Refrigeration system failure analysis summary
If the refrigeration system fails, it is generally impossible to directly see where the fault occurs, and it is impossible to disassemble and dissect the components of the refrigeration system. Only the external inspection can be performed to find out the abnormal phenomena in the operation and conduct comprehensive analysis. In the inspection, the operating status of the system is generally known by watching, listening and touching.
1. Refrigeration system pressure and temperature detection
(1) Pressure concept of refrigeration system The refrigeration system can be divided into high and low pressure parts during operation. The high pressure section is from the exhaust port of the compressor to the front of the throttle valve. This section is called high pressure. The suction port pressure of the compressor is called the suction pressure, and the suction pressure is close to the evaporation pressure. The difference between the two is the flow resistance of the pipeline. Pressure loss is generally limited to below 0.018 MPa.
For convenience, both the evaporation pressure and the condensing pressure of the refrigeration system are detected at the suction and exhaust ports of the compressor. That is, it is usually called the suction and exhaust pressure of the compressor. The purpose of detecting the suction and exhaust pressure of the refrigeration system is to obtain the evaporation temperature and the condensation temperature of the refrigeration system, thereby obtaining the operating state of the refrigeration system.
(2) Temperature concept in the refrigeration system The temperature in the refrigeration system involves a wide range of surfaces, such as evaporation temperature te, suction temperature ts, condensation temperature, exhaust temperature, and the like. Determining the operating conditions of the refrigeration system is the evaporation temperature te and the condensation temperature tc.
a. Evaporation temperature te refers to the temperature at which the liquid refrigerant is boiled and vaporized in the evaporator. For example, the air conditioning unit te. 5 to 7 degrees as the best evaporating temperature of the air conditioning unit, that is to say, the design of the air conditioning unit te is between 5 and 7 degrees. When the air conditioning unit after the maintenance is in debugging, if the te is less than 5 to 7 degrees The expansion valve should be operated at a high speed to detect the suction pressure of the compressor. The purpose is to understand the evaporating temperature of the unit during operation, and te can not be directly detected, only by detecting the corresponding evaporating pressure to obtain its evaporating temperature (by referring to the refrigerant thermodynamic property table).
b. The condensing temperature tc is the temperature at which the superheated vapor of the refrigerant condenses into a liquid after releasing heat in the condenser. The condensing temperature cannot be directly detected, but only by detecting the corresponding condensing pressure, and then by referring to the refrigerant thermodynamic property table. The condensing temperature is high and the condensing pressure is relatively increased, and they correspond to each other. The condensing temperature is extremely high, the unit load is heavy, the motor is overloaded, and the operation is unfavorable. The cooling capacity is correspondingly reduced, and the power consumption is increased, and should be avoided as much as possible.
c. Exhaust gas temperature td refers to the temperature of the compressor exhaust port (including the temperature of the exhaust port nozzle). The temperature of the exhaust gas must be measured by a temperature measuring device. Generally, the small machine is not set up. The temporary measurement can be detected by a semiconductor thermometer, but the error is large. The exhaust temperature is affected by the suction temperature and the condensing temperature. The suction temperature or the condensing temperature increases, and the exhaust temperature rises accordingly. Therefore, the intake temperature and the condensing temperature must be controlled to stabilize the exhaust temperature.
d. The suction temperature ts is the gas temperature of the compressor suction connection pipe. The temperature measurement device is required to detect the inhalation temperature. Generally, the small unit does not set the temperature measurement device. Generally, it is estimated by hand touch during the inspection and debugging. The inhalation temperature of the air conditioning unit generally requires control of ts=15 degrees. Exceeding this value has a certain effect on the cooling effect.
2. Influence of suction pressure change refrigeration system
When the refrigeration system is running, its suction pressure is closely related to the evaporation temperature and the flow rate of its refrigerant. For systems with expansion valves, the suction pressure is related to the degree of opening of the expansion valve, the amount of refrigerant charge, the cooling efficiency of the compressor, and the magnitude of the load. With a capillary system, the suction pressure is related to the condensing pressure, the cooling capacity, the compressor cooling efficiency, and the load. For this purpose, when checking the refrigeration system, a pressure gauge should be installed on the suction pipe. Detecting inspiratory pressure plays an important role in failure analysis.
(1) Factors with low suction pressure: the suction pressure is lower than the normal value, and the factors are insufficient cooling capacity, small cold load, small expansion valve opening, low condensing pressure (using a capillary system), and the filter is not smooth. .
