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 hammers, 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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What Is Meant By A “Bank” Of Chilled Water Coils

For those that work with HVAC installations on a regular basis, you have run across the problem of needing to install new chilled water coils in very tight, confined areas. The coil is too big to fit in the Chilled Water Coilselevator, and/or the HVAC room is so small that you are likely to damage the coil simply by moving it. As a solution to this challenge, chilled water coils are often installed in “banks” of coils. You are most likely to see this configuration in Air Handler Units, as well as “built-up” systems. Due to face velocity limitations across the coil, you will need larger coils in order to meet your required face area. With this in mind, there are a few specific reasons why you want to avoid having a single, large coil in one of your units.  Starting with the obvious: larger coils are much more difficult to transfer and install. This is especially true for older buildings, where the rooms were essentially built around the HVAC system.

As you’ve probably experienced, some of these areas can barely fit a single person, so installation – if even possible – is a logistical nightmare. Also, the larger the coil, the easier it is to damage during transport to the jobsite. To avoid these issues, simply break down the single, larger coil into smaller coils. When piped together, those smaller coils are stacked into “banks” of coils in the system. If installed correctly, this “bank” should have the same performance as the larger, single coil.

Casing

There are many different casing options available, but “stackable” flanges are required for heavy chilled water coils that are “banked”. The flanges are often inverted inward and down to give added strength to the casing, which is needed due to the fact that another coil of equal weight will be stacked on top of it. When ordering coils in a “bank” configuration, be sure to let the manufacturer know that they will be “stacked”.

Many engineers also use stainless steel casings on chilled water coils. While more expensive than traditional galvanized steel, stainless steel protects against excessively wet coils and/or corrosive elements in the airstream. Keep in mind that the majority of coils fail because of old age and its casing, as opposed to failure with the coil’s core. With that in mind, doesn’t it make sense to select heavy-duty stainless steel casings that are more durable and meant for stackable installations?

Drain Pans & Water Carryover

Water Coils

All chilled water coils must be sized so that the face velocity across the coil does not exceed 550 ft/minute. Water on the outside of the coil is carried away from the coil’s leaving air side in an arc, while water in the highest point of the coil is carried further down the unit or ductwork. “Stackable” coils often require intermediate drain pans under each coil to catch the excess water carryover. Each coil in a bank requires its own drain pan, as a single, large pan under the bottom coil is not enough.

Circuiting/GPM

If all of the coils in a “bank” are of equal size and handling the same CFM, then the GPM of each coil will also be the same.

Always feed the bottom connection on the supply header on the leaving air side of the coil. This ensures counter air and water flow. This also prevents the coil from short circuiting because the header fills first and circuits all of the tubes equally.

Designing Banks Of Coils

Almost all coil “banks” perform more efficiently if you design something more square in shape, as opposed to long and/or high. In a “bank” of coils, you may find that one coil has points of 300 ft/minute, with other points at 800 ft/minute. Scenarios such as this will cause water-carryover! You generally want to be as close to 550 ft/minute as possible in order to allow equal airflow distribution across the face area of the coil.

Anytime you are designing and/or building coils, work closely with the manufacturer as an added resource to ensure that you are getting the ideal solution for your HVAC system. Capital Coil & Air works on similar jobs such as these daily, and we welcome the opportunity to work with you in whatever capacity is needed.

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Condenser Coils Failing? Here’s probably why….

Did you recently turn on your DX systems only to find your Condenser Coils are not working?  Simple fix right?  Unfortunately, no.  If you get lucky, you can send us the model number of the unit, and there’s a great chance we’ve already built it.  In the case that we do not have that model number on file, you have two options.  You can go back to the OEM, wait (5) months for a part and pay through the roof.  Or you call Capital Coil, and we’ll walk you through the engineering it takes to replace a condenser coil.                                                                      Condenser Coils

Very rarely do condenser coils ever freeze so the first thing you’re going to want to know is if your coil died of corrosion, old age, or possibly vibration.  Old age is obviously preferable because with a few easy dimensions, we’ll have enough to price up your duplicate coil.  Condenser coils are usually outside and are easily accessible for measurements and digital pictures.  With just the size, the rows, and fins/inch, you can get a price.  And digital pictures of the headers and return bends will give us a good idea of the circuiting and sub-cooler circuits. 

