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tinotech
07-03-2012, 04:54 PM
Copeland scroll compressor - Overheating - What is the cause and how can it be fixed?
The system was built with a Copeland ZH30K4E-PFJ; TEV Danfoss TEZ5-5,0/No.2; Evaporator with 38,4 SQM(for AIR) and 19,2 SQM for SUN ; there is an oil separator 2,5l.; Reciever 6L; Filter dehydrator Danfoss 164s; System charged with 2,2L R407C. Condenser-Plate heat exchanger 1,2sqm; pump 4cbm/hour; Buffer 600L.
After three months of work in the period 11.11.2011 - 12.02.2012 there was a breach in the evaporator, there was a loss of refrigerant and the machine has stopped at Lp=1,5bar. Before it stopped there was an increase in noise. After the leak has been fixed, the filter dryer has been changed, the system was cleaned with (N), the system was sealed and loaded but also starts working louder, you can hear the oil dispenser system working more often and the discharge temp. rises very quick to 91C, to which temp. the safety trips as it was set to this temperature. The clixon on the output has never switched on.
Ambient temp 0C on Air
22 C water, buffer 600l
SUCTION PRESSURE ...2,8 BRA AND -13C AT INLET
LIQUID PRESSURE ......12,5 BRA AND 27,8C (AT TEV INLET is approximately equal in temp. to the water output of the condenser).
DISCHARGE PRESSURE 12,5 BRA AND TEMP AT OUT LET grows up really quick (from 1 sec./10th of C in the beginning to around 30sec/0,1C upon reaching 80C)
AMPERAGE HIGH @19,5 AMP
NORMALLY AROUND 14-15 AMP
After 20’ :
27,6C water
SUCTION PRESSURE ...2,0 BRA AND -22C AT INLET
LIQUID PRESSURE ......13,5 BRA AND 30,8C (AT TEV INLET is approximately equal in temp to the water output of the condenser).
DISCHARGE PRESSURE 13,5 BRA AND 83C AT OUT LET

AMPERAGE HIGH @19,4 AMP
After 32’ :
30C water
SUCTION PRESSURE ...2,0 BRA AND -22C AT INLET
LIQUID PRESSURE ......14,5 BRA AND 34C (AT TEV INLET is approximately equal in temp to the water output of the condenser).
DISCHARGE PRESSURE 14,5 BRA AND 91C AT OUT LET and the adjustable temp. defense switches on and trips. By a temp of around 84C there is a slight stagnation in the increase in temp. after which the tempo of increase goes to around 7sec/0,1C
Delta T condenser water(in/out) = 1,8C

During the next start after 9 min. the system works for around 15 minutes and reaches :
SUCTION PRESSURE ...2,0 BRA AND -22C AT INLET
LIQUID PRESSURE ......15 BRA AND 34,8C ( temp of the heated evaporation reaches 91С )
Water temp : 31,5С
During next start in 9’:
Works for 58’ and reaches:
SUCTION PRESSURE ...2,2 BRA AND -18C AT INLET
LIQUID PRESSURE ......16 BRA AND 37C ( the temp of the heated evaporation reaches 91C and the system trips. ( the head of the compressor has a temp of around 60C in the beginning). With this setting for protection the temp of the head of the scroll reaches 102-105C.
Water temp 35,5C
During the next start after 9’:
Works for 13’ and reaches
SUCTION PRESSURE ...2,4 BRA AND -17C AT INLET
LIQUID PRESSURE ......16 BRA AND 37C ( the temp of the heated evaporation reaches 91C and the system trips.)
During the next start after 9’:
Works for 6’32”


What could be the reasons for the system to overheat so fast, taken the fact that it has worked perfectly for 3 months before the refrigerant leaked ?
Please advise!

chemi-cool
07-03-2012, 06:22 PM
Sounds like you got a lot of moisture in the system.
Disconnect the compressor, pour out all the oil and check for acidity. flush the system with R141, check again with OFN, vacuum, charge and run. I hope you didn't loose the compressor.

aramis
07-03-2012, 07:07 PM
What’s a BRA? (I mean in refrigeration!)

If it is Bars you are talking about, your system is working way out of its rage! If it is Bara then even more wrong! If it is NOT bars please don’t read any further!

You don’t have to let it work for more than five minutes to know that something is wrong, so don’t let it work in these conditions.

