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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.

An Energy Efficient Environmental Control System (EEECS) for a patrol-type aircraft has been developed and tested. Benefits of the system include not only substantial fuel savings, but also significant increases in avionics reliability through reduced cooling air temperatures supplied to aircraft electronics by the system. Testing was conducted in a laboratory to demonstrate energy efficiency throughout a wide range of operating conditions and in a Navy P-3C aircraft to demonstrate flight-worthiness of the system. This paper discusses the results of both the laboratory and flight tests. The heart of this vapor-cycle system is an electrically-driven, variable-speed centrifugal compressor that operates at speeds from 30,000 to 70,000 RPM. The compressor uses oil-less, tilt-pad, hydrodynamic bearings for maintenance-free operation.