The U.S. Navy had 850 chillers that were using the ozonedepleting substance (ODS) CFC-114. A drop-in replacement for this refrigerant was desired that met the operational needs with respect to cooling efficiency and maintenance while being a non-ODS.
The overall objective of the project was to assist the Department of Defense (DoD) in identifying, testing, evaluating, and selecting alternative refrigerants and systems to replace ODSs, which are being phased out of production under national policy and international (Montreal) protocol. An immediate goal was to aid the U.S. Navy in selecting a non-ozone depleting retrofitable refrigerant to replace CFC-114 in existing shipboard chillers.
HFC-236ea and HFC-236fa, both non-ODSs, were evaluated as replacements for CFC-114 in Navy chillers. The Navy selected HFC-236fa (1,1,1,3,3,3- hexafluoropropane), a non-stratospheric ozone depleting substance, to replace CFC-114 in its shipboard chillers. Testing included determination of atmospheric lifetime, global warming potential, key thermophysical properties, and modeled performance as well as selected toxicity tests. Following these promising test results, engineering studies (e.g., lubricant selection, heat transfer, and refrigerant performance) using small- and large-scale testing were completed and showed these HFC isomers to be suitable replacements for CFC-114. Advanced toxicity tests were performed with emphasis on HFC-236fa. The major risks were that HFC-236fa would not meet regulatory requirements, the Navy’s health and safety criteria, or the Navy’s engineering retrofit criteria.
Following the Environmental Protection Agency’s (EPA) inclusion of HFC-236fa in the Significant New Alternatives Policy program, as was announced in the Federal Register on December 19, 1995, the Navy selected this new chemical as the backfit replacement for CFC-114 in its shipboard chillers. Reports on HFC-236ea and HFC-236fa concerning their lubrication and heat transfer performance with selected lubricants and heat exchanger tubes, respectively, were provided, and the EPA’s acceptance of these reports c ompleted requirements by Iowa State University for its SERDP-supported work. Various toxicity tests were performed to ensure safety for handlers and others possibly exposed to releases of material. These included rabbit metabolism and development studies, human blood:air partition coefficient tests, and cardiac sensitization studies. All studies were favorable. About 6,000 pounds of the chemical remaining or recovered from the test was transferred to the Navy for future use in backfitting shipboard chillers. This transfer should save the Navy about $100,000 in its HFC-236fa procurement. The Navy’s replacement program began with one chiller retrofit in 1997 followed by fleet conversions starting in 1998. This project was completed in FY 1996.
The most immediate environmental benefit was the replacement of a stratospheric ODS (CFC-114) by a non- ODS (HFC-236fa) of potentially lower global warming potential. With about 850 shipboard chiller units subject to replacement, a savings of about 500 million dollars would result if retrofitting rather than replacement of these chillers was technically feasible. The production of CFCs was slated to end by December 31, 1995, in the U.S. The HFC-236 isomers do not suffer from the disadvantages of other replacement refrigerant alternatives (such as being ozone-depleting or having a higher global warming potential, unsuited thermophysical properties for chiller operation, or lower efficiency). In addition, these isomers appeared promising for high temperature heat pumps, foam blowing (insulation) agents, and fire suppression/control as replacements for substances that were being phased out by international agreement.