A corrosive environment must be clearly identified and understood before proper coil protection can be selected.
In addition to proper coil protection, indoor air quality codes and generally-accepted practices must be addressed. Corrosive environments may have a detrimental effect on indoor air quality.
Potentially corrosive outdoor environments include areas adjacent to the sea coast, industrial sites, heavily populated urban areas, some rural locations, or combinations of any of these environments. In air-handling applications, some indoor environments such as swimming pool areas, water treatment facilities, and industrial process areas can produce corrosive atmospheres.
Many emerging HVAC markets have a majority of their populations located in coastal areas. This leads to an increased number of air conditioning applications located in potentially corrosive environments.
Coastal or marine environments are characterized by the abundance of sodium chloride (salt) which is carried by sea spray, mist or fog. Most importantly, this salt water can be carried as far away as 5 miles from the coast. Even if the HVAC equipment is a substantial distance from the ocean, corrosion from salt-water contamination can still occur if the equipment is not properly protected.
Line-of-sight distance from the ocean, prevailing wind direction, relative humidity, wet/dry time, and coil temperature will determine the severity of corrosion potential in the coastal environment. As a result, the following should be considered when the potential for coastal contamination exists:
Is the unit within five miles of the ocean?
Visit the proposed installation sight. Is the ocean visible from the building roof or outdoor mechanical area? If so, the potential for severe coastal corrosion should be expected and appropriate protection is strongly recommended.
Will the condenser coil face the ocean?
If the condenser coil faces the ocean or faces into the prevailing winds from the coast, there is a high probability of seawater contamination. Appropriate protection is strongly recommended.
Is there corrosion on exterior structures, other HVAC equipment, or other equipment with dissimilar metals?
Look around the installation site and surrounding areas. If there is evidence of corrosion, chances are high that coastal corrosion exists and suitable protection is required.
Industrial applications are associated with a host of diverse conditions with the potential to produce various atmospheric emissions. Sulfur and nitrogen oxide contaminants are most often linked to industrial and high-density urban environments. Combustion of coal and fuel oils releases sulfur oxides (SO2, SO3 ) and nitrogen oxides (NOx ) into the atmosphere. These gases accumulate in the atmosphere and return to the ground in the form of acid rain or low pH dew.
Not only are industrial emissions potentially corrosive, many industrial dust particles can be laden with harmful metal oxides, chlorides, sulfates, sulfuric acid, carbon, and carbon compounds. These particles, in the presence of oxygen, water, or high humidity environments can be highly corrosive.
Salt-laden seawater mist, combined with the harmful emissions of an industrial environment, pose a severe threat to HVAC equipment life. The combined effects of salt mist and industrial emissions can accelerate corrosion. This environment requires superior corrosion resistant properties for air-conditioning components to maintain the optimum level of product quality. Complete encapsulation of the coils should be considered.
Highly populated areas generally have high levels of automobile emissions and increased rates of building heating fuel combustion. Both conditions elevate sulfur oxide (Sox ) and nitrogen oxide (NOx ) concentrations. Corrosion severity in this environment is a function of the pollution levels, which in turn depend on several factors including population density for the area.
Any HVAC equipment installed immediately adjacent to diesel exhaust, incinerator discharge stacks, fuel burning boiler stacks, or areas exposed to fossil fuel combustion emissions should be considered an industrial application. Postcoated aluminum-fin coils would offer the best protection in these environments.
Rural environments may contain high levels of ammonia and nitrogen contamination from animal excrement, fertilizers, and high concentrations of diesel exhaust. These environments should be handled much like industrial applications with postcoated coil protection.