At present, R22 is still widely used in domestic refrigeration industry. However, due to its damage to the ozone layer and high greenhouse effect, China has decided to phase out its use before 2010 according to relevant international agreements. Many domestic manufacturers of refrigeration products have begun to accept and use HFC green refrigerants, such as R404A, as the substitute of R22. Although R404A and R22 have similar refrigeration performance, there are still many differences between them in practical use. In order to help you better use HFC green refrigerant, this paper briefly analyzes and expounds some problems that should be paid attention to when using R404A refrigerant in the refrigeration system of piston compressor.

1. The major problem of using R404A to replace R22 is lubricating oil. PVE ester oil must be used to replace R22 mineral lubricating oil. Ester lubricants and water are of high affinity and poor dehydration, so they should avoid contact with the outside air as far as possible. After opening, they should be used as soon as possible and sealed after use. Keep away from oxidizing agents, strong bases and strong acids, and keep them in good ventilation. When using, avoid touching skin and eyes, and avoid inhaling steam and spray.

2. The exhaust pressure of R404A refrigerant is about 1.2 times of R22, and the mass flow rate is about 1.5 times of R22. Generally speaking, the heat transfer capacity of condenser is increased by 20% - 30% compared with R22.

3. At the same temperature, the saturation pressure of R404A and R22 is different, so the action mechanism of R404A thermal expansion valve is different from that of R22. At the same time, due to the different solubility of R404A refrigerant and lubricating oil to sealing material, the sealing material of expansion valve should be changed accordingly. Therefore, R404A special expansion valve should be selected in the selection of thermal 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 liquid reservoir and gas-liquid separator. At the same time, the setting value of safety valve and fusible plug installed on the system accessories should be changed accordingly. Because the gas density of R404A is about 50% higher than that of R22 under the condition of the same displacement, the pipe diameter of R404A should be larger than that of 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 AC contactor, thermal relay and cable of compressor should be adjusted. In the aspect of system protection, the setting value of high pressure switch is adjusted from 2.45mpa to 2.7mpa.

6. Because the saturation pressure of 404a is different from 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 to prevent R404A configuration change.

7. R404A is a non azeotropic working fluid. The composition concentration of the non azeotropic mixture changes with temperature and pressure, which brings certain difficulties to the production, commissioning 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 refrigerant of the system needs to be completely drained and replaced, so as to ensure the proportion of the mixed components and achieve the designed refrigeration effect, otherwise it will be worse and worse. Since R404A refrigerant and lubricating oil have good compatibility with water, the requirements for moisture, residue and cleanliness of the system are higher than those of R22 refrigerant. The moisture control and impurity control of R404A system is an important index, and the corresponding filter device in the system should be changed.