This episode of the HVAC school podcast is made possible by our great partners and sponsors carrier carrier. Air conditioning you-know-who carrier is, you can find out more by going to carrier comm. We deal carrier at Kalos services and I've been a big fan for many years. Mitsubishi.

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So this is part two of the basic refrigerant circuit episode talking with Burton Kieran. Oh, by the way, this is the HVAC school podcast, the podcast that helps you remember some things you might have forgotten along the way as an HVAC technician as well as helps you remember some things you forgot to know in the first place and we're getting back To the basics, again here with episode, 2 of the basic refrigerant circuit revisited Willis carrier when he invented air conditioning. What did he actually invent? What was the system that he invented, and I think you were in the class when I just talked about this - he invented he was blowing through water right correct, so he was using ground water. He was working in Buffalo, New York, and so he had very cold groundwater, and so he was conditioning the air meaning simultaneously controlling its temperature, its humidity and the cleanliness of the air filtering, the air using cold ground water right, and so he was able to accomplish All those things using that - and that was still air conditioning it just wasn't compression refrigeration.

What they realized is. They started looking at what was happening already in the ice making industry and in the refrigeration industry and that started becoming more and more efficient and what they were doing was changing the states of matter from liquid to vapor back and forth back and forth, using compressors. Using changes in pressure - and so that's what we're doing in this compressor when we take this low density vapor into this compressor, and we Jam those molecules together, we take them and we force them together, we're not really adding that much heat inside the compressor. We are picking up heat from the motor.

We are picking up heat from the friction inside the compressor itself and adding that to the refrigerant, but really the reason why the temperature of that discharge line is so hot to us. Why we see such high temperature - and we would say man, I think burns me - is because you're taking these molecules and you're jamming them together and when you jam molecules together, they start bouncing all over the place which gets us to what the definition of temperature is. In the first place, so what is that bird? The definition of temperature in the first place is a high velocity molecule. Well, the speed of molecular movement granite speed of molecular motion.

So in fact it's the average molecular velocity or the average speed of the molecules and the reason why it's the average speed, not the specific speed is because, within that substance, there's some molecules are going faster than others right. In fact, if you've ever wondered, why, if you look out at a lake, this is one of the big things that I've struggled with for most of my adult life and then finally realized what the heck was going on here and you see the moisture rising off The lake that's evaporating off the lake. I was always like what the heck is going on there, because that water's not boiling. Why are molecules leaving that water? Because it's not at its boiling point? Well, the reason why they are is because it's the average molecular velocity.

So, there's some molecules that are going fast enough to break the bonds. It's not all of them right when you get to the point of 212 degrees at atmospheric pressure. Now, that's when all of the molecules have enough energy in them to begin breaking those bonds. Does that make sense that would be some sort of temperature glide.

I guess so. Temperature Glide is a way that we describe mixed refrigerants and there are different boiling points. That's the way that we describe that. That's the way I've found right.

The reason why that occurs in a lake is because it's an uncontained system and so those molecules can escape, and then they just can go away, whereas if we took a lake or we took our body of water, for example, as a lake would be a bad Example of this but say we take some water and we put it in a glass jar and we take that glass jar and we set it on a counter in a hot counter. You're gon na see that there is some evaporation, but then it just returns back to the closed system. It can go anywhere right, but when you have water evaporate, some of those little molecules have their little capitalists and they really want to make it on their own and they have higher energy than the other guys around them, and also the specific direction. Some of them hit that surface and then they break free and make it away and when they do, their energy is subtracted from the total energy of that lake, which is why a perfect example.

This is when you sweat when you sweating, the water is not boiling off of your skin right. What's it doing well, it's evaporating off of your skin, meaning some of those molecules are breaking free of the bonds and whenever one of those molecules breaks free of the bonds, it reduces the average energy of what's left right. If that makes sense, because it's the most ambitious guys who are breaking free mm-hmm, so lowering the temperature correct, because temperature is average molecular speed, average speed of the molecules right. And so, if you think about vapor vapor is lower density than what's going to be in the discharge line.

The section line vapor coming in is lower density than what's going to be in the vapor going out of the compressor right. And so what happens is when you have these molecules. They're kind of all separated and they're moving real slow because their lower temperature and you take them and you pack, those guys together. It's like packing a bunch of bouncy balls together right.

You have a bunch of bouncy balls bouncing around right and they're bouncing kind of slow, and then you Jam them all together. Well, they start ricocheting off of each other. Friction is increased and that temperature goes sky-high. Now, it's not that you somehow added more heat because we would say: oh the suction line is cold and the discharge line is hot.

