Environmental Requirements For Compressors

With the development of industry, the pollution of the Earth is becoming increasingly serious, and environmental protection has become an important issue of global concern. Preventing the destruction of the atmospheric ozone layer and global climate change has attracted widespread attention from countries around the world, and has reached consensus among international governments, signing relevant agreements.
compressor
compressor
In the field of refrigeration and air conditioning, the destruction of the atmospheric ozone layer by CFCS and HCFCS, as well as global warming caused by energy consumption, are issues that should be highly valued in compressor design.
As is well known, the selection of refrigerants is one of the many factors that affect compressor design that should be highly valued.
In order to develop new compressors using alternative refrigerants, designers first encountered two issues:
Firstly, the compressor must redefine its working volume to meet the pressure requirements of different flow rates;
Secondly, the compatibility between various materials in contact with the refrigerant in the compressor, such as synthetic rubber and lubricating oil, must be addressed.
In past history, more than fifty substances have been used as refrigerants. After World War II, in addition to the use of ammonia in the range of large cooling capacity, almost all refrigeration and air conditioning fields were dominated by haloalkane CFCS and HCFCS. The CFCS substitution specified in the Montreal Protocol in 1974 has been realized in industrialized countries, while the HCFCS substitution plan will be completed in 2020; For developing countries, it will be discontinued in 2010 and 2040, respectively. However, in some developed countries, they are prepared to achieve it ahead of schedule. Figure 6 shows the application fields and potential substitutes of CFC-11, CFC-12, HCFC-22, and R502, which were previously commonly used in Europe (below the horizontal arrow line).
CFC-11
CFC-11 is a low-pressure refrigerant mainly used in centrifugal chillers, and its transition substitute is HCFC-123. In addition, HFC-245ca or HFC-245fa are also low-pressure refrigerants, but they have flammability. Therefore, their combustion reduction methods and toxicity need to be studied, and their use is not as efficient as CFC-11 and HCFC-123. Therefore, many enterprises have switched to using HFC-134a in centrifugal chillers.
CFC-12
Due to its wide range of applications and leakage issues in automotive air conditioning, CFC-12 is the first object to consider as a substitute. HFC-134a can be used as a substitute in household refrigerators and car air conditioners. HFC-134a has a cooling capacity and efficiency similar to CFC-12 in the medium to high temperature range. However, under operating conditions below -23 ℃, it loses its attractiveness due to its lower cooling capacity and efficiency compared to CFC-12. Although HFC-134a has a zero ODP value for ozone depletion potential, its GWP value for global warming is as high as 1300 (based on the GWP value of CO2), which in the long run will also affect its development and use.
HCFC-22
HCFC-22 has been widely used in commercial refrigeration, commercial and residential air conditioning, and heat pumps, with an ODP value much lower than that of CFC-11 and CFC-12, only 0.055. But its GWP value is quite high, about 1700. It is precisely for these reasons that some countries in Europe, such as Germany, are rapidly being phased out. There are already several mixed refrigerants as substitutes for HCFC-22. The American Refrigeration Association has recommended four types in its refrigerant replacement evaluation program (AREP): HFC-134a, R407C, R410A, and R410B. However, compared to the other three, HFC-134a has lower refrigeration capacity and pressure, and using it as a refrigerant requires a significant redesign of the system. Therefore, the possibility of using it as a substitute for HFCF-22 seems to be minimal, but the possibility of using it in larger chillers still exists. Non azeotropic refrigerant R407C is likely to be a "drop in" substitute for existing machines, as it is closest to HCFC-22. After replacement, minimal modifications are required to the system equipment, and acid lubricants are used to replace mineral oil. Attention should also be paid to adapting to the large temperature slip of the refrigerant (up to 5-7 ℃). Near azeotropic refrigerants R410A and R410B are two mixtures of the same HFCS, with the only difference being the mixing ratio. R410A is suitable for split type small air conditioners, but its evaporation pressure is about 1.5 times that of HCFC-22. Therefore, the system using this working fluid needs to be completely redesigned, so it is only used in new refrigeration and air conditioning systems. The optimized design of this system can increase its efficiency by 5%.
R502
R502 has been widely used in low-temperature refrigeration systems. AREP recommends two possible alternatives: R404A and R507. R404A has a cooling capacity and efficiency similar to R502, but it requires more testing of system components, especially compressors, when adopted. There is a component in the mixed component of R507 that plays a flame retardant role, which has similar performance to R502, but toxicity testing is still ongoing in the United States; But in Europe, it has been applied to supermarket refrigeration equipment.