Recently, the widely used refrigerant in the domestic refrigeration industry is still R22, but due to its damage to the ozone layer and high greenhouse effect,
In accordance with relevant international agreements, China has decided to phase out its use by 2030.
Many domestic refrigeration product manufacturers have taken precautions and have begun to gradually accept and use HFC green environmentally friendly refrigerants such as R204 replacement R404A.
Although R404A and R22 have similar cooling performance,However, there are many differences between the two in practical use.
In order to help you better use HFC green refrigerant, this paper briefly analyzes some problems that need to be paid attention to when using R404A refrigerant in piston compressor refrigeration system.
1. The problem of 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 lubricants have a high affinity for water and a poor dehydrogenation. Therefore, it is advisable to avoid contact with the outside air as much as possible.
After the container is opened, it should be used as soon as possible. It should be sealed and stored after use. Keep away from oxidizing agent, strong alkali and strong acid. Keep it 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, the mass flow is about 1.5 times that of R22, the exhaust velocity increases and the resistance increases
Generally speaking, the heat transfer capacity of condenser is 20% ~ 30% larger than that of R22.
3. The saturation pressure of R404A and R22 is different at the same temperature, so the operating mechanism of R404A thermal expansion valve is different from that of R22
Meanwhile, because R404A refrigerant and lubricating oil have different solubility to the sealing material, the sealing material of expansion valve should also be changed accordingly
Therefore, in the choice of thermal expansion valve to choose R404A special expansion valve
4. Since the saturation pressure of R404A is higher than that of R22, the design pressure of pressure vessel in the system should be changed to ensure safety. Such as the reservoir and the gas-liquid separator
At the same time, the safety valve and fusible plug Settings 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 volume, the pipe diameter chosen is larger than R22 when using R404A refrigerant for piping design
5. For the same compressor, the current of R404A is greater than that of R22, so the ac contactor, thermal relay and cable diameter of the compressor should be adjusted
In terms of system protection, the setting value of high pressure switch was adjusted from 2.45mpa to 2.7mpa.
6. As the saturation pressure of 404A is different from that of R22, the pressure of air tightness test is greater than that of R22.
Meanwhile, the vacuum degree of the system is higher than that of R22, and the water content is lower than that of R22. The refrigerant should be filled in liquid form to prevent the change of R404A configuration
7.R404A is a non-azeotropic mixture. The composition concentration of the non-azeotropic mixture varies with temperature and pressure, which brings certain difficulties to the production, debugging and maintenance of the refrigeration system
The thermal conductivity of the system will also be affected, especially when refrigerant leakage.The system refrigerant needs to be completely drained and replaced, so as to ensure the proportion of each mixed component and achieve the designed refrigeration effect, otherwise it will get worse and worse
Since R404A refrigerant and lubricating oil themselves are well soluble with water, the system's requirements for water, residues, cleanliness and so on are improved compared with that of R22 refrigerant
The water control and impurities control of R404A system is a relatively important index. The corresponding filtration device in the system needs to be changed.