2021 Volume 60 Issue 1 Pages 113-118
Refrigerant leakage of an air conditioner caused by formicary corrosion has been found more in highly airtight and highly heat–insulating houses. Our initial survey indicated that the leakage cases occurred chiefly in the houses in which a large amount of Japanese cypress wood was used. To clarify the corrosivity of these environments, 24 samples of condensed water were collected from the indoor units of air–conditioners with and without refrigerant leakage and they were analyzed by ion chromatography. The chemical composition of the water extracts from the sawdust produced from Japanese cypress and Japanese cedar wood before application of the termite repellent was also investigated. Furthermore, the corrosivity of those extracts to the copper tube was assessed. The pH of the condensed water collected from highly airtight and highly heat–insulating houses ranged from 4.6 to 5.2, which was significantly lower than the pH of 5.7 to 6.9 of those found in the general wooden house. Ion chromatography detected much more formic acid and acetic acid in the condensed water from leaked air–conditioners. Laboratory corrosion test showed that formicary corrosion developed in C1220 tubes that were exposed in the test cell filled with Japanese cypress sawdust, but not with Japanese cedar. The chemical analysis revealed that the water extracts from the Japanese cypress sawdust contained 33 mg/L of formic acid and 115 mg/L of acetic acid and the pH of the extracts dropped down to 4.3, suggesting that volatile substances contained in the Japanese cypress affected the formicary corrosion of the copper tube. Another corrosion test for C1220 tubes exposed to the vapor in touch with 1vol% formic acid solution with different pH demonstrated that formicary corrosion occurred when the pH was equal to or lower than 5. These results suggest that pH measurement of condensed water is an effective technique for detecting the potential risk of refrigerant leakage caused by formicary corrosion.
