Why are HVAC Coils Copper Tube and Aluminum Fin?

Chilled Water CoilsIt’s really not a coincidence why HVAC coils use copper tubes and aluminum fins. Copper is great for heat transfer, and aluminum – while still very effective -is simply not as good. The first goal of any HVAC coil is to cool or heat. Heat transfer is always the first consideration. Cost is the second. Copper works well for the tubes, but would be prohibitive for the fins. You would need a compelling reason for the fins to be copper, and sometimes there are reasons to do just that. However, the vast majority of HVAC coils that you see are built with copper tubes and aluminum fins. That combination offers the most effective heat transfer at the most efficient cost. 

To begin, fins are responsible for a surprising 65% – 70% of the heat transfer on any coil, while tubes are responsible for the remaining 30% – 35%. Additionally, in order for your coil to work at optimum performance, you need to have a terrific fin/tube bond. Fins are known as secondary surface, while tubes are referred to as primary surface. While this may seem counterintuitive, the secondary surface is responsible for twice the amount of heat transfer as the primary surface.

The tubes are expanded into the fins, and for that reason, the fins become secondary. As mentioned above, the fins are responsible for 65% – 70% of all heat transfer that takes place in the HVAC coil.  When you think about it logically, it really makes sense. At 8 fins/inch or 10 fins/inch, and with fins that run the height and depth of the coil, there is much more fin surface than tube surface. However, it also points out how good the fin/tube bond must be in the expansion process. Without that bond, the fins cannot perform their job.

Understanding the role and importance of the materials used in HVAC coils cannot be overstated. There is a distinct reason why the vast majority of coils are constructed using these materials. While coils can be built with other tube materials, such as steel, 304/316 stainless steel, 90/10 cupro-nickel, as well as various different fin materials, none of these are as efficient or economical as copper/aluminum.

Capital Coil & Air is here to help you with any and all coil selections, and we look forward to working with you on your next project.

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Chilled Water Coils – Circuiting Made Easy

Chilled Water Coil

Circuiting chilled water coils is one of life’s great challenges in the coil business. You’re bound to run across folks with years of experience in the industry that can not effectively explain this concept. While not the most exciting of subjects, the necessity of circuiting chilled water coils can not be overstated. Capital Coil & Air has attempted to simplify the idea of circuiting as much as possible.

For starters, circuiting chilled water coils is ultimately up to the performance of those coils. Circuiting is really a balancing act of tube velocity and pressure drop. In other words, think of a coil as a matrix. Each coil has a specific number of rows, and a specific number of tubes within each row. For example, a chilled water coil might be 36 inch fin height and 8 rows deep. The coil has 24 tubes in each row, and multiplied by 8 rows, there is a total of 192 tubes within the coil. While you can try to feed any number of tubes, there are only a few combinations that will work.

    • Feeding 1 tube – you will be making 192 passes through the coil, which will essentially require a pump the size of your car to make that process work.
    • Feeding 2 tubes – equates to 96 passes, and your pressure drop will still be enormous.
    • Feeding 3 tubes – 64 passes, which is still too many.
    • Feeding 4 tubes – See above.
    • Feeding 5 tubes – Impossible as 5 does not divide evenly into 192 (passes).
    • Feeding 6 tubes – Still constitutes far too many passes, which again leads to additional pressure drop.
    • Feeding 7 tubes – Same rule for feeding 5 tubes.
    • Feeding 8 tubes –  Same rule for feeding 6 tubes.
    • Feeding 24 tubes – This feed consists of 8 passes, which is in the ballpark, and with a pressure drop you can live with.
    • Feeding 32 tubes – 32 tubes will see 6 passes. You might see a slight decrease in performance, but it’s off-set by a continuously better pressure drop.
    • Feeding 48 tubes – The magic combination, as 4 passes typically elicits the best performance and pressure drop simultaneously.

 

Rule #1: The number of tubes that you feed must divide evenly into the number of tubes in the chilled water coil.

Rule #2: The chilled water coil must give you an even number of passes so that the connections end up on the same end.

Rule #3: Based on the number of passes, you must be able to live with the resulting pressure drop. Acceptable tube velocity with water is between 2 and 6 ft. per second.

