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Abe
13-08-2003, 10:59 PM
I finally got to fill in one of those " Trouble Shooting Data Collection" reports. Problem now is, Ive got the data, "what do I do with it?

Its one of those situations, its a system that is not performing or doing what it is designed to do. And I cant find anything wrong.

My prognosis is that the :

1:Condensing Unit is too small for the task
2: Condensing Unit is not sited correctly

This is the situation

Williams Freezer Room
Size: 5.5 metres x 2.5 metres x 2 metres high
Condensing Unit is sited on top of the room. ( Monobloc)

Freezer Room is housed within a brick building of size 10 metres x 6 metres x 5 metres high
Alongside Freezer room is a Chiller Room of same dimensions as Freezer Room. Again Condensing Unit located on roof.

No fresh air input into room. Small 200mm duct with in line fan extracts air to outside.

With both units running, there is heat build up in this shell. I took the ambient reading in the morning when the doors were opened allowing some heat to escape and the ambient was 32C

These are my reading:

Condensing Unit is Le Unite Hermetiqu TFH 2511Z
Refrigerant R404
Air Cooled Condenser
High Side
Saturated condensing temp 300psig
Discharge pipe temp 50C
Condenser Air In 31C
Condenser Air Off 38C

Liquid Line Temp 34C
Liquid Line before Exp Valve 10C

Low Side

Saturated Evaporating Temp 25Psig
Evaporator Air In -8C
Evaporator Air Off -10C
Suction pipe leaving tem 5C

Freezer Room is designed to operate at -20C

The suction and liquid lines are strapped together so difficult to get accurate readings.

Again, I am of the feeling that the CU is too small for the task. I also feel the heat extraction duct is not up to the job. I feel there should be a duct bringing fresh air from outside into the room as well.

Does anything look amiss here? A proffessional opinion would assist me

Regards

Abe

Abe
13-08-2003, 11:02 PM
I forgot to mention.........after a whole night of running, room shows a temp of around 2C
During the day, with the doors of building open allowing some heat to escape, it comes down to around -7 to -9 Celcius

Abe
13-08-2003, 11:05 PM
When I say CU is located on roof.........Not roof on the outside of building. Roof of cold room within the building itself. Ie: it is not external open to the environment. CU is within the shell of the building itself.

If I was installing I would have located it outside of the building

Dan
14-08-2003, 04:12 AM
Hmmmm. Looks like my detailed reply didn't make it. I think your superheat is too high.

Gary
14-08-2003, 04:18 AM
The SCT @ 300 psig is 47C.

The liquid line temp at condenser outlet is 34C.

47 minus 34 = 13C subcooling at the condenser outlet.

There is liquid refrigerant backing up into the condenser, reducing its capacity. The subcooling should be no more than 8C. The system is overcharged.

Since the evap air in is well above design temp, I would expect the superheat to be a little high. Is that suction line temp at the coil outlet or the compressor inlet? If that's at the compressor inlet then it looks about right. If that's at the coil outlet, I would open the TXV one full turn.

I agree on the need to get more fresh air intake.

herefishy
14-08-2003, 03:00 PM
Typically, the unitary refrigeration systems on "step-in" or walk-in coolers, are designed to be for indoor use (i.e. in air conditioning or ambient temperatures NOT exceeding 90degF). For every 10F increase in ambient, you lose about 6% in capacity.

Gary
14-08-2003, 04:27 PM
I'm thinking with liquid backed up in the condenser, in effect downsizing the condenser, the percentage would be considerably higher.

In any case, the sizing seems borderline to the point where opening the building doors makes a big difference, so we need to squeeze all the capacity we can get out of it.

Latte
14-08-2003, 08:12 PM
Hello Aiyub, I don't think whateve you adjust its not going to make a huge difference. I have the same problems in Pizza Express restarants, strangly also williams equipment.
at the end of the day these units are designed to have a certain amount of cold air getting to the condenser & certainly require more extraction than you have got. My assesment would be don't waste too much time trying to sort this out, you dont stand a chance with such an ambient

Gary
14-08-2003, 08:25 PM
Aiyub, here is a procedure for testing the TXV superheat:

http://www.refrigeration-engineer.com/chat/showthread.php?threadid=1280

At this point the procedure is theoretical. Care to test it for us? If it works, it could cure a lot of headaches. :D

rbartlett
14-08-2003, 09:23 PM
unless you get the head down below 250 you will struggle to get the suction down below 25 psi this is the reason you are not getting anywhere near the -20c


i had this problem where a williams through the roof unit wouldn't get below -10 in an oxford university

however the above ceiling was nearer 40 than 30 but it had bad ventilation -a 300 mm extract only but the void was less than 4 foot..williams are rated at 28 deg'c on coil cond.

