The phaseout of R-22 is impending, and the use of mineral oil with those systems is diminishing in popularity. Synthetic oils, such as Polyolester (POE) oil, are being largely accepted due to their benefits when used with hydrofluorocarbon (HFC) refrigerants in compressors.

POE oil has added benefits, but it's also necessitated some changes in the HVAC industry.

“POE oil allows the oil and refrigerant to mix well, so you get good oil return back to the compressor,” said Joe Marchese, author, instructor, former HVAC contractor, and current Refrigeration Service Engineers Society (RSES) international president. “The original oils used in compressors were not really compatible with the HFC refrigerants that have come out, so they’ve come out with this synthetic oil, which is the POE.”

As some contractors discovered, POE oil needs to be handled much differently than mineral oil.

“It’s reactive to water, in that it’s more hygroscopic than mineral oil,” said D. Brian Baker, president, Custom Vac Ltd., Winnipeg, Manitoba, Canada. “We were told that POE can absorb about 10 times more moisture than mineral oil. So that becomes a real issue, because again, POE has a saturation point where free water exists at about 1,500 ppm. If it’s left open to the atmosphere, in an hour, your system may be contaminated. So that’s the biggest issue, trying to keep that out. If you get that down and you contaminate too much, that POE oil reverses its composition and reverts back to an organic acid and alcohol base. That’s what causes all the problems in our refrigerant systems.”

That point was echoed by Marchese, who noted, because POE oil has a high affinity for moisture, the service practices of contractors cannot be the same as they were in years past, when less hydroscopic mineral oil prevailed.

“You have to pretty much be cautious to not leave the oil exposed to the atmosphere for too long. If you do, the moisture in the atmosphere gets absorbed by the oil, then you have problems,” Marchese said. “Your service practices have to be such that when you’re piping in a system, and when you’re working with a compressor, you only leave the compressor open to the atmosphere as long as you have to. If there’s going to be extended periods of time, you should seal and cap the ends, so you don’t allow much moisture to be absorbed by the oil. I’ve also found that when you store it, you should store it in a metal container, because the old plastic containers allow moisture to absorb through their walls. If you have a gallon plastic container, it actually swells over time. So your service practices have to be changed slightly.”

Manufacturers Chime In

When it comes to determining which oil to use, compressor manufacturers obviously play a big role. Joel Moseley, senior vice president, sales and marketing, Bristol Compressors Intl. Inc., said POE oil has had a very favorable impact on the performance of compressors. He noted the industry is aware and has adjusted to the oil’s hygroscopic nature. However, he warned, all POE oil is not created equally.

“What’s the old saying ‘motor oil is motor oil?’ Well, just like motor oil, POE has significant performance differences depending on the formulation and additives,” Moseley said. “Bristol Compressors has spent hundreds of thousands of hours testing POE to identify the right POE for the various refrigerants and applications. The end result is the right POE outperforms traditional lubricants, with respect to operating envelope, EER, reliability, and sound performance. POE can be used in a wider variety of products and refrigerants, including R-22. POE also allows for standardization within Bristol’s products and operations, and a more robust design for our customers.”

Frank Landwehr, vice president, air conditioning marketing, Emerson Climate Technologies Inc., said the use of POE oil in HVAC compressors has increased dramatically since the phase out of R-22/mineral oil systems from OEM production in 2010.

“Our experience throughout the R-410A/POE compressor and system transitions has been favorable as we’ve realized improvements in our in-warranty claim rates and other reliability measures,” Landwehr said. “Although some of these improvements were driven by both compressor and system designs during this period, we believe that some of this improvement was associated specifically with improved lubrication designs built around the new POE oil. It was not just the oil, but the combination of the new oil and the whole lubrication design within the system.”

Landwehr said the industry has generally done a good job with these new designs, but the adoption of POE oil has not been without challenges.

“While POE miscibility with refrigerants is markedly better than that of mineral oil, other characteristics, like dynamic viscosity and the potential for acid formation, were more challenging,” he said. “POE’s propensity to absorb moisture quickly also had to be addressed by both system and compressor manufacturers as well as the contractors who install and service systems in the field. It is likely that this increased attention to moisture has actually helped the industry be more disciplined about addressing noncondensables, which can become trapped in the system.”

Looking Ahead

Even though POE oil has been around since the mid-1990s, Baker said, for some contractors, they might not have experience with it yet — either by choice or ignorance — though he added, in 10 years, he hasn’t had a compressor with POE oil and an HFC refrigerant break down yet.

“POE oil is going to be a real new thing to a lot of people. There are a lot of people who haven’t installed an HFC system yet,” said Baker. “They’re hanging onto these R-22 systems as long as they can because they don’t want to tool up or they don’t believe in updating.”

And, no matter what the future holds for oils, contractors said they’ll continue working with what’s in front of them.

“The bottom line is, as contractors, our job is to use the oil that the manufacturers lay out and recommend we go to,” Baker said. “The problems, though, which we see in the systems, are what we have to be able to identify.”

Publication date: 3/31/2014 

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