Why do Low-temperature Cold Storage Use More R404 Refrigerant?

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Compared with our commonly used R22 refrigerant, we often use R404A refrigerant in refrigerated low-temperature warehouses.

Our common R22 refrigerant is pure difluoro-monochloromethane, a single-component refrigerant, which can be either gaseous or liquid when charged with fluorine. Non-environmentally friendly refrigerants have been phased out in developed countries in Europe and the United States.

The R404A refrigerant is a mixed refrigerant, which is generally filled with fluorine in a liquid state. It is an environmentally friendly refrigerant and is used in conjunction with POE lubricating oil.

Why is R404A refrigerant commonly used in low-temperature cold storage?

The latent heat of R404A refrigerant is larger than that of R22, the thermal efficiency and cooling efficiency are high, and the circulation volume of the system is small, so the refrigerant filling amount is also less than that of R22, and the cooling speed is faster than that of R22.

Some people think that the evaporating temperature of R404A refrigerant is lower, in fact, this is wrong. Evaporation temperature is the temperature at which the heat in the evaporator boils. It can only be said that the corresponding temperature of R404A refrigerant under a certain pressure is lower than that of R22.

In addition, the differences between R22 and R404A are as follows:

1. The R404A refrigerant and lubricating oil have good compatibility with water. Therefore, the system’s requirements for moisture, residues, cleanliness, etc. are higher than those of the R22 refrigerant. The moisture control and impurity control of the R404A system are relatively important indicators, the corresponding filter device in the system needs to be changed.

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 pressure of R404A and R22 are different at the same temperature, so the action mechanism of 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 with sealing materials, the sealing material of the expansion valve should be changed accordingly. Therefore, the R404A special expansion valve should be selected for the 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 should be changed to ensure safety. Such as accumulators and gas-liquid separators. At the same time, the safety valve and fusible plug setting value installed on the system accessories should also be changed accordingly. Since the gas density of R404A is about 50% larger than that of R22 under the same exhaust volume, when using R404A refrigerant for piping design, the selected pipe diameter is larger than that of R22.

5. The current of the same compressor using R404A is greater than that of 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 that of R22, the air tightness test pressure is greater than that of R22. At the same time, the vacuum degree of the system should be higher than R22, and the water content should be lower than R22. When charging the refrigerant, it should be charged in liquid form to prevent the configuration of R404A from changing.

7. R404A is a non-azeotropic mixed working medium. The composition concentration of the non-azeotropic mixture changes with the temperature and pressure, which brings certain difficulties to the production, debugging, and maintenance of the refrigeration system, and also has certain effects on the thermal conductivity of the system. 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 cooling effect, otherwise it will get worse.

8) The biggest problem when using R404A to replace R22 is the lubricating oil problem. PVE ester oil must be used to replace the mineral lubricating oil for R22. Ester lubricating oil has a high affinity with water and poor dehydration, so try to avoid contact with outside air during use. After opening the container, it should be used as soon as possible. After use, it must be sealed and stored, away from oxidants, strong alkalis, and strong acids, and stored in a well-ventilated place. Avoid contact with skin and eyes during use, and avoid inhalation of its vapors and sprays.


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