You’re bound to run into different terminologies depending on the manufacturer. More times than not, the different verbiage confuses more than it clarifies. However, understanding the basic tenets of chilled water coil circuiting will remove much of the perceived difficulty.  

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Are Your Quick-Ships Shut Down When Needed Most???

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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OEM Replacement Coils: Repair or Replace???

When considering OEM replacement coils, there are multiple reasons why coils can fail prematurely. Sometimes, OEM Coils simply freeze and can never be repaired. Other times, the coil was selected incorrectly, which in turn, made the coil significantly underperform. Many times, there is substantial corrosion or something else in the system that causes the coil to fail. However, most coils, when selected correctly, and in systems that are properly maintained, can last anywhere from 10-30 years!  10-30 years is also a pretty wide range, and there are many variables in how long you can expect a coil to perform. Factors, such as ongoing maintenance, air quality, and water/steam quality all have an effect on a coil’s lifespan.

OEM Replacement Coils

Reasons Why Coils Fail Of Old Age

  • While the coil’s tubes are considered the primary surface, 70% of all coil performance is performed by the finned area on a coil, which is known as the secondary surface. The fin/tube bond is easily the most important manufacturing feature in any coil. Without the bond between the tubes and fins, the coil could never properly function. Like all things however, over time the fin/tube bond becomes less efficient with constant expansion and contraction. While the construction of the coil, as well as the fin collars, does not allow the fins on the coil to move, that fin/tube bond naturally weakens a coil’s life over time after installation. Because of this, it is not a stretch to say that a coil is easily 30% less efficient after (20) years.
  • Cleaning coils often pushes dirt to the center of the coil, and this occurs even more so on wet cooling coils. Just remember that coils can become great air filters if not properly maintained. The BTU output of any coil is in direct proportion to the amount of air going through the coil. If you decrease the CFM by 20%, you are also decrease the BTU’s by 20%!
  • Cleaning agents often corrode aluminum fins. Since every square inch of fin surface matters in performance, corrosion of the fin surface is always detrimental to the coil’s performance.
  • Many times, there are coil leaks simply because of old age. No coils are immune to erosion. You might find the brazing in the tubes, as well as the brazing in the header/tube connections failing over time. Steam can be both erosive and corrosive under higher pressures. Water travels through the coil at 2 – 5 ft/second, so erosion is an enormous part of coil failure, regardless of how well-maintained. Erosion is always there, whether you realize it or not.
  • Water/steam treatment and the corrosive effects of bad steam/water can all be causes of coil failure…which then necessitates the need for a reliable manufacturer for OEM replacement coils.

So What Is The Solution?

Some coils can last 5 years, and some coils can last 30 years. As you have read, there are numerous factors that contribute to a coil’s life. In the end, there will most likely have been multiple attempts to repair that coil to make it last as long as possible. The depressing news is that most of these “Band-Aid” attempts do not work well. The most likely outcome is that you are buying a new coil anyway, so why waste the time and money on a temporary solution?

Coil failure is a “pressure event”, which is a fancy way of saying that a coil is leaking. We’ve listed some of the most common repair methods that you are likely to come across:

  • Drop leaking tubes from the circuit: Keep in mind however that every dropped tube reduces the coil’s performance by triple the surface area of the tube that is dropped. Again, while ok in the short-term, this is simply another “Band-Aid” fix. Over time, your energy costs will rise exponentially, and you will probably end up buying a new coil anyway.
  • Braze over the existing braze: As mentioned above, erosion has caused the original braze to fail, so all that you are really doing is pushing the pressure to another braze, which will then begin to fail as well.
  • High Pressure Cleaning: This method bends the fins, further restricts the airflow, and pushes dirt more to the center of the coil, which can never be adequately cleaned.

The real reason why coils need to be replaced rather than repaired is due to energy costs. If your coil is not operating near desired levels, you’ll need to increase the energy to make it work at its peak performance. Energy increases might be slight at first, but they are guaranteed to continue to rise over time. For example:

  • Somebody adjusts the fan drive for higher speeds, higher CFM’s and higher BTU’s.
  • Someone adjusts the boiler; the water and steam temperatures are higher.
  • Someone adjusts the chiller (1) degree higher for colder water to the chilled water coil.

