Top 10 Tips For Measuring Coils

1. When measuring 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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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?

Chilled Water Coil

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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Construction Vs Performance: Need To Know Terminology

If you have ever dealt with commercial HVAC coils, you have probably come across numerous “industry terms” with little to no explanation as to what these terms actually mean. To further confuse you, some verbiage is specific to the actual construction of the coil, while others are only important when determining a coil’s performance. If you do not work with coils on a frequent basis, it is hard to decipher what exactly these terms are referring to. To help translate this industry verbiage, Capital Coil & Air has come up with a list/glossary of the most common and relevant terms that you are likely to come across on most coil jobs.

 Performance

  • AHRI (Air-Conditioning, Heating, and Refrigeration Institute): Developed industry standards for air conditioning, heating, and commercial refrigeration equipment. All of CCA’s coils are AHRI-certified, so you know you’re getting dependable quality and performance in every product.
  • Air Pressure Drop: Air Pressure Drop is a result of Flow Rate, Fin Type, Rows and Fins per Inch. In addition, on either Chilled Water or DX (Evaporator) Coils, the air pressure drop is affected by the condensate on the fin surface.
  • Airflow (CFM): Cubic Feet per Minute, which refers to the amount of air flowing across the coil. A typical cooling coil should produce between 400-500 FPM. You want to avoid exceeding 550 FPM on all Chilled Water & DX Coils. Too little airflow means your coil is not running at peak capacity, while too much airflow can result in excess water carryover.
  • Entering Air Dry Bulb Temperature: You guessed it! The sensible temperature of the air entering the coil.
  • Leaving Air Dry Bulb Temperature: The sensible temperature of the air leaving the coil. Why does this matter? If you are trying to replace and duplicate a coil’s performance, making sure that your new coil can meet or exceed the old coil’s leaving air temperature is a crucial factor.
  • Entering Air Wet Bulb Temperature: This temperature signifies the amount of moisture in the air entering the coil.
  • Leaving Air Wet Bulb Temperature: Conversely, this temperature refers to the amount of moisture in the air exiting the coil.
  • Total Capacity: The sum total of a coil’s sensible and latent capacities.
  • Steam Pressure: Only relevant to steam coils, the saturated steam pressure at the inlet of a steam coil. Steam pressure is usually relative to the steam coil’s total capacity.
  • Steam Condensate: Again, applies only to steam coils and is a measure of the condensate generated by that steam coil.

Construction

  • Casing Type: The supporting metal structure for tubes and the header. Different casing options include Flanged (standard), Slip & Drive, Inverted, Stackable, and Collared End Plates & End Plates only. Steam Coils require Pitched Casing to allow for adequate condensation drainage.
  • Casing Material: The coil’s casing can be made from a variety of different materials. Options include: 14 or 16 Gauge, Galvanized Steel; 304 or 316 Stainless Steel; Copper & Aluminum. Please contact us directly to see about options other than those listed.
  • Connection Material And Type: Standard connection types are MPT (Male Pipe Thread, threaded on the outside), FPT (Female Pipe Thread, threaded on the inside), ODS (Sweat Connections, no threads)
    • Water & Steam Coils: Copper MPT, FPT, (with options for steel MPT & FPT)
    • DX & Condenser Coils: Copper ODS normally
  • Circuiting/FeedsCircuiting is determined by the number of tubes in each row divided by the total number of tubes fed (or feeds). Feeds are also known as the number of parallel circuits in the coils. Always feel free to call Capital Coil’s sales department with any circuiting-related questions.
    • Water Coil: Enter the coil’s performance data into CCA’s coil selection program, and select the “auto” sizing option to determine the optimal number of feeds.
    • Condenser Coil: Since the condenser is a rating program only, the user must enter a value for the number of feeds. A good rule of thumb is to have approximately 8 – 15 psi refrigerant pressure drop in the condenser.
    • DX Coil: Enter coil’s performance data into CCA’s coil selection program, and select the “auto” sizing option to determine the optimal number of feeds.
    • Steam: Always a full or double circuit
  • Fin Height: FH is measured in the direction of the fins, or perpendicular to the direction of the tubes.Water Coil
    • For 5/8″ tube coils, fin heights are available in increments of 1.5”
    • For 1/2″ tube coils, fin heights are available in increments of 1.25”
    • For 3/8″ tube coils fins are available in 1.00″ increments
  • Fin Length: FL is always measured in the direction of the tubes, regardless of which direction the tubes are running.
  • Fins per Inch: Represents the fin spacing on the coil. The number of fins per inch is an essential component when ordering a replacement. Using a standard ruler, simply count the number of fins per inch on the coil.
  • Number of Rows: Rows represent the coil depth and are always counted in the direction of the air flow, regardless of how the coil is mounted. Count the number of rows by viewing the header end or the return bend end of the coil.
  • Hand (Left or Right): A coil’s hand is determined by the direction of the airflow. Look at the finned area of the coil, and if the air is hitting you in the back of the head, look to see which side of the coil the headers are located. If the header(s) are located on the right side, then the coil is right-handed. Likewise, if the header(s) is located on the left side, it is left-handed. An important point to remember is that you always want the airflow to run counter to fluids, refrigerant and steam flow.

Miscellaneous

  • Laminar Flow: Tends to occur at lower fluid velocities, below a threshold at which it becomes turbulent. In other words, laminar flow is smooth while turbulent flow is rough. Greater heat transfer occurs in a coil with turbulent flow as opposed to a calm, laminar flow.
  • Dry Weight: The estimated weight of the coil; not counting internal fluids or packaging.

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