Case of Chocolate biscuits to whoever can help me!!

[desA]

nike123 - when you say evaporator mounted vertically, do you mean:



or :



Sorry pics so large - does anyone know how to reduce their size?

[nike123]

I mean both picture, and I suppose one (second in your post) is wrongly oriented. I concluded that from other pictures.

I mean thermal camera picture shows natural orientation of evaporator.

[desA]

Mmmhh... I see what you mean. If it is the thermal camera picture, I'd have expected to see the distributor facing in the opposite direction - with thin, off-take tubes at the lower end of the evap. Higher velocity after split carrying the oil.

Would like to hear what other folks think.

Can the OP please clarify the operating orientation for the evaporators?

[JoeReade]

Thanks for the help Nike!
I've done one further test, which was to eliminate any effects of the ducting on the airflow over the evaporator. I removed the panelling behind and in front of the evaporator, so that there was no restriction on the airflow whatsoever. Below are the temperature results I got.
evap3.jpg
What do you think of the results? To me it seems that there is too much variation, and the gas cannot be circulating evenly. (Please bear in mind that the right-hand temperature measurements may not be very meaningful, since they were taken very close to the return manifold, and will be affected by the temperature of gas returning from the other circuits).
Would you conclude from this picture that the gas distribution was not even?
We think that if this is the case, the next course of action will be to optimise the TXV position and pipe routing immediately before the evaporator (invert the distributor, minimise elbows, follow your guide for the minimum straight distance after an elbow etc).

The pipe between the TXV and the distributor is 720mm long, and has three elbows in it. This is well in excess of the limits you suggest. However, I think the pipe arrangement is the same on the other two units, and they work much better.

Also - do you think there remains the possibility of a restriction somewhere else in the system, perhaps between the compressor and the TXV? Or can we discount that, based on the temperature readings we made along the pipe? This is one point I am unclear on.

Thanks again.

Joe

[frank]

Joe

I mentioned a few posts ago that the evaporator was starved leading to poor performance and Mad Fridgie said that your evaporator was configured incorrectly.

Nike also has identified that the problem lies with the evaporator. 700mm from TEV to distributor? you could have mentioned this before.

Your thermal pictures show an unusual amount of superheat and now you are telling us that there is ducting on the evap....come on mate..tell us the whole story.

I can't understand why this is baffling your local fridge engineer..

A question I asked a few posts ago...have you adjusted the TEV to reduce the superheat?

[nike123]

J
I can't understand why this is baffling your local fridge engineer..

Probably because he is not real fridge engineer, or, he is not competent for the job!

Also, i expect that someone who buy that equipment, should at least have commissioning done by competent and authorised engineer by equipment supplier.

In 10 min., competent fridge engineer will discover all defects we discussing here, at least one week already now.

[nike123]

@Joe Reade

If that thermal camera reading is any good, than, if pipe is covered in ice in any portion (like on evaporator picture before), it should read 0°C. I don't see any reading of 0°C, and therefore, that camera reading is not relevant to me, if pipe was anywhere covered with ice during that measuring.
All IR thermal measurements should have compensation for emissivity from different surfaces. Therefore, if emissivity is not adjusted for every spot, measurement is faulty.

As I said earlier, your "fridge engineer" should rectify obvious, scool things, first, and then, if necessary, proceed further.

We (you) cannot solve this problem if we (you) disregarding obvious errors, no matter what other units, as you say, "work satisfactory".

We established that before TXV you have enough subcooling, we also established that evaporator is starved. And, we established that you have excess distance (in both case, with or without equivalent length off elbows) between TXV and distributor. All other is influenced with that. Remove that influence (and all other obvious errors while rectifying that, since system will be opened) and we can proceed further with troubleshooting.

This is exact science with very little space for wandering!

