chiller not performing R410a

[moondawn]

hi all i attended site to a chiller which was not cooling very well the chiller is a r410a with two compressors both linked together.

I think the make of unit is clivet, this had a E009 fault: system pressure alarm and it also had various other faults which i cant recall now.

I put my gauges on and ran the system with both compressors running and found discharge pressure was 29 bar and discharge pipe temp 68degrees c.

pipework going in to condensor was 60 degrees c and pipework out of the condensor 43 degrees c 17 deg diff.

I put my gauges on to the liquid line and got 27 Bar .
across the liquid line i found no temp difference staying at 43 degrees c

after the expansion device which was a EEV i got 31 deg c
Suction was 12 bar and suction pipe temp 18 degrees c

From this i came up with subcooling low 1deg
and superheat at 5deg

subcooling is low so lack of liquid going to metering device do you think dragging the gas out would be best and would you say short of gas could be likely?

hope to learn something from your replies

cheers lee

[Pingo]

Hi Lee
We need to know the temperature of chilled water into the unit and out ?

Chiller are normally designed on between 5c to 7c at full load, so with inlet water at 12c, off water temp at 6c = 6c diff.

I would say that with your 5c superheat, that the EEV is OK and the Refrigerant charge is OK.
Try running with one compressor at a time to see if there is a different performance between the compressors.

Regards pingo

[stufus]

Hey Lee
What are your flow and return temperatures and also what's the pressure drop across the evap , is it a PHE or shell and tube .
Before reclaiming the charge make sure all is ok on the water circuit ,flow rate ,pressure drop , vented of air etc etc
Once you have ruled out all that start with checking the drier and then the operation of the eev and it's driver.Although at 5c SH the eev sounds ok
The charge may well be the culprit but unlikely better to rule out all the crap that could compound the problem first.
Cheers
Stu

[Tradewinds]

Hi Lee,

Have you got a model number of the chiller to read the manual.

DP = 29Bar = 49'C seems a little bit high. Is the condenser clean( air or water cooled)?

Your SST of 15'C is pretty high as well. You will want to get that down to about +5'C. So if you can bring the HP down (clean coils, speed up fans, etc) it might help.

17K across you condenser isn't bad though. Should be 12-20k.

SC = 3K (should be 4-8K)
SH = 2K (should be 4-8K)

Is this running at full load? All fans on, EEV 100%?

[moondawn]

hi all i am a newbie with chillers so will try to answer questions as best as but go easy please. :-0
The set point for the chiller is 6.5 deg c. the return temp is 24 deg c and out temp is 17 deg c. when the chiller started it ran with one compressor and then the second came on did not notice any difference in pressures on discharge and suction when the second compressor came on.

the inlet of evap to outlet of evap was 31 deg c /18 deg c
the type of evap is shell and tube
Stufus i am unsure on checking the water side as have no experience whatsoever on them, in the history log it did mention something about antifeeze ???? but can not recall the error message the error was E012 though.

The model of the unit is KCCC-0-602-02-0-0-0-0-1

The condensor i think was a little dirty to look at it it was not clogged but defo could do with cleaning. its air cooled and all the fans were running flat out,


Tradewinds how have you got them calculations as their different to mine could you explain if poosible to help me along

many thanks lee

[moondawn]

I took the liquid pressure which is 27 bar discharge pressure was 29 bar.

[marc5180]

That sounds like a WSAT-XSC chiller.

With the 27bar liquid pressure (44C SCT) and 43C actual temperature then from my calculations it is 1K subcooling which is very low.

Which could be caused by either shortage of gas or the condensing side not condensing fully.

As you say the coils are dirty, so maybe worth giving them a clean. Were all the condenser fans running?

Also suction at 12bar (13.5 SST) and 18C actual temp then the superheat is 5.5K which looks like the EEV is doing its job and controlling superheat.

[mad fridgie]

nothing wrong with it, your load temp is high, the rest seems to balance

[marc5180]

Nothing wrong with it apart from it's not cooling ;-)

[moondawn]

hi marc all the fans were operating and seemed to be running flat out.

[mad fridgie]

all data, given indicates the unit is balanced with the load, but what should be of concern is the second compressor, you indicated no changes in the system when this came on, here lies the problem.
Can you run the second comp only?

