The air conditioning refrigeration system is a relatively complex system, generally consisting of a plurality of subsystems such as a compressor, a condenser, an evaporator, and a throttling device. At the same time, the substances in the system cycle are five kinds of refrigerants, oil, water, air and other impurities. The first two are necessary to ensure the normal operation of the system. The latter three substances are harmful to the system, but they are not absolutely eliminate. The refrigerant itself has three states of vapor phase, liquid phase, and vapor-liquid mixed phase. Therefore, once the air conditioning and refrigeration system fails, its symptoms and causes are more complicated. It has the following characteristics: the symptoms of the fault are more complicated; the cause of the fault is more complicated; the relationship between the fault symptom and the cause is more complicated. A variety of symptoms can be induced by a variety of failure symptoms, and multiple failure causes can also show the same symptom; there is no strict logical and quantitative relationship between the parameters of each part of the system, that is, a certain degree of ambiguity; there are many parameters inside the system. It is difficult to measure and is usually not measured. Therefore, in order to study the fault diagnosis of air conditioning and refrigeration systems, it is necessary to set up a test case to obtain the set of fault samples required in the diagnostic program, so as to realize the training and diagnosis functions for programming.

There are four problems in the selection of sampling parameters: (1). Completeness of the measurement set. If we only describe the object space with some common normal and fault components, the appropriately selected measurement set can uniquely describe the object. The individual elements of the object space.

(2). The scalability of the measurement set In the experiment, we will find that some factors were not considered when the measurement set was selected, which led to the discovery that the measurement set was not complete in the experimental stage. In this case, the measurement set needs to be expanded. .

(3). Redundancy of measurement sets In order to reduce the cost of experiments, redundancy should be minimized.

(4). Easy to implement measurement set There are many physical parameters in the refrigeration system that are inconvenient to measure and generally not measured. Under the premise of ensuring the completeness of the measurement set, these physical parameters should be avoided as much as possible. Measurement parameters also require a simple test method, and the sensor is moderately priced and easy to implement.

Simulate the choice of fault, the relationship between fault and cause, refrigeration and air conditioning. The choice of simulated faults is not available for some reason due to the limitations of the experimental sampling equipment. For this condition, only some faults that are easy to sample can be selected. In this experiment, eleven kinds of faults are simulated: the fan does not turn; the air conditioning room is overloaded; the cooling water flow is too small; the cooling water inlet temperature is too low; the cooling water The inlet temperature is too high; the compressor suction and exhaust valve plate is damaged; the expansion valve opening is too small; the circulating water pump does not rotate; the filter is blocked; the refrigerant is insufficient; the refrigerant is excessive.

Selection of sampling parameters The main signal data is collected as follows: (1) temperature signal: cooling water inlet; cooling water outlet; compressor suction; compressor exhaust; thermal expansion valve inlet; air conditioning room; refrigerant condenser inlet; .

(2) Pressure signal: compressor suction; compressor exhaust.

The relationship between the fault and the cause (1) There are two reasons why the fan does not turn the fan. First, the electrical fault, the control circuit is not connected; the second is the mechanical failure of the fan shaft. When the room air conditioner fan does not turn, the temperature of the air conditioner room will rise, and the suction pressure and exhaust pressure of the compressor will decrease to some extent. After the air-conditioning fan is not turned, the heat exchange efficiency of the heat exchange coil in the air-conditioned room is reduced. When the heat load of the air-conditioned room is constant, the temperature of the air-conditioned room will rise, and the temperature of the refrigerant in the heat exchange coil will be relatively low due to insufficient heat exchange. The original temperature is lowered, that is, the evaporation temperature becomes smaller, and the refrigeration coefficient of the system is lowered. The evaporator outlet temperature felt by the thermal expansion valve is also lowered, so that the opening of the thermal expansion valve becomes smaller and the refrigerant is correspondingly reduced, so the suction and exhaust pressures are all reduced. The overall effect of the reduction in refrigerant flow and the reduction in the refrigeration coefficient is to reduce the cooling capacity of the system.

(2) Excessive load on the air-conditioned room Due to the effects of disturbances and external disturbances in the room and the influence of various factors, the air-conditioned room temperature rises due to the excessive load of the air-conditioned room, and finally the temperature index that should be maintained in the normal air-conditioned room is not reached.

At the same time, the two most affected parameters are the compressor suction and exhaust temperatures. Due to the influence of the heat capacity of the air-conditioned room, the influence of other parameters will be obvious after a certain period of time.

(3) The cooling water flow rate is too small. Due to the relationship between the cooling water pipe and the cooling water valve, and the configuration of the cooling tower in the system is too small or the scale in the cooling tower is too much, the cooling water flow is too small and the cooling water inlet temperature is too high. failure.

When the flow rate of the cooling water is too small, the heat exchange effect of the condenser is lowered, so that the temperature of the refrigerant at the outlet of the condenser rises, and the condensation temperature of the refrigerant rises, which lowers the refrigeration coefficient and affects the refrigeration effect. Under the same conditions, the temperature of the air-conditioned room will also rise to a certain extent, and the suction temperature of the compressor will also rise. But the most obvious change is that the temperature difference between the cooling water outlets will increase.

(4) The cooling water inlet temperature is too low. As the cooling water temperature decreases, the compressor discharge pressure, exhaust temperature, and filter outlet temperature are all reduced. The temperature of the air-conditioned room remains the same, because the cooling water temperature has not dropped to the extent that it will affect the cooling effect. If the temperature of the cooling water drops to a certain level, the condensing pressure will also decrease, resulting in a decrease in the pressure difference between the two sides of the thermal expansion valve, a decrease in the flow capacity of the thermal expansion valve, and a decrease in the refrigerant. Therefore, the cooling effect will be reduced, air-conditioned rooms, etc.: The temperature of the air-conditioning refrigeration system will be increased by experiment.

