers
The timers include a minimum On time, a minimum Off time and a
minimum time between two consecutive starts.
These parameters can be set on
screen Caf35:
The logic is described in the following graph:
min ON
time
min OFF
time
min time to start
same compressor
10s
time
ON
Comp
OFF
Fig. 6.d
C
ompressor prevent function:
by managing the envelope, compressor "Prevent" actions can be applied
to attempt to avoid shutdown due to the high discharge pressure and
temperature thresholds.
The settings are made on the following screens:
Force compressor
O
FF:
The compressor can be forced OFF if the suction pressure falls below the
threshold for a set delay time; these parameters are set on the following
screen:
S
tart-up
Hecu CO2 manages compressor start-up in the best way possible,
adapting operating speed so as to guarantee that the desired conditions
and excellent lubrication are reached very quickly.
For this reason, when starting the compressor is operated at a settable
fi xed speed (Cag52) for the minimum ON time, Fig. 6.c. During this stage,
the out-of-envelope alarm is disabled, but speed control remains active
if approaching or exceeding zone 2 (maximum compression ratio), 3
(maximum condensing pressure) or 4 (current limit).
The corresponding parameters are found under
Compressors
Æ
Advanced
Æ
screen Cag52: