Top 10 Hints for Replacing Tube Bundles in U-Tube Exchangers

There are basically three kinds of shell and tube heat exchangers:

  • “U” Tube heat exchangers where it is possible to remove the entire bundle
  • Fixed tube heat exchangers where the tube sheet are welded to the shell and stationary and the bundle is not removable
  • Floating tube heat exchangers where one tube sheet is fixed and the other floats axially.  This tube bundle is also removable.
  1. The shell for this type of shell & tube exchanger can/will last just about forever. However, the copper tube bundles located inside will often need to be replaced. The idea here is to slide the old bundle out and replace it with a new bundle, using the least amount of labor possible.
  2. One very important question to ask is which types of tube bundles are replaceable? “U” tube bundles and straight tube bundles with “floating tube sheets” can be replaced, while fixed tube sheet bundles must be re-tubed rather than replaced.
  3. Replacing a bundle is pretty straightforward and easy. Simply slide the bundle out and measure the overall length (including the tubesheet). Keep in mind that the bundle’s OAL will always be several inches shorter than the shell’s OAL. Tube Bundles
  4. The next step is to determine the size of the tubes in the bundle. While the vast majority of bundles have ¾” OD tubes, it is possible to have ½” OD, 5/8” OD, or 1” OD.
  5. Next, decide on the tube thickness that you need. Thicker tubes will last longer, but will obviously be more expensive. Typically ¾” tubes will have a .049” wall thickness, but you can easily upgrade if needed.
  6. Including tube supports or baffles, the number of tubes in the bundle should always be the maximum number that you can fit inside the shell. If you are not sure of the # of tubes, contact us, and Capital Coil can tell you the maximum number.
  7. You also want to make sure to count the tube supports or baffles on the length of the shell. While tube supports only serve to keep the bundle together, baffles actually direct the fluid on the shell side to go back & forth across the bundle. If you are unsure which is which, tube supports run the complete circumference of the bundle, while baffles are generally staggered and look to cover only a portion of the tubes.
  8. The only real way to not get the bundle correct is if the tubesheet is not duplicated correctly. First, measure the thickness of the tubesheet. ¾”, 1”, 1 ½” are examples that you’re likely to see.
  9. Next, you want to determine the number of bolt holes, as well as the center to center distance of the bolt holes. Doing this basically determines the bolt hole pattern. The bolts are responsible for connecting the head and the tube bundle to the shell, so they all must match up exactly! But, please also keep in mind that it is possible to have no bolts in the tubesheet as the bolts then bypass around the tubesheet.
  10. Lastly, every bundle has a number of passes that create fluid which runs through the tubes. That fluid will ultimately end up back at the same end. (2) pass, (4) pass, or (6) pass are among the most common. Gasketing and head design determine the number of passes.

 

Replacing a bundle is pretty easy, and it should take you approximately 15 minutes to gather all of the necessary information. But if you happen to run into any difficulties, please call us here at Capital Coil & Air, and we’ll help walk you through everything. We have the capability to build almost any kind of bundle of various construction types and different tube materials. Please give us a try on your next project as we want to be your go-to resource for all bundle replacements.

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Different Types of Steam Coils

There are two types of steam coils:  standard steam coils, which are used in most reheat applications, and steam distributing coils, which are used in applications where the entering air temperature is below 40 F degrees.  Many times, this type of coil is also known as a “non-freeze” coil, but that name is misleading because in reality, there is no such thing as “non-freeze”. 

Standard Steam

Standard steam coils operate a lot like hot water coils, but the construction is very different even if the coils appear to be constructed the same.  The supply and return connections are often on the same end like a hot water coil.  But, steam is very different than hot water, and the coil must be built for and circuited for steam.  Keep in mind that steam is always more erosive than hot water.  The brazing and tube wall thickness must account for steam. ALWAYS remember that even low pressure steam is more erosive than hot water, and a steam coil needs to be built accordingly.

Steam Distributing (Non-Freeze)

Steam distributing coils are a completely different type of coil because they are constructed as a tube within a tube. Every place that you see an outside tube or header, there is an inside tube and header that you can’t see. The steam on the inner tube keeps the condensate in the outer tube from freezing.  The purpose of the Steam Coiloriginal coil design was to distribute the steam evenly along the length of the coil and to eliminate any dead spots on the coil.  A byproduct of this coil was also found.  The coils didn’t freeze nearly as easily as the standard steam coil, so the coils became known as “non-freeze”, which as mentioned, is not completely accurate.  Any coil can freeze under the right conditions, but, this design is what needs to be used when the entering air is under 40F degrees!!! 

Steam Coil Design

Steam coil designs can be very tricky.  Steam coils are totally a function of the system and installation, while other coils operate more independently of the system.  There needs to be correctly designed traps, and they need to be installed in the correct place and depth in the system.  Often, vacuum breakers are also needed in the system.  The piping must also be installed correctly to make sure the steam is entering the coil and not the condensate.  Even with all of those factors, you’ll need a correctly designed steam coil that matches the steam pressure, length of the coil, and the entering air temperature.  Coils can freeze easily.  Coils can be too long in length and the steam cannot travel the length of the coil and distribute evenly.  Condensate can easily be trapped somewhere in the coil, and the result is water hammer. 

Capital Coil & Air has years of experience designing steam coils, and is here to answer any questions and help to design the right coil for your project! 

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HEATING SEASON WILL SOON BE UPON US

 

Hot Water Coils & Heating Season

The real ability and competency in selecting hot water coils or any other heating coil is to know and understand the products that are available. Our goal here is to help simplify your selection process. Just as you’d spend time researching cars before a purchase, you want to be as educated of a buyer as possible!Hot Water Coil

HOT WATER COILS

The HVAC industry classifies coils as “Hot Water” if they are (1) or (2) rows deep, and “Chilled Water” if the coil is (3) to (10) rows deep. One important fact to remember is that whether the water is hot or cold, a water coil is still just a water coil. Just because you do not need as many rows for hot water applications, all water coils are built the same. Tubes can be 5/8 ” copper or 1/2 ” copper, and water can travel through the coil’s tubes at temperatures up to 200˚F. Capital Coil’s selection program is very user-friendly and can greatly assist in your selection process.

STANDARD STEAM COILS

While steam coils look very similar to water coils, the construction and circuiting of the coil are usually very different. Specifically, the brazing for the tubes and headers has a higher percentage of silver solder in the brazing. The tubes are generally thicker (.025”), and the circuiting of the coil minimizes the passes to allow for easy condensate removal. Unless you have (2) PSI or (5) PSI steam, hot water coils and steam coils are not interchangeable! Steam pressure is extremely important to take into account.

STEAM DISTRIBUTING COILS  “NON-FREEZE”

The construction of a “non-freeze” coil is completely different than that of a water coil or standard steam coil. Steam Distributing coils are manufactured as a tube within a tube. This application should always be used when the entering air temperature on a coil is 40˚F or below. There are (2) types of designs for steam distributing coils. They can be constructed with 5/8” (outer-tube) / 3/8” (inner-tube)  &  1” (outer-tube) / 5/8” (inner-tube).  A Capital Coil sales rep is always available to help with proper selections.

HOT WATER BOOSTER COILS

Hot water booster coils are primarily used in duct applications for reheat purposes. In addition to hot water, booster coils can also be used for low pressure steam. The best part is that Capital Coil has a standard (1) week lead time for booster coils. We value speed and quality as much as you.

Capital Coil manufactures all of the above for whatever heating application you may need. All coils are also available on our quick-ship program – if you need your coil built in 3, 5, or 10 days. Capital Coil & Air welcomes the chance to work with you, and be your source for quick answers and immediate service. Please give us a call on your next project!

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