[chemi-cool]

Well guys, look at my first post here, cheap, shiny chinese stuff.
In a way, i feel sorry for businesses whom spend money on such units,

Its not the biscuits but the challenge to help a friend, there are some of the best fridgys here in the world.
But even though, bad product are imposible to fix and I hope someone will prove me wrong.

[nike123]

To some extent, it could be fixed. If it is bad construction and bad execution, we can fix bad execution. I am not putting expenses to that equation for now.

[JoeReade]

Joe

700mm from TEV to distributor? you could have mentioned this before.

Well that's kind of why I am after the kind assistance of the posters here! If I knew exactly which things were relevant and which weren't, I might be able to fix it myself.....

Joe

Your thermal pictures show an unusual amount of superheat and now you are telling us that there is ducting on the evap....come on mate..tell us the whole story.

DesA suggested that I make sure that there is even airflow over the evaporator. The purpose of that test was to remove all possible impediments to the free flow of air, and to see if it resulted in a more even temperature distribution across the evaporator. It did not seem to, therefore I conclude that air circulation is not a significant factor. I was looking for some confirmation that my conclusion was correct.

Joe

I can't understand why this is baffling your local fridge engineer..

Well it is.... which is why I am here. He has tried all of the easier answers and can find no fault. He's also tried many of the solutions that have been proposed here. Obviously what we have is a fault of manufacture or design rather than damage or failure of a component. That seems a bit harder to diagnose. I should explain that we are on a relatively remote Scottish island, and we are lucky to have any fridge engineer at all resident here; and as is common in a small community he has to wear many different hats in order to make a living. He does not benefit from the breadth of experience that you have. Which is why I am very grateful for the help you all are offering.

Joe

A question I asked a few posts ago...have you adjusted the TEV to reduce the superheat?

Sorry if I missed that one. Yes. He fitted a new one because the original was internally equalised, and adjusted it correctly.

[mad fridgie]

Some things are predictable and other things are less so.
Because you have issues with the expansion valves, position, type and size, then your results are somewhat less predictable. (applies to all 3), this is why you are see difference in performance.
So fix what you know is wrong, change all expansion valves, move all expansion valves. Have some different orifices in stock. (pressure drop across distributor is not known).
a new equalibrium will be reached. Only when this is done, can we move onto the next stage. (if there is a next stage)

[JoeReade]

Mmmhh... I see what you mean. If it is the thermal camera picture, I'd have expected to see the distributor facing in the opposite direction - with thin, off-take tubes at the lower end of the evap. Higher velocity after split carrying the oil.

Would like to hear what other folks think.

Can the OP please clarify the operating orientation for the evaporators?

I think my orientation of the thermal camera has confused things - sorry! Below is a picture showing the evaporator mounted in its cabinet. I've also added some arrows showing the airflow to and from the tunnel compartment above. You can see the TEV on the right too - the total length of the pipe from it to the distributor is 700mm. The last straight section is 120mm, which is 7.5 times the OD of the pipe (16mm). But from what you all are saying, we have to move the TEV right up to the distributor and turn the distributor 180 degrees.

I wondered whether the evaporator had been mounted upside down - but it appears not to be, judging by the labelling and the position of the condensate drain.

evap4.jpg

[nike123]

Sorry if I missed that one. Yes. He fitted a new one because the original was internally equalised, and adjusted it correctly.

It cannot be adjusted with that size of oriffice. In fact, it should not be adjusted at all, before all other things are sorted. That is last adjustment which should be done.
Tell him to make it back to factory adjustment, and forget to further adjustments, at least for now!

[JoeReade]

@Joe Reade

If that thermal camera reading is any good, than, if pipe is covered in ice in any portion (like on evaporator picture before), it should read 0°C. I don't see any reading of 0°C, and therefore, that camera reading is not relevant to me, if pipe was anywhere covered with ice during that measuring.
All IR thermal measurements should have compensation for emissivity from different surfaces. Therefore, if emissivity is not adjusted for every spot, measurement is faulty.

