R404a refrigerant replacement R22 needs to consider these issues
The most widely used refrigerant in the domestic refrigeration industry is still R22. However, due to its destruction of the ozone layer and high greenhouse effect, China has determined that its use will be eliminated before 2030 according to the relevant international agreement. Therefore, more and more refrigerated refrigeration equipment is using R22's replacement R404a, although R404A and R22 have similar refrigeration performance, but in actual use, there are still many differences between the two to be noted. Refrigerant R404a instead of R22 need to consider the following issues.
1. The biggest problem of using R404A instead of R22 is lubricating oil. PVE ester oil must be used to replace R22 mineral lubricating oil. Ester lubricants have high affinity for water and poor dehydration, so try to avoid contact with the outside air in use. After the container is opened, it should be used as soon as possible, and it should be sealed and stored after use; away from oxidants, strong alkalis, and strong acids. Store in a well-ventilated place; avoid contact with skin and eyes when using, and avoid inhaling its vapor and spray.
2. The exhaust pressure of R404A refrigerant is about 1.2 times that of R22, and the mass flow rate 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% ~ 30% higher than that of R22.
The saturation pressure of R404A and R22 is different at the same temperature, so the action mechanism of R404A thermal expansion valve is different from R22. At the same time, due to the different solubility of R404A refrigerant and lubricating oil to the sealing material, the sealing material of the expansion valve should be changed accordingly. Therefore, the R404A special expansion valve should be selected in the selection of the thermal expansion valve.
Since the saturation pressure of R404A is higher than that of R22, the design pressure of the pressure vessel in the system should be changed to ensure safety. Such as reservoir and gas-liquid separator. At the same time, the set value of safety valve and fusible plug installed on the system accessories should also be changed. Since the gas density of R404A is about 50% higher than that of R22 under the condition of the same exhaust gas volume, the pipe diameter selected is larger than that of R22 when the R404A refrigerant is used for piping design.
5. For the same compressor, the current of R404A is greater than R22, so the wire diameter of AC contactor, thermal relay and cable of 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 should be greater than R22. At the same time, the vacuum degree of the system is higher than R22, and the water content is lower than R22. Refrigerant should be charged in liquid form to prevent the configuration of R404A from changing.
7. R404A is a non-azeotropic mixture. The component concentration of non-azeotropic mixture changes with temperature and pressure, which brings certain difficulties to the production, debugging and maintenance of the refrigeration system, and also has a certain impact on the heat transfer performance of the system. 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, it is also possible to achieve the design cooling effect, otherwise it will get worse and worse.
8, due to the compatibility of R404A refrigerant and lubricating oil itself and water is very good, so the system for moisture and residue, cleanliness and other requirements have improved compared with R22 refrigerant, R404A system moisture control and impurity control is a more important indicator, the system of the corresponding filter device to be changed.