[mad fridgie]

Nothing wrong with it apart from it's not cooling ;-)
But it is, in 24C out 17C, i have always called a reduction in temperature "cooling":D

[moondawn]

hi mad fridgie

not sure if i can run the one compressor on its own i guess it can be done though
i am pretty sure i did not see a change in pressures as the second compressor came on line.
where would the best place to start with trying to rectify the not so good cooling its giving out?

many thanks lee

[mad fridgie]

You may just be able to change your compressor contactor control feed between the two compressors, or worse case just change the power feed to the two compressors (sorry do not know the machine)

[marc5180]

But it is, in 24C out 17C, i have always called a reduction in temperature "cooling":D

Ok my bad, maybe I should have said "not getting down to temp" as opposed to "not cooling" :-)

[marc5180]

Turning off the breaker for one compressor on one if these units will give you a compressor module fault, think it's an "e108" fault.

Easiest way to do it as Mad Fridgie says would be to swap the control feed to the contractor (that comes from board AP3).

Have u tried a pump down test on these compressors?

[moondawn]

hi marc, when u say swap the control feed how do you mean, when the system started first compressor came on and a couple of mins later the other came on.?

tried pumpdown test by closing liquid ball valve but could not fully say whether the system fully pump downed it got to 0 but the system tripped out on faults.

cheers lee

[james10]

nothing wrong with it, your load temp is high, the rest seems to balance
i agree the chw temp is high raise the set point and bring the chw temp down gradually once there you will be able to check the unit is operating correctly at it's design spec

[marc5180]

hi marc, when u say swap the control feed how do you mean, when the system started first compressor came on and a couple of mins later the other came on.?
cheers lee

The control feed comes off board AP3 and energises the coil on the compressor (KM1 & KM2).
try swapping these around so when it calls for compressor 1 to start then compressor 2 will start instead.

Did u take the amps of both compressors? From memory these usually pull around 35a per phase.

[NoNickName]

It's a cooling a lot more than it should. And it's probably evaporating out of envelope having 31°C return temperature, 18°C leaving.
13K delta across evap also seem to show a grossly wrong selection of pump.
I wouldn't touch the chiller, at this time.

[moondawn]

what would be next to check if you feel that the refrigeration side is operating?

thanks in advance lee

[moondawn]

marc - i did not test amps from the compressors when they were both in opeartion
cheers lee

[mad fridgie]

Just one question, do you know if this unit has HOT GAS INJECTION, between the EEV and the evap

[moondawn]

the unit does not have hot gas injection mate
cheers lee

[NoNickName]

It's a cooling a lot more than it should. And it's probably evaporating out of envelope having 31°C return temperature, 18°C leaving.
13K delta across evap also seem to show a grossly wrong selection of pump.
I wouldn't touch the chiller, at this time.

I quote myself, as it seems it was unnoticed.

[mad fridgie]

I quote myself, as it seems it was unnoticed.
I read it as temp entering the evap at 31C (strange) and leaving at 18C and SST of about 12.5C, also no change in any conditions when the second comp cuts in.
We simply need more data.

[Neddy]

Correct me if I'm wrong but on the PT chart (PE) 27 bar equals 46 degrees Celcius for R410a. If your liquid line temp is 43 this gives 3 degrees Celcius Subcooling. Suction 12 bar equals 16 degrees Celcius. If your suction temp is 18 this is 2 Degrees Celcius Superheat. This is worked out using gauge pressure not Absolute pressure.

[frank]

what would be next to check if you feel that the refrigeration side is operating?

The first thing I would do is to give the condenser a really good clean then check all of your measurements again to see what effect that has on performance. You did say it looked dirty.

[moondawn]

hi there read the above suggestions yes temp wise after coming out the condensor i had 27 Bar on the liquid shreader and 43 degrees with my temp probe.
after the expansion device entering evap 31 degrees with temp probe coming out the evap 18 degrees and suctiion port reading 12 bar.

please could someone do the calculation as i am not good with working this out i had help doing it to give you lot the figures and then i can learn from checking over the calculations?

i agree the coil was dirty i would not say was blocked though but i agree a good place to start.

thanks all for your replies

[marc5180]

Lee the calculation for superheat and subcooling is very simple,

Take the pressure (27bar or 12 bar) and look at the chart below follow it across and that gives you the corresponding saturation temperature. Then subtract the actual pipe temp that you took to give you superheat and subcooling temperature.

http://www.gas2010.com/pdfs/r410a_pressure_temp.pdf

[moondawn]

hi marc cheers so i done the calculation and got SH 4deg and SC 2deg.