As I said earlier, your "fridge engineer" should rectify obvious, scool things, first, and then, if necessary, proceed further.

We (you) cannot solve this problem if we (you) disregarding obvious errors, no matter what other units, as you say, "work satisfactory".

We established that before TXV you have enough subcooling, we also established that evaporator is starved. And, we established that you have excess distance (in both case, with or without equivalent length off elbows) between TXV and distributor. All other is influenced with that. Remove that influence (and all other obvious errors while rectifying that, since system will be opened) and we can proceed further with troubleshooting.

This is exact science with very little space for wandering!

Thanks Nike. Quite possibly the thermal readings are not accurate. Those measurements above were actually taken using an IR thermometer, I just used the thermal image for context. The IR thermometer is reasonably accurate, and at the time of measuring there was no frosting. In that test I was trying to remove uneven airflow as a significant factor, but removing much of panelling that directs the air to and from the tunnel compartment above.

I think it's clear what we need to do now, as you say, to remove the obvious errors. We'd better get on and do the work. Fingers crossed!

[JoeReade]

Some things are predictable and other things are less so.
Because you have issues with the expansion valves, position, type and size, then your results are somewhat less predictable. (applies to all 3), this is why you are see difference in performance.
So fix what you know is wrong, change all expansion valves, move all expansion valves. Have some different orifices in stock. (pressure drop across distributor is not known).
a new equalibrium will be reached. Only when this is done, can we move onto the next stage. (if there is a next stage)

Thanks Mr Mad Fridge. I'm already looking at postage costs for New Zealand and all the other far flung places you guys are posting from....

[JoeReade]

But even though, bad product are impossible to fix and I hope someone will prove me wrong.

"All things are possible until they are proved impossible - and even the
impossible may only be so, as of now."
Absolutely!

[desA]

This picture is worrying me! I'd like to hear others' opinions on the evaporator orientation.

I would expect to see the following:
1. TXV high up & close to distributor;
2. Distributor facing in opposite orientation to that at present.

With the current orientation, I'd expect issues, as follows:
a. Oil logging in the pipe between TXV & distributor. Oil could slug intermittently.
b. Three 90 degree elbows prior to distributor will have liquid/gas separation occurring.
c. (c) basically means that it will be very difficult to see an even refrigerant (two-phase) feed into the distributor. Liquid will prefer one route, vapour another.
d. I have to wonder if there is operational vibration in the line between TXV & evap.

If your refrigeration lad is brave, he'll probably have to rotate the evap through 180 degrees until the distributor is correctly oriented - then move TXV to its correct position - close to distributor. In other words, to the other side of the cabinet. Sporlan has some useful literature on the best set-ups between TXV & distributor.

You'll probably be better off getting all evaps correctly oriented, followed by TXV re-location. After that, at least you have a part-way decent configuration, to begin adjusting. What a job you have on your hands.

At the temps you're working at, the outlet manifold looks remarkably free from moisture. I'd be expecting puddles of water below the manifold. What am I missing?

[desA]

Also, looking at air the flow space before entry to the evaporator, I'd expect a fair amount of air flow maldistribution across the face of the evaporator.

If you are able to locate an air anemometer, this would tell you a great deal - in terms of air-flow.

[Magoo]

Hi JoeReade. your last photo is worth a thousand words, the TXV and distributor should be only sweating, either the TXV is starving evap or lack of load from evaporator is closing TXV. Interesting the red arrows for air flow. Can you sketch the air pattern over product, if air dwell over product is too short the cold return air to evap will force TXV closed and starve coil, the conditions indicated in photo

[mad fridgie]

The distributor, we could have a separate thread about this, but as long as the TEV is close coupled, and the distributor is vertical (up or down) then this should not be a major problem.
The coil well maybe up side down, but if you look at the circuits, the flow is up/down and side wards, so little difference would be made by changing it.
The airflow, OK the name plate seems to indicate a high volume, higher than I would expect, but it is just a name plate. It is induced so air flow will be relatively even (The fan would be better further away, to even out) But this is not the major issue at the moment. There is also a bit of air by-pass, not to worry at this stage.
The air temps are not to cold to shut down the TEV, SST is low and SH is high.

