Why should the refrigerant be filled in liquid form? What are the filling methods?


1. Whether the refrigerant is added liquid or gas    Re […]

1. Whether the refrigerant is added liquid or gas
   Refrigerants can be divided into 3 categories: single working fluid refrigerant, non-azeotropic mixed refrigerant, and azeotropic mixed refrigerant.
  The composition of the single-working-substance refrigerant will not change regardless of whether it is gas or liquid, so it can be charged into gas when the refrigerant is charged.
  Although the composition of azeotropic refrigerant is different, because the boiling point is the same, the composition of the gas and liquid is also the same, so it can be filled with gas;
Non-azeotropic refrigerants have different boiling points, so liquid refrigerants and gaseous refrigerants are actually different in composition. At this time, if you add gas, it will inevitably lead to different refrigerant components, such as only a certain gaseous state. Refrigerant, so only liquid can be added.
In other words, non-azeotropic refrigerants must be added with liquid, and non-azeotropic refrigerants start with R4. This type of liquid must be added. Common non-azeotropic refrigerants are: R40, R401A, R403B, R404A, R406A , R407A, R407B, R407C, R408A, R409A, R410A, R41A.
   As for other common refrigerants, such as: R134a, R22, R23, R290, R32, R500, R600a, no matter how to add gas or liquid, it will not affect the composition of the refrigerant, so how easy it is to come.

2. Common refrigerant charging methods and drawbacks
   (1), observe the bubbles in the sight glass;
   (2), measure the high and low pressure;
  (3), measure the compressor current;
   (4), weighing and punching.
   We need to understand that if the refrigerant charge in the refrigeration system is too low, the cooling capacity will decrease, the input power will decrease, the EER will decrease, and the life of the equipment will be shortened. If the refrigerant is charged too much, the cooling capacity will decrease, the input power will increase, the EER will decrease, and the equipment life will be shortened.
   (1). Observe the bubbles in the sight glass:
   This method does show that there are bubbles that indicate a lack of refrigerant, but we must understand that the pressure loss of the liquid pipe can also cause bubbles. If the pressure loss of the liquid pipe is large, the liquid refrigerant will flash into a gas, and the flash gas will reduce the flow of the refrigerant when flowing through the expansion valve and will also corrode the expansion valve. If the subcooling of the system is small, the pressure loss can easily generate bubbles seen in the sight glass. Remember, if there is no liquid but steam, it will be transparent when seen in the sight glass.
   If the refrigeration engineer with experience or careful observation will find that when the system is charged correctly, bubbles or flashes can also be seen in the sight glass. This is because the resistance in the liquid pipe in front of the sight glass causes a pressure drop, causing the refrigerant to flash. If the expansion valve is unstable or fluctuates with liquid, the expansion valve opens sharply, and the flow rate increases to produce enough pressure drop to cause the outlet of the liquid reservoir to form a flash. The sudden change in condenser pressure is also the cause of flash.
   For example: suddenly changing the fan speed in a cold storage can easily change the condensing temperature from 5.5°C to 8°C. At this time, the liquid temperature in the liquid reservoir will be higher than the saturation temperature corresponding to the changed condensation pressure, and evaporation will occur at this time, and the evaporation will not end until the liquid temperature drops below the saturation temperature again.
   (2), measure the high and low pressure of the refrigeration system:
   This method is believed to be frequently used by many refrigeration practitioners. However, we should note that if the condensing air volume and the evaporating air volume are not satisfied, the test refrigerant pressure will be affected. If the condensing air volume is insufficient, the high pressure will be very high, and if the evaporating air volume of the expansion valve system is insufficient, the low pressure will be very low.
Therefore, we must understand that before testing the pressure of the air-conditioning system, we must confirm that the condensing air volume and the evaporation volume are sufficient, the fin coil and filter should be clean, and the fan speed should be correct; check that the fan blades are not deformed or damaged, and are correctly installed on the shaft. , Because these directly affect the judgment of refrigerant charge
   (3), measure the compressor current:
This method is also used more, but it should be noted that the current tested under different conditions is also different. For example, the current is affected by the voltage value of the main power supply, the deviation of the voltage value causes the current deviation, and the refrigerant is overcharged. Current changes, etc.
   Condensation on the suction pipe:
  If the air volume of the evaporator is normal, the refrigerant will flow through the evaporator according to the load change, preventing the formation of the frost pipe. If the load is reduced, the liquid refrigerant will flow through the evaporator, and when it enters the suction pipe, the water vapor in the surrounding air will condense on the copper pipe. If there is enough liquid refrigerant, tube exposure will occur. But in the thermal expansion valve refrigeration system, the occurrence of the exposed pipe does not mean that the amount of refrigerant injected is too much, because the expansion valve will automatically adjust the temperature. It can be seen that it is not scientific to observe the frosting of the suction pipe to determine the refrigerant charge.
   (4), weighing punch:
   weighing and filling method is the only true correct method, it is suitable for any refrigeration system. The method is to weigh the weight of the refrigerant charged, and what needs to be done is to find out the amount or range of refrigerant that should be charged from the relevant information. Especially when the hydrocarbon refrigerant (R290) is charged, it must be weighed strictly, because this directly affects the energy saving rate and effect of the system.
   This is not just an observation method, but a real filling method. As long as the manufacturer indicates the correct filling amount of the water-cooled cabinet or split machine on the nameplate, the system can be fully dried and evacuated, and then used for weighing and charging using a steel rod scale, electronic scale, dial scale or other weighing device Note. This method is the approved recommended filling method.

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