Refrigerant quality in rack systems?

[round_the_rack]

Hi All,
I'd really like to hear your ideas on monitoring and remedying refrigerant quality issues in parallel rack setups. I inherited a batch of supermarkets this past winter, and I've noted a few sour charges here & there when working on a case or a rack. Do you use the acid test kits and your sense of smell alone to monitor this problem? Or is there a better way?

How do you go about cleaning a 500 kilo rack, aside from changing the filters, oil, and refrigerant. Especially in systems with POE oil?

(Just a few of the many questions that pass through my grey matter while I'm keeping my own company in a darkened motor room.) :)
Thx!

by

[GXMPLX]

You have to tackle two problems simultaneously:


Solve the CAUSE of ”low quality” refrigerant
Clean it up


The causes are known, but just in case:


Your rack is producing chemical reactions
You had motor burn outs that were not correctly handled
Someone used low quality uncertified refrigerant to charge.


In a POE environment chemical reactions are produced because:


You have leaks and moisture is coming in. Please don’t post that with positive pressure this won’t happen or I’ll have to swear and get banned from posting for a while!
Your discharge temperatures are too high. Three main causes are low suction pressure, high superheat, high condensing pressure but others are a combination of the three previous, electrical problems like phase unbalance, lack of compressor (external) cooling like oil cooling, …
Friction surfaces reach high temperatures even for short periods of time, caused by lack of lubrication. Either no oil or oil too hot, metal particles in the oil,...


Usually you cannot stop operation to clean out so what you should do is:


Check that suction filters were sized correctly. This is a major problem with rack manufacturers they usually install too small a filter and tell you to remove the cores later. People who do this have their brain cells more fried than mine!
Install suction filters and liquid line filters and replace them in a regular maintenance operation that should be triggered by oil test, smell or taste if you want!
Try to isolate an clean as much as possible and install temporary liquid filters (oversized) and with bypass in that area. If there is the possibility of backflow like when hot gas defrosting install correctly sized suction filters too.
If you could stop operation (never seen this) do a general cleaning.


But install and operate correctly sized suction filters, taking into account the mass flow of ALL compressors that may be running simultaneously (even if there is a slim chance)!

No better way that I know of...

[Mark]

http://www.temprite.com/main_content.asp?sitename=temprite&pagename=home

Sound advice from GXMPLX, we have had some excellent results cleaning up systems, fitting Temprite Oil Separators.

With Kind Regards
Mark

[GXMPLX]

http://www.temprite.com/main_content.asp?sitename=temprite&pagename=home

Sound advice from GXMPLX, we have had some excellent results cleaning up systems, fitting Temprite Oil Separators.

With Kind Regards
Mark

With coalescent filters?

The problem is that the system may be acid too.

[round_the_rack]

GXMPLX...

Thanks for the reply. Very clear & easy to understand.

I suspect all three causes you list are at play. In one of the older stores, the scale & sludge are 3-4mm thick in the low-temp circuits. A previous fridgie snipped the inlet strainer screens from the TXV's, so I'm replacing valves there at a wholesale rate. Haven't cut into the med-temp circuits yet, but I suspect they are the same. Filtration appears to have been less than an afterthought.

Right now I'm still assessing the extent of the problem throughout all of my stores, but I'll be increasing filtration where I can. You've given me a few things to consider. And you won't get any challenges from me over moisture penetrating fissures in a positive pressure vessel. I still remember enough about capillary action and "the magnetism of cold" to understand the science behind that one.

I do have one question. You mention heat as a problem, i.e. high discharge, high condensing... Is this measurably more of a problem for POE than for mineral or alky-benzene? Thanks.

by

[round_the_rack]

Mark

I'm curious about the Temprites, but until I clear the existing stock of Turbasheds from our warehouse, I'll need to hold off. Thanks for the thought though.

by

[GXMPLX]

Internally equalized TEV installed in any position but upright + sludge may produce modulation problems (don’t open as they should after some time with sludge in the system).

Filtration won’t solve the problem if you have chemical reactions, filter wil only improve the situation until they saturate.

I’m not a chemist but POE and AlkylBenzene are called “ecological” oils. This means that the time they remain on earth before decomposing is short therefore are chemically unstable compared to mineral oils. The temperature at which they start reacting with the refrigerant (which is also less stable) is lower. So you must keep a close eye on discharge temperature. Check your compressor manufacturer recommendations for this.

I did not mention HEAT as a problem but discharge temperature which is produced by heat of compression.

One of the causes of high discharge temperature is superheat which is not equal to heat, it is a temperature difference search superheat in RE you will get zillions of advice on it!