Top 10 Tips For Measuring HVAC Coils

1. When measuring HVAC coils, performance has very little to do with accurately measuring for replacement coils. Fitting the coil in the existing space with the least amount of labor has everything to do with measuring a coil.  If you duplicate the coil in almost every respect, the performance will match and take care of itself.  New is always more efficient than old.

2.  If you’re ever in doubt about a dimension, smaller is always better than bigger. You can always “safe off” around any coil as long as you can fit it in the space.  If a coil is too big, it makes a really ugly coffee table in your shop.  Too big is the enemy of measuring coils.

Chilled Water Coil

3.  The fin height and fin length are not the determining factors in measuring a coil. The overall casing dimensions are the most important, and you work backwards to determine fin dimensions.

4.  The depth of any coil is the total casing depth in the direction of airflow. The height is the number of tubes high in any row.  Depth is a function of rows deep and height is a function of tubes in a row.

5.  Overall length (OAL) is not the fin length and it’s not the casing length. It is the length from the return bends to include the headers that are inside the unit.  Again, it is necessary to work backwards to get the other dimensions once you know this critical dimension.

6.  Circuiting is the number of tubes connected to the supply header. Generally, you just want to count the number of tubes connected to the header and that will tell you whether it’s full, half, or even a double circuit.  It does not matter how the return bends are configured.  Your goal is to count the number of supply tubes and all performance is based on that.

7.  Fins are measured in fins per inch. Hold a tape measure up to the coils and count the number of fins in one inch.  If you can’t get in to take the measurement, a safe rule of thumb is 10-12 fins/inch.  That will work on almost every coil.  The exception to that rule is a condenser coil.  14-16 fins/inch on a condenser coil is usually pretty safe.

8.  Connection locations are difficult only if you are using the existing piping in the system (which are welded). Copper piping is brazed and can be changed easily.  If a system is old and the piping is being replaced as well as the coil, the connection location is not a major deal.  It’s very easy to match up!

9.  With replacement coils, the concept of “left hand vs. right hand” doesn’t actually exist. Connections are “top left-bottom right” or vice versa.  Ideally, all coils should be counter-flow which means that the water and air flow in opposite directions.  The air hits row one first and the water is piped into row eight first.  However, there are lots of installations that are piped backwards, and they work just fine.  Just match them up, and the coil’s performance will be equal to the old coil.

10.  Connections are not measured from the top of the header! They are measured from the top of the casing to the centerline of the connection.  Or the bottom of the casing to the centerline.  You need a point of reference, and the header height can be anything just as long as it doesn’t stick above or below the casing height.

 

All of the above “suggestions” or “secrets” are in no particular order.  They are just things that you should know to ensure that you are selecting the correct replacement coil. While most seem like common sense, your best bet is to talk with the sales team at Capital Coil & Air, who can walk your through the entire process and help you to fill out coil drawings when trying to measure the dimensions.

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Why are HVAC Coils Copper Tube and Aluminum Fin

HVAC 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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Guidelines For Air Velocities

The height, length and resulting air velocities greatly figure in everything in determining the size and performance of a coil. Step # 1 in determining the size and performance of a coil is dependent upon understanding face & air velocities of air across the coil. Whether you use CCA’s coil selection program to help size the coil, or you are replacing an existing coil; the height, length and resulting velocity determine everything.

Hot Water Booster Coils

air velocities

Every coil has a specific, optimum velocity, so you want to make sure you are within 30% (+ or -) of that number. For example, booster coils have an optimum velocity of 800 ft/minute. That means that you can drop your velocity to 600 ft/minute, or conversely, increase the velocity to 1,000 ft/minute. The duct velocities are almost always higher, which means that you will need to transition to a larger coil. Try to get to as close to 800 ft/minute as possible, while sizing your coil to make the transition as easy as possible. Everything with coils is a balancing act.

Hot Water & Steam Coils

Like booster coils, hot water and steam coils should also have face velocities at approximately 800 ft./minute. Both steam & hot water coils have only sensible heating, which is why their face velocities can be the same. Face velocities ultimately control the coil’s cost, so 800 ft./minute really is a heating coil’s “sweet spot”.

If you are purchasing an air handler unit, oftentimes the heating coil is smaller than the cooling coil because the face velocities on heating coils can exceed those of cooling coils. Due to water carry-over, cooling coils cannot exceed 550 ft/minute, while heating coils only deal with sensible heat.

