Different industries have different requirements for industrial chiller refrigeration temperature, so the choice of refrigerant is also different. In generally, refrigerant types mainly include R12, R134, R600, R152/R22, R410A, R404, R23, etc. Several years ago, many manufacturers use Freon as refrigerant. However, with the continuous development of environment protection, the environmentally unfriendly refrigerant R22 has been abandoned and environment-friendly refrigerants such as R404 and R23 have been used. During the replacement process, the following points need to be noticed.
As the saturation pressure of R404A is higher than that of R22, the design pressure of pressure vessel in the system should be changed, such as liquid reservoir and gas liquid separator, to ensure safety. The action structure of R404A thermal expansion value is different from that of R22 due to different saturation pressure at the same temperature. The solubility of R404A refrigerant and lubricating oil are different for the sealing material, so the sealing material of the expansion valve will be changed accordingly. Therefore, R404A special expansion valve should be selected.
The gas density of R404A is about 50% higher than that of R22 under the same discharge volume. The exhaust pressure of R404A refrigerant is about 1.2 times that of R22, and the mass flow rate is about 1.5 times that of R22. as a result, the exhaust velocity and resistance increases. In generally, the heat exchange capacity of R404A condenser is 20% ~30% higher than that of R22. Therefore, when using R404A refrigerant for piping design, the selected pipe diameter should be large than that of R22.
When using the same compressor, the current using R404A is grater than R22. therefore, the compressor AC contactor, thermal relay and cable diameter need to be adjusted. In terms of system protection, the setting value of the high-pressure switch is adjusted from the original 2.45 Mpa to 2.7 Mpa.
Refrigerant R404A is a non-azeotropic mixing medium. The composition concentration of non-azeotropic varies with temperature and pressure. This brings some difficulties to the production, commissioning and maintenance of refrigeration system, and also affect the thermal conductivity of the system. Especially, when the refrigerant leakage occurs, the system refrigerant needs to be completely drained and replaced, so as to ensure the proportion of each mixed component and achieve the refrigeration design effect. Otherwise it is going to get worse and worse.
Environmental protection refrigerant is different from CFCS. Its advantage is that it has zero potential to destroy ozone layer. It is green and environmental protection, is one of the current choice of refrigerants. On the other hand, the refrigerant has small molecules, light molecular weight, strong permeability, and is easy to absorb water, and does not dissolve with mineral oil. Therefore, the refrigeration dose requires higher cleanliness of circulate chiller equipment. Thus, the adoption of fully closed circulation pipeline can reduce the occurrence of refrigerant leakage, improve the operation efficiency of circulating water refrigeration equipment, and reduce the cost of enterprises.