1995-07-01

Retrofit of U.S. Navy Aircraft Vapor Cycle Systems to Accommodate Non-CFC-Based Refrigerants 951455

The U.S. Navy has undertaken the task of retrofitting the vapor cycle cooling systems on each of 11 different aircraft platforms to accommodate non-Chlorofluorocarbon (CFC)-based refrigerant fluids. This action is in response to governmental protocol that terminates production of CFC-based refrigerants at the end of calendar year 1995 due to their connection with the destruction of the earth's ozone layer. In addition, military legislation regulates acquisition of systems that use CFC-based fluids.The three CFC-based refrigerants used in Navy aircraft vapor cycle systems, CFC-12, -500, and -114, are being replaced by hydrofluorocarbon-based fluids, HFC-134a in most cases. These fluids have a zero ozone-depletion potential. The retrofit process begins with analysis and testing to determine the effects of the candidate replacement fluid on system cooling performance and reliability. In some cases, performance and reliability are adequate with only the minor modifications necessary to accept the different chemical characteristics of the new fluid (seals, hoses of different material, different oil). In other cases, the impacts are so extensive that, in essence, the system becomes an entirely “new” one.As a result of the varying degrees of effort required to accomplish the retrofit of the various systems, and funding availability in some cases, the programs are in different stages of completion. This paper discusses the test results for two systems and the plans for retrofitting a third aircraft with a newly designed system. The Navy is in the process of obtaining EPA approval for the replacement refrigerant of choice for another application. Although all platforms have not yet been retrofitted, as much information as is available regarding the measures being taken to accomplish retrofit will be presented in this paper.

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