In truth, the amount of energy heat energy in those two lines is actually very similar, but it's just that it's they're packed much more densely in the discharge line, which means the molecules move faster right, make sense. So now we have these molecules that are bouncing all over the place: they're fully vapor, it's really high temperature and we've got to get them down to their condensing temperature. We got to get them settled down again to where they begin to not only settle down to the point that they were before, but to actually start to turn into a liquid, and so we start to reject that heat. And where do we reject that heat house? Had air outside air rejected in the condenser to the outside air, so you have these molecules: they're bouncing all over the place.

You got to get the heat off and the heat is going to move out of them to the outside air, and why is that? Why does the heat move out of them to the outside air? The ambient temperature is lower than the vapor refrigerant, leaving the compressor in the discharge line today, condense it right, because high temperature goes to low temperature right and so now what you've done is by jamming those molecules together, you've increased their temperature. He doesn't go from high heat content to low heat content. It goes from high temperature to low temperature. I could have something that has a lot of heat content and be very low temperature.

Perfect example. Suction line section line has a lot of heat content. There's a lot of heat in there. You just pulled all that heat from outside, but it's still a low temperature we've packed them together.

Now we increase the temperature. Now we can get that heat back out, because we've increased that discharge temperature above the outside temperature right mm-hmm, high temperature to low temperature. So now we start running through that condenser. Well, the first thing it's got to do is it's got to get to the saturation temperature, which is just another name for the boiling or condensing temperature, the temperature at which it changes right and that's dictated by the pressure.

So, as the pressure goes up that condensing temperature goes up, as the pressure goes down, the condensing temperature goes down right, so we've got to get that heat out of there. First we've got a D superheated. We got to get it to that temperature. So the first thing that happens in a condenser and if you look at a condenser, the refrigerant goes into the top of the condenser when it comes out of the compressor.

You've never noticed this before this is how pretty much all of them work goes into. The top of the condenser in those first couple rows our D superheating rows. It's got to get to the condensing temperature and then the bulk of that condenser is the condensing part. This the part where it's actually changing state and you'll notice.

If you measure with us a laser thermometer or something you notice, the first couple passes our high temperature higher temperature and then you get to the middle and all those rows are the same temperature, because while it's in the process of condensing that's called latent heat transfer, That's where all of this massive amount of heat is exchanging, and that is the heat that it takes to change the state of the refrigerant from vapor to liquid. But it doesn't change the temperature. But here's what's important that condensing temperature has to be above the outdoor temperature. If that condensing temperature isn't above the outdoor temperature, then there will be no energy transfer you'll be super heat.

That's it right! It's not going to condense now, there's reasons why that really doesn't happen practically, but it's a way for you to think about it when you're looking at the condensing temperature. That's why we compare that to the outside air, so we use this measurement called CTO, a condensing temperature / ambient. We look at the condensing temperature and it should be within a certain range over ambient, depending on the size and efficiency of that condenser coil. But that's why we look at that? Okay and so, when you have a condensing temperature, that's too low you're not going to get heat transfer.

If you have a condensing temperature, that's too high you'll get heat transfer, but that means that your head pressure is higher than it should be. I just mentioned head pressure, so let's tie that dog real quick when we say head pressure, we're talking about the high pressure side of the system, which is from the discharge line of that compressor all the way through until you get to the metering device. So everything on that side we call head pressure and they're, not all the same. The discharge line pressure is not going to be exactly the same as the liquid line pressure, because you do have pressure drop that exists there.

We call the low side everything from the outlet of the metering device through the evaporator coil, through the suction line, all the way back to the compressor and they're, not all necessarily going to be the same either you're not going to have the exact same pressure. All the way through that entire so, but we call all of those the low side reading right, yeah make sense yeah. So you go into that condenser, your condensing and then once it's fully condensed. Once it's fully changed to a liquid, then you can drop below the condensing temperature and that's what we call sub cooled: sub cool right, cooling, sub cooling.

I heard this analogy the other day bear with me: it's super childish. But if you imagine looking at the ocean, okay, so what's above, the ocean is what is it vapor or liquid vapor, it's a vapor, its air, what's below the ocean vapor or liquid liquid? Okay? What do you call a ship that goes under the water that travels under the water submarine below the water? It means it's liquid, so if you imagine the ocean as being your saturation line at any given pressure, the the actual level where the ocean meets the sky right who's, the guy, who has all the powers who comes from outer space, who saves the fly? Who can fly? What's his name? Oh Superman, Superman flies in the air above the ocean. That's super heat submarine goes below the ocean. That's sub cooling! I don't even know why we call them sub cooling, I mean anymore.

We should be calling this the submarine line. I mean this is great: okay, stop! Okay! So that's a way for a newbie to remember that. But if you imagine that ocean, where the ocean meets the sky, that is the saturation line, that is the boiling or condensing temperature. When you go below that, that means it's fully liquid the further you go below it, that's the more sub cool you have the further you go above it, that's the more superheat you have, but as soon as you have any superheat you're, fully vapor and as soon As you have any sub cool you're fully liquid right, that's why you can't have negative sub cool.

