Application range

For a safe compressor operation with frequency inverter, the following limiting factors must be strictly observed:

These limits define the application limits (see below) and can vary according to frequency ranges and operating conditions.

Speed and frequency ranges

Minimum frequency for all Bitzer scroll compressors is 35 Hz: This has been demonstrated as the minimum safe speed required to deliver adequate lubrication to the compressor bearing system. Running at lower speeds risks loss of lubrication and bearing failure.

Maximum frequency is 75 Hz for ORBIT compressors and 65 Hz for the remaining scroll compressors, due to the increasing centrifugal forces which affect the mechanial stability of the scroll wraps.

Speed and frequency ranges of Bitzer scroll compressors with external frequency inverters (also observe the application limits and the maximum current consumption of the motor)

Compressor

Frequency range [Hz]

Speed range [min-1]

ESH7

35 .. 65

2000 .. 3800

ELH7

35 .. 65

2000 .. 3800

ELA7

35 .. 65

2000 .. 3800

ORBIT

GED6 .. GED8

35 .. 75

2000 .. 4400

GSD6 .. GSD8

35 .. 75

2000 .. 4400

GSU6 .. GSU8

35 .. 75

2100 .. 4500

ORBIT tandem / trio

see below (Tandem and trio operation)

Application limits

In general, compressor models approved for operation with frequency inverter have undergone complete load cycling testing at minimum and maximum speeds. Normally, the application limits correspond to the fixed speed limits published e.g. in the Bitzer Software. However, some special considerations may require restrictions at certain speeds.

The following figure shows an example of application limits for an Orbit compressor at different frequencies. The compressor may only be operated below the indicated frequency lines ‒ otherwise, select a special voltage motor (Special voltage motors).

Exemplary and simplified application limits for an Orbit scroll compressor with frequency inverter at 60, 70 and 75 Hz (limits due to motor temperature or maximum current). The compressor may only be operated below the indicated frequency lines.to: evaporation temperature, tc: condensing temperature, Δtoh: suction gas superheatGrey area: limitations for frequencies < 50 Hz possible.
Exemplary and simplified application limits for an Orbit scroll compressor with frequency inverter at 60, 70 and 75 Hz (limits due to motor temperature or maximum current). The compressor may only be operated below the indicated frequency lines.
to: evaporation temperature, tc: condensing temperature, Δtoh: suction gas superheat
Grey area: limitations for frequencies < 50 Hz possible.

Specific application limits for particular compressors, motors and refrigerants are given in the BITZER Software or available on request.

Vibrations

Compressor vibrations and pressure pulsations are normally very low by design. However, they can evoke resonance frequencies in piping and heat exchangers (i.e. meet the natural frequency of the system) which result in system sound, vibration, and potentially in piping fatigue and leakage. Possible sources of vibrations are:

The frequency of these vibrations is related to the compressor operating frequency, which can vary over a wide range. Compared to single speed systems (without frequency inverter), this problem is intensified in variable speed applications: Even if the piping is adequate at a given compressor speed, it may not be so at other speeds set by the frequency inverter. For this reason, piping vibrations must be checked throughout the speed range of the compressor, both during the system design development activity and also at commissioning of each individual system (Configuration of the frequency inverter).