One of the most important steps of industrial chillers before leaving the factory-debugging, many small partners will encounter a problem during actual commissioning and maintenance, that is, the problem of refrigerant charge, how to accurately charge refrigerant for novices It's a big problem; but experienced masters have their own methods to judge;
Common judgment methods are as follows:
1. Touch the suction pipe and exhaust pipe with your hands to sense the heat and coldness of the copper pipe;
2. Observe the bubbles in the sight glass;
3. Measure high and low pressure
4. Measure the current of the compressor
5. Calculate the superheat
6. Calculate the degree of supercooling
7. Measure the temperature difference between the inlet and outlet air of the condensing coil and evaporating coil
8. Observe the condensation on the suction pipe
9. Weighing and filling
The following editor will elaborate one by one, the above method to determine the amount of charge, where is the problem? What factors need to be considered:
1. Perceive the hot and cold of copper pipe
Considerations:
1) How to know the temperature is the best state
2). The temperature perceived by the human body is 37 ℃ or higher (the highest skin feel is 49 ℃)
3) The exhaust temperature of 49 ℃ is not the best state
Elaborate:
Everyone feels different about hot and cold. If you have calluses on your hands, then the temperature you feel is higher than the actual temperature. Usually the human body feels hot for temperatures above 37°C and cold for temperatures below 37°C.
The temperature limit that the skin perceives is 49°C, so the temperature of the liquid tube that your hand perceives is not necessarily a good condensation temperature.
in conclusion:
This method only tells you that the compressor is running.
2. Observe the bubbles in the sight glass
Considerations:
1), gas boiling
2), the pressure drop of the liquid pipe is too large
3) No overcooling
Elaborate:
This does indicate that the presence of air bubbles indicates the lack of refrigerant, but the pressure loss of the liquid pipe can also cause air bubbles. If the pressure loss of the liquid pipe is large, the liquid refrigerant will flash into gas, and the flashing gas will reduce the flow of refrigerant when flowing through the expansion valve and will erode the expansion valve. If the supercooling of the system is small, the pressure loss can easily produce bubbles seen in the sight glass.
If you see that the bubbles in the sight glass are caused by the pressure loss rather than the lack of refrigerant, then you continue to add refrigerant to eliminate the bubbles, you will find that the high pressure rises and causes a jump.
in conclusion:
This method cannot correctly judge the refrigerant injection volume of the system
3. Measuring high and low pressure
Considerations:
1) Dirty condenser coil
2) Dirty evaporation coil
3) Dirty filter
4) The speed of the evaporator fan is incorrect
5) Incorrect condenser fan blades
Elaborate:
Unsatisfactory condensing air volume and evaporating air volume will affect the refrigerant pressure tested. If the condensing air volume is insufficient
The high pressure will be very high. If the evaporative air volume of the expansion valve system is insufficient, the low pressure will be very low.
Before you test the pressure of the air conditioning system, you must confirm that the condensing air volume and the evaporating air volume are satisfied. The finned coil and filter screen must be clean and the fan speed is correct; check that the fan blades are not deformed or damaged, and they are correctly installed on the shaft.
4. Measure the current of the compressor
Considerations:
1) Inject cold Freon in cold weather
2) Injecting Freon on hot days
3) The cleanliness and dirtiness of the coil
4) Dirty filter
5), wear of motor bearings
6) The main power supply voltage is too low
7) The main power supply voltage is too high
Elaborate:
The current tested is different in different situations. For example, the current is affected by the voltage value of the main power supply, and the deviation of the voltage value causes the deviation of the current. The current is also affected by the lubrication of the motor bearings, hot and cold weather.
5. Calculate the superheat
Considerations:
Capillary system
1), hot days
2) Cold weather
3) Latent heat load
Expansion valve system
Too much liquid in the condenser
Elaborate:
The superheat degree is calculated by measuring the suction temperature and pressure value of the suction pipe on the evaporator, and the pressure value is converted into the temperature value minus the suction temperature value, which is the superheat degree.