[JoeReade]

The distributor, we could have a separate thread about this, but as long as the TEV is close coupled, and the distributor is vertical (up or down) then this should not be a major problem.

You say it does not matter which way up the distributor is, so long as its vertical? This is supported by the Danfoss literature. It shows the distributor with the small pipes downward, but does not say it 'MUST' be this way. It certainly shows the distributor on its side with a cross through it - that is the only position that is explicitly ruled out.
Inverting the distributor is the larger part of the work we think we need to do - are you sure it's OK the way it is? So we could just move the TEV much closer and leave the distributor as it is? This would be a lot easier.

[r.bartlett]

The picture looks more like a freezer evap... but I am interested in the moving the tev closer thing as my gut instinct is that it will make eff all difference, so I want him to move it so I can learn.



Have you tried a larger orifice as suggested as to flood the evap and see what happens...?

[install monkey]

distrubutor tubes should be all the same length for even distribution!- do i get to choose what flavour biccys???

I think my orientation of the thermal camera has confused things - sorry! Below is a picture showing the evaporator mounted in its cabinet. I've also added some arrows showing the airflow to and from the tunnel compartment above. You can see the TEV on the right too - the total length of the pipe from it to the distributor is 700mm. The last straight section is 120mm, which is 7.5 times the OD of the pipe (16mm). But from what you all are saying, we have to move the TEV right up to the distributor and turn the distributor 180 degrees.

I wondered whether the evaporator had been mounted upside down - but it appears not to be, judging by the labelling and the position of the condensate drain.

evap4.jpg

[JoeReade]

The picture looks more like a freezer evap... but I am interested in the moving the tev closer thing as my gut instinct is that it will make eff all difference, so I want him to move it so I can learn.



Have you tried a larger orifice as suggested as to flood the evap and see what happens...?

Currently #2, and we've tried #3, which seemed to make no difference. But general concensus is that we should have bigger orifices.

[JoeReade]

distrubutor tubes should be all the same length for even distribution!- do i get to choose what flavour biccys???

If only it were that simple....

[r.bartlett]

Currently #2, and we've tried #3, which seemed to make no difference. But general concensus is that we should have bigger orifices.

take the nut off the adjusting screw (one with not any pipe coming out of it) and open it up fully anti clockwise to see if the pressure rises and frost clears.

[mad fridgie]

Just move the TEV directly onto the distributor, no need to re pipe evap.
The pipe and bends, acts as separator, so the distributor does not get an even mix of liquid and vapour.
At this stage DO NOT adjust the expansion valves.
The orifice size, is yet to be known we do not the pressure drop of the distributor. It maybe a 4.
The coil does look like low temp with the defrost heaters.
Until we can get a fully wetted evap do not worry about other issues.

[JoeReade]

Just move the TEV directly onto the distributor, no need to re pipe evap.
The pipe and bends, acts as separator, so the distributor does not get an even mix of liquid and vapour.
At this stage DO NOT adjust the expansion valves.
The orifice size, is yet to be known we do not the pressure drop of the distributor. It maybe a 4.
The coil does look like low temp with the defrost heaters.
Until we can get a fully wetted evap do not worry about other issues.

OK - going to get that done. Will let you know how we get on......

[install monkey]

are all 3 tev's the same distance from the distributor?

[r.bartlett]

Just move the TEV directly onto the distributor, no need to re pipe evap.
The pipe and bends, acts as separator, so the distributor does not get an even mix of liquid and vapour.
At this stage DO NOT adjust the expansion valves.
The orifice size, is yet to be known we do not the pressure drop of the distributor. It maybe a 4.
The coil does look like low temp with the defrost heaters.
Until we can get a fully wetted evap do not worry about other issues.

