Compressor lubrification issue

[RODRIGO BR]

I'm facing an issue regarding to the compressor fail. After compressors laboratory analysis it was identified fail due lack of oil.
it was observed after about 2 hours of operation, the oil level of the compressors goes down to 1/4 of the oil sight glass and remained too low after this time.
The system oil charge apparently is correct as infomed by the equipment manual. The system oil charge is based on the system refrigerant charge.
During the equipment operation it was observed in the remote condenser (V shape), some tubes in the lower part are cold and the liquid line pipe in the outlet of the condenser warm.
At the lower part of the condenser has a schrader valve, where was found the presence of cold oil, during equipment operation.
The condensing pressure is setting to 27 bar (R410A).
The evaporator unit and remote condenser are in the same level, piping has about 50 m of equivalent lenght. The unit have 100KW of total cooling capacity with 2 compressor Copeland mod: ZP154KCE-TFD-523. Two independent circuits.


Is it possible the oil is being trapped on the condenser, and no returning to the compressor?
Is there other possible reasons for this kind of issue?


Thanks a lot!

[Glenn Moore]

V coil condensers often cause liquid supply problems due to pressure imbalance between the two ‘V’ coils. There is always a dominant coil with an easier gas flow, whereas the slave coil which has a higher pressure drop will have liquid backing up in the coil.
The outlet pipework of the ‘V’ coils must be connected to balance the pressure drops of the coils. .
The outlet pipe work connections should have drop legs of approx 1 metre before being teed together . This allows the drop legs to have liquid columns to balance the 2 coils so that equal flow occur between the coils.
If it is not possible to have these drop legs due to space limitation , then it is possible to use an injector tee to to the outlet junction so that the dominant coil flow induces the slave coil to also flow.
It is easy to check if the coils are out of balance by simply holding the 2 out let pipes with your hands, they should be the same temperature, if there is a definite temperature difference then you have one coil that’s backing liquid and oil and the other coil passing liquid and hot gas . This will also cause poor system duty as the liquid quality onto the expansion valves will have little or no subcooling onto the expansion valve , this will cause excessiv flash gas and hence poorer capacity.
From what you say about the tubes in the condenser being cold and the outlet connection being warm I suspect this is your problem

[RODRIGO BR]

Hi Glenn,

First of all thanks for your reply.
In this case the two coils are not connected because each coil is refering to an circuit. The unit has two independent circuits.
Please see the pictures of the behavior of the condensers.
Due the fact the evaporator and condensers be installed at the same level, and could be a problem? Or condenser oversized?

Thanks a Lot,



Screenshot_20200516-055737.jpgScreenshot_20200516-055726.jpg

[RODRIGO BR]

Hi,

Just to give a feedback about some informativon I had received from the condenser's manufacturer of this case.
This specific model condenser from this manufacturer, it is only recommended and suitable to install the V-Shape condenser at 1,5m above the compressor's level. Below this height the condenser could retain oil.

Thanks to everyone who helps some way.

Rodrigo

[monkey spanners]

Makes me wonder if the condenser has been made correctly? If there is a dead circuit with an inlet but no outlet oil could collect in it. Just an idea!