That's why you can't have negative superheat, because negative sub cool is super heat and negative. Super heat is sub cool right, make sense. Now, when you do have it it's because there's something wrong with your testing or testing with it in most cases or something really crazy is going on in the system. But it's not.

There is no such thing as negative, so cool. If you have refrigerant glide, it makes a little more confusing, but we'll get into that later anyway, for your typical systems for ten eight hour, twenty two 4:04: what we typically work on, you don't see significant glide. So anyway, there you go so now you go out of the condenser and it is a sub cooled liquid. So it's fully liquid.

It needs to be fully liquid in the liquid line. It has to be full liquid-liquid line. Now. Are there circumstances under which the refrigerant could come out of the condenser as fully liquid, but by the time it gets to that metering device that it could actually no longer be fully liquid? Yes, okay, what would the circumstances be? Well, you could have a really long line through an attic and your attics 130 degrees, and so now you're adding heat energy to it.

It's higher temperature than the liquid line yep that could cause it mm-hmm. It could be a really long line, just a really long line. They causes enough pressure, drop that it actually causes it to become no longer sub cooled by the time of hits the Mater device or the restriction restriction. And what would be a common restriction in liquid line? Not the liquid line? Dryer? Yes, the birds getting bored of answering the questions right, he's very rebellious.

One. Take a second and talk about my friends over at refrigeration technologies. Refrigeration technologies is just a really good company. I talked to John Pasteur reloj he's the founder of refrigeration technology, he's a really dynamic guy, the kind of guy who, once he starts talking to you, you're gon na be there for a while, because he's really passionate about the HVAC industry and specifically chemicals in the Hvac industry John actually started out as a technician, so he started making products because he saw a gap in the industry where the industry wasn't innovating.

They weren't making products that really suited the technician, and so his mission is to make products that really work well, are safe to use on the equipment and are also safe for technicians to use as well as for customers. Because, as you know, customers are getting more and more sensitive to chemicals in their homes, and so we shifted. We changed away from the more chemical type of cleaners, the alkaline or the acidic cleaners over to the Viper condenser, cleaner, the Viper, HD, condenser and evaporator cleaner. Because of how safe it is to use and John points out that when you use a chemical, that's not as harsh, you do need a little more dwell time.

So when you spray the Viper HD on your condenser coil, you got to let it sit a little bit, so it can break up that soil. But when it's all said and done, it's gon na do the job just as well as any other cleaner out there, and we've really seen that. Also, they make the nylon products which is assembly lubricant and thread sealant, that's based on and or POA OLS, depending on which one you get it's safe to use inside the system, not that you want to get it in the system, but it's not gon na hurt Anything if a little does get in the system, it doesn't harden it's just a really really good multi-purpose lubricant that you can use when making flares. When assembling threaded connections, we use it all the time in both the AC and refrigeration portions of our business and people who use it, don't go back to anything else, so that is refrigeration technologies.

You can find more by going to our EF our IG tech comm. Until those guys that HVAC school sent you all right, --, so liquid line dry air would be a common cause. So that's why, when we're looking for these types of problems, we'll often check the liquid line temperature outside and compare it to inside on a split system and see what is the difference or we'll just assess all right? We got a hundred and thirty foot liquid line here and it's going through a super hot attic, so that can cause a problem there right. If you walk up to an air handler - and you hear it going, what does that tell you that you have a piston and you're a little bit under charged no leak? No okay! Now we're guessing didn't, have a customer who was convinced it was leaking.

It's been leaking for months in most cases when you hear that sound, if it's not when it just started up it's because you have a mixture of vapor and liquid in your liquid line before it hits the meter. Oh yeah, you're. Hearing that turbulence the turbulence of that mixed, liquid and vapor, hitting the front side of that metering device yeah, it's good, it's good word all right so goes through the liquid line. It should be fully liquid, meaning it should be sub cooled and most of the systems.

We work on you're, gon na see, manufacture, sub cools. Eight to fourteen degrees is the most common that you're gon na see. Sometimes you see a little more. Sometimes you see a little less, but in most cases it's gon na be in that range.

It means it's fully liquid and it has enough sub cooling that you know typical line. Lengths and typical conditions aren't going to result in that issue of having some flash gas as the term that we use for it in the liquid line before it hits the metering device. Now when it hits that metering device, what's the metering device do the metering device? Is that separation point between the high side and the low side? Another way of saying that is the metering device creates that pressure drop. That's the way you should think of a metering device, don't make it any more complicated than that creates a pressure drop across the meteor device and when we have systems the more complex they get where we're trying to control our evaporator pressure.

So we get a specific temperature and we're trying to control our condensing temperature so that we can have this perfect transfer. Sometimes we run into situations where we don't have a great enough drop across that metering device. And that's when you see things, especially when you work in climates, not like ours here in Florida, where you have these low ambient kits, where you have to artificially drive up the head pressure in some way in order to create enough of a pressure drop across that Majoring device, most metering devices that we work on in light commercial and residential, require about a hundred psi difference, meaning it might be fully liquid but you're. Still not gon na have a big pressure drop across it yeah.