Whichever method is used, performance begins to suffer and adjustments to the system occur. These adjustments cost energy efficiency and ultimately, money!

If you have ever experienced repairing a coil, then you know it is labor intensive and typically will not work as a permanent solution. With very few exceptions, repairs should be seen as nothing more than temporary until you’re able to replace that coil!

Capital Coil & Air has seen every “repair” method used, as well its inevitable outcome, so instead of putting yourself through that, call Capital Coil and allow us to be your coil replacement experts.

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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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Top 10 Chilled Water Coil Facts

Every Chilled Water Coil selection is about balance. Your coil selection balances the rows/fins versus the cost of the coil pressure drops/performance. Trying to cut corners on your initial selection may save you money upfront, but you will inevitably pay it back down the line through added energy costs. This is a truism for every manufactured coil.

  1. Fins cost less money than rows/tubes. A good cost-cutting tool when selecting a coil is to choose 14 fins/inch. This will turn your (8) row coil into a (6) row coil, which will dramatically lower your costs. If you choose to go this route, one thing to keep in mind is that 14 fins/inch will be semi-inconvenient to any maintenance crew tasked with cleaning the coil. Don’t expect a Christmas card from them that year.
  2. That raises the question of whether or not you can even clean a deep (6) or (8) row coil? In short, you can, but it is not easy. Chilled water coils are especially difficult to clean because they are almost always wet. Due to this fact, they typically attract dirt and additional particles that other coils do not. Generally, when cleaning a coil, most of the dirt get pushed to the middle, and for that reason, 14 fins/inch may not be the best idea after all. Chilled Water Coils
  3. Did you know that fins do approximately 70% of the heat transfer in a chilled water coil, while the tubes are only responsible for the remaining 30%? This is precisely why the fin/tube bond is so important. Without a perfectly crafted fin/tube bond, coils become inefficient very quickly. You pay for that inefficiency through increased energy costs.
  4. How long does a coil last? At what age can I expect my coil to fail? Unfortunately, there is no single answer to either question. Everything is dependent on a combination of maintenance, duty, and numerous other factors. If your initial selection was correctly chosen, and proper maintenance was kept, 15-20 years is a good timeframe.
  5. You may have a situation where your coil is 20 years old, and everything appears to be operating in good condition. There are no leaks and all looks ok. However, over that length of time, what you don’t see is that the fins have thinned and are no longer bonded to the tubes, and the coil is dirty in places that you cannot see. Again, while the coil may look to be running in top form, it’s probably only running at 60% capacity. Most likely, the tubes have also thinned over time, so when the next deep freeze occurs, you can guess the likely outcome.
  6. You really need to replace the coil, but have been told to make do with the current coil? To make up for the lack of efficiency, you might try to “jury-rig” your system. One method is to change the drive on the fans to deliver more CFM. This increases the air pressure drop, which in turn increases motor brake horsepower. Another option to help increase the coil’s efficiency is to lower the temperature of the chilled water from the chiller. We tend to mess with the system and apply temporary Band-Aids, when replacing the coil is the only guaranteed long-term solution.
  7. If you want to spend money wisely on a chilled water coil, simply make the tubes thicker. The tube thickness for a 5/8” tube coil is .020” thick, so increase the tube thickness to .025”. The same applies for a ½” tube coil, with a tube thickness of .016”. Increase it to .020”. By doing this, you get the added bonus of making your return bends thicker, which also helps to extend the life of the coil.
  8. Not quite sure about circuiting on a chilled water coil? You are going to have a hard time making an accurate selection unless you understand how to circuit a coil. Circuiting is really nothing more than selecting the number of tubes that you want to feed, and how many passes the water makes through the coil – depending on your GPM. Circuiting is one of the most important factors in ensuring that your coil is running at peak-performance.
  9. Curious about the balance between cost, size, materials, and maintenance? Every chilled water coil needs to be maintained for its entire life-span. If you’ve made your selection, and something seems off about the coils, chances are mistakes were made during the selection process. Some indicators include the coil being too big for the space allowed, or incurring out of control energy costs. What is the point of saving $500 on a chilled water coil if you have to spend $5,000 in maintenance over its life-span?

