Overcondensing that much?!

[paul_h]

* Titled changed from 'overcondensing' to 'poor engineering' to keep NoNickName happy.

I've got a 1.5T ice machine on R22 with a couple of problems, the main one is slow ice production.
The condenser fans cycle on at 1700kPa (the ambient here today was 17C).
Now the 1m tall upright receiver capacity is about 80kg (uses refrigerant from it to harvest).
When the condenser fans are not running and the hp is ~ 1500kPa, the reciever column sightglass shows it's about 1/3rd full of liquid, and the sightglass before the TXV shows full.

Whenever the condenser fans switch on at 1700kPa HP, the HP drops to about 1400Kpa until the CF cycle off.

The really wierd thing is the moment the CF fans cycle on, the entire receiver empties of liquid refrigerant.
The level of refrigerant drops about 1cm a second, and then sightglass at the TXV is almost empty.
About a minute or two later, the CF cycles of, pressure starts climbing again and the receiver fills up to about 1/3 capacity again.

[RANGER1]

Maybe the pressure is dropping that fast its flashing off in reciever & liquid line giving the appearance of a dissapearance .
Either that or its syphoning back up into condenser .
You could add more refrigerant to see what happens .

[Sandro Baptista]

...or its syphoning back up into condenser .
You could add more refrigerant to see what happens .

Paul, can you explain us how is connected the air condenser to the receiver?
Do you have "P" traps?

Is the liquid receiver located at a very warmer place compared with the ambient temperature?

[paul_h]

There is no traps that I have noticed (there's an oil separator next to the compressor).
I'd say the receiver is warmer than the ambient or the condenser.
The remote condenser is on the roof, and it's winter here, ambient was 17C today.

The receiver is sitting just above the compressor inside the factory, and the machine (patkol pk-1500) is in a factory with other ice machines so warmer than ambient where the receiver is right now, especially with the heat from the compressor.

[Sandro Baptista]

So let me see if I understand: you have the liquid receiver mounted on an ambient around that is warmer than the ambient where is the condenser mounted?
Does the ambient temperature around the liquid receiver is higher than the condensing temperature on certain periods of compressor/condenser operating? Does the temperature around the receiver is higher than when the condensing temperature when you are operating with the condenser fans?

If that so, and if may need to increase the discharge liquid line from the condenser to the liquid receiver or mount an equalizing line between the the liquid receiver (upper side connection) with the inlet of the condenser. Make sure you have around 2 meters of level difference between outlet condenser and liquid receiver.

[Grizzly]

Paul
I suspect you have already sussed this one .

It seems to me that the remote condenser and fans are creating very low pressure temps.
IE. R22 @17c = less than 7.5 bar.
Being a remote condenser I would assume the liquid line between is subject to the same ambient.
At a guess, the liquid is travelling between the condenser and receiver.
Because the condenser is over condensing!
But as you say it all is strange!
Grizzly

[Sandro Baptista]

Not so strange Grizzly if occur some or all of things I mentioned next (as I have said on the previous emails):

1) Existing a "P" trap between the receiver inlet and the condenser outlet. Or if the inlet of the liquid receiver is underneath of this one.

2) If there is the condition 1) and if there isn't a equalizing line between this one (vapor from receiver communicated with the condenser inlet)

3) If the discharge liquid from the condenser line haven't traps or not enters underneath the receiver and haven't equalizing line. If the discharge liquid line have small DN.

As ranger said try to put more refrigerant, untill on normal operation you have about 3/4 of the level on the receiver.
In this way you compensate that "freak". Almost sure that the liquid/vapor ups an keep retained on the condenser until an equilibrium of weight forces and pressures are reached. So if you don't want spend money and you have refrigerant to compensate it think you should keep it that way. Of course your penalization is a higher condensing pressure of maybe about
+40ºC when you could have it ~+30ºC (higher COP, higher capacity) and still feed well with liquid the ice machine.