So the challenge becomes when you're dealing primarily with TX fees. A TX v requires that proper pressure drop in order for it to function properly. That's the primary use case here, and so, if you have a system, that's running, say: 220 psi on the high side. You can't expect to have a suction pressure of any higher than 120 again.

This is a rule of thumb, but it's a pretty solid rule of thumb right unless you go to a different type of highly precise expansion valve like a electronic expansion valve, but that's the zone where we start to run into this problem where we have to start To artificially drive up the head pressure, because if you remember we're transferring heat energy from that condenser coil to the outside temperature to the outside ambient air right. So as that outside ambient air drops, our head pressure will also drop naturally, and so what will happen in some cases? Is you may have a condition where you have a designed evaporator temperature, your evaporator temperatures based on the boiling temperature of the refrigerant in the evaporator coil? And so you want to hit a certain pressure target and you don't want it to go lower than that, because you may have bump into freezing we're gon na talk about that in a second. And so you have these range that you need to be. But you're aiming conditions aren't providing what you need, and so that's where you would install controls that may be slowed down.

The condensing fan in order to drive up that head pressure or intermittently shut off the condensing fan or in some light commercial applications may be shut off one of the condensing fans. There are some applications where the discharge is used to bring up the head yeah that what's called a head master control, yeah yeah, that's minutes a trade name for it as a head master control, but it's a head pressure control. There's different head pressure, control strategies that we talk about, but when you think about a metering device, I bring this up because a metering device needs a couple things to do its job. It needs to have a full line of liquid entering it.

Mm-Hmm. It's not gon na work properly. If it's got flash gas mixed, vapor liquid coming into it, so needs subcooling. Basically, it needs to have some sub cooled refrigerant entering it and it needs to have the sufficient pressure drop a design pressure drop.

But if it has those two things, then it should do its job based on the type of metering device that it is different metering devices do the job differently. This is not a podcast about the differences between capillary tubes, electron expansion, valves, thermostatic, expansion, valves and pistons. They all operate a little bit differently, but the job is to create a pressure drop, that's what it comes down to, and so you have this high-pressure liquid. Coming in to one side, it hits this pressure drop and coming out the other side.

Now, there's much less refrigerant density and those molecules now separate. So if you think we packed them together in the compressor, we kept them in fairly small lines. You'll notice, the suction line is a larger line right. It goes into the compressor and comes out of a discharge line, which is a smaller line, goes through that condenser and it comes out an even smaller line in the liquid line.

So we're packing everything pretty tightly together. Then it hits that metering device and when it comes out of that metering device, there's fewer molecules exposed to larger volume, mm-hmm, okay, which means they expand. That's why we call it the expansion line. They expand they're exposed to the heat of the indoor air and they begin to boil that boiling is a cooling process is a simple way of thinking about it.

So when we think of boiling, we think oh boiling is hot, because water boils at 212 atmospheric pressure, but refrigerant boils at very low temperature. In fact, at atmospheric pressure I think r410a boils at negative 44 degrees. I think something like that. So it boils at a very, very low temperature and we affect that pressure.

What do you think Bert? I think it's 61 for 10a 61 for 10a, I'm not looking at a PG chart, but I think it's 44, so you can tell us who's. Also thinking 61 degrees that Copeland wants their compressors. Oh you think it actually boils at 61 degrees at atmospheric. I'm pretty sure that's wrong, maybe negative 61, but not so yeah.

Now we're controlling that pressure in that of a protocol hitting a target so that we can get an evaporator coil temperature that we want. Okay, this is actually the piece of the air conditioning system and cooling that really does the work. This is the part that we consider to be the cooling part right. It's the lower temperature than the indoor air.

We transfer heat energy from that indoor air into that evaporator coil right, and so we have to have a temperature difference, just like we did in the condenser. In the case of the condenser that condenser coil has to be a higher temperature than the outdoor air to get the heat out now, the evaporator coil has to be lower than the indoor temperature to get the heat in, because hot goes to cold. Right. Mmm makes sense yeah, so we got to get heat in it and it's actually the heat from that inside air.

That's boiling that refrigerant, and so this is why, if you run a air conditioner and you shut the blower off you'll notice that your suction pressure starts to drop right, I'm sure everybody's working on air conditioners seen this in one case or another blower goes off suction Pressure drops, you can accidentally leave the door off of an air handler a fan coil when you're working on it. For example, you're gon na see your suction pressure drop because the air is not being forced to the coil and the reason that that is is because that of a protocol needs the heat from inside. To boil that refrigerant and it's that heat that causes that pressure to go up, because it's again when you increase the temperature of something you're increasing the average molecular velocity they're bouncing more forcefully against the walls, it's creating more pressure, so they'll bounce right out of the Liquid and dance around as a vapor as long as they get enough motivation to move around that much. It takes time for it to go from fully a liquid to fully a vapor, and it's that in-between that we leverage.