(2) Factors with high suction pressure: the suction pressure is higher than the normal value, and the factors include excessive refrigerant, large refrigeration load, large expansion valve opening, high condensing pressure (capillary system), and poor compressor efficiency.
3. Effect of exhaust (condensation) pressure changes on the refrigeration system
When the refrigeration system is in operation, its exhaust pressure corresponds to the condensing temperature, and the condensing temperature is related to the flow rate and temperature of the cooling medium, the refrigerant inflow amount, and the cooling load. When inspecting the refrigeration system, an exhaust pressure gauge should be installed at the exhaust pipe to detect the exhaust pressure as an analysis of the fault data.
(1) Factors with high exhaust pressure When the exhaust pressure is higher than the normal value, there is generally a small flow rate of the cooling medium or a high temperature of the cooling medium, an excessive refrigerant charge, a large cooling load, and a large expansion opening.
The above factors will cause the circulation flow of the system to increase, and the condensation heat load will increase accordingly.
Since the heat cannot be completely dissipated in time, the condensation temperature rises, and the exhaust gas (condensation) pressure rises. In the case where the flow rate of the cooling medium is low or the temperature of the cooling medium is high, the heat dissipation efficiency of the condenser is lowered to increase the condensation temperature. In the case where the flow rate of the cooling medium is low or the temperature of the cooling medium is high, the heat dissipation efficiency of the condenser is lowered to increase the condensation temperature. The reason for the excessive refrigerant charge is that the excess refrigerant liquid occupies a part of the condenser, which reduces the condensation area and causes the condensation temperature to rise.
(2) Factors with low exhaust pressure: the exhaust pressure is lower than the normal value, and the factors are low compressor efficiency, insufficient refrigerant amount, small cold load, small opening of the expansion valve, and the filter is not smooth, including the expansion valve filter. And the temperature of the cooling medium is low.
The above factors will cause the cooling flow of the system to decrease, the condensation load to be small, and the condensation temperature to drop.
From the above-mentioned suction pressure and the change of exhaust pressure and exhaust pressure, there is a close relationship between the two. Under normal circumstances, the suction pressure increases and the exhaust pressure rises accordingly; the suction pressure decreases and the exhaust pressure decreases accordingly. The general situation of the exhaust pressure can also be estimated from the change in the intake pressure gauge.
If the refrigeration system fails, it is generally impossible to directly see where the fault occurs, and it is impossible to disassemble and dissect the components of the refrigeration system. Only the external inspection can be performed to find out the abnormal phenomena in the operation and conduct comprehensive analysis. In the inspection, the operating status of the system is generally known by watching, listening and touching.
1. Refrigeration system pressure and temperature detection
(1) Pressure concept of refrigeration system The refrigeration system can be divided into high and low pressure parts during operation. The high pressure section is from the exhaust port of the compressor to the front of the throttle valve. This section is called high pressure. The suction port pressure of the compressor is called the suction pressure, and the suction pressure is close to the evaporation pressure. The difference between the two is the flow resistance of the pipeline. Pressure loss is generally limited to below 0.018 MPa.
For convenience, both the evaporation pressure and the condensing pressure of the refrigeration system are detected at the suction and exhaust ports of the compressor. That is, it is usually called the suction and exhaust pressure of the compressor. The purpose of detecting the suction and exhaust pressure of the refrigeration system is to obtain the evaporation temperature and the condensation temperature of the refrigeration system, thereby obtaining the operating state of the refrigeration system.
(2) Temperature concept in the refrigeration system The temperature in the refrigeration system involves a wide range of surfaces, such as evaporation temperature te, suction temperature ts, condensation temperature, exhaust temperature, and the like. Determining the operating conditions of the refrigeration system is the evaporation temperature te and the condensation temperature tc.
a. Evaporation temperature te refers to the temperature at which the liquid refrigerant is boiled and vaporized in the evaporator. For example, the air conditioning unit te. 5 to 7 degrees as the best evaporating temperature of the air conditioning unit, that is to say, the design of the air conditioning unit te is between 5 and 7 degrees. When the air conditioning unit after the maintenance is in debugging, if the te is less than 5 to 7 degrees The expansion valve should be operated at a high speed to detect the suction pressure of the compressor. The purpose is to understand the evaporating temperature of the unit during operation, and te can not be directly detected, only by detecting the corresponding evaporating pressure to obtain its evaporating temperature (by referring to the refrigerant thermodynamic property table).
