These issues need to be considered when R404a refrigerant replaces R22 in cold storage refrigerators

　　【】The most widely used refrigerant in the domestic refrigeration industry is still R22, but due to its destruction of the ozone layer and high greenhouse effect, my country has determined that it will be phased out before 2030 according to relevant international agreements. Therefore, more and more refrigeration and refrigeration equipment are using R404a, a substitute for R22. Although R404A and R22 have similar refrigeration performance, in actual use, there are still many differences between the two that must be noted.

　　 Refrigerant R404a to replace R22 needs to consider the following issues:

　　1. The biggest problem of using R404A to replace R22 is the problem of lubricating oil. PVE ester oil must be used to replace R22 mineral lubricating oil. . Ester lubricating oil has high affinity with water and poor dehydration, so you should avoid contact with outside air as much as possible during use. After opening the container, use it as soon as possible. After use, it must be sealed and stored; stay away from oxidants, strong alkalis, and strong acids. Store in a well-ventilated place; avoid contact with skin and eyes, and avoid inhalation of vapor and spray.

　　2, the exhaust pressure of R404A refrigerant is about 1.2 times that of R22, and the mass flow is about 1.5 times that of R22. The exhaust flow rate increases and the resistance increases. Generally speaking, the heat exchange capacity of the condenser is 20% to 30% larger than that of R22.

　　3. The saturation pressures of R404A and R22 are different at the same temperature, so the operating mechanism of the R404A thermal expansion valve is different from that of R22. At the same time, due to the different compatibility of R404A refrigerant and lubricating oil to the sealing material, the expansion valve sealing material should be changed accordingly. Therefore, R404A special expansion valve should be used in the selection of thermal expansion valve.

　　4. Since the saturation pressure of R404A is higher than that of R22, the design pressure of the pressure vessel in the system must be changed to ensure safety. Such as accumulators and gas-liquid separators. At the same time, the safety valves and fusible plugs installed on the system accessories should also be changed accordingly. Since the gas density of R404A is about 50% greater than that of R22 under the same displacement, the pipe diameter should be larger than R22 when using R404A refrigerant for piping design.

　　5. For the same compressor, the current of R404A is greater than R22, so the diameter of the AC contactor, thermal relay and cable of the compressor should be adjusted. In terms of system protection, the setting value of the high-pressure pressure switch is adjusted from the original 2.45MPa to 2.7MPa.

　　6. Since the saturation pressure of 404A is different from R22, the air tightness test pressure is greater than R22. At the same time, the vacuum of the system is higher than R22, and the water content is lower than R22. When charging the refrigerant, it must be charged in a liquid form to prevent the configuration of R404A from changing.

　　7. R404A is a non-azeotropic mixture. The component concentration of the non-azeotropic mixture changes with temperature and pressure. This brings certain difficulties to the production, debugging and maintenance of the refrigeration system. The heat transfer performance of the system will also have a certain impact, especially when the refrigerant leaks, the system refrigerant needs to be completely emptied and replaced, so as to ensure the proportion of each mixed component and achieve the designed refrigeration effect, otherwise it will get worse. .

　　 8. Because R404A refrigerant and lubricating oil itself have good compatibility with water, the requirements of the system for moisture and residues, cleanliness, etc., are improved compared with R22 refrigerant. R404A system moisture control and impurity control is a relatively important indicator, and the corresponding filtering device in the system needs to be changed.