[moondawn]

JUST FOUND THIS THAT GARY POSTED ON RE FORUM. SEE BOLDED TEXT

The subcooling tells you if there is not enough refrigerant (low subcooling) or too much refrigerant (high subcooling) in the high side of the system.

The superheat tells you if there is not enough refrigerant (high superheat) or too much refrigerant (low superheat) in the low side of the system.

If there is not enough refrigerant in the high side (low subcooling) and not enough refrigerant in the low side (high superheat), then there is not enough refrigerant in the system (undercharged).

If there is too much in the high side (high subcooling) and just enough or too much in the low side (normal to low superheat), then the system is overcharged.

If there is not enough or just enough in the high side (normal to low subcooling) and too much in the low side (low superheat), then the metering device is overfeeding or the compressor is inefficient.

If there is just enough or too much in the high side (normal to high subcooling) and not enough in the low side (high superheat), then the system is restricted/underfeeding.

None of the above is accurate unless you have sufficient airflow through both the evaporator and the condenser, so always check the airflow first.


Last edited by Gary; 21-01-2008 at 05:54 PM.

[moondawn]

would my calculations SH 4deg and SC 2deg lead me to look at eev or compressor?

i know i have been suggested that compressors could be not operating properly. could i possibly rule out Electronic expansion device due to having 31 degc to 18 degc differential??

[stufus]

I'm not convinced the problem is on the fridge side (although condenser needs to be cleaned as a matter of course)
Has any work been carried out on the water circuit,Additional load or piping, new pumps , valves etc. Check any strainers in the water circuit .Check the pressure drop across the evap there should be binder points on the flow and return your looking for a drop of less than 0.5 bar.Also check that the evap isn't full of air there should be a vent screw on the top , if you're going to check for air in the top of the evap hold a refrigerant detector to the vent as you open it on the off chance you're losing refrigerant to the water circuit via a duff gasket.But i still think the water circuit is the issue.
But I could be totally wrong:confused:
Cheers
Stu

[moondawn]

hi stufus we got an engineer going back next week so will see how things get on first thing will do is clean condensor and check compressors. i know previously the chiller had a leak on it last year but thats all i know history wise.

thanks for your post and will see if we can check the following you have mentioned

[marc5180]

If there was a lack of chilled water flow then suction pressure would decrease not increase.

With a high LP, high HP and low subcooling this indicates lack of condenser capacity.
Did u take the air in/out of condenser?

[moondawn]

hi marc i never checked the air in / out of condensor but judging from posts this is the best place too start by checkin the airflow and also cleaning the condensor

cheers lee

[stufus]

If there was a lack of chilled water flow then suction pressure would decrease not increase.

With a high LP, high HP and low subcooling this indicates lack of condenser capacity.
Did u take the air in/out of condenser?

Mark I agree the condenser is an issue and there appears to be an obvious lack of capacity.
But there is a 13k delta T across the evap and a history of antifreeze alarms which could be down to either flow or lacked refrigerant.
As just about everyone has said at this stage we will just have to wait and see how they get on after the condenser coil has been cleaned.
Cheers
Stu

[moondawn]

But there is a 13k delta T across the evap and a history of antifreeze alarms which could be down to either flow or lacked refrigerant.

Hi what is normal delta t across the evap? 8-10deg c ??

