Operation Management and Common Faults of Central Air-conditioning Screw Chiller Units
Refrigeration equipment is a complex system composed of refrigerators, chillers, evaporators, expansion valves and many equipment accessories that are interconnected and affect each other. Therefore, once the refrigeration equipment fails, attention should not only be focused on a certain part, but a comprehensive inspection and comprehensive analysis of the entire system should be carried out. This requires the accumulation of practical experience and theoretical guidance. Through the summary of long-term practice, the operator has explored a lot of experience in fault inspection, and summarized it into a set of basic methods of "listening, touching, looking, and analyzing".
"One listen": listen to whether the sound of the compressor, expansion valve and other equipment in operation is normal;
"Two touches": touch the temperature and heat changes of relevant components and pipe connections in the system, and touch the cooling and heat conditions and vibration of the compressor;
"Three look": Look at the size of the high and low pressure values, the size of the oil pressure, and the size of the water pressure during operation. The size and price of the setting value of differential pressure relay, temperature relay and pressure relay. Look at the oil level and liquid level, look at the frost and condensation on the evaporator, return gas pipe and infusion pipe;
"Four Analysis": Use the relevant theories of refrigeration equipment to analyze and judge the phenomenon, find the cause of the accident, and eliminate it in a targeted manner.
1. The sign of the normal operation of the unit
When the refrigerator is started, you should first know whether the refrigeration system is operating normally. The following is a brief introduction to the normal content and signs:
1. The cooling water of the condenser should be sufficient, the water pressure should be above 0.12MPa, and the water temperature should not be too high. For screw refrigeration units, the reading of the oil pump pressure gauge should be 0.15~0.3MPa higher than the exhaust pressure.
2. Under any circumstances, the oil temperature should not exceed 70℃, and the minimum temperature should not be lower than 30℃. Under normal operating conditions, the lubricating oil should not foam (except for fluorine refrigerators).
3. The exhaust temperature R22 of the refrigerator does not exceed 125°C. If the excessively high exhaust temperature rises further, it will be extremely small with the flash point (160°C) of the refrigeration oil, which is unfavorable to the equipment. Therefore, from the point of view of use, the exhaust temperature should not be too high. When it is too high, the machine should be shut down to find out the reason. Different refrigeration forms have different requirements for temperature. For example, the exhaust temperature of a refrigerator working under air conditioning conditions is higher than that of a refrigerator working under standard conditions, which is normal.
4. The level of condensing pressure. It is mainly determined according to the water source, the structure of the condenser and the refrigerant used. Under normal circumstances, for water-cooled condensers, R22 and ammonia do not exceed 1.8MPa. In addition, when the condenser is first turned on, it is normal for the pressure to be higher in a short period of time due to the large load of the condenser.
5. The liquid level of the accumulator is not lower than one-third of the liquid level indicator, and the oil level of the crankcase is not lower than the horizontal centerline of the indicator window (if there are two oil level indicator windows, the oil should be in two between glass centerlines).
6. The automatic oil return pipe of the fluorine oil separator should be normal when it is cold and hot, and the cold and hot cycle is about 1h. There should be no significant temperature difference before and after the filter of the liquid pipeline. There can be no frosting, otherwise it is blocked. The fluorine refrigerator should be flat side cool and dry side hot. Each joint of the fluorine system should not seep oil, and oil seepage indicates fluorine leakage.
7. When the horizontal condenser is touched by hand during operation, the upper part should be hot and the lower part should be cool; the junction of cold and heat is the refrigerant liquid level, the oil separator is also hot in the upper part, and the lower part is not too hot, and the junction of cold and heat is the oil surface or liquid surface . The safety valve or bypass valve of the refrigerator should feel cold at the low-pressure end.
8. During operation, the steam pressure and the suction pressure should be similar, and the exhaust pressure at the high-pressure end is similar to the condensing pressure and the pressure of the liquid accumulator. If they are not similar, it is not normal.
9. Under a certain water flow, there should be a temperature difference between the cooling water and the cooling water. If there is no temperature difference or the temperature difference is very small, it means that the heat transfer surface of the heat exchange equipment is dirty and needs to be shut down for cleaning.
10. The refrigerator itself should be sealed, and no refrigerant and lubricating oil should leak. For the shaft seal, when the standard cooling capacity is 12.6×1000 kJ/h, the shaft seal is allowed to have a small amount of oil leakage, and the refrigerator with the standard cooling capacity>12.6×1000 kJ/h is not allowed to leak more than 10 drops of oil per hour Phenomenon, fluorine refrigerator shaft seal must not have dripping oil.
11. The expansion valve body is evenly frosted or dewed, but there should be no thick frosting at the inlet. Only a dull, tiny sound can be heard as it flows through the expansion valve.
12. The pointers of each pressure gauge in the system should be relatively stable, and the thermometer indicates correct.
Second, the failure analysis of the compressor
The reasons for the failure of the refrigerator to start are nothing more than two aspects: the failure of the motor and the mechanical failure of the refrigerator, which are described as follows.
1. First check the main circuit, whether the power supply has electricity? Is the fuse blown? Are the switch contacts in good contact? Does it run without phase? When one phase of the three-phase power supply is burned out, the motor can also rotate, but the sound is abnormal and the speed will slow down. If you find this situation, you should stop the machine immediately, otherwise it is easy to burn the motor.
2. If the power supply voltage is too low, the sound of the motor will be abnormal after starting. The voltage should not be lower than 90% of the rated voltage, otherwise the rated power of the motor will drop significantly and the compressor cannot be driven; when the allowable current of the input line is small and cannot meet the needs of the motor, the motor will also not be able to drag the compressor.
3. The differential pressure relay, high and low voltage relay should be checked. Because the differential pressure relay and the high and low pressure relay are both relay protection adopted for the safe operation of the refrigerator, when the oil pressure (high pressure and low pressure) of the refrigerator is abnormal, the refrigerator can be stopped. Check whether the contact of the pressure relay is disconnected, and check whether the relay is disconnected because the high pressure setting value is too small or the low pressure setting value is too large. In addition, the valve in the system is not opened, which will also cause the pressure relay to disconnect. . Check whether the contact of the differential pressure relay is disconnected. If the oil pressure cannot be established, the contact will be disconnected. If the reset button is not pressed during startup, the contact is in the self-locking disconnected state. After the relay works once, it will take 5 minutes to reset. If it is within 5 minutes, the heating element will still cause the contact to be disconnected, so it cannot be started. .
