Case of Chocolate biscuits to whoever can help me!!

[JoeReade]

I have a problem with a cooling tunnel that is baffling our local refrigeration engineer. If anyone here can suggest the solution, I'll happily send them a case of chocolate biscuits (made on said cooling tunnel)
The tunnel has three identical copeland refrigeration sets along its length. Unit 1 works badly - the lowest temperature we can achieve in that section of the tunnel is 13c with the compressor running constantly. Unit 2 works well - in exactly the same circumstances it can get down to 3c. Unit 3 is somewhere between the two. Our concentration has been on unit 1. I have tested all three units in ideal and controlled conditions - ie cool ambient temperature with no passing product and both ends of the tunnel blocked. The problem remained and therefore must be with the units themselves, not the circumstances. Here's what we have checked:
Gas - All full of gas until no bubbles in the sight glass.
Evaporator - fans working in the right direction, not frozen and air not by-passing it. Also checked to see that ice forms evenly by blocking the airflow with cardboard, therefore there are no blockages in an individual pipe.
Defrost heaters - definitely not on, not even partially.
Compressor rotation - correct (three phase units)
Condenser - clean and clear, fan running well and in the correct direction.
Solenoid valve - operating correctly
Orifice - clean and clear. Tried orifices of different sizes too, no change. Currently using the same size orifice as unit 2 that works well.
Gas pressure - there are gauges fitted to the low and high pressure sides. The readings are:
Unit 1 (the faulty one) high pressure 1 Mpa, low pressure 0.1 Mpa
Unit 2 (works well) high 1.4 Mpa, Low 0.02Mpa
Unit 3 (doesn't work briliantly) high 0.8Mpa, low 0.02Mpa

The pressures are therefore different, but not sure if the range of difference is significant. Would these pressure measurements suggest the compressor(s) is not generating enough flow?

The compressors are Copeland ZB21KQE-TFD-558.

If anyone can suggest the solution and get it right, those biscuits will be on their way!

Thanks.

[frank]

What refrigerant are you using on the 3 stages and what temperatures are you trying to achieve on each stage?

[r.bartlett]

I think we have already had discussions on this issue. It would have been better to use the old thread you started back in June.

[JoeReade]

Sorry, the old post related to the same machine but was a slightly different question. Then I was trying to establish what performance we SHOULD expect; now I have thoroughly tested it all three units and have a benchmark from the best performing unit. The question I'm now trying to answer is what on earth is wrong!! Our local fridge man is stumped. Any suggestions? I have just checked that each unit has the same model of evaporator installed - and they do.

[The Viking]

As said above +,

You need someone with their hands on the machines to solve this for you.
A good starting point for whomever that is would be to check subcooling and superheat then take further actions from there.

[JoeReade]

Thanks. The refrigerant is R134A. I'd like to achieve 8 - 10c on each of the three units. But currently number 1 will not go lower than 13c in the best circumstances (15-18c if ambient temp is warmer than usual). To compensate I have the second unit set at 6c, which it achieves no problem, with the compressor cycling on and off. Unit 1 runs continuously and gets no lower than 13c.

[frank]

Has the gas charge been checked?
Are you able to post more details, such as
evap air on temp
evap air off temp
condenser air on temp
cond air off temp
High side pressure and pipe temp at time of reading
Low side pressure and pipe temp at time of reading
Pipe temp entering TEV
Pipe temp leaving TEV

[JoeReade]

Thanks. Can you clarify the measurements you need? See below.
Joe

Has the gas charge been checked? Yes. All have been filled until there are no bubbles visible in the sight glass. In the case of unit 1, that's just under 3kg.
Are you able to post more details, such as
evap air on temp Do you mean the temperature of the air entering the evaporator?
evap air off temp Do you mean the temperature of the air exiting the evaporator?
condenser air on temp as above - the temp entering?
cond air off temp - temperature of the air exiting?
High side pressure and pipe temp at time of reading no problem
Low side pressure and pipe temp at time of reading no problem
Pipe temp entering TEV What's the TEV?
Pipe temp leaving TEV

[frank]

Yes and yes
The TEV is the metering device where the orifice fits

[camelCase]

Wow... so your low side of #1 is some 400% higher than the low side of #2 and #3 (0.1Mpa vs 0.02Mpa)? That might have something to do with not being able to pull as much heat out.

[RANGER1]

Thanks. Can you clarify the measurements you need? See below.
Joe

Compressor amps might be helpful as well.

