Suction accumulator

[lana]

Hi there,

Zeotropic blends have different compositions in liquid and gas states :

Is it OK to use suction accumulator for a system using Zeotropic blends (400 series)?

Cheers

[Tony]

Hi lana,

Yes is the short answer.

There are numerous R407C systems out ther with them fitted.

[nike123]

Page 23 bottom, last sentence:
http://ra.danfoss.com/TechnicalInfo/....004.A3.22.pdf

[TRASH101]

Good find Nike

I wonder why as some protection must be better than less.

[nike123]

Good find Nike

I wonder why as some protection must be better than less.

Because of fractionation of R407C!
I presume, if we use suction accumulator, eventually all refrigerant will fractionate in it because there is not enough pressure differential (7K) to ensure evaporation of all components.
I also could be wrong!

[Sandro Baptista]

Because of fractionation of R407C!
I presume, if we use suction accumulator, eventually all refrigerant will fractionate in it because there is not enough pressure differential (7K) to ensure evaporation of all components.
I also could be wrong!

I agree with NIKE. I think it should be ensure that the superheat been higher than the glide temperature. Otherwise on the HP side the pressure will increase.

[Thermatech]

Back in the 1990's some VRV manufacturers were retrofitting R407c into new R22 systems because consultants were demanding R407c equipment before the manufacturers had fully developed new equipment which was optamized for R407c.
Generally the systems worked ok provided the oil was changed to synthetic.
However in time a small problem became apparent. This was called fractionation.
This tended to occur when the compressor ran at very slow speed for long periods of time due to very low load & the suction accumulator is then almost full of liquid refrigerant because only a small amount of refrigerant is circulating in the system.
What tends to happen at the suction accumulator in this operating condition is that the compressor takes the vapor from the accumulator but it tends to be a high consentration of high pressure refrigerant & the low pressure refrigerant (R134a) gets left in the accumulator as liquid.
So most of the R134a is sitting in the accumulator & only the higher pressure refrigerants of the blend are circulating arround the system.
In this situation the discharge pressure gradually gets too high & can trip on HP.
As the manufacturers delevoped the new R407c optamized systems this problem was designed out with clever monitoring & electronic control stratagy.

If you have a system with direct on line compressor then fractionation may not be a big problem but if you have capacity control & possibilty of slow compressor speed then I would suggest looking carefully at the posibilty of fractionation.

[NoNickName]

AHahahah... almost all systems with R404a have got suction accumulators.

[Sandro Baptista]

AHahahah... almost all systems with R404a have got suction accumulators.

NoNickName, the R404A glide is very smal less than 1K so maybe that problem don't get so significant.

[NoNickName]

Maybe, but that's not what is written in Danfoss document.

[nike123]

I suppose that, if pressure drop in suction accumulator is smaller than R404A glide, then it will fractionate too!

[lana]

Hi everybody and thanks for your reply.

Still I am not sure if it is YES or NO.

Split air conditioning units with R410 with heat pump have suction accumulator because of mode change????

Any comments?

Cheers

[nike123]

Split air-conditioners have obligatory suction accumulator because rotary compressor they use takes suction directly in cylinder and housing is on high side. If they don't have suction accumulator, they will be ruined by first few droplets of liquid refrigerant in suction pipes.

It should be added here that, in rotary compressors, suction accumulator is welded on compressor body and good thermal contact is with hot compressor housing, and that all liquid in it is evaporated during off cycle. Therefore, separation in this case is not likely. That also helps in cooling of compressor.

That is not the case with separated suction accumulator and fractionation is more likely.

I suppose that simmilar is with scroll compressors. They are constructed in way that some small quantity of liquid in housing is harmless and, when compressor is in off cycle that small quantities are evaporated by heat of housing and motor. Therefore, suction accumulator is not necessary.

[nike123]

http://www.hvacrforums.com/showthread.php?t=8

[lana]

Thanks everyone.

It has been a long time since I read anything from Marc .

Cheers

[Sandro Baptista]

I suppose that, if pressure drop in suction accumulator is smaller than R404A glide, then it will fractionate too!

With R404A for dry expansion with a superheat higher than 4 K no harm will happen.

With R404A for pump system I think the R134a tends to stay in the suction acummulator with the % for new phases equilibrium/new little change of the evaporating temperature. The others two components that go to the HP side are the same of the R507 (only the percents are a little-little differents).

[D.D.KORANNE]

In order to get around the problem of liquid carryover to compressor , accumulator , pump down cycle and ensuring a superheat in part or combination can support compressor life. However , many times with all the fine tuning on pump down cycle plus tex superheat , flood back to compressor is addressed by incoroprating an accumulator in system . Accumulator will also useful in arresting liquid since tex valve is fully open during start up when suction pipe is warm unless mop is used. Accumulator is an added security to te system in majority of cases.

[assidly09]

No pressure sensor is useless in the suction housing the problem is that most of or data has been taken from those spot on the suction housing so if your were to tell me pressure reading I would not have any data to refer to. On the new boat we have installed a Race Pack system so we have as many as 72 sensors so we will be able to able to receive more data than we will know what to do with.

[DEVIL]

my opinion is a strong YES , but if you make shore some conditions are met

Practically the suction accumulator is just for protection so only in the worst case scenarios you use it, if all the system is sized correctly it ain't the case.

At the beginning of using blended refrigerants Daikin added in the electronics of the system a procedure that was protecting it against oil not returning and fractionation effect , so if you have a inverter unit you should make shore the unit is not running for a long period of time in low demand mode, and if it dose add a safety procedure that revs am an 100% demand , ore u could do a technical pump down so all the refrigerant gets back in the liquid receiver and your safe.

But the case depends an wat TYPE of system is it , AC, refridge , and so on.