Control Concepts And Activation Of The Solenoid Valves - Bitzer 4PTEU-6LK Technical Information

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
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 Capacity control range
type
4-cylinder 100% .. 25% ①
com-
100% .. 50%
pressors
6-cylinder 100% .. 66%
com-
100% .. 33%
pressors
Tab. 2: CRII system for reciprocating compressors for transcritical
CO applications: Control concepts
2
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:
100%
>50%
≤50%
Capacity regulator de-energized
Capacity regulator constantly activated
Capacity regulator activated intermittently (cycle time
depending on load condition)
8
applications, it is possible to
Number of
required
CRII cylin-
der heads
CRII (1) CRII (2)
/ /
6-cylinder compressors:
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-
2
pressed in the corresponding cylinder bank and the
compressor is running in part-load operation. This al-
1
lows perfect adjustment to the cooling demand of the
system and a rapid reaction to system changes. This
1
allows suction pressure variations to be limited to a
2
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
Larger variations of the
room temperature
Fig. 7: Qualitative curves of the suction pressure and the room tem-
perature (various methods as a function of time)
CRII (1) CRII (2)
CRII mechanical VARIPACK
capacity control Technology
2nd setpoint
Reduced variations Precise, stepless
through high switching capacity adjustment
frequency of the CRII without variations
system
KT-102-1