[mad fridgie]

The 31C after the EEV, should not be occuring
could it be:
just a simple mistake in writing down the data, should it read "13C" (which then would seem to make more sense)
There could be a distributor, if the evap is using the tubes, not the shell (do not know the machine) hence a pressure drop
I have seen these type of temps after an expansion device before, but only when little or no condensing occurs, (which does not quite seem to be the case) as we are still achieving considerable cooling effect (water temp split)
Could it be a trapped air pocket, which is holding back the liquid/vapour mix leaving the EEV, wheres the air pressure remains high, but the velocity remain lows (no air entrapment in the refrigerant flow) and but the liquid density is high enough to pass through the air and enter the normall evaporating cycle

[moondawn]

i am fairly positive i was getting 31 deg after the eev the type of evap is shell and tube.

will post back when the engineer has been to clean the condensor and check compressors operation.

cheers

[moondawn]

A engineer attended today and the weather was not as hot as when i was last there, this is the details he gave me:

arrived on site found both compressors running with a chilled water flow temp of 14C and a return of 19.5C.

Carried out non condensables test and confirmed none were present.

Cleaned Condensor Coil Checked pressure before and after But no difference.

Discharge pressure with 1 compressor running was 22 bar (R410a) and with 2 compressors increased to 25bar.

Discharge temp way 61C
Liquid temp before expansion valve 34C
Liquid temp after expansion valve 22C
Suction temp 13.6C

Liquid pressure before expansion valve 23bar
Liquid pressure after expansion valve 16bar
Suction pressure 9.3bar

Air in to condenser 15C
Air out of condenser 35C

Compressor amps on both compressors around the same 38-40amps

Unable to check water strainer as there are no shut of valve in the cw supply pipework.

Possibility that the load is too high, next step would be to install binder access points and work out the flow rate to then work out the capacity the chiller is provided.


Any other pointers guys

[frank]

Do you know the plate rating of the chiller duty? If so, we can work out the flow rate for you from the above figures.

With a liquid temp after the TEV of 22C makes me wonder how the machine can provide a leaving water temp of 14C?

[mad fridgie]

Good data,

it would look like you have a distributor plate between the TEV and the evap heat exchange area.

I would say that your system is incorrectly sized for load. (as per thread "8")

[moondawn]

Hi all,
Full model number of the chiller is a wsat xsc602.

The evap is a plate heat exchanger not a shell and tube like I first thought.

Like Frank says how can cooling be taking place if liquid temp into the evap is 22c yet water in/out of evap is 19c/14c?
How is this working ??????

Between the eev and the evap there is no distributor that I could see... What is a plate distributor?

The kw of the unit is 76kw

Madfridgie - please could you post how your workings out on here or pm so I could learn from you?

[nike123]

Liquid temp after expansion valve 22C
Suction temp 13.6C

Liquid pressure after expansion valve 16bar
Suction pressure 9.3bar


Where exactly did you take this measurments? Could you provide some photo of measuring, or refrigerant diagram with points on it where measurments are taken?

[moondawn]

On the panel it says FLI 75kw but in the manual it says 155kw cooling capacity???

here are a few pics

Image.jpg is pic of plate heat exchanger (EVAP)
photo1.jpg is pic of liquid line eev and liquid line port just entering evap
photo2.jpg is pic of suction pipe and port
photo.jpg is pic of same as photo 2 only took further away.

The liquid pressure was taken before the eev and after the eev using the schraeders as shown on photo1.jpg .
The actual temperature was taken from the same place the gauges were connected and the pressure taken.

There doesn't look like there could be a restriction after the eev because it goes straight into the evap.

I previously check for any signs of pre expansion in the liquid line across the drier and the liquid line shut off valve - everything seemed ok.

thanks all

[marc5180]

Do you know the plate rating of the chiller duty? If so, we can work out the flow rate for you from the above figures.

With a liquid temp after the TEV of 22C makes me wonder how the machine can provide a leaving water temp of 14C?

In the manual for this chiller the cooling capacity is rated at 155 kw and the flow rate should be 7.5 l/s.

How would you work out what the actual flow rate is Frank?

[frank]

In the manual for this chiller the cooling capacity is rated at 155 kw and the flow rate should be 7.5 l/s.

How would you work out what the actual flow rate is Frank?

Q = m c dt

Q = 155
m = ?
c = 4.18
dt = (t1-t2) = (19.5 - 14) = 5.5

So: m = Q/(c x dt)
= 155/ (4.18 x 5.5) = 6.74l/s

[marc5180]

Whats 'C' Frank? and why 4.18?

Is that figure for water? would it change much if glycol was added to the water?

[nike123]

c is specific heat in W/kg for water. And yes, it will be different for glycol.

