In the air conditioning refrigeration system, the compressor compresses the low-temperature and low-pressure refrigerant vapor into high-temperature and high-pressure superheated steam, and its exhaust temperature is generally much higher than the condensing temperature. Excessive exhaust temperature will cause the lubrication performance of the refrigeration oil to decrease or even carbonize, thereby overheating and wearing and damaging the service life of the compressor.
The exhaust temperature of the compressor is mainly affected by the suction temperature of the compressor, the compressor load and the type of refrigerant (adiabatic index).
Factors leading to high exhaust temperature:
1. High suction temperature
The exhaust temperature of the compressor is obtained after compression and pressure increase based on the suction temperature. Therefore, every 1°C increase in the suction temperature will inevitably lead to an increase in the exhaust temperature of 1~1.3°C.
The reasons for the high suction temperature include insufficient or leaking refrigerant, too small an expansion valve opening, blockage of the expansion valve or filter, etc., which all result in a small amount of liquid supply to the evaporator, insufficient evaporation in the evaporator, and continued overheating after evaporation, resulting in a large suction superheat, high suction temperature, and high exhaust temperature.
2. Heavy load on the compressor
When the load on the compressor is heavy, the power consumption and current of the compressor are also large, and the compression work is eventually converted into heat, which increases the exhaust temperature.
The reasons for the heavy load on the compressor are heavy external load, excessive refrigerant, large compression ratio, and large heat dissipation of the motor.
Excessive refrigerant causes the compressor to have a heavy load, high power consumption, and high exhaust temperature. Combined with the previous, it can be seen that whether there is too much or insufficient refrigerant, the exhaust temperature will increase.
The compression ratio is the pressure ratio between the high-pressure side and the low-pressure side. The larger the compression ratio, the greater the power consumption required for compression lifting, resulting in more compression heat and high exhaust temperature.
For compressors that use return air cooling motors, the heat dissipation of the motor is also large when the load is large, which increases the exhaust temperature. Usually, air-cooled heat pump units do not use return air cooling motors, so the exhaust temperature is not affected by the heat dissipation of the motor.
Blockages in the refrigeration system, including ice blockage, dirty blockage, and oil blockage of the expansion valve, filter dryer, etc., will cause insufficient refrigerant in the evaporator and reduce the low pressure, and excessive refrigerant in the condenser and increase the high pressure, resulting in a large compression ratio and high exhaust temperature.
Poor heat dissipation of the indoor unit, such as filter blockage, air circulation short circuit, fan failure, evaporator frosting, etc., all reduce the flow and heat exchange effect of the indoor air, making the evaporator absorb less heat from the outside, evaporation less and suction pressure low, resulting in a large compression ratio and high exhaust temperature.
On the contrary, when the exhaust temperature is too high, appropriately increase the opening degree of the expansion valve, increase the liquid supply of the evaporator, increase the evaporation pressure and temperature, not only increase the suction pressure, but also reduce the suction superheat and suction temperature, which can effectively reduce the exhaust temperature.
3. High condensation pressure
The condensation pressure increases, and the corresponding condensation temperature is also high, and the exhaust temperature is the superheated steam temperature higher than the condensation temperature, so it will force the exhaust temperature to increase. At the same time, the increase in condensation pressure also means that the compression ratio becomes larger, which also increases the exhaust temperature.
The main reasons for the increase in condensing pressure and temperature are poor heat exchange between the condenser and the external medium, including excessive refrigerant, non-condensable gases such as air, insufficient external cooling water, high cooling water temperature, insufficient cooling air volume, too high air temperature, and scaling of the internal heat exchange copper tube.
In summary, the exhaust temperature is the temperature obtained after compression and pressure increase based on the suction temperature, so it increases with the suction temperature and the load during compression. The compressor load increases with the refrigerant flow rate and the compressor ratio, and the increase in compression ratio includes an increase in the condensing pressure on the high-pressure side and a decrease in the suction pressure on the low-pressure side. By analogy, the causes of these changes in the system may all be the cause of the increase in exhaust temperature.