So when it comes out of that metering device immediately, a certain percentage in this varies depending on the system change directly from liquid to vapor. So if it comes out of that metering device, a lot of people will say 30 percent. So it comes out of that metering device and now immediately it's 70 percent liquid in 30 percent, vapor right off the bat mm-hmm and then it throughout that evaporator coil you're boiling that refrigerant throughout. But again, it's important to recognize that it's the heat from that indoor air, that's doing the boiling right right in the same way that it's the inside the compressor, it's the compressor, compressing them together and forcing them together.

That creates that temperature change in this case we're absorbing heat from that indoor air and that's what's doing the boiling. If it doesn't have indoor air to absorb from well, then it's not going to keep boiling it's gon na hit an area of stasis and it's going to still boil, but it's gon na be very, very slow. Do based on the air. That's surrounding that coil itself, which is why, when you have a system that has low air flow, this is a reason I'm saying this, because it's such a common problem when you have a system that has low air flow or no air flow.

That's why your suction pressure drops like crazy, because it relies on that heat from the inside air to boil that refrigerant and keep that pressure up, and so we have a couple limitations in our evaporator coil a couple design areas that we really have to consider. One of them is, is that in most climates we want to dehumanize well as cool, which means that the evaporator coil needs to be cold enough low enough temperature that it hits dew point. So we have to hit the dew point of that air mm-hmm and also we want it to be lower temperature because the lower temperature, you can get it the more heats going to be transferred the greater the differential. So we know that when we're cooling the air in most cases, we want the coil to be cold right, but there's also a limitation of how cold we can get it.

And that is 32 degrees. As soon as we get that of a per two coil 32 degrees or colder we're gon na freeze up right, so we got to keep that pressure that boiling temperature up above that 32 degree mark what it comes down to is, in most cases, we're gon na Run about a 40 degree of a protocol, that's sort of our target, it's gon na change based on the indoor temperature. So if your indoor temperature is higher, then your coil temperature is gon na be higher. If your indoor temperature is lower, it can be a little lower, but it can't be much lower because when you get below 32 now you're gon na freeze, that's sort of the drop-dead point.

There are some modern units that will allow you to run below 32. For a short period of time, because it's not like as soon as you hit 32 ice just builds up in a second, and it takes a little bit of time. So you can run below 32 for a short period, but not for very long before you're gon na build up ice and the coil is 35 degrees. Below I mean that's.

On average yeah and again the type of system is gon na vary. We've been talking a lot recently about the new Bosch units and they do it a little differently, but for most traditional air conditioners that we've worked on for years. In most cases, your coil temperature is designed to be about 35 degrees lower than your indoor ambient temperature. Your return temperature really more appropriately.

So if you take your return temperature and it's 75 degrees, then your coil temperature is going to be about 40. If your return temperature 70 degrees, then your cloth temperature is gon na be about 35, which is why, if you run a system much colder than 70 degrees for a period of time, you can eventually freeze that unit up that that makes sense. It's an over diagnosed problem, so a lot of technicians think that just setting the thermostat to 65 will immediately freeze it and that's not how it works. It actually has to get there.

It actually has to get to that low temperature, which often doesn't happen, but it can cause that problem so we're controlling, ultimately the amount of boiling refrigerant in that evaporator coil and at what temperature it boils, and we do that by controlling that pressure drop and keeping It at the right point providing the coil with the right amount of air proper amount of air at the proper temperature gives it the right amount of heat that helps it boil at the right pressure as well. So it's not just that that metering device it creates a pressure drop, but it can't exactly dictate what the pressure is going to be in that evaporator coil, because it's not up to it. How much heat is exposed to that I've? A per two coil to boil that refrigerant off right, so you have this dance that you do. The metering device is just there to create that pressure drop in to feed the proper amount of refrigerant into that evaporator coil right it leaves the evaporator coil by the time it leaves the evaporator coil.

It should be completely boiled off, should no longer be boiling and that's what we call super superheat, exactly the higher the superheat. That means the earlier it stopped boiling in the evaporator coil mm-hmm. Whenever I say that maybe burped, maybe you can come up with a better way of saying this people's lose me when I say that sentence earlier earlier sooner when you have higher superheat more of the coil is used for increasing the temperature above boiling, then is used For boiling yeah, that's good way, mm-hmm, and the way I like to say it is - is that higher the superheat, the sooner in the evaporator coil boiling, ended mm-hmm. You buy that because once boiling has ended, then there's gon na be a rapid increase in sensible temperature.

