What Is a Refrigeration Compressor?

The refrigeration compressor is the core and heart of the refrigeration system. The capacity and characteristics of the compressor determine the capacity and characteristics of the refrigeration system. In a sense, the design and matching of the refrigeration system reflects the capabilities of the compressor. Therefore, the refrigeration industry in all countries around the world has invested a lot of energy in the research of refrigeration compressors, and new research directions and research results continue to appear. The technology and performance levels of compressors change with each passing day. There are many types of compressors. According to different working principles, refrigeration compressors can be divided into fixed displacement compressors and variable displacement compressors.

Refrigeration Compressors

(Mechanical Engineering Terminology)

Refrigeration compressor is the core energy-consuming component of a refrigeration system. The most direct and effective way to improve the efficiency of a refrigeration system is to increase the efficiency of the compressor, which will bring a significant reduction in system energy consumption. At the same time, this also avoids collecting only on the system.

Standard Q / Y B00J02.02

Significant increase in material consumption caused by measures (such as blindly increasing the area of the heat exchanger). As the world s energy shortage situation becomes more serious, various countries are paying more and more attention to energy-saving work, and have made higher and higher requirements for the efficiency of energy-consuming products.

Due to various losses, such as friction, leakage, harmful heat transfer, motor loss, flow resistance, noise and vibration, etc., the actual efficiency of the compressor during operation is much lower than the theoretical efficiency. Therefore, in theory, any measure that can reduce any kind of loss can improve the efficiency of the compressor. This objective fact has led to a wide range of research and directions for energy conservation of compressors, with various research topics and research results.

The international energy conservation research work on compressors is mainly focused on several aspects: research

In recent years, with the rapid development of the international refrigeration compressor industry,

Classified by working principle

Volumetric compressor, speed compressor

Classified by working evaporation temperature range

For single-stage compressors, they can generally be classified into high temperature, medium temperature and low temperature compressors according to their working evaporation temperature range, but the specific evaporation temperature area is not uniformly divided. The general temperature range is: high temperature refrigeration compressor: -10 ~ 10; medium temperature refrigeration compressor: -20 ~ -10; low temperature refrigeration compressor: -45 ~ -20.

Classification by sealing structure

Open compressor, hermetic compressor

1. The refrigeration capacity of most hermetic reciprocating compressors does not exceed 0.5KW. It is mainly used in household refrigerators / freezers and small commercial refrigeration equipment. ^[3]

At present, most of China's refrigeration compressor market is mainly occupied by some refrigeration companies in Europe, Japan and the United States. With the development of society, the amount of cooling required by users is getting higher and higher. In addition, due to the requirements of energy saving, centrifugal units have an increasingly broad market.

As the form of energy becomes increasingly tight, energy saving and consumption reduction is a major trend in product development. In addition, as China s urbanization level continues to increase and building energy consumption continues to increase, centrifugal chiller units with the highest performance coefficient will undoubtedly become a hot spot in the market. In recent years, sales of centrifugal chiller units have continued to increase.

Most Chinese companies that develop centrifugal chillers only buy imported compressors, and basically have little profit. Foreign centrifuge manufacturers will not easily transfer their core technology. If they want to develop refrigeration compressors, they have to take the road of independent development. With the continuous maturation of design and manufacturing technology, the development of domestic centrifugal refrigeration compressors becomes possible.

The reasons for the high exhaust temperature of the refrigeration compressor are:

Basic performance parameters of refrigeration compressors

1. Actual gas transmission volume (referred to as gas transmission volume)

Under certain operating conditions, the mass of gas delivered from the suction end to the exhaust end per unit time is called the compressor's mass air delivery volume in this operating condition, and the unit is If it is calculated based on the volume of the inspiratory state, the volume of air infusion is in units of. then

Volume efficiency

The volumetric efficiency of the compressor is the ratio of the actual air delivery volume to the theoretical air delivery volume

It is used to measure the effective utilization of the working volume of the cylinder of a displacement compressor.

Third, the cooling capacity

Refrigeration compressor is an important part of the refrigerator and works with other components in the system, such as heat exchangers, throttling devices, etc. to obtain the effect of refrigeration. Therefore, its working capacity must be intuitively expressed by the amount of cooling produced in a unit of time-the amount of refrigeration. The unit is one of the important performance indicators of a refrigeration compressor.

Where-the unit mass cooling capacity of the refrigerant under a given refrigeration condition, the unit is;

-Refrigerant volume per unit volume of refrigerant under given refrigeration conditions, the unit is.

In order to facilitate comparison and selection, it is necessary to specify the refrigeration capacity of the compressor according to its unused operating conditions. Table 4-1 lists the different forms of single-stage small-scale reciprocating refrigeration required by the relevant national standards in China. The nominal operating conditions of the compressor and its operating temperature. According to the standard, the heat absorbed by the overheating of the suction working medium should also be included in the refrigeration capacity of the compressor.

Fourth, heat removal

Exhaust heat is the sum of the refrigeration capacity of the compressor and the equivalent heat input power of some compressors. It is discharged through the condenser in the system. This parameter is a very important performance index for the compressor in the heat pump system; it must also be known when designing the condenser of the refrigeration system.

Actual refrigeration cycle

The actual refrigeration cycle or heat pump cycle diagram shown shows that the heat dissipation of the compressor under certain conditions is:

It is not difficult to find the compressor energy balance diagram.

In the above two formulas

-The specific enthalpy of the working fluid at the compressor inlet.

-The input power of the compressor.

