-
Ice on Strip of Evaporator
Hello. I have a problem with a room with two evaporators (air defrost) using R-404A, the room is supposed to be at 2°C, but I can't get to lower it more than 8°C because there has been ice building up just in a horizontal strip (all long of the back of the evaporator), the distributor and the pulp tubes are also frozen, but at the suction side only the 3 tubes of the circuits on the strip where there's ice are frozen.
Suction pressure: 56psi
Suction temp: 0°C
Superheat: 6°C
This room is part of a system supplied from a Parallel Compresors Rack, there are another 4 rooms working fine.
Any help is appreciated!
-
Re: Ice on Strip of Evaporator
How's your defrost cycle programmed.
At what distance is the evaporator from the back wall. Is there any product piled up underneath the evap that may be blocking the airflow?
What's the fan diameter.
Anything blocking the air in front of the fans that may be causing cold air recirculation?
-
Re: Ice on Strip of Evaporator
THank you for your quick response aramis. Here are the answers to your questions:
Quote:
Originally Posted by
aramis
How's your defrost cycle programmed.
4 times a day - 30 minutes
Quote:
At what distance is the evaporator from the back wall. Is there any product piled up underneath the evap that may be blocking the airflow?
Aprox. 1.5mt from the wall, the evaporator is on a aisle so there no product near it.
Quote:
What's the fan diameter.
24 inches
Quote:
Anything blocking the air in front of the fans that may be causing cold air recirculation?
Nop, there's nothing on the back neither on the front of the evaporator.
Hope you can help.
-
2 Attachment(s)
Re: Ice on Strip of Evaporator
Here are some pictures, visual reference always help.
Attachment 8750Attachment 8751
-
Re: Ice on Strip of Evaporator
Strange, I can't say I've seen this before.
The pictures were a good idea.
Is the frosted section only one circuit? If so I would go first for possibility 2 below.
My best guess is that you either have something in the coil that is blocking air flow on those rows or this row is not being fed the same amount of refrigerant than the others.
1) You should check with a lantern and compare the light pattern directly above and below with the frosted section, preferably after defrost.
2) For mal distribution you should check that there are no bumped curves or anything strange in the copper tubes. This includes the distribution tubes, see that no one has been squeezed. The distributor would be my next check, impossible to do on the outside.
I hope this helps.
-
Re: Ice on Strip of Evaporator
Oh and ... ¡Viva México Lindo!
-
Re: Ice on Strip of Evaporator
I think this room is the last one to be fed from your system and not getting the benefit of 100% liquid to expansion valve.
-
Re: Ice on Strip of Evaporator
This is not the last room to be fed, in fact is the second of four, but this system has Electronic EPR valves, I noticed this morning there was an erratic functioning on this particular EPR and the opening percentage was at 25%, when I correct it the opening percentage went up to 100%.
Does this erratic opening of the EPR has something to do with the ice problem?
I will be monitoring the function of the system to see if it gets better.
-
Re: Ice on Strip of Evaporator
Quote:
Does this erratic opening of the EPR has something to do with the ice problem?
The immediate cause of the strip is poor distribution or refrigerant.
Starving the evaporator causes low flow which causes low pressure drop in the distributor and it doesn't feed the circuits correctly.
You need a pressure drop of (about) 15 psi through the distributor for it to work correctly.
You may well see the problem solved tomorrow (crossing my fingers).
-
Re: Ice on Strip of Evaporator
If you know you have a solid liquid supply to expansion valve, and it is feeding correctly through the distributor, than there will be an even feed through all evap circuits. EPR is there to restrict vapour return to compressor, (to maintain a desired pressure in evaporator that is higher than the fluctuation suction pressure in multi room systems) I see one circuit is feeding far more than the others in that evaporator.
That is why i was looking at liquid supply. Might be worth your time to pull apart expansion valve and check the orifice..Mike.
-
Re: Ice on Strip of Evaporator
Mikeref is right you should check your expansion valve.
The EPR could also be the problem because if it closes too much increases the pressure in the evaporator, this decreases the pressure differential in the expansion valve and you get low refrigerant flow which also causes maldistribution.
If the EPR is working erratic, you will have this problem at random, probably when you are not there to measure but the ice lasts longer and you see it.
Not to mention that you could have dirt, humidity and many other problems that could cause this.
Still have my fingers crossed!
-
Re: Ice on Strip of Evaporator
This morning the ice is thiner and seems to be melting and the room temperature is lower, I will force a manual defrost for 1hr and see if this takes away all the ice. I'll keep you posted.Thanks.
-
Re: Ice on Strip of Evaporator
I checked this afternoon and the ice is gone. The room is at desired temperature and everything seems ok.
I didn't uninstall the TEV, just the adjustment on EPR....:eek:
-
Re: Ice on Strip of Evaporator
See, crossing fingers does work!