i got down and opened some windows on the far side of the room (ie up in the ceiling void along the coldroom roof and down to the sliding windows)

this helped hugely but recommended a supply and extract fan

soomehow the customer never quite gets that the unit needs cool air...

check the room sizing via dean and woods etc..

cheers

richard

herefishy
14-08-2003, 11:36 PM
You should compare the TEV rating to the condensing unit. Check the condensing unit capacity at the ambient that you are seeing (perhaps 110degF - or derate 12% from the standard rating which is typically 90F or around [32C?]). compare the existing TEV rating from the standard chart (if it is a Sporlan, use the table and do NOT adjust for anything, just read the chart straight). You may find that at the higher temps, there is a better selection (lower capacity) expansion valve for the application.

Even if you DO balance the desired SST and (derated) condensing unit capacity via lower capcity TEV, that does not mean that you will necessarily satisfy the load. BUT, if the box is used in a "storage" type function, and does not require a quick pulldown, you may be able to achieve satisfactory results.

But again, the system was designed for indoor use, and the room absolutely must be ventilated - period. If it is ventilated to the great outdoors, the above may still apply.

:)

Dan
15-08-2003, 04:30 AM
Low Side

Saturated Evaporating Temp 25Psig
Evaporator Air In -8C
Evaporator Air Off -10C
Suction pipe leaving tem 5C

Let me try this again.

25 psig = -9 deg F
5C leaving temperature = 41 deg F.

It appears that you have 50 deg F superheat at the coil.

I do not see a problem with your condensing temperature. It is 115 deg F. Normally these units are sized for a 20 deg F TD, you recorded an ambient of close to 90 deg F. Even if the unit was sized for 80 deg F, we would not expect to see the problems you are experiencing.

Gary makes a good point that I failed to make in my disappeared message. Your subcooling is high out of the condenser.

I don't think that the ventilation of the room nor the positioning of your condensing unit are the immediate problems. Your superheat is way too high, if I understand you correctly, and your subcooling is also high. Over-charged unit and clogged, or maladjusted TEV just shouts at me.

But congratulations, Aiyub. You provided the measurements needed. This could be a first.



:)

Abe
15-08-2003, 11:15 PM
I think I believe there is "some problem" at the evaporator....

There is a clump of solid ice just after the valve and its covering all the distributor pipes.

Coil otherwise is frosted all the way through

Dan
16-08-2003, 12:08 AM
5C leaving temperature = 41 deg F.
Coil otherwise is frosted all the way through

Hmmm. Perhaps I am misunderstanding your superheat. Is 41 deg the superheat at the coil? If not, what is the superheat at the coil where the TEV bulb is positioned?

Also, I have seen on larger unit coolers what you describe regarding the ice. This may present a problem if you have an MOPD powerhead. Perhaps the professor has some thoughts on this.

Gary
16-08-2003, 02:47 AM
Let me try this again.

25 psig = -9 deg F
5C leaving temperature = 41 deg F.

It appears that you have 50 deg F superheat at the coil.


Ouch... I screwed up the translation from C to F. I came up with 18F superheat. I forgot to add 32F. Duhhhhh...

You are right, of course.


But congratulations, Aiyub. You provided the measurements needed. This could be a first.


It sure makes it easier, doesn't it? Now if the world would just switch to F. :D

Dan
16-08-2003, 05:10 AM
LOL Gary! But you must share my joy that Aiyub snatched the Techmethod measurements. Or at least gave it a fine effort. Getting those 8 critical measurements is really difficult. But a necessity.

I am less involved in refrigeration these days and more involved in Lean management. Whether it is in within a corporate environment, or whether it is in the field, there is an abiding principle.

Everything has to be perfect before you hand it to the next person.

Your insistence on key measurements is a necessary thing. Aiyub's attention to what you require is a necessary thing. I can see that when it is handed to the next person, the same must be required.

Nothing is ever perfect, however. When Aiyub handed me a superheat reading, I did not question it properly.

You made a small math error. What is good about this process is that we can provide immeditate feedback, confessing that we may have accepted observations without questioning them properly.

The techmethod is a model for lean troubleshooting. It demands perfect information to be handed to the next person who has to do something with it. the next person in line has to do the same thing.

As a person who is the next person down the line, it is my responsibility to push back to Aiyub regarding his superheat measurements.

This is important that I demand perfection from him. More than likely the misunderstading is mine, but I cannot accept imperfection.

Aiyub sighs and curses either me or somebody, but realizes he has to cover in better detail what his problem is.

