Low Humidity Rooms

[Brian_UK]

I'm supposed to be looking at a low humidity (2%RH) room in a couple of days which has in the past lost the compressor on a regular basis (yearly I think).

Apparently they now keep a spare on site.

Apart from trying to find the (hopefully) obvious type of faults with the system has anyone had experience with low RH rooms and if so then any particular pratfalls to watch out for?

Brian

[acman]

Obviously,you've been to site since you posted this.What did you find? Anything unusual? I imagine you're dealing with a direct expansion system , combined with reheat coils.
I would check the superheats,under low load conditions and beware of sluggings.They probably try to keep the evap as flooded as possible to drop more moisture from the air.Also I would check for hot gas bypass.

[Gary]

Good advice, acman. I would also check the records to see if the past compressor failures were mechanical or electrical. An autopsy would be even better.

[Brian_UK]

Originally posted by acman
Obviously, you've been to site since you posted this.

No not yet, your reply was only about 4 hours after my post and as it was dark here in the UK I thought it best to wait until the sun came up. Boy, that would be nice, to see the sun

Anyway, back to the matter in hand; your advice as to where to start looking at the system are welcome and as Gary said I am really hoping that some records have been kept.

Apparently this firm make dry-cell batteries and have the odd fire or two during manufacture. I suppose that is one method of defrosting the coils but I'm sure there must be a better way

Brian

[Brian_UK]

Just winding up this thread again.....Well, I finally got a look at this low humidity room on Friday and gained a bit more knowledge.

The system was designed and built as a skid system by Harris Environmental Systems of Andover, MA and uses two Copeland 35hp compressor packs. I have not been able to find out what caused the earlier compressor failures but my initial thoughts could be that they were due to oiling problems.

I still have to trace information on some of the kit fitted but am always looking for advice or comments from others.

The pack comprises Copeland N3DH-3500-TSD compressor with an AC & R S-1901 oil separator, remote air cooled condenser with a Sporlan ORI-10-65/225 (liquid) head pressure valve working in conjunction with a Sporlan ORD-4/20 (hot gas) head pressure valve to maintain pressure in the lquid receiver.

The evaporators have SVE-2-L1 valves with ORIT EPRs, the high pressure line to the ORIT is taken after the solenoid valve serving the hot gas bypass system used for capacity control. There is also a liquid quenching system to control the suction temperature.

We also have two Refrigeration Research 3704V suction accumulators with the quench system TEV(SVE-2-L1) sensing bulb located after the first accumulator.

First impressions are that there may be a problem with the oil separator on one system in particular. The oil returns from the separator via a hand valve, Sporlan C053S filter, sightglass and solenoid valve directly to the compressor crankcase.

When off the oil level in the crankcase is very nearly at the full sightglass level. With the compressor running there is froth on top of the oil and extreme agitation of the oil itself. The oil return sightglass is constantly running with what appears to be high temperature gas carrying oil with it. It does not look like oil with gas in it! My thinking is that the separator is not collecting oil and returning it but is open all the time.

If I shut off the hand valve then the crankcase oil level begins to drop and the agitation action reduces. I did not run this test for long as time was limited and I did not want to lose oil into the system late on a Friday

My first question of the accumulated minds out there is - does anyone have experience of the AC&R oil separator? Should it hold back the oil until released or just blow it back where it came from?

[acman]

I would be concerned about compressor cooling,especially with ORI and ORD head pressure controls,also,is there unloaders and/or hotgas bypass?????
Make sure you are getting good dense vapour back...
check differential pressures across ORD valve,they can stick,let us know how you make out.

[Gary]

Every oil separator I am familiar with has a float. When enough oil accumulates, it opens and sends the oil back to the compressor, then closes. It should not be constantly leaking back hot gas.

[Brian_UK]

Thanks guys, I now enough evidence, smart word for advice, to put forward a repair/investigation proposal to my manager.

I am unwilling to wait for the next compressor failure, just because they have a spare one doesn't mean you have to use does it?

Now I'm thinking sideways but.... anyone got any bright ideas on how to impart some rotation onto the spare compressor just to prevent flat spotting the shafts.

[Brian_UK]

Well, it's happened.

I put in a report to my new manager on 4th June detailing my concerns and included PDF files from HenryTech regarding the oil separators, potential problems and remedies.

I also included thoughts from this forum.

I did a further check visit at the end of June when I found the crankcase temperatures at around 70°C ; this was also reported. (I could lower the temperature by shutting off the oil return which was a good test )

Anyway report issued and apparently totally ignored, the compressor went down over the weekend

Just what is the point in trying some times ?

[Brian_UK]

Originally posted by Fridgetech
Hey, getting pissed about that stuff is traditionally my expertise, remember, or you been influenced

Sorry Marc, didn't mean to step on your toes !

Anyway it just gets better and better. They some lads in last night to fit the spare compressor, who they where or exactly what they did I don't know yet but I have a feeling that perhaps if they had RTFM which was on site the new compressor may have lasted a little longer than 3 minutes. Which is how long it took before all the crap hit it

I think they may consider changing the oil separator and some filters or two......

Anyway, like they say after an exciting TV episode..."The story continues tomorrow.."

[Brian_UK]

I think they may consider changing the oil separator and some filters or two......

Well our guys checked the oil separator and found it full on metallic sludge (surr - priiiise!!) with the float so heavy it couldn't lift if it wanted too.

Got a team of 'experts' in the complete the repairs.... If anyone recognises this job then please jump in.

[Brian_UK]

Call the experts - point well taken Marc (and number noted), I'm still learning about my new manager and His contacts etc .

I am also awaiting the post mortem results on the compressor failure.

[subzero*psia]

Have you heard what caused the compressor failure yet?

[Brian_UK]

No, sorry Dean, I haven't any news at all on these compressor failures.

My 'new' service manager is no longer with us so any hope of contacting 'his mates' is now gone.