Does no1 have any unloaders on it reducing its capacity.

Carry out compressor valve leak test, maybe broken suction or discharge valves.

[install monkey]

think your problem lies with ur fridge monkey
what biscuits do i win???

Gas pressure - there are gauges fitted to the low and high pressure sides. The readings are:
Unit 1 (the faulty one) high pressure 1 Mpa, low pressure 0.1 Mpa
Unit 2 (works well) high 1.4 Mpa, Low 0.02Mpa
Unit 3 (doesn't work briliantly) high 0.8Mpa, low 0.02Mpa

[passandscore]

Scroll compressors are pretty bullet proof! What type of condensing units do you have? I would suspect a system problem over a compressor problem. Are all 3 TEVs set the same and sized properly? What is your superheat reading? Are the bulbs located at the right position on the suction line, before the equalizer line and properly insulated? Do you have equalizer lines? If not that's a problem!

What is your distance of pipe from the condensing units to the evaporators and what size of pipe are you using?

What is your subcooling reading?

We're going to figure this out!

[JoeReade]

I'll get the measurements and get back to you!

[FreezerGeezer]

Some more questions:
Are all three systems supposed to reach the same temperature?
Are the heat loads the same for all three systems?
Do all three condensers have good air flow & plenty of space around them? Is there any way the condenser air off is recirculating to the air on side, or might the condensers be side discharge & blowing from one to the other?
Have you recovered the refrigerant, triple evacuated the systems & recharged with fresh R134a?
Are there any solenoid valves on the systems? If so, are they working properly? I had an issue recently where the apprentice had put one back together the wrong way around.

[frank]

We're going to figure this out!

Steady on......I'm not going to share the biscuits....I asked first

[install monkey]

googled biccy manufactures in scotland- as if it shortbread-u can fix it frank- if its jaffa cakes-im going to site for an induction! haha

https://www.google.co.uk/search?q=sc...hrome&ie=UTF-8

[frank]

Chocolate Shortbread.....Yuk....

[JoeReade]

OK - I have some measurements that I hope will shed some light. Let me know what you think...

Measurements for unit 1, which is not cooling well:
Pressure just after the compressor 160psi
Pressure just before the compressor 20 psi
Pipe temperature just before compressor 15.5c
Pipe temperature just after compressor 70c (measured with infra-red rather than surface probe for all other measurements, so may be a little inaccurate)
Pipe temperature just before condenser 57c
Pipe temperature just after evaporator 8.6c
Air temperature entering the condenser 36c
Air temperature leaving the condenser 43.3c
Air temperature entering the evaporator 16.9c
Air temperature leaving the evaporator 14.6c

Measurements for unit 2, which cools well:
Pressure just after the compressor 200psi
Pressure just before the compressor 14psi
Pipe temperature just before compressor 6.5c
Pipe temperature just after compressor 76c (measured with infra-red rather than surface probe for all other measurements, so may be a little inaccurate)
Pipe temperature just before condenser 62.7
Pipe temperature just after evaporator 4.4c
Air temperature entering the condenser 27.2c
Air temperature leaving the condenser 39.3c
Air temperature entering the evaporator 11.1c
Air temperature leaving the evaporator 6.9c

Ambient temperature for both units 28c – but locally higher around unit 1 as can be seen from the air temp entering the condenser. This unit definitely working harder but with less effect.
To recap on previously mentioned points:
Both units cooling the same volume of air
Both units have good gas load (sight glass bubble-free)
Both units have same size of orifice fitted
Both units checked for air bypass, fan rotation, compressor rotation, both set to 6c.

That case of biscuits is primed and ready for the right answer.....

[nike123]

You should measure pipe temperature just before TXV (with contact thermometer or with calibrated IC thermometer adjusted for correct emissivity) to get rate of subcooling (if any).

Ambient temperature for both units 28c – but locally higher around unit 1 as can be seen from the air temp entering the condenser. This unit definitely working harder but with less effect.

This should be rectified. Air entering condenser 1 temperature is too high. Why is that way?
It looks like recirculating air from another unit condenser. Any photography of condenser location?

What is distance and what is placed after liquid line sight glass and before TXV on both units. Are the evaporators above or below condensers and what is height difference?


What is oriffice number and TXV model #.

I propose you to put some black insulating tape over sight glasses until we resolve the issues here.