Chilled Water & DX Coils

Due to the limited face velocities of cooling coils, your choices are more limited. With cooling coils, your face velocity must be somewhere between 500 ft./minute-550 ft./minute. Remember that when dealing with cooling coils, you are dealing with both sensible and latent cooling, so the coil is wet. When you exceed 550 ft./minute, water carry-over occurs past the drain pans.

If you are purchasing an air handler unit, you probably will not have worry about the coil’s face velocity as most coils come pre-sized at the acceptable face velocities. Fan coils also come pre-sized with the correct CFM’s. However, if you are replacing an existing cooling coil, the face velocity must remain at or below 550 ft/minute!!

 Air Stratification Across The Coil

Air does not travel equally across the face of a coil. If you were to divide a coil into (9) equal sections, like a tic-tac-toe board, you would see a high percentage of air travelling through the center square, rather than the corner squares. In a perfect air flow scheme, 11% of the air would travel through each of the 9 squares, but that is not what happens. Because more air travels through the center of the coil, you want to avoid putting a fan too near the coil. Due to central air flows, most systems are draw-thru, rather than blow-thru. This is also why you want to avoid installing your coil near any 90 degree angles/turns in the ductwork. Avoid any situations that contribute more than the “natural” air stratification to help ensure your coil is at maximum efficiency.

In some situations involving cooling coils, you will have water carry-over even when the coil is sized correctly. How can this happen? Think about the tic-tac-toe board again. Air velocities are exceeding 700 ft./minute in the coil’s center, while the corners are around 300 ft./minute. This cannot and will not work.

Coils do not have any moving parts. They simply react to the air across the outside of the coil and whatever is running through the inside of the coil. Coils are 100% a function of your entire system, as well as the installation in general.

Capital Coil & Air is here to help with any coil selections that will help avoid costly missteps that lead to wasted time and money. Call us on your next project, we greatly look forward to working with you!

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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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How to make your HVAC OEM Replacement Coil Buying Process Easier??

Roughly 100% of HVAC OEM replacement coil shipments use some kind of trucking company or common carrier. There are occasions when the shipment is small enough to use UPS or FedEx, but the vast majority of HVAC shipments are sent by way of truck. Anyone who has frequently used freight companies has experienced damaged shipments and/or late arrivals. In our industry, these annoyances and inconveniences are typically written off as “the cost of doing business”. Think of the airline industry as an example. Our expectations have been reduced to point where we expect something to go wrong and are pleasantly surprised when the trip is smooth from start to finish.

Many folks might not know this, but even before the pandemic struck, the trucking industry in general had been experiencing a gross shortage of drivers throughout the country. Some estimates have put this shortage of drivers as high as 50,000 throughout the country.

So what does this shortage mean for the HVAC industry? Put simply, it translates into complications and confusion for all involved.

  • Longer delivery times. For example, a delivery that used to take (3) days is now (5-7).
  • One major reason for the longer delivery times is that trucks now have many more stops than in years past. There are also many instances of more trips through connecting terminals as well.
  • More time on the truck usually equates to both “visible” and “hidden” freight damage.
  • The shipments become harder to track, and with fewer people at the trucking companies doing more work, shipments can and will get lost entirely.

Because the freight process is at the very end of the OEM replacement coil buying cycle, Capital Coil & Air has developed some simple strategies for the entire buying process that should help in avoiding many of the annoyances listed above. We’ve also added a very useful “hint” to counter longer freight delivery times.

  • Getting a price, delivery & accurate proposal from your vendor: Capital Coil responds to every quote request quicker than any of our competitors, and we are always willing to put that claim to the test. A (2) day delay in receiving your quote is the same as a (2) day freight delay on the back end.
  • Receiving your submittal drawings in a timely fashion: You need to approve these drawings, so once again, how is a (2) day delay in receiving approval drawings any different than receiving your order (2) days late?
  • Quick-Ships: As you’ve probably experienced numerous times in the past and/or present, other coil manufacturers seem to be consistently shutting down their quick-ship programs with little to zero notice for the customer. Why is this? Many manufacturers take on a glut of OEM replacement coil 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 NEVER shuts down our quick-ship programs, and we emphasize NEVER! Over the last (2) years, CCA has hit approximately 99% of all quick-ship orders.

  • Crating equipment to minimize freight damage.OEM Replacement Coil
  • Shipping on time: Simply put, we consistently ship when we say we’re going to ship.
  • Select a freight carrier that delivers to your area without interlining or stopping at several terminals: This is when freight damage is most likely to occur!
  • Pay the carrier fee for a guaranteed delivery date: Although seemingly not well-known, most carriers offer a guaranteed delivery date for a fee of $50-$100. Paying the fee will ensure that your order is now a “priority”, and most freight companies schedule deliveries based on these “priorities” first. If both your order and delivery are critical and time-sensitive, Capital Coil can help you with exploring these delivery options.