b. The condensing temperature tc is the temperature at which the superheated vapor of the refrigerant condenses into a liquid after releasing heat in the condenser. The condensing temperature cannot be directly detected, but only by detecting the corresponding condensing pressure, and then by referring to the refrigerant thermodynamic property table. The condensing temperature is high and the condensing pressure is relatively increased, and they correspond to each other. The condensing temperature is extremely high, the unit load is heavy, the motor is overloaded, and the operation is unfavorable. The cooling capacity is correspondingly reduced, and the power consumption is increased, and should be avoided as much as possible.
c. Exhaust gas temperature td refers to the temperature of the compressor exhaust port (including the temperature of the exhaust port nozzle). The temperature of the exhaust gas must be measured by a temperature measuring device. Generally, the small machine is not set up. The temporary measurement can be detected by a semiconductor thermometer, but the error is large. The exhaust temperature is affected by the suction temperature and the condensing temperature. The suction temperature or the condensing temperature increases, and the exhaust temperature rises accordingly. Therefore, the intake temperature and the condensing temperature must be controlled to stabilize the exhaust temperature.
d. The suction temperature ts is the gas temperature of the compressor suction connection pipe. The temperature measurement device is required to detect the inhalation temperature. Generally, the small unit does not set the temperature measurement device. Generally, it is estimated by hand touch during the inspection and debugging. The inhalation temperature of the air conditioning unit generally requires control of ts=15 degrees. Exceeding this value has a certain effect on the cooling effect.
2. Influence of suction pressure change refrigeration system
When the refrigeration system is running, its suction pressure is closely related to the evaporation temperature and the flow rate of its refrigerant. For systems with expansion valves, the suction pressure is related to the degree of opening of the expansion valve, the amount of refrigerant charge, the cooling efficiency of the compressor, and the magnitude of the load. With a capillary system, the suction pressure is related to the condensing pressure, the cooling capacity, the compressor cooling efficiency, and the load. For this purpose, when checking the refrigeration system, a pressure gauge should be installed on the suction pipe. Detecting inspiratory pressure plays an important role in failure analysis.
(1) Factors with low suction pressure: the suction pressure is lower than the normal value, and the factors are insufficient cooling capacity, small cold load, small expansion valve opening, low condensing pressure (using a capillary system), and the filter is not smooth. .
(2) Factors with high suction pressure: the suction pressure is higher than the normal value, and the factors include excessive refrigerant, large refrigeration load, large expansion valve opening, high condensing pressure (capillary system), and poor compressor efficiency.
3. Effect of exhaust (condensation) pressure changes on the refrigeration system
When the refrigeration system is in operation, its exhaust pressure corresponds to the condensing temperature, and the condensing temperature is related to the flow rate and temperature of the cooling medium, the refrigerant inflow amount, and the cooling load. When inspecting the refrigeration system, an exhaust pressure gauge should be installed at the exhaust pipe to detect the exhaust pressure as an analysis of the fault data.
(1) Factors with high exhaust pressure When the exhaust pressure is higher than the normal value, there is generally a small flow rate of the cooling medium or a high temperature of the cooling medium, an excessive refrigerant charge, a large cooling load, and a large expansion opening.
The above factors will cause the circulation flow of the system to increase, and the condensation heat load will increase accordingly.
Since the heat cannot be completely dissipated in time, the condensation temperature rises, and the exhaust gas (condensation) pressure rises. In the case where the flow rate of the cooling medium is low or the temperature of the cooling medium is high, the heat dissipation efficiency of the condenser is lowered to increase the condensation temperature. In the case where the flow rate of the cooling medium is low or the temperature of the cooling medium is high, the heat dissipation efficiency of the condenser is lowered to increase the condensation temperature. The reason for the excessive refrigerant charge is that the excess refrigerant liquid occupies a part of the condenser, which reduces the condensation area and causes the condensation temperature to rise.
(2) Factors with low exhaust pressure: the exhaust pressure is lower than the normal value, and the factors are low compressor efficiency, insufficient refrigerant amount, small cold load, small opening of the expansion valve, and the filter is not smooth, including the expansion valve filter. And the temperature of the cooling medium is low.
The above factors will cause the cooling flow of the system to decrease, the condensation load to be small, and the condensation temperature to drop.
From the above-mentioned suction pressure and the change of exhaust pressure and exhaust pressure, there is a close relationship between the two. Under normal circumstances, the suction pressure increases and the exhaust pressure rises accordingly; the suction pressure decreases and the exhaust pressure decreases accordingly. The general situation of the exhaust pressure can also be estimated from the change in the intake pressure gauge.
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