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Hi!
Im operating a system where the expansionvalve thats installed is for 404A while the refrigerant Im using is 407C. The suction pressure is around 1,5 bar, and the suction manifold on the compressor is covered with ice.
The system is for coldrooms (meat and fish) and the temp in the rooms maintain around -22 deg celsius.
Is it the wrong exp. valves that are causing the compressor to freeze?
Any guidance would be appreciated.
Valve should be somewhere near what is the suction superheat?
Ian
change it anyway, they make R404A TEV,s and they make R407/22 tev,S, you may get it something like by ajusting the superheat but you will get it right with the correct TEV.
Hi there,
I suggest that you first check the TEV catalog and see if the TEV used has the same capacity. If the capacity is near what you need then try to adjust the superheat. If the capacity is too high then you have to change it for sure.
If this doesn't work then, you know what to do.
Cheers
Hello Kentbf
I think you have a bad expansion valve, maybe the nozzle is not right.
other thing is why are you using R407C on a freezer room ? sounds like it was set up to run on R404A and for whatever reason its been changed to R407C,i have never seen this used on low temp and as with R22 doubt its success, i would put it back on R404A,tried and tested.
I ask the same question again what is the suction superheat, without knowing what it is you cannot actually know if there is a problem or whether the frost is because the suction gas is so cold and the plant room has a high humidity level. Any diagnosis is purely guess work without the required information.
I agree with OGB in not having seen R407C used on a deep freeze coldroom but looking at the PH chart it should work reasonably well.
Ian
They make for each refrigerant the proper TEV.
So..???
Pooh has a point, without knowing SH, you only can guess.
R407c, what SH is the bulb measuring with the glide you see with R407c? Andis this measurement a correct 'translation' to the right SH?
Hi again, and thanks for your tips.
The last days I have learned a lot by reading the posts here. Thank you all for a great resource!!
I understand the lack of information on the initial post, so here are some more info.
The system uses 407C. Its on an offshore installation so we try to minimize the use of different refrigerant.
Its one media for both ac units and cold rooms.
The system consist of a:
-carlyle 5F60, 15kW compressor.
-A fresh water cooled condenser.
-Danfoss expansion valves model TES 2 total 7 pc.(404A)
1.Meat room, orifice #3
2.Fish room, orifice #2
3.Veg room, orifice #3
4.Lobby, orifice #2
5.Dry prov store, orifice #2
6.Dairy room, orifice #1
7.Potato room, orifice #1
-Muller evaporators.
-Back pressure valves (evaporating press regulators) Danfoss KVP-22E
The compressor and condenser is located 10 meters below the coldrooms where the ambient temp is around 35-40 deg C.
The whole thing started with the vegetable room. The evaporator just became an iceblock over night, just after fresh veggies was received. I defrosted and started again. Even the backpressure valve and stop valves kept freezing. The suct pressure was set to arround 3 bar. I adjusted it up to 4,5 and trottled on the stop valves before and after the expansion valve, they are just crack open now. That way I managed to keep the temp in the veg room at 6 deg C. Cant play to much because we need the veggies and fruits :-)
Still, the gas side is freezing but the evaporator doesnt. So I can live with that for a while.
Anyway, I started to look at the plant and found several things.
The txv bulb is fitted 3-5 meters after the evaporator. on pipe that is not horisontal but 45 degrees upwards.
I hooked up the gauges on the compressor today. Suction was 0,4bar and discharge was 14 bar (measured on top of the condenser) Suction temp is hard to determine, I have a fluke 62 mini infrared termometer, When I removed the ice from the suction manifold i measured -10 deg C. But this could be even lower, dont trust the infrared when its ice on the surface. Liquid temperature is 34,2 deg.
The compressor was set to cut out on 0,1 bar!
Coolingwater temp in is 33 deg and it was full flow. Temp out was 34.
I adjusted the lp switch to to cut out on 0,8 and in on 3 bar. It just kept starting and stopping. I throttled the cooling water outlet so now its 37 deg out of the condenser. I will continue tuning tomorrow.
I think I'm on the right track, but still a long way to go. I'll continue tomorrow. It's fun too you know. Hope I can rectify all faults that is not design issues.
any thoughts and tips are welcome.
Thanks in advance.
bit of a complex system there but your on it, can you not tweak the defrosts on the veg room to help a bit, its one of those jobs where you need to get your head round it first, sure you will sort it,good luck.
Hi kentbf,
Would you please clarify two points here.
1- The system was designed and worked with R404a and now you changed it to R407C but the TEV stayed the same as before? Is this right?
2- Was the system working without problem before changing the refrigerant?
Waiting for your reply.
Cheers
Hi Lana.
This is a newly commissioned system, although badly. It is designed for 407C, but I think the company who built it bought the wrong parts, and just didn't care to change it. They just removed the ID tag on top of tev, and hoping no one would notice, at least that is what im thinking.
It seems like I have a sub cooling of about 2 kelvin. I can see some bubbles in the sight glass on the liquid line straight after the condenser. Should be all clear right?
Should the sub cooling be even more since it has to lift the liquid 10 meters before it enters the tev?
What about the bulbs for the expansion valves, they are fitted on 45 degree pipe up to 4 meters from the evaporator. What impact has this "configuration"?