Capital Coil & Air will work with you throughout the entire buying and shipping process because you as the customer, deserve to work with a hands on manufacturer that will not turn its back on you once the order has been placed. Please give Capital Coil a try on your next project!

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What Does “Splitting” DX (Evaporator) Coils Mean

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“Splitting” DX (Evaporator) coils is one of the toughest concepts to understand in the coil business. “Splitting” the coil simply means that (2) or more compressors can operate off of the same coil. One obvious advantage, or reason that you might “split” DX (Evaporator) coils is that you can shut down (1) of the compressors when the cooling load does not require it. This in turn saves energy, which saves $ when the cooling load is not operating at maximum design conditions. For example, let’s use a coil that is designed to give you (40) tons, but the coil is split so that (2) 20-ton compressors are feeding the same coil. If you only require ½ of the maximum load on any given day, you can shut down (1) compressor completely and operate the other one at 100%. This is a money-saving feature that you need to be aware of if you deal with DX coils on a regular basis. This requires special circuiting arrangements, and this is where the confusion starts with most folks. There are three primary ways to deal with this:DX (Evaporator) Coils

FACE SPLIT

Splitting the coil is nothing more than putting (2) completely separate fin/tube packs (coils) into one common casing. When you hear the term “face-splitting” a coil, you are drawing a horizontal line from left to right across the face of the coil and dividing the coil into a top and bottom half. It is like having two separate coils in one casing in that each half is circuited by itself. You hook up (1) compressor for the top half, and (1) compressor for the bottom.

In practice, this configuration is no longer used with much frequency because this arrangement leads to air being directed across the entire face of the coil. This disadvantage is especially apparent when only one half of the coil is in use because you’ll need a complicated damper/duct system to ensure that air is only directed to that portion of the coil in operation.

Row Split

“Row splitting” a coil is dividing the coil by drawing a line vertically and putting some portion of the total rows in (1) circuit, while putting the remaining rows in the other circuit. With this configuration, the air passes across the entire face of the coil, and will always pass across the rows that are in operation.

Please be aware that this configuration also comes with certain issues in that this kind of split makes it very hard to achieve a true 50/50 split. Let’s use an (8) row coil as an example. You would like to “row split” this coil with (4) rows/circuit, which would appear to be a perfect 50/50 split. The problem here is that the first (4) rows, located closest to the entering air, pick up a much higher portion of the load than the last (4) rows. In actuality, this coil’s split is closer to 66% / 34%, which will not match the 50/50 compressors. Another option is try to split the coil between (3) & (5) rows. While not 50/50 either, this configuration is closer. However, a new challenge arises because you have now created a coil that is very difficult to build and correctly circuit. In short, you need almost perfect conditions along with a degree of luck to achieve a true 50/50 split using this method.

Intertwined Circuiting

The most common to split coils today is to “intertwine” the circuiting. This means that every alternate tube in the coil is included in (1) circuit, while the other tubes are included in the (2nd) circuit. For example, tubes 1, 3,5,7,9, etc. in the first row are combined with tubes 2, 4, 6,8,10, etc. in the second row. The same tubes in succeeding rows form (1) circuit. You are essentially including every alternate tube in the entire coil into (1) circuit, which (1) compressor will operate. All of the remaining tubes not included in the first circuit will now encompass the second circuit.

The advantage of this configuration is that the air passes across the entire face of the coil, and, if one of the compressors is on, there are always tubes in operation. Every split is now exactly 50/50 because it cannot be any other way. Most DX coils are now configured in this manner due to these advantages.

Capital Coil has been, and will remain, the most reliable source for all commercial and OEM replacement coils. Our #1 job is to make to your job easier, so please reach out. You will be glad you did.

 

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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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Tips on Hand Designation & “Counter-flow”

Are your chilled water coils right hand or left hand?  Are you looking into the face of the coil with the air hitting you in the back of the head?  What exactly is counter-flow and why is it important?  Are you completely confused by why right hand vs. left hand even exists?  Most manufacturers probably do not know or understand the technical reasons themselves.

