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Fig. 4: 4+4-cylinder ECOLINE tandem compressors. Left: side view, right: view of the grey bearing cover: CRII capacity control
Additional cooling
In compound systems, compressors and condensers are frequently installed separately from one another. This is
why, depending on conditions, additional cooling may be necessary (see application limits) ‒ either by means of
• air (additional fan)
• and / or electronically controlled refrigerant injection (RI)
• or water (water-cooled cylinder heads for compressors 4JE .. 4FE, 6JE .. 6FE).
When a compressor is shut off, its additional cooling must also be shut off in each case. With a fan, this is done by
simply coupling the compressor and fan contactor. When using the electronic compressor module CM-RC, the aux-
iliary fan is controlled according to the discharge gas temperature if required. A solenoid valve that shuts off the
water flow when the compressor is at standstill must be connected upstream of the water-cooled cylinder head.
Continuously switched-on additional cooling increases the risk of refrigerant condensation in the cylinder head and
reduces the effect of the oil heater. This can lead to a high concentration of refrigerant in the oil.
3.1
Selection using the BITZER Software
The BITZER Software can be used to design compound systems for semi-hermetic/open drive and 2-stage recip-
rocating compressors. The procedure is illustrated here by way of example:
Refrigerant
Refrigerating capacity
3 compressors
Operating conditions
Conditions in power
supply
Capacity control
Tab. 1: General conditions for a calculation example in the BITZER Software. Evaporators are each equipped with an internal heat exchanger.
KT-600-6 // PDF Download
R134a
100 kW
t
= -10°C
o
t
= 45°C
c
t
= 20°C
oh
400 V / 3 / 50 Hz
Compressor 1 with frequency in-
verter and 50% power, compressors
2 and 3 each with 25%.
CRII (2)
CRII (1)
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