View Full Version : OK, Now I need chiller help.
07-08-2004, 08:11 PM
I finished an annual on an RTHA300 heat recovery chiller last week.I noticed it was running on evap limit when I fired it back up.The discharge SH was over 60 degrees so I add 60# of gas, 10% of the factory charge and first time since S/U in 92 it has ever had any put in.Well it didn't make even the slightest bit of difference so I informed the customer that I would pull the charge and weigh it whilst also replacing the relief valves as a couple were leaking slightly.I pulled the charge and it was still 40# short so I change the reliefs and dump an extra 30# in.Didn't make even the slightest bit of difference, water flows were right on the money but approach was horrendous at FLA, upwards of 18-25 degrees.So I think OK, lousy approach means low suction pressure which equates to high DSH.I decide to pull the elbow off the evaporator to look at the tubes as my flows are right at design.Well tubes are clean as a whistle, so now I am scratching my head.I talked to the factory and they said add more gas to get DSH close,well I knew that wouldn't do it but I added another 30#.Now as you know these are a critical charge machine, 10# over and it carrys over but still nothing.So now I am at 30# over nameplate charge, refrig filter is ok, temp- sensor is Ok, charge is OK, oil level ok, flows are ok,chiller loads and unloads fine but approach at full load sucks and with a 47 degree leaving water temp the refrig temp drags down to 31 degrees.I have to believe that there is a restriction in the orifice plate going to the evaporator which would give me this problem.Have any of you guys run across this or have you on a teardown ever found crap in the orifice plates.I am stumped and now I think there is only one thing left to do, teardown, but the last one JCI beat us up by 35% and I only threw 80 hours at it for a total O/H, that one , the slide valve is stuck open and it stalls on transition.
07-08-2004, 08:21 PM
What is your subcooling?
07-08-2004, 08:33 PM
You is starving for refrigerant and you know it.
Dirty Evap. tubes, Low Evap. Water flows and even a blown out divider plate gasket on the Evap. head will not "Raise" your Suction Superheat one iota..(What the hell is an iota??)
The orifice plate has gotta' be looked at, and you knows it..Them chillers got many holes in them, while the orifice plates my company uses has but one...I have enlarged......a few....
I have added a few more to a couple of the RTHA's..
All will be well when your Suction Superheat gets back down to 2°-3°f at Load....
C'mon'....Get down on the floor & get nasty...Pop that orifice plate & let us know what Ya' find....
07-08-2004, 08:42 PM
how did it run before you did the annual maintance?
07-08-2004, 08:47 PM
It ran the same as it does now , I have 5-6 degrees subcooling but being heat recovery throws a bit of a wrench into it,because design is 85 in ,107 out on the condensor with 55-45 on the evap.You would think with the higher condensor pressures that the suction pressures would rise but it doesn't.It definately was a 100# short so I am getting headed in the right direction, howver slow it maybe.
07-08-2004, 09:08 PM
if you havent already, i would change the refrigerant filter. before pulling the orfice plate you might check with trane and get the specs on the plate so when you pull it you can check the diameter and number of holes.
07-09-2004, 10:00 AM
Oh, also it used to have good DSH a few years ago but it is the first time I have been in there as the other tech quit that used to look after it.It was right on 28 degrees at start up so I know the plate is the right one.
07-09-2004, 10:27 PM
My partner did one last week, Same thing, terrible DSH, Plate obstructed and trash in evap tubes both. Running great now. ALSO this unit has a history of losing freon out the relief. at least twice we have found it a couple hundred lbs. low.
07-22-2004, 11:16 PM
had the same problem with the reliefs too, what i found was a good idea is to remove the freon and install 3 way valves so you can change a relief with out removing the freon.
and also installing rupture disk before the relief so you tell if the relief had blown, but make sure the rupture disk matches the relief pressure.
one other question, i have alway measured the level of freon by using 2 hoses with a sight glass in the middle and using the weld on the evap as the proper level of freon.
anybody else hear of this
07-23-2004, 09:16 PM
I only use that method of liquid level indication after it has been marked on inital start-up with the proper weighted charge. The weld line is pretty close.
08-05-2004, 10:53 PM
Ok , I found the problem on this chiller.The refrigerant filter which has never shown a temp drop across it had disintegrated and the paper was stuck in the orifice plate.
Powered by vBulletin® Version 4.2.0 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.