Frozen Steam Coils: How Do You Prevent This?

Regardless if you have steam coils or steam distributing (non-freeze) coil, you can freeze ANY coil.  When freezes happen, everyone immediately looks to the steam coil as the cause.  When in fact, there are numerous reasons that must be looked at well before the coil.

Freezes generally happen in older systems, however if your new system is not maintained properly or correctly installed, your steam coil can and will freeze.  For instance, you’d be surprised at how many times dampers are left open, controls fail, freezestats don’t work, etc.Steam Coils

In a Standard Steam or Steam Distributing Coil, a freeze-up can occur when condensate freezes within the tubes of the steam coil.  The two most common reasons for freezing steam coils are the steam trap and the vacuum breaker.  The function of steam trap is to remove the condensate as soon as it forms.  Condensate usually collects in the lowest part of the coil.  If your steam trap isn’t installed properly, that condensate will lay in the coil and it will inevitably freeze as soon as it sees outside air.  The vacuum breaker also helps clear the condensate, minimizes water hammer, and helps with uneven temperatures. This must be installed on the control valve and always above the steam trap.

Unfortunately, there are no ways to determine exactly where your steam coil will freeze.  And a common misnomer is that the condensate turns to ice and the expansion is what causes the tubes of the coil to pop.  In reality, it’s the pressure that builds up between freeze points.

Here’s couple tips in your coil design that can help prevent your standard steam and steam distributing coils from freezing:

  • Standard steam coils should NEVER see any outside air below 40 degrees.  If it does, steam distributing is the only way to go!
  • 5/8” OD Steam distributing coils over 72” long are recommended to have a dual supply
  • 1” OD Steam distributing coils over 120” long are recommended to have a dual supply
  • Make sure your steam coil is pitched if possible.  This slopes the condensate to the return connection making it easier to remove the condensate

Give Capital Coil & Air a try on your next project. Our engineering, pricing and service is the best in the industry!

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Need A Replacement Heat Exchanger/Tube Bundle?

To begin with the obvious, shell & tube heat exchangers consist of a tube bundle surrounded and protected by a steel shell. While the shell can seemingly last forever, the tube bundle inside most certainly cannot. The tube bundle is not attached inside the shell, which means that the bundle can be removed if needed to be replaced. In other words, you can simply replace the tube bundle without having to replace the entire heat exchanger. A good comparison can be found with coils inside Air Handling Units (AHU’s). Due to erosion, corrosion or both, coils tend to fail before the entire AHU and subsequently need to be replaced. If everything is done correctly, the new coil should simply “slide” into the place of the old coil. The same is true of tube bundles in that ideally you want to be able to remove the old bundle, and slide in a replacement with little to no extra work. Capital Coil & Air is here to help you throughout the entire process.

Replacement Tube Bundle

The easiest route to ensure that the correct duplicate is built is to first try to cross-reference the model #. While you may not have that information at your fingertips, there is a very good chance that Capital Coil has already built that specific bundle, and/or has the ability to cross-reference whatever model that you are looking to replace. Simply send us a picture of the tag with the model & serial number, and we will do the rest.

Regarding tube bundles, the most common type of replacement bundle can be found in “U” tube type exchangers. These types of bundles are typically water/water or steam/water exchangers.

Steam/Water Bundles

When looking to duplicate a tube bundle, you HAVE to know the bundle’s correct diameter, as well as the diameter of the tubes in order to duplicate the tube area. Additionally, you must duplicate both the tube length and the flange on the bundle to match it up correctly to the shell.

Steam/Water bundles are rather basic in that water is in the tubes, with steam filling up the rest of the shell. Matching performance is almost never the problem, but matching up the dimensions is PARAMOUNT!!  

Water/Water Bundles

Water/water bundles really only differ from steam/water bundles in that there is now water on the shell side as well. Steam automatically fills the shellside, but water does need to be redirected back & forth across the bundle by a series of baffles that operate on GPM & water velocity. The baffles are also an integral part of the bundle, so if duplicated correctly along with the other physical dimensions, performance will not be an issue.  Once again, physical dimensions are PARAMOUNT!

How Can We Go Wrong?

The surest and most common mistake is not correctly matching up the bundle tubesheet to the rest of the exchanger. The tube sheets must fit between the head and the flange on the exchanger, and the bolt-hole pattern must also be an exact match. The bolts are inserted through all three parts simultaneously, and the pattern should match up with all three parts. Sometimes other tube sheets fit between the head and flange, but are also smaller in diameter. The bolts simply bypass the tube sheet and go around it. There needs to be a concerted effort to ensure that the tube sheet dimensions are correct and not too big. Additionally, the gaskets need to be sized and replaced correctly. 

Capital Coil & Air has an established track record of building tube bundles efficiently and quickly. And, in all probability, we already have information on whatever unit you need to get replaced. Like coils, replacing tube bundles usually has a level of emergency attached to it, so we offer multiple quick-ship options if needed. Please give us the opportunity to work with you on your next project, and let us help to take a lot of the guesswork out of your next project.

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