I supposed you loaded the correct amount of refrigerant, and replaced it not just tapped, this is something important and if you are not sure, you should check it by recovering weighting and refilling. If you refilled refrigerant you may not have R407c in your system and should dispose of it and change with new R407c.

Check if the “breach” at the evaporator was caused by freezing, if so it never worked correctly!

R407c is not a good refrigerant to use for suctions below 4.7 bar.

Your high pressure is also low, this is why I suspect of insufficient charge, but several other problems could be present simultaneously and all add up to your problem.

High discharge temperatures are caused by:

High condensing pressure. Don’t think this is your problem now.

Low evaporator pressure. Definitely part of your problem.

High superheat. Does not seem to be part of your problem now.

You have to check the thermal load of your evaporator, it could recirculate cold air or you may have low ambient temperatures or it may accumulate ice, maybe you need to check or install heaters.

nike123
08-03-2012, 09:09 AM
R407c is not a good refrigerant to use for suctions below 4.7 bar.



Could you elaborate this?

nike123
08-03-2012, 10:09 AM
What could be the reasons for the system to overheat so fast, taken the fact that it has worked perfectly for 3 months before the refrigerant leaked ?
Please advise!


I would say damaged compressor mechanically.
If your pressures are in Bar relative than your current should be 10,7A at 230V power supply voltage.
Change compressor.

padraic
08-03-2012, 08:40 PM
is there liquid injection cooling on the compressor and if so is it working...? there might be a blocked filter before liquid valve or if the unit is running short of gas the first thing that will starve is the liquid injection

nike123
08-03-2012, 10:34 PM
It is obvious that high amperage draw is what is causing overheating of the compressor. That compressor at that suction and discharge pressure should draw only 10,7A (at 230V). Since current is almost twice of that, mechanical problem in the compressor is most likely cause.

tinotech
09-03-2012, 10:14 AM
BRA = Pabs(bar)

The oil has been checked and there is no acidity, the system is loaded with the exact quantity of refrigerant (as much as in other working systems anyway) the evaporator malfunction was caused by a mechanical defect in the material and has been removed.

Questions : Is it possible that the problem might lie because of the high hydraulic resistance in the return line of the evaporator ?

What would happen if I replace the TEV nozzle with number. 3, now is a no.2. (since the beginning of the working of this system the temperature of the heated evaporations was a bit higher (83-87C). as compared to a similar machine working at (75-77C).

Another question : What is the normal difference between the evaporating temperature and the ambient temperature of the evaporator?




What’s a BRA? (I mean in refrigeration!)

If it is Bars you are talking about, your system is working way out of its rage! If it is Bara then even more wrong! If it is NOT bars please don’t read any further!

You don’t have to let it work for more than five minutes to know that something is wrong, so don’t let it work in these conditions.

I supposed you loaded the correct amount of refrigerant, and replaced it not just tapped, this is something important and if you are not sure, you should check it by recovering weighting and refilling. If you refilled refrigerant you may not have R407c in your system and should dispose of it and change with new R407c.

Check if the “breach” at the evaporator was caused by freezing, if so it never worked correctly!

R407c is not a good refrigerant to use for suctions below 4.7 bar.

Your high pressure is also low, this is why I suspect of insufficient charge, but several other problems could be present simultaneously and all add up to your problem.

High discharge temperatures are caused by:

High condensing pressure. Don’t think this is your problem now.

Low evaporator pressure. Definitely part of your problem.

High superheat. Does not seem to be part of your problem now.

You have to check the thermal load of your evaporator, it could recirculate cold air or you may have low ambient temperatures or it may accumulate ice, maybe you need to check or install heaters.

tinotech
09-03-2012, 10:31 AM
In general - what would you suggest in order to fix the problem and to avoid it in the future ?

nike123
09-03-2012, 11:52 AM
SUCTION PRESSURE ...2,8 BRA AND -13C AT INLET
LIQUID PRESSURE ......12,5 BRA AND 27,8C (AT TEV INLET is approximately equal in temp. to the water output


In this data you gave us pressures in Bara (Bar absolute) and temperatures in °C measured with thermometer. Is that correct, or you gave us saturation temperatures read from gauges?

I ask this because there is practically no superheat and no subcooling by this set of data.

R407C
2,8 bara= -13,12
12,5 bara= 26,95°C

Superheat -13-(-13,2)= -0,2K Negative superheat (impossible)
Subcooling 26,95-27,8=-0,85K Negative subcooling (impossible)

nike123
09-03-2012, 12:01 PM
SUCTION PRESSURE ...2,0 BRA AND -22C AT INLET
LIQUID PRESSURE ......13,5 BRA AND 30,8C (AT TEV INLET is approximately equal in temp to the water



Same is here!

