4 Refrigeration Compressor Types And Related
The refrigeration compressor is the core and heart of the refrigeration system and the core energy-consuming component of the refrigeration system.
The capabilities and characteristics of the refrigeration compressor determine the capabilities and characteristics of the refrigeration system. The design and matching of the refrigeration system reflect the capabilities of the compressor.
The most direct and effective way to improve the efficiency of the refrigeration system is to improve the efficiency of the compressor, which will bring about a significant reduction in system energy consumption, which also avoids collecting only on the system.
Refrigeration Compressor principles
In the vapor compression refrigeration system, the refrigeration compressor increases the refrigerant from low pressure to high pressure and continuously circulates the refrigerant so that the system continuously discharges internal heat to an environment higher than the system temperature.
The refrigeration system inputs electrical energy through the refrigeration compressor to discharge heat from a low-temperature environment to a high-temperature environment, which achieves a refrigeration cycle from compression to condensation (heat release) to expansion to evaporation (heat absorption).
The energy efficiency ratio of the refrigeration compressor determines the energy efficiency ratio of the entire refrigeration system. Since the ambient temperature changes frequently, the compressor is in a partial load state most of the time, so the compressor must have energy regulation.
Refrigeration Compressor Classification
According to the working principle, it can be divided into the volumetric compressor and speed compressor; single-stage vacuum compressors can generally be divided into three types: high-temperature, medium and low-temperature compressors according to its working evaporation temperature range, but in specific division of evaporation temperature areas is not uniform; it is classified according to the sealing structure form, open compressor and closed compressor.
The following is a brief introduction to the four types of refrigeration compressors according to mechanical classification:
Volumetric Type
Volumetric compressors rely on changes in the volume of the working chamber to achieve processes such as steam suction, compression, and exhaust. This type of compressor includes reciprocating compressors and rotary compressors. The speed-type compressor relies on the high-speed rotating T-wheel I1 to do work on the steam, increase the pressure, and complete the task of transporting the steam.
This type of refrigeration compressor includes centrifugal and axial flow compressors, with centrifugal compressors being commonly used. It is widely used, has mature manufacturing technology, simple structure, low requirements on processing materials and processing technology, low cost, strong adaptability, can adapt to a wide pressure range and cooling capacity requirements, and has strong maintainability.
Disadvantages: It is impossible to achieve higher speeds, the machine is large and heavy, and it is not easy to achieve lightweight. The exhaust is discontinuous, the airflow is prone to fluctuations, and there is a large vibration during operation.
Due to the above characteristics of crankshaft and connecting rod compressors, few small-displacement compressors adopt this structural form. Crankshaft and connecting rod compressors are mostly used in large-displacement air conditioning systems of buses and trucks.
Screw Type
A screw refrigeration compressor is a rotary positive displacement compressor. It uses changes in the slot volume and position of the screw to complete the process of inhalation, compression and exhaust of steam. Oil-free screw compressors were introduced in the 1930s and were mainly used to compress air. Later, screw compressors with oil injection in the cylinder appeared, and their performance was improved.
Oil-injected refrigeration screw compressors have become one of the main types of refrigeration compressors. Screw compressors are divided into two categories: twin-screw and single-screw. Twin-screw compressors are customarily called screw compressors.
Variable Displacement
Variable displacement refrigeration compressors can automatically adjust power output based on set temperatures. The air conditioning control system does not collect the temperature signal of the evaporator m air outlet, but controls the compression ratio of the compressor based on the pressure change signal in the air conditioning pipeline to adjust the m air outlet temperature automatically.
During the entire refrigeration process, the refrigeration compressor is always working, and the adjustment of refrigeration intensity is completely controlled by the pressure regulating valve installed inside the compressor. When the pressure at the high-pressure end of the air conditioning pipeline is too high, the pressure regulating valve shortens the piston stroke in the compressor to reduce the compression ratio, which will reduce the refrigeration intensity.
When the high-pressure end pressure drops to a certain level, and the low-pressure end pressure rises to a certain level, the pressure regulating valve increases the piston stroke to increase the refrigeration intensity.
Fixed Displacement
The exhaust volume of v increases proportionally with the increase in engine speed. It cannot automatically change the power output according to the cooling demand and has a relatively large impact on engine fuel consumption. Its control is generally achieved by collecting the temperature signal from the evaporator outlet.
When the temperature reaches the set temperature, the refrigeration compressor stops working; when the temperature rises, the refrigeration compressor starts to operate. The pressure of the air conditioning system also controls fixed displacement compressors. When the pressure in the pipeline is too high, the compressor stops working.
Mechanical Characteristics
- The cooling capacity of most fully enclosed piston refrigeration compressors does not exceed 0.5KW, and they are mainly used in household refrigerators/freezers and small commercial refrigeration equipment;
- The cooling capacity of scroll refrigeration compressors ranges from 0.75 to 15KW (excluding special models), and most are between 3 and 5KW. They are most commonly used in small household air conditioners and commercial air conditioners. This type of refrigeration compressor is not used in refrigeration conditions of minus 5 degrees Celsius;
- Centrifugal refrigeration compressors are mainly used in chillers under air conditioning conditions;
- The screw compressor has a single cooling capacity of 30kw-1500kw and can be used in cold storage, artificial ice rinks, and chillers;
- The semi-hermetic piston refrigeration compressor has a wide range of uses. The cooling capacity of a single machine is from 3kw to 100kw. It can also be used in parallel with multiple heads. Therefore, it can provide a cooling capacity ranging from 3kw to 1000kw. It can be used in multiple working conditions and can be used in both refrigeration conditions. , and can be applied to air conditioning conditions;
- Turning on the piston refrigeration compressor is only commonly used in cold storage, and only some chillers are in air conditioning conditions.
