Hey there Brian this episode's about microchannel coils. You probably knew that because it's in the title, but before we get into that, need to mention our great sponsors first off. I want to mention refrigeration, technologies, refrigeration technologies, makers of wet rag, Viper nigh log, the pan and drain spray, a lot of really good stuff. I really like refrigeration technologies.

You can find out more by going to refridge tech comm and when you're at the counter. At your local supply house next time ask them to consider stocking the refrigeration technologies products, also Mitsubishi Electric cooling and heating uei in the hub, smart kit, the hub six hug for and hub two smart kits. You can find out more by going to Yui. I test comm and you can find those products at true tech tools: comm TR, you, tech tools, comm arrow Asus makers, of the bipolar in Nano and I've mentioned this before, but I would encourage you to go on to their website.

Go to arrow, Asus comm /go. That's our special hvac school forum and fill out the information there, and that way you can figure out where you can get the product you can find out. The pricing get some support locally for your contracting company. Even if you're just a technician, you can still go on there and get some information because they also have a program where you can get some products at a very discounted price for your own use.

So you can try them out and see how they work. Ask about that on there and again, if you use that form they'll know you came from me. They'll know you came from HVAC school, that's arrow, Asus, comm /go for some great indoor air quality products. Also, I want to mention biz pal org, my friend Patrick long.

If you're looking for a technician, that's the place to go biz pal org, he uses some really fancy tools in order to get your job posting out there for the world to see and then finally carrier carrier, longtime sponsor the podcasts makes it possible big thanks to Carrier for all their support, so let's talk about micro, channel, coils, micro, channel coils have a pretty bad rap and some of its deserved there's definitely been some issues with micro channel coil. So let's talk about what a micro channel coil is in the first place, because you may have heard of it and not really even know micro channel coil is kind of like a car radiator. It's basically the same idea. Instead of having separate tubes for refrigerant to flow through, it's got a channel, that's kind of split up like a honeycomb the inside, and it goes all the way from front to back.

So if you're, looking at a microchannel, coil you're, looking at that condenser coil or evaporator coil on the face of it, those little sections that go in between the crisscross fins, that's actually the coil itself and inside. That is the refrigerant and it goes all the way from the front surface to the back surface. So a lot of the issues that happen with microchannel coils again, this is my experience and that's saying it's true of all of them is because you have refrigerant flowing so much closer to the surface of the coil or, if you think, about a copper coil with Aluminum fins you've got the copper tubing, but then you've got that space between the copper tubing and the aluminum fins that kind of acts as a buffer. So if you were to go up in whack, a coil that has aluminum fins on it, whether it's copper tubing on the inside or aluminum tubing on the inside you're gon na bend the fins, you would have to hit it pretty hard for the fins not to Absorb that initial impact, now, obviously, you could hit it hard enough that it would cause damage to the tubes underneath, but generally, that hit is going to be taken by those fins, whereas with a microchannel coil.

When you hit it, if you hit it in the right spot, you're going to be hitting the actual refrigerant carrying microchannel, because it goes right to the face of that coil, and so it's easier for them to leak based on impact or damage of those sorts of Things, it also means that the refrigerant carrying tubing or whatever you want to call it Channel. I guess it's a channel. I keep wanting to call it tubing, but it's not tubing. It's just closer to the areas that it's gon na be exposed to corrosion.

From sake cleaners and things like that, as well because again, when you clean a typical fin and tube condenser, even if it's all aluminum you're, mostly cleaning the fins you're, not really cleaning the part that contains the refrigerant as much now you're gon na get some cleaner. In but mostly you're gon na be hitting those fins, whereas with a microchannel you're gon na be hitting right on where the refrigerant is and depending on that thickness, you could be really close to compromising that coil. So what we've seen is more leaks on micro channel coils than on their Toobin fin counterparts, and it's not the fact that they're made of aluminum micro Channel coils are made of aluminum and there's nothing wrong with that part aluminum. It's not quite as good of a conductor as copper, but it has some other great benefits.

It's less expensive. It's lighter, and it also doesn't tend to have as much form of carry corrosion, which is a big problem with copper coils. So a lot of people have gone to aluminum, coils aluminum coils are fine. You just have to obviously design for the that they don't have the same conductance, but it makes up for it in the weight and so aluminum coils are fine, aluminum tubes, aluminum fins, but with the aluminum microchannel, now you're, exposing the refrigerant carrying channel again closer to That edge, it's more likely to have issues with things like cleaners, for example, because there are a lot of cleaners out there.