R407c

2 bara= -21,44°C
13,5 bara= 29,87°C

Superheat -22-(-21,4)= -0,6K Negative superheat (impossible)
Subcooling 29,87- 30,8= -1,07K Negative subcooling (impossible)

nike123
09-03-2012, 12:07 PM
In general - what would you suggest in order to fix the problem and to avoid it in the future ?

Change compressor and take, note, and post here full set of measurments.

aramis
09-03-2012, 01:46 PM
Could you elaborate this?

Yes.

Vapour density falls fast (25% between 0°C and -6°C) this lowers heat transmission coefficients.

Glide is high, probability of changing composition with a leak in the evaporator goes up!

Isentropic coefficient lowers, together with glide produce higher discharge temperatures.

aramis
09-03-2012, 02:20 PM
BRA = Pabs(bar)

Never too late to learn something new!



Questions : Is it possible that the problem might lie because of the high hydraulic resistance in the return line of the evaporator ?


I suppose you mean pressure drop in the refrigeration side of the evaporator, the answer is definitely yes. It is difficult to measure this value, more with a zeotropic mixture.

As I mentioned in my first post “…several other problems could be present simultaneously…”. For the amount of information you posted you don’t seem like someone who would overlook moisture, but BRANIAC has a very valid problem you have to check.

High amps could be caused by low voltage so measure the voltage and the amps you should read are TestVoltage * CatalogAmps / MeasuredVoltage. If this value is within 15% of your amp measurement you may be OK, if it is not you may have lubrications problems like he mentions.

Never let a system far outside it’s supposed (or ideal) working conditions work for too long. Only exception is if your system is noticeable tending to the ideal condition, but you have to be careful.



What would happen if I replace the TEV nozzle with number. 3, now is a no.2. (since the beginning of the working of this system the temperature of the heated evaporations was a bit higher (83-87C). as compared to a similar machine working at (75-77C).



Low suction could be caused by the expansion valve too. You have to check weather the output of your N°2 orifice matches your expected load and conditions. If it does, the orifice is not the problem.
If you put a larger orifice the system will work better, but the problem is still there. So you may get away with it at the risk of producing a future failure due to an oversized orifice when the real problem is no longer present.



Another question : What is the normal difference between the evaporating temperature and the ambient temperature of the evaporator?
[/QUOTE]

This is something the designer of the evaporator can answer. There is no “normal” value for it depends on the evaporator surface, air volume, face speed, …

You could estimate this value if you can estimate the compressors capacity (at the working conditions) and can estimate the latent heat (amount of water and temperature you are condensing and/or weight of ice formation per unit time) then the sensible heat should approximate to capacity - latent heat. All you need now is to measure the inlet temperature and look for Cp of the air in tables. This is a lot of work and measures that need to be precise.

Suggestions

Check what BRAINIAC says.

The expansion valve doesn’t seem to be the problem because you have 5° superheat at 2 Bara with -22°C.

Try increasing the load of the evaporator (heat it up). The system could start having symptoms of low refrigerant charge. If this happens you should really check if it needs heaters.

Contact the manufacturer, he may have many more ideas.

desA
10-03-2012, 07:07 AM
Taking a few steps backwards - Can you tell us more about the water situation in the condenser?

Air entrapment in plate hx? (Reduces effective condensing surface area).
What dT across water connections?
Could the phe be fouled on the water side?
Are there air bleeds in the water circuit? At highest points of piping system?
What is the real water flowrate? How do you know that?

tinotech
10-03-2012, 11:58 AM
Thanks for the answers. I would like to make some corrections and clarifications as it seems that I have given some misleading data. In reality the pressures that I have pointed are in fact BARG and the temperatures are according to a table. The mistake is mine.
The facts are :
- the compressor heats up too fast
The body of the scroll has temperatures:
- down bottom of scroll60C-80C
- at the suction line 45C-75C
- above ( before the spherical part) up to 80С
- on the very top there an excess of heat (in the middle)
- the temperatures have been measure at the clixon (at 120mm from the body) of the output line
- the oil has been checked and is not acid, the filter is brand new
- the water circulates normally with 4cbm/hr, there is no air in the system 100% sure. no fouling of the phe on the water side 100%.