For capillary systems, measuring the correct capillary flow depends on pressure and resistance. If in order to ensure the correct superheat injection system on cold days, excessive refrigerant will appear in the system on hot days. For the capillary system with maximum heat load, more refrigerant will be added. Since the maximum heat load is imaginary, it will reduce the area of the condenser and increase the high pressure.
For the expansion valve system, it will be easy to overfill. Because the expansion valve will automatically open and close, excessive or insufficient refrigerant flow through the coil will maintain the constant superheat. If this point is recognized, it will cause the condenser More refrigerant accumulates inside, causing high pressure to rise, the current is too large, and the compressor wears out.
6. Calculate the degree of subcooling
Attention factors:
1) What is the degree of supercooling
2) Winter season
3) Summer season
4) How much pressure drop
Elaborate:
The supercooling degree is calculated by measuring the liquid temperature and pressure values on the liquid pipe, and the pressure value is converted into the temperature value minus the liquid temperature difference, which is the supercooling degree. Because the degree of supercooling is equivalent to the degree of condensation of the refrigerant liquid in the condenser. If the liquid condenses too well, reduce the area of the condenser. In this way, the high voltage increases and the current is excessive. If the supercooling is low or does not exist, you can see bubbles caused by the pressure drop of the liquid tube in the sight glass. The supercooling degree of the expansion valve system is 8~12℃.
Note: The degree of supercooling only represents the condensation effect.
7. Air temperature difference
Measure the temperature difference between the inlet and outlet of the condensing coil and evaporating coil
Considerations:
1) What is the correct temperature difference of the condenser
2) What is the correct temperature difference of the evaporator
3), high latent heat load environment
4), the correct evaporator fan speed
5), the cleanliness of the filter
6) Static pressure of air duct system
7) Cleanliness of the condenser
Elaborate:
We take the air-cooled unit as an example:
The design temperature difference of the air-cooled air-cooled condenser is 16.7℃, and the design temperature difference of the evaporator is 11.1℃. Under high latent heat load, the △t of the evaporator will decrease. , This will be detrimental to the operation of the compressor.
Since the air volume will affect △t, it is necessary to determine the correct air volume of the condenser and evaporator before measuring and calculating △t. Frequently used measuring tools such as pressure gauges, anemometers, and fan curves. △t value is just a signal value of injection
8. Condensation on the suction pipe
Considerations:
1) Expansion valve system
2). Capillary system
3) Air flow
4), condensation point
5), high load
6) Insufficient injection volume
Elaborate:
For the capillary system when injecting refrigerant, the condensation of the suction pipe will be observed. This injection method depends on the refrigerant liquid flow rate of the capillary and the pressure difference between the two ends. The heat transfer effect of the evaporator can be fully exerted only when the capillary tube is operated under the design conditions.
If the evaporator air volume is normal, it is found that the refrigerant flows through the evaporator according to the load change, preventing the formation of frost tubes. If the load is reduced, the liquid refrigerant will flow through the evaporator and enter the suction pipe, and the water vapor in the surrounding air will condense on the copper pipe. If there is enough liquid refrigerant, dew exposure will occur. However, when this method is used in a thermal expansion valve system, it will be found that the production of the dew tube does not indicate the amount of refrigerant injection (even if an excessive amount of refrigerant is injected), because the expansion valve automatically adjusts the temperature.
9. Weighing and filling
Weighing and filling method is really the correct method, it is suitable for any refrigeration system.
The method is to weigh the refrigerant charged, and all that is required is to find out the amount or range of refrigerant that should be charged from the relevant data. This is not just a method of observation, but a true method of filling. As long as the manufacturer indicates the correct filling amount of the water-cooled cabinet or split machine on the nameplate, after the system is completely dried and evacuated, a rod scale, electronic scale, dial scale or other weighing device can be used for weighing and filling Note.