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Duty007
30-03-2017, 11:50 PM
Hey guys
Got a heat-recovery chiller that does 180F hot water on the condenser and 85F water on the evap, refrigerant r-134a and poe oil with brazed plate heat exchangers and 2 circuits.Each circuit has a set of identical tandem copeland scroll compressors ( all 4 compressors are the same tonnage)with an oil equalizer line between them and they sit on top of the heat exchangers.Both circuits share the same heat exchangers but like i mentioned above they are independent circuits..This is a fairly simple design electronic expansion valves ,cranck-case heaters ,no oil separators and no pump down..Issue is we've been loosing compressors mechanically,usually they"ll last a couple of months sometimes even less before they die mechanically..Compressors don't seem to be slugging liquid refrigerant, am suspecting maybe an oil return issue ( to much restrictions through those heat plate exchangers) especially when one compressors is running alone ,oil degradation or the design itself high temperature/discharge pressures since its a heat recovery application ..Was thinking maybe adding liquid injection on the discharge line and even oil separators..I welcome any suggestions or information..thanks!

HVACRsaurus
31-03-2017, 09:11 AM
Hi,

So, without knowing which make / model compressor your are using...

http://emersonclimate.com/europe/ProductDocuments/CopelandLiterature/TSC102-EN_OptzdHeatingCompr_vs7_0.pdf

Page 6 bottom left shows a little chart - something called "operating envelope"

For this chart and for the evaporating / condensing temperatures (85F / 180F) both are outside the operating envelope (Compressor is not rated for use outside these limits)

Suggest confirm operating envelope for yours..


Happy tinkering!

RANGER1
31-03-2017, 09:31 AM
Hi,

So, without knowing which make / model compressor your are using...

http://emersonclimate.com/europe/ProductDocuments/CopelandLiterature/TSC102-EN_OptzdHeatingCompr_vs7_0.pdf

Page 6 bottom left shows a little chart - something called "operating envelope"

For this chart and for the evaporating / condensing temperatures (85F / 180F) both are outside the operating envelope (Compressor is not rated for use outside these limits)

Suggest confirm operating envelope for yours..


Happy tinkering!

Good advice by HVAC, if in correct envelope cut one open, see what happened, or get a report from company that specialises in reconditioning ompressors.
Liquid injection is only used to keep certain compressors in design
parameters.
If not looked into correctly could make it worse, as only controls discharge temperature as well as motor cooling.
Oil in PHE would be pushed through easily as there is little room in it to store or have oil laying around.

piewie
06-04-2017, 09:27 PM
Oil return might also be the issue I might suggest an oil return float pot on the bottom of the heat exchanger, I have seen in the past where the velocity of the oil/liquid is simply not enough at low load conditions and the oil does not make it back to the compressor.

The Viking
06-04-2017, 11:11 PM
and no pump down..I

How is the system operated when the set point is reached?
I have seen similar issues in the past when there haven't even been solenoid valves. The chilled water continues to flow through the evaporator and the evaporator gets full of liquid refrigerant when the compressor stops, this leads to the compressor getting pure liquid through the suction line when it restarts.

Just a thought.

:cool: