Trane RTHD chillers in series help

[chipper2]

First off - I'm an engineer - never serviced a piece of HVAC equipment in my life but don't hold that against me.

That being said - I noticed the slick interactive website for the CH530 controller from another post and it got me thinking.

I have two RTHD's in series and local Trane guys can't figure out why they keep tripping out on motor overloads. Looking at the Trane literature it says the CH530 should control this and unload so as not to trip out.

We also have been getting a low evap refrigerant temperature shut down - but it's inconsistent. Happens in the middle of the night, middle of the afternoon, all over - but never in the really warm weather. Only happens on the downstream chiller (always the lead machine). The motor overloads occur only during the warmest weather and it will occur on both machines.

The evaporator flow is good - well over the minimum flows for the machine.

My question is this - anyone out there have these chillers working in series? Local Trane guys don't have any applications where these particular style chillers are in series application. If so - ever come across these problems and how'd you solve them? Are these chillers and the CH530 new that Trane needs to work some bugs out? Don't have a real warm and fuzzy from the local Trane boys can figure out what's wrong and then fix it.

Any thoughts would be appreciated.

[mfi]

What are you cooling? Never seen a series config before, except for low temp purposes.

[Carrene #2]

I'm familiar with some series applications.
Don't know why any engineer would design a system this way ( well actually I do ). It always looks good on paper and in theory and if set point is critical ( tough on a lead lag situation where the lead is alternating ).
I don't have any with the chillers you that you mention.
From my experience any chiller will run fine under the conditions it was designed for, oh ya, except for the odd lemon.
Look at the periphial stuff. Usually a BAS gives me grief and of course whose to blame, the chiller! Look for condenser temp control, chilled water flow ( alternating pumps ) they like to stop one then start the other, etc., etc..

[Edited by r718 on 12-22-2005 at 05:40 PM]

[absrbrtek]

The series chillers Ive serviced are usually designed for a 5F delta each. They are usualy a single pass aplication in order to reduce the pressure drop.

The CH530 should control the chiller from having the nuisance trips your getting. Your probably right about your local rep, the only thing theve got going for them is the emblem on their shirts. :)

[airworx]

what your saying is the chillwater supply from one chiller is piped into the chillwater return on the other chiller.
now i have worked on dx systems that the evap coil from one system is in front of the the other system. which requires hot gas bypass and unloaders. we programmed the setup with reliable controls.

now if the chillwater piping is in series out of one chiller into another then out to the pump and air handlers then i would think that glycol will be needed if water temps are below 40 degrees. but your problem sounds like your having refrigeration problems. i would check and make sure compressors are loading and unloading, compressors are not flooding, head pressures are not to low and causing oil return problems, charge and check volts, amps etc..,

[acjourneyman]

Don't worry about the series config, just treat each chiller seperately.Check the current transformers and make sure they all read equally and are the correct ones, make sure the O/L's settings are configured properly.Chillers can trip on O/L if a slug of warm water hits the chillers so check for this.Flow sounds like the suspect to me as this will cause both conditions you are experiencing,you probably have a bypass in this system so make sure it is not hunting.

[climpro]

chipper2 I have on service pm 2 rthc with ucp-2 in series , not rthd with ch-530 , desing, first unit ,54-49,sec chiller 49-44 ,first unit always shut-down over-load ,i called trane pueblo factory servicetech John Bassett ,I overhauled the slide-valve ,there,s service-bulletin on it,now it, ok ,so far so good

[chillrdude]

I doubt the piping configuration has anything to do with the overload trips, probably something with the slide valve. These machines are notorious for not starting with cold tower water, I would look there for your low evap problems or possibly your evap piping and flow.

When the CH-530 came out we thought it was a joke, they stuck the thing on air cooleds first and had 2 different models available, one that would give you no information and the upgrade model wasnt that much better, now they are going on everything, compare it to a York Optiview and it makes you wonder what LaCrosse is thinking when it comes to marketing.



