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I Need a Replacement Commercial HVAC Coil. Where Do I Start?

Posted by Gregg Fletcher on Oct 13, 2021 8:26:29 AM

As a custom coil manufacturer, we often speak with facilities managers and maintenance professionals about coil replacements, upgrades, and retrofits. These jobs often require us to design a coil for an existing space, which can be tricky if you're not sure what to look for. For this post we’ll explain that process, including:

  • Common size-in-place scenarios for commercial HVAC coils
  • Some best practices when replacing a coil
  • Other important coil replacement considerations

Common Size-in-Place Scenarios for Commercial HVAC Coils

Given the custom nature of our work, the replacement jobs we take on tend to be more involved than standard catalog replacement. Sometimes it’s a school looking to replace an old coil at the end of its life. Other times, it’s a hospital whose coils froze and they’re in need of a quick replacement. But whatever the reason for the failure, when customers call us looking for a replacement coil, it’s usually because they can't find the part elsewhere due to situations like:

  1. The system/unit in question is no longer supported by the original equipment manufacturer (OEM) or the OEM is no longer in business.
  2. Their coil is a standalone or add-on component that’s not part of an original OEM unit.

For option number one, it’s not uncommon for the outgoing coils to have spent 40+ years in service. And technological developments mean that a Trane coil in a 40+ year old system sometimes can’t be replaced with a more modern component.

For example, refrigerant regulations during the lasts 50 years or so have completely transformed how refrigerants are formulated and used in the industry. Many popular refrigerants from the past half century, such as R-22, have been regulated out of production or are in some type of phasedown. Refrigerants like R-22 are considered among the best-performing refrigerants ever developed, and it can be a challenge to replicate their performance using today’s compliant substances.

So, the challenges are:

  • Matching the old coil’s performance with technology available today
  • Fit the new coil within the space occupied by the old coil

Best Practices when Replacing a Coil

While the factors outlined above can pose challenges when working to get a perfect performance replacement, our goal is to get as close as we can. To help us do that, the best first step is getting as much information as possible about the coil and the system.

Once you’ve decided that your current coil needs to be replaces, we recommend getting values for:

  • Working fluid: refrigerant? Fluid? Steam?
  • Air flow
  • Entering air temp.
  • Desired leaving air temp.
  • Desired entering fluid temp.
  • Desired leaving fluid temp.

With the exception of condenser and evaporator replacements – which may require some additional calculation – the above values are good places to start. Additionally, by giving a company like SRC a holistic breakdown of the coil’s requirement, we can then look for any opportunities to gain performance and make recommendations to that end. 

Other Important Coil Replacement Considerations

On our end, there are some important considerations that we examine when replacing legacy coils. Oftentimes, we’re basically reverse-engineering the coil. The information above is what helps us do that, but there are also some unique factors at play with replacements.

Designing according to spatial constraints is a must on our end. We can make a heat exchanger to operate according to the values provided by the customer, but half the battle is designing it to fit within a predetermined space. So, we need to design those replacements with regard to things like:

  • Installation practicality: It’s not uncommon for older systems to have been designed to fit in one space at the time, and that space has since changed. Things like updates to adjacent equipment, or system upgrades can mean leave very little room to operate in a facility’s equipment room.

So, just because a coil is designed to fit into a predetermined space within the system doesn’t mean it can necessarily get there. It’s important to consider both the spatial constraints of the coil and the path it will take to get there.

  • Connection sizes and locations: This also related to the practicality of the replacement’s installation. Our coils must be designed for compatibility with existing connections.
  • Dimensions of headers and other elements: In the past, cast iron was a popular choice for header material. They’ve since fallen out of favor due to durability concerns, but they often had a smaller profile than modern copper headers, sitting flusher against the fin pack.

If we designed a replacement with the same header dimensions, the coil likely wouldn’t meet the system requirement. So, we would need to make up that performance gap in another way. Usually that means adding some height to the coil’s face area when possible, or using a fin enhancement to improve heat transfer. However, both actions will have an impact on air friction, which might necessitate adjustments to other equipment in the system (fans, motors, pumps, etc.). Check out our guide on fin enhancements for more details.

If you’re looking for a replacement coil and aren’t quite sure what you need, give us a call. Our replacement experience runs deep and we take pride in being able to get you set up with the part you’ve been looking for.

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