Precautions for Using Rotary Refrigeration Compressors

2025-02-17

In a rotary compressor, the motor doesn't need to convert the rotational motion of the rotor into the reciprocating motion of the piston. Instead, it directly drives the rotating piston to rotate to compress the refrigerant vapor.

Precautions for Using Rotary Refrigeration Compressors1739805758690

This type of air compressor is more suitable for small - sized air conditioners, especially being widely used in household air conditioners. It adopts a cooling method where part of the refrigerant liquid from the condenser is led to the compression chamber through pipes and sprayed inside the cylinder, thus improving the cooling effect.

Discharge Temperature
The discharge temperature is generally required not to exceed 115 °C. The discharge temperature directly affects the safe use of the compressor. Most household rotary compressors are of the high - pressure - chamber type, and their motors are cooled by the discharged gas. Therefore, it must be strictly controlled. Under no circumstances should it exceed the specified upper limit. When used in an air - conditioning system, if the discharge temperature is too high, the refrigeration system should be redesigned, the refrigerant charge and throttling device should be adjusted, or bypass cooling measures should be added.
Discharge Pressure
Depending on different refrigerant types and the compressors of various manufacturers, the discharge pressure has different upper limits. If the discharge pressure is too high during operation, the following faults may occur:

Excessive rotor load, resulting in poor lubrication, severe wear and seizure of sliding parts, exceeding the compressive strength of the compressor.
Excessive load torque, causing motor failure.
Excessive current, causing faults in the electrical control system.
Rapid increase in compressor temperature, resulting in insulation failure of the motor winding, deterioration of the lubricating oil, motor burnout, and wear or even jamming of the mechanical running parts.

Suction Temperature
The control of the suction temperature is mainly manifested in two aspects:
(1) The upper limit of the suction temperature generally should not exceed 35 °C. Otherwise, it is likely to cause the discharge temperature to be too high.
(2) Lower - limit control of the suction temperature. To control its lower limit, a certain degree of superheat needs to be maintained to avoid the problem of liquid hammer caused by inhaling liquid refrigerant.
Suction Pressure
The suction pressure has different range values according to different refrigerant types and the actual situations of various manufacturers. If the suction pressure is too low, the following faults will occur:

Insufficient lubricating oil, resulting in wear of lubricated parts.
Reduction in the refrigerant circulation volume, reducing the cooling capacity.
It is easy for air to enter the system, especially under negative pressure, affecting the compressor and the entire refrigeration system, and reducing the effect.
Water in the system freezes, causing ice blockage.
If the system pressure is too high, the following problems will occur:
Overheating of the compressor, causing over - heat faults.
Excessive discharge of lubricating oil, affecting lubrication and reducing the heat - transfer efficiency of the heat exchanger, thus affecting the refrigeration effect.
It is easy to cause excessive liquid return, resulting in a liquid - hammer phenomenon and damage to the mechanical components of the compressor.

Compression Ratio
The compression ratio depends on the suction and discharge pressures. Under the premise of meeting these two pressures and during normal operation, it generally ranges from 2 to 8. If the compression ratio is too small, it may lead to excessive circulation volume and cause faults. If the compression ratio is too large, the following faults may occur, affecting the service life of the compressor:

High refrigeration load, resulting in excessive rotor load and causing mechanical wear.
Increase in compression heat, too high discharge temperature, and overheating inside the motor.
Excessive current, burning out electrical components.

Motor Winding Temperature
The general upper - limit temperature of the compressor motor winding is 120 °C, corresponding to the insulation class "E". If the temperature is too high, it will cause the insulating varnish of the motor copper wire to age and fail. In severe cases, the motor will burn out, affecting the performance of the lubricating oil and causing rapid mechanical wear. The motor temperature generally cannot be measured directly. In engineering, the resistance method is used for measurement, and the motor winding temperature is calculated according to the following formula.
Housing Temperature
Regarding the high - temperature requirement, there is generally no specific value, basically following the principle of not exceeding the specified discharge temperature.
Regarding the low - temperature aspect, if the housing temperature is too low, the refrigerant will condense in the housing and mix with the lubricating oil, reducing the effect of the lubricating oil and accelerating the wear of mechanical components. Therefore, the housing temperature should be higher than the saturation temperature of the refrigerant, and generally, the superheat requirement is > 5 °C.