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samux12
02-10-2013, 10:35 AM
Hello everybody,

There is heating/air conditioning system with two heat pump. Those two heat pumps have seperate refrigerant cycles with two evaporators for each - one air source and one water source. System's principle scheme is shown below:

10800

There are two seasonal modes in this system. In the summer mode solenoid valve installed in the refrigerant cycle close the cycle to the air source evaporator and the heat pump works like a water to water heat pump and the refrigerant cycle goes through the water source evaporator. In that mode warm water coming from fancoils installed in the office facilities are cooled and than it is supplying back to the fancoils. The energy taken from the offices are used to heat DHW and when the water temperature reaches setpoint it is directed to the technology line. That's how the summer mode works.

In the winter mode second solenoid are closed and refrigerant cycle is directed to the air source evaporator which takes the heat from exhausted air from technology and bring it to the DHW and heating system. in this mode heat pump works like an air to water heat pump.

After a half of the year one the heat pump's compressor broke up. Malfunction symptoms:
1) Metallic sound inside compressor;
2) Higher working current than usual;

Guys, what do you think is the main reason for this malfunction? Could it be due to oil returning issue? Oil seperator isn't installed. (Forgot to mention compressor type - it is Copeland SCROLL compressors)
Maybe oil is trapped somewhere in one of the evaporators and cannot return?
I will be very thankful for your help.

samux12
02-10-2013, 10:38 AM
System's principle scheme
10801

The Viking
02-10-2013, 04:24 PM
To accurately diagnose this you will need someone with experience actually getting his(her?) hands on your system.

From what you are describing it could be liquid refrigerant entering the compressor but it could also be a number of other faults/issues/problems.

:cool:

samux12
03-10-2013, 06:06 AM
I'm 100% sure that liquid don't come back to the compressor.

But what do you think about my thoughts that due to two diffrenent evaporators somewhere oil is trapping and don't come back to the compresso? It could be the reason why mechanic matallic sound appears in compressor.

spikour2011
03-10-2013, 08:15 AM
I agree with The ViKing. Someone with experience actually getting his(her?) hands on your system.
Before anything be sure that oil traps (with or without risers?) installed properly and check the height difference between the evap and the compressor. You must also check the level of refrigerant in a proper way. Also check the temperature on the head of each compressor. Is it too high or cold? Too cold is an indication that maybe liquid refrigerant entering the compressor.

samux12
03-10-2013, 08:34 AM
Level diffrence between compressor and evaporator is 2m (from water evap) and 3m (from air source evap). So diffrence of level isn't big. Why I'm so sure that liquid don't come back to the compressor? because the suction pressure was even to low (6.5bar). For that reason, refrigerant gas returns with high superheat (~30k), and head of the compressor is relatively in high temperature.

Could this malfunction occur due to lack quantity of refrigerant? Or maybe filter-drier can be clogged up (refrigerant is taken from liquid receiver, after that he pass filter-drier and than sight glass), because the sight glass isn't full of liquid. And maybe for this reason suction pressure is so low (The second heat pump standing in next to it, works with 9bar suction pressure)

The Viking
03-10-2013, 06:36 PM
Why I'm so sure that liquid don't come back to the compressor? because the suction pressure was even to low (6.5bar). For that reason, refrigerant gas returns with high superheat (~30k), and head of the compressor is relatively in high temperature.

:eek:
OK, so you do know what the issue is...
What answers do you think we can give you without even looking at the system?
A compressor running with a 30K superheat will eventually damage itself, before it grinds to a halt it will even make funny mechanical noises...

You really do need an experienced engineer to get his hands on your system.

:cool:

Peter_1
03-10-2013, 08:02 PM
Given the guys schematic and some of his arguments, I can decide he's not a novice at all.
But we need more readings. What interest us most is SH, SC, TE, TC and discharge temperatures in both heating and cooling. Water in, Waterout,...
You say 6.56 and 9 bar but without giving the refrigerant (must be R410a, otherwise, there's something completely wrong with your system) You see, we have to guess.
Is it a new, just commissioned system, has it run fine at the beginning, do you have readings from the startup,..

mad fridgie
03-10-2013, 09:08 PM
your compressor ran out of oil.
look at installing an oil balance pipe, if possible. (between the oil sight glasses)

samux12
04-10-2013, 06:33 AM
This system has worked smooth for a more than a half. At the first start up everything looked fine. Technical data during first start up:

Water supply (to the system): +45C/40 (in the heating mode);
Refrigerant - R410A (sorry I forgort to mention before)
Tcon - +50C; 30bar SC - I have checked;
Tevap - +2C; 8.5bar; (Exhausted air from technology - ~+40/18-20C)
Discharge temperature - Haven't checked.

