Fault Analysis of Air Source Heat Pump Unit Compressor
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Keywords: heat pump compressor failure
1 Introduction
Air source heat pump unit is widely used in recent years because of its own hot and cold sources, easy installation and other characteristics; but due to air conditioning load and the impact of the external environment, the scope of the work fluctuations, the unit operating time under non-standard conditions Longer, in some of the more severe conditions, the compressor unit has some problems. In this paper, some problems of compressor failure occurred in the actual operation of air source heat pump unit are analyzed in detail, and the corresponding improvement measures are put forward.
2 symptoms
Air source heat pump units used in many types of compressors to fully enclosed piston compressor is common, and fully enclosed piston compressor failure problems, mostly occurred in winter heating operation. Through the failure of some fault compressor anatomical observation of the situation, the compressor fault can be divided into three categories:
(1) compressor suction and exhaust valve rupture
Phenomenon: Compressor oil level is normal, compressor bearings, crankshaft, connecting rod intact, suction and exhaust valve rupture.
(2) compressor stall (such failures more)
Phenomenon: compressor oil is black, the upper and lower bearing sleeve off or wear, connecting rod fracture, the friction surface of the crankshaft and the bearing and the friction surface of the crankshaft and connecting rod have traces of wear and tear, the motor rotor wear marks, suction and exhaust valve intact.
(3) compressor motor burned
Phenomenon: Compressor insulation to 0, the compressor bearings, crankshaft, connecting rod intact.
3 reasons analysis
The following detailed analysis of the above three types of faults:
(1) compressor suction and exhaust valve rupture
It can be seen from the breakdown phenomenon that the main reason causing compressor suction and discharge valve rupture is that the water side of the unit is broken and water enters the compressor to form a liquid hammer and cause the valve to break.
Water-side system rupture there are two main situations:
(1) When the unit is in cooling operation, the water system will be interrupted. Because some users switch the flow switch shortly, the unit can not perform protective action and the water in the water-side heat exchanger (especially the flooded heat exchanger) will freeze. Resulting in heat transfer copper pipe cracking, resulting in water-fluorine intermixing, water into the compressor to form a liquid hammer damage.
â‘¡ In winter, when the user does not use the unit, it does not operate in accordance with the rules and releases the chilled water inside the water-side heat exchanger or does not perform the corresponding anti-freezing measures. The water inside the water-side heat exchanger is frozen to cause the heat exchange copper pipe to freeze Split, so that water fluoride intermixing, and other units turn on again, the water into the compressor caused by bad.
(2) compressor blocked
Judging from the anatomical phenomenon of such a fault compressor, the internal compressor is not short of oil, and the blocking of the shaft is caused by the transient lubrication failure. The main reason for the poor lubrication is that the lubricating oil quality has changed: the oil is diluted or The oil level is raised by the refrigerant liquid.
Reasons for the unit back to liquid are:
(1) The refrigerant in the refrigeration cycle is usually accumulated in the part with the lowest temperature and condensed. When the unit is shut down for a long time, the compressor enters the lowest temperature part of the refrigeration cycle as the heat capacity of the compressor is larger than the heat capacity of the condenser, the evaporator and the accumulator. Because the lubricant dissolves the refrigerant well, the refrigerant that accumulates in the compressor dissolves in the lubricant, a phenomenon known as "melt-in". Depending on the amount of refrigerant charged, the structure of the refrigeration cycle, and the length of the downtime, the amount of "solvent" in the refrigerant varies from approximately 30% to 100% of the amount of lubricant when saturated. Diluted oil can cause poor lubrication, causing the shaft to hold.
In addition, if the unit stops for a long time, the lubricant will depend on the temperature of the compressor enclosure, the type of refrigerant and lubricant, and the liquid phase separates into the lower part of the refrigerant liquid (refrigerant, refrigerant and Less oil mixture), the upper part of the lubricating oil (lubricating oil, lubricating oil and refrigerant mixed less) this situation. When the compressor is started in such a state, the oil supplied to the bearing and other moving parts is a "lubricant" of almost only the refrigerant liquid. Therefore, in a short period of time after start-up, parts such as a bearing portion and a connecting rod Will produce stuck and worn.
