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kevinlyoung78
10-11-2008, 10:36 PM
Hi folks , this is my first post and im not a reefer engineer but only a lowly marine one so be gentle with me.
Recently we noticed that our walk in freezer room was not reaching its normal temperature (-19) and only managing to get to approx -14 and after much head scratching we decided to top up the system (R22) so now we have no bubbles in the sight glass and LP of just over 0.2 bar and HP of about 15 bar which i assume to be normal for this system.
We then changed the filter driers in the system but as there was no change in temperature between inlet and outlet prior to the change this was just clutching at straws i guess.
All the orifices have been checked and all valves checked and double checked with no problems found,
We then adjusted the TX valves ( a big no no i guess) but still no improvement was noticed so these were returned to their previous position.
So as it stands just now we are no further forward although i did notice some oil carry over in the system and the compressor is now short cycling and still not reaching the required temperature.
Also we recently opened the standby compressor and noticed some wear on the piston rings and a few scratches in the cylinder as well as some wear on the con rod bearings so im wondering if the compressor thats running now had lost some of its efficiency....
Sorry if this is all very vague but i will try provide as much information upon reply..
HELP PLS LOL

jsimon
10-11-2008, 10:42 PM
put the gauges on and front seat the suction line valve only with the system running you should pull a good vaccumn 28" if not this is a very good sign of internal wear
If this is ok then i would presume that you have a very small leak and have pulled air into the system and this has settled in the evap coil usually noticeable by a loud hissing sound from the expansion valve into the coil

Gary
10-11-2008, 11:10 PM
Sorry if this is all very vague but i will try provide as much information upon reply..


Low side:

Evap air in temp
Evap air out temp
Saturated suction temp (SST) converted from pressure
Suction line temp at evap outlet

High side:

Cond air in temp
Cond air out temp
Saturated condensing temp (SCT) converted from pressure
Liquid line temp at receiver outlet

Peter_1
10-11-2008, 11:13 PM
What's your evaporator superheat? Looks you have a partial restricted TXV.
Or evaporator filled up with oil.
Or some blockage somewhere in the suction line.
Can you measure LP at the evaporator?
Evaporator is completely free and all fans running?

kevinlyoung78
11-11-2008, 08:00 AM
hi again. We dont think it is air in the system as there is no hissing noise and the suction side (ruturn to the compressor) appears to be frozen. We have also changed over the expansion valves between this room and the cold room but there was still no improvement so i dont think there is a problem with the expansion valve being partially blocked..
Thanks all for the quick responses but still pulling my hair out.

Peter_1
11-11-2008, 09:24 AM
We need the figures Gary is asking for, otherwise we can't help and we will stuck by guessing.

kevinlyoung78
11-11-2008, 10:39 AM
L.P = 0.2 br @ 15 degrees c
HP = 14.4 BR @ 104 degrees c
condenser inlet = 67 degrees c
outlet = 19 degrees c
Sea water inlet to condenser = 17 degrees
Sea water outlet = 19 degrees c
Evap inlet = -15 degrees
Evap outlet = -11 degrees

These were taken using a infra red gun so not sure on accuracy

Peter_1
11-11-2008, 11:15 AM
L.P = 0.2 br @ 15 degrees c
HP = 14.4 BR @ 104 degrees c
condenser inlet = 67 degrees c
outlet = 19 degrees c
Sea water inlet to condenser = 17 degrees
Sea water outlet = 19 degrees c
Evap inlet = -15 degrees
Evap outlet = -11 degrees

These were taken using a infra red gun so not sure on accuracy
Some assumptions will depend on the precise locations you have taken your measurements.
First of all, in your first post, you said you adjusted the TXV, not replaced as mentioned in a later post.
Let's see, 0.2 bar (2.9 PSI) is evaporating at -37°C (-25.6°F for our friends over the water)
Inlet evaporator =-15°C (5°F) depending where your measured it ( you have to measure it somewhere on an evaporator bend 1/4 from above) This is - if measured right - too high and points somewhere in the direction of a not sufficient feeding of the evaporator.

Second fact which points to the same is your outlet which is -15°C (12.2°F) or a superheat of +/- 22K.

Third fact which proves this is the very high discharge temperature due to the high SH.

Or there's a blockage in the distributor.
Measure once the temperature on all the bends of the evaporator on the same horizontal line and look once if you notice big temperature differences. You're IR is fine for that, you only have to search for differences.

