The Advantages of Micro-Channel Coils
Back in the summer of 1986, I was teaching a series of classes to the engineers and quality-control people at Carrier Corp.’s residential air-conditioning plant in Collierville, TN. As I was covering the subject of condenser coils and the advantages of their then spine-fin all-aluminum coils, one of the engineers spoke up and pointed out that Carrier was dropping the design, going back to the manufacture of traditional copper-tube aluminum-fin coils. This disturbed me, and it resulted in my second-ever published magazine article (published in The ACHR News that year), “The Death of the Aluminum Coil.”
Later on at a winter meeting, I met up with the then-president of Carrier Corp., and he asked me what I had in mind by writing such an article. So I explained to him: Joining dissimilar metals (as in copper to aluminum) creates electrolysis, which results in a constantly deteriorating bond and degrading system efficiencies.
Then he told me that they had to make such a change to remain price competitive, because the price of aluminum had risen so much higher than copper back then. And I suggested: “Then, why don’t you manufacture a copper-tube copper-fin coil?”
The then-president turned to his head of engineering (who was standing immediately behind him) and asked: “Why don’t we do that?” And the head of engineering replied, “Because our conveyor belts couldn’t handle the extra load.”
So much for my one chance to change the industry.
First, in addition to the fact that such coils will hold their efficiency longer, micro-channel coils can be significantly smaller and still allow for high-efficiency designs. And with the recent legislation requiring minimum A/C efficiencies of 13-SEER, most standard copper-tube aluminum-fin have gotten much larger, which many customers are objecting to. So, other than going to micro-channel designs, the only other choice is to make coils deeper, making them harder to clean.
Another advantage of micro-channel coils is that all the exterior aluminum parts are zinc coated, which makes them even more reliable; and since zinc is a natural anti-microbial, micro-channel evaporator coils will be less prone to grow molds and bacteria. However, the zinc coating was not designed for this purpose, but to allow the aluminum parts to be assembled and soldered.
What I think will be the kicker, which will eventually lead to widespread industry adoption of this design, is that these coils are simpler and less costly to manufacture.
But what if aluminum prices start rising higher than copper? Might I again suggest going to all-copper coils? Or would that be too much of a burden on factory conveyor belts?
I just want to point out that a dear friend disagrees with my view about the industry success of micro-channel coils. He is concerned that the extreme narrowness of the refrigerant channels will tend to solidify circulated lubricants, especially in heat pumps in far-northern locations - but time will tell.