Correct because when it's actually in the boiling state, it's using all that energy to boil not actually to raise the temperature sensibly right, it's using the energy to boil, but when there's no more boiling to be done, then the rest of that heat is going straight into Just creating a higher temperature right when we say sensible and latent sensible means you can measure with a thermometer, there's actually change in temperature right. We say latent. That means that there's no change in temperature, the it's going to a change in state, so inside the middle of that condenser, when it's condensing there's no change in temperature inside the middle of that of a protocol when it's boiling there's no change in temperature. They're.

Actually again - and this is where blended refrigerants become tricky, because in a blended refrigerant, it's just that you have two different refrigerants in there, so one refrigerant begins boiling before the second one does and then the second one begins boiling. So there's a little bit of glide there, but that doesn't mean that these rules don't hold true. It's just that you've throw an extra monkey wrench in the mix by adding an additional refrigerant into the mix right. The rules hold true latent transfer happens at a single temperature for a single refrigerant and then once it's done completely boiling or completely condensing, then it can either sub cooler ship read, so we see a higher superheat.

That means we're using less of the evaporator coil for latent heat transfer and means the evaporator coil is less efficient, was what it comes down to the higher your superheat, the lower your capacity almost absolute rule there, and so we really want our superheat to be as Low as it can be, while still being safe enough, that we're not gon na run a risk of slugging our compressor we're not gon na run a wrist of, I said: slugging flooding our compressor. We don't want liquid refrigerant to end up back at that compressor. So let me just go on this, taking based on what you just said just go on this trailer here. So what if we designed our evaporators to be completely flooded saturation mm-hm and then once we got outside, we had a little mini coil sitting out there to generate the rest of that superheat.

That way, we're safely bringing superheat into our compressor and our whole evaporator is in a flooded state. That way we can maintain a constant temperature. Tell me why not! No, there is no reason why not? There are systems that similarly exist. That way, then, when I'm coming up to a system and I'm getting a zero super heat and a 15 degree split, I adjust the charge to a better superheat and I actually have more, like a 21 degree split.

Why is that evaporator more efficient, not flooded? Okay, you're giving me a hypothetical situation. No, this has happened. Okay, you can flood evaporator and it'll be less efficient. Okay, you can yes, but that's beyond five degrees of superheat.

So say you change in evaporator, coil from five degrees of superheat to fifteen degrees of superheat. No, no, I met zero, superheat, correct zero to say ten or whatever. Then yes, absolutely because the most efficient way to feedin of a per coin is exactly 100 percent in no more because as soon as you add in more refrigerant now, you potentially drive up the suction pressure. That means you drive up the evaporator temperature slightly there and that now you're becoming less efficient in the evaporator.

That's why correct yeah, so a perfect evaporator coil is one in which it's fully flooded with liquid refrigerant and no more it's a hypothetical situation. It's like talking about perfect combustion radar. It's too risky to run perfect combustion in a car to run perfect combustion and a furnace, so we give this little wiggle room because again, the problem is is that we have tools that are measuring plus minus two degrees. In some cases, so you could swing two degrees either way.

You could think that you had two degrees of superheat when you actually had zero right in a lot of cases, and so that's why we can't just be that tight. Nothing is that precise right, especially if you have slight load condition, changes or whatever, which is why, in general, you're gon na see anywhere from as low as four degrees of superheat in, like a nice machine application, really critical application up to situations with a fixed metering Device where you could see a design superheat of twenty five degrees, depending on the conditions right. So it varies quite a bit and that's all for that wiggle room, whereas with a TXV in general, when you measure at the outlet of the evaporator coil you're gon na see six to 14 degrees, superheat, it's gon na be ten degree, superheat being the most common That you're gon na see with the TXV and when you measure it outside it can obviously be higher because now you've had some heat gained in that suction line, which is the next thing I want to talk about, because, when you're measuring superheat a lot of guys, Will ask, do you measure superheat at the air handler fan, coil furnace evap coil, or do you measure it outside, and the answer is yes, because both of them tell you different things. So when you measure suction temperature and calculate superheat inside that tells you much more about how the evaporator coil is being fed the efficiency of the system, because ultimately, it's the evaporator coil that matters for the cooling capacity of the home right.

What happens in that? Suction line doesn't matter as much directly for cooling capacity, but it does matter for the compressor for the compressor right, because if you have a zero superheat, that's bad because that's flooding back right! If you have a 30 degree superheat at the compressor, then that's bad, because that's higher temperature and now your compressors going to run hot because it relies on that refrigerant to cool it. Hmm right, and so we care about them for different reasons. And that's why we'll actually talk about manufacturers? Will talk about evaporator, superheat and they'll? Talk about compressor, superheat, compressor, superheat is measured at the suction inlet of the compressor. Technically, not even at the condenser is really measured right at the compressor and evaporator superheat is measured at the evaporator.

