Ship AC problem

[Marinex]

Hi all

My vessel has two Carlyle (Carrier) 5F60-149 AC compressors both independent to the air handling unit with an expansion valve for each and running on R22. Both have sea water cooled condensers. We are all new on here so the history etc is patchy! Both machines were on although the discharge pressures were low at 10 - 11bar. the suct press is 4 bar Then one machine was running but didn't appear to be doing any work and the return was cold as was the compressor. When pumped down the condenser was 1/2 full of liquid. I can regulate the HP by throttling the sea water valve but feel this isn't correct. If it was a valve problem wouldn't this show as too too higher suction pressure? Could it need more gas?

lots of questions I know but we don't profess to be experts! And the charterers soon complain.

thanks

steve

[US Iceman]

Welcome to the RE forums.

What makes you suspect you have a problem?

If the sea water temperature is cold, the condensing pressure would be lower than what you might expect. And, if the TXV's were properly sized they should be able to work under this condition.

Before we get started with a lot of questions, can we start with my first one?

[Marinex]

Hi Iceman

The sea water is 28 celsius and the outside temperature about the same. I believe there is a problem as the compressor is cold and sweating whereas the other day it was hot. Past experience in similar climates with similar machines the HP is always in the 17 to 18 bar range. With my limited knowledge I am now thinking that there is maybe an airflow restriction in the evaporator? However to access this necessitates shutting the system down and that causes problems with the Brazilians etc resulting in downtime. To my mind we shouldn't be running two machines in these temperatures?

I hope this makes sense and appreciate any professional help! your motto at the end is very apt and whilst ship's engineers are Jack of all trades we can never be master of all.

Steve

[brunstar]

with that one, well it is cold but you may have an iced up evaporator, is that all clear, do you have air on and off the evaporator.
Are you sure that you are taking the discharge pressure and not the liquid line as i would expect the discharge pressure to be higher but if you are taking the pressures on the liquid line this seems to be an ok pressure youo have.

[abet_meneses]

marinex,

1.are filters and evap fan motor,fan blade ok,i mean not dirty,air velocity in the diffuser ok.
2.any of the above will cause ice build up hence,lower than normal discharge pressure.

any other info,
regards,

[nike123]

Ignore, double post!

[nike123]

Your condensing pressure is too low. 28°C is 10,3 bar which is exactly what your pressure is. That could be because condenser water regulating valve doesn't work and you have over condensation. Because of that, you could have low pressure differential at TEV and lower evaporation temperature.
You should try to restrict water flow (or readjust valve)to rise condensation pressure until you have condensation temperature around 40°C ( or 100°F) then you should check evaporation pressure/temperature to be around 16-20K (32-40°F) below evaporator air in temperature.
Then you could check that Evaporator air in - air out temperature is around 8-10K (16-20°F).
If all that is OK after that adjustment, you should adjust or change or repair condenser water flow regulating valve.

[Gary]

We can't see the systems from here, so we need a detailed description in order to help you. And as Nike has pointed out, we need much more information.

For each system we need to know:

Evap air in temp
Evap air out temp
Low side pressure/temp
Suction line temp near evap outlet

Condenser water in temp
Condenser water out temp
High side pressure/temp
Liquid line temp near receiver outlet

This is the minimum information needed for a proper evaluation... and the info you should be logging for each system.

[Marinex]

Gary / Nike - Thanks for the input. I believe i am seeing the light thru' the trees now!

At present the two independent compressors are supplying two evaporators built into one fan unit supplying the whole ship. For clarity these are compressor 1 & 2. All readings are in bar and celsius

Evap air in temp 28 deg
Evap air out reading 13 deg

*Low side press / temp No 1 4.1bar 19 deg
*Low side press /temp No 2 3 bar 33 deg
Suct line temp near evap outlet No 1 10deg
Suct line temp near evap outlet No 2 15 deg

Condenser water in No 1 30 deg
Condenser water in No 2 30 deg

Condenser water out No 1 38 deg
Condenser water out No 2 39 deg

** high side press/temp No 1 17bar 33deg
** High side press/temp no 2 15.5 bar 97 deg

Liquid line temp nr receiver outlet No 1 42 deg
Liquid line temp nr receiver outlet No 2 46 deg

* This is the LP guage reading and temp measured at the inlet to the machine
** This is the HP guage reading and temp measured at outlet of machine

The air filters are clean in the fan unit but access to the evaporator to see if that is blocked is restricted and involves plant shutdown.

Surprisingly the ship is only 8 years old and there isn't a flow regulator to the condensers, just butterfly valves and human interface. I have sailed on previous ships with this equipment fitted but invariably it isn't maintained. On most ships with sea water cooling you struggle to get enough water flow without restricting it!

My interpretation is that there is a problem with No 1 machine?. On No 1 the liquid level is at the bottom of the glass in the condenser and in No 2 1/3 of the way up.

The living conditions are bearable - its just that i think there is scope for improvement when the outside temp hits the 30s

Once again thanks for your help

Steve

[nike123]

Are you sure in this measurement:
** high side press/temp No 1 17bar 33deg

Is this temperature measured on discharge pipe near compressor?

[nike123]

Circuit no2 is short of gas!


Do you have sight glass before TEV?

[nike123]

Circuit no.1 performs much better but it still have higher than normal superheat and it could require TEV adjustment, after checking all other options before that!

[Marinex]

yes and I added some more Gas so there was about a couple of inches in the condenser and the temp is now 46.

There are sight glasses before the TEVs but no liquid showing. Should I be adding more gas?

[Gary]

The evap delta-T (air in minus air out) is 15K/27F. This is much too high. You have insufficient air flow through the evaporators. Until this problem is resolved, we can't tell anything else about these systems.

[Gary]

The water flow through the condenser seems low also. Are the water valves wide open?

Make sure the fans and pumps are turning in the right direction.

[Gary]

* This is the LP guage reading and temp measured at the inlet to the machine
** This is the HP guage reading and temp measured at outlet of machine

What we are looking for is the gauge pressure converted to temperature using a pressure/temperature chart.

[Gary]

Circuit no.1 performs much better but it still have higher than normal superheat and it could require TEV adjustment, after checking all other options before that!

There is a pretty good chance that the systems need more refrigerant and they may or may not need TXV adjustment (doubtful) and we can raise the high side pressure to make up for low load picked up in the evaporator by restricting the water flow (bad idea given the water temp), but all of these things are a band-aid approach masking the symptoms but doing little to improve performance. All of these will further increase the delta-T, bringing us right back to the core problem. The evaporator airflow is grossly insufficient.

[nike123]

There is a pretty good chance that the systems need more refrigerant and they may or may not need TXV adjustment (doubtful) and we can raise the high side pressure to make up for low load picked up in the evaporator by restricting the water flow (bad idea given the water temp), but all of these things are a band-aid approach masking the symptoms but doing little to improve performance. All of these will further increase the delta-T, bringing us right back to the core problem. The evaporator airflow is grossly insufficient.

I totally agree with you my friend. In my first post I said:

Then you could check that Evaporator air in - air out temperature is around 8-10K (16-20°F).

Than later this:

and it could require TEV adjustment, after checking all other options before that!

I just wanted to give fellow colleague my first impression on what is probably wrong in there.