R 407 C fractionation

[Argus]

I am hearing some rumours about unexplained fractionation of the refrigerant charge during operation when applied in certain VRF systems using R407C.

There seems to be more heat than light on the subject, does anyone have any experiences they can share?

Is this another anomaly or something to worry about?

[frank]

Argus

VRF or VRV

We are Daikin dealers so there lies the question.

We have insalled many of these systems and have not really experienced any problems that relate to your question. The electronics within each system are designed to provide the correct operating parameters no matter what the refrigerant, i.e. R22 systems electronics will be totally different fron R407c electronics. Fractionation is taken care of within R407c systems by the sensors and controls.
What kind of problems are you experiencing or what are your concerns - more specifically? (sp?)

[DaveWright]

The problems seem to occur during low heating and/ or cooling requirements and manifests itself by lack of performance or unexplained high pressure and high discharge temperature trips during cool ambient conditions.
Sometimes, if the ambient is low enough the refrigerant will migrate to the condensing unit where the blend is corrected and the system operates correctly on restart, but in other, more severe cases the system needs be pumped down or the refrigerant recovered and recharged back into the system to effect it.

[Argus]

Frank, Dave,

Thanks for your replies, I’d begun to think that this one had fallen on stony ground…
I’m not in this line of business any more, Frank, so I don’t have an axe to grind, but there are a number of reports, mostly apocryphal, that are circulating.

I am not using any brand names whatsoever, so I’ll stick with the generic term, VRF, because this separation under certain load conditions is a potential problem for all makers.

It is the inexplicable loss of performance and unstable pressures described by Dave that intrigues me. The more I think of it, there is no reason why the phenomenon should be confined to variable multi-splits, is there?

Some makers may have recognised this with automatic pump down cycles incorporated in the operation controls…..

One of the apparent sales points with this type of equipment is the ability to operate at low capacities, so perhaps a turn-down to 4 or 5 per cent is not really desirable.
Add to this the high risk of component failure, compressors etc, plus (and I am not sure how the resultant composition of gases would stack up), any separation and migration of the 134a component would leave a resultant mixture resembling R410 mixture. I cannot find any research on the subject of how a system would behave in these conditions. More to the point – what causes it? There were some tests done in the early 90s that simulated leakages on a system assuming fractionated gas leaks followed by a refill – but not the same thing.
We all know that R407C is not considered suitable for flooded evaporators, but VRF systems are mainly pipework assemblies and don’t tend to have the large voids that promote separation.

Is this a result of the undue haste to ditch HCFCs in the EU? After all, R22 was considered far more effective in these applications than some of the replacement blends.

[frank]

Argus

I can't say that I have witnessed any of the symptoms that you describe in any VRV or VRF systems (lets face it - they are the same thing ).

Lets take the mode of operation of these systems:

Cooling operation.

Inverter driven compressor that senses suction pressure to vary the load. Each indoor fan coil has an EEV which throtles back as set point temperature is neared causing suction pressure within the common suction line to decrease. This enables space temperatures to be controlled within one half a degree of set point.

Fractionation will only take place within the evaporator as each component of R407c has a different boiling point, so the make up of the refrigerant entering the evaporator will be different to the make up of the refrigerant leaving . As set point within the space is neared the valve will pulse to close and restrict the flow of refrigerant throught the coil. As this happens the evaporator will then be starved of refrigerant. The key to the control is the space sensor and the EEV constantly modulating to reach set point.

As refrigerant velocities reduce during low load conditions, the electronics are programmed to carry out an oil recovery sequence every 8 run hours. This is achieved by the compressor ramping up to full speed and all the indoor EEV's opening 100% for a short period. To control air off temperatures during this oil recovery time the indoor fan is either set to low or switched off. All the time the compressor just ramps up and down depending on the common suction pressure. The temperature of the refrigerant and therefore glide does not really form part of the control strategy although temperatures are compared across the system as a whole every 20 seconds and are measured against a database within the software, any vast deviation would then be flagged up as a fault.

Heating operation.