I greatly look forward to seeing the measured difference. As I say my gut suggests little or no measurable difference in this case. However I am more than willing to take this lesson on board should it prove to be otherwise

I would be interested if you could walk me through this particular case on the pictures and show where the uneven distribution actually occurs. Is there laminar flow along the pipe section or is it turbulent for instance. ?
If it is laminar then the 'gas' should stay on the top which means as it bends round vertical it will be on the right side of the pipe, then what?
Does it speed up to the distributor because it's less dense than the liquid or does it travel at the same speed?

If turbulent who cares as the gas will be evenly distributed in any case?
(why are all splits two phasing for up to 50m in some cases and don't suffer from this issue?)

Why not just insulate that section to reduce the flash gas?
Are you expecting to see a wetted evap just by moving the tev?
if not, or are you then going to say, "now change the orifice to a no/4?"
If you do end up suggesting he changes the orifice (which has been mentioned many times already and remains a possibility) why not try it first to see the difference as we seem to be off on a flight of theoretical ideals at someone else’s expense

TIA :-)

[mad fridgie]

In short, you are getting move vapour through the distributor, which cases a bigger pressure drop and leaves the coil short of liquid, the liquid and vapour separate in the line. The distributor is part of the expansion process, that why when sizing an expansion valve we need know the the pressure drop across the distributor, liquid pressure - pressure drop across valve - pressure drop across the distributor - evaporating pressure.
The flash gas is to reduction in pressure mainly, not absorbed energy (not to say there is not some)
On a split the evap line "the pipe between the expansion device and the evaporator" (or liquid line to you), is small keeping the mixture in a homogeneous state.

[r.bartlett]

In short, you are getting move vapour through the distributor, which cases a bigger pressure drop and leaves the coil short of liquid, the liquid and vapour separate in the line. The distributor is part of the expansion process, that why when sizing an expansion valve we need know the the pressure drop across the distributor, liquid pressure - pressure drop across valve - pressure drop across the distributor - evaporating pressure.
The flash gas is to reduction in pressure mainly, not absorbed energy (not to say there is not some)
On a split the evap line "the pipe between the expansion device and the evaporator" (or liquid line to you), is small keeping the mixture in a homogeneous state.

Thanks this poses more questions than it answers but:

I would be even happier if you went down my questions one by one as that way I can learn as you seemed to have skipped most of the points.. Especially highlighting on the pictures what and where this has occured.

Out of interest a 3/8 pipe running 50m has far more opertunity to change state % end to end than 500mm of 1/2 inch would you not agree.
Does change of state % only occur in larger pipes or can it exist in smaller pipes ?

If by homogeneous you mean there is no difference from condenser to evaparator (50m) then what is keeping it that way? Insulation? 3/8 v 1/2 pipe??



tia

[mad fridgie]

Thanks this poses more questions than it answers but:

I would be even happier if you went down my questions one by one as that way I can learn as you seemed to have skipped most of the points.. Especially highlighting on the pictures what and where this has occured.

Out of interest a 3/8 pipe running 50m has far more opertunity to change state % end to end than 500mm of 1/2 inch would you not agree.
Does change of state % only occur in larger pipes or can it exist in smaller pipes ?

If by homogeneous you mean there is no difference from condenser to evaparator (50m) then what is keeping it that way? Insulation? 3/8 v 1/2 pipe??



tia

It has already changed state, but as the pressure drops further flash will be produced. The fllash gas is being produced because of reduction of pressure and not infiltration. "vapour fraction"

Homogeneous, I mean that the liquid and vapour say evenly mixed.

By moving the TXV yes expect to see wetted evap (I am talking about the internal of the walls having liquid refrigerant on them, no flooded but wet)

I can not say what size the orfice is because I DO NOT know the pressure drop through the distributor.
Nike has already sized using basic rules and has said present size is reasonable, not going to question Nike on this.

