Oil Migration

[NorthSeaTech]

Hi guys,

I am experiencing problems with oil migration. I have Trane CRHM200 liquid cooled units. The units run fine unloaded however as soon as they are loaded the oil literally disapears out the sight glass on the compressor. This problem has been ongoing before i came to work on the system.

The system consists of 2 trane crhm 200 compressors, 2 bitzer condensers and trane evaporator. Both compressors loss oil on load although i am only running one at the moment (unloaded).

Any Ideas

Thanks in advance

[Gary]

Does one gain what the other loses?

[NorthSeaTech]

Does one gain what the other loses?

Hi Gary,

No one does not gain. The oil is migrating to the condenser again only on load. The strange thing is that in this particular application we have two skids of the same equipment. One skid has no oil migration problems where as this one does.

Thanks

[sedgy]

hi northseatech,I think you answered your own question , when you said running un-loaded

[desA]

What kind of gas velocity is there in the compressor discharge line?

[chemi-cool]

Hi NorthSeaTech,

Oil dont just disapear, I think what you see is only the out come of another problem.

All the problem I had so far with oil migration, turned out to be a faulty TXV. Please have it checked!

You did not mention how the unit works, is it a pumpdown? Electronic TXV?

When the compressor unloads, what is the pressure situation? Doe's it stay low? Doe's refrigerant flow back to the compressor?

You have to check the system at a full cycle and then come with the results.

Important thing - Do not add oil as you did not lost any.

[Gary]

As I understand it, you have two compressors in parallel. There must be some form of oil equalization between them. Possibly an oil separator, reservoir and float system?

Does the system have an accumulator?

Have you checked the subcooling?

Have you checked the superheat?

[chemi-cool]

Hi Gary,

As I see the problem, oil migrates at start up, therefor it in the compressor before the compressor unload.

That brings me to think of flood back at upload.

[desA]

What happens at the system full-load steady-state?

Does the oil return from the condenser, via the TXV, to evaporator, to compressor? How are the oil-level gauges connected to the compressor? Any pictures?

To make sense of this, a lot more information is required: a full set of system readings at low-load/high-load, piping sizes & pictures.

[lowcool]

im with gary,check condensing temp to design,check gas charge then check superheat across evap whilst fully loaded

[D.D.KORANNE]

gas & oil balancing lines needed since parallel operation of two skid mounted compressors . in either case loaded or unloaded condition, probably oil will balance out . second, oil will need to be kept warm yo avoid gas condensation in crank-case .

[onetastyburger]

Could the failure of the internal baffles on the evaporator cause this?

If the baffles have failed and are not allowing the refrigerant to evaporate fully at full load then liquid would return to the compressor and wash out the oil. Wouldn't particularly need a lot of liquid, just a constant flow of it.

During part load operation the liquid is sufficiently evaporated off and only gas returns to the compressor.