Overheating of the exhaust temperature in refrigeration systems may involve multiple reasons. In order to ensure the stable operation of the system, we need to explore these potential factors in depth and take corresponding solutions. Next, we will explore these causes and solutions to help you better understand and deal with this problem.
In the daily operation of refrigeration systems, abnormal increase in exhaust temperature is often regarded as an important warning sign. This problem may not only mean that there are some faults or design deficiencies in the system, but also have a serious impact on the performance and life of the compressor. To understand this phenomenon more deeply, we will comprehensively analyze the main factors that lead to excessive exhaust temperature and explore corresponding solutions.
Excessive exhaust temperature is an issue that needs to be taken seriously. Its possible reasons include but are not limited to the following:
1. High return air temperature:
Compared with the evaporation temperature, if the return air pipeline is not properly insulated, the superheat may exceed 20°C. As the return air temperature rises, the suction temperature and exhaust temperature of the cylinder will also increase accordingly. Specifically, for every 1°C increase in return air temperature, the exhaust temperature may increase by 1 to 1.3°C. For semi-hermetic compressors, the temperature rise of the refrigerant in the motor cavity usually ranges from 15 to 45°C. It should be noted that in air-cooled (wind-cooled) compressors, there is no problem of motor heating because the refrigerant does not flow through the windings.
2. Motor heating
In return air-cooled compressors, motor heating is an inevitable process. When the refrigerant vapor flows through the motor cavity, it will be affected by the motor heating, which will lead to an increase in the cylinder suction temperature. The heat generation of the motor is closely related to power and efficiency, while power consumption is affected by many factors, such as displacement, volumetric efficiency, operating conditions, and friction resistance. Therefore, in return air-cooled semi-hermetic compressors, the temperature rise of the refrigerant in the motor cavity also exists.
3. Excessive compression ratio
There is a significant correlation between exhaust temperature and compression ratio. The larger the compression ratio, the higher the exhaust temperature. In order to reduce the exhaust temperature, the compression ratio can be changed by adjusting the suction pressure or the exhaust pressure. The suction pressure is mainly affected by the evaporation pressure and the resistance of the suction line. Increasing the evaporation temperature can effectively increase the suction pressure, thereby reducing the compression ratio and exhaust temperature. However, it is worth noting that the lower the evaporation temperature, the better. Too low an evaporation temperature may reduce the cooling capacity of the compressor, while increasing the load, resulting in longer operating time and increased power consumption. Therefore, these factors need to be considered comprehensively when optimizing the system.
In addition, reducing the resistance of the return air line is also an important means to increase the return air pressure. By replacing the clogged return air filter, shortening the length of the evaporator pipe and the return air line, the return air pressure can be effectively increased, thereby reducing the exhaust temperature. At the same time, ensuring sufficient refrigerant is also one of the key factors to maintain stable suction pressure.
4. High condensation pressure
The increase in condensation pressure is also a factor that cannot be ignored in causing the exhaust temperature to rise. This may be due to a variety of reasons, such as insufficient heat dissipation area of the condenser, fouling, insufficient cooling air volume or water volume, or even too high a temperature of the cooling water or air. In order to effectively deal with this problem, we need to carefully select a suitable condensation area and ensure sufficient flow of the cooling medium.
5. Anti-expansion and gas mixing
After the suction stroke begins, the high-pressure gas in the cylinder clearance will undergo an anti-expansion process. During this process, these high-pressure gases will contact and absorb heat from the high-temperature surfaces of the valve plate, the top of the piston, and the top of the cylinder, resulting in the temperature of the gas not dropping to the suction temperature at the end of the anti-expansion. Then, the real suction process begins. At this time, the gas entering the cylinder will not only mix with the anti-expansion gas and heat up, but also absorb heat from the wall to further heat up. Although these two processes are short and the actual temperature rise is limited (usually less than 5°C), their impact on the exhaust temperature cannot be ignored.
6. Compression temperature rise and refrigerant types
Due to their unique thermophysical properties, different refrigerants will have different increases in exhaust temperature after the same compression process. Therefore, when selecting a refrigerant, the refrigeration temperature requirements must be fully considered.
In summary, the compressor should not have overheating phenomena such as high motor temperature or excessive exhaust temperature within the normal operating range. These overheating phenomena are often warning signs of serious problems in the refrigeration system or improper use and maintenance of the compressor. If the problem is with the refrigeration system itself, then improving its design and maintenance practices are key to resolving the problem. Simply replacing the compressor may not eliminate the root cause of these overheating problems.