He realizes that he should have asked his question only after providing the measurements that the Techmethod requires.

I could go on with this thinking.. because it is good thinking... But I have a granddaughter on my lap.

As a last thinking. . I am being quite distracted...

Managers have to insist that key measurements are recorded during a service call. Oh, crap... it appears tha I am ticklish on my right side.

Let me close quickly... with a summary.

I know Aiyub is marketing oriented, and that Gary has a theory broader than simple refrigeration thinking. I am now beginning to learn about process flow.

I apologize. I have this wild woman in my lap. She's 6, by the way.

Gary
16-08-2003, 12:25 PM
LOL Gary! But you must share my joy that Aiyub snatched the Techmethod measurements. Or at least gave it a fine effort. Getting those 8 critical measurements is really difficult. But a necessity.


Information is always a good thing. :D

With a little practice and the proper tools, gathering the measurements isn't that difficult, and well worth the effort. The numbers tell us nothing. The spaces between the numbers tell us everything. Refrigeration is a series of heat transfers, and we can see each transfer as it happens. Reading between the lines, we can sense the flow of the system.

What do you hear, Grasshopper? :D

Dan
16-08-2003, 07:03 PM
It's my sense that the unit is overcharged and that the coil is not feeding properly. But if the superheat measurement was taken at the compressor, I could be wrong. The coil fully frosting is distracting... I don't think the unit is undersized or that the condenser is inside the room is the major problem. Those are marginal issues in my mind.

In Lean design there is a word called Poka Yoke. It is a warning that a defect is found immediately when one process hands off to another process.

It is a demand of perfection, so to speak. It applies interestingly not only to our discussions, but also to the spaces between the numbers in the Techmethod. The compressor may be handing off refrigerant to the condenser perfectly, and the condenser may be handing off the refrigerant to the receiver perfectly, but the receiver may not be able to receive it all properly, etc.

Aiyub gave us superheat measurement but also mentioned it was difficult because of a heat exchanger. That was a poka yoke, as well.

What do you hear, Master?

cooltrain
17-08-2003, 01:49 PM
:D
Hi! Aiyub,

You mentioned the following data as I qoute:

Liquid Line Temp 34C
Liquid Line before Exp Valve 10C

Is'nt this prob. a plain liquid line restriction? There's a big temp drop which probably a result of restriction in any accessories along the liquid line towards the exp. inlet. The evap is starving thereby unable to reach the desired setpoint.

Frosting at the TEV outlet is a visual sign of an excessive pressure drop across the TEV.

The subcooling is high too reflecting a slow flow of liquid across.

The condensing TD which is the condensing temp and air inlet diff. is about 16C. This for me is quite high. It could be due to poor ventillation around the condenser.

Regards

Gary
17-08-2003, 04:06 PM
That's entirely possible, depending on the situation. The drop in temp could be from a liquid line restriction. But it could also be from the liquid line being in the low temperature environment. Any sudden temperature drop along the way would indicate a point of restriction. Or the restriction could be in the TXV (adjusted too high) or inlet screen.

Abe
17-08-2003, 11:13 PM
I have perused all the posts carefully on this thread and am appreciative of all the help and analisis.

I have not returned to site as the primary contractor , Williams Refrigeration are undertaking their own survey.

But I will report the findings once this becomes known.

Gary
18-08-2003, 09:14 AM
Therein lies the rub. We can troubleshoot a system online, given enough information, but each time we find a problem and make a change we need all of the measurements again. Then we need to look for further problems. This is extremely difficult unless we are online at the job site and communicating in realtime.

While we may not agree on the analysis, I think it is very clear that none of us could have reached the conclusions that we have without the list of temperatures/pressures that Aiyub has provided. If nothing else, I think we have established the value of using the list. Without it, trouble shooting online in an exercise in futility.

Dan
21-08-2003, 05:01 AM
I couldn't agree more. I was the one always saying that it is hard to get all the measurements, and Gary would chide me that it is not so difficult.

I think in retrospect, I just meant that it is harder than most people are used to achieving for a diagnisis. As a habit, it is likely easily ingrained.

Made for a good discussion and wish Aiyub were there for the final diagnosis.

Dan
21-08-2003, 05:02 AM
I couldn't agree more. I was the one always saying that it is hard to get all the measurements, and Gary would chide me that it is not so difficult.

I think in retrospect, I just meant that it is harder than most people are used to achieving for a diagnisis. As a habit, it is likely easily ingrained.

Made for a good discussion and wish Aiyub were there for the final diagnosis and repair.

Abe
21-08-2003, 11:07 PM
Hope to check units again next week and take a whole host of readings