[750 Valve]

I have witnessed a similar thing with a single condensing unit running a freezer room about 10 years ago. I ditched the fan cycling HP and fitted a speed controller to the condenser fan, it stopped the cyclic emptying and provided stable consistent condensing.

[paul_h]

I have witnessed a similar thing with a single condensing unit running a freezer room about 10 years ago. I ditched the fan cycling HP and fitted a speed controller to the condenser fan, it stopped the cyclic emptying and provided stable consistent condensing.

Yeah that's exactly what I was thinking.
Problem is I was called in for an unrelated repair, and just noticed this while checking the system after my work was done.
It would be a hard sell to say the system was never working properly before I touched it anyway.

It's probably always done this, but it's taking slightly longer to make ice now that what it used to since I touched it, but that issue is the only thing I can find that would be the cause of the longer cycle time.

edit: BTW I have tried adding more refrigerant, it just made the reciever hold more while the condenser fan was off, didn't stop it emptying of refrigerant.
Also as a side note, the CF used to cycle on at 1500kPa, it was me that adjusted it to 1700Kpa as soon as I saw what was happening. At 1500kPa, it was hardly making any ice at all overnight.

[Sandro Baptista]

Paul,

Can you tell me if any of the conditions on 1), 2), 3) of my previous email exist on your condensing unit?

[paul_h]

None of them?
I wasn't sure what you meant, there's no traps, equalizing lines or anything.
Just two pipes going straight up to the roof top condenser.
1 from the compressor, and 1 back down to the receiver sitting above the compressor. Both lines straight up and down.

[desA]

I've got a 1.5T ice machine on R22 with a couple of problems, the main one is slow ice production.
The condenser fans cycle on at 1700kPa (the ambient here today was 17C).
Now the 1m tall upright receiver capacity is about 80kg (uses refrigerant from it to harvest).
When the condenser fans are not running and the hp is ~ 1500kPa, the reciever column sightglass shows it's about 1/3rd full of liquid, and the sightglass before the TXV shows full.

Whenever the condenser fans switch on at 1700kPa HP, the HP drops to about 1400Kpa until the CF cycle off.

The really wierd thing is the moment the CF fans cycle on, the entire receiver empties of liquid refrigerant.
The level of refrigerant drops about 1cm a second, and then sightglass at the TXV is almost empty.
About a minute or two later, the CF cycles of, pressure starts climbing again and the receiver fills up to about 1/3 capacity again.

Logic flow:
1. System in ~ equilibrium at 1700kPa.
2. HP fans kick in, equilibrium disturbed.
3. Condenser now begins to condense more vapour (increased airflow) => Q',cond increases.
4. First law of thermodynamics states:
Q'evap + W'in = Q'cond
=> Q'evap = Q'cond - W'in
5. Q'evap must increase.
6. Q'evap up => mass flow up.
7. Mass pulled out of nearest available receptacle - to balance system heat-transfer. Hence receiver empties momentarily.
8. Over time, as system moves towards thermal equilibrium, the reservoir level will re-balance at some other value.

[Sandro Baptista]

None of them?
I wasn't sure what you meant, there's no traps, equalizing lines or anything.
Just two pipes going straight up to the roof top condenser.
1 from the compressor, and 1 back down to the receiver sitting above the compressor. Both lines straight up and down.

okay...no equalizing line...so does the discharge liquid line has DN big enough to only achieve at maximum about 0,5 m/s?

And what about the connection of the discharge line to the receiver is above them or underneath of this one? If it is underneath of this one (it will be like a "P" trap) that will be worse, because you will not equalizing line and the vapor inside the receiver will push out the liquid upward to the condenser.

[Sandro Baptista]

Logic flow:
1. System in ~ equilibrium at 1700kPa.
2. HP fans kick in, equilibrium disturbed.
3. Condenser now begins to condense more vapour (increased airflow) => Q',cond increases.
4. First law of thermodynamics states:
Q'evap + W'in = Q'cond
=> Q'evap = Q'cond - W'in
5. Q'evap must increase.
6. Q'evap up => mass flow up.
7. Mass pulled out of nearest available receptacle - to balance system heat-transfer. Hence receiver empties momentarily.
8. Over time, as system moves towards thermal equilibrium, the reservoir level will re-balance at some other value.

desA,

You are partial right but according with Paul it seems that the fluctuations on the liquid receiver are not only because a mass flow increase on the evaporator.

