Considering only the effects of atmospheric corrosion, the expected 

 service or physical life of standard condenser coils is much shorter 

 in severe environments than the service life of other packaged components, 

 as illustrated by the following tabulation: 



Expected Service Life of Standard 

 Commercial Equipment - Years 



Severe Moderate Mild 

 Component Exposure Exposure Exposure 



Compressor, motor, controls 5 10 15 



and cabinet 



Air cooled, plate-fin 1-2 4-6 10-15 



condenser 



Thus, it can be expected that in severe exposure locations such as Guam 

 and Diego Garcia the standard commercial, uncoated condenser- -i o e a plate- 

 fin unit with aluminum fins mechanically attached to a copper tube--might 

 have to be replaced as often as three times during the lifetime of the 

 unit„ This compares to a single replacement in moderate environments 

 such as Pearl Harbor and coastal CONUS locations, or even less frequently 

 in mild environments at semi-desert, interior locations in the Southwest 

 Uo S, such as El Centro, CA or Phoenix, AZ„ 



Expected performance characteristics of selected coil alternates in 

 a severe marine environment are as follows: 



Lifetime Coil 



a„ Performance — No significant performance degradation or failure 

 over the physical lifetime of other unit components „ 



bo Cost -- Maximum cost of unit 1.8 times cost of standard commercial 

 unit; replacement coil cost no more than 4.0 times cost of standard commer- 

 cial coilo 



Co Candidate materials — All copper coil with hot dipped tin or 

 electroless nickel (MIL-C-26074A) coating of 1.0 mil minimum thickness „ 



do Design criteria for coil sizing -- Inlet air temperature 100°F; 

 condensing temperature 120°Fo 



Superior Coil 



a» Performance -- Coil performance satisfactory over physical lifetime 

 of other components in comfort cooling unit application, within acceptable 



Industry practice is to use 7072 high-strength zinc alloy fin stock of 

 approximately 0»006" thickness with integral, flared "collars" around 

 holes punched for the copper tubes „ These collars serve to separate 

 the fins at spacing of 12-14 fins per inch, covering and protecting 

 the soft copper tube after it is expanded into them by either hydraulic 



„„ (cont'd next page) 



