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CSZ Refrigeration Retrofit Guidelines

The Basics

We have discovered that managing the lubricant switch-over is more demanding than the refrigerant retrofit.

As CFC refrigerants are becoming more difficult to find for servicing existing equipment, and as they become more expensive, several CSZ customers have called us asking for guidelines to retrofit new HFCs into their systems. Still others are moving to change-out their CFC refrigerants to create an environmentally friendly facility by corporate direction. Whatever your reason, a change of refrigerants has never required more consideration than today, because HFCs require polyol ester lubricants and can’t be used with the mineral oils in CFC systems.

During the last few years the chemical companies have done a fine job of providing us with compatible lubricants and refrigerants that permit us to use existing compressor displacements to have "drop-in" substitutes for capacity and efficiency (usually defined as ±5% from the baseline CFC performance). We’ve been given guidelines to flush out the mineral oils so that the system is clean and will not have any residual mineral oil to interfere with the flow and lubrication of polyol esters. Most manufacturers have been warned about the highly hygroscopic nature of polyol esters and that systems and polyol ester cans should be kept closed; they can absorb enough moisture in thirty minutes exposure to the atmosphere that system performance can suffer or acids may form, breaking down internal motor winding insulation. We have discovered that managing the lubricant switch-over is more demanding than the refrigerant retrofit.

Lubricating Hardware

Knowing that a polyol ester lubricant is required for HFCs or PFCs is necessary, but insufficient to make the right choices. Since every compressor manufacturer’s design philosophy may be different, they may recommend different polyol esters for use in their compressors.

Several compressor manufacturers have run polyol esters in their CFC machines to determine the best lubricant for their designs and also whether the designs hold up under this new lubricant’s characteristics.

The overriding concern is: can we recommend that the polyol ester is as good as the mineral oil it replaces in providing lubrication for compressors originally designed for mineral oil? Unfortunately, it can take years of use, or alternatively, some serious accelerated testing to determine whether the polyol esters provide all mechanical moving parts in a compressor with the lubrication needed for long life.

As a result of these tests, one manufacturer has redesigned the running gear of its hermetic line of refrigeration compressors to use the polyol esters. Still another has had to redesign valve plates, which had excellent reliability with mineral oils and CFCs, but failed with polyol esters and HFCs. To use HFCs, a third manufacturer had to redesign the bearing surfaces and lubrication system to achieve the high reliability they demand.

Lubricant Recommendations

Copeland recommends Mobil Arctic EAL 22-CC (22 centistoke) polyol ester in their compressors.

Carlyle recommends Mobil Arctic EAL 68 centistoke or CPI Solest (32 centistoke) POE, depending on the refrigerant.

Bristol recommends Mobil Arctic EAL 22A (22 centistoke) polyol ester.

Notice that each manufacturer recommends a different lubricant for their products, even if they are the same viscosity but differ only by the additives. This is a very important factor. Many lubricants are on the market which are compatible with HFCs and PFCs, but only a few are recommended for use by the original equipment manufacturer. Always follow the OEM‘s application advice for lubricants.

The Problem

In CSZ’s experience, the HFC refrigerants aren’t the problem. The new lubricants are!

In CSZ’s experience, the HFC refrigerants aren’t the problem. The new lubricants are! Polyol esters are excellent solvents, carrying debris, solder, flux, dirt, and oxidized metal throughout the system affecting valves, compressors, capillary tubes, and filter/dryers. They are highly hygroscopic and absorb water which is almost impossible to drive out, causing high discharge temperatures. Refrigerants are much more soluble in polyol esters than in mineral oils, causing low oil pressure, and the oil is carried by the refrigerant throughout the system in much higher concentration than mineral oils, forcing system manufacturers to take extra precautions to assure efficient oil return, especially from the colder sections of the system. System cleanliness and proper piping practices are much more critical elements when using polyol esters.