-
Re: Ice on Strip of Evaporator
Yeah! I will cross my fingers from now on!!!!
Thank you aramis and mikeref.
Regards.
-
Re: Ice on Strip of Evaporator
I think the problem will come back very soon :-(
-
Re: Ice on Strip of Evaporator
-
Re: Ice on Strip of Evaporator
Quote:
Originally Posted by
Peter_1
I think the problem will come back very soon :-(
Right! The reason for maldistribution under low flow conditions is still present.
But you can get by avoiding low flow.
-
Re: Ice on Strip of Evaporator
EPR incorrectly set, first problem solved.
Looks like a forced draft evap, you may find that it is not a refrigeration distribution problem, but an energy distribution problem. Less air flow through the center of the coil, so compared to the outer circuits. hence more frost leaving the middle circuits! Hope that makes sense.
-
Re: Ice on Strip of Evaporator
Looking at pics, there is heavy ice build up on distributor tails for +2'C room. They should be reasonably clear of ice if feeding correctly and distributor orifice and tail length and diameter are sized correctly. Suggest that the selection of total pressure drop across TXV distrib orifice and tails is too low and TXV will be hunting. The EPR is masking the real problem.
-
Re: Ice on Strip of Evaporator
Quote:
Originally Posted by
mad fridgie
EPR incorrectly set, first problem solved.
Looks like a forced draft evap, you may find that it is not a refrigeration distribution problem, but an energy distribution problem. Less air flow through the center of the coil, so compared to the outer circuits. hence more frost leaving the middle circuits! Hope that makes sense.
It does make sense, was my first choice too. Georgedvf should make sure the air flow through this circuit is not obstructed.
But you see that the ice follows a circuit perfectly up to the collector, besides these are 24” fans.
I think this circuit was getting more liquid than the others so it is the only one that worked ok while the evaporator was starved.
Quote:
Originally Posted by
Magoo
Looking at pics, there is heavy ice build up on distributor tails for +2'C room. They should be reasonably clear of ice if feeding correctly and distributor orifice and tail length and diameter are sized correctly. Suggest that the selection of total pressure drop across TXV distrib orifice and tails is too low and TXV will be hunting. The EPR is masking the real problem.
Good point Magoo. There could be more causes of low flow than just the EPR. This should also be checked.
Also the tubes or this circuit should be inspected and the distributor too.
-
Re: Ice on Strip of Evaporator
... or just keep fingers crossed.
-
Re: Ice on Strip of Evaporator
Quote:
Originally Posted by
aramis
... or just keep fingers crossed.
Sorry aramis. Can't let that one go as if it was my system, i'd pick it apart until i found out why the problem happened in the first place ;). Sooner or later, this problem will come back to bite you in the butt. Been there, done that and bought the shirt as well. lesson learnt a lifetime ago. Mike.
-
Re: Ice on Strip of Evaporator
Sporlan have and excellent software program for selection of TX, orifice and distrib tail length and sizing.
Hi Mikeref, I totally agree, I have always wanted to understand why some thing is not working in balance in a system. Rules of thumb don't work for me and certainly not crossing thumbs. Things have got simpler with the net and software programs, saves alot of time reading manuals.
-
Re: Ice on Strip of Evaporator
What is the pack saturated suction temp?
-
Re: Ice on Strip of Evaporator
Quote:
Originally Posted by
Magoo
Sporlan have and excellent software program for selection of TX, orifice and distrib tail length and sizing.
Hi Mikeref, I totally agree, I have always wanted to understand why some thing is not working in balance in a system. Rules of thumb don't work for me and certainly not crossing thumbs. Things have got simpler with the net and software programs, saves alot of time reading manuals.
Evening Magoo.Hope your Frydee nite dinner hit the spot along with the odd ale ;) ...:off topic:
-
Re: Ice on Strip of Evaporator
Quote:
Originally Posted by
mikeref
Sorry aramis. Can't let that one go as if it was my system, i'd pick it apart until i found out why the problem happened in the first place ;). Sooner or later, this problem will come back to bite you in the butt. Been there, done that and bought the shirt as well. lesson learnt a lifetime ago. Mike.
Me too! .
-
Re: Ice on Strip of Evaporator
I'm happy others are thinking just as I did that the problem isn't solved yet.
Possible causes for me are
1. partially blocked distributor or cap lines between coil and distributor blocked
2. Wrong orifice plate in the distributor or tilted in the distributor.
3. No airflow over the coil where it is frosting up.
4. No feeding at all or severe blocked refrigerant feeding to the rest of the coils
5. Too low DP over the distributor /TEV
The EPR is for me not the cause.
-
Re: Ice on Strip of Evaporator
Perhaps I missed something but did it work properly in the past or is this a new install?
I think that this circuit is responsible for the SH the TEV/EEV is regulating. The TEV controls this one circuit with its lower energy load, resulting in blocking off all the others. If you could make a thermal scan, you should 'see' the problem.
