The tips for Refrigerant R404a replaces R22 needs to be considered
Recently, the most widely used in China is still R22 refrigerant. However, due to its destruction of the ozone layer and high greenhouse effect, China has decided to phase out its use by 2030 according to relevant international agreements. Many domestic refrigeration product manufacturers have taken precautions and have begun to gradually accept and use the refrigerant gas R22 alternative R404A.
Wait for HFC green refrigerant. Although R404A and R22 have similar cooling performance, in actual use, there are still many differences between the two. In order to help everyone better use HFC green refrigerant, some problems that need to be paid attention to in the use of R404A refrigerant in the piston compressor refrigeration system are briefly explained.
1. The biggest problem with using R404A instead of R22 is the problem of lubricating oil. It is necessary to use PVE ester oil instead of mineral oil for R22. Ester lubricating oil has high affinity with water and poor dehydration. Therefore, it should avoid contact with outside air during use. After container is opened, it should be used as soon as possible. It should be sealed and stored after use. Keep away from oxidant, strong alkali and strong acid. Store in a well ventilated place; avoid contact with skin and eyes when in use, and avoid inhalation of vapors and sprays.
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. In general, the heat transfer capacity of the condenser is increased by 20% to 30% compared to R22.
3. 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 that of R22. At the same time, because the R404A refrigerant and lubricating oil have different compatibility with the sealing material, the expansion valve sealing material should also be changed accordingly. Therefore, the R404A special expansion valve should be selected in the selection of the thermal expansion valve.
4. Since the saturation pressure of R404A is higher than R22, the design pressure of the pressure vessel in the system should be changed to ensure safety. Such as liquid storage and gas-liquid separators. At the same time, the safety valve and fusible plug setting values installed on the system components will also change. Since the gas density of R404A is about 50% larger than that of R22 under the same exhaust gas amount, the pipe diameter selected is larger than R22 when piping design using R404A refrigerant.
5. For the same compressor, the current using R404A is greater than R22, so the wire diameter of the AC contactor, thermal relay and cable of the compressor should be adjusted. In terms of system protection, the high pressure switch setting is adjusted from the original 2.45 MPa to 2.7 MPa.
6. Since the saturation pressure of 404A is different from that of R22, the air tightness test pressure is 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. The refrigerant should be charged in liquid form during charging to prevent changes in the R404A configuration.
7. R404A is a non-azeotropic mixture. The concentration of non-azeotropic mixture changes with temperature and pressure. This brings certain difficulties to the production, debugging and maintenance of the refrigeration system. The effect, 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 also achieve the design cooling effect, otherwise it will get worse.
Since the R404A refrigerant and the lubricating oil itself have good compatibility with water, the requirements for moisture, residue, cleanliness, etc. of the system are improved compared with the R22 refrigerant. The moisture control and impurity control of the R404A system is one. The more important indicators, the corresponding filter devices in the system, etc. are subject to change.