[frank]

C = Specific Heat Capacity = 4.18kj/kg for pure water. Have a read up here (http://en.wikipedia.org/wiki/Water)
With glycol/water mix , the Specific Heat Capacity would alter depending on the concentration.

[Gingerair]

Specific Heat Capacity of Water ??

Moondawn, don't forget to insulate your temperature probes when taking readings..

That's my tupence :o)

.....Missed second page of thread...dooh !

[Gary]

A engineer attended today and the weather was not as hot as when i was last there, this is the details he gave me:

arrived on site found both compressors running with a chilled water flow temp of 14C and a return of 19.5C.

Carried out non condensables test and confirmed none were present.

Cleaned Condensor Coil Checked pressure before and after But no difference.

Discharge pressure with 1 compressor running was 22 bar (R410a) and with 2 compressors increased to 25bar.

Discharge temp way 61C
Liquid temp before expansion valve 34C
Liquid temp after expansion valve 22C
Suction temp 13.6C

Liquid pressure before expansion valve 23bar
Liquid pressure after expansion valve 16bar
Suction pressure 9.3bar

Air in to condenser 15C
Air out of condenser 35C



35C - 15C = 20K dT. This should be no more than 16K and preferably less. Clean or not, the condenser is not getting enough airflow.

Make sure the blade is clean, turning in the right direction, scooping the air and not backhanding it, the right motor and fan blade, etc.

[moondawn]

think it may be worth jet washing the condensor to try to totally eliminate bad airflow on condensor the unit is outside in a compound so this would be easily done.

cheers gary.

[mad fridgie]

Been away in Aus for a few days.
I think a bit of design knowledge is required (i do not know the plant )
Firstly FLI 75Kw, more than likely means Full Load Input
This equates to 2 Copeland ZB 385 (or equivilent)
The Duty of 155KW indicates that the design SST would be around 1C and SCT woukd be around 47C (15C split at 32 ambient) all within a couple of %
Your SST is some what higher, so your actual cooling duty is greater than the 155Kw, just short of double if SCT remained constant! But your condensor will have been sized for design heat of rejection, so the SCT will rise, and reducing the capacity at your present SSTs (but still greater than the design duty) You are greating large fluctuations in duty because you are getting large swings in air "on" ambients temps.
Depending upon the make and style of your PHE you can have an internal distributor, hence giving this elevated pressure and temp after the EEV but before the evap.
All data indicates that the machine is doing what it should for the conditions it has.
Maybe you could give us some data on the load "what is the final thing it is cooling"

[mad fridgie]

think it may be worth jet washing the condensor to try to totally eliminate bad airflow on condensor the unit is outside in a compound so this would be easily done.

cheers gary.
Not the problem

[mad fridgie]

What is the chiller water cooling.

[moondawn]

hi mad fridgie thank u for your replies, the other engineer has given this extra data for you:

It is cooling data rooms in a college but also possibly classrooms as well (although the site staff aren't too sure)

Do the design operating parameters depend on the duty of the load? Or for all high temp applications is the SST around 0/1°C and the condensing temp the maximum ambient air expected i.e 35°C.

It makes sense that there is an internal distributor fitted to the PHE but i'm not sure there is.

I've looked in the manual and it doesn't mention anything about the PHE

[mad fridgie]

Hi, I do not know your partcular machine and how it was designed, but if this is designed as standard air cond chiller, it is likely rated at 12C water on and 6C water off. The SST needs to be less than 6C.
I do have data on copeland compressors, so taking into account all the data you have given me, i am able determine some sort of basic design conditions.
Remember a nominal design duty, is just that "nominal" and is given at fixed steady state condition. If your condtions change so will your machine performance.
Your load, has there been any extra equipment installled in the data rooms, or extra air handles installed.
How old is the application, how many years have they had of trouble free cooling.
Is there a new control system or a new person managing the control system.
"Example only of what could be happaning", maybe the client is turning of all the air handles at night, (data transfer is minimal) during the night the data rooms build up some residual heat. When it is fired up in the morning a large load now exists.

[moondawn]

hi mad fridgie, the site is fairly new to us and therefore we are unsure what areas the chiller is feeding, also no one has been back to site since so will have to update at a later time


cheers lee