Bitzer 4CTEU-30LK, Technical Information

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KT-102-1 8
5.2 Control concepts and activation of the solenoid
valves
Due to the universal application options of the CRII sys-
tem for transcritical CO
2
applications, it is possible to
implement capacity control with increased switching
frequency. In this process, the control algorithm is spe-
cifically adapted for each particular system with re-
duced deviation from the setpoint (see chapter Operat-
ing the CRII capacity control with the system controller,
page 11).
Compressor
type Capacity control range Number of
required
CRII cylin-
der heads
4-cylinder
com-
pressors 100% .. 25% ①
100% .. 50%
2
1
6-cylinder
com-
pressors 100% .. 66%
100% .. 33%
1
2
Tab. 2: CRII system for reciprocating compressors for transcritical
CO
2
applications: Control concepts
① in future controllable down to 10%, quasi-stepless
capacity control (activated intermittently)
Full equipment (see chapter Connections and
dimensional drawings, page 4)
• 4-cylinder compressors: 2 cylinder heads
• 6-cylinder compressors: 2 cylinder heads
• Compounding systems with a higher number of com-
pressors:
Increased control accuracy can also be obtained, if
desired, using one CRII cylinder head each per com-
pressor. However, in this case, the range of control
of the individual compressors is limited.
4-cylinder compressors:
CRII (1) CRII (2)
100%
>50%
≤50% / /
Capacity regulator de-energized
Capacity regulator constantly activated
Capacity regulator activated intermittently (cycle time
depending on load condition)
6-cylinder compressors:
CRII (1) CRII (2)
100%
>66%
>33%
Capacity regulator de-energized
Capacity regulator constantly activated
Capacity regulator cyclically activated (cycle time de-
pending on load condition)
Activation via CRII solenoid valves
Specially designed solenoid valves activate internal
components such that the refrigerant is not com-
pressed in the corresponding cylinder bank and the
compressor is running in part-load operation. This al-
lows perfect adjustment to the cooling demand of the
system and a rapid reaction to system changes. This
allows suction pressure variations to be limited to a
minimum, compared with the switch-on/switch-off oper-
ation, see figure 7, page 8. This allows the room
temperature to be maintained at a much more stable
level. Moreover, CRII is often a good alternative to
BITZER VARIPACK frequency inverters, allowing very
good control accuracy for a stable suction pressure.
On / Off intermittent
operation
CRII mechanical
capacity control
VARIPACK
Technology
2nd setpoint
Suction pressure (bar)
Room temp. (°C)
Larger variations of the
room temperature
Reduced variations
through high switching
frequency of the CRII
system
Precise, stepless
capacity adjustment
without variations
Fig. 7: Qualitative curves of the suction pressure and the room tem-
perature (various methods as a function of time)