Frank, I will give you biscuits if you give me some of yours Pales.

[joe-ice]

Compressor 2 seems to be under serious pressure going by these readings condensing at 55c .With the air entering condenser 1 at 9k warmer than system 2 i would not be suprised if the compressor is worn and not pumping fully which the readings might suggest.I have also come across systems running high heads under pressure like this where the gas had just broken down and lost its efficiency ,but these were 404 systems .by the way a gas change and a filter and a cleaned condenser cured these

[r.bartlett]

Is that not an R404a compressor?

https://opi.emersonclimate.com/was.e...web/OPIServlet
https://opi.emersonclimate.com/was.e...terfaceServlet

[r.bartlett]

Compressor 2 seems to be under serious pressure going by these readings condensing at 55c .With the air entering condenser 1 at 9k warmer than system 2 i would not be suprised if the compressor is worn and not pumping fully which the readings might suggest.I have also come across systems running high heads under pressure like this where the gas had just broken down and lost its efficiency ,but these were 404 systems .by the way a gas change and a filter and a cleaned condenser cured these

Can you tell me exactly which readings suggest the compressor isn't pumping?

[install monkey]

run 1 system at a time to get it working correctly
see if ur figures are any different
check gauzes on ur orifices
check u havent got biccy crumbs in ur evap fins- compressed air is good for that

[hookster]

SEVERE OUTDOOR LOW AIR FLOW = High superheat, suction pressure, head pressure & current draw. Low indoor TD & subcooling. . nike123

http://www.refrigeration-engineer.co...ling-scenarios

It does look like the condenser air on temp should be investigated.

[joe-ice]

Can you tell me exactly which readings suggest the compressor isn't pumping?

He said in one post its 134a ,200 psi is pretty high for this, The unit working ok has high head 200 and low back pressure 14 .The unit not working ok has higher air temp going to it (9k more) but has a lower head pressure and is not able to pull down the back pressure which would suggest to me its not pumping fully or as ive come across with 404 the high head it would have been operating has broken down the gas (in correct running order it should have been running higher head than current good unit due to hotter air on)

[Peter_1]

Air in compressor 2?

[r.bartlett]

He said in one post its 134a ,200 psi is pretty high for this, The unit working ok has high head 200 and low back pressure 14 .The unit not working ok has higher air temp going to it (9k more) but has a lower head pressure and is not able to pull down the back pressure which would suggest to me its not pumping fully

Indeed, this is the one which worries me the most:

Pipe temperature just before compressor 15.5c

[joe-ice]

[QUOTE=r.bartlett;28384nndeed, this is the one which worries me the most:[/QUOTE]

How is that ?

[nike123]

@joe-ice
Signatures in our posts does not have anything with actual posts. It represent our global attitude. I am sure that Peter_1 as teacher (and moderator here ), has some good reasoning for showing that statement as his signature.


To the subect:

Circuit 1

Te=-5,6°C (air in 16,9°C air out 14,6°C)
Tc=46,5°C (air in 36°C air oit 43,3°C)
Tsh=14,2K
Evaporator:
TD=22,5K
dt=2,3K (not much heat collected)
Approach=20,2K (starving)

Condenser:
TD=10,5K
dt=7,3K
Approach=3,2K (not much heat to reject)

Circuit 2

Te=-10,5°C (air in 11,1°C air out 6,9°C)
Tc=54,8°C (air in 27,2°C air out 39,3°C)
Tsh=14,9K
Evaporator:
TD=21,5K
dt=4,2K
Approach=17,3K

Condenser:
TD=27,6K
dt=12,1K
Approach=15,5 K

Approach of condenser in circuit 2 is too high (15,5K) and approach of evaporator is also to high (17,3K).

Something is probably wrong with that refrigerant inside that unit, or vacuum is not sufficient (or not done at all) prior to refrigerant charging and possible noncondensables are occupying condenser volume or unit is heavily overcharged (my bet is here) with filter dryer dirty or some other obstruction in liquid line region.


Superheat in both circuits is similar (around 15K), but without knowing for real subcooling before TXV, I cannot make any further judgment.

Condenser issues in both circuits should be examined before further evaluation.

Based on given numbers, to me, circuit 1 is working with better numbers but with starving evaporator and recirculating condenser air than circuit 2 with less starving evaporator but with condenser which cannot reject heat efficiently.

