KT-420-4 // PDF Download
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Introduction
A frequency inverter allows the stepless control of the cooling capacity to the cooling demand of the system by
speed control. The following description explains the design, operation, application range and special characterist-
ics of
• BITZER reciprocating compressors
• in combination with external frequency inverters for speed control, e.g. the BITZER VARIPACK.
All BITZER reciprocating compressors are suitable for operation above and below the supply frequency and can
thus run over an exceptionally broad capacity range.
Features of the operation with a frequency inverter (FI):
• higher system efficiency, especially in part-load
• more exact temperature control possible
• precise coolant temperature for sensitive process cooling resp. heat-transfer fluid temperature for heat pumps
• higher effective evaporation temperatures, therefore less dehumidification of unpacked foods and raw material in
cold stores, as well as less icing at the evaporator
• fewer compressor starts
• less strain on the motor and the power network due to integrated soft start: starting current is lower than with dir-
ect start, softstarter, star-delta or part-winding start
• higher refrigerating capacity often possible by operation above supply frequency (allows use of a compressor
with lower displacement at supply frequency 50 or 60 Hz, i.e. possibly lower costs per kW refrigerating capacity)
The figure below shows the smaller temperature fluctuations with frequency inverter control:
• On/Off regulation, left third: large temperature fluctuations, relatively low average effective evaporation temperat-
ure (fine dotted line)
• Stepped mechanical regulation, middle third: reduced temperature fluctuations due to faster regulation, higher
average effective evaporation temperature and thus higher efficiency
• Regulation with frequency inverter, right third: very steady room resp. coolant temperature (± 0,5 K possible) due
to stepless control, higher average effective evaporation temperature and thus higher efficiency as well as e.g.
lower dehumidification of unpacked foods and raw material
With frequency inverter operation, the average evaporation temperature can be raised e.g. from -7 to -4.5°C. Rising
the evaporation temperature by 1 K increases system efficiency by up to 3%.
