Blast freezer oil problem

[MDB456]

Hi

Ive recently taken over a site where they have blast freezers, Bitzer HSN 7471 screw package running at -30'C evap, + 35'C cond. System was changed from R22 to 404A, all running well, reaching temp easily. Only problem is the oil keeps pumping from separator. any ideas on what can cause this?

[Fri3Oil System]

Hi,

what type of oil is it? and how did they retrofit this isntall?

Regards,

Nando.

[NoNickName]

What does it mean "keeps pumping from separator"? You mean oil needs to be skimmed out of it?

[MDB456]

oil type is CPI Solest 170 as per Bitzer recommendation, pumping might not be the right wording, it carries over oil from teh seperator.

What I understand from the owner is they flushed the system, changed TEV and changed oil from B100 to Solest 170

Bitzer also says that no oil cooling is needed on 404A at this temp, is that correct?

[Fri3Oil System]

oil type is CPI Solest 170 as per Bitzer recommendation, pumping might not be the right wording, it carries over oil from teh seperator.

What I understand from the owner is they flushed the system, changed TEV and changed oil from B100 to Solest 170

What do you mean by flush? a blow with OFN?

Regards,

Nando.

[MDB456]

Spoke to the owner, he reckons they used 141B cleaning agent to rinse the system and rushed it through with Nitrogen.

[Fri3Oil System]

May I ask you where are you based? R141b has been banned in Europe for a long while now.

[NoNickName]

So if I understand well, it looks like the oil separator does not separate the oil properly, and some of it is flowing in the circuit and carried along with refrigerant.
Is that correct?
Did you check the oil separator technical specs against the use of R404a? The refrigerant mass flow of R22 is different from R404a, and so the efficiency of it may be degraded.

[MDB456]

Thats what it look like NoNick.
Checked oil sep specs with supplier(Bitzer), same oil sep used for R22 and 4040A

Im based in South Africa.

[NoNickName]

Does it happen more frequently when unloading? I would expect a worse separation at low load.

[mad fridgie]

When was the retrofit completed, has it been a problem since the retrofit, how long does it take for the compressor set to loose the oil. and most importantly what do you do when the comp set has no oil, do you just add more.

[NoNickName]

Just to make clear, those compressors don't have any oil, because the oil separator is external. There is just oil circulation in them, but no oil reservoir.

[Magoo]

I would be concerned that it has no oil cooler, at design operating conditions it may not require one, but during high load during pull down after defrosts etc., I am sure it would need an oil cooler. High oil and discharge temps will alter the viscosity of oil and higher velocities would prompt oil carry over from separator.
Have you checked the oil heater operates in off cycle, have you checked the discharge check vav after separator, you may find the seating material has deteriorate with R404A and is leaking back in off cycle causing liquid to condense in oil.

[mad fridgie]

Just to make clear, those compressors don't have any oil, because the oil separator is external. There is just oil circulation in them, but no oil reservoir.

Hi I use the term "compressor set" to mean the package, including moter, oil sep and other sundries built around the compressor, sorry for not making that clear.

[MDB456]

Hi guys

Problem started after retrofit.

I have added more oil thinking that the flushing of the system has obviously removed all the oil from evap and condensor, you will always have some oil stuck in the system. As I have added 50l of oil I think its time to stop!
The oil volume in oil sep is 20l and 14l in oil cooler, that totals to 34l, you guys think the system could use another 15l in piping, evap and condensor?

The oil cooler from the R22 days are still installed and operational, Bitzer just said that its not required.

As this is a blast freezer it never really runs in unloaded conditions for long, oil loss occurs when machine is running 100%

[MDB456]

Also the evap is about 3m lower than the compressor package, this could also be a problem, would you guys suggest a manual return from the evaporator into the suction accumulator?

[mad fridgie]

Any time lines

[MDB456]

system runs for a day with no real problems, then next day client phones, low oil alarm! when system has been standing for a while i start and the oil comes back, maybe its just stuck in the evap?

also the retrofit was done about 4months ago

[Emmett]

What brand and model oil seperator are you using?

[MDB456]

Its a Bitzer OA1954 oil seperator

[lma]

Is your expansion valve rated for R22 or R404a ?

[mad fridgie]

"I assume" when you are there, there is a load and all seems well, suction pressure and temps (SST) are close to design, when you leave, load reduces, this would either cause your SST to drop or the screw unloads. I suspect that your new oil (of which I have no details on) becomes "thicker" (brain freeze can think of the right term) than that of the original oil, reduceing natural oil return at either lower SST or mass flow (unloaded), you either could look at a different oil (a lower flock temperature) which is still acceptable to Bitzer, install an additional coaleser oil sep to reduce, the amount oil leaving the compressor set (masking the system oil return problem) and/or look at your piping arangement (are you using oil traps in your risers and evaps, do you need double risers) and can you ensure better oil return by for example extending defrost, keeping the evap coil warm for longer to give the oil a chance to return to the comp set.

[NoNickName]

"I assume" when you are there, there is a load and all seems well, suction pressure and temps (SST) are close to design, when you leave, load reduces, this would either cause your SST to drop or the screw unloads.

My bet also. Lower refrigerant flow rate, lower straining effect in the separator, because of reduced centrifugal effect.

[mcunliffe4]

install p - trap on outlet of Evap.

[mbc]

you need oil cooler check Bitzer software .
you are using Compressor in blast freezer so you have to check all temp.
are you using ECO. in your system

[MDB456]

ive got a oil cooler installed, yes im using ECO

[juma]

what are your temperature and pressure readings for;suction and discharge at full load capacity using R404a?Also cooling water temperatures ?Mine is also bitzer HSN 7471-75-40P,using clavus R68 OIL and R404a.IT has oil cooler, ECO,water cooling condenser and oil seperater.Its aplication is to liquifying co2.