For an OSA environmental system, NAVSEA would specify the dimensions (size, weight modularity, etc.) and ship/compartment interfaces (attachments, shock/vibration mounting, ship services, etc.) for the system, as well as similar requirements for interfaces between the system and those components that can be commercially supplied. This requires extensive Navy laboratory testing of the system and potential COTS components to define where the Navy must retain control of system design and where commercial "plug-and-play" solutionc are appropriate. Ths will not eliminate all risks because the Navy would still rely on commercial components whose design and availability are not controlled by the Navy, but it will strike a technical and cost balance between the realities of warship rquirements and the spirit of acquisition reforrn.
Ozone Depleting Substances
Navy ships and submarines rely on two types of chemical compounds, chlorofluorocarbons (CFCs) and Halons, for mission-critical cooling and fire protection, respectively.The commercial production of these compounds ceased several years ago amid concerns about their destruction of stratospheric ozone. No direct substitutes exist for any of these ozone-depleting substances (ODSs) in the Navy's applications. All potential alternatives pose performance, space, weight, or other penalties in shipboard applications. Furthermore, altematives must not introduce new environmental, safety, or health risks. Many design and engineering challenges must be surmounted to use altemative substances in existing ship systems.
CFC-12 and CFC-114 are used as refrigerants in various air-onditioning and refrigeration (AC&R) systems to provide cooling for weapons aud electronic systcms, food preservation, medical storage, and crew cornfort. The design and backfitting of entirely new AC&R plants is not economically viable, so the Navy's strategy has been to develop backfit "kits" that allow non-ODS refiigerants to be used in existing cooling systems. Conversron of shipboard CFC-12 AC&R plants to operate with HFC-134a involved various combinations of compressor speed changes or new compressors, new lubricants, new dehydrators, refrigerant leak detectors, new seals, new thermal expansion valves, and other hardware modifications. As of July 1999, the CFC-12 AC&R plants on 147 ships had been converted to HFC-134a refrigerant. Backfit kits are also being developed to convert existing CFC-114 A/C plants to use HFC-236fa refrigerant, central to which is a new compressor design with a variable-geometry diffuser(VGD). The first shipboard CFC-114 plants were recently converted to HFC -236fa on a cruiser for at-sea demonstration. In addition to using a non-ODS refrigerant these plants will be more fuel efficient, quieter, and able to operate more effectively with higher seawater temperatures (e.g., in the Persian Gulf). All converted AC&R plants are also being equipped with a new sophisticated microprocessor-based controller to improve reliability and troubleshooting, reduce control system complexity (by eliminating pneumatic/electromechanical controls), and reduce manning. A new family of AC&R plants optimized for the new refrigerant HFC-134a is being developed for future Fleet applications, starting with DDG 51 FLIIA ships and the LPD 17 Class. The flexibility of new ship designs offers the opportunity to incorporate state-of-the-art technology into the cooling systems. The 200-ton A/C plant design, for example, uses a VGD, variable hot-gas bypass, titanium condenser, enhanced heat transfer surfaces, and the universal microprocessor controller.
Halon is used as a fire suppression agent throughout the Fleet. Whereas it is relatively easy to determine the cooling behavior of candidate refrigerants based on their thermodynamic and physical properties, it is much more difiicult to predict the fire extingnishing capabilities of different chemical compounds. Extensive screening of potential candidate agents followed by small-, medium-, and large-scale testing is required to empirically observe and demonstrate fire suppression behavior.
