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Acid in HVAC Systems

If you haven’t updated your methods for dealing with acid, your HVAC system might go the way of the dinosaurs, says Advanced Engineering’s Technical Director Colin Pratt.

Since HCFCs and CFCs were found to be environmentally-damaging, almost all responsible HVAC engineers and facilities managers have set about phasing them out – usually in favour of HFCs.

But while most are doing everything they can when replacing systems, refrigerants and oil, many are in danger of shooting themselves in the foot by using out-of-date methods for preventing acid build-up.

What’s the problem?

It was once believed that inorganic (or mineral) acid – which is the stronger, and most damaging kind – could not form in polyol ester oil / HFC systems. Indeed, burn-outs are much rarer in this kind of equipment, which seems to bear this out.

However, while that may be true in theory, in practice it is nearly impossible to prevent tiny traces of air or water infiltrating any system.

This is a problem because HFCs do not have the same excellent anti-wear properties boasted by the older, ozone-unfriendly refrigerants they are replacing.

To make up for this loss, extra additives are put into the supporting POE oils. This trade-off makes the refrigerant more stable… but the oil less so.

As a result, POE oils break down when combined with water, forming organic acids. While relatively harmless in themselves, these organic acids react with local metals, forming a sludge which blocks vital parts of systems such as expansion valves and oil ways These blockages put additional pressure on the compressor, therefore shortening its life.

As if this weren’t enough, in certain conditions it has been shown that additives in some synthetic oils can, in fact, create the far more dangerous mineral acids, which can result in a burnout in as little as 40 hours.

The ideal solution would be to keep air and water out of POE systems completely, but in practice this proves almost impossible, especially when performing proper repairs and regular maintenance.

All it takes are trace amounts of water: POE oil is incredibly hygroscopic, being 100 times more sensitive to water than the old mineral oils… for example other common types of synthetic oil can absorb up to 400 times as much water!

Getting rid of the acid – what NOT to do

Given that complete prevention is an unrealistic solution, what is required is an effective way to deal with acid in systems.

This is not as easy to find as you may think. Although there are plenty of products on the market which claim to deal with the issue by introducing an alkali to neutralise the acid, it’s really not a good solution for HVAC systems.

As you might remember from school, combining an acid with a base will always produce salts and – you guessed it – water. Even in the older mineral oil systems, the salts – either solid (“sludge”) or dissolved into liquid – formed from the reaction added wear to the system, and the extra water reacts with the oil, forming yet more acid!

Not only that, but it’s almost impossible to gauge the amount of alkali that needs to be added. Too little and it won’t neutralise the acid… too much and the alkaline starts to damage the system instead!

With the new HFC systems, though, there are even greater problems with using an acid neutraliser. Due to the way that synthetic oils are created in order to work with the HFCs, exposing them to alkali can cause oil to break down and form extra solids in the system, actually accelerating compressor wear.

Acid neutralisation, then, is a method that should have died out with the dinosaurs of HCFCs and CFCs.

The REAL solution

Instead of neutralising the acid, what we really need to do is remove it.

Filter-driers are good at acid removal… but painfully slow if used on their own. If the acid present is strong, then a great deal of damage may be done before the filter-driers have the opportunity to remove it.

What Advanced Engineering recommends is the use of an acid flush.

This is a viscous liquid that chemically attaches itself both to water and acid, and carries them directly to the filter-drier, speeding up removal.

Of course, it’s no good adding a solution that creates more problems – and with such hydroscopic lubricants, adding something to the system that lets in more water or air will only make matters worse.

It needs a combined approach – and the only really trustworthy solution we’ve found so far is the QuikInjector, which adds its partner Quikshot Acid Flush in completely waterless conditions.

This means that the problem of acid and water in an HVAC system gets solved, without causing the same issue to re-emerge further down the line.

HVAC technology is always evolving. This brings brilliant new possibilities, but inevitably it introduces new obstacles to overcome as well. Without a thorough technical understanding, disasters can, and will, strike – seemingly out of nowhere.

It is therefore the duty of good engineers to employ maintenance methods that are appropriate to these new technologies. Anything else is just leaving your system open to an acid attack… and that can be a real HVAC catastrophe.

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Acid in HVAC Systems PDF