[maxgeyer]

this is a common problem with incorrect designs
check following
is the tev the correct size(probably not) or faulty
check compressor capacity with regard to the condensor
check subcooling and superheat
to see if the system is undercharged
the eye glasses should all be full no bubbles
vairables fans or shutters also help
remember that once ambient goes under most designs start to over condense that is why u have a reciever to store extra refrigerant

[maxgeyer]

sytems start to over condense under 21 degrees c or 70 degrees f sorry left temps out in reply

[Sandro Baptista]

Is it is ease mount the receiver underneath the condenser so they will be at the same environment temperature.

[Magoo]

Had a similar problem with a packaged icemaker, the HP pressure sustaining valve was faulty, so system operated on HP fan control. The press sus valve injects hot gas into the liquid drain after condenser, maintains optimum liquid line pressure for constant feed rates to evap.,

[paul_h]

Is it is ease mount the receiver underneath the condenser so they will be at the same environment temperature.

Not really possible to move the receiver, as I said, it uses the warm reciever vapour for defrost instead of discharge refrigerant, so would require a lot of piping. wouldn't fit under the condenser, so would need a little house built for it to keep it out of the sun in summer.

Had a similar problem with a packaged icemaker, the HP pressure sustaining valve was faulty, so system operated on HP fan control. The press sus valve injects hot gas into the liquid drain after condenser, maintains optimum liquid line pressure for constant feed rates to evap.,

Yeah, this system doesn't have anything that advanced.

Basically the problem is in winter, this will happen, and it's due to the design (nothing I did to it ). Maybe adding heaps of refrigerant might help, but that's a bit of a waste IMHO, it would take about 30kg more of R22 and it's already got 20kg-30kg in it. And then I think the fan will just cycle a lot then anyway. Factory HP cutout for this system is designed and set at 2000kPa too.

I'm happy to tell them that and just suggest the easiest solution is some type of better condenser temp control, variable fan speeds and/or fans switched on in stages etc, so the condenser doesn't get so much cooler than the receiver.
They probably will still think I did something to it, but as long as it makes some ice they probably won't want to spend any money on the problem.

From my belief, what is happening is the refrigerant isn't boiling off or migrating, the current liquid in there is going into the evap, but the condenser isn't supplying any more liquid due to overcondensing. So keeping the condenser warmer in winter is all that needs to be done?

[Sandro Baptista]

Paul,
One of the easiest ways, despite the frequency control of the fans or increasing the setpoint of the condensing pressure would be install an equalizing line (as as said in a previous post). You would have good results due to an equilibrium of pressures between the condenser and receiver so in that way the vapour formed on the receiver would be to the condenser inlet and the receiver and the condenser would be at same pressures without issues.

[paul_h]

Thanks for your thoughts. I'll have another look at it next week and see how it's behaving and what is possible as far as options.

[paul_h]

Another twist to the story.
I was called back today because it was cutting out on low oil pressure.
I didn't have time to do much, so I decided just to try charging more refrigerant, even though that isn't my preferred fix, but I didn't have time to do much more.
Anyway I was charging by the liquid line after shutting off the receiver.
While this was happening, the oil level was a clear 3/4 full.
I was charging with some nearly empty r22 cylinders at the time.
Each time the cylinders were out of liquid, the system cut out on low oil pressure, not LP. This happened at least 3 times so not a one off.

evap pressure 300kPa, comp suction 100kPa due to CPR valve, hp always 1400-1700kPa due to fans cycling.

After I charged an extra 16kg R22 and opened the receier it seemed to run OK, but I noticed the clear oil level drop in the compressor and just be low level and all foam. So I don't know whether I'm dealing with an oil problem as well here or not.

