Printable View
had a look at a copeland scroll compressor today on LT pack.
comp has desuperheater vapour injection.
solenoid coil for desuperheater energised when comp contactor pulls in and comp runs.
no liquid flooding back all other 6 comps ok and no evap coils iced up etc, the solenoid valve for desuperheater is not passing either all checked.
question......if the valves are passing in the comp could this cause the comp body to ice up.
has anyone come across this problem before?
What are your suction and discharge pressures? If the scrolls are stuffed and te compressor is not pumping and your liquid injection is operational it sounds like you might be getting excessive liquid hanging about the compressor while it is operating. ..is the sump heater operating in the compressor off cycle? Sounds like an interesting fault, tell us what you find.
he either has liquid injection and it is letting by or he has an economiser and its ruptured internally letting liquid flow back down the vapour line to compressor.. vapour injection can not desuperheat !- quote from a well respected fridgie-
It should be liquid injection which is used to cool discharge temperatur?.
Just checked copeland web site and found vapour injection system with economiser sub cooler, sounds like hou hit nail on the head with liquid getting back to compressor through economiser circuit install monkey.
The Copeland Scroll compressor does not have valves.Quote:
Originally Posted by cold.man
It does have a small mass retention valve at the exit of the discharge tube. This retention valve could let refrigerant in if it had a liquid column on the discharge line.
I’ve seen systems condensing in the discharge line when the system stops. Could this be happening? It would mean you get frosting when the compressor (or more probably the whole system) is off.
Chemuss could be right if frosting happens when system is on.
I respectfully disagree.Quote:
Originally Posted by install monkey
You can get desuperheating just by mixing two streams at different enthalpy you get a mixture that is proportional to the mass flows and entry enthalpys.
It is a small amout if the mass of the lower enthalpy mass flow is low but it could be high if it’s much higher than the flow you are desuperheating.
also with respect Aramis, I cant see on this sytem anywhere you would get a suitable vapour to desuperheat [not useful anyway] with unless its a mixed vapour from the economiser
I would be inclined to think its either the liquid injection letting by or the economiser is feeding liquid back down the vapour line to compressor
have seen a few in the last few weeks which all turned out to be a problem with liquid injection
R's chillerman
I was thinking in something similar to this one (with more compressors): http://www.pattonnz.com/site/patton/...ter_July08.pdfQuote:
Originally Posted by chillerman2006
If it is, you’ll see in page 3 where the vapor comes from in the blue line, and in page 4 an enthalpy diagram showing the mixture of vapor flows.
This was also published in the ASHRAE journal volume 45 number 4, April 2003.
I fully agree. This is the most probable cause just like Install Monkey says.Quote:
I would be inclined to think its either the liquid injection letting by or the economiser is feeding liquid back down the vapour line to compressor
My option’s probability is one in many thousands, but I´ve seen compressors turning not to a “ball of ice” like cold.man says but to a frozen suppository, because of poorly designed discharge lines!
Hi Aramis
yeah thats an economiser and if the hx tev is stuck open it can cause liquid to flood back
in cold.man's case he only as this happening to one compressor which would suggest to us [as agreed] liquid injection
still open to another explanation though
R's chillerman
sussed it- does it have an endocube fitted? :o
does it have increased run times
less stop/starts
increased setpoint but still reaches desired temp
and all with an imaginary energy saving of 30%
if the answer to all the above then yes as its a case of http://www.facebook.com/photo.php?fbid=188272907951780
R's chillerman
I'm also suggesting liquid in from a different and very strange direction.Quote:
Originally Posted by chillerman2006
This requires a discharge check valve not closing completely, this could happen in only one compressor ... or it could depend on the design of the discharge line.
I thought you decided to illiminate that one as its effect would be a bumplug ;) size and not a great ball of ice
R's chillerman
ps: just to be sure, my last post was aimed at taking the michael out of Endocube's claims of energy savings http://www.refrigeration-engineer.co...light=hoodwink
This is just a matter of perspective.Quote:
Originally Posted by chillerman2006
I didn't go in there on purpose ... Don't get me started please!Quote:
ps: just to be sure, my last post was aimed at taking the michael out of Endocube's claims of energy savings
Go on !Quote:
Originally Posted by aramis
As I'm starting to doubt myself as this cubes the dogs danglies [supposedly]
But then again the league of doubters in that thread so far, could re-invent the wheel between them
More the merrier though :)
R's chillerman
hi guys thanksfor the replies.
the pack does have a econimiser, comp has a 13/16" UNF diameter injection stub and just an ordinary 1/2" liquid line solenoid valve the model of the copeland comp is a ZF18 vapour injection.
solenoid valve opens when comp is running. the vapour injection valve is not passing.
obviously as some LT copland models do have liquid injection not vapour.
there is no liquid returning to the pack from what i can see from checks done and as i say this is only happening to 1 x comp.
refrigerant injection is designed to keep discharge gas temp at a safe limit....
vapour injection is designed to cool compressed refrigerant and extends the operating envelope....
if the econimiser was faulty i would have liquid return to all comps i would suspect but this is not the case.
we had a spare comp in the stores so replaced now the problem is solved no icing on the comp.
but still where was this liquid coming from.....
we had a spare ZF18 comp in the stores so i replaced the comp and this comp is fine checked twice since replaced no ice building up on the comp body.
so to be honest i am still baffled as to where this liquid was coming from.....
You could check the discharge retention valve of the original compressor and don’t throw it away.
... when you have eliminated the impossible, whatever remains, however improbable, must be the truth? ... Sherlock HolmesQuote:
Originally Posted by cold.man
From the discharge line!
Can you give us a picture of the discharge collector and say if the system stops or works at low ambient hours with less compressors?