After a half a year when the system started fail I noticed that the strange metallic sound appears and when I check the parameters, it was:
Water supply (to the system): +30C/24C (in the heating mode);
Tcon - +36C; 22bar SC - I have checked;
Tevap - -6.5C; 6.5bar; SH- ~30K (Exhausted air from technology - the same);
Discharge temperature - Haven't checked.

I noticed that there is something wrong and I decided to fill a little bit of oil in the compressor, but unfortunately it didn't help and after a day of my last service visit, compressor broke down.

I see the to possibilities what could happen:
1) Compressor worked without oil and bearings have no lubrication and finally burned out.
2) Compressor discharge temperature was to high (but in that case Copeland ZP91 has "high discharge temperature safety device". It cut off the compressor when the temperature reaches +140C)

samux12
04-10-2013, 06:59 AM
Mad fridgie, those two heat pumps has completely separate refrigerant circuits with one compressor inside on each.
I totally agree with you when there are two or more compressor's installed in tandem, oil equalization line must be installed. But in this case I don't need it.

Oil could leave the compressor in other reason. It can be something incorrect in the refrigerant piping istalation. Maybe the oil is trapped in one evaporator when the the circuit runs through another one and when the circuit is changed by solenoid valve (compressor is on), oil in an evaporator remains there until the next circuit change.

RusBuka
04-10-2013, 03:04 PM
Why died 1 compressor, and the other works?

The systems are the same and separate circuits. Therefore the problem in the circuit.
The most common options: leak ( no ***** - no oil in the crankcase), liquid operation ( no lubrication, washed away the oil from the crankcase), the work with large SH ( oil not returns from evaporators)
That oil would not come back from condenser must be large leak or not set correctly.

Cut out compressor and look at the amount of oil + what happened with spirals
If you have something like CPS 700, pump down ***** and weigh

samux12
04-10-2013, 04:01 PM
One compressor died and the other is still working well because for this system where those heat pumps are installed mainly is enough one heat pump to cover all energy demands. That's why almost all the time only one heat pump has worked (and now it broke down).

Yesterday we pumped down the refrigerant and the amount of it was the same like we has filled it up. So, refrigerant leakage possible can be rejected.

Next week we're going to cut the compressor and we'll see what is inside and what had happened to him

The Viking
04-10-2013, 06:42 PM
Samux,

One question just to make sure we are talking about the same thing.

When you say the superheat is 30K, how did you calculate it?
At 6.5 Bar, R410A's bubble point is ~ - 1.7C. That would make the suction line about 28C to get a 30K superheat. Is it really that warm outside in Lithuania at the moment? Otherwise there might be more than meets the eye with this system...

:cool:

joe-ice
04-10-2013, 07:13 PM
Agree with rubuska open the compressor to see oil amount if it is oil.also is there a control to keep back pressure up when you switch to water chilling .The pressures above are close to and below freezing.

mad fridgie
05-10-2013, 03:37 AM
oops,
learn to read young mad!

mad fridgie
05-10-2013, 03:42 AM
How are your suctions connected, and is there any height difference.
Could the oil be falling into the non used evap.

samux12
07-10-2013, 06:15 AM
Viking, these units is install for energy utilization from warm exhausted air (warm air approx 40C degrees is exhausted from industrial driers at textile factory).

Thats why the SH is so high.

samux12
07-10-2013, 06:39 AM
Mad fridge. I take a few picture to see refrigerant cycles:10805

mad fridgie
07-10-2013, 08:53 AM
looking at the pic first glance all seems OK, but there MAYBE a problem with one of the liquid solenoid valve, you need to check that in can be mounted in a vertical pipe. (not all brands suggest it as an option). So it could be passing to some degree, either logging the coil with oil, or causing a wet suction (when off), was the oil away.

nike123
07-10-2013, 09:17 AM
When unit is working in mode where process exaust air is used, what is air entering and leaving temperature at evaporator?