The overcondensing is causing havoc with the ice production. Not as bad now with even extra refrigerant. But the liquid leaving the receiver goes through a heat exchanger before entering the TX.
When liquid, it leaves at 38C, goes through the heat exchanger and enters the TXV at 5C. When vapour (when the condenser fans cycle on), it leaves at 38C as vapour and enters the TXV at 38C vapour. SO not only starving the evap, but adding a lot of heat to it and it takes 3min or more just to rcvover and start cooling again.

[Sandro Baptista]

Liquid may be dragged to the compressor due to the bad TEX control caused by the warming of the ice cylinder/temperature bulb. This may cause a uncontrolled open of the TEX.

Liquid to the compressor will foam the oil and LP cut out.

I still think if you mount an equalizing line you may avoid that cycling fluctuation of liquid at the receiver which affect liquid feeding.

[paul_h]

Yeah I'm not ignoring your advice, I appreciate your thoughts, just have to get around to more testing, and trying to find a way to tell the owner "their install is too blame, here's a quote to fix it, even though it worked before(somehow?) fine"

I can't see how there's liquid at the compressor, it's about 20C warm.

Anyway, I was going to post in this other thread and ask, http://www.refrigeration-engineer.co...hlight=foaming, but thought it would be better to update here.
Temperature or low pressure or refrigerant level can cause foaming?
I don't want constant low oil pressure trips to add to my problems as I have enough. Just thought i'd say that with the receiver closed and charging liquid from the cylinder, oil level was 3/4 and not foaming at all.
When LP dropped while charging due to empty cylinder, low oil pressure switch tripped even though oil level was fine.
And after finishing some r22 charging, then I opened up the receiver and let it run. Only then was the oil sight glass is all foam and low. But it was fine while liquid charging?
Like I said, I just want this problem gone while I get some time to attend the overcondensing part of the problem. Overcondensing I can deal with later, daily oil pressure trips I can't.

[Sandro Baptista]

I can't see how there's liquid at the compressor, it's about 20C warm.

It was just an idea...but something is happen to your oil.

Does the crankcase gets cold when the oil is foaming?

Does the plant has oil separator? Does it working fine the oil return line and it's float valve?

[paul_h]

edited above.
Crankcase is warm and oil constantly foaming.
yes to oil seperator.
I suspect problem with seperator except for one thing, how well the system ran with the receiver outlet closed, oil stayed not foamed up and at 3/4 full level just fine. Edit: but with reciever outlet closed and system in pump down mode, I don't know what effect that has on crankcase, oil, oil separator, check valve etc.

[Sandro Baptista]

As far I understand with the receiver closed you were charging always supplying liquid without interruptions/fluctuations of feeding. If you close the liquid receiver outlet and no charging also there is no sufficient liquid to be dragged to the compressor since all is evaporated...the true may pass not so far of this...

[paul_h]

What about a leaking heat exchanger?
Liquid getting into the suction line that way?

Would it explain why it's foaming even though the suction is warm?

And why it wasn't foaming when the receiver was shut in pump down mode and I was liquid charging near the TXV entry after the heat exchanger.

Don't know why some liquid from the liquid line getting into the suction via a het exhanger wouldn't drop the suction temp even a little bit though.

And I don't know this patkol machine, what type of heat exhanger it has. Eveything is buried under heap of insulation I'd have to cut open just on this hunch.

So warm suction line, only 300kPa too. But oil in compressor only foams when liquid line was open.


edit: Ideally would love to hear from someone who has had a heat exchanger fail. I've heard of it, but never seen it. Or someone who knows these patkol machines.

Also when there's liquid from the reciever, the liquid line is very cold, like 38C in and 10C out. So the liquid line is losing a lot of heat, expansion possible. When the reciever empties and it's only vapour going through the heat exchanger, it's 38C in and 38C out, no sensible heat lost through the heat exchanger but a lot of latent heat it seems when there is a liquid supply.