-The amount of heat dissipated by the compressor to the environment.

Table 2-2 lists the nominal operating conditions of the compressors used in heat pumps specified by the American Refrigeration Association ARI520-85 standard.

Five, indicating power and indicating efficiency

The indicated work consumed by the actual cycle per unit time is the indicated power Pi of the compressor, the unit is kw, which is equal to

Where Withe actual cycle indicating work of each cylinder or working volume, the unit is J.

The indicated efficiency hi of the refrigeration compressor refers to the ratio of the theoretical work of the isentropic cycle required for compressing 1 kg of working fluid to the actual cycle indicated work. It is used to evaluate the completeness of the completion of the thermal process inside the compressor cylinder or working volume.

Six, shaft power, shaft efficiency and mechanical efficiency

The power transmitted from the prime mover to the compressor's main shaft is called the shaft power Pe, and the unit is kW. One part of it, namely, the indicated power Pi is directly used to complete the working cycle of the compressor, and the other part is the friction power Pm, in kW , Used to overcome the frictional resistance of moving parts in the compressor and drive auxiliary equipment, such as lubrication hydraulic pumps.

Seven, electric power and efficiency

The power input to the motor is the electric power Pel consumed by the compressor in kW. Electrical efficiency * is the ratio of theoretical power to electrical power of isentropic compression. It is used to evaluate the degree of perfection of the input power of the motor.

Performance coefficient

In order to finally measure the power economy of a refrigeration compressor, a coefficient of performance (COP) is used, which is the ratio of the refrigeration capacity of the refrigeration compressor to the power consumed under certain operating conditions.

China's domestic refrigeration compressor companies have long been accustomed to large-scale production models and used quantity to seek benefits. However, under the situation of fierce price competition, with the declining profitability of products, when the production of millions of compressors can only achieve profits of several million yuan, some special refrigeration compressors may be a way out. Special refrigeration compressors are all-inclusive, and it is impossible to list them one by one here. However, their common characteristics are small production scale, high profit per unit, fast product transformation, and in most cases, special designs for user requirements. Such products have increasingly attracted the attention of Chinese compressor companies. For example, several companies in China are developing or have the production capacity of car refrigerator compressors. ^[4]

When the refrigeration compressor is started, the current of the motor will be 5-6 times higher than the rated one, which will not only affect the service life of the motor but also consume more power. In the design of the system, there will be a certain margin in the selection of the motor. The speed of the motor is fixed, but in actual use, it sometimes runs at a lower or higher speed, so it is very Necessary. The inverter can realize the soft start of the motor, achieve the purpose of energy saving and speed regulation by changing the input voltage frequency of the equipment, and provide the equipment with protection functions such as overcurrent, overvoltage, and overload. There are three well-known inverter manufacturers in China.

1. Frequently check whether there are foreign objects or even conductive objects in the motor, whether the coil has been damaged, and whether the stator and rotor are rubbing, otherwise the motor will burn out after the motor starts;

2. Pay attention to the hygiene of the constant temperature and humidity test box compressor and its equipment and environment. Regularly clean the ash on the compressor condenser. Because too much dust accumulates, it can cause equipment to overpressure or fail to refrigeration.

3. Observe whether the oil level in the oil tank of the fuselage and the lubricating oil in the oil injector are below the scale line. If it is low, you should fill up in time (stop with the dipstick to check);

4. Carefully check the operating sounds of the cylinders and moving parts of the constant temperature and humidity test box to determine whether it is working properly according to "listening". If abnormal sounds are found, stop the inspection immediately;

5. The lubricating machine used must be precipitated and filtered. Compressor oil should be used separately from winter and summer.

6. If it is a water-cooled compressor, if the water cannot be immediately supplied after the water is cut off, avoid cracks in the cylinder due to uneven hot and cold. After the vehicle is stopped in winter, let the cooling water out to avoid freezing cracks in the cylinder and so on. Suddenly cold and hot can be, the manufacturer suggests it is best to leave it in a standard laboratory, equipped with air conditioning, the temperature can be constant constant temperature of 25-28 degrees is appropriate.

7. Check if the temperature of the suction and exhaust cutting cover at the cross rail of the high and low temperature alternating humidity and heat test box is normal by hand.

8. Check whether the temperature and flow of cooling water in the constant temperature and humidity test box are normal;

9. Check whether the compressor is vibrating and whether the anchor screws are loose and falling off;

10. Pay attention to whether the indication values of the pressure gauges at all levels of the constant temperature and humidity test box, the pressure gauges on the gas storage tank and the cooler, and the lubricating oil pressure gauges are within the specified ranges;

11. Check the supply of lubricating oil in the constant temperature and humidity test box and the lubrication system of the moving mechanism (Some compressors are equipped with plexiglass baffles on the side of the crosshead guide of the fuselage. You can directly see the movement of the crosshead and the lubricant. Supply situation); Cylinders and fillers can be inspected by one-way cutting for oil discharge. You can check the condition of oil injection into the cylinder by the injector;

12. Pay attention to whether the temperature rise of the motor, bearing temperature, voltmeter and ammeter indicate that the situation is normal. The current must not exceed the rated current of the motor. If it exceeds, find the cause or stop the inspection;

13.Is there any abnormal noise during motor heating?

14.Check whether the pressure regulator or load regulator of the constant temperature and humidity test box is sensitive to safety cutting;

15. Regularly clean the refrigeration system, especially the copper tube and bottle body. Check the Freon balance regularly.

16.The gas storage tank, cooler and oil-water separator must always release oil and water.