Refrigerant Blends

[bernard]

When I was working in light commercial I was always taught that when a system was short a Refrigerant say R404a then all gas had to be recovered, leak found and recharged with fresh gas due to the glide beween the mixture.

In the supermarkets we find the leak repair it and top up,Will this eventually cause problems due to incorrect blends and if so what symtoms would I expect to see??

Regards Bernard

Have ammended to include repair leak

[chillin out]

When I was working in light commercial I was always taught that when a system was short a Refrigerant say R404a then all gas had to be recovered, leak found and recharged with fresh gas due to the glide beween the mixture.

Our packs contain 100's of KG, no way will we reclaim each time.

Even if the gas lost its properties over the course of a few leaks then that problem can be addressed at the time. To repair this fault then you would reclaim and vacuum the system and put in a fresh gas, but how many leaks would contribute to this ?


Chillin

[bernard]

Hi

What symptoms would you expect to see,this is for theoretical purposes only.

Regards Bernard

[chillin out]

The cases not working.LOL

The pack and the cases would not perform like it should do.

R404a as I mentioned before seems always to do exactly as you want.

I am more of a touchy feely tech rather than looking at graphs and things. I put my hand on a pipe and see if it feels good. I confirm this by using a thermometer.


Im not really the best person to ask, maybe Marco or someone can give a better answer.

Chillin

[slingblade]

What symptoms would you expect to see,this is for theoretical purposes only.

A reduction in duty and increased head pressure is one symptom.

[Argus]

In the supermarkets we find the leak and top up,

I would be very careful about that - it?s very deep water.

Since July 2005 in the UK, all refrigerants not in use in a system are classed as Hazardous Waste.

In my interpretation, apart from being exceptionally bad practice not to repair the leak, any emission is wastage and it is, therefore, technically illegal to knowingly allow an emission to continue without repair. This is no longer a grey area ? it?s a fact.

If you are a mobile technician, you are, as far as the law is concerned, a mobile waste remover and your company will need to be registered by law. Additionally the supermarket will also need to be registered if it produced more than 200kg of all waste annually. As it probably is, you need to know their registration number.

Don?t get caught.

As far as blend quality is concerned, there is an efficiency penalty connected with blends that are out of specification. Provided that the refrigerant is ?clean? in terms of contamination, you can return the stuff to the manufacturers for reprocessing.

Johnny Rod has posted on the efficiency losses of refrigerants recently, because his company did a survey on the subject. As a chemist, he will know more about that than I do.

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[Steve Wright]

Where can i find the data Johnny Rod posted about eff losses with blends, I looked through all his post and can not find. Point me in the right dirrection.

Many thanks Steve

[Argus]

Where can i find the data Johnny Rod posted about eff losses with blends,

Steve,

It was in a thread I started last September about contamination chemistry. I hope this link to the thread works:

http://www.refrigeration-engineer.co...ead.php?t=3069

John posted a link his findings here, it?s a link to a Magazine article:
http://www.boc.com/news/article_925_11aug05.asp

I?m sure that John will read this sooner or later on get back to you.

Good luck.

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[adam]

doesn't it depend where in the system the leak is? i thought that with blended refrigerants the mixture seperates on the low side

[Argus]

doesn't it depend where in the system the leak is? i thought that with blended refrigerants the mixture seperates on the low side

Not exactly.

Mixture separation, or fractionation, occurs wherever the mixture is in the vapour or gas phase anywhere in the system, or in the cylinder in the back of your van for that matter.

When the vapour separates, the mixture proportions in the remaining liquid are different, too.

This can be anywhere in the system including evaporators, condensers and the vapour space in liquid receivers and accumulators.

You can?t assume that fractionation is predictable either. The amount of gases that separate out of the mixture at any one time will vary in proportion to the remaining mix according to the temperature / pressure at the time, the glide characteristics of the gas and the vapour pressure.

An alternative to the perceived negative effects of glide is to select an azeotrope if possible, or a near azeotrope with minimal glide. This probably provides one of the reasons why there is a move nowadays toward R410A from R407C in small high temp systems. The former has a mean glide that is a fraction of 1 degree.

To determine the glide, (R407C is a good example with a mean glide of about 6 degrees) look at the pressure / temperature tables, then subtract the bubble point temperature from the dew point temperature and you will see that it is not constant across the range for any particular mixture.

In short, your refrigerant supplier sells you a quantity of a mixture blended to specified tolerances. As soon as it gets into the system and reaches a working equilibrium, it becomes something completely different.


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[piston broke]

It's the old question of time and money.

Yes the correct thing to do would to decant, pressure test, repair leak, evacuate, repressure test and charge with exact quantity of refrigerant. But on large systems this is very expensive and very time consuming. Is the customer prepared to spent this money and have their equipment out of action for a period of time especially since Joe Bloggs down the road will try and come in do a quick repair and top up, making him look superefficiant and thus stealing your customer.

Always try and do things the correct way but always explain to your customer in laymans terms what is going on and not just hit them with a bill at the end of the job. Also, keep refrigeration records, quantity used, quantity reclaimed etc.

Anyone who does not adhere to proper procedure should be reported. Don't let the sharks steal our work.

PB

[Johnny Rod]

I'm afraid the info in the press release didn't have any efficiency loss info relating to blends per se, but the stats there show that a lot of systems with blends in them are not as they should be.

Changes in blend composition (of non-azeotropes) occur when there is a vapour leak from a 2-phase part of the system, e.g. headspace of a receiver, or part-way along an evaporator tube, as the vapour has a different composition to the liquid, so some components are lost quicker than others. In single-phase sections (all liquid or all vapour) there is only one fluid to lose so the change in comp is minimal or none at all. Usually the higher-pressure components are lost so the sytem pressures decrease, and generally cooling capacity is reduced. The only way to fix this is replace the refrigerant, DIY reblending is a bad idea and they're all covered by patents anyway.

Some 400s have a small glide so in practice topping up a small amount of leakage would mean the blend was a bit out but practically it will still do its job, and 404A has a low glide. By the book you are supposed to recover, fix all leaks, and recharge with good stuff (which may be the old stuff if you're lucky). Recovering 100s of kilos can be a bit of a job without the big-ass kit though...