RTHD , oil return issues .

[Screwit]

Servicetech 32, Sounds more like you have an oil migration issue than an oil loss problem as your oil loss diagnostic is occurring on start up following an extended shutdown. If you had a master solenoid problem you would more likely be experiencing “loss of oil – compressor stopped” diagnostics.

POE lubricant’s are chemically engineered for a strong molecular attraction to the refrigerant. The advatage is this bonding helps overcome oil return issues but a downside is oil migration can occur if external conditions cause thermal movement of the refrigerant charge. For this reason RTHD chillers ship with oil sump vent line valve closed to reduce solar induced refrigeration migration during shipment

The oil sump vent line valve is then opened when the chiller is commissioned but if the chiller is subject to temperature swings in the off mode refrigerant charge migration can occur in such quantities that the sump heaters cannot prevent washout of oil from the sump. If the temperature in the evaporator is allowed to cyclically exceed the temperature in the condenser you will have problems with oil migration regardless of the operation of the sump heaters.

We have sites where weekly operation of the condenser water pump for chemical dosing circulation with the chillers off has caused oil charge loss through refrigerant migration. The chemical circulation was necessary for corrosion control so while it may not of been a “factory fix” to overcome the problem on affected sites have installed a solenoid valve (normally open for fail safe operation) to the oil sump vent line that is energized closed whenever the chiller is off. Have also experienced oil migration issues in cooler climates where the plant room is open to the ambient temperatures which has been corrected with the addition of the vent line solenoid.

Only thing I can't figure is why it would occur on one chiller and not the other - could be site configuration related

[servicetech 32]

You have made some very good comments and seem very educated. This plant does cycle the condenser valves on a weekly basis for the same reasons you describe as I recall. The condenser water temperature would be about 5 degrees warmer than the ambient room temperature that the chillers are in. I will give this some thought.

My question would be why would one chiller be effected and not the other? Both sit in the same room and experience the same chemical treatment cycle.

You speak of oil sump vent lines. Our chillers oil sumps vent two ways. One is through the master oil solenoid valve and the other through the oil separators. It seems hard to imagine oil filling the oil separators to the point that the oil itself would float out of them and into the condenser. I have witnessed it is possible with enough flow from a liquid pump from the evaporator to the oil sump to cause this so I guess it may be possible. That is why I think slower is better. You have given me some things to think about and I thank you for that.

[Screwit]

RTHD chillers also have an oil sump vent line from the top of the oil sump to a valve on top of the condenser with the purpose of venting the oil sump to the condenser to prevent a vapor lock of the oil sump, the isolating valve on this vent line ships closed.

I am also scratching my head why only one chiller on a site would be affected by refrigerant migration caused oil loss but it could be due to the configuration of the site, plant operating sequence, chiller size (if they are not identical) or for reasons other than the above.

The root cause of the refrigerant/oil migration problem is the micisbility of the POE lubricant and the R134a even when in vapor form, when temperature changes occurs refrigerant migrates through the system and carries the oil with it - having the oil sump vent line closed helps prevent refrigerant migrating through the oil sump and the resulting oil migration as the refrigerant is boiled out.

[milkyway]

I resent it. Its just a demo on the CH530. The first one is the one about the oil system,operation,etc.

hey bud, do u think i could get that demo? thanks

[rover]

I have two RTHD chillers in the same plant. One has problems with loss of oil about twice a year. The other has never had a problem. The gas pump always checks out fine using the discharge superheat method. The original installer could not figure it out. Local Trane techs have looked at it several times and say they are stumped as well.

I thought that I fixed the problem a couple years ago when I replaced the master oil solenoid. When the machine shuts down you can hear oil flow through the oil sump if you carefully put your ear to it. If you close one of the ball valves on the oil feed line the sound stops. Open valve sound starts again. Seemed like the solenoid was leaking by. Discharge pressure would push oil out of the sump and into the compressor. Replaced the solenoid. Sound was still there but seemed better and ran for a year or two without a problem. Anybody else notice the oil flow sound after shutdown? Any other explanation other than oil flow?

I will request the service bulletin on Monday as a Google search did not reveal anything helpfull. Figured we would just have to live with this problem.

The oil and refrigerant charge are all correct. A really good tech from the factory pulled both when he changed out the liquid level sensor and weighed all back in. I always pump the bottom of the evaporator into the oil sump to return the oil.

You don't control chiller plant call or stage up do you . See if chw pumps are running on or starting when they shouldnt be. Oil sump on rthd sits above cooler vessel.????

[servicetrane]

keep the vent valve closed

[Tech Rob]

If migration due to water flow or the room's temperature control is the issue, maybe isolation valves or a different thermostat setting are the answer...?

[svc]

Do you have condensor water regulating valves controlled by the ch530? Maybe settings are different between the 2 machines. Could it be that the chiller having the issue is starting up under different conditions than the other? If the condensor water regulating valve is N.O. vs N.C in the off state. All the rthds I have started up since 2009 have had this valve. I was thinking that they made this required.

[svc]

keep the vent valve closed

Say What?
The valve is closed during shipping. It is opened at start up.

[txhvac]

Do you have condensor water regulating valves controlled by the ch530? Maybe settings are different between the 2 machines. Could it be that the chiller having the issue is starting up under different conditions than the other? If the condensor water regulating valve is N.O. vs N.C in the off state. All the rthds I have started up since 2009 have had this valve. I was thinking that they made this required.

I've only heard of the regulating valve as an option, same as the RTHC.

