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HVAC advice about evaporator coils.

Posted by savdbigrace (huntspatch@gmail.com ) on
Sun, Feb 23, 14 at 20:00

I need feedback primarily from those of you working in the HVAC field. I'm about to replace a gas pack unit and in the course of my research am finding a lot of complaints about evaporator coils leaking. Several local HVAC contractors have confirmed what I've seen online as well : an industry wide problem with evaporator coils leaking coolant, primarily due to "Galvanic Corrosion" in copper tube & aluminum fin assemblies. And, as a result of this corrosion wherever the two dissimilar metals are joined, the need for costly repairs or in many cases complete replacement. I have read about the all - aluminum evaporator coils in T's "Spine Fin" design and the " Micro - Channel" units by Nord.( which only came out in 2010). Are these all - aluminum assemblies proving more durable in the field than their copper/aluminum counterparts? Or are they prone to leakage also and or to other repair or maintenance problems as well? And, is there another option I've not mentioned that addresses this? Please be as explicit and detailed as possible. I know many other homeowners are grappling with this as well and need your expert advice - like me - to make an informed decision. So, please help and thank you up front.


Follow-Up Postings:

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RE: HVAC advice about evaporator coils.

The all-aluminum coils are relatively new so, unfortunately, it will be another 5-10 years before any real conclusions can be drawn (there were some all-aluminum coils back in the early 80s but there weren't enough for a reliable assessment and they were probably a very different beast from those becoming available today).

In addition to the galvanic corrosion form dissimilar metals used in the coils, there is formicary (acidic) corrosion which was thought to be exacerbated, at least in part, to the recycled copper used in coils over the last 10+ years. This is primarily what the all-copper coils are trying to get around.


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RE: HVAC advice about evaporator coils.

Thanks sktn77a for the response. Am I to understand from your reference to "all copper coils" that they are still mated with an aluminum fin? I guess I'm hoping for a truly radical shift in material technology used to address this problem. I noticed for example a site out of India offering stainless steel evaporator coils! I'm sure it would last much longer. Whether it would sufficiently dissipate heat or even be affordable would be interesting to know.


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RE: HVAC advice about evaporator coils.

I have never seen evidence that pack coils experience anything split system coils don't nor that al fins on cu tubes cause inordinate problems. I would be interested to hear why a coil would be more pron to failure when used on a pack as apposed to split.
Offhand I see three important advantages copper has over aluminum. Better heat transfer and better resistance to work hardening from vibration then cracking. And copper is far easier to repair in the field if the need should arise.


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RE: HVAC advice about evaporator coils.

Thanks sktn77a for the response. Am I to understand from your reference to "all copper coils" that they are still mated with an aluminum fin? I guess I'm hoping for a truly radical shift in material technology used to address this problem. I noticed for example a site out of India offering stainless steel evaporator coils! I'm sure it would last much longer. Whether it would sufficiently dissipate heat or even be affordable would be interesting to know.


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RE: HVAC advice about evaporator coils.

The problem with using materials other than aluminum or copper is that they are expensive and have high thermal coefficients of heat transfer. The higher SEER ratings required by law are forcing manufacturers to use these materials to achieve a SEER specification.

I have also read that copper coils are failing because they are made from recycled copper. The copper coils of 30 years ago where thicker and made from virgin copper. They rarely failed.


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RE: HVAC advice about evaporator coils.

"This is primarily what the all-copper coils are trying to get around."

I did, of course, mean all-aluminum coils!

:)


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RE: HVAC advice about evaporator coils.

Thanks for your input klem1. None of the people I've spoken to or heard from disagree that copper probably has the best properties. But several sources - like the americancoolingandheating.com article -"Aluminum Condensing Coils vs. Copper Coils..." made these qualifiers : " Galvanic corrosion is common in all copper tubing. To remain competitive (due to high copper costs), new (HVAC) units are shipping with substandard quality coils. The thinner the copper, the more difficult it is to repair." And of course, the thinner the copper the more quickly corrosion and acids can create pin holes and leaks. The thin gauge tubing - like sktn77a pointed out earlier, the use of recycled copper - are likely the biggest factors. Compare that to the 32 yr.old gas pack I'm replacing. I don't recall it ever loosing coolant or requiring a recharge of R22 freon. The gauge was much,much heavier & more durable than today.


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RE: HVAC advice about evaporator coils.

My friends I'm convinced that there is a problem of evaporator/condenser durability in HVAC equipment made in recent years until now. The question is: What is the industry doing to rectify it? We've talked a bit about the aluminum alternatives - Spine Fin and Micro - Coil. But as sktn77a pointed out, it may take some time to know their reliability. Yesterday, I came across several articles that talked about Pre-Sealers (at manufacture) and Post-Sealers(after manufacture) which were applied to the coil/fin assemblies. They ranged from baked on chemicals & E-Coat (electrocoat) - as Pre - Sealers, to sprayed on Silane and one using polyurethane with metal pigmentation - as Post -Sealers . All were said to help seal the coil/fin assembly from oxygen and corrosion (both galvanic and formicary types) - without significantly dampening heat transfer. And the E-Coat, through testing, was found to hold less air born dirt. Does anyone know of any manufacturers currently utilizing sealers in their condensers and evaporators ( meant for the homeowner market) as a means of addressing the corrosion problems we've discussed? Any info or expertise you could share about them would be great. And if so, mabey you could abbreviate the names or Email me directly - so they won't get censored out here!


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RE: HVAC advice about evaporator coils.

There has been a problem and the industry is addressing it by changing their coil designs. Carrier introduced the tin plated copper coil a few years ago and now is moving to an aluminum coil. I highly doubt sealers are being added but others may know better than me.

I rarely buy extended warranties, but for HVAC equipment I recommend home owners consider purchasing extended factory warranties. It only takes the labor charge of one coil replacement to pay for the warranty.


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RE: HVAC advice about evaporator coils.

"It only takes the labor charge of one coil replacement to pay for the warranty."

Ain't that the truth!


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RE: HVAC advice about evaporator coils.

Good advice mike_home about the warranty. I'll definately be looking at extending coverage on both parts and labor. It's interesting to hear Carrier is opting for aluminum. I saw an article on Wikipedia titled : "Copper in Heat Exchangers". Scrolling down to Thermal Conductivity it reads as follows : Silver - 247.87, Copper- 231, Gold - 183, Aluminum - 136. So copper is 59% more thermally efficient! Stainless steel - by the way - came in 7th @ 8.1! Easy to see the industries reluctance to change. That means that by whatever design - Micro - Channel , Spine Fin, etc. they will have to make it up in surface area to have equal efficienciy - right?


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RE: HVAC advice about evaporator coils.

Thanks to everybody for your generous input. It would appear that the current trend is shifting away from traditional copper/aluminum condensers and evaporators to all-aluminum ones. Now I have to make a decision on whos design best offers those otherwise elusive qualities of durability, reliability and affordability. I understand Trane started producing their aluminum Spine Fin design back in 1968. I guess they are "the standard" for comparison at this point. If anyone has anything else to add - I'd like to hear from you. Otherwise, I'll bring this thread to a close.


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