ways to customer demand for improved efficiency. Reference 9 is 



intended to be the basis for efficiency labeling of industry's consumer products. 



Catalogs on industrial package units now provide information on a unit's 



energy efficiency ratio (EER) which is defined as BTUs per watt-hour. 



However, catalogs give only the design value; no information was provided 



by any questionnaire respondent on the value of this performance parameter 



over time or under typical field conditions . 



Even though condenser design seems fairly well standardized throughout 

 the industry, proprietary details are probably involved because no respondent 

 provided data on the heat transfer factor used for sizing coils in his 

 package designs* „ For industrial, air-cooled condensers a plate-fin coil 

 is normally used. It has copper tubing for easy piping assembly by brazing, 

 and aluminum fins for economically providing a large convective heat transfer 

 surface. Fins are of 7072 high-strength zinc alloy aluminum with collars, 

 which are flared openings through which the copper refrigerant tubing is 

 inserted,, The collars provide sufficient spring so that a good mechanical 

 bond and effective heat transfer results when the copper tubing is 

 mechanically expanded into them. The collars space the fins, typically 

 12-14 fins per inch. They also cover the copper tube with aluminum, which 

 may limit the severity of galvanic corrosion. Several tubes pass through 

 each fin and are joined at the end by return bends. Fins are usually 

 flat, but may also be configured to create turbulence for improved heat 

 transfer. Because fin thickness is typically only 0.006", the assembly is 

 subject to damage in handling and the fins themselves can deteriorate 

 physically from corrosion in adverse environments. The aluminum fin 

 material is anodic to the copper tubing, i.e. is consumed when a galvanic 

 couple is established by any aqueous surf ace film of electrolyte such as 

 ocean spray. The galvanic potential difference between copper and aluminum 

 is 0.45 volts, a difference which is almost double the 0.25 volt maximum 

 suggested for reducing intermetallic contact problems by reference 10. 



The aluminum industry has been promoting the adoption of an all- 

 aluminum condenser for many years. Success has been achieved only recently, 

 since the introduction of an ALCOA developed process of ultrasonic brazing. 

 This process eliminates the corrosion caused by a residue of salts that 

 are difficult to remove after brazing with conventional fluxes. A large 

 percentage of mass-produced window air conditioning units now have all- 

 aluminum coils, fabricated in much the same way as the more conventional 

 copper tube/aluminum fin coil described above. Trane Co. air-cooled rooftop 

 and remote condensing units in the 5-15 ton size range have all aluminum 

 coils; units of 20-ton capacity and above have the conventional copper/ 

 aluminum coil. Automotive oil and transmission coolers and some automotive 

 radiators are now also being made of aluminum. These units have been 

 successfully protected from the corrosive effects of salts applied to 

 roads for ice melting with a chromate conversion coating followed by paint. 



* This should not be taken as an indictment because condenser performance 

 is normally obtained from tables of face area, depth, air velocity, 

 and temperature difference. 



47 



