limits of degradation,. Possibility of 50% that coil replacement will 

 become necessary in essential refrigeration or equipment cooling installa 

 tions, where performance degradation cannot be permitted,, 



b„ Cost — Maximum cost of unit 1 5 times cost of standard commercial 

 unit; replacement coil cost no more than 3 o times cost of a standard 

 commercial coil. 



Co Candidate materials -- All copper coil with surface pre-treatment 

 and organic coating, or standard coil construction using electroless 

 nickel (MIL-C-26074A)~pre-coated aluminum fin stock and tin or nickel 

 plated copper tubing, with suitable organic coating „ Alternate coating 

 for standard coil is 3„0 mil thickness Heresite baked phenolic resin 

 coating (MIL-C-18467A) „ 



do Design criteria for coil sizing -- Inlet air temperature 95 F; 

 condensing temperature 120°F„ 



Improved Coil 



a» Performance — At least one coil replacement necessary over lifetime 

 of unito 



bo Cost — Maximum cost of unit 15% more than cost of standard com- 

 mercial unit; replacement coil cost no more than 1,5 times cost of 

 standard commercial coil. 



Co Candidate materials — Standard commercial or all aluminum coil with 

 chromate conversion treatment (MIL-C-5541B) after fabrication, and suitable 

 organic coatingo 



d. Design criteria for coil sizing -- Inlet air temperature 95°F; 

 condensing temperature 125°F. 



In moderate or mild environments longer coil lifetimes and fewer coil 



replacements would be expected; this factor is taken into consideration 



quantitatively in developing the life-cycle cost estimates^ of tables 1 

 through 4. 



5 



(cont'd) 



or mechanical means. The copper tubing is usually proof tested at 450 

 psi. When aluminum tubing is used, it is typically a high ductility 3003 

 manganese alloy slightly lower in the electromotive series than the 7072 

 finSo This difference affords some protection from galvanic corrosion 

 Aluminum tubing is also expanded into the collared, plate-type fins, 

 eliminating the severe corrosion that formerly resulted from residual 

 brazing salts when all aluminum condensers were first introduced. 



In addition to NAVFAC P-442, a useful discussion is contained in 

 "Analyzing HVAC Life-Cycle Economics on a Calculator", by Robert A 

 Walker, Specifying Engineer, November 1978 



33 



