Reviewing the HVAC/R Coil Manufacturing Process
Although you may know how commercial HVAC systems work and function, you might not be too familiar with how they are built. You know that the HVAC coils absorb the heat from the air and that a central air system can only operate with both a condenser coil and evaporator coils. Despite this, the process of building a coil is best understood differently. An air conditioning system can only be understood by how indoor and outdoor coils are manufactured on their own, before adding it to the sum of its parts. In this article we’ll cover how the HVAC/R coil manufacturing process works.
1. Start with the Fins
If you are familiar with HVAC/R coils, then you may know that fins are responsible for up to 70% of the heat transfer process. This means that manufacturing fins are a critical part of the coil production process. There are various fin dies that begin by cutting the fins to the proper height, and depth.
The fin die also does four other things while stamping out the fins, ensuring:
- That the edges of all fins are not straight. The leading edge of the fin must be rippled to properly break up the air as it hits the fin.
- The fin will never be flat. Fins are corrugated to ensure air bounces back and forth between the coil, to the front or back. This is known as the V-waffle.
- Tube diameter holes are punched through the fins. This must match the diameter of the tube, as well as how many tubes can pass through the fins.
- A fin collar is punched into the fin to create an air gap between fins. This gap is essential because it is used to space the fins from one another, but also helps connect the tubes to the fins. At the end, all of the fins will be pressed tightly against each fin collar but allow enough air to circulate over the coils and fins for heat transfer to occur.
2. Expansion Process
Once the tubes and fins are connected, it will look closer to what we know as a coil. The fins are still loose on the tubes, so it is essential to create a bond between them. If there is no bond between the tubes and fins, then there will be no heat exchange.
This is where the expansion ball comes in. An expansion ball will be sent through the tubes and there is where it expands the tube into the fins. This is not the only method of expansion, this process can also be done hydraulically as well. Overall, the outer diameter of the tube must be slightly larger than that of the interior diameter. This is the area where 70% of all heat transfer takes place.
If coils are over-expanded, it means that the thickness of the tube wall is too thin. It is essential to keep the tube balanced in diameter and keep the wall uniform.
3. Tubesheets and Casing Installation
Taking the perfectly-sided tube sheets, the casing will then be installed around the coil. This step is required to keep the heavy fin and tube core as one. Casings are typically produced from 16 Ga. or 14 Ga. galvanized steel but stainless steel can be used in special applications.
4. Fully Building the Coil
To finish the process of fully building the coil, all return bends and manifolds will be welded to the tubes. The connection stubs must also be attached to the manifolds to make it fully functional.
5. Testing the Coil
Because even the smallest leak could be detrimental to heating and cooling, the coil will now be tested for leaks. This will ensure the heat pump can connect with the coils, and that cool air flows through as well.
Testing is possible by dropping each coil in a tank of water. All of the connections will be blocked off, then using a compressor the coils are filled with Nitrogen gas to ensure no water gets inside the coils. Coils should be leak tested at 400 P.S.I.G. for indoor or residential coils, and left for 10 minutes to identify leaks.
HVAC/R Coil Manufacturing ProcessExperts
From the air handler to the air conditioner & the coils, all aspects of the HVAC equipment work together. At Rahn Industries we manufacture HVAC coils with the utmost care and detail. We create custom and OEM HVAC coils to meet any specification. Rahn Industries is also a leader in the coating of HVAC equipment and coils creating an antimicrobial layer ensuring a longer life for the equipment. Contact us to learn more about the coils and coat coatings we offer. Contact us today by calling (800) 421-7070 to learn which solution will work best for you and your business.