Buying ANYTHING from McQuay is far worse than what you've got :)

[chiller mekanik]

chipper2,
I don't want to ruffle any feathers of the factory guys, but, check chillergroup.com & hopefully there is a contractor in your area that can help you.
I only say this because you expressed discontent with who you are currently using.
In my area, to be fair, the Trane service dept. has some very good mechanics on the payroll.


Alot of us that aren't factory work for contractors in that group.

[climpro]

chipper2 talk with my trane local dealer ,Kestrel view software for ch-530 ,trend log , data log you can view what happend and download the file at factory trane.com for investigation.

[lord of the screws]

wondering if you are using glycol and if so what the percentage of glycol you have you never did specify what your leaving water temp actually is I know for a fact there are issues with flo and glycol we have one machine that is within specified flows and we get lo evap. temps,we increase flows and problem goes away quickly if you do have glycol you can make adjustments to lo evap. temp trip point also I wonder if tripping on current overload after a lo evap. temp trip?

[chipper2]

Thank you for your responses.

I have them in series because it's a lab application where I need 52F supply air at all AHU's 24 hours a day for humidity control. I don't have variable flow so if they were in parallel there's no way I could guarantee 44F chilled water supply at all times (half of the water would bypass and mix with the active chiller raising the CHW supply temperature)

I do have 30% glycol. For the first couple of months the service tech's thought we had too much. 3 indpendant tests verified it was exactly 30% which is what the chillers were selected for. The other couple of months the service techs complained the flow was too low. The pumps are constant volume and actually slightly over the design flow rate. Trane says minimum flow for these chillers with glycol is 350 gpm. We have 620 gpm - verified independantly and by Trane service techs.

Funny thing is this - the chillers and the whole system design worked just great during the first 95F+ summer conditions. 2 of the systems use 100% outside air and we maintained temperature and humidity within tight spec for the lab. Owner loved it - everything was perfect.

One cool weekend, however, the BAS (Trane) let the pumps run when the chillers were off. The chillers blew their refrigerant charge and the local service techs under warranty recharged the system. Until this event the chillers worked great - they were not limited in any way nor did they ever trip on overload. Since this event if the chillers are not limited to 90% capacity both will trip on motor overload and the downstream chiller (always lead) will trip on low evap refrig temperature.

Any other thoughts or friendly suggestions I can offer to the local Trane service group on what to look for would be appreciated.

[joeywpittman]

what is the discharge superheat, with the machine loaded above 80% ???

[chipper2]

I don't know.

I've asked repeatedly but the Trane service techs won't give me any information in writing. No start up sheets, no data, nothing.

[climpro]

ask your trane dealer a copy of start-up log,your first post ,looking at literature,look at page 110 iom bulletin rthd-svx01a-en ,i think trane must recovery r-134a charge ,change all relief valves,weigh ref.charge , name plate charge. look at iom p.128 , 30½ glycol low rfgt temp cutout is 1 .6 deg

[jogas]

I heard about a hospital chiller plant in PA that had series chillers. It was done to overcome the "low delta T" efficiency problem common to primary-secondary chilled water plants.
Jogas

[t4e]

Kick your local Trane reps in the 'er, brain and tell them to look hard at the slide valves, and the loading and unloading solenoid control. You didn't mention which chiller is tripping, upstream, downstream both? Sounds like some intermittant sticking in the piston/cylinder. Hope this helps.

[chillrdude]

Originally posted by chipper2
I don't know.

I've asked repeatedly but the Trane service techs won't give me any information in writing. No start up sheets, no data, nothing.



Chipper2,
I spent 14 years with the Factory office up the road from you and I cant count how many times I had to get start up logs for engineers, if you tell your NES salesman you want them, I bet he gets them for you, they are probably in someones laptop waiting to be printed out, if you really want to piss them off I can come down and hook up Kestrelview to them and take a look see around the programming and setup.

[jogas]

Aren't start-up and log sheets in every chiller IOM manual?
Jogas