The evaporator is made with flat solar panels with direct refrigerant evaporation
and with natural circulation, 12 pcs with a size of 2000/800mm. This makes the active surface to work with air 38,4sq.m and 19,8sq.m to work with the sun. The panels are connected parallel and equal (connected all in the same way with same lengths and sections of the liquid line). The return line from the evaporator has been made in the same way and from here there is probably a higher hydraulic resistance as compare to a working analogical machine ( with it the outputs of the panels are directly plugged into the return pipe in the shortest way). The element base and the quantity of ***** is exactly the same. The difference is only in the return line of suction. During the three monts of work the temperature of the hot vapors was around 10C higher than in the working analogical machine.
During a breach in one of the panels and loss of refrigerant and after restoring the system - the scroll begins to trip because of a temp. prtotection at 90C. After a few starts with a varying working time untill the protection system trips I have concluded a low resistance to the corp/body (R=515om when the corp is warm and around 66Kom when cold). After a change in the compressor with ZH13KVE-PFJ ( I had this one available at the time and is quite the same) I have not connected its line for direct injection. The current is 25A with a maximum of 30A, which for 17-19 BARG seems high. Obviously there is good refrigerant movement, especially after the change of the filter dryer, but the excess heat remains and in the range of 10-15 mins it reaches 85C, which is the tep set for protection trip. Ergo its behavior is similar to the previous scroll used but much more quiet in terms of noise.

With an ambient temperature of 8C and prtection trip at 85C:

SUCTION PRESSURE ...2,2 BARG
LIQUID PRESSURE ......17,3 BARG AND (AT TEV INLET is approximately equal in temp. to the water output of the condenser).
Начална Tcompressor=15C
Тwater=35,2C inlet ; 40,4C outlet
Works for 33’ - protection trips.

after 9’:
SUCTION PRESSURE ...2,5 BARG
LIQUID PRESSURE ......17,0 BARG
Тwater=35,4C inlet ; 39C outlet
Works 10’- protection trips.

After 9’
SUCTION PRESSURE ...3,5 BARG
LIQUID PRESSURE ......17,5 BARG
Twater=36,3C inlet ; 39,8C outlet (After 6-7’ work Тoverheat=82,4С)
Works 10’- protection trips.


New Questions :
1. If I connect according to the direct vapour injection scheme from Copeland would this make the picture better or worse?
2. If I change the orifice with a higher number what negative effect can be expected?
3. If I use the line for direct evaporation and through it supply some of the cold vapours would that unload the heat load of the scroll’s head ?
4. Is it possible that the electrical malfunction of the scroll is caused because of its use in a mode varying 83C-87C?

tinotech
10-03-2012, 01:14 PM
"- at the suction line 45C-75C"
Sorry, the correct data is : - at the suction line 45C-47C

monkey spanners
10-03-2012, 03:07 PM
If i read your information correctly the system is evaporating between 2.2 and 3.5 bar, so about -16C to -7C and the temperature of the suction line near the compressor is 45C to 47C!!!!!!

The difference between these two temperatures is called suction superheat, it is gennerally 7C at the evaporator outlet, maybe a couple of degrees lower in low load conditions and a few degrees higher in high load conditions.

By the time the gas has reached the compressor it will have warmed up a bit more (last system i did was running around 15/16C superheat (so actual temperature at compressor was around 0C) with an evaporation temp around -15C, the body of the compressor is cool and only the head was warm)

Compressor generally don't want more than 20C suction superheat (though have seen 30C for specific models)

You system has around 60C superheat! High super heat into a compressor will result in high superheat out which is what i think your system is tripping on.

Sounds like there are some serious issues with either the system design, component selection or application.

What is the system designed to do?

How well does the compressor duty match the heat load?

How are you feeding multiple evaporators with just one expansion valve?

tinotech
10-03-2012, 08:54 PM
„If i read your information correctly the system is evaporating between 2.2 and 3.5 bar, so about -16C to -7C and the temperature of the suction line near the compressor is 45C to 47C!!!!!!”

This is the temperature of the scroll at the height of the suction pipe, these are not the temperatures of the gases sucked in the scroll.


The difference between these two temperatures is called suction superheat, it is gennerally 7C at the evaporator outlet, maybe a couple of degrees lower in low load conditions and a few degrees higher in high load conditions.

