The Crii System For Bitzer Reciprocating Compressors For Transcritical Co Applications; Control Principle - Bitzer 4PTEU-6LK Technical Information

5 The CRII system for BITZER reciprocating
compressors for transcritical CO
The completely newly developed CRII system for capa-
city control for BITZER reciprocating compressors for
transcritical CO applications in combination with the
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compressor module CM-RC-01 allows easy and flexible
operation of the compressor. The capacity adjustment
to the demand over a wide range from 100% to 25%, in
future even to 10%, covers, among other things, the
large differences between summer and winter opera-
tion, allows a finely tuned capacity in a compounding
system and an increase in the coefficient of perform-
ance COP of the system due to a more stable and
higher average suction pressure.

5.1 Control principle

The CRII system for capacity control is based on the
principle of cylinder switch-off. In this process, the suc-
tion-side gas flow to the individual cylinder banks is
blocked by means of a control piston.
Full-load operation
In full-load operation the compressor delivers on all cyl-
inders. The magnetic coil (see figure 6, page 7) is
de-energized. The bypass channel is closed, inflow and
compression take place.
Part-load operation
In part-load operation, the magnetic coil is energized
(see figure 6, page 7). By means of a servo valve, a
control piston is lifted and a bypass channel opened.
This interrupts gas delivery from the switched-off cylin-
der bank, since the gas is flowing from the discharge
gas side to the suction side. A return of refrigerant from
the gas cooler / condenser is prevented by an internal
check valve on the valve plate. The integrated control
algorithm ensures minimum heating of the compressor.
The thermal protection of the compressor is guaranteed
by the compressor module CM-RC-01.
KT-102-1
applications
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Fig. 6: Structural design of the CRII capacity regulator
1 Magnetic coil
3 Discharge gas cham-
ber
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2 Suction gas chamber
4 Check valve
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