That air should not be introduced at evaporator at high temperature. It shuld be mixed and introduced at level of about 10C max.

If it is higher than that, high suction superheat and therefore high discharge superheat can lead to compressor and oil overheating and damage on compressor bearings (copper plating) due to changed oil cemistry.

Clarify what is happening at evaporator in this heat pump mode.

Also, who has made that project? Any documentation?

samux12
07-10-2013, 11:38 AM
Mad fridge, there is installed Castel solenoid valves, and according to documentation it can be installed in vertical possitions.

Nike123, according to compressor's working envelope return gas temp. can't exceed 25C. So it doesn't matter what temp. air enters evaporator. The most important thing is return gas temp. Return gas temp can be lowered by reducing air flow volume through the evaporator
10806

In my case air temp entering the evaporator is +40C and leaving at +20C degrees. After the first start up when system worked properly, return gas temp was +20C (it not exceed the limits), after the last service I found it at +30C, so it worked out of limits.
I agree with you nike123, high return gas temp could be one the reason why compressor failed.

samux12
14-11-2013, 12:32 PM
My last assumption about too high return temperature confirmed. The compressor was overheated.

I have dissected compressor's head and I found that connection between shaft and Scroll was burst. The metal was overheated and you can see it from the picture below. Some of the particles changed its color into purple.
10912

The oil amount was the same like it's declared by producer. But it was in dark brown color - it was overheated too.

This is happened due to high suction temp, which was about 30C degrees (limit of the compressor is 25C). Evaporating temperature +5C, SH 25C, Suction temperature +30C.

In summary, seeking to avoid this malfunction in the future air volume entered through evaporator have to be reduced in order to reduce evaporating capacity.

RusBuka
14-11-2013, 12:47 PM
You did not think that it is necessary to configure throttling device to the desired SH?

samux12
08-01-2014, 12:11 PM
Hello again,

I want to reopen the thread.
As I wrote above I though that I fond the reason of malfunction which was too high return suction gas temperature (it was 25-30C).
So I made some system corrections - I replaced the compressor into new one, wrote the program to control the speed of the fan so I could regulate the temp. of suction return gas.

After the start up and commissioning at first sight the heat pump worked perfectly:

Refrigerant - R410A
Ambient temp: +40C
Temp. after evaporator: +18C

Evaporating temp: +4C
Suction gas return: +19C
Suction pressure: 8Bar

Condensing temp: +42C
Liguid temp: +38C
Condensing pressure: 24,5bar
Return/Supply water temp: +35/40C

Compressor: Copeland ZP91KCE-TFD - Compressor has Advanced compressor overheating protection
Condenser: Alfa laval CB60-50
TEX: Danfoss TCAE orifice No3

After a day I went to check how it works, but it was stopped and the compressor Manual Motor Starter was tripped.
When I started the heat pump again I checked the Amp and it was 17A for each phase (normally it should be 11,5A).
I have no idea why it happened, why the amperage is so high and what could be the reason for it?
Why the new compressor failure after a day of work?

I am exhausted of the assumptions and don't have any ideas what to do next, and how to solve this problem.
Could anybody help me to get away from a tricky situation.

samux12
08-01-2014, 12:15 PM
Hello again,

I want to reopen the thread.
As I wrote above I though that I fond the reason of malfunction which was too high return suction gas temperature (it was 25-30C).
So I made some system corrections - I replaced the compressor into new one, wrote the program to control the speed of the fan so I could regulate the temp. of suction return gas.

After the start up and commissioning at first sight the heat pump worked perfectly:

Refrigerant - R410A
Ambient temp: +40C
Temp. after evaporator: +18C

Evaporating temp: +4C
Suction gas return: +19C
Suction pressure: 8Bar

Condensing temp: +42C
Liguid temp: +38C
Condensing pressure: 24,5bar
Return/Supply water temp: +35/40C

Compressor: Copeland ZP91KCE-TFD - Compressor has Advanced compressor overheating protection
Condenser: Alfa laval CB60-50
TEX: Danfoss TCAE orifice No3

After a day I went to check how it works, but it was stopped and the compressor Manual Motor Starter was tripped.
When I started the heat pump again I checked the Amp and it was 17A for each phase (normally it should be 11,5A).
I have no idea why it happened, why the amperage is so high and what could be the reason for it?
Why the new compressor failure after a day of work?

