Tandem and trio operation

Inverter driven Orbit scroll compressors may be connected in tandem and trio arrangements (ESH7: tandems only, EL.7: single application only). In these cases, however, observe the respective maximum range of frequencies (see tables below): They are necessary to ensure adequate lubrication resp. oil return from the system when compression capacity is reduced. Whether by staging or inverter operation, capacity reduction reduces the refrigerant mass flow rate in the system. Special care must be taken to avoid oil traps and ensure that at low loads and low ambient temperatures, the flow velocity is sufficient to return oil from evaporators and any suction accumulators.

For general information on how to integrate Orbit compressors into the refrigeration circuit:

• EST-600: Integrating BITZER ORBIT scroll compressors into the refrigeration circuit

Individual rather than common drive operation

Equipping each compressor with a frequency inverter (= individual drive operation) allows individual compressors to be stopped or started independently of the others ‒ within certain ranges, which are listed in detail in the tables below. With BITZER Advanced Header Technology (BAHT), it is possible to combine fixed and variable speed Orbit compressors with the same pipes as used for conventional on/off operation. For ESH7, only the standard piping system is available.

In contrast, it is not recommended to use one inverter for several compressors (= common drive operation), because e.g.:

• Due to small differences in manufacturing of the motors and electrical connections, large currents will flow at undesirable places and destroy the compressor motors over time. Some inverter manufacturers have special “sinus” filters which should eliminate the problem, but the manufacturer must be consulted.
• For each start of one compressor, all others have to be stopped (thus reducing overall efficiency), and contactors are necessary.

Compound systems of 2 or 3 Orbit scroll compressors utilizing BAHT

Due to the pressure difference necessary to achieve oil distribution, the variable speed options are limited to speeds that will achieve the pressure differentials for proper functioning of the oil management system.

Relevant parameters for possible combinations of Orbit compressors are:

• supply frequency in the local power grid (50 or 60 Hz)
• number of compressors in the compound (2 or 3)
• how many compressors in the compound are equipped with a frequency inverter
• which compressor is equipped with the frequency inverter (to identify the mounting position, refer to the respective compound assembly drawings - please contact Bitzer)

After selecting the compressors in the Bitzer Software according to the required refrigerating capacity, possible combinations of fixed and variable speed drives can be checked in the following tables.

For parallel operation of GSU, GED, GSP and ESH7 scroll compressors, please contact BITZER.