HVAC Closed loop corrosion, fouling and loss of heat transfer impacts overall system energy efficiencies. Here is a short list of things that can go wrong:

• Poor combination or isolation of mixed metallurgy
• Insufficient circulation time.
• Insufficient chemical.
• Insufficient dumping of system.
• No dumping …. chemical left in system.
• Chemical never added …. system never cleaned
• No proof of performance report
• Any combination of the above.

Closed loop maintenance begins after construction and pre-cleaning has been completed. The corrosion inhibitors used in a closed loop are designed to protect clean surfaces and do not easily penetrate layers of foulants or corrosion by-products. Maintenance items include adding a corrosion inhibitor to protect the closed systems and changing sidestream filters on a regular basis.

In most cases the system operates without apparent problems for the first 2 to 4 years, depending on the concentration of foulants that could be allowed to accumulate. If side-stream filters are installed and changed regularly, a lot of suspended debris can be removed over time, and closed loop problems kept to a minimum.

However, deposits can collect in the low flow areas of any system and under-deposit corrosion could be occurring. Samples that are always dirty water or samples with high iron or copper counts are obvious indicators that a problem exists.

Over time, coil plugging can affect the low flow areas. Small diameter piping and associated low flows are the most susceptible areas to plug. At this point it is easy to blame the closed loop corrosion inhibitor, but if a proper monitoring program was not implemented right at start-up, a careful analysis will show the condition developed over time because of an Out-of-sight, Out-of-mind attitude towards the closed loop system.

For any closed loop system, always add a side stream filter. Where possible, back-flush the low flow areas on a seasonal basis. On a regular basis, thoroughly analyze the system sample, and when evidence indicates a there’s problem, take whatever steps are available to clean that system and replenish the corrosion inhibitor.