In citing a specific instance, he asked, "Why would a retail supermarket decide to retrofit R-22 racks to R-404A without changing to POE oil? I have asked myself that question, especially since the mechanics are the ones who have to live with the problems. I am hearing of product loss, performance issues involving recovery time, and valves blowing out.

"When analyzed, all can be attributed to oil logging. The mineral oil is lying in the evaporator, causing poor heat transfer that the expansion valve can't control, poor coil performance, oil and liquid slugging, and on and on. I now understand that there is a wholesale conversion to POE on these projects."

A FIELD EXPERIMENT

Terry described trying to use R-404A with mineral oil as "at best a field experiment." He noted the information available is limited to small systems. "Data on supermarket-size systems under these conditions has not yet been developed."

He said there are those within the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) who are looking at the issue, but "these are just the beginnings of the investigative process. They are discussing whether there is a need to study this, determine line sizes, analyze problems encountered, etc.

"If the need is determined, then the task group may become a full technical committee with funding."

At this time, he said, "without a sound engineering foundation, the attempts at retrofitting in such a manner prove costly and are unnecessary."

WHERE TO GO NOW

While R-404A, the most popular refrigerant for commercial supermarket refrigeration, is labeled as needing POE oils, the industry has introduced a range of HFC refrigerants that do work with a range of lubricants, including mineral oil, for specific retrofit applications. Several manufacturers offer such products.

At ICOR, the first to be introduced was R-414B (marketed by ICOR as Hot Shot®), a retrofit option on R-12 systems.

"ICOR's next focus was on the replacement of R-22 and -502," said Terry. "ICOR learned of another company, Star Refrigeration, located in Scotland, which had been blending refrigerants longer than anyone.

"Star's approach to R-22 and R-502 replacements was similar to ICOR's. After discussing our convergent approaches in 2001 and working with Star's partner in manufacture and distribution, Rhodia, ICOR started manufacturing NU-22® [R-417A], an HFC replacement for R-22 applications.

"In 2004, ICOR introduced One Shot® [R-422A]," which can be used as an R-502 retrofit as well as for use in low-temperature R-22 systems. "Both One Shot and NU-22 are formulated to be used with mineral and alkylbenzene [AB] as well as POE oils," Terry said.

HOW DO THEY DO IT?

So how do you get certain HFCs, such as R-417A and -422A, to work with mineral oil? One factor is the use of a small amount of a hydrocarbon while still maintaining a nonflammable safety rating for the refrigerants. This was also done with R-402A and -402B.

Said Terry, "While these refrigerants are not totally miscible with AB and mineral oils, total miscibility is not a requirement for oil transport in the applications the refrigerants are designed for."

"Transport is a complex function of various parameters, such as velocity of the refrigerant through the pipes, degree of solubility, viscosity of the oil-refrigerant mixture, refrigerant density, operational temperatures, and pipe sizing and layout.

"It is also well known that refrigerants like R-22 or -502 are not fully miscible with mineral oils, but maintain partial solubility and have been used successfully for many years.

"It is also well known that hydrocarbons have a very high solubility in mineral oils. Additionally, they have total miscibility with fluorocarbon refrigerants. This relationship results in a mutual solubility effect when the refrigerant blend is mixed with mineral oil, for example.

"Substantial amounts of the fluorocarbon refrigerant will also dissolve in the oil sufficiently, providing the necessary oil transport properties."

CASE HISTORY

One example of a supermarket moving from an HCFC to an HFC while still using the mineral oil is the Bigg's Supermarket in Florence, Ky. The medium- and low-temperature racks were converted from R-22 to -422A.

George Ronn, manager for EPA Compliance and System Controls, said in a preliminary assessment, "We have experienced no problems with mineral oil return, migration, or separation in either of the two racks. In fact, we had a significant amount of oil return to the racks from the evaporator after the conversion took place."

Terry said those involved in retrofit decisions should consult with refrigerant and equipment manufacturers to understand retrofit options.

For more information, visit www.icorinternational.com.

Publication date: 02/06/2006