R22 refrigerant characteristics and advantages
R22 (chemical name: difluoromonochloromethane, also known as HCFC-22) is a hydrochlorofluorocarbon refrigerant that was once widely used. It is used as a heat transfer medium in air-conditioning systems and refrigeration equipment, and is favored for its good thermodynamic properties, relatively low cost, and good compatibility with a variety of commonly used refrigeration system materials.
Efficient refrigeration: R22 has a high refrigeration capacity and latent heat of evaporation, can provide a strong refrigeration effect at a relatively low temperature, and is suitable for a variety of refrigeration needs.
Chemical stability: It shows good chemical stability in the refrigeration cycle, is not easy to decompose or deteriorate, and is suitable for long-term stable operation.
Cost-effectiveness: Due to its high production technology and market maturity, the price of R22 is relatively economical, and for some large refrigeration units, the cost per unit of refrigeration capacity is low.
Destruction of the ozone layer: R22 contains chlorine, which has a certain destructive effect on the atmospheric ozone layer, so it is being gradually phased out in developed countries2.
High Global Warming Potential (GWP): Although the ODP value is relatively low, R22 is still a potent greenhouse gas with a GWP value of 1810℃.
Characteristics and advantages of R404A refrigerant
R404A is a chlorine-free hydrofluorocarbon (HFC) mixed refrigerant, which is a mixture of three components R125, R143a and R134a in a specific proportion. It is widely used in commercial refrigeration systems, such as supermarket freezers, refrigerated transportation, etc., and is popular for its excellent low-temperature performance, high energy efficiency ratio and good compatibility with mineral oil and synthetic ester lubricants.
ODP value is 0: R404A is a chlorine-free non-azeotropic mixed refrigerant with an ODP value of 0, which will not damage the atmospheric ozone layer and meet the requirements of international environmental protection agreements.
High refrigeration efficiency: Compared with R22, R404A can provide higher refrigeration efficiency, especially in medium and low temperature refrigeration systems. For example, it can reduce the temperature of a space or object faster, and the system has a smaller circulation volume and less filling volume.
Strong compatibility: R404A is well compatible with materials in modern refrigeration systems, including certain types of seals and lubricants. However, it should be noted that it requires the use of POE ester oil rather than mineral oil as a lubricant, because this type of lubricant has a good affinity with water, which helps to improve the cleanliness of the system.
Increased system design complexity: Since the working pressure of R404A is higher than that of R22, there are many factors such as the pressure vessel, pipe size and electrical component selection of the entire system.
Maintenance difficulty caused by non-azeotropic properties: As a non-azeotropic mixture, the composition ratio of R404A will change with temperature and pressure, which puts higher requirements on the commissioning and maintenance of the system. If a leak occurs, the refrigerant in the system needs to be completely emptied and refilled to ensure the correct ratio of each component.
The main difference between the two refrigerants and their systems:
R404A refrigerant and its supporting lubricant have good water solubility. This means that compared with systems using R22, systems using R404A have higher requirements for moisture, residues and overall cleanliness. In order to ensure the efficient operation of the system and extend its service life, it is necessary to strengthen the control of moisture and impurities, and adjust components such as filtration devices accordingly to meet more stringent cleaning standards.
When comparing the two, it can be found that the exhaust pressure of R404A is about 1.2 times that of R22, while the mass flow rate is about 1.5 times. This shows that under the same conditions, the use of R404A will result in a larger exhaust flow rate and resistance. Therefore, for the condenser, its heat exchange capacity needs to be increased by 20% to 30% compared with the R22 system to adapt to the higher workload.
Due to the difference in saturation pressure between R404A and R22 at the same temperature, the action mechanism of the thermal expansion valve required by them is also different1. In addition, considering the different compatibility of R404A refrigerant and its lubricating oil with sealing materials, the sealing material of the expansion valve also needs to be changed accordingly. To ensure optimal performance, an expansion valve designed for R404A should be selected.
Given that the saturation pressure of the R404A system is higher than that of R22, all involved pressure vessels such as liquid receivers, gas-liquid separators, etc. must be able to withstand higher pressures. At the same time, the setting values of the safety valve and fusible plug should also be adjusted appropriately according to the new pressure level. In addition, considering that the gas density has increased by about 50%, a larger diameter pipe should be used in the piping design to ensure sufficient circulation space.
When using the same model compressor, the current consumed by the R404A system will be slightly greater than that of the R22 system. Therefore, related electrical components such as AC contactors, thermal relays and cable diameters need to be re-evaluated and may need to be replaced with larger specifications to ensure safe and reliable operation. In addition, the setting value of the high-pressure pressure switch has been increased from the original 2.45MPa to 2.7MPa to adapt to the higher working pressure environment.
Air tightness and vacuum standards: The air tightness test pressure of the R404A system should exceed the requirements of R22, and the vacuum of the entire system should also be maintained at a lower level to reduce the water content. It is worth noting that the refrigerant should be charged in liquid form to prevent problems caused by changes in the mixing ratio.
As a non-azeotropic mixture, R404A is composed of different components, and the proportions of these components will change with changes in temperature and pressure. This characteristic brings additional complexity to the production and maintenance of refrigeration systems, especially when dealing with leaks. It is usually recommended to completely drain and refill the refrigerant in the system to maintain the correct component ratio and ensure the expected cooling effect.
Lubricant compatibility: Last but not least, the R404A system cannot continue to use traditional mineral-based lubricants, but needs to be used with PVE ester oils. Although this type of lubricant has a good affinity with water, it is not easy to dehydrate, so special attention should be paid to avoid exposure to air or contact with other chemicals during storage and use. In addition, care should be taken to protect operators from potential hazards, such as avoiding direct contact of the skin and eyes with the lubricant and its vapor.