Also, as compressor is R404A model, possibly is that TXV is also R404A model and somebody has decided just to switch refrigerant without changing TXV. We need to clarify that also.

Is this new equipment just installed or used one from some other project and someone has decided to use it with R134a instead of R404A?

We need more background of these units since:

The average heat transfer coefficient of R404A is estimated to be 26 to 30% higher than that of R134a for the same saturation temperature.

http://www.tandfonline.com/doi/abs/1...0#.Ug81iIKHqxQ

If equipment is designed to work with R404A, than with use of R134A instead of it, you have 30% less capacity then designed, just by using wrong refrigerant. Therefore, you should provide here all equipment specifications and data to troubleshoot that.

[install monkey]

but joe have u seen some of the posts on here! haha
thats why newbies always start off- hello im new please be gentle-!!!!!

apart from the pricks floggin mobiles/ipads!
go to your settings and u can create a signature-

How is that ? On a sidenote peter 1 you posted a very short wording so i ended up reading the crap you wrote after it instead . Why do you feel the need to have a funny statement after your name .?. If i was first time posting on this site i would find it most offensive .

[JoeReade]

Here are answers to various questions! -

The tunnel is brand new, and designed to run on R134a, with correct expansion valves, which are Danfoss TN2 (internally equalised) units with orifice number 02 on units 2 and 3. Number 1 unit has been fitted with a Danfoss TEN2 (externally equalised) but with no discernible improvement over the TN2s (fitted recently to unit 1 to try to improve performance)
There's no unloader on any of the three units, the TXV bulb is in the correct place.
Length of pipe between condensor and evaporator max 2 metres.
There is nothing between the sight glass and the TXV.
Condenser and evaporator are on the same level, with 3/8 inch liquid line and 3/4 inch suction line.
There are solenoid valves and they appear to open and close correctly (suction pressure decreases if we lift the coil off)
A new orifice has been fitted to unit 1, with a new strainer.
Unit 1 was vacuumed and fresh 134A used to re-fill it.
A new compressor was fitted to number 1 some months ago, because we suspected it wasn't pumping properly. It was pressure tested back at the supplier and they found it be working fine.

We've removed all panelling from around the compressors / condensor to maximise airflow, with no improvement seen in the cooling effect, but it is certainly now cooler around the condenser. We've blasted all 3 condensers with compressed just to be absolutely sure they are good and clean. Very slight improvement in head pressure as a result.
Condenser fans run in parallel with the compressor, not thermostatically controlled.

We haven't been able to measure the current.

Number 2 works well in the sense that it cools well - though it has been pointed out that the pressure is suspiciously high. Units 2 and 3 have not been touched, and have the original gas load in them. It's possible that number 2 has got too much in it, but it's number 1 that concerns us because it's just not cooling.

[nike123]

This should be rectified. Air entering condenser 1 temperature is too high. Why is that way?
It looks like recirculating air from another unit condenser. Any photography of condenser location?

...................

Any liquid receiver there?
Any picture of TXV bulb placement?

[frank]

Do you know what air volumes you have on both the condensers and evaporators?

[JoeReade]

Thanks for the quick reply, much appreciated.
Here's a picture of the compressor / condenser unit so you can get the general idea. It's close to the ground, and did have perforated panels to the front and rear. I took them off today to make sure there was good airflow. The temp of air entering the condenser definitely went down a good deal, but there was no discernible improvement in the cooling effect in the tunnel. The neighbouring unit 2 is a mirror image of this unit with the same space around it, but it cools much more effectively.
IMG_1657[1].jpg

Here's a pic of the txv on unit 1, with the bulb clamped to the suction line leaving the evaporator. Are you asking if there is a liquid receiver at the txv? There is one just after the condenser; then a drier; then a solenoid valve (open whenever the compressor is running) then a sight glass then back to the TXV.

Capture2.JPG

Some other pics of the compressor for good measure (not running):
Capture3.jpg
Capture4.jpg
Capture5.jpg

Is it possible that we have some kind of obstruction in the high pressure line? The drier? The solenoid valve not fully opening?

Cheers

Joe

[chemi-cool]

Pictures makes sense,

Its all Chinese s****, it will work properly.

Had to dump 4 new condensing units very similar to your pictures and get real condensing units.

[JoeReade]

Hi Frank

No - I don't know what the air volumes are... I could get details off the units. But I can tell you that the fans on all three identical units are working well, without doubt. Units 2 and 3 have exactly the same spec as unit 1, but cool much more effectively (10c cooler). Shall I get the air volume numbers, or is it sufficient to know that the other identical units are working fine with the same fans?