The only thing that bugs me is the low SP, high HP, and warm suction, (wouldn't any liquid getting into the warm suction boil off anyway?), they don't fit into my theory. But as I said, never witnessed a heat exchanger fail and don't know this machine.

[Sandro Baptista]

Also when there's liquid from the reciever, the liquid line is very cold, like 38C in and 10C out.

After or before passes the filter dryer?

[paul_h]

Nah, nothing to do with the drier, same temp in and out the drier.

I'm saying that after the suction/liquid heat exchanger, the liquid line is very cold, colder than you'd expect a heat exchanger to make a liquid line.

[Sandro Baptista]

Well, all depend of the U.A (W/K) of the heat exchanger but also could be the heat exchanger promote a high pressure drop on the liquid line (due to bad design, or as you have said the heat exchanger be "leaked"). Is the heat exchanger of the coaxial type?

[paul_h]

There's not much in the manual on the heat exchanger type.

I'm just trying to tie in: foaming compressor sump sightglass, losing oil, cutting out on low oil pressure and problems I have had with the liquid level in the receiver into a nice little theory that fits with high suction temp still.
How is the oil foaming with high suction temps?
rhetorical questions:
Why did the oil not foam when receiver closed and liquid charging from cylinder into a schraeder valve situated just before TX?
If oil foaming in compressor causing low pressure cut out, what is causing the oil to foam with a warm suction?
If it is indeed liquid refrigerant, maybe coming from liquid line as it wasn't foaming when liquid line closed.

Like I said, a nice theory I have, but not explained with the high suction temps, but it's all I have to explain it

also where has all the refrigerant gone, and where is it going in the circuit now. It could have been a slow leak, but really it's not losing much right now as I look at it, and I've given it an extra 20kg, and it's still not working right, so something has changed the way the refrigerant is working as it's got a heap of problems that aren't refrigerant charge related.
But at the same time, ice production time is normal now, just the oil pressure cut out and foaming in the sump.
So I think that the refrigerant is doing something different.
Air?
TXV? - well cycle time is normal, and the heat exchanger is working (if a little too well), so seems to be plenty of refrigerant in the evap. Doesn't seem to be too much refrigerant metered from the TXV as suction is warm.

But any ideas appreciated. I woke up at 6am today (too early for me), so I laid down on the couch watching TV, and the words "heat exchanger" appeared in my thoughts like a bullet. So I jumped up and replied to this thread.
Not a scientific approach I know, I'm just bouncing ideas as there's not many straws left

Don't forget this uses the reciever to defrost the evap, so I'm going to shut the valves to that solenoid. But if that makes no difference the heat exchanger bypass by cutting and welding pipes is all I can think off

[Sandro Baptista]

No much I can said on this side of the world

Just note:

1) heat exchanger leaked I meant on previous post that could be between the liquid and the suction (liquid HP goes to suction LP) as you have told, despite the fact the suction is warm it could not be well mixed on the pipes

2) Also see again thread #23

3) Oil separator float valve malfunction?

[paul_h]

Thanks for all your input. I know it's hard to help with just suggestions when you're not here yourself.

2) the foam/threat of oil pressure cut out is constant, doesn't seem to fluctuate with the reciever being full or empty. I was charging refrigerant though a schraeder, no where near what the compressor/receiver could output
3) Well if it was oil separator, it would be getting problems with oil pressure cut out and foam when I was charging liquid from a cylinder. But when charging from a cylinder, it was the only time when oil level clear and full in the sump sight glass. So refrigerant and foaming not coming from oil separator IMHO

[Sandro Baptista]

yes, good point.

the point 2) maybe could avoided if you equalizing the receiver pressure with the condenser because you will get a supply of R22 more stabilized. When you charge from the cylinder you guarantee that liquid is alway supply to the ice machine and she isn't get warm and the TEX not flutuate/get total open.

I would try equalize the line. It is simple and cheap and sure will finish the problem you said at the beginning of this thread.