A BEGINNER’S GUIDE TO: COMPRESSORS
few compressors will actually wear out. However, if an issue occurs then there is an advantage in being able to disassemble screw and reciprocating compressors – the problem can be found and they can be repaired.
Mr Glass points out: “You can’t necessarily work out why a scroll compressor has failed, because you can’t normally get into it.”
Recycling
Scroll compressors are not designed to be repaired and are thus disposable, but due to the nature of their construction, both screw and reciprocating compressors can be recycled. This is where Bitzer’s Green Point comes in, remanufacturing compressors by replacing broken components with original manufacturer parts. Clearly there is some environmental benefit to this, too.
When choosing which compressor to use, Mr Glass recommends taking a ‘decision tree approach’. In addition to bearing in mind system size, application type and how much refrigeration is required, the type of refrigerant used should also be considered. There are two main types of refrigerants – synthetic and natural. Natural refrigerants include ammonia, hydrocarbons and R744 (CO2
). Combining
the system in question with the most appropriate refrigerant can have a tangible impact on that
system’s efficiency and its ability to function correctly.
Ammonia is aggressive to materials containing zinc and would not be used, for example, with a semi-hermetic compressor containing a motor. CO2
meanwhile, works at a much higher pressure. Mr Glass elaborates: “A conventional synthetic refrigeration system works at a maximum discharge pressure of 25-30 bar. A CO2
in the region of 90-100 bar discharge pressure.” Therefore with CO2
be appropriate. Indeed, when CO2
a scroll compressor would not refrigeration was
introduced, reciprocating compressors experienced a consequential surge in popularity, with Bitzer being the first company to work with CO2
in retail refrigeration.
There are safety considerations which should be heeded, too. While hydrocarbons are potentially flammable, CO2
can be explosive and ammonia is
toxic when released to the atmosphere. Training to work with both hydrocarbons and ammonia is a legal requirement under the F-Gas regulations. While this is not extended to CO2
, it is highly recommended.
Beyond choosing the most appropriate compressor and refrigerant to combine with a particular system, Mr Glass also views correct installation and commissioning as vitally important. “One can select the most efficient key components
system will be working
for a system, but poor installation or commissioning invariably end with problems, costing the owner money in energy and the installer in remedial work visits. This also goes for servicing. Poor service practice can actually make a well-performing system perform worse than it did before.” Regular maintenance is necessary to detect problems early, and is especially important for refrigeration systems. “The vapour compression process behind refrigeration and air conditioning systems is the same, but air conditioning systems have a lot more electronics and alarms attached to monitor for issues,” Mr Glass explains. Also beneficial is the logging of data in order to build a comprehensive life history of the plant, providing a useful reference point to aid in finding faults. While maintenance is essential in ensuring efficiency, technological advances are also increasingly significant. Looking to the future, Bitzer is pioneering intelligent operation with its IQ systems. These monitoring devices allow automatic optimisation, continually tuning the compressor to operate at the most efficient point.
Even as technology continues to improve, well- trained, skilled personnel remain indispensable. “Without them, the systems are designed and built well, but not installed correctly and not operated to the best possible level of efficiency.”
Fujitsu
www.acr-news.com
November 2017 31
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