A couple of caveats: Don’t mix R-408A with R-502, or use it to top off existing systems.

R-408A has shown in independent laboratory testing that it saves an average of 8% in energy costs compared to R-502, says Ricketts, “and it’s the only retrofit refrigerant that was found to be more efficient than 502.” So supermarkets have found this replacement refrigerant to be an attractive retrofit solution, he adds, and are widely applying it.

Uses include food display and storage cases and cold storage rooms.

Like an azeotrope

Refrigerants used in the past were either single-component products or blends having a small glide that behaved like a single component. For the most part, blends like R-408A that have a small glide will perform the same as an azeotrope like R-502. Keep in mind that:

• The temperature glide of R-408A is less than 1°F (0.6°C). This glide is usually not noticeable compared to normal temperature changes due to pressure drops across the tubing, for example.

  In general, manufacturers have not indicated special considerations for low-glide blends in normal retrofit applications.

• R-408A will not significantly change in composition due to fractionation. However, there will be a slight difference in composition in the vapor phase, which is in equilibrium with liquid, such as in a cylinder.

Always transfer R-408A as a liquid from the cylinder to charging equipment or systems.

Retrofit considerations

R-408A can be used in most existing R-502 installations, with the following considerations:

• Performance — In most retrofit applications, the capacity and efficiency of R-408A is slightly higher than R-502. The compressor, line sizes, and other components will not need replacement and should operate the same.

• Lubrication — R-408A can be used with mineral or alkylbenzene oil. Polyolester lubricants might also be suitable.

  Systems using R-502 and mineral oil that show adequate lubricant return to the compressor can continue to use mineral oil with R-408A. Alkylbenzene alone or in combination with mineral oil is the best choice to improve lubricant miscibility and return to the compressor. Consult the manufacturer’s guidelines for additional recommendations.

• Material compatibility — Check with the refrigerant supplier and obtain recommendations from equipment manufacturers regarding compatibility of materials with R-408A. In general, Ricketts states, “Any system that’s operating with 502 could operate with 408A.”

  However, he notes, “There may be slight adjustments that need to be made on the expansion valve.”

Retrofit procedures

To retrofit a refrigeration system with R-408A, Elf Atochem recommends the following steps:

1. Gather baseline data while the system is still operating on R-502.

2. Check the system for leaks to identify necessary repairs.

3. Recover and weigh the existing R-502 charge.

4. If needed, remove mineral oil and replace with alkylbenzene or polyolester.

5. Replace the filter-driers.

6. Evacuate the system using a deep vacuum (at least 250 microns).

7. Charge the system with R-408A using liquid phase only. (Approximate charge will be 75% to 85% of R-502 nominal charge.)

8. Properly mark and identify the R-408A refrigerant charge for the retrofitted system.

9. Start the system and adjust the expansion device, if needed.

Note: Some original equipment manufacturers (oem’s) may have different lubricant, safety, or retrofit requirements. Consult the oem’s guidelines for details.

For more information on R-408A, contact 215-419-7000; 215-419-7930 (fax); www.elf-atochem.com (website).