Why Coils Fail

At Marlo, we go to great lengths to ensure that our coils deliver long lasting performance for our customers. That includes expert design and engineering, high quality materials in heavier weights/gauges than are used by most coil producers, state-of-the-art manufacturing in an ISO 9001 certified facility, and stringent testing procedures before any coil goes out our door.

But despite all these safeguards, coils still fail prematurely way too often. The good news is, all the common causes of coil failure can be prevented with some relatively simple and common-sense steps, including choosing the right coil materials for your application, installing coils properly and performing basic maintenance on a regular basis.

Here are some of the most common reasons why commercial and industrial HVAC coils don’t reach their normal life expectancies, and how early coil failure can be avoided.

Freezing

One of the most common causes of coil failure is freezing. When fluid inside the coil’s tubing freezes, it expands to the point where it can damage or even burst the tube. This can occur in all types of coils, even in steam coils if condensate builds up and freezes. In climates where temperatures fall to near or below freezing, steps should be taken to minimize this risk

For chilled water coils, after the cooling season, coils should be drained completely to eliminate the chance of freezing. If coils are not drained, another option is to add glycol to the system. For steam coils used is cold climates, distributing steam coils should be chosen over standard “straight-through” steam coils. These coils – often call freeze-proof coils – feature a tube-in-tube design that distributes the steam more evenly, eliminating cold spots.

Corrosion

Corrosion of a coil’s tubes can occur when the metal reacts with moisture or other elements in the air. When corrosion is allowed to build up, it will weaken the metal and eventually lead to failure. Regular coil cleaning can prevent or minimize the effects of corrosion. So coils should be inspected often, and any dirt/debris should be removed.

Another source of coil corrosion is exposure to caustic chemicals. This can come from the fluid or air flowing through the coil in industrial processes, or from chemicals in cleaners used in certain environments. This type of corrosion can be easily avoided by choosing corrosion-resistant materials for the coil and/or treating the metals with special coatings. Your Marlo representative can help you choose materials and coatings for your application.

Poor Water Quality

When high-sediment water sources – such as lake or river water – are used in water coils, buildup of dirt and other foreign materials can accumulate in the coil. This buildup restricts the water flowing through the tubes, reducing the efficiency of heat transfer, and eventually causing the system to fail.

The solution in these types of environments is to first choose a coil that allows access to the tubes for cleaning. Marlo manufactures cleanable coils with removable plugs on the tube ends, as well as coils with removable box headers. Both of these coil types can provide long life, even using water with high sediment content, if regular cleaning is performed.

Vibration

Excessive vibrations from HVAC systems can cause wear and tear on coils over time, which can ultimately result in cracked joints, causing leaks. This problem is usually due to improper installation and/or maintenance, so it can easily be avoided. The use of vibration isolators can minimize the effects of vibration, and consistent inspection of HVAC equipment after installation can also help to identify vibration issues.

Marlo coils are particularly suited to environments where vibration can occur. All of our tubesheets have extruded holes which provide a more robust support system for the tubes that support the headers and fin pack. For extreme environments, copper ferules (small “gromets”) can be added to isolate the tubes from any contact with tubesheets.

Incorrect Sizing, including P-Traps and Steam Traps

If coils are not properly sized for the HVAC system and the space it serves, the coils may not be able to handle the load. This can lead to excessive strain on the coils, causing them to fail prematurely. In addition, proper sizing of P-traps and steam traps is also critical to long-term coil performance.

A P-trap is necessary to remove condensate from a coil and prevent air from entering. An improperly sized P-trap can prevent the coil from functioning properly and lead to damage. With steam coils, a steam trap that does not effectively remove condensate can cause “water hammer”, a condition that occurs when condensate builds up and creates pressure surges within the coil, which can cause serious damage.

The Keys to Long Coil Life

Despite all the potential ways a coil can fail, it’s relatively easy to achieve long-term coil performance. First, start with a coil that is design for your specific application, including the materials chosen for each components. Then make sure the coil is installed properly and perform regular inspection and maintenance procedures to get the longest life possible.

As a custom manufacturer of replacement commercial and industrial HVAC coils, Marlo will always make sure you get the right coil for your application!