If the coil has been eaten away by corrosion, it was an improper design to begin with.  Most people don’t know that salt in the air will ruin aluminum fins within a year or two.  There are two ways to combat this.  The first option is to make the switch to copper fins and stainless steel casings.  While this will extend the life of your coil considerably, most people are not too happy about the additional cost over aluminum fins.  The second option is to use a coating.  Coatings are the much more popular choice.  They are a fraction of the cost as copper fins and only add (1 – 2) weeks to your lead time. 

When your HVAC coils are installed near a moving piece of equipment, vibration can occur and cause leaks.  The area where these leaks occur is very important and will clue you in to if the problem is vibration.  If they are near the tube sheet and look like they are slicing through the tube, the coils should be isolated from the rest of the system to prevent vibration from causing damage.  One way to combat this is by oversizing the tubesheet holes, but many manufacturers will not do this.  Condenser coils are usually the most common victims of vibration.

The last concern is with cleaning condenser coils.  Since condenser coils see outside air almost exclusively, they need to be cleaned more than other coils.  The reason for this is most condenser coils have fin spacing of 12-20 fins/inch.  With fins that tight together, the coil can and will act like a filter.  And when the coil is clogged up, the performance suffers greatly.  Recently, we’ve been getting more and more calls about using a heavier fin thickness.  This is to help with high pressure cleaning and corrosive cleaning agents. 

When dealing with an HVAC coil manufacturer, partner up with one who will walk you through the engineering and explain it along the way. Capital Coil & Air has well over a decade of experience and has seen every issue to make sure your everything from the quote to the installation go smoothly! Give us a try on your next project!

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5 Work Day Quick-Ships on HVAC Coils – Why Capital Coil does it right

Day 1 – 38% of all orders sent to Capital Coil are on some kind of quick-ship, whether it be on a (5 day, 10 day, or 15 day). We enter the order immediately so that all departments in the plant have the project in their systems and are ready to move on it right away. The coil isQuick-Ships engineered, routing sheets are sent to the shop floor, and everybody now knows what needs to be built. 

Day 2 – Sheet metal casings are cut and sized, headers and connections are fabricated, while tube sheets are fabricated.

Day 3 – All tubing and fins are cut, stamped and assembly begins. You can see what the coil will look like upon final assembly at this point. Coils can be seen sitting on assembly tables.

Day 4 – Tubes are then expanded into the fins, and keep in mind that this is not a short process. Headers are then brazed to the tubes, and if there are return bends, they are connected. The coil is completely assembled and moved to the testing tank. The coil is tested under water for 20 minutes at 550 PSI. About 3% of coils have small leaks someplace in the brazing and are sent back to braze again.

Day 5 – The coil is crated and sent to shipping for routing to the customer. Then most importantly, your coil will be shipping in the guaranteed (5) days.

As you can see by this description, with quick-ships, there is not a lot of room for error in the timing and shipping with OEM HVAC replacement coils. We’ve been doing this for a while now, and we’ve had an approximately (97%) success rate fulfilling all quick-ship requests. We offer quick shipments 365 days per year, with both (10) day shipments & (15) day shipments also available for lower premiums.

diagram 

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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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Fan/Coil Units Without the Mysteries

Lots of companies in the HVAC business attempt to keep their products as complicated as possible in order to lend a certain “mystery” to the industry, which has never made sense to us at Capital Coil. We have all been in this information age for quite some time with more information/data available to more people than ever before. We feel that by removing some of the “secrecies” surrounding fan/coil units, our customers will be able to better understand the products as we do.

Most of our potential customers know Capital Coil strictly for our HVAC coils, which makes sense because the word “coil” is in our company’s name. But some people may not be aware that we do in fact offer multiple fan/coil models with various quick-ship options, or that fan/coils comprise a significant portion of Capital Coil’s overall business.