As far as tubeulent and laminar, bends also cause eddies. so not as predicable as one thinks.

Moving the TEV to the right place is only a small job, 10-15 mins, not that long to make right a Known error.

Look at the frost on each circuit, you can see an imbalance, but the main problem is lack of liquid entering the evap.

[mad fridgie]

Is no news, good news?
My cup of char needs some dunking material!

[chemi-cool]

8059120.jpg

Untill you get the Scotish ones......

[frank]

Patience chaps....I think that the local fridgie is half way through the alterations as we speak (post)...

Hope they are dark chocolate...mmmmm

[desA]

The joys of buying Chinese quality products.

[hookster]

Do Chinese chocolate biscuits taste different to Scottish ones???
and if I dunk one in a glass of Talisker would I notice the difference?

[chemi-cool]

if I dunk one in a glass of Talisker would I notice the difference?

I think they will float......

[If you can afford a bottle of Talisker]

[desA]

Lol...

[nike123]

15 days passed without update on what is current development on this case! These cakes, what are they made off?
Chocolate cannot be that much precious to avoid given promises.

[mad fridgie]

???????????????????????????????????????

[nike123]

I have seen this many times! Problem solved, nobody cares cares to inform us about development. Since there is no problem anymore, there is no need to responce to this thread.

[r.bartlett]

send Joe an email and tell him what you thing of him joe(remove this bit)@islandbakery.co.uk

[marc5180]

I've emailed him and asked him if he wouldn't mind replying which I suspect he will be doing shortly.

[JoeReade]

Hello!
Sorry for the silence. For various reasons we have only just been able to move the expansion valve. We've run it for a day since then, and we definitely have significant improvement. The TEV is now mounted directly below the distributor. Whereas before that section if the tunnel would go no lower than about 11c, it now reaches 8c.
It's still not running as well as unit 2 however...it will cycle on and off at 6c no problem, and will reach 1c if running constantly.
The gas pressure on the faulty unit is about 110psi. On unit 2 it's 160psi.
On the assumption that this could be caused by some kind of restriction, as a next step we're going to put in a new drier and remove the solenoid valve altogether. (It's not doing anything anyway; it's just wired in with the compressor and opens when the compressor runs.
Anyone got any better suggestions?

[JoeReade]

Me again. I think it's probably time for a round of biscuit deliveries. Nike123 and mad fridgie are the first recipients. Can you both please pm me your addresses ? Cheers.

[marc5180]

Hello!
Sorry for the silence. For various reasons we have only just been able to move the expansion valve. We've run it for a day since then, and we definitely have significant improvement. The TEV is now mounted directly below the distributor. Whereas before that section if the tunnel would go no lower than about 11c, it now reaches 8c.
It's still not running as well as unit 2 however...it will cycle on and off at 6c no problem, and will reach 1c if running constantly.
The gas pressure on the faulty unit is about 110psi. On unit 2 it's 160psi.
On the assumption that this could be caused by some kind of restriction, as a next step we're going to put in a new drier and remove the solenoid valve altogether. (It's not doing anything anyway; it's just wired in with the compressor and opens when the compressor runs.
Anyone got any better suggestions?

So it's made a considerable difference, the works that you have done so far.
Did you use the same TEV with the same size orifice? If so would it be possible to post a new set of measurements including the superheat across the Evaporator.

Do the compressors have crankcase heaters? If not then the solonoid valve has probably been fitted to stop liquid migration to the compressor in the off cycle.
You should have something in place to stop this.

[install monkey]

if theres no temperature diff accross the drier then theres no point in changing it, as mark mentions check ur orifice size as undersized orifice will affect operating pressures and maybe use the solonoid as your control to pump down when at setpoint

[mad fridgie]

Focus on the evap, do we have even frost/cooling all over coil.
Suction pressure and superheat please