The Effects of Galvanic Corrosion on Air Conditioner Performance

Abstract

Corrosion of air conditioner outdoor heat exchangers (condensers) poses a significant problem for consumers living in coastal regions. This research sought to experimentally determine effects of galvanic corrosion on air conditioner condenser coils when subjected to high salt environments such as those found along the Gulf coast of the southern United States. The particular coil configuration investigated was comprised of copper tubing and aluminum fins, which form a galvanic couple in the presence of an electrolyte (salt water). Corrosion at the tube/fin junction results in a decrease of contact area through which heat is transferred. As a result, degradation of air conditioner performance occurs. An experimental plan was developed to operate two air conditioners for a period of approximately one year at a testing site in Galveston, Texas. Psychrometric evaluation of these units was conducted prior to exposure, at the midpoint of exposure, and at the conclusion of exposure. In addition, samples of copper and aluminum coils and coupons were subjected to the same coastal environment and investigated for corrosion attack. An accelerated corrosion test was also conducted to determine the effects of increased temperature, relative humidity, and salt concentrations on these samples. Air conditioner performance was measured during steady state cooling tests at outdoor conditions of 75⁰F (23.9⁰C), 82⁰F (27.8⁰C), 95⁰F (35.0⁰C), and 105⁰F (40.6⁰C) with an indoor temperature of 80⁰F (26.7⁰C) dry-bulb and 67⁰F (19.4⁰C) wet-bulb. Results of this testing showed that both units demonstrated average decreases in both cooling capacity and system EER. Sensible and latent capacity degradation for both package units showed decreases of approximately 4.6% and 20.9% respectively. System EER dropped over the course of the field investigation by 11.5% for one of the units and 8.3% for the other. An average corrosion rate for sample coupons subjected to the Galveston environment was calculated to be 0.13 MPY. Microscopic evaluation of aluminum from these galvanic couples after approximately one year of exposure showed an average pit depth approximately 19% of the aluminum thickness at the material interface. In comparison, aluminum fin collars at the material interface had an average pit about 22% of the thickness. Accelerated corrosion testing revealed some pitting, but not to the extent exhibited by field samples. A detailed description of the experimental setup, procedure, and results are provided.