As coil replacement experts, we run into this issue every day. Our goal is to work with you to ensure your selections are correct the first time. The person in charge of budgets will be grateful to you over time. Capital Coil & Air welcomes the opportunity to work with you on your next coil project! We want to be your coil replacement specialists.

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Why Are Fin Designs On HVAC Replacement Coils Important?

Replacement HVAC Coils

At first glance, fin designs on HVAC replacement coils seem about as exciting as watching grass grow. “Why would I ever care about fin designs on any coil” was probably your initial response to our question. Nevertheless, we would not dedicate a newsletter to this subject if fins were not important.

One of the primary reasons fins are so important is that you want to keep your coil as clean and maintained as possible. In order to properly maintain your coil, you need to have an understanding as to how HVAC replacement coils are constructed. While fins do not look like much, they are MUCH more complicated than what you can observe at the entering or leaving airside of the coil.

To begin, fins are responsible for a surprising 65% – 70% of the heat transfer on any coil, while tubes are responsible for the remaining 30% – 35%. Additionally, in order for your coil to work at optimum performance, you need to have a terrific fin/tube bond, (which we will discuss below).

  1. Fins are known as secondary surface, while tubes are referred to as primary surface. While this may seem counter-intuitive, the secondary surface is responsible for twice the amount of heat transfer as the primary surface.
  2. There are special dies (see picture) that stamp out aluminum or copper fins with the correct thickness, height, and depth to make the coil the correct size. For example, a coil might be 36” (height) x 96” (length) x (8) rows deep x 8 fins/inch.
    1. Fin Height: 36”
    2. Fin Depth: 12”, (8) rows deep
    3. # of fins in the coil: 768 (8 fins x 96”)
  3. Each fin has 192 holes stamped in the fin for 5/8” OD tubes (8 Rows x 24 Tubes), and each fin is identical.
  4. Each hole has extruded metal, which is more commonly referred to as the fin collar. The collars are sized to self-space the fins and allow for later expansion of the tube into the fin collar. This practice is also known as “bonding” and is essential to having your coil run efficiently/correctly.
  5. Each fin is rippled at the entering and leaving edge of the fin to help create air turbulence.
  6. Each fin is corrugated in the direction of airflow to allow for greater air turbulence. This is important to remember because turbulence creates heat transfer.

So again, what is the point of understanding the importance of fins in HVAC coils? While coils can be built with flat fins for various reasons, the vast majority of coils are built with enhanced fins. Enhanced fins help to ensure that the airflow is not running straight through the coil.

Regardless of fin type, keep in mind that HVAC coils can and will act as great “filters”. The tubes are staggered and not in-line; while the fins are designed to help break up the airflow and not facilitate an easy, straight-through air path. Dirt and/or other particles in the air get caught easily, which again, is why coils can act as great filters. Additionally, coils with more rows will usually get dirtier than coils with less rows. Lastly, chilled water or DX coils are typically wet coils, which results in them catching virtually everything in the air.

The amount of BTU’s through any coil is in direct proportion to the amount of air through the coil. For example, if you are only getting 90% of the design air through the coil, then you are only getting 90% of the BTU’s.

Coils require good filtration and periodic maintenance. If not done correctly, you’ll pay the price of higher energy costs on an inefficient coil.

By now, you have hopefully come to the realization that HVAC coils are much more complicated than they appear, and that fins are an integral part of the coil as a whole. Again, while admittedly not the most exciting topic, understanding the role and importance of fins in HVAC coils cannot be overstated. Capital Coil & Air is here to help you with any and all coil selections, and we look forward to working with you on your next project.

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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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Chilled Water, DX (Evaporator) Coils & Moisture Carryover

Moisture carryover is present on DX (Evaporator) Coils or Chilled Water coils where dehumidification happens.  Many people do not think it’s a problem…until you have moisture running down ductwork or spewing all over the inside of an air handler. If you’ve ever experienced that then you probably know all of these rules regarding moisture carryover.

