In my previous blog post I said we would take a more detailed look at each of the elements in the 6 step process I suggested for addressing corrosion issues in HVAC equipment.

1. Identify the corrosion mechanism.

2. Understand the environment, both external and internal.

3. Understand the equipment - materials of construction, operating cycles, hours.....

4. Identify alternatives - materials, coatings, limiting operating envelope, changing the environment (water treatment, alternative lubricants/refrigerants, filter the air, etc.), redesign the machine (better drainage, eliminate contact of dissimilar metals, .....)

5. Implement change.

6. Monitor results.

In that last post I went on to address step 1, so now the time has come to look at step 2:

2. Understand the environment, both external and internal.

If we consider that the purpose of step 1 in this process was to determine how things are failing, the purpose of the next couple of steps is to determine why things are failing. Understanding the environment an air conditioner or heat pump operates in is usually pretty straightforward, but there are pitfalls, particularly as that environment relates to corrosion failures. Particularly with outdoor equipment, the operating environment often is not constant. The temperature, prevailing winds, pollution levels, chemical discharge from surrounding buildings, etc., etc. vary over time.

Since many corrosion failures take a significant length of time to occur, the operating environment at the time of failure may not be the same as the operating environment that caused the failure to initiate. Even with indoor equipment the operating environment changes with time. Take the example of an indoor coil in a heat pump; in the cooling mode, the coil is wet and that is when corrosion initiates. When the heat pump switches over to heating, the coil dries out, corrosion stops or at least slows down, but the operating pressure in the coil increases and often that is when damage that occurred during the cooling season causes refrigerant leaks to occur.

The process I like to use in assessing the environment that HVAC equipment operates in is the following:

1. Be observant. Look at the condition of other equipment in the vicinity of the HVAC, is it corroded? Are there chemicals stored nearby? Do you smell anything strange? Are there residues on the equipment?
2. Ask questions. Ask the service personnel about what they have observed in the environment. Ask about other failures. Ask about cleaning/maintenance practices and chemicals that are used. Ask about neighboring businesses, what they produce and what they discharge into the environment.
3. Gather historical data, not just a one time snapshot. If you obtain water quality data, for example, get a years worth, not just from the time of the failure. If you gather air quality samples, do it over time, not just once. If you are assessing a work environment, talk with employees about what chemicals they use in doing their jobs.

Just like all the other steps in this process, the better job you do in understanding the operating environment for the equipment, the better prepared you will be to find a robust, cost effective solution to the corrosion problems you are experiencing.

Editor's Note: CR4 would like to thank PJ Sikorsky, PE for contributing this blog entry.