Compressor before the start without preheating or warm-up time is not enough crankcase electric heater power is not enough, it will be impossible to avoid the above situation, resulting in compressor damage.
â‘¡ When the unit is in heating operation, especially when operating in the environment with high humidity, the fins are easy to contact with the frost. If the defrosting method is not perfect, the defrosting can not be done in time or the defrosting is not complete, which will cause the low pressure to be low A large number of compressor back to liquid, causing compressor failure.
(3) Motor burned
As mentioned above, back to the liquid is the main factor for the shaft, due to bearing shaft caused by eccentricity, resulting in motor stator wear, resulting in the phenomenon of short-circuit the motor burned there. But for a pure motor burned, whether the return of liquid? I believe that fully enclosed piston compressor tubular structure, it determines the liquid is not sensitive to the liquid, even if part of the liquid refrigerant into the compressor, the general will not A direct result of valve damage, it will not directly cause the motor burned.
At the same time, because the closed compressor lubrication mostly centrifugal splash, there is no pressure difference control, so the compressor in the absence of oil lubrication can also run. At this point, the compressor current continues to rise until the air switch (overcurrent protector) jumped out, this process is the compressor overload operation, the current larger, the motor coil temperature rise quickly, until the embedded PTC action. Because the PTC temperature rise rate of the compressor is very sensitive under full load or overload conditions, and the air switch is in front of the PTC action, therefore, lack of oil directly causes the motor to burn is also lack of basis.
The author believes that there are two reasons compressor pure motor burned:
â‘ motor temperature is too high.
Because the fully enclosed compressor motor is cooled by the return air, the winter heat pump mechanism is hot, the working conditions are harsh, especially when the ambient temperature is very low, the heat is very small, the refrigerant circulation is small, return air pressure Low, coupled with the electric control on the defrosting is not timely and not complete, will lead to insufficient motor cooling, coil fever. This continuous heat will form a high temperature, and PTC is not sensitive to low current when the load is low, so the compressor after several starts, when not reached the higher temperature will cause insulation damage due to overheating, the motor short circuit burned.
â‘¡ internal refrigeration system is not clean, contains impurities, corrosion and wear of motor coils, resulting in short circuit burned.
4 improvement measures
For the above analysis of the reasons to make the appropriate improvements:
(1) The control should have antifreeze control function (that is, in the shutdown state, when the ambient temperature is below a certain value, the pump or electric heating should be put into operation to prevent freezing of the water system), while the water system should be provided with drainage Device, when the unit is not in use for a long time, should drain the water within the water exchanger to prevent freezing damage.
(2) In order to ensure the normal operation of the unit, the flow switch and various protection switches can not be short-circuited by themselves; when the unit is running, it is necessary to observe frequently and find out when the temperature difference between the water inlet and outlet of the unit is too large, check the water system in time: Whether the pump is normal, water flow and water filter cleaning.
(3) increase in the electronic control program to ensure the compression crankcase heater heating time conditions before starting to ensure that the compressor can fully preheat to prevent damage.
(4) to improve the defrost method to ensure timely defrosting and defrosting thoroughly improve the reliability of electronic control, to prevent malfunction or non-action.
(5) Improve the system design, especially in the low-temperature heating conditions, the expansion valve and gas-liquid separator should be reasonable match, or take measures to increase the bypass of high and low pressure to prevent back to the unit problem.
(6) Improve the technology, strengthen the management and enhance the awareness of quality, ensure that the refrigeration system is clean, clean and free of moisture. The quality of manufacturing and processing is an important factor that affects the quality of generating units. Many problems must be avoided in order to avoid any major failure.
(7) to enhance the user's use, operation and maintenance training.