View Full Version : Trane RHTB-150 high %RLA
06-24-2006, 12:41 AM
I went to this Hotel to solve an electrical problem with a motor circulating pump starter but while there, I noticed that the compressor RLA was 93% and it was only 8:15 in the morning. I taught that was quite high for the time of the day so I asked if they had problems and I was told no. Refrigeration is not my specialty but saving my customers energy is. So, I was giving the 2005 log book for this unit.
First, all readings are taking in the morning, between 8 and 9 o’clock.
Second, the Expansion valve position was always at 98% to 100%.
I looked up the R-22 table to compare values and found that Evaporator Refrigerant Pressure and Saturated Evaporator Temperature were according to table.
I could not find a troubleshooting manual on the internet but luckily I found this forum and an explanation giving by skyhawk and other to clarryd (10-25-2005 04:13 PM) regarding an overloaded compressor.
Within the data, there were days that the unit operated between 55% and 65%RLA (about one week in feb).
Please go ahead and ask questions that may help understand what keeps the expansion valve at 98% and the %RLA high. Remember, I have not worked on the unit. I’m only studying the old data (presently the same conditions exist).
Note: Both the compensating pump and chiller pumps have no flow control. By the way, the Local Trane Rep does a monthly inspection and service to this system and after each inspection, they take readings and leave. Since I mentioned that something is wrong, I was asked to solve this problem. So, know I find myself studying refrigeration. Please give some guidance…..and remember I’m new in your field.
RTH B 150 FL F 0 L W 0 0 0 0 U N N 3 L F 2 L
Chillrdude, I could not see the pictures you sent to clarryd on 10-24-2005 03:45 PM. Can you repost them with some advice? Thanks.
06-24-2006, 12:46 AM
06-24-2006, 09:29 AM
if you had a return load coming into that uit it could be that,what was you evap splits,and on the no flow controls on the pumps.the UCP within the chiller monitors the water in and out to protect the barrel and oil within the circuits.dirty tubes blocked stariners on the condenser can add to that percentage how about the water in and out of the condenser https://www.trane.com/Commercial/Equipment/ProductDetails.aspx?prod=17
[Edited by maxster on 06-24-2006 at 09:38 AM]
06-24-2006, 10:20 AM
Problem could be from a knucklehead control guy fresh out of college.I was on a job where the compressors kept tripping and I couldn't find a problem with the chiller, air cooled scroll.I scratched my head for a couple of hours 3 different days when I walked past a little note on the wall that read, " circulate chilled water pump for an hour before starting chiller".Needless to say when the chiller started with an 80 degree loop it would already be up against the hi pressure limit. Look at how the equipment is being operated. PS , do they need another chiller, I can make them a hell of a deal!!!!!!!!!!!!!!!!!
06-24-2006, 10:52 AM
Please explain about the return. Are you asking if return load is directly piped into chiller suction side?
I made a table of pressure and temperature differential for water in evaporator and condensing units.
Feb 18, 2005
Condenser :6psi, 5.6ºF
Evap: 13psi, 4.7ºF
August 8, 2005
Condenser :22psi, 9.3ºF
Evap: 19psi, 2.3ºF
According to my understanding, they do not have flow control, so as you mention the dirty tubes will cause increase press drop, but how does this interact with the loading system? and why the exp valve never goes below 98%?
Remember, Im new to your refrigeration world.
06-24-2006, 11:12 AM
I dont think that is the case. The system is running 24 hours. It does not trip, but is running loaded without a real cooling demand (early mornig) and may vary very little from that condition during the rest of the day. Voltage unbalance 0.6% current unbalance 5.74%.
Probably dirty contacts or termination.
I need more information and what would keep the expan valve cont at 98% and how to test the loading/unloading system.
06-24-2006, 11:41 AM
wildelectron, every Trane machine ever built has what is called submittal data. It is basically the chiller design data which includes: design chilled water pressure drop, design chilled water gallons per minute (GPM), design temperature drop, and design entering and leaving chilled water temperature. The same info for the condensor is provided. It also provides design volts and amps at full load.
You start off checking the performance of the machine against the design data.