With that said – what are fan/coil units (FCU’s) exactly?fan/coil units

  • Fan/coils are easy to understand when you remove a lot of the complex terminology. Our definition of a FCU unit is one that is direct drive and not belt driven…easy enough to understand, right? There is a fan, a coil, and sometimes a filter. Capital Coil offers numerous model types, but the only thing that really differentiates the various models from each other is the casing on the outside of the unit. And the casing is typically based on how and where you want to install the unit.
  • The fan is directly mounted on the motor, and the maximum CFM that can be used in these units is typically 1,200 FT/min. However, Capital Coil does offer some units that can have a CFM as high as 3,000 FT/min, or (7.5) tons.
  • FCU’s can be divided into two groups based on airflow – Horizontal and Vertical. Think of fan/coils installed in a hotel or classroom. These are typically vertical units because the air goes from the bottom of the unit to the top discharge airflow.  Horizontal units have horizontal airflow with inlet and discharge both horizontal as well.
  • As mentioned, fan/coil casings are determined based on how and where you want to install the unit. But figuring that out involves asking some additional questions, such as is the unit hidden above the ceiling or is it exposed? Is the unit horizontal or vertical? Does the unit need a filter?
  • Like most any product, there are several “packages” that you can select, such as certain valves, that will make the unit more expensive and complex. But once you strip away the complex terminology and are able to understand the basic design and concept of FCU’s, they are pretty easy to work with.

Now you know that Capital Coil is very much in the fan/coil business, and when you are looking for something fast, Capital Coil should be your first call or email!

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Why are quick-ships so important??

Christmas season is in full-swing, and your current coil supplier has suspended all Quick-Ships with little to zero notice to its customers. Does that sound familiar these days? Additionally, the clock is ticking to complete those projects that need to be done by the end of the year. In this industry, this scenario is when “Quick-Ship” availability is an absolute must. Right now, the vast majority of coil manufacturers are scrambling to complete standard orders on regular lead-times, and if by dumb-luck they are able to temporarily offer any type of expedited build, the added premiums are so astronomical that very few customers can afford to use those options.

If you need a new coil, your first inclination will probably be to call the OEM. But more times than not, they are not flexible or nimble enough to handle your emergency within an acceptable time-frame. Quick-ships are generally based on emergency conditions, and that is precisely the worst time to discover that your regular supplier has suspended Quick-Ships.

So why do so many manufacturers seem to get so overwhelmed at various point every year? In short, many manufacturers take on a glut of OEM business, or other large projects with small profit margins. In many cases they do this simply to keep the factory running during the slower periods of the year. This has the effect of delaying standard lead times, and in many cases, cancelling Quick-Ships altogether. It is very hard to do business with companies that make themselves unavailable when you need them the most.

Capital Coil’s primary duty as the leading OEM replacement coil manufacturer is to fill in those gaps and work with you to help alleviate any emergencies. Whether you need a coil in (3) weeks, or (5) days, Capital Coil has got you covered.

Capital Coil does not try to be all things to all customers, and we’re most comfortable “staying in our lane”. Our #1 goal is to ensure that we have multiple quick-ship options open all year around…even if that means turning away an order to ensure sure that our Quick-Ships are ALWAYS available!!  Quick-ships

Because Quick-Ships make up such a substantial portion of our overall business, Capital Coil has hit 99.9% of our quick-ship requests over the last (2) years. An unfortunate forklift mistake makes up the other .1%. Throughout the first 6 months of 2022, approximately 80% of all orders were/are quick-ships, and they have either all been completed on time, or are 100% on schedule.

An RFQ that sits on a desk unanswered is useless to everyone involved. If you need a quote, you’ll have your price and any required submittals that same day. It really is that simple and easy! Working with Capital Coil will remove many, if not all of the annoying and unannounced shut-downs that come with other manufacturers, so please let us help you when you need it the most!

 

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