PDA

View Full Version : Compressor Loss



rrayuckac
28-09-2008, 08:42 PM
I am a facility manager at a small research campus. I have had several Copeland compressor failures on the same building system over the past 4 years. The chiller on this building is 40 tons installed in a 45 year old office building and has a well supplied water cooled condenser barrel that goes to recycle for irrigation. The compressor may not be sized exactly the same as it is not original since before my time here. Most of the failures have been burnouts, however the most recent was a mechanical failure with valve and piston damage that sounds to me like slugging. In the case of each failure, if memory serves, they have occurred during spring or fall when temperatures are more mild and the unit may be partially unloaded. My lead mechanic thinks that the problem is related to times when it is running unloaded. He has replaced the compressor and for now, has the set points such that it will run only fully loaded to set point then pump down. I believe he had set the superheat at 10 degrees. I feel like the repeated failures are all related and this cycle of repeated change outs needs to stop. We need to find out the root cause. I asked him to replace the TXV and asked him if installing an accumulator may help. He is worried about oil return if an accumulator is installed. My questions are: Could this be from oil buildup in the evap barrel? Overcharge? Bad TXV? Any pointers would be appreciated. I am not as versed in refrigeration troubleshooting and am open to any good ideas.

Thanks

Gary
28-09-2008, 09:18 PM
Is this a water chiller?

wambat
28-09-2008, 11:04 PM
Low loads can cause refrigerant flow controls to hunt and not control properly. Unloaded operation and resultant low refrigerant velocities will cause oil to pool in a chiller barrel not designed for these flows.
Loss of lubrication is also frequently the result of oil trapping, which occurs when the suction gas does not have enough velocity to return the oil to the compressor. This condition is most often found on systems using unloader-equipped compressors, where the compressor operates unloaded for extended periods of time. The reduced vapour flow caused by prolonged unloaded operation, and/or low suction pressures due to loss of charge, is a major cause of oil loss in compressors. S0 when inadequate cylinder bore lubrication takes place, discoloured(grey) pistons, worn rings, and worn pistons result. This lack of lubrication is most frequently associated with lack of oil return during loss of charge or unloaded operating conditions. Insufficient load on the evaporator prevents all the liquid from vaporizing causing liquid flood back unless an accumulator or other protective device is installed. You may want to use a balanced port TXV as they perform better with large changing loads. You may want to intergrate a temp recorder on the discharge line and /or a temp cut out on the discharge line to make sure you don’t exceed 225 *F

rrayuckac
28-09-2008, 11:08 PM
It's for a two pipe system with a three way valve and separate natural gas boiler

rrayuckac
28-09-2008, 11:11 PM
Low loads can cause refrigerant flow controls to hunt and not control properly. Unloaded operation and resultant low refrigerant velocities will cause oil to pool in a chiller barrel not designed for these flows.
Loss of lubrication is also frequently the result of oil trapping, which occurs when the suction gas does not have enough velocity to return the oil to the compressor. This condition is most often found on systems using unloader-equipped compressors, where the compressor operates unloaded for extended periods of time. The reduced vapour flow caused by prolonged unloaded operation, and/or low suction pressures due to loss of charge, is a major cause of oil loss in compressors. S0 when inadequate cylinder bore lubrication takes place, discoloured(grey) pistons, worn rings, and worn pistons result. This lack of lubrication is most frequently associated with lack of oil return during loss of charge or unloaded operating conditions. Insufficient load on the evaporator prevents all the liquid from vaporizing causing liquid flood back unless an accumulator or other protective device is installed. You may want to use a balanced port TXV as they perform better with large changing loads. You may want to intergrate a temp recorder on the discharge line and /or a temp cut out on the discharge line to make sure you don’t exceed 225 *F
Thanks, I was out Friday during the latest failure, however my lead mechanic told me that the valve was mangled and damage to the piston was evident. Previous failures were burnouts and a tear down was not done to investigate.