The Choices

Your environmental equipment may have any one of several different refrigerants in the high side or the low side system, depending on the age of the chamber. And, you will have several choices for zero ODP refrigerants in a retrofit. The following table offers some suggestions:

Table 1 - Refrigerant Recommended for Zero ODP

  Currently In Your Chamber New Refrigerant(1)
High Side CFC-502 or HCFC-22 HFC-404A(2)
Low Side CFC-13 or CFC-503 HFC-23 or PFC-508B(2)
Notes:  
1.  All the HFCs or PFCs require polyol ester lubricants.
2.  Several manufacturers produce HFCs or PFCs they consider equivalent. CSZ’s chambers are shipped with DuPont SUVA refrigerants as standard.

Having the ability to replace a CFC with a commercially available zero ODP refrigerant is comforting. Having a choice of several different refrigerants that fulfill the requirement can be confusing. For instance, on the low side, either HFC-23 or PFC-508B (also known as SUVA® 95) can be substituted for CFC-13 or CFC-503 in low temperature applications. In the past, CSZ has recommended HFC-23 as a replacement for CFC-13 at temperatures down to -73°C (-100°F), and SUVA® 95 to replace CFC-503 at temperatures down to -84°C (-120°F). CSZ would now recommend either HFC-23 or SUVA® 95 for applications down to -73°C. At -84°C, the choice is much more obvious. While there are many criteria to consider when choosing a refrigerant, system designers look for good capacity at the operating temperature, low discharge temperatures, and suction pressure above atmospheric. At -84°C, SUVA® 95 is the clear choice. The next table indicates this advantage.

Table 2 – Operating Pressures

At -73°C At -84°C
CFC-13 7.6 psig 4.5 in Hg vacuum
HFC-23 9.0 psig 3.9 in Hg vacuum
CFC-503 17.6 psig 3.7 psig
PFC-508B (SUVA® 95) 16.8 psig 2.9 psig

In addition, SUVA® 95 has about 25% higher capacity than HFC-23 at -73°C and about 30% higher capacity than HFC-23 at -84°C, bringing back all the performance of CFC-503, especially at -84°C applications. Another feature of SUVA® 95 is that it has lower discharge temperatures at -84°C, improving system efficiency and reliability versus HFC-23.

Recommendations

CSZ is often asked whether a retrofit of newer refrigerants is recommended for environmental chambers. Our answer is:
  1. If your chambers are functioning properly, there is no legislated reason to change-out CFCs in favor of non ozone-depleting refrigerants.
  2. If your equipment is in need of service, you should consider several options.
    1. If the repair is minor and the replacement CFC refrigerant is available, you may elect to continue using the CFCs.
    2. If the repair is major and requires changing the compressor(s) as part of the service, follow a recommended flushing procedure and upgrade to the new HFC or PFC refrigerant. Be certain to ask for specific recommendations from the chamber manufacturer because of the possible need to change valves or other components.
    3. If the repair is extensive and the chamber is rather old, obsolete the unit and purchase a new chamber which may incorporate many new performance features in addition to the new refrigerants.
  3. If there is a corporate mandate to eliminate CFCs from your facility, always follow the original equipment manufacturer’s recommendations on the advisability of simply flushing the system and changing to HFCs or PFCs. The more expensive option is to perform a compressor change-out with components designed for HFCs or PFCs. The OEM will then decide whether the new system will result in performance that meets your original specifications while retaining acceptable reliability.
  4. CSZ recommends that hermetics over three years old should be replaced and semi-hermetics over five years old should be replaced, rather than simply flushing the system. These guidelines should be confirmed for your specific environmental chamber.
Remember that other components, such as valves, oil separators, filter/dryers, or expansion tanks may need to be modified to accommodate the newer refrigerants. And, with the passing of the Clean Air Act and its updates, all refrigerants must be handled as controlled substances by properly certified service personnel.

We Can help

CSZ can help if you have a question about retrofitting HFCs or PFCs in your CSZ chambers. Please call us at (513) 772-8810 and ask to speak to our Technical Service Department, or e-mail us at indtechsupport@cszinc.com. We can develop a detailed recommendation for you or your local service company to implement.