Cold room/ Freezer combo.

[dogma]

Hi Guys.

I just built and installed a Cold room/ freezer combo on R404A for a hotel. The Freezer and cold room run off independant circuits.


The Freezer (-20degC) has a copeland scroll and has no pump down solinoid nor suction accumulator..


Is there a problem with this? Is it likely that liquid will come back to the compressor, (the lowest point in system), in the off cycle?? The compressor has no crankcase heater either.


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Is this sytem design ok...

[Brian_UK]

You should really have a solenoid valve on the liquid line so that the evaporator cannot become logged with refrigerant during the off cycle.

Also, during defrost you may get an unwanted pressure build up.

[US Iceman]

I would recommend a liquid line solenoid be installed to provide a pumpdown circuit for compressor protection also.

Refrigerant migrates to the coldest location in the system. That is the evaporator (most of the time, except possibly in winter).

[Andy W]

You imagine R404a after a defrost, the pressure inside the evaporator, on start up the compressor has got to handle that increase in pressure at least 4 times a day and if there is no CPR valve fitted I bet the compressor will have a short life span.

As said, fit a liquid solenoid valve on pump down, if it is a short pipe run also fit an accumulator and if the compressor is equipped with a crank case heater, wire it in even if it means running a new cable from the panel, all these will result in a long and healthy life and will reduce unnecessary warranty call outs.

[dogma]

so what damage will this cause... How long will the scroll compressor last?

[US Iceman]

It is hard to say how the compressor will last, however, I think it is safe to say the compressor will last much longer if the system is provided with the necessary safeguards.

[dogma]

My biggest concern is this;

If the refigerant migrates to the evap on off cycle, When thermostat calls for cooling again won't liquid come straight back to the compressor?? The original evaporator was too wide to fit in the freezer so my boss simply put a shorter one in. Same number of circuits and runs as the original, but a foot shorter. There is no Accumulator.


I just want to know if he's right in his design. He doesn't take critisism well so I've stopped asking questions and just do as i'm instructed.

[Andy W]

If the evap is full of liquid then yes it will flood back on start up, this will be evident with the suction line frosting right up to the compressor on start up as well as a change in tone of the compressor as compressors are designed to pump vapour not liquid, then the frost will slowly disappear as the liquid is compressed and boiled off, an accumulator will reduce the amount of liquid returning to the compressor if sized correctly, just fit a mag valve controlled by the stat or controller.

[dogma]

Please excuse my ignorance Andy W but I'm not familiar with a "mag valve". Could you please explain?


Regards

Dogma

[Gary]

My biggest concern is this;

If the refigerant migrates to the evap on off cycle, When thermostat calls for cooling again won't liquid come straight back to the compressor??

Not necessarily. If the suction line goes up above the evap before going down to the compressor then the liquid is trapped in the evap. On startup the liquid boils off rapidly in the evap and may or may not reach the compressor, depending on the amount of liquid and the design of the coil.

[Andy W]

Good point Gary.

Mag valve (magnetic valve) also known as solenoid valve.

[dogma]

Ok, Thanks guys...

So Gary, I can stop bitting my fingernails now?? The system should be fine?

THe pipe does go "up" first from the evap. It's a rise of 400mm 3/4", then horizontally for 1500mm, Drops another 2100mm, before the final few bends along 1400mm.


Another dumb question..... Would use recomend the use of a CPR valve on this system??


_Dogma_

[nike123]

Another dumb question..... Would use recomend the use of a CPR valve on this system??


_Dogma_

What defrost system you have there?

[dogma]

electric heaters, in built into the evap controlled by a Dixel controller. 6 hour intervals at 20 mins.

[nike123]

electric heaters, in built into the evap controlled by a Dixel controller. 6 hour intervals at 20 mins.

Then, if you have MOP TXV there is no need for CPR valve!
If you don't have MOP TXV, it could be required or not, depending on compressor motor.