It this is a new evaporator, then there's a fault in it. can it be water or an oil/water mixture frosting up in the cap tubes? What happens if you de-ice them completely and start up again?
-
Re: Ice on Strip of Evaporator
Wow, lot of answers.
Quote:
Originally Posted by
mad fridgie
What is the pack saturated suction temp?
It is R404A - 56psig - 0°C
Quote:
Originally Posted by Peter_1
1. partially blocked distributor or cap lines between coil and distributor blocked
2. Wrong orifice plate in the distributor or tilted in the distributor.
3. No airflow over the coil where it is frosting up.
4. No feeding at all or severe blocked refrigerant feeding to the rest of the coils
5. Too low DP over the distributor /TEV
I haven't checked No.1,2,4 and 5, I can't shut off the room the client has product on it; No. 3 the airflow is even on the evaporator.
Quote:
Originally Posted by Peter_1
Perhaps I missed something but did it work properly in the past or is this a new install?
It worked propoerly for 2 months, and then the client calls me because the temperature rised and will not drop to the set point again.
Today the evaporator is running normally, no ice on it.
-
Re: Ice on Strip of Evaporator
No excessive moisture in the system?
-
Re: Ice on Strip of Evaporator
No, tested the oil and result = ok, also no visual sign on the sight glass.
-
Re: Ice on Strip of Evaporator
I am struggling here a Bit, if the rack SST is 0C how can ice be forming. I believe it has to be much lower.
I suggest that your EPR )(hunting) was fighting the PID loop on the EEV, and that irregular flow occurred, along with vapour entrapment with in the evap circuitry. (showing as mal-distribution). This could also cause slight oil logging in the distributor legs. With a more continuous flow, the distribution becomes more even.
I have to say from experience that it rare to see 100% perfection in distribution, and this normally masked by the superheat requirement.
-
Re: Ice on Strip of Evaporator
Sorry, 0°C is the thermometer lecture at the copper tube... SST is around -6°C according to the Sporlan P-T chart...
-
Re: Ice on Strip of Evaporator
Ah, rereading origional post, you said this room has 2 evaporators. What was the other evap doing while this one had that problem?
-
1 Attachment(s)
Re: Ice on Strip of Evaporator
Copying the other one ja!
It had the same problem as the other, just that the ice was on the bottom.
On this picture you can see both:
Attachment 8753
Sorry I did not mentioned it before...
-
Re: Ice on Strip of Evaporator
As per my earlier comment, the combination pressure drop across valve orifice and distrib tails is too low, the liquid is flashing off in the tails giving uneven distribution to the coil. If both evaps has similar frost build then the problem is factory fitted. Or else an undersized TX vav.
Can you indicate the TXValve rated duty,[ name and model/size ] the length and diameter and number of tails on distributor, and the rated duty of evaporator. SST and liquid entering temp at TXValve.
-
Re: Ice on Strip of Evaporator
Quote:
Originally Posted by
Magoo
As per my earlier comment, the combination pressure drop across valve orifice and distrib tails is too low, the liquid is flashing off in the tails giving uneven distribution to the coil. If both evaps has similar frost build then the problem is factory fitted. Or else an undersized TX vav.
Can you indicate the TXValve rated duty,[ name and model/size ] the length and diameter and number of tails on distributor, and the rated duty of evaporator. SST and liquid entering temp at TXValve.
I am going to disagree, only because it is now working. Yes poor distribution, but i would say because of irregular liquid feed. EEV and EPR fighting.
If you are not getting a consistent regular feed to the distributor, you will not get a regular flow pattern.
The different distributors are more than likely sitting in a slightly different position, hence the different circuits showing frost. But I do not mind being wrong!
-
Re: Ice on Strip of Evaporator
Hi MF,
looking at pics way back in post, the TXV looks to be a sporlan externally equalized, possibly a balanced port type, the EPR and balanced port vav would be fighting each other.
Plus a +2'C room and SST at -6'C is a evap system TD of 8 degrees, too wide. The TXV will be hunting big time with a balanced port vav.
It would be interesting to have a sightglass in liquid line right at the TXV. Possible liquid line losses with length and diameter and vertical separation is creating flashing in liquid line, more complications
I still reacon there is a factory fitted problem with the ice build on distrib tails that will complicate everything if delta P is below 35psig across orifice and tails for 404a. Have a look at Sporlan cattledog [ nz slang for catalogue.]
-
Re: Ice on Strip of Evaporator
That is right, TEV is Sporlan externally equalized type S, 7 TONS, not balanced port.
Distributor has 14 tails, 3/16 inches diameter and 25 inches lenght.
Evaporator is rated 76,000BTUH (6.3 TONS aprox.), I didn't get liquid temperatures readings when there was the problem.