Both alkaline and acid cleaners can eat away at that surface and when the refrigerant is so close to the surface on that micro channel coil, it's more likely that you're going to breach it and you're gon na have a leak. If you have aggressive cleaners which, by the way shameless plug Viper cleaners, probably one of the best out there for not damaging micro Channel coils, now a lot of micro channel manufacturers, they're gon na tell you shouldn't use any cleaner at all. But in some cases we know that's, not realistic. You end up in cases where you need to clean the coil with a cleaner, because it's got significant soil on it and if you are going to do that, then use a cleaner.

That is not heavily alkaline and definitely not acid. So the Viper cleaner is a great compromise there. Now again, I'm providing you my opinion, I'm not telling you to go against what the original equipment manufacturers say. I would never tell you to do that.

I'm just giving you an opinion basically that in some cases you may need to use a cleaner, even if the manufacturers say don't use a cleaner and if you do be careful about the cleaner, you use. That's mostly what I'm saying here. So that's one thing about micro Channel: you got to be really careful how you clean them. You got to be really careful that you don't impact them with something, because they're gon na be more likely to leak.

If they take that impact - and then another thing is, is that micro Channel coils they hold less refrigerant, and so this is a key differentiation that I think this will be helpful for you to get your head around. A lot of people think the amount of refrigerant. That's in a circuit has something to do with the velocity of the refrigerant or the pounds of refrigerant. That's moving through a particular point at a particular time, and so when we think about the amount of refrigerant that you have to move, we would call that mass flow right.

It's the pounds of refrigerant that we have to move through a coil over a given amount of time, and so with a microchannel coil you're still going to move those same pounds of refrigerant through the coil, but the coil itself holds less refrigerant, and this in general, Is a good thing I mean when you have less refrigerant. The system holds less charge, so that means it doesn't cost as much to recharge the thing which is nice, but there's some unintended consequences that go along with that, and one of them is that many cases micro channel condensing units have to be shipped without their full Charge and so even if you have a very short line set, you have to add more refrigerant once you get, it started up, we're used to typically having a brand new unit is charged to a you know. 25 foot line set something like that right out of the box in the case of micro Channel. That's not generally gon na be the case because you just can't fit as much refrigerant inside that coil.

The other thing: that's, a big danger - is trying to pump down a micro channel coil, because if you try to pump it down, it's not designed to hold all that liquid. You can actually have a hydraulic liquid, lock and you can actually build up tremendous pressures and burst the coil. So that's not something you want, obviously, for obvious reasons. So that's a big safety danger.

There is technicians not recognizing that it's a micro, channel, coil and attempting to pump it down. The other thing is, is that you have less flexibility in the charge. The charge becomes more critical with micro Channel because you have less excess volume inside the system. So even a small, overcharge or small under charge can have a more significant impact on a micro channel coil system than a typical system, and this becomes especially important in things like heat pumps.

If you have a micro channel coil inside and out where you have some variation in the load, conditions that they're operating under and heat pumps can operate under pretty wildly different load conditions, and so that can make your refrigerant charge extremely important. You can drive up your head pressure really quickly and even things like some manufacturers. Now they don't have a fixed sub cooling, because the internal volume of those coils is so small that different load conditions can change your sub cooling. So, instead of being able to go up on a TXV system and set it to a factory setting of 12 sub cool, you actually have to use a chart and plot the changes in load conditions in order to hit a sub cooling on a spectrum.

So you're gon na have more variation there, because again, sub cooling becomes more critical, the less internal volume that you have - and this is why, in refrigeration systems that have receivers, nobody even looks at sub cooling, because you have this extra liquid refrigerant, I'm if you're working At a grocery store and you've got a giant receiver, you're not worried about sub cooling, because you've got all this extra liquid to work with, because you have all of this extra internal capacity. You go to regular air conditioning. We do care about sub cooling, but when you go to an air conditioner that has a microchannel coil now we really got ta care about it, because your charge becomes that much more critical. It becomes that much more important that you have the exactly correct amount of refrigerant in that system, because you don't have this excessive volume where the refrigerant can go, there's nowhere for it to go.

If you get it wrong, so it becomes more important that you get it as you get it right, and so you're gon na be using your scale. A lot you're gon na have to recover them or you're, not gon na be able to pump down. In summary, here about microchannel, you just got to be careful with it: it's not a bad technology. It's been around for a long time in cars, but cars obviously they're lower pressure, so we're working out some of this stuff.

Personally, I haven't been a huge fan of it. I would rather see tube and fin condensers, but again sometimes we can't fight these things, so you got to know it when you see it so that way, you don't try to pump it down, and you know that you're gon na have to set your charge a Little bit differently and also you're gon na have to think about what cleaners you use when you've got a microchannel coil. So hopefully that helps we'll talk to you next time on the HVAC school podcast.