[JoeReade]

Pictures makes sense,

Its all Chinese s****, it will work properly.

Had to dump 4 new condensing units very similar to your pictures and get real condensing units.

What could be wrong with the condensers? they're clean, and the fans are running well. Surely after that there's not much that can go wrong??

[nike123]

Give us make and model# of condenser!
Does air on condenser fan flow from condenser to compressor or from compresor to condenser?

[nike123]

This should be rectified. Air entering condenser 1 temperature is too high. Why is that way?
It looks like recirculating air from another unit condenser.

Still no answer! From what I see at pictures, these condensing units are placed inside of production room near the obstacles which can prevent proper air circulation and can make part of discharged air to recirculate.

Bad placement.

In order too cool, unit need to reject heat properly.

[nike123]

Circuit 1
Measure again all, but now include liquid pipe temperature just before TXV (15-20 cm) but after solenoid valve and drier. Also, using same thermometer, preferable contact type, measure pipe temperatures just before and after drier (looking in direction of refrigerant flow). Check for correct orientation of drier and solenoid valve regarding refrigerant flow.

[chemi-cool]

What could be wrong with the condensers? they're clean, and the fans are running well. Surely after that there's not much that can go wrong??

These are very old design condensers, I dont believe they were checked for flow, pressure controlls set can not be changed,

to be honest with you, it is impossible to find a fault from here, you are not familiar with the physics of refrigeration.
My 5 pennies worth advice, get the design papers, a good fridgy and sort your problem once and for all.

And don't forget to give him the cookies box.......

[frank]

Are the condenser fans 3 phase or single phase?

[frank]

Hi Frank

No - I don't know what the air volumes are... I could get details off the units. But I can tell you that the fans on all three identical units are working well, without doubt. Units 2 and 3 have exactly the same spec as unit 1, but cool much more effectively (10c cooler). Shall I get the air volume numbers, or is it sufficient to know that the other identical units are working fine with the same fans?

Joe

It would be helpful if you could measure the airflow but if that's not possible, can you give the make and model numbers of the condensing units/evaporators?

[install monkey]

insulate ur tev bulbs

[frank]

OK - I have some measurements that I hope will shed some light. Let me know what you think...

Measurements for unit 1, which is not cooling well:
Pressure just after the compressor 160psi
Pressure just before the compressor 20 psi
Pipe temperature just before compressor 15.5c
Pipe temperature just after compressor 70c
Pipe temperature just before condenser 57c
Pipe temperature just after evaporator 8.6c
Air temperature entering the condenser 36c
Air temperature leaving the condenser 43.3c
Air temperature entering the evaporator 16.9c
Air temperature leaving the evaporator 14.6c

Ambient temperature for both units 28c – but locally higher around unit 1 as can be seen from the air temp entering the condenser.

The saturated condition of the discharge gas at 160psig is 46.5C and with a measured temp of 70C you have a superheat of 23.5K...a little high

The saturated condition of the suction gas at 20psig is -5.6C and with a measured pipe temp of 8.6C you have a superheat of 14.2K, but then your suction temp just before the compressor is 15.5C so your superheat at this point is 21.1K. You are picking up too much heat in the suction line. Is it insulated?

If the gas charge is correct?(are you saying the charge is correct because the sight glass is full) I would say that you have a restriction, as your evaporator is starved. Has the TEV been adjusted to try to bring the superheat under control?

If the ambient temperature is 28C, where is the additional 8K of heat coming from onto the condenser?

[mad fridgie]

Incorrect circuiting of the evap and overcharged.

[Magoo]

Hi JoeReade.
Your problem is that there are three cooling systems in one cooling tunnel, each one is fighting the other.
I have done a few in the past for Cad Sch and all were single blower systems with counter air flow to product flow full length tunnel with high suction heat factor evaporators.

[JoeReade]

Are the condenser fans 3 phase or single phase?

Three phase, but they're running the correct way (ie drawing through the condenser and toward the compressor)

[JoeReade]

Hi JoeReade.
Your problem is that there are three cooling systems in one cooling tunnel, each one is fighting the other.
I have done a few in the past for Cad Sch and all were single blower systems with counter air flow to product flow full length tunnel with high suction heat factor evaporators.

Definitely not the problem.