The expansion valve is controlled by compressor discharge superheat. If the superheat is above setpoint the expansion valve will open further to try to bring the superheat back to setpoint. The machine in question, if fully charged with refrigerant and operating close to design conditions, will normally have an expansion valve position of between 40 and 60 % open. In most cases, an expansion valve at 98%, tells me that the machine is low on refrigerant. In fact, if I walked up to that machine and found the X-valve at 60%, I would begin thoroughly checking the machine against design.
You stated that the machine is "running loaded without a real cooling demand (early morning)".
If the machine is seeing design conditions or above, their IS a load!!! Where the load is coming from is immaterial to the operation of the machine!!!
06-24-2006, 01:08 PM
if you have a load inside...the machine will do what it has to do to satisfy that setpint add a cool night the % should drop with the cooler condenser water from the nightand the load within staying the same.then the day ambient load will effect the running of the % up with the sun and temps rising on that tower.
lord of the screws
06-24-2006, 06:06 PM
tou can go into service test and test both the EXV and the load/unload system you should first have some more literature before going at it blind either an IOM or there is a service bullitan that explains all operating systems on the machine and yes if the EXV is wide open the first thing I would check would be the charge.
lord of the screws
06-24-2006, 06:07 PM
you can go into service test and test both the EXV and the load/unload system you should first have some more literature before going at it blind either an IOM or there is a service bullitan that explains all operating systems on the machine and yes if the EXV is wide open the first thing I would check would be the charge.
To help we need real data:
Condenser water pressure in:
Condenser water pressure out:
condenser water temp in:
Condenser water temp out:
Evap water temp in:
Evap water temp out:
Evap water pressure in:
Evap water pressure out:
all taken with the same gauge/thermometer
Refrigerant suction pressure:
Refrigerant discharge pressure:
Refrigerant suction temp; measured at compressor:
max % rla:
Min % loading:
These are just a few basic readings to begin with.
Does the machine ever stop?
My initial impression is an undersized chiller for the load. The delta-p across the condenser sounds high also.
I just tried looking for the iom for this chiller on line, and could not find it. I did find the pressure curves. Look ad trane.com click commercial in bottom rt corner and follow link to literature.
Remember to multiply your pressure differential by 2.31 as the readings are in feet of head.
06-24-2006, 09:20 PM
To determine why the chiller is at full load you really need to look at evap Delta T, and Delta P. Additionally you should look at evap and condencer approach. As far as the EXV position, you need to look at discharge superheat "control point", compared to actual superheat.
Without knowing much info here my gut feeling is the unit is low on charge. That can be further confirmed if their is a large difference between the SH control point and actual SH. If the EXV is 98% open but the discharge superheat is way above the control point that usually is an indication of a low refrigerant charge.
I suspect the RLA status is a a whole other issue.
06-25-2006, 01:59 PM
Here are the pics for you to see what is inside there from my post to clarryd back in October, as I recall his machine would not unload and we thought the slide was stuck or something, he never came back to let us know.
With your machine I agree with all the advice given so far, probably low on gas but could use a full log to help determine. Kind of strange your pressure drops across the barrels changing so dramatically over 5 months, unless you got VFDs on everything.
06-25-2006, 10:34 PM
some friendly advice,if you dont have much experiance with a.c. service and you are out there charging them for your time it will catch up to you the fact that your not an air conditioning person. if you want to learn this stuff download the o and m manual otherwise you might want to let there ac contractor look at it,if by coincidence some major f up happens to that machine after you touched it your going to be blammed than the next thing they ask is why is a unexperianced person messing with our expensive equipment
06-26-2006, 09:28 AM
My guess with the pics you posted is a cracked 1/4 " line. In the 1st pick you posted you will see a 1/4" female fitting just above the slide valve on the compressor. We used to have problems with this fitting cracking, then causing high side pressure to be vented into the load solenoid valve port. This resulted in an un-controlled loading of the compressor. Usually it resulted in a lot of low evap trips or current overload. Another one was a plugged solenoid valve screen.
I would think the origional poster would have noticed some other abnormal operation if there was a problem like you describe.
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