First, let’s figure out what coils even need a hand determination.  Chilled Water Coils, Direct Expansion (Evaporator) Coils, and Condenser Coils are the only coils that need this figured on almost every job.  Hot Water Coils, Booster Coils, and Steam Coils rarely need this determination!  The reason for this is when the coils are only 1 or 2 rows deep, they can be flipped over.  When a chilled water coil is 3+ rows deep, hand determination is much more important because it needs to be counter-flow.  With most suppliers determining hand designation with the air hitting you in the back of the head….do you want the connections on the right or left?

Chilled Water CoilsYou’ve probably heard the term “counter-flow” countless times, but here’s the simplest explanation.  For peak performance, you want the air and the fluid traveling in opposite directions through the coil.  Is it the end of the world if your coils are not counter-flow?  The short answer is no, but you will lose approximately 5% of the output.  So if your coils are piped incorrectly, don’t expect to get the full performance, but they will still be more effective than whatever you’re replacing.  Steam and hot water coils are 1 or 2 rows deep, so again, counter-flow is pretty much irrelevant.  However, it can make a difference with any chilled water or direct expansion coils (3-12) rows deep.

We also get asked many times “what is the proper way to pipe coils?”  Put simply, steam coils should always be fed on the highest connection and the return on the lowest connection.  Water coils should always be fed on the lowest connection and returned on the top connection to ensure that all of the tubes are are fed the same volume of fluid. 

Hand designation and counter-flow are two pretty simple concepts when they are properly explained.  When dealing with a 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 in handling pretty much any scenario that you may come across, so we want to be your coil resource for any and all projects. Please give us a try on your next job!

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You should never have to worry about performance on replacement coils…Well, almost never!

 

Coils and Counter-flow: 5 Common Questions

1)  Coils and counter-flow?

The first thing to remember about coils and counter-flow is that chilled water coils are always built to be piped in counter-flow. This means that the air flows in the opposite direction as the water. For example, with counter-flow, the air flows through rows 1-8, while the water runs through rows 8-1. Water always travels through the coil in the opposite direction of the air; hence the term “counter-flow.”  Direct Expansion Coils (Evaporator Coils) are also piped in the same manner.

With that said, what happens when you do not pipe cooling coils counter-flow? Almost all coil selection programs you will see or use will be based on counter-flow conditions. If you opt to not counter-flow a chilled water coil, you’ll have to reduce the coil’s overall performance by a certain percentage. That percentage reduction varies based on each coil’s unique dimensions, but a reliable estimate is a loss of 8-12%. Simply piping the coils in the correct manner from the beginning would seem to be the easiest and most cost-effective solution.

2)  Why do you feed from the bottom of the coil?

DX Coils

You always want to feed a water coil from the bottom connection so that the header fills from the bottom on up and feeds every tube connection evenly. All tubes must be fed evenly with the same amount of water. If you try to feed the header from the top, you greatly increase the risk of “short circuiting” the coil and having a higher water flow through the top tubes in the coil.

3)  What is a Water Hammer in a Steam Coil?

On a long Steam Coil, you will be hard pressed to get the steam through the length of the coil. Slowly but surely, that steam converts into condensate, which is pretty much the worst thing that can happen to any system. If not evacuated, the condensate just lays in the coil when the system is shut off. This problem comes into play when the steam is turned back on and meets the condensate laying inside the coil. In addition to the noise, the steam and condensate cause huge amounts of additional stress on the coil’s joints. As a result, over time, your coil will inevitably fail.

4)  What else happens if you do not evacuate condensate?

When you cannot or do not evacuate the condensate on long steam coils, the condensate ends up blocking the steam. A steam coil should never feel cool to the touch, but when condensate blocks steam, one part of the coil will be warm while the other will be cool. Again, that should not happen. Steam coils are interesting in that they are more dependent upon the system and installation than any other type of coil. A steam coil must be pitched to the return end of the coil. Obviously, steam is not water. Traps, vacuum breakers and other steam accessories must be installed and located properly for the system to function.

5)  Is it necessary to pipe steam and/or hot water coils in counter-flow?

Simply put – no! Circuiting a coil is only necessary to ensure the connections are on the side of the coil that you want. The rows and tubes in the coil dictate how and where you feed, but the steam supply always needs to be the high connection. This method ensures that the leaving condensate is on the bottom of the coil and below the lowest tube within the coil. Whatever else you do, know that the condensate must leave the coil!

If you have any questions or need assistance with ordering and/or installation, please contact a sales engineer at Capital Coil & Air. We will walk with you step-by-step through your entire project should you require any assistance. CALL OR E-MAIL US!  We look forward to the opportunity to work with you on your future projects.

 

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