They both have challenges. The challenge with evaporator superheat in a typical split system, is in order to get an accurate superheat. You have to measure the pressure and temperature at the exact same point and, as you know, we don't have ports inside so that makes it kind of tricky. So you have to take the pressure outside and the temperature inside generally there's not going to be a lot of pressure drop down a section line because it's a pretty large line, but there can be some so that can impact it and then measuring it outside has A problem because that's of course telling you about your compressor, but it's not actually telling you that much about.

What's going on at your evaporator, you could have five degrees of temperature increase from inside to outside. So you could be have a 10 degree superheat at your evaporator coil and you could have 15 outside very easily pretty commonly correct, and so that's where, when guys talk about well, why is it important to insulate your suction line? Well, this is exactly why it's important, because you want your refrigerant, be as cold as possible, lowest temperatures possible entering your compressor while still being superheated mm-hmm right, because that helps the compressor cool itself. And so, if you have an uninsulated suction line, going underneath a slab or wherever and it's picking up a bunch of heat before it gets to that compressor. Well, not only is that bad for the compressor, but that's also now heat that has to be rejected in the condenser right.

So that's gon na artificially drive up your head pressure higher than it needs to be there's a lot of little unintended consequences that can go on in the system based on that and so now we're back to the other side. So it just comes out of the evaporator coil. Now, in the suction line, goes back to the compressor all the heat that was absorbed in that evaporator coil is in that section line and all that he went to old the nice old suction line, yeah beer-can, cold, section line, yeah grab that thing and you think, Oh, my goodness, that must be the cold line. Oh it's! Actually, all the heat from the house has gone down that back to the compressor and now you're back to where you started now.

Obviously, like we didn't go deep into anything here I mean even saturation alone is a concept that technicians really struggle with. So if you hear saturation, you have no idea what that means literally go to HVAC our school comm type. In the word saturation. I've written like five articles on it just talking about specifically what it is in different applications.

That's a key thing to understand, yeah and it's a hard one, because it's a fancy sounding word. It's really very simple: if there's the point where it's completely vapor or liquid right, so saturation is just the point any time that you have liquid and vapor at the same place. At the same time, you're at saturation that interface, a lot of people will say. Well, okay, saturation is when refrigerant is boiling or condensing.

Well. The first thing I'll point out is take a tanker refrigerant out for your truck, it's not in the process of boiling or condensing, there's liquid in that tank at the bottom and there's vapor in that tank. At the top and there's a liquid vapor interface, where the vapor and liquid touch each other, that's its saturation, it's not in the process of doing anything but any place where liquid and vapor are touching each other. That saturation right.

That's the point cooled when it's 100 percent vapor 100 percent liquid, a hundred percent. That would also be saturation right and that's probably a technical way of explaining it when it's fully saturated you know like is when it's a hundred percent, but again how we practically look at. That is that's when you have zero superheater, zero sub cool. We call saturation point when you have zero.

Superheat is cool real quick. I just want to mention biz pal org. If you are a company and you're looking for technicians and who isn't right now, I think you really need to look at Bisping org, Patrick long over at biz pal I'll tell you when he first talked to me about how he does this, how he uses social Media to recruit technicians - I was skeptical, but we used it and we actually got an experienced technician. We actually found a really good tech using this program, but we've been using it now for about a month.

I've been very impressed by Patrick and how much work he puts into this. It's a great process, great system that he uses leveraging social media and technology in order to recruit good technicians in your area that suit your credentials. So it's not just boilerplate. He actually uses your requirements in order to find technicians that are going to suit you, your business, your location and the type of that you do so.

If you're interested in finding out more just go too busy I'll, be eyes, epal, dot, org. So, let's go through everything again: just do a quick review! Actually berdahl! Let you do the quick review, compressor, quick review compressor, so the compressor takes in refrigerant, vapor gas, low temperature, low velocity into the compressor chamber, and the compressor is cooled by that and then it'll pull it into if it's a piston or a scroll whatever into the Compression chamber and that compression generates a high temperature high velocity gas that then comes shooting out of that compressor into the discharge line. So a discharge line is fully vapor. It was fully vapor going in its fully vapor coming out.

That's right right, that's right and then the vapor circulates through the condenser coil and immediately begins to de su / heat right and then and starts to condense. It starts to condense right right and that's what we call saturation in the condenser coil right and hopefully most of that coil is under saturation until the end of that condenser coil, it cools enough and PSI comes down enough to be don't say: psi comes down enough. All right, no psi net, don't know! That's not you think about that where your temperature drops enough that it hits saturation saturation is also called latent heat. Transferring heat, blatently mm-hmm the same temperature throughout most of that condenser coil, except for the slight changes in pressure.

Then it gets the order to get rid of the gages in my head. What I talk about stuff right, I understand yeah, it's done. It is tough and then it starts to sub cool Yeah right now. We're sub cooling we're actually going below that saturation point.