(5) The cooling water inlet temperature is too high. The cooling water inlet temperature is too high, which will cause the refrigerant to be too cold, the condensation temperature is too high, the condensing pressure is too high, the compressor pressure ratio is increased, the shaft power is increased, and the gas transmission coefficient is increased. Reduced, thus reducing the cooling capacity of the system. Therefore, the overall cooling effect will be reduced and the temperature of the air-conditioned room will rise.

(6) Damage to the suction and exhaust valve of the compressor For the reciprocating compressor, the damage of the suction and exhaust valve of the compressor is a common mechanical failure. This experiment simulates the method of bypassing the suction and exhaust ports of the compressor. of. When the fault occurs, the inhalation temperature and the inspiratory pressure will rise, and the exhaust temperature and exhaust pressure will decrease. This is equivalent to the actual air volume of the compressor is reduced, so the cooling effect is poor, and the air conditioning room temperature will be very high. Fast rise, when the situation is severe, the low voltage relay will stop the compressor.

(7) The opening degree of the expansion valve is too small. The opening degree of the expansion valve is too small. In terms of the normal refrigerant charge of the refrigeration system, the expansion valve opening is too small. In the failure of the entire system, the refrigerant is insufficient in the whole system. The conditions remain unchanged, and the liquid formula can not fully satisfy the gasification and heat absorption at low pressure, so the return superheat is very large, the temperature of the exhaust and exhaust air and the temperature of the air-conditioned room rise, and the suction and exhaust pressure will decrease (Figure 7 ). The temperature of the condenser outlet refrigerant will decrease (that is, increase the refrigeration capacity of the system), because the heat exchange capacity of the condenser does not change, but the refrigerant flow rate circulating in the whole system is small, although the refrigeration coefficient is increased at this time, The unit cooling capacity has increased. However, the total cooling capacity is reduced, so the temperature of the air-conditioned room will rise.

(8) When the circulating water pump does not turn the refrigeration unit during commissioning and operation, the system circulating water pump should be opened first. When the circulating water pump does not rotate, the temperature of the cooling water outlet and the temperature of the refrigerant outlet of the condenser rise most obviously. Due to the sharp drop in the cooling effect of the condenser, the suction temperature and the exhaust temperature of the compressor also rise rapidly, and the condensation temperature The rise also causes the evaporation temperature to rise, but the extent of the rise in the evaporation temperature is not as large as the increase in the condensation temperature, so the refrigeration efficiency is lowered and the temperature of the air-conditioned room rises rapidly. Such as (9) filter clogging filter blockage is the system is dirty. Under normal circumstances, dirty plugging often occurs at the filter. This is because the filter's filter screen blocks the passage section and filters out dirt and metal chips. After a long time, the cooling and air conditioning are blocked. In the experiment, the dirty plugging simulation method is to change the passage of the refrigerant, close the normal passage of the refrigerant, and open the blocked passage parallel with the normal passage. The result of the filter blockage is that the refrigerant circulation is reduced, and many of the causes are expanded. The valve opening degree is too small, such as the compressor suction and exhaust temperature rises, the compressor suction and discharge pressure drops, and the air conditioning room temperature rises. The difference is that the filter outlet temperature is getting lower and lower. This is because the throttling begins at the filter, causing the local temperature of the system to decrease, and in the case of severe conditions, local frost or ice formation may occur.

(10) Insufficient refrigerant refrigerant is usually caused by two reasons: First, the product is not enough before the factory shipment, generally small occurs; Second, the unit runs all the year round, because the system valve or welding part leakage causes too little refrigerant Therefore, it is a more common fault. There is no significant difference between the two refrigerant failures and the fact that the expansion valve is too small. Theoretically, the refrigerant condenser outlet temperature should be different, because in the case of insufficient refrigerant, the system is insufficiently charged with refrigerant, and other operating conditions remain unchanged, then the temperature of the exhaust and exhaust is The temperature of the air-conditioned room will rise, the suction and exhaust pressure will decrease, and the temperature of the condenser outlet will decrease. Because the heat transfer capacity of the condenser has not changed, the thermal expansion valve opening is too small. Both of them are consistent with the failure of the refrigerant, except that the refrigerant condenser outlet temperature (ie, the supercooling temperature) will rise. When the refrigerant charge is normal, if the thermal expansion valve opening is too small, the refrigerant circulation is reduced. The refrigerant that is not involved in the cycle is stored in the condenser in a liquid state to affect the heat exchange effect of the condenser, so the outlet temperature of the refrigerant condenser should rise, and this factor causes the cooling capacity to change in a downward direction.

(11) Excessive refrigerant refrigerant is caused by blind refrigerant charging, which is not uncommon in the maintenance of refrigeration systems. This will reduce the effective heat exchange area in the condenser, reduce the heat exchange effect, cause the condensing temperature to rise, the condensing pressure to increase, and the high pressure to be too high. Excessive refrigerant entering the evaporator fails to be fully vaporized and is inhaled by the compressor, resulting in low pressure, condensation or frost on the cylinder head of the compressor, and a liquid cylinder accident in severe cases. Part of the liquid refrigerant enters the compressor, the motor load is increased, the starting is difficult, the current is overloaded during operation, and in severe cases, it is burnt due to motor overload.

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