Bitzer KT-600-4 Manuel D'installation page 50

Module CM-RC-01
Fig. 14: Application example with compressor module CM-RC-01
To secure the overall system against the pressure being exceeded, the specifications of the standard safety regula-
tions and standards (e.g. EN378, ISO5149) must be observed. To monitor the minimum permitted suction pres-
sure, a common low pressure limiter set to a lower pressure level than the suction pressure control is usually suffi-
cient. It only serves as protection against a possible failure or a fault in the system control.
Information on SE-B compressor protection devices: KT-122
Information on oil pressure monitoring (Delta‑PII, MP54, 55A): KT-170
Information on opto-electronic oil level monitoring (OLC-K1): KT-180
System control
A compound system is controlled either as a function of the suction pressure or of a defined process temperature.
For systems having a relatively high number of evaporators, a suction pressure control adjusted to the demand is
customary. To this end, the manufacturers of regulators offer a wide range of products. The control algorithm
should guarantee at least the following:
• Demand-dependent switch-on and switch-off of individual compressors and their capacity control (finely tuned
mechanical or speed control), as a function of a defined suction pressure with a narrow bandwidth. In doing so,
the design criteria described above should be taken into account ( see page 30 ).
• Securing the max. cycling rate and minimum running time of the compressors. This is possible, for example,
through a time limit from start to start as well as a minimum running time secured by the control algorithm, which
may only be fallen short of during safety cut-outs.
• Automatic change of the lead compressor for uniformly distributed operating hours of the compressors. This en-
sures a balanced load and minimum wear.
• When the lead compressor is switched off in controlled fashion (via the min. suction pressure), you must ensure
that the solenoid valves in the liquid line or the electronic expansion valves can only be activated following a
possible time delay of the lead compressor. This is also true when all compressors are shut down by a safety
device (e.g. high pressure switch-off). This avoids flooding of the evaporators with liquid.
• Adjustment of the suction pressure to demand, for example automatic increase at reduced load
• Reasonable control of the condensing temperature ( see page 48 )
The operation of reciprocating compressors with frequency inverters is described in the Technical Information
KT-420 .
KT-600-4 // PDF Download
Modbus (or: compressor start and set point signal)
Power connection CM-RC-01
Power connection compressor
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