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The accessory module will only become active after a previous calculation!
The Accessories window opens and suggests a VARIPACK frequency inverter for compressor 1 and a common re-
ceiver for all 3 compressors.
4
Oil management
4.1
Oil and gas equalisation between crankcases
For compressors with small to medium capacity, previously oil and gas equalisation between crankcases was fre-
quently selected. This is a low-cost option, but has decisive drawbacks: Due to the pipe joint between the crank-
cases, suction gas (in the bypass) will keep flowing also through shut-off compressors. Under unfavourable condi-
tions, this may lead to the migration of oil into compressors that are in operation. This can result in faults to the oil
balance and to damage to the compressor ‒ a pressure differential of as little as 0.01 bar corresponds to an oil
level difference of approximately 11 cm. This is why in particular the methods described below are recommended
( Parallel compounding with optimized suction header , Parallel compounding with oil level controllers ).
BITZER compressors of series BE5 and BE6 (4JE-13 .. 6FE-50) can be designed with separate, generously sized
oil and gas equalising lines between the crankcases. Suitable connections are available as standard (see operating
instructions KB-100 ) and suitable adaptors are available as accessories. The connecting lines should be kept as
short as possible. Deviations from the exactly straight horizontal connection by slight bends are allowed in the gas
equalising line only upwards and in the oil equalising line only downwards. However, in view of the remarks made
above, this version, too, is rather suitable for systems which (on the basis of practical experience and tests) are
built either as standard or at least repeatedly.
4.2
Parallel compounding with optimized suction header
This version was previously used in particular in factory-made liquid chillers or specially tested systems. Although
this prevents a direct oil migration between compressors, uniform oil distribution requires, however, special meas-
ures and requirements.
The internal oil recirculation system of the compressors has been designed such that the oil carry over changes as
a function of the oil level in the crankcase. In connection with an optimized suction header and an intelligent com-
pressor rack controller, this leads to a self-regulation effect.
General requirements and recommendations
• The concept is applicable to systems with
– ≤ 4 compressors of equal capacity and without capacity control
– identical lubrication system for the compressors and monitoring of the oil supply by an oil level switch (centri-
fugal lubrication) or oil pressure limiter (pump lubrication). Compressors with centrifugal and pump lubrication
may only be combined when designed with oil level controllers ( Parallel compounding with oil level control-
lers ).
• Load sequence switching at a rate of max. 1 h is required to ensure that the temperature of shut-off compressors
does not drop too much. Ideally, the cylinder heads should not be cooled below the condensing temperature, in
order to avoid back condensation. A higher temperature also reduces the refrigerant concentration in oil, thus re-
ducing oil carry over during the compressor start.
• System design / Pipe works: The prerequisite for safe operation is a uniform oil transport in the system during
full load and part load. To ensure this, the pipe works must be carefully designed with respect to the minimum
flow velocities.
• System control: An intelligent control logic should be used which guarantees an automatic sequence change and
uniformly long compressor running times at minimum switching frequency.
KT-600-6 // PDF Download
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