Running Freezer as a Chill???

[ronaldo9]

Just wondering if anyone can help,

I diagnoised a burnt out compressor the other day. Basically the operators have taken over a section of a factory with two coldrooms which were both orginally freezers. They need a chill so they decided to use one of these freezer rooms.

The room is set up with two evaporators and one condenser/compressor. To achieve the higher chill temp in the room they turned off one of the evaporators and set the temp of the other evap to chill. using panel mounted controllers.

If i get this compressor re-wound is this just going to happen again?
The second "off" evaporator is still open to the common suction line, this has to be effecting the compressors operation?
Its a big enough compressor, cant remember its Hp but it was rated at 40amps .

Thanks in advance.

[nike123]

That depend on what caused that compressor burn.
You need first to find what caused that burn out.

[mad fridgie]

One the condensor will be sized for freezer duty (low SST) Low Heat of rejection, Even with one evap your condensor may be to small, causing a very high discharge pressure.
The second evap does this have a liquid sol valve, if not the flood back is likley to be occuring.
If the product is fresh food product, your delta T is going to be high this could be drying out the product.
I Think you are better to match a new compressor to suit the evaps at the correct conditions. When you have balance this, then look at the condensor sizing (increase if required)

[abet_meneses]

yes, burn out will happen again.existing motor compresor was intended for low temperature application.re-design the refrigeration equipment for chiller use. ;)

regards,

[mad fridgie]

yes, burn out will happen again.existing motor compresor was intended for low temperature application.re-design the refrigeration equipment for chiller use. ;)

regards,
100% correct abet:D

[ronaldo9]

thanks guys,

Yes the other evap has a solenoid valve no flood back, id say mad fridgie is right high discharge could have caused protection around motor windings to break down, My biggest problem is that they dont want to spend any money so any redesign of the system or new equipment is out of the question. I read in a couple of other posts ppl using a different gas eg 134a for the higher temp chill. Is this possible or is there anything else i can do?

Thanks

[tonyelian]

hi
u can fit a smaller compressor so ur condenser is gona be ok
u need to change the expansion valve
selection of the compressor according to condenser and evaporator but if the owner insists to use it as freezer and chill room fit a larger condensor with fan cycling control

[nike123]

thanks guys,

Yes the other evap has a solenoid valve no flood back, id say mad fridgie is right high discharge could have caused protection around motor windings to break down, My biggest problem is that they dont want to spend any money so any redesign of the system or new equipment is out of the question. I read in a couple of other posts ppl using a different gas eg 134a for the higher temp chill. Is this possible or is there anything else i can do?

Thanks

If they are not wiling to do it as you (and any other sound technician) suggest, than it is best for you to pass that job to someone other who is wiling to risk his reputation...

[mad fridgie]

thanks guys,

Yes the other evap has a solenoid valve no flood back, id say mad fridgie is right high discharge could have caused protection around motor windings to break down, My biggest problem is that they dont want to spend any money so any redesign of the system or new equipment is out of the question. I read in a couple of other posts ppl using a different gas eg 134a for the higher temp chill. Is this possible or is there anything else i can do?

Thanks
Are you using R404a (R507), you may find that just reducing the compressor size is all that is needed, or if you want to go really cheap install a CPR, set below max ratings of the compressor.
Changing to R134a, your LT comp would then become a MT R134a comp, you still need to check the balance between the evaps and the condensor.
What is the client cooling? Does the quality of the product count (humidity levels)
You do not have to redesign the plant in the context of whole new equipment, but you have to redesign around the existing equipment (2 hrs work max.)
1 basic heat load,
2 condensor duty at required delta T
3 duty of evaps (Kw/C) * deltaT (to be determined)
4 Run hours /day

From here you can determine compressor size and TXV orifice sze.

The the only long term issue maybe piping size (more than likely suction will be to big for oil return) but if pipe run is short and the unit is lower than the evaps (no risers to say) then you will more than likely get away with it

[mad fridgie]

If they are not wiling to do it as you (and any other sound technician) suggest, than it is best for you to pass that job to someone other who is wiling to risk his reputation...
Excellent advice nike123

[ronaldo9]

very true nike123, when it fails again my fingerprints will be on it. Not a happy camper.!! Thanks mad fridgie, good advice, ill keep ye posted

[Sledge]

The real problem here is your compressor:
It is oversized for the application (one evap instead of the original design of 2).
Also the compression ratio of the compressor is too high...which has 2 problems: The compressor will always be working very hard as it is pull down mode and it will result in the suction pressure being pulled down too fast.
If this is running on a low pressure control the system will be short cycling.

The coil will be wrong for a fridge (am assuming chill=fridge), fin spacing will be too big a gap for proper heat transfer, as freezers require bigger fin spacing...which will multiply the problem of the compression ratio and chort cycling.

If this is running on a thermostat...am thinking it will run, freeze the coil, off cycle defrost while ice melts...might work best with thermostat, but definitely short term as lousy design.