Compressor too Large??

[JamesMac]

I am working on a Hitachi RP-15WLS unit that has had its screw compressors removed and replaced with a Carlyle 06DA5372BA reciprocating compressor with Sea water cooled condenser. The evaporator has a cooling capacity of 32.6kW and is served by two TE5 expansion valves (no.0.5 and no.1). The system uses R407C and the discharge pressure is about 18 bar while the suction pressure works down from 3.2bar. There is a long run from the compressor to the expansion valves/evap (30 meters). The condenser is of ample size and clean and there is a good charge of gas. Any advise would be very welcome.

[Peter_1]

What are your temperatures and pressure at outlet evaporator? ou only can diagnose correctly if you have also corresponding temperatures

[JamesMac]

It about 12'C at 3.4bar. Condenser outlet is 18 bar and about 30'C?

Thanks for the reply Peter

[The Viking]

James,

Your system is about right...

Unfortunately, we who sit many miles away from your system have no chance to see what is going on with it unless we are provided accurate data of what is happening.

If your sub cooling is about 6-8K and your superheat around the 4-6K mark your system is probably OK.
BUT…
We do need to get accurate and adequate inputs.
Does the system reach a stable running condition? If so, how long does it take to get there and does it stay there?
What is the operating pressures? (OK, I believe you given us these)
What is the discharge temperature? Liquid line leaving condenser? Liquid line entering TEVs?
What is the suction line temperature leaving the evaporator? Entering the compressor?
What is the temperature of the water entering and leaving the condenser?
What is the temperature entering and leaving the evaporator?

Oh, is there a problem with this system and if so what?


:cool:

[RANGER1]

Does it have unloader's & what pressure do they load/unload?

[JamesMac]

So
Compressor Discharge 17Bar
Compressor Suction 2.4bar +3'C
Evaporator pressure 2.6bar -3'C
Condenser SW in/outlet 24/28'C
Liquid line leaving Condenser 26'C Entering Txv 26'C
Evaporator air in/out 25/15'C

There is a pressure actuated unloader. The adjustment is wound right in which means its about 6bar load up.
I have changed the orifices from ((1x)No.2 (1x)No.1) to ((1x)No.1 (1x)No.0.5) as I thought they were too large before?

The problem is the evaporator is icing up from the Tx v/vs. I thought the larger Tx valves were causing flooding in the evap and I was hoping the smaller (10.7kW and 19.6kW)would match the evap(32.6kW)better and might of helped the suction pressure rise and helped stop the icing up? Am I taking non-sense and need a reboot?

[Peter_1]

Your discharge pressure seems high compared to water temperatures.
Is condenser big enough? If so, non condensables (NC) in the system?
Temperature rise and pressure drop along suction seems no to be the cause.
I should evacuate the refrigerant in a cylinder, vacuum your empty system deep enough.
In the meantime, check pressure versus temperature of the recovered cylinder to find out if NC are possible in the recovery cylinder. You then can find out if those were present in your system.
Recharge with only liquid and leave 1 kg in your cylinder so that NC remain in the cylinder. Fill just enough to get a stable SH of +/- 7K (don't look to the sightglass)
Monitor in the meantime if HP doesn't rise fast (overcharge)
Recheck high pressure after gas was changed.
All this can be done in 1 hour.
If HP is still high, you have a SH of +/ 7K, then I suspect your condenser too small. Or compressor to large for the condenser :-)

[JamesMac]

Thanks for the advise Peter. I unfortunately haven't got the capacity in my reclaim bottle to take the full charge. I was thinking about connecting the reclaim bottle onto the bleed valve on the top of the condenser. Is this a sensible action to take?

Would I be right in thinking a suction pressure of anything less than 3.6bar would cause icing up?

[xxargs]

Going from 26 degree C liquid temperature of R407C and adiabatic expansion, you receive 0.07 degree C with 5.5 Bar absolute pressure or 4.5 Bar pressure over atmosphere (Bar A) and quality 0.177 of mass boiled up.

Ie suction pressure need above 4.5 Bar A if guarantee not ising up after TXV...

If Evaporator pressure are 2.6 Bar A, give -11.7 degree C (and quality 0.24) short distance after TXV and last of R407C boiled up at -6.85 degree C if suction pressure are 2.6 Bar A whole way in evaporator. So in this way whole evaporator should frozen up after time...

[RANGER1]

Sounds like it could be poor air flow over evaporator causing imbalance, icing & poor superheat control.
Use a torch, you should see light through coil on right angle.
Clean filters if any & clean coil anyway.

[JamesMac]

The fan is of the original unit and although it is on a frequency drive, it is blowing full pelt. The evap is clean.

I found a leaking valve after the drier I am sure was drawing air in when I was pumping it down. The leak is fixed and I have removed the air (not 100% sure all has been removed).

Pressures now 15bar discharge
1.3 Suction

I am unconvinced about the compressor because it is retrofitted and was. Could it be sucking to hard? Or is there a simplier solution?

[RANGER1]

James I could not see a superheat reading.
Its essential for accurate troubleshooting.

Also give us amp readings for unloaders.