bitzer condensing unit

As the core and the most expensive component in the HVAC industry, the compressor’s performance and maintenance have always been the most concerned issues for users. Now share the use of refrigeration oil in the use and maintenance of compressors.

How to choose refrigeration oil

1. Refrigeration oil is equipped according to the refrigerant used in the compressor unit.

HFC refrigerants mainly require POE oil, such as R134a, R32, R410a and R407c;

CFC refrigerants or HCFC refrigerants mainly require Mineral oil, such as R11, R12, R115 and R22.

2. According to the operating conditions of the compressor to equip the refrigeration oil

The air conditioning compressor unit is matched with the refrigerant oil with a kinematic viscosity of 30 to 50 at 40℃;、

The cold room and freezer room compressor unit is matched with the refrigerant oil with a kinematic viscosity of 20 to 40 at 40℃;

The high-temperature screw compressor unit are matched with refrigerant oils with a kinematic viscosity greater than 100 at 40°C

Tips for using refrigeration oil in compressors

1. Confirm the amount of refrigerant oil used by observing the amount of refrigerant oil return in the sight glass

After the installation of the whole refrigeration system and the trial start-up operation, the return amount of refrigerant oil should be in the middle line of the compressor sight glass

If the oil return is too high, the refrigerant will be diluted too much, resulting in low cooling efficiency; if the oil return is too low, the lubrication, heat removal, sealing, and insulation performance of the refrigeration oil will decrease. Therefore, when the pipeline of the installed unit is long, the refrigeration oil should be properly replenished.

2. The refrigerant oil needs to be replaced

In order to ensure optimal operation, safety and service life of the compressor unit, maintenance and regular inspection of the compressor is essential, which includes the change of the refrigerant oil. Changing the refrigeration oil includes cleaning the filter. 
The first change is performed after 100 to 200 hours of continuous operation of a new compressor, and then once a year thereafter.
Of course, the replaced refrigerated oil should be treated according to the country’s waste oil treatment method, otherwise it will cause unsafety and pollution.

3. Use of POE oil

When using HFC refrigerant, POE oil should be selected for the compressor, only this type of oil can ensure good miscibility with the refrigerant. 

But it is very important to note that POE oil is very hygroscopic, which means it absorbs and retains moisture from the refrigeration system or the atmosphere. This places high demands on the cleanliness and dryness of the equipment installed by the engineers and operators who install the refrigeration system. 

When the residual humidity is 100ppm, it may cause damage to the whole system.

4. Multiple mineral oils can be mixed

According to the experimental results of BOCK compressors in Germany, FUCHSDEA, MO-BIL, ICI, and LUBIL refrigeration oils can be mixed with the same viscosity. As standard, FUCHS Reniso SP 46 is pre-filled in Bock compressors. It can be mixed with, for example, LUBIL4GS refrigerant oil.

Examples of problems with compressor oil

1. High paraffin content

When the working temperature of the compressor unit drops to a certain value, paraffin begins to precipitate out of the refrigerant oil, making it cloudy. 

If the paraffin wax precipitated from the refrigeration oil exceeds the standard amount, it will accumulate at the throttle valve and block the throttle valve, or it may accumulate on the heat-conducting surface of the evaporator and affect the heat transfer performance.

2. The freezing point is too high

The temperature at which the refrigerant oil cools to stop flowing under experimental conditions is called the freezing point. In refrigeration systems, heat exchange equipment and pipes, usually work at low temperatures and thus an oil film layer will appear on the pipe wall. 

If the freezing point of the oil is too high it will affect the flow of the refrigerant, increasing the resistance to flow and affecting the heat transfer effect. 

Generally speaking, for refrigeration equipment, its freezing point should be as low as possible. In refrigeration systems, the freezing point of the refrigeration oil must be 5°C below the lowest evaporation temperature of the system.

3. Low chemical stability

Pure refrigeration oil is chemically stable, does not oxidize, and will not corrode metal. However, corrosion occurs when refrigerant or moisture is contained in the refrigerant oil.

After the refrigeration oil is oxidized, acid will be generated, which will corrode the metal. Coke will appear in refrigerated oil at high temperature. If the coke adheres to the valve plate, it will affect the normal operation of the valve plate, and it will also cause the blockage of the filter and throttle valve

Therefore, it is necessary to choose a refrigeration oil with good chemical stability and oxidation resistance.

4. Mechanical impurities and moisture content exceed the standard

If the refrigerated oil contains water, it will deteriorate the oil, cause corrosion to the metal, and also cause “ice blockage” at the throttle valve or expansion valve. 

The refrigeration oil contains mechanical impurities, which will aggravate the wear of the friction surface of the moving parts, and quickly block the filter and throttle valve or expansion valve.

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