By the time the gas has reached the compressor it will have warmed up a bit more (last system i did was running around 15/16C superheat (so actual temperature at compressor was around 0C) with an evaporation temp around -15C, the body of the compressor is cool and only the head was warm)

Compressor generally don't want more than 20C suction superheat (though have seen 30C for specific models)

Тhe suction superheat does not exceed 20С in any case.


You system has around 60C superheat! High super heat into a compressor will result in high superheat out which is what i think your system is tripping on.

Sounds like there are some serious issues with either the system design, component selection or application.

The system is a copy of a working system. It has worked for 3 months before it lost its refrigerant.


What is the system designed to do?
It’s design is for heating with the utilisation of direct evaporation of the refrigerant in the solar panels.


How well does the compressor duty match the heat load?
A copy of the working system.


How are you feeding multiple evaporators with just one expansion valve?

Using liquid distributors

https://lh6.googleusercontent.com/r-zxIRnLMR4HWaNbsxSCaY7Bc6z5D5myK_g3c1jZ8eCsZWaPyMt5SeA_VqLhz9zhL4c84XO0L576nJwnqweTr0eUvwPeSgWDMleeHz p2dQSsWqf6VJM

aramis
11-03-2012, 12:00 AM
I agree with monkey spanners too.

You now have two of the three causes of high discharge temperatures, and these are based on normal operating compressors.

Yu must make your suction pressure go up and your superheat down. At the same time check for the reason of overconsumption.

An electrical/lubrication problem in your compressor also contributes to overheating the compressor.

Two refrigeration systems are similar ONLY if they use the same refrigerant and their temperatures and PRESSURE DROPS are similar. IT DOESN’T MATTER IF THEY LOOK ALIKE!

So you probably overlooked something you don’t see and have to measure to discover it.

Oh! And don’t get distracted with Bras until you fix the problem!

tinotech
16-03-2012, 02:17 PM
Hello and thank you all for advice.
After replacing the compressor changed with larger orifice.I did and the system for direct vapor injection.The resultsare as follows:

Ambient temperature 8C, sunshine,buffer 600 liters of water

SUCTION PRESSURE ... 5,3 BARG (evaporation 9,8C)
LIQUID PRESSURE ...... 19,2 BARG (condensation 51,5C)
T hot gas = 63,5 C, Tsuction gas = 25,6 C (superheat 15,8C)
Start Tcompressor = 45,7 C
Twater= 36,8 C inlet and 43,9 C outlet; T before tve = 45,4 C

After30 ':
SUCTION PRESSURE ... 4,9 BARG(evaporation 7,9C)
LIQUID PRESSURE ...... 21,2 BARG(condensation 55,8C)
T hot gas = 79,7 C, Tsuction gas = 22,3 C (superheat 14,4C)
Thead compressor = 102,1 C
Twater= 40,6 C inlet and 47,6 C outlet; T before tve = 49,0 C

After30 ':
SUCTION PRESSURE ... 4,6 BARG(evaporation 6,2C)
LIQUID PRESSURE ...... 22,2 BARG(condensation 57,5C)
T hot gas = 81,9 C, Tsuction gas = 22,9 C (superheat 16,7C)
Thead compressor = 104,1 C
Twater= 42,5 C inlet and 48,9 C outlet; T before tve = 50,5 C

The system works stable.
Problem is that the trigger system(LIQUID PRESSURE ...... 13,2 BARG) current is 26.2A,as much as in LIQUID PRESSURE ...... 19,2 BARG, and at LIQUID PRESSURE ...... 22,2 BARG,current is 27.2A at maximum current of 30A. Perhaps I have a problem with current clamps? There are no reasons for the high current loading.

What optimization measures can be proposed?

aramis
16-03-2012, 09:31 PM
You have two measurements with the same time stamp.

Checking your clamp meter would be a good idea. Also amp measurement must be made together with voltage measurement and you have to check that the test voltage for your compressor matches or you have to compensate like I mentioned before.

I suppose you have lots of sunshine on the evaporator to evaporate at +9.8°C with +8°C ambient.
First define what you want to optimize.

The ZH line can work up to 75°C condensing (about 35 barg) so if you want to optimize your water temperature you should try increasing your condensing pressure but check with your Copeland wholesaler what is the maximum discharge temperature it can withstand.

If you want to optimize the time it takes to heat up the 600 liters to a minimum temperature you should try to increase your thermal load in the evaporator.

Both have pros and cons so ask the customer what he expects of the system and try to comply. Leave optimization work for a lab!