[svc]

I looked it up. You are right it is in option! However it would be a requirement under certain conditions for the chiller to operate within its design envelope. RTHD chillers rely on differential pressure between the compressor discharge and suction to move oil through the compressor rotors and bearings for cooling and lubrication. It also requires an oil pressure differential in order to load the compressor. Lower temperature and pressure in the condenser (and higher temperature and pressure in the evaporator) can reduce the chiller’s differential pressure below the minimum required for proper cooling, lubrication, and loading. The chiller is protected from compressor damage by the CH530 control system. However, inadequate pressure differential will keep the chiller from operating. The most effective way to maintain the required differential pressure during chiller startup and operation is to apply condenser water temperature control.

[txhvac]

I looked it up. You are right it is in option! However it would be a requirement under certain conditions for the chiller to operate within its design envelope. RTHD chillers rely on differential pressure between the compressor discharge and suction to move oil through the compressor rotors and bearings for cooling and lubrication. It also requires an oil pressure differential in order to load the compressor. Lower temperature and pressure in the condenser (and higher temperature and pressure in the evaporator) can reduce the chiller’s differential pressure below the minimum required for proper cooling, lubrication, and loading. The chiller is protected from compressor damage by the CH530 control system. However, inadequate pressure differential will keep the chiller from operating. The most effective way to maintain the required differential pressure during chiller startup and operation is to apply condenser water temperature control.

Agreed 100%. The Carrier 30HXCs are the same way, the machine is not sold with a regulating valve, but one can be field installed, set-up, & the chiller will control the valve. People really need to have to have good control of their towers w/ these machines.

[Phisher]

Trane recomends controling the condenser bypass based on the pressure difference between the condenser and evaporator. A minimum of 23# delt-p between the condenser and evaporator needs to be maintained for proper oil flow. The condenser water needs to be 17deg higher than the chill water with in 2 min of startup. A 25deg. deta-t must be maintained.

[latchingfault]

try setting your delta P to 240kpa (2vdc) min and 480kpa (10vdc) max for your cond regulating valve

[milkyway]

yep., there are 5 reasons why this machine need this control
and 4 methods of control.

[corwin401]

I have two RTHD chillers in the same plant. One has problems with loss of oil about twice a year. The other has never had a problem. The gas pump always checks out fine using the discharge superheat method. The original installer could not figure it out. Local Trane techs have looked at it several times and say they are stumped as well.

I thought that I fixed the problem a couple years ago when I replaced the master oil solenoid. When the machine shuts down you can hear oil flow through the oil sump if you carefully put your ear to it. If you close one of the ball valves on the oil feed line the sound stops. Open valve sound starts again. Seemed like the solenoid was leaking by. Discharge pressure would push oil out of the sump and into the compressor. Replaced the solenoid. Sound was still there but seemed better and ran for a year or two without a problem. Anybody else notice the oil flow sound after shutdown? Any other explanation other than oil flow?

I will request the service bulletin on Monday as a Google search did not reveal anything helpfull. Figured we would just have to live with this problem.

The oil and refrigerant charge are all correct. A really good tech from the factory pulled both when he changed out the liquid level sensor and weighed all back in. I always pump the bottom of the evaporator into the oil sump to return the oil.

Just how do you get the oil back to the sump once its lost to the evap? Use a magnet to open the drain solenoid? until llid reads wet in sump? What if pressures are pretty much equal? Can you cycle open the CW valve to get lower loop temp to create differential?
THanks
Ken

[chillerguy81]

Just how do you get the oil back to the sump once its lost to the evap? Use a magnet to open the drain solenoid? until llid reads wet in sump? What if pressures are pretty much equal? Can you cycle open the CW valve to get lower loop temp to create differential?
THanks
Ken

Look at post #60 of this thread for the answer to your question.

[corwin401]

There was some oil loss on the two oil solenoids that I changed out, so I shut the discharge oil filter ball valve and added about 1/3 of a gallon of new oil. added another 1/3 after wet indication came back on. Let it warm up overnight and It did just fine the following day. This is the second RTHD 2009 that Ive had both oil solenoids leaking from the top, like someone used a can opener on them. I've seen the 2003 bulletin that said they "got rid of those valves and since then have had no problems." Now why did they make a confidential SB that said pretty much the same thing except for dates? (and also paid for the parts and some labor.) It looks like they really didn't get rid of the "bad" solenoid valves just slowly put them back in the system. I find it odd that my customer is out a ton of cash for refrigerant and parts that should have never been put in in the first place. In over 30 years of commercial service, I have yet to see this kind of failure, nor can I find any other seasoned tech to say the same. But anyway they are both working fine except for some more refrigerant to bring up the charges before summer.

[valdelocc]

There was some oil loss on the two oil solenoids that I changed out, so I shut the discharge oil filter ball valve and added about 1/3 of a gallon of new oil. added another 1/3 after wet indication came back on. Let it warm up overnight and It did just fine the following day. This is the second RTHD 2009 that Ive had both oil solenoids leaking from the top, like someone used a can opener on them. I've seen the 2003 bulletin that said they "got rid of those valves and since then have had no problems." Now why did they make a confidential SB that said pretty much the same thing except for dates? (and also paid for the parts and some labor.) It looks like they really didn't get rid of the "bad" solenoid valves just slowly put them back in the system. I find it odd that my customer is out a ton of cash for refrigerant and parts that should have never been put in in the first place. In over 30 years of commercial service, I have yet to see this kind of failure, nor can I find any other seasoned tech to say the same. But anyway they are both working fine except for some more refrigerant to bring up the charges before summer.

Are you talking about the gas pump solenoids? I would like to see the confidential SB.

[jman2794]

I going through all the RTHD post I can find before I do a gas pump replacement. The correct reading is "wet" for the oil optical sensor when its covered with black electrical. I just dont want someone to be confused.