Application limits for part load operation
When capacity control is used – i.e. in part load operation – the thermal load of the compressor increases due to
- reduced refrigerant mass flow,
- reduced motor cooling and
- electrical and mechanical losses.
This is why the application ranges for capacity controlled compressors are somewhat limited. If a compressor module is used, it monitors the relevant parameters such as motor temperature and thus the application limits.
The BITZER Software displays the application limits for residual capacities of, for example, 66%, 50%, 33% and 10% in diagram form. In addition, any operating point can be checked by query. The BITZER Software also provides average factors for power consumption at different residual capacities for the respective operating point.
Observe the information on discharge gas and operating temperatures as well as lubrication conditions in the operating instructions!
Additional cooling in part load operation
In part load, additional cooling is often necessary in a specific range. Two variants are possible here:
- Additional fan: Additional fans are available as an option for many compressor models. The compressor can also be installed in the air flow of the condenser. To achieve a cooling effect equivalent to that of an additional fan, the air velocity must be at least 3 m/s.
- Water cooled cylinder heads: Water cooling is also available as an alternative for the older compressor models 4Z-5.2 .. 4N-20.2 and for all open compressors. This requires special cylinder heads with water connections. They are fitted as standard on the ammonia version of the open drive compressors (W/A series).
Details on both variants:
- KT-140: Additional cooling for BITZER reciprocating compressors
In the case of air-cooled condensing units, the fans of the condensing units can be equipped with speed controllers. The air flow must then be regulated in such a way that the compressor is sufficiently cooled at all times, too.
Capacity control combined with refrigerant injection (RI)
The RI system is an operating function of the CM-RC-02 compressor module with extension board. It injects liquid refrigerant as required, thereby ensuring the thermal application limits for low temperature applications. Details:
- KT-242: Technical Information Extension board CM-IO-B for CM-RC-02