Selecting a proper coil replacement takes some effort on behalf of the servicing contractor to first determine what exactly is needed. A replacement is most often required because of simple formicary corrosion or excessive exposure to salt environments. All coils experience some degree of corrosion at varying times in their life.
The first thing to do is to determine what type of coil needs replacing: basic water, booster, standard steam, steam distributing, condenser, or direct-expansion evaporator.
The next thing to do is start measuring the coil to be replaced. You can obtain blank coil drawings from manufacturers, such as Colmac, where all you do is simply measure the coil and fill in the blanks on the data sheet drawing.
Having this in hand takes you step-by-step through the coil and all of its characteristics, including the materials of construction and critical dimensions.
Next, take some digital pictures of the coil from as many different angles as possible. If you happen to be missing any information when you get back to the office, you can then refer to the photos and identify the missing information. Pictures are especially helpful for the more custom coil that might have some special features in its construction.
Once you’ve gathered the physical measurements and taken some pictures, you should ask yourself the following questions:
“Is this the best coil for the application? Can I add engineering value to improve performance, prolong life, or to improve the ease of installation?”
Some common things to look for to value engineer a replacement coil are:
1. Tube Thickness:Thicker, heavier weight tubing translates into longer coil life.
2. Casing:A common solution for a corroded casing is to use a stainless steel casing as a replacement. Other options include galvanized steel, aluminum, or copper casings.
3. Ferrules:Sometimes adding ferrules to the coil tube sheets is another option that greatly extends the life of a coil. A ferrule is a small copper collar that is placed around the tube where the tube passes through the sheet metal (tube sheet) and prevents the tube from rubbing on the sheet metal and therefore over time causing a leak at that spot on the tube. Ferrules are commonly used on steam coils where the coil tubing experiences a great deal of expansion and contraction during operation.
4. Tube and Fin Materials:Sometimes tube and fin materials are incorrectly specified for a coil environment. For example, aluminum fins should not be exposed to a marine atmosphere because this environment will corrode an aluminum fin. A copper fin is more suitable for this application. Sometimes a coil might need to be constructed of stainless steel tubes, or cupro nickel tubes, etc.
5. Coatings:Offering a surface treatment such as a heresite or electrofin-type coating is another option you can offer for the coil that is experiencing severe corrosion.
6. Circuiting:You may be able to improve coil performance by taking the time to review circuiting. For example, a water coil performs best when circuited for counter flow circuiting.
The proper circuiting of coils ensures the correct fluid velocities in the coil tubes. Fluid velocities that are too low result in poor heat transfer. Tube velocities that are too high can lead to premature failures from velocity erosion.
7. Configurations:Try to determine if the old and new coils will fit through the existing hole in the cabinet. Installation of the new coil is sometimes easier if you design it as a stack of two smaller coils. Another option is to replace the coil with two smaller coils placed side-by-side. Smaller coils are generally easier to handle and install; this will save the installer time and money.
As you can see, it is easy to add value to a replacement coil by taking a technical approach and offering your customer some of these options. Generally you’ll find this is a great way to solve a problem for your customer and keep them calling you for all of their replacement needs.
Publication date:01/29/2007
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