Why do low-temperature cold storage use more R404 refrigerant?
Compared with our commonly used R22 refrigerant, we often use R404A refrigerant in refrigerated low-temperature storage, so why use relatively high-priced R404A refrigerant in low-temperature storage? I believe that after reading this article, you can explain clearly to customers from a professional perspective. Our common R22 refrigerant is pure difluorochloromethane, a single-component refrigerant. It can be filled with fluorine and can be gaseous or liquid. It is a non-environmentally friendly refrigerant. The developed countries in Europe and the United States have already phased out their use and use mineral oil.
The R404A refrigerant is a mixed refrigerant, generally filled with fluorine in a liquid state, is an environmentally friendly refrigerant, and is used in conjunction with POE lubricating oil.
Why, R404A refrigerant is 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 filling amount of refrigerant is also less than that of R22; the cooling speed is faster than R22. Some people think that the evaporation temperature of R404A refrigerant is lower. In fact, this is wrong. The evaporation temperature is the temperature when the heat in the evaporator boils. It can only be said that the corresponding temperature of R404A refrigerant at a certain pressure is lower than that of R22. In addition, the differences between R22 and R404A are as follows: 1) R404A refrigerant and lubricating oil have good compatibility with water. Therefore, the system has requirements for moisture, residues, and cleanliness compared with R22 refrigerant. Improved, R404A system moisture control and impurity control is a relatively important indicator, the corresponding filter device in the system must 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 pressures of R404A and R22 are different at the same temperature, so the operating 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 to the sealing material, the expansion valve sealing material must be changed accordingly. Therefore, the R404A special expansion valve should be used in the selection of 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 must be changed to ensure safety. Such as accumulators and gas-liquid separators. At the same time, the safety valves and fusible plugs installed on the system accessories will also be changed accordingly. Since the gas density of R404A is about 50% greater than that of R22 under the same displacement, the pipe diameter should be larger than 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 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 R22, the air tightness test pressure should be greater than 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 mixture working fluid. The component concentration of the non-azeotropic mixture changes with temperature and pressure. This brings certain difficulties to the production, debugging and maintenance of the refrigeration system, and also affects 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 and achieve the designed refrigeration effect, otherwise it will get worse.
8) The biggest problem of using R404A to replace R22 is the problem of lubricating oil. PVE ester oil must be used to replace R22 mineral lubricating oil. Ester lubricating oil has high affinity with water and poor dehydration, so you should avoid contact with outside air as much as possible during use. After opening the container, use it as soon as possible. After use, it must be sealed and stored; stay away from oxidants, strong alkalis, and strong acids. Store in a well-ventilated place; avoid contact with skin and eyes, and avoid inhalation of vapor and spray.
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