  • Entering air temperatures of 80/67 of return air in the Northeast carry far less moisture than an outside 95/78 entering air temperature in Florida. Outside air always has more moisture. Chilled Water Coil

    Your location plays a part as well. The drain pans will absolutely have be sized differently. Florida’s will be much larger in size.

  • Fin design is irrelevant when it comes to moisture carryover. Whether you have copper corrugated fins, or aluminum flat fins, plate fins or even the old fashioned spiral fins, none of it has any effect on moisture carryover.
  • Lastly, be careful when installing a new chilled water or DX (Evaporator) Coils in a system. Many end users like to increase the airflow on older coils because those old coils can act like filters, the fins are covered in dirt/dust and you’re not getting the same airflow through the coil. This dirt on the coil also semi-prevents moisture carryover. When that brand new chilled water coil is installed, the airflow might be higher than that 550 ft/minute and that, of course, will cause moisture carryover problems. 

Please give us a call with any questions about your coil, your system or its design. Capital Coil is here to help you avoid situations like the one described in this post, and we would love for the chance to work with you!

 

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Chilled Water Coil

1. Hot or chilled water coils are still water coils. There is really no difference between hot water coils and a chilled water coils in construction. Hot water coils are usually 1 or 2 rows and chilled water coils are usually 3 to 12 rows deep.

2. The vast majority of chilled water coils are constructed from either 1/2″ OD tubes or 5/8″ OD tubes. A lot of that depends on the tooling of the original equipment manufacturer and what is more economical. Either size can be used and substituted for each other, which makes replacing your coil that much easier.

3. 1/2″ Tubes are on 1.25″ center to center distance. 5/8″ tubes are on 1.5″ center to center distance. For example, if a chilled water coil has a 30″ fin height, there will be (24) 1/2″ tubes per row or (20) 5/8″ tubes per row. The tube area of the coil is remarkably the same. They are almost interchangeable.

4. The quality of the coil often times is directly tied to the tube thickness. Many installations have water not treated properly or tube velocities that are too high. There are few perfect installations in real life. Increasing the tube wall thickness on a chilled water coil is a great way to ensure longer life.

5. Fins make great filters! Of course, they are not designed to be filters, but it happens. You can make any coil cheaper by making them 14 fins/inch with less rows rather than 8 or 10 fins/inch. Just remember that deep coils are very difficult to clean. Cheap is not the way to go most of the time!

6. Fins are designed for maximum heat transfer. They are much more complicated in design than they appear to be when looking at the chilled water coil. They are rippled on the edge to break up the air. They are corrugated throughout the depth of the fin. The tubes are staggered from row to row and the fin collars are extended. All of this to maximize heat transfer. Unfortunately, the byproduct of this is the fins can end up being great filters. Be careful in the design of any chilled water coil.

7. Fins are aluminum for a reason! They give you great heat transfer at an economical cost. You need a compelling reason to switch to copper fins as copper is very expensive, and you’re likely to double (or maybe triple) the cost of the coil. Coatings are popular for this very reason.

8. Many chilled water coils are built with 304 stainless steel casings. The casings are stronger, they last longer, they are stackable, and it’s fairly inexpensive. After all, what is the point of building the best coil possible and have the casing disintegrate over time around the coil? Sometimes, it’s money well spent!

9. Circuiting the coil is the tricky part of any coil. Circuiting is nothing more than the number of tubes that you want to feed from a header. There are two rules. You must keep the water velocity over 1 foot/second and below 6 feet/second. 3-4 feet/second is optimum. The second is the number of tubes that you feed must divide evenly into the number of tubes in the coil.

10. Replacing  your chilled water coil is easy. Rarely do you have to worry about the performance. When you replace a 20 year old coil, it is dirty and the fin/tube bond is not good. The coil is probably operating at 1/2 of its capacity at best. When you put a new coil on the job, your performance will automatically be terrific. Your main concern is now making the sure the coil physically fits in the space allowed. And always have this in the back of your mind: Smaller is always better than too large. Smaller you can always work with, whereas too large makes for a very ugly and expensive coffee table.

There you have it – everything you need to know about chilled water coils. Interested in learning more, please reach out to Capital Coil & Air! We look forward to the opportunity to be your coil replacement specialists!

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