Screw Type or Reciprocating Type
November 12, 2015
There is no simple answer to the constantly recurring question of whether it is best to use screw compressors or reciprocating compressors. Both types are viable alternatives in virtually all applications, and both types are normally capable of doing the job.
• capacity required
Larger screw compressors use less energy, whereas reciprocating compressors are most energy-efficient at capacities less than approx. 1200 kW.
• operating conditions
Screw compressors and reciprocating compressors differ greatly in efficiency when not operating at or near their design conditions.
Screw compressors are significantly less energy-efficient under off-design conditions, especially if they have a fixed internal volume ratio. Screw compressors with variable volume ratio are therefore more efficient.
• part-load requirements
If a compressor is to run at part load much of the time, reciprocating compressors are significantly more efficient.
• energy consumption
In smaller plants operating at evaporating temperatures of
-10°C or higher, single stage reciprocating compressors will have lower power consumption than screw compressors. In larger plants, the opposite is the case.
In applications that operate at lower temperatures, a two-stage installation is the best choice. Power consumption for such a two-stage unit is about the same for both compressor types, depending on plant size.
• temperature levels
In air conditioning and other “high-temperature” applications, reciprocating compressors normally use 5–15% less energy than small screw compressors.
Screw compressors working at lower temperatures, and in larger-size installations, use less energy than the corresponding reciprocating compressors.
• refrigerant to be used
The refrigerant usually only directly influences decisions about compressor type when high-pressure refrigerants such as R410A and R744 (CO2) are to be used.
In such cases, reciprocating compressors have significantly lower energy consumption.
• ease of maintenance
Reciprocating compressors have many moving parts compared to screw compressors, which means that more maintenance is needed. However, this maintenance work is relatively simple and can always be done on site.
With screw compressors, on the other hand, replacements and main overhauls usually mean that the entire compressor has to be sent back to the factory.
• financial resources
In smaller plants where one or two reciprocating compressors can handle the requirements, these are normally the cheapest solution.
The opposite is normally the case in larger plants. One or two screw compressors are normally cheaper than six to eight reciprocating compressors.
• available space
Screw compressors are much more compact than reciprocating compressors, especially at larger capacities.
One single screw compressor with double the capacity can normally replace at least two ”recips”.