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Why Are Variable Refrigerant Flow Systems Breaking Down at a Faster Rate?

Shannon Ramey, PE, CFEI

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Oct 3, 2019

Last year, students and faculty at a large high school in Oregon arrived for the day and found themselves in an ice-cold classroom. All over the school, rooms were either overheating or completely devoid of any warmth. After only six years in service, eight of the twelve heat pumps for conditioning the school were shut down. Based on advice from their local representative and external consultant, school officials sued the installing contractors for replacement of the heat pump systems for the entire school. However, they didn’t want to replace in kind and worried about the equipment failing again. An investigation was needed to determine why these failures were occurring, and what to do next.

For over 100 years, water-based HVAC systems have been used for cooling and heating most large buildings. More recently, VRF (Variable Refrigerant Flow) systems with central heat pumps are being installed where water-based systems were once utilized. These refrigerant-based VRF systems are starting to see higher failure rates – systems that should be lasting decades are breaking down five or six years after installation. Why is this happening? And what can be done?

The Difference Between Water-Cooled and Refrigerant-Cooled Systems

The old water-based systems used hot and cold water, requiring two different systems to provide heating and cooling. That meant lots of pipes, coils, fan units and ducts. The new refrigerant-based concept only requires one system that heats and cools the refrigerant. Many buildings are adopting the new system because it’s cheaper, more flexible and more efficient.

Typically, the tubing system in the new refrigerant systems is made of copper. In some instances, however, aluminum tubing has been used to keep costs down. The aluminum tubing needs to be assembled with mechanical connectors, which have been shown to be unreliable in many installations.

HVAC Corrosion

Now, for a little science. Aluminum is a reactive metal that can corrode when it touches a different kind of metal such as steel, the material used to fabricate mechanical connectors for aluminum tubing. A reaction called galvanic corrosion will occur and will cause the aluminum tubing to corrode.

Another reaction called chemical corrosion is a common cause of failure in these refrigerant-based systems. Like a cold glass of water on a table, pipes carrying cold refrigerant will experience condensation. Foam insulation, usually containing chlorine, is used to limit condensation and associated water damage. However, the condensation can leach chlorine out of the insulation and cause the aluminum piping to corrode.

In both reactions, the corrosion eventually leads to holes in the aluminum tubing that allow refrigerant to leak. When the refrigerant leaks out, the heat pump stops performing. Since compressor oil leaks out with the refrigerant, just replacing the refrigerant without fixing the leaks causes further loss of oil and ultimately, failure of the heat pump compressors.

Symptoms and Resolution

You’ll notice a couple things if your system is leaking:

  • Certain rooms won’t get heating or cooling
  • Error messages and alarms in the HVAC control system
  • Frequent service calls
  • Occupant complaints

Usually misdiagnosed, small leaks can wreak havoc for years before the situation becomes critical. Repair costs and temperature complaints rise. Eventually, it’s evident that expensive repairs are needed on a relatively new system. The owners will look to the contractors to correct the situation, either through warranty or litigation.

We investigated the VRF systems at the Oregon high school and proposed a scope of work to the parties involved for the proper way to have the system repaired. Knowledge about the cause of the failures established a course of action that the parties could agree to. After settlement, the school retained us to help implement the repairs and make the systems operational.

We’re experts in investigating all types of mechanical failures within buildings and helping you determine the root cause, reach out to learn more.