The condensing point marine, suddenly you're in the ocean yeah under the ocean liquid state, can't even see Superman at this point. He's waiting for us around the corner, all right. So liquid then travels through the liquid line to the metering device mm-hmm, and it is high pressure because it's backing up against the metering device and the median device. It's actually not high pressure, because it's backing up again.

So that is why it's high pressure. No, it actually isn't high pressure is not generated by the compressor, and so what do we say? The metering device creates a pressure drop. So don't think about the backing up against I mean that does occur, and that's why liquid important is generated. It's important but just think of the metering device it will cause you less trouble down the road yeah think of the metering device as a pressure drop pressure, regulator, pressure regulator, sure pressure, drop pressure, drops right, boss, yeah, right, yeah, all right, so there's a pressure drive Across the metering device - and you are now in the an optic capillary submarine together - yes, yeah in most cases, is just a distributor - just go straight out of the meter device into a distributor to the event.

So now the submarine has surfaced and Superman is sitting on the top of the submarine he's stopped it all right. So you've left the metering device. Okay, so now we're in a state of saturation again and we're boiling this time right. We're not condensing comes that.

We call it a flash gas. It starts to boil taking all the heat from right in the inside air, so it then it goes into the evaporator where it fully expands. What does fully expands me? Okay, all right so at the metering device you have refrigerant expands because it goes from a high pressure, high volume to a lower volume, lower pressure, lower vault, no, not lower volume. It goes from a low volume to high volume in the liquid liquid line is lower volume, it's more compacted less space, yeah you're right when I think high volume, I'm thinking more compacted, think about that backwards.

Okay, right, you're, saying it backwards. Yes, so low volume lower space in the liquid line and it goes to higher space, a pressure drive higher space mm-hmm and then that's the expansion line or distributor. Or what did you call it? Oh, the two-phase: the two-phase line: yeah, that's how they say, though, of course the pond first upon amazing, I mean so it goes into the evaporator and expands even more. At that point, the heat and the BTUs.

It's eaten up them, BTU. Yes, it's hot there's de cold right, so you've got this boiling refrigerant. Hot goes to cold. High temperature goes to low temperature, so it's bringing in my pulp.

I live it's spinach, taking it yeah. Let's go it's picking up the high-velocity action inside that air and sharing that action inside the refrigerant okay, it's like abstract, refrigeration or Brazilian stream. Okay, so it goes through that evaporator coil it's at saturation, it's boiling the temperature stays the same throughout the center of that of a protocol as it's in the process of boiling, and then it hits this point where it's completely boiled off all boiled off right, then, What starts to happen so then it begins to raise in sensible temperature right. So it goes from hypothetically 40 degrees up to anywhere between 58 and 45 pending on me, like a you, just had to throw numbers out there, yeah it's gaining sensible heat and that's called superheat.

It's vapor much like Superman flies through the air superheat right, it's higher, which means that it's further away from the boiling temperature yep you know, and then it goes down the section line, still absorbing heat from the heat, and we load that and we don't want it To absorb heat anymore, we really only wanted absorbing heat from the evaporator coil, any other heat absorbed as heat. We then have to reject some things. We kind of stopped some things. We cannot control exactly.

Ideally, we would have no heat transfer into that suction line whatsoever, because any heat that you put into that section line we then just got to take out again in the condenser mm-hmm. Can you use like keep blocking gel to do that and a completely unrelated note? Refrigeration technologies makes a great product called wet rag that you can use, wall, brazing or soldering, protect your valves shower or compress. They do make a heat blocking gel as well quick note, the heat blocking gel is not to be sprayed on to like valves and things. That's what wet rag is for the he blocking gel is to protect things like studs or walls that you're working around okay.

So you can cover that surface, and so you don't accidentally burn something right kind of makes sense right. It does yeah. It does so like if I don't want to light this insulation on fire near my braze. I mean just spray it down right with he blocking gel, but you use the wet rag on the valves TXV these compressors.

I won't need to unplug all that stuff as well all right. So there we go. That's the basic refrigerant circuit. Hopefully you guys got something out of that.

Meandering conversation thanks. I did we're gon na talk about the evaporator coil, there's just so much there. I just. I felt like I was lost a little bit and I want to be found.

I can't get hey. Thank you guys, appreciate you yeah. Thank you. So, as we mentioned, Karen is from Great Britain.

He actually apprenticed over in Great Britain and now he's apprentice sing with us and should be in a truck pretty soon. Really smart guy really appreciate having him on the team. He actually listens to the podcast he's one of the few employees. Those who do - but you know there are challenges with the British phraseology and he called in the other day and he said: hey boss uncle to call in sick.

Today. I've got a week off and I said you've got a week off and he said: oh thanks, boss, see you next week, get it a week off. We cut okay, never mind all right. Thanks for listening, we'll talk to you again soon on the HVAC school podcast.

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