I still believe in a partial restricted XV, a too small orifice , or a restricted drier (which you replaced already)
Has the liquid line the same temperature from outlet condenser till inlet TXV?

nike123
11-11-2008, 11:31 AM
These were taken using a infra red gun so not sure on accuracy

When you measuring with infrared gun, you should wrap pipes (which temperature you measure) with black (self-adhesive electrician) insulation tape on places where you measuring temperature.
Or, if you have possibility to adjust emissivity at gun, than adjust emissivity to proper value for measured material.
Also, you must pay attention to radius to distance ratio of your gun to avoid reading of surrounding temperature of spot you are trying to measure.
Then your measured data could be considered as pretty accurate.
Could you confirm that you have had these thing on your mind when measurements are done?

kevinlyoung78
11-11-2008, 12:30 PM
Will measure temperatures again as described in the previous posts and then revert back, in the mean time the chief engineer believes that we may have used a faulty batch of R22. Is this a common complaint?.
This morning i also blew the through with nitrogen and then vacuumed the system and also how am i able to determine the correct size of orifice to use afer the expansion valve.
Thanks again all who have helped and i will keep plugging away with my limited knowledge.
Cheers Kev

Peter_1
11-11-2008, 12:52 PM
Kev, about the TXV size, what's the make and type of compressor and evaporator and TXV?
Faulty batch of R22? Mmmm... much more possible is that you've added something else than R22.

abet_meneses
11-11-2008, 02:38 PM
keviniyoung,

yes,even on a tight leak system a not so good R22 could cause air in the system as we have experienced before on a comp rack.We have no alternative but to recover the faulty refrigerant vacuum the system and charge new R22.

regards,

Gary
11-11-2008, 03:22 PM
L.P = 0.2 br @ 15 degrees c
HP = 14.4 BR @ 104 degrees c
condenser inlet = 67 degrees c
outlet = 19 degrees c
Sea water inlet to condenser = 17 degrees
Sea water outlet = 19 degrees c
Evap inlet = -15 degrees
Evap outlet = -11 degrees

These were taken using a infra red gun so not sure on accuracy

I am having a hard time figuring out what everything on this list means because you have changed the words to describe the temperature readings. What temperatures are you measuring and where are you measuring them?

An infrared does not give accurate readings. Use a real temperature tester.

Peter_1
11-11-2008, 04:01 PM
I am having a hard time figuring out what everything on this list means because you have changed the words to describe the temperature readings. What temperatures are you measuring and where are you measuring them?
An infrared does not give accurate readings. Use a real temperature tester.

These must be the right numbers I guess

Low side:
Evap air in temp:-15°C
Evap air out temp:-11°C
Saturated suction temp (SST) converted from pressure:-37°C
Suction line temp at evap outlet:he had 15°C at the inlet of the compressor I suppose.

High side:
Cond air in temp:water in is 17°C
Cond air out temp;: water temp out = 19°C
Saturated condensing temp (SCT) converted from pressure: 40°C
Liquid line temp at receiver outlet: 19°C

Discharge : 110°C

Please, comment on these figures KEV.

If you use a good IR , reflected on a black surface or emissivity factor set right for copper (0.78 for oxidized black copper), then you will have an accurate reading.

Gary
11-11-2008, 07:05 PM
Since discharge superheat and compressor inlet superheat are directly related to each other, I think your assumptions are probably correct, Peter.

The suction line at the coil outlet can be no warmer than its surroundings and the compressor inlet superheat is very high, so we can assume -15C at the TXV bulb.

Low side:

-11C minus -15C = 4K dT indicating sufficient airflow.

-15C minus -37C = 22K TD indicating low load absorption.

-11C minus -15C (assumed bulb temp) = 4K approach indicating sufficient heat transfer.

-15C minus -37C = 22K SH indicating low refrigerant flow.

High side:

19C minus 17C = 2K dT indicating sufficient water flow.

40C minus 17C = 23C TD indicating high load rejection OR regulated water flow (far more likely as we know the load is in fact very low).

19C minus 19C = 0K approach indicating sufficient heat transfer.

40C minus 19C = 21K SC indicating refrigerant overcharge OR air in the system.

There is insufficient refrigerant flow through the evaporator due to restriction somewhere between the condenser outlet and the TXV outlet. Look for plugged TXV inlet screen, plugged drier or kinked liquid line.

pingu
11-11-2008, 08:15 PM
Hi mate, have you got a ball of ice where your expantion valve should be? if so, you might have a slight blockage, ( may be moisture moisture) warm the valve up and see how you go if the system gets better performance,,,, reclaim, get new driers and virgin 22