Lesson 9 - Refrigeration Technology SAQ

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a)   What are the advantages and disadvantages of screw and reciprocating compressors?

b)   How would you make a choice between them?

Response:

a)   Advantages of screw compressors include:

• They have a simple structure and fewer moving parts than a reciprocating compressor, so they generally require less maintenance over longer intervals.

• They have small footprints.

• They are suitable for large loads.

• They can be operated with variable speed drives.

• Their outlet temperatures are lower than those for reciprocating compressors.

• They have low vibrations.

• They are resistant to damage caused by liquid entering the compressor.

Disadvantages of screw compressors are:

• They have lower efficiencies compared to reciprocating compressors at temperatures typically found in brewery applications.

• They are not viable for small loads.

Advantages of reciprocating compressors include:

• They have higher efficiencies compared to screw compressors (although this depends on their operation).

• They have less oil carry-over and thus simpler oil separation.

• They are more efficient when used for part loads.

• Their maintenance is simple and can be easily carried out in-house.

Disadvantages of reciprocating compressors are:

• They have high maintenance costs.

• They are very susceptible to damage if liquid enters them.

• They have high vibrations, and thus require civil structures that are capable of handling this.

• They have large footprints.

• They have higher gas outlet temperatures (although this could be considered an advantage, as heat energy can easily be recovered).

b)   The choice you make depends on the size of compressor required and the profile of refrigeration required. The efficiencies at the expected loads must be calculated, and you must compare the savings you make from this to the difference in maintenance cost. Other things for you to consider are space and civil structure capacity, as well as in-house maintenance expertise.