Scroll racks

[bersaga]

Contemplating putting some hermetic scrolls on a rack-tyoe system. The only issue here is oil management - these scrolls do not have sight glasses, oil or gas equalisation ports (unlike recips).

Any ideas how to ensure good oil equalisation between the scrolls ?

[angryk]

What would the downfalls of scrolls on a rack system be? Bear with me here, I've only worked on one rack system.

[Dan]

Don't do it.

Hahaha. Over the last two years, I would have passionately agreed with Marc's sentiment. We introduced fairly large racks with 100+hp. As many as 10 compressors on each rack and we had a fury of failures.

What our engineers and, I suppose, Copeland were remiss in considering was the much higher flow of oil through the scroll compressors when compared to semi-hermetic reciprocating compressors.

Our solution was to provide additional oil reservoir capacity to insure a quantity of available oil at all times. We also employed the newer oil filters with greater filtering capabilities... scrolls appear to create a higher content of metal filings as they run-in when compared to pistons with rings.

The problem seems to have gone away as a result of employing these remedies.

But there is something to be said for the value of a positive displacement oil pump and manually resettable oil failure control when compared to a tiny float that resets automatically.

[aruiloba]

Check for good ingformation at:
[url]http://www.ecopeland.com/Literature/eCopeland/en_C060205.pdf

Augusto

[Mark]

hi besaga etc
Thought this jpg would be of some interest.My friend had just done routine maintanence,On this HT scroll pack/rack.
regards mark

[bersaga]

Thanks Mark - 10 scrolls !!

[Peter_1]

Same comment as Marc, don't experiment.

I should use scrolls who are provided for this like Marc proposed, with sight glass and pressure egalisation line.

It is possible a rack with scrolls but... with the proper compressors.

Clivet of Italy has a Chiller line - Spin Chillers - which are built only with scroll compressors, sometimes 10 in parallel and 800 kW. Saw them building in Italy and it was overwhelmingly.
see www.clivet.com
or http://web.clivet.it/spinchiller/eng/spinchiller.pdf

Peter

[Mark]

hi everyone
The HT pack i sent a jpg of is built to enviroguard spec.Local electromechanical oil regulators and strainers are taken care of.
For everyone reading i have enclosed a link to the piping methods of an enviroguard system.

http://www.tylerrefrigeration.com/mechanical/ENVIRO.HTM

Have a look.
regrds mark

[Peter_1]

Hi Mark,

Nice drawing. These are drawings you can learn something from.

Some questions, almost so many I see now that I become almost ashamed to ask them all here in this forum:

What is the purpose of the SPR in system 1 and what is an SPR? It can't be a suction Pres. Reg.

I don't see a Pressure Differential Check Valve (NRD of Danfoss) at the outlet of the oil reservoir. Is this correct?

How do they reduce the refrigerant quantity? You need as much as all the evaporators needs when all cooling together + the content in the tubes and some reserve in the receiver?

What did they mean with early warning of dirty condensers? I suppose this is done by measuring electronically pressure and/or temperatures.

IN system 2, what is the meaning of the SV between receiver and suction manifold?

The heat exchanger around the discharge line, is this for some sort of precooling? Has this any use because I should think - but I can be wrong - that seen pure energetically, this is a zero operation.

What is the meaning of the bypass with SV in system 2 at the outlet of the condenser.

The lower head pressure is done by placing over sized condensers? I agree that the best thing we can do to reduce running costs is to reduce the HP. But even we don't do it for several reasons: because it's so established to hold a constant HP, our client has specs where they describe this method. The only thing we often do is placing air handling units with an additional condenser in it to heat certain parts of the shops in wintertimes.

We once serviced an LT rack (R22) where they had used a compound compressing system (into the HT rack, difficult to explain for me, the same principle you often see in NH3 systems) . It took me some time to figure out what was going on. We dismantled these racks and it's a pity I didn't take any picture of it. We worked of course with very low condensing pressures on the LT rack.

We had in the past a rack manufacturer who always made stainless steel collectors and all the tubes where machine bended. Very nice.

Take your time Mark, (or the others who won't find it to hard to answer these questions) but your answers can perhaps be usefully for some others here in this forum.

We better start a new thread for this -

Those who know the answers, don't laugh. I'm never to old to
learn something.

The Ispell worked marvelous Webram (only 11 faults)

[Peter_1]

Thanks Marc.
I wish I could make Flash presentations the way you did.

What surprises me is that a lot of refr. technicians can handle very well all kind of computer stuff, some of them including you really can program very well, as is it there main job rather then refrigeration.

The pack manufacturer we mostly working with is Profroid/France (a division of ECR or also Carrier like Tyler, +/- 3.000 packs/year) but they even have no website.

We bought also two racks at Sodifri France but they went bankrupt.

We once bought a small rack at Schiessl in Germany and we need two small racks (80 a 100 kW HT) racks in the very near future. I will ask Tyler perhaps for a quote but they will be to expensive I think due to the transport.

[Dan]

I think it'll answer a lot of questions you have about enviroguard. Understanding the Enviroguard principle takes one along way up the great mountain of refrigeration understanding in general.

So what does Enviroguard do? I see a lot of valving. Looks like a repairman's nightmare.

[750 Valve]

Dan its not that bad, can cause some strange things in winter if its not engineered perfectly... throw all case sst ratings out the door.
We found we could lift the suction setpoint by around 2 deg celcius when picking up max subcooling but then during summer needs to be dropped back down (pain in the arse) it also throws out rack cycling during winter as the cases run cold they can quite often cycle off on a safety temp setting say -3 deg celcius dairy... end up cycling big systems (48ft of case) on solenoid - not good for comp cycling but I suppose when they don't run they don't cost!
Over large periods of time cases tend to ice from txv end, guess this comes down to txv selection and finding a happy medium. The perfect valve in summer is not the perfect valve winter (PD across valve will change from 10 to 12 bar summer to down to 7 bar in winter (lower is possible but also has consequences).
Gas leaks show up real quick.

[Mark]

And if some idiot hits the emergency stop button for the condenser fans .Most of the refrigerant ends up in the expansion tank.
mark