Why Use Insulated Chilled Water Coil Cabinets in Duct Systems?

Coil cabinets are one of the HVAC world’s best kept secrets. Almost any facility has hot water duct reheat coils in their buildings. They are small (1) or (2) row coils that are approximately the size of the ductwork, and are meant to reheat the air to anInsulated Coil Cabinets acceptable temperature. Although in many cases, these coils cannot be built exactly to the duct size, they are still pretty close because the coil face velocities are usually close to the air duct velocities. Coil velocities are usually in the 600 Ft/min – 1,000 Ft/min range.

So what does any of this mean? This means that if you have 2,000 CFM, a coil is required to be 12” x 24” (2 Sq. Ft – 1,000 Ft/min), or 12” x 30” (2.5 Sq. Ft – 800 Ft/min). The idea is to build the coil as closely to the duct size as possible, while keeping the velocity between 600 Ft/min – 1,000 Ft/min.

What is less well known is that you can also design the same kind of duct coil for chilled water coils. The MAJOR DIFFERENCE is that the face velocity across the coil cannot exceed 550 Ft/min! Face velocities larger than 550 Ft/min will cause water carryover off of a wet coil, and the water is then carried down the ductwork and past any drain pans. This means that the height and length of the coil need to be substantially larger than the size of the ductwork. While this may seem annoying and/or difficult, there really is an easy solution to this kind of installation. Capital Coil builds chilled water cooling sections as cabinets that include the Chilled Water or DX Coil. Capital Coil’s cabinets are fully insulated, and the coil is placed within the cabinet to allow the air to use the coil’s entire face area. The coil is sealed within the cabinet, and there is a stainless steel drain pan that extends to the leaving air side of the coil. Basically, you are only required to hook up the ductwork on the entering and leaving side of the coil section, as well as hook up the piping to the drain connection on the drain pan. This is easily the fastest and most economical method to install any cooling coil system in ductwork.

CCA’s coil sections can be built from 12” x 12” (500 CFM) to 54” x 90” (18,000 CFM). Capital Coil can build the coils in either 5/8” O.D. tubes, ½” O.D. tubes, or 3/8” O.D. tubes. The sizes are custom to match the size of your ductwork, or your CFM. An important point to remember is that allowable duct velocities are much higher than allowable coil velocities, so a transition will be required.

Capital Coil & Air realizes that our customers are looking to upgrade their equipment solutions whenever possible, and if those solutions involve easy installation, then so much the better. Here are some of the main features of Capital Coil’s coil cooling section:

  • 1 ½” flanged connection on the entering and leaving air sides of the coil housing for easy duct connections.
  • 16 Ga. or 18 Ga. galvanized sheet metal housing.
  • 1” insulation with 4.2 R value.
  • 18 Ga. stainless steel drainpan with 1” stainless steel MPT drain connection. The draIN pan is double-pitched.
  • 5” connection sub-outs on all coilS.
  • Chilled Water or DX (Evaporator) Coil custom designed for your application.

All insulated cabinets are available in 3 – 4 weeks, as well as both (5) & (10) day quick-ships. Capital Coil can build double wall insulated or stainless housings if needed. Our sole purpose is to make your job as quick and easy as possible, and there is nothing faster or easier than cabinet cooling coils by Capital Coil & Air. We look forward to working with you on future projects!

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10 Things You Need to Know About Chilled Water Coils

Chilled Water Coil

1. A water coil is a water coil. 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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