The system has never worked properly, thats for sure.
Best regards.
Kent
Possible cause: problem with the measurement of the glide where the SH is wrongly measured .
Or the gas is decomposed due to a leak or filled via the gas phase instead of liquid.
First thing would be to reposition the TEV phials to the outlet of each of the evaporators, secondly check the settings of the EPR's they should equate to approximately 8deg C below the required room temp however with the veg room that may be as little as 2 deg C if it has been designed properly to stop the product drying out. are there any thermostats on the coldrooms or off loading on the compressor. My initial feeling is that the guy who designed it should read some more books but I may be wrong.
Ian
It's also possible they desinged the system for 404a but had problems with the pipes "banging" and decided to change it to 407c! The only difference, aside from the glide, is 134a!
Your superheat is 20K and your subcool near zero!
Looks like it's also lacking refrigirant but can also be due to the bulp's off the tev's being far from the evaporator and possibly not mounteed correctly, thus measering the oil!!!!
Hi kentbf,
Everything is said so far could be the reason.
Just to summarize :
1- Change the TEV bulb position to the evaporator exit and before the external equalization line.
2- Let the system work to stabilize.
3- Measure the SH and SC. Remember: with LP read the dew point and deduct the evaporator outlet temperature to get the SH. With HP get the bubble point and deduct the liquid line temperature to get the SC.
4- If the sub cooling is less than 4°C and LP is low, then there is a lack of refrigerant. If sub cooling is low and also HP is high then there is a condenser problem.
5- As Peter said, this problem might be for the "wrong" refrigerant inside.
If nothing works then I suggest that you change the TEV for correct one and re-change the system properly.
Good Luck
Keep us posted.
Cheers:)
Hi there! Firstly if the refrigerant used is r404a then you have to fit the correct tx valve... not a r407 valve as it designed to work with r22/r407c. If anything you will increase capacity running on r404 as opposed to r22/r407c.... so even if it is designed to run on r407c you should be ahead with r404a. Secondly it will be near inpossible to correctly determine the gas charge and superheat as the tx valve is incorrect causing it to operate outside it's designed criteria! change the valve and see from their.....
Kentbf, have you found the answer?
This thread is intriguing so please complete.
Another name to add to my "don't-answer-a-problem- question-the-next-time-because-we -never-hear-something-back-after-the-problem-is-solved- or-this- forum-helped-the-poster-with-a possible-solution."
We all can learn from it.
I call it common manners of good behavior.
Another thing: if yo want to measure temperature with an IR, don't measure on ice because its emmisivity factor is far away from a black surface.
And these Flukes are calibrated for a black surface.
So, stick first some black tape on the surface you want to measure and point on this black tape.
I find it difficult enough to convert degrees C to degrees F, now my head is spinning trying to convert bar to psi and then to saturation temps.
With all of these evaporators, surely the compressor must have unloaders? Are they working?
IR thermometers are not to be trusted for reading line temps. Get a real thermometer.
Let's start with the evaporators:Quote:
Originally Posted by kentbf
What is the desired temperature for each of these rooms? What are the EPR settings for each? Are all evaporators clean and all fans working properly? What type of defrost is used (where needed)?
Since all of your systems have R404A TXV's, why not just use R404A in the systems rather than changing all of the TXV's?
If I remeber right R407c has similiar press temp relationships as R-22, R404a has a much higher temp pressure relationship, It is in my opion that You may be able to use this valve you are currently using if the valve has a way of adjusting the superheat setting. This takes boring lengthy time and the aquired patience.Quote:
Originally Posted by kentbf
Regards Shawn
Capacity of val Danfoss in 407 is bigger than 404, electric motor HP ?, at this temp compresor need water cooled headers, water is hot, need evaporative tower. Need electronics valves and particular software to work. diferent temperatures with only one compresor is not good.
You're all replying to thread that the poster put up in april and has never returned.
It's like watching a movie and then missing the ending. We keep hoping they will come back to tell us what happened, but they rarely do.
Well I guess i was not paying attention to that. I juswt like reading and replying with my two cents worth.
Yeah he dies the end, falls off an oil rig.:eek:Quote:
Originally Posted by Gary
At least we know how it ended, now. :)
Quote:
Originally Posted by Gary
Hi gary,
I am learning that the offshore industry has some funny ways of doing things. Coming back to this thread and re-reading it now i am in this game gives me a new insight, that being that it's just all designed wrong. It amazes me that any of these systems ever work. There are some voltages that can catch you off guard, like 690v for compressors. And lots of belt drive stuff that lots young engineers like myself don't come across from day to day onshore. From now on in future all offshore breakdowns will be checked to see if they are designed and installed correctly,is the TEV and orifice correct?,is the gas correct? is the voltage correct,has there been a change with the generator ? The maintenance crew also like to mess with things like valves and gas so you have to take that into account has air got in the system? is the system overcharged? has it been charged as a vapour ? I'm learning that it's not just a case of something has gone wrong and when it's fixed all will be ok, because there's a chance that it had never worked very well to start with !
My supervisor told me on my a job where the back pressure was too high to close the tev right down.Where do you go from there ,when thats your advise .I've also seen danfoss philes fitted at 12 o'clock on 1 3/8" suctions ,what do you do if you find that?