I am exhausted of the assumptions and don't have any ideas what to do next, and how to solve this problem.
Could anybody help me to get away from a tricky situation?

RusBuka
08-01-2014, 02:41 PM
http://www.mbfrigo.hr/uploads/MB_Frigo/zastupstva_download/Copeland/Catalogue_2012_EN.pdf
15 page
max A 16

SH must be near 10K, or smaller.

samux12
08-01-2014, 06:47 PM
RusBuka,
Could you explain, why the SH should be near 10K? Why it's restricted to this value and why it's so important?
In my opinion the most important is the Suction gas return temperature which can't be higher than 25C due to the of compressor cooling

nike123
09-01-2014, 12:02 AM
Most important for compressor health is discharge superheat. High suction superheat mean high discharge superheat.

What is your discharge line temperature 20 cm after compressor?

Take full set of measurments!
High amperage mean compressor is overloaded.

samux12
09-01-2014, 07:27 AM
Okey Nike123 I'll check it.
Maybe do you now what is the limit of disharge line superheat.?

RusBuka
09-01-2014, 12:12 PM
Refrigerant - R410A
Ambient temp: +40C
Temp. after evaporator: +18C

Evaporating temp: +4C
Suction gas return: +19C
Suction pressure: 8Bar

I don't believe this.

nike123
09-01-2014, 08:36 PM
Normal is beetwen 30 and 40K!

shooter
09-01-2014, 09:52 PM
insulate the suction line as the headtemperature will be too high,and 8 bar suction is not correct.

samux12
10-01-2014, 07:14 PM
Bushka, Why do you say that, why you don't believe?

This is the system where heat pumps (evaporator) take energy from hot extracted technological air (~40C). Thats why parameters is so high.

samux12
10-01-2014, 07:27 PM
In my case Discharge temperature is definitely ebove 40K. But to be honest I have no idea why is that, because there is the second completely the same heat pump standing next to this one and pressure parameters the same except discharge temperature, and amps. One of it amperage is 9A on each phase and the second, bad one amp is 13A.

nike123
11-01-2014, 07:31 AM
Discharge temperaturer of what is above 40C?

Discharge temperature of normal operating air conditioner scroll compresor is between 60C and 90C.

shooter
11-01-2014, 11:30 AM
now it is clear:

what you hear is probably the discharge valve, as it will be a hermetic compressor nothing to repair on them. or replace the compressor or buy a new unit. (whichever is cheaper)

heatpumps are they hermetic?
and are inside them no heatexchangers or you mean inside heatpump is only a compressor.

and yes correct about the oiltrap. especially in plateexchangers.make a line from expansion valve to suction, when exchanger is stopped open this line and the oil will be pressed inside the suction line.

as you have multiple expansion valves on one suction line use a surge drum in suction line.
another way is to put both evaporators in series, and switch the fan or the waterpump.

this 45 C is rather low, i hope it is around 80 or higher. This is superheat, however very easy to use in the DHW exchanger. and the outlet goes to the heating system tank to get down to 35 C.
The process exchanger is good as this is the money maker. however do not run both systems at same time but switch over as the processwater is coming in at 10 C so the liquid will be around 15 leaving this exchanger and the condensation temp will be around 35 C.
you could use the program Coolpack (freeware) to check this.

50 degrees condensation is 24 bar and no 30.
30 bar is way too much for any compressor. you must stay below 20 bar as absolute max.
look at compressorplate what is maximum.

In your process the COP is about 1.8 thus the return on investment is too low to rectify the use of a heatpump.

to clarify us please make two diagrams 1 for winter and one for summer operation, giving as much readings as possible.

Action 1 replace compressor
Action 2 check feasability and operationvalues.
get straight with the engineer as he will find out how bad the system was designed (sorry) yes i realize it is out of the book however the book is theory not concerning safety, feasability, cost or efficiency.
contact is shooter@home.nl

shooter
11-01-2014, 11:46 AM
i have looked up your compressor and yes the pressures are fine.
the cop will not be 3.1 but about 1.8 max.
and yes probably the oil is the problem.
in hermetic ones it is a big problem to see the level and they should only be used in simple 1 closed loop having only one evaporator and one condenser.

As the compressor broke down 1 day after service you are in deep ****, however talk to the technical engineer and explain him about your problem. As this system has much volume in piping and exchangers it is a oilproblem.
hoping you will find a solution.