We were discussing this in another topic.

It is my opinion and experience that the fastest and most effective way to rid a system of non condensibles is to pull the charge, evac the system and recharge with liquid from the tank.

Since air is non condensible, adding only liquid means you've eliminated the air.



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The trick to that is keeping the liquid from boiling and agitating the air&nons. You have to charge slowly and what we use to do is place the tank in a plastic milk carton crate with a garbage bag and ice, similar to how we would recover rooftop 1 on 1's in the middle of summer. Chill the tank, charge slowly and the air& nons stay at the top and aren't mixed back in.

 

If you are removing liquid, the liquid isn't going to boil much.

Also, while I didn't mention it, it is good practice to stop charging before all liquid is removed from the cylinder to prevent any air entering the system.

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Doesn't the liquid and air seperate in the cylinder and blowing the top (vapor port) of cylinder off until PT falls into place a good place to start

 

At that point after you recovered the refrigerant then vacuumed the system why would you put the contaminated refrigerant back in and run the risk of putting the non condensibles back in the system. Why not put new refrigerant that you know has no non condensibles


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At that point after you recovered the refrigerant then vacuumed the system why would you put the contaminated refrigerant back in and run the risk of putting the non condensibles back in the system. Why not put new refrigerant that you know has no non condensibles

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I actually mentioned this in my op but I do not believe - and I'm open to valid discussion to the contrary- that you can contaminate the refrigerant itself with non- condensables. POE oil sure but not the refrigerant itself. Not to mention the cost of 200 lbs of 22. Hell with retrofitting to 407-C. I don't mind changing oil- I do mind the glide/fractionation potential especially since system is prone to leaks no matter how hard we try to stay on top of them

 

By doing that, you are boiling the liquid refrigerant, causing it to drop in temp.

It will work, but simply removing liquid refrigerant from the tank works faster.

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True- but therorically wouldn't letting the temp rise back to ambient and fall repeating do it. I agree with the temp drop by purging vapor- I'm just educating myself here. So pumping down- cooling condenser and purging off header is just a myth?

 

You are right. Theoretically, purging from the highest point in the system can and will work.

I've done it on larger systems where recovery is impossible.



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Yes put more often then not the condenser is not the highest point and in many remotes with no receiver there isn't enough pump down capacity to pump down entire charge into cool. I suppose one could install a tap in the true highest point of the system on liquid line and 100% liquid should expell- within epa guidelines of course

 

It doesn't matter where the highest point in the system is, when the compressor is running, it will collect the non-condensibles in the condenser and trap them there with a liquid seal until the off cycle.
Theoretically, installing an access port on the highest point of the condenser would allow you to bleed off gas while running.

 

Which is another argument for doing it my way.




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Which is another argument for doing it my way.


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True true

 

Moisture is taken care of by the drier. Change the drier if you suspect moisture. Non-condenseables typically mean 'air'.

I wouldn't bother recovering from the liquid side of the condenser, no non-condenseables there, just the gas side. And doubtful you'd be pulling everything out. Probably stop once the [air cooled?] coil started to frost or the temperature of the condenser drop appreciably. If it is a water cooled condenser, there are other considerations.

If you had no change in operation from doing that, then your problem is probably somewhere else.

If you did get a noticeable and favorable change in operation, you could always schedule to run that procedure again. Explaining to the customer that you are doing it this way due to the request to have minimal down time.

 

I do not agree that non condensibles are collected in the condenser.

The flow rates of refrigerant through the system will carry them along rather than allowing them to collect in any one place.

The exception would be places of low flow such as the tops of receivers or suction accumulators.

 

Then why do purge units hook up to the condenser to remove air and non-condensables? Why do cooling towers have taps to purge non condensables from the high side discharge piping? Why does the condensing area reduce due to air and non condensables? Why are they called air and non condensables? They do not condense so they don't pass through the condenser. And when I make that last statement I'm fully aware that some minuscule amount probably does get carried through, but the vast majority stays in the condenser.

 

Here's more tips for increased recovery in those circumstances when minimal down time is required.

You do not want any core depressors in your hose. You do not want any shraders in your fittings. Ice the recovery tank. Be sure to have a couple of 50 pounders, you'll probably be surprised how much recovery you can get done by removing the restrictions and icing the tank.

Heck, run the outlet of your recovery unit through another set of gauges and feed two 50 pounders at once, being sure to ice both tanks.

We'll be calling you Mega-recovery-Dave in no time at all !!

 

No I hear ya in fact I always affix a hose with cold water to spray down and keep recovery cylinder cool. Especially since a lot of the times I'm dealing with 100 lb recov cylinders. Also on a good hot July day it's a necessity because my apion is a damn fine machine- recovers fast- but damn does she run hot. Not sure why. No condenser in machine be to lighten product. Don't know fast- but runs hot

 

What is the flow rate in most systems? I'm sure it varies but what's the rage? Never needed to consider it before.

 

http://www.achrnews.com/articles/85270-refrigeration-piping-i-here-are-the-piping-basics

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"Purging" non-condensables



"Refrigerant line velocities
Economics, pressure drop, noise, and oil entrapment establish feasible design velocities in refrigerant lines. These are:
Suction line - 700 to 4,000 fpm

Discharge line - 500 to 3,500 fpm

Condenser drain line- 100 fpm or less

Liquid line - 125 to 450 fpm"


I didn't realize it was that high.

8-58 FPS entering the condenser seems to me to lend itself to the argument that NCs would be swept along like the oil.

 

That's kind of what my thinking and what my experience with this has shown.

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I can never remember who made what gas law or what they say exactly but the long and short of it is they "shirnk" the condenser. One thing that hasn't been hit is the non-condensables "contaminating" the refrigerant. Hydroscopic oil and all aside- which is hard to do this day in age- I am of the belief that that refrigerant itself cannot be "contaminated" by air. Dunno. Could be wrong

 

Dalton is the name you're looking for. Dalton's law of partial pressures.

Air is a terrific insulator in comparison to all the other components in a refrigeration system, and it will cause the effective size of the condenser to be smaller.


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Put it in a tank over night and blow air off till tank saturation matches ambient.

 

I fixed a Liebert minimate once where the nitrogen in the fancoil was left and it did in fact hang out in the evap. Pressures on the roof were really goofy so I pulled the blower panel downstairs and there was a diagonal stripe across the evap from lower left to upper right. Below the stripe -- ice. Above it none. Condensor was on the roof. Due to the parallel refrigerant paths and the trap at the evap outlet the nitrogen just sat there. Likely some in the condensor too. Sure wish I had taken a picture.