Regarding the oil return of the refrigeration system, keep these points in mind.

Regarding the oil return of the refrigeration system, keep these points in mind.

  • 2020-11-27

1. Overview

Although there are oil separators in the equipment, it is inevitable that a small amount of lubricating oil will enter the condenser and other components and pipelines with high-speed airflow. Therefore, the design of the components and the installation of the pipelines must be carefully considered.

A poor refrigeration system is designed and installed. The oil returned to the compressor is less than the oil from the compressor exhaust, and the compressor will gradually lack oil.

If additional oil is added to the compressor, it can only be maintained for a period of time, and the addition of excess oil in the system will affect the heat transfer of the evaporator and condenser. In order to ensure a good oil balance in the refrigeration system, there must be a few points to note when designing and installing the pipeline, as follows:

2. Flow rate and slope

The horizontal pipeline of the system should have a slope of (0.5%~1%) with the flow direction of the refrigerant, so that the lubricating oil can move forward

3.U type oil return bend

The upward flow of gas The bottom of the vertical riser needs a U-bend for oil accumulation. When the U-shaped bent oil is continuously increased, the cross-sectional area is gradually reduced, and the air flow speed is increased, thereby facilitating the gas to be oiled.

If the riser is above 6 m, add a U-bend. The U-bend should be made as small as possible to avoid accumulation of too much oil.

4. Parallel Compressor

1) When the number of compressors is paralleled, in order to adapt to the system load change, two vertical risers should be made. The U-bends at the bottom of the two risers are high and low, and the height difference is greater than 2 times the diameter.

2) The system load is small, the number of compressors is small, the refrigerant flow rate is small, the flow rate is low, the oil return is unfavorable, the U-shaped bent oil with low position is gradually increased, and the oil seal is formed, and the refrigerant gas can only be from another tube. The passage of the road increases the gas flow rate and ensures that the gas carries oil.

3) In order to prevent the refrigerant liquid from entering the compressor, the parallel unit needs to install a gas-liquid separator. If it is a gas-liquid separator, the gas riser of the gas-liquid separator should also be made in two ways to make it have a reasonable flow rate and good oil return.

4) For equipment with multiple evaporators or multiple condensers, due to the complexity of the pipeline and the variability of equipment operation, the oil return is slow, and it is necessary to install an oil separator separately.

5. Compressor suction pipe

The suction pipes of the compressor are connected in parallel, and they are connected to the suction manifold.

Due to the difference in the level of the suction manifold and the difference in the path, it is necessary to consider that the oil returning from the suction manifold to the compressor should be equal.

If the suction pipe of the compressor is connected to the lower part of the pipe, it will make the oil return uneven. Therefore, it should be connected by the method shown below to bring the oil at the bottom of the suction pipe back to the compressor at the speed of the air flow.

6. Oil storage device

The oil storage device of the parallel unit needs to have enough reserve oil. Some parallel unit systems are relatively large, the equipment may have different degrees of oil storage dead angle, and some oil is also dissolved in the refrigerant. Therefore, some lubrication is needed in the system. The oil, generally can be added according to 0.5% of the refrigerant charged.

After the unit has been running for a while, you should observe the oil reservoir and observe the oil mirror to correct the oil quantity.

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