This obviously works in the reverse with the indoor fan coils acting as condensers, each feeding liquid into a common liquid line and this time the common liquid line pressure is monitored. During low ambients, you would assume that the system would be working in heating mode and therefore the outdoor coil would be acting as the evaporator. Liquid migration would not be a problem as the suction accumulator would prevent liquid hammering, and any fractionation within the coil would be reduced due to low ambients. As each indoor space nears set point the EEV pulses closed and the liquid line pressure drops which slows the compressor.

Heating/Cooling operation

This gets a little more complicated control wise but the general operation does not alter. It is just a case of diverting dischage gas/liquid/suction gas through multiple sets of soloenoid valves to ensure that each individual indoor fan coil gets either hot gas in and liquid out or liquid in and suction gas out. With a balanced indoor circuit the outdoor coil is not required.

With all the measurements, safety circuits and electronic controls built into these machines I have never seen any effects from fractionation that give the symptoms you describe, or the concerns you have.

The selling points of these types of systems is purely the efficiencies and the ability to cool and heat simutaneously. I have seen studies of the use of R407c compared against R22 and one study clearly proved that 407c was about 5% less efficient than 22 at evaporating temperatures down to +5C and efficiencies then drastically reduced below +5C. It was also clear from the study that 407 is not suitable for low temp applications.

Frank

i was speaking to a friend who has fitted loads of 407 a/c kit and had a lot of trouble with the capilaries blocking a'la 134a fridges..

he has also had a lot of 410 stuff with leaks from the factory -he suspects it's 407 kit with 410 shuved ib it to look 'trendy '

i wonder if we shall be looking at an a/c disaster in 3-5 yrs time...??


cheers

richard

[Abe]

In a nutshell............R407 is crap
407 does fractionalise , is less efficient, and heavens you have a leak, you in " deep" ****
Time our "industry" stood up to the manufacturers and dictate what we want
Manufacturers dont care a hoot about the installer , end user or if a cap tube or compressor fails after a year
Their assembly lines must be kept operational 24 hours, and the more they break down the more money they make
We the installers are the front line troops or the pawns, we are the cannon fodder
I have installed R407C systems, give me R22 anyday

[Prof Sporlan]

Aiyub, consider R-407C as your temperamental kid…

With lots of love and care, he/she will turn out almost as well as your R-22 kid.

[Jasper]

With lots of love and care, he/she will turn out almost as well as your R-22 kid.


I have to agree with the prof, cleanliness during instalation is vital, high pressure ofn testing is a must and if a system has a leak all refrigerant must be reclaimed, the leak repaired and new refrigerant weighed into the system.
As long as these rules are followed there should be no problems encountered.

Having fitted numerous R407C systems i have never come across any of the problems described.

[Abe]

I must add to be fair, that to date, I have had no problems with R407 systems that I have installed. But then I am critical about the quality of workmanship that goes into an installation.

My fears stem more from fear of fear itself. ie: Try teaching a dog new tricks.

Fingers crossed, I hope this new baby comes aboard and we dont have probs emanating a short way down the line.

With the support the prof has thrown, I feel a little more comfy then I did before....

So , like it or leave it, Im all for steaming on.........

been talking to someone who knows..

toshi does have a problem with fractilisation in 407c..there are several systems that have caused real big head aches diagnosing WTF is going on.....

it would appear if certain systems run too long in cool/heat breakdown 'can' occur in the accumlator causing it to separate to give 410 in the top part of the acc. and because of it's higher -boyles law etc- pressures blow the relief valve..this causes performance problems and the fun starts..

mitz and dai don't seem to have these problems...yet

(names disguised to protect the guilty;-)
cheers

richard

[Latte]

There must be some problems with fractionation with R407c, The subject has made it into to autumn Service Engineer Magazine (Available from HRP). As per usual the manufactures say there should not be a problem, but i guess as its in the mag there most be some problems with it. We will wait and see

[Big Ed]

To be fair, the article says "Fractionation will only happen in a few very exceptional circumstances and anamolous pressures can occur for other reasons."

The Institute of Refrigeration's Guidance Note lays it all out pretty well - see www.ior.org.uk