Refrigeration Compressor Maintenance
1. Need to check regularly whether there are any foreign objects or even conductive objects in the motor, whether the coil is damaged, and whether there is friction between the stator and the rotor. Otherwise, the motor will burn out after starting;
2. Pay attention to the temperature rise of the motor, the bearing temperature, and whether the indications of the voltmeter and ammeter are normal. The current must not exceed the rated current of the motor. If it exceeds, find the reason or stop the machine for inspection; whether there is any abnormal noise during the heating process of the motor.
3. Observe whether the oil level of the oil pool of the machine body and the lubricating oil in the oiler are below the scale line. If it is low, add enough oil in time (stop the machine for inspection if using the dipstick);
4. The lubricating machine used must be precipitated and filtered. Refrigeration compressor oil should be used differently in winter and summer.
5. If it is a water-cooled refrigeration compressor if water cannot be immediately supplied after the water is cut off, avoid cylinder cracks due to uneven temperature. After parking in winter, the cooling water should be drained to prevent the cylinder from freezing and cracking; for air-cooled compressors, as long as the indoor temperature is not hot and cold, the manufacturer recommends that it is best to place it in a standard laboratory with air conditioning, and the temperature can be kept at 25-28 degrees for a long time;
6. Use your hands to feel whether the temperature of the suction and exhaust valve cover at the cross guide of the high and low temperature alternating wet heat test box is normal;
7. Check whether the refrigeration compressor vibrates and whether the anchor screws are loose or falling off;
8. Clean the refrigeration system regularly, especially the copper tube and the bottle body. Check the remaining amount of Freon regularly;
9. The gas tank, cooler, and oil-water separator should be drained of oil and water frequently.
In addition, the constant temperature and humidity test chamber needs more attention:
- Check whether the cooling water temperature and flow rate of the constant temperature and humidity test chamber are normal;
- Pay attention to the hygiene of the refrigeration compressor of the constant temperature and humidity test chamber and its equipment and environment, and clean the dust on the compressor condenser regularly because too much dust accumulation will cause overpressure or non-refrigeration failure of the equipment;
- Carefully check the action sound of the cylinders and moving parts of the constant temperature and humidity test chamber at all levels. According to “listening,” distinguish whether its working condition is normal. If abnormal sound is found, stop the machine immediately for inspection;
- Pay attention to constant temperature and humidity. Check whether the indicated values of the pressure gauges at all levels of the test chamber, the pressure gauges on the gas tank and cooler, and the lubricating oil pressure gauge are within the specified range;
- Check the lubricating oil supply of the constant temperature and humidity test chamber and the oil supply of the lubrication system of the moving mechanism (some compressors are equipped with plexiglass baffles on the side of the crosshead guide rail of the fuselage, which can directly see the crosshead movement and lubricating oil supply); the cylinder and packing can be drained with a one-way valve for inspection, and the oil injection of the oiler into the cylinder can be checked;
- Check whether the pressure regulator or load regulator of the constant temperature and humidity test chamber, the safety valve, etc., are sensitive.
Environmental Impact
Noise has been considered as one of the serious pollution. As the power source and heart of household refrigeration equipment, the noise problem of refrigeration compressors has become an important indicator to measure its comprehensive performance. The main noise sources of refrigeration compressors are composed of three parts: aerodynamic noise radiated by the intake and exhaust, mechanical noise generated by mechanical moving parts, and drive motor noise:
Aerodynamic Noise
The pressure pulsation of the air flow in the intake pipe causes the intake noise of the refrigeration compressor. The fundamental frequency of the intake noise is the same as the gas pulsation frequency in the intake pipe and is related to the rotation speed of the compressor. The exhaust noise of the compressor is caused by the pressure pulsation generated by the airflow in the exhaust pipe. Exhaust noise is weaker than intake noise, so the aerodynamic noise of the compressor is generally dominated by intake noise.
Mechanical Noise
The mechanical noise of the compressor generally includes the impact and friction of components, the vibration of the piston, the impact noise of the valve, etc. These noises are random and have broadband characteristics.
Electromagnetic Noise
The electric motor generates the electromagnetic noise of the compressor. Motor noise is weak compared with aerodynamic noise and mechanical noise. Among the compressor noise sources, the inlet and exhaust aerodynamic noise is the strongest, followed by mechanical noise and electromagnetic noise.
Through in-depth research, it can be further believed that the compressor noise mainly comes from the vibration of the casing (produced by the spring, refrigerant medium pressure pulsation and suction, exhaust pipe and lubricating oil excitation) and propagates to the surrounding air medium to form noise.
Noise Control
To reduce compressor radiation noise, many manufacturers have taken a series of measures: increasing the overall rigidity of the shell structure to increase the resonance frequency and reducing the vibration amplitude, avoiding sudden changes in the curvature of the shell.
For curved surfaces, the natural frequency is inversely proportional to the radius of curvature, so the shell shape should adopt the smallest radius of curvature; move the suspension spring support to a position with higher rigidity; the shell should use as few flat surfaces as possible; the coupling of bending stress and membrane stress (which only occurs on curved surfaces) will be making the casing itself has greater rigidity, so the compressor casing should use as little planar structure as possible.
Specific issues related to refrigeration compressors need to be handled by professional personnel to ensure safety and accuracy.
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