Introduction

In parallel compounding, several compressors are combined in a common refrigerant circuit. The systems are often complex and have special requirements, in particular with respect to oil return, oil distribution between compressors and system control. This is why this document includes important information for planning and execution. In addition, system-related criteria and special manufacturer specifications related to additional components (e.g. oil separators, oil level controllers) have to be taken into account, making it necessary to adjust design and accessories, if required.

Furthermore, the recognized technical rules and the current safety regulations must be observed.

Refrigerant

This document considers compound systems with HFC and HFO refrigerants and R744. For compound systems with R717 (NH₃), see Technical Information AT-640.

Advantages of parallel compounding

The aspects for or against parallel compounding are too different for a general evaluation ‒ however, there are a series of advantageous features:

• Optimum power adjustment to the demand, in particular in case of additional capacity control of the compressors (CRII system or frequency inverter)
• Low power supply load during start by stepwise switch-on of the compressors
• Upon failure of a compressor or frequency inverter, system operation can be initially maintained
• Easier and lower-cost pipe installation for widely branched systems compared with separate refrigerant circuits