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You be more efficient and productive visit, zum lot, comm for more information. The suction line is beer-can cold. It's good enough looks like you found the HVC school podcast, the podcast that reminds you of all the things about the HVAC, our trade. You forgot, or you forgot to know.

In the first place I am Brian and don't listen to Darth technician. We do make jokes about beer can cold, but this episode is probably about the furthest thing from beer can cold. You can get in the refrigeration circuit. We are going to be talking first, some basic refrigerant circuit stuff, with Carter Stanfield, one of my favorite educators and authors in the in the industry.

I've been having a lot of authors on lately, but Carter is actually part of the HVAC school Facebook group, which I really appreciate, means a lot that he's there, along with a lot of other, really smart folks, but today we're gon na actually talk about the pressure. Enthalpy chart the dreaded pressure enthalpy chart, so if you are the kind of guy who just wants to grab the suction line and never take super heat or sub cool, this is like the other side of the industry. From that, you may not want to listen to this one, but we get into it. If you want to follow along with this, then I would suggest that you find some sort of pressure enthalpy chart.

We actually talked about the specific page you can go to in Carter's book, but grab a pressure enthalpy chart, so you can plot along if you're, driving or whatever don't do that. That's not safe. Here we go Carter, Stanfield talking about the basic refrigeration circuit and the pressure enthalpy chart alright. So today, on the podcast I have Carter, Stanfield and Carter has done a lot of things in HVAC our education, one of the most notable, was that he wrote the fundamentals of HVAC are many of you may have seen it.

It's got a Ice Cube on it. That's on fire, you know, so it's a very. It's got a very dramatic cover and it's a great resource. So I asked Carter to come on and we're going to talk a little bit about the pressure enthalpy diagram, which is you know, traditionally a very technical seeming and almost on the edge of being unnecessary for the average technician.

But I want to kind of humanize it and I figured there was nobody better to do that than Carter. So first off, thank you for coming on the podcast Carter sure glad to do it. If I can do one little correction or edit, I'm one of two authors on that, but my partner David scavs, wrote half of it and it's listed by my name a lot, so he frequently doesn't get the credit that he truly deserves. I could not have written that book by myself did to make sure that everybody's properly attributed somebody who's been doing as long as you have.

I know that there's a family business element to this that was involved with this, but I'd like to know. Well, how did you get in the business in the first place and then how did you get into education? My father started an air conditioning business. I want to say around 1968 I was 14 or 15 years old at the time when Dad would go somewhere, especially night calls weekend call. You know I wrote along.

I was 15 years old and doing manual Jay stuff down at the office for estimates and things rappin ducked on weekends and in the summers, so that was kind of my introduction into air conditioning teaching it. To be honest, I sort of backed into that my dad came to me and said you know, they're looking for a teacher at the tech school and at the time I was like 23 years old, I said daddy, they would hire me anyway. He bugged me about it so to get that off. My back, so I could say I went out talked to him.

I did go out talk to him. I showed up to my interview in orange and white tie-dyed pants. I took some tests, you know and talked to him and to my great surprise they called me back and you know about a week and then wanted to hire me and then I had a decision to make. I actually dropped out of college, so I could start teaching.

I don't think that would happen today if they knew that you're. You know somebody they're gon na hire is I just gon na drop out of school to start teaching there there's no way they would hire. You, if I showed up today with the same kind of credentials that I had back then, which were pretty sparse, there's no way I'd be hired even for an adjunct. Anyway, that's how I got into teaching - and it's been good to me - everyone who I talked to who started in teaching you know long ago, it's like they came out of the field, and then they sort of have these stories about working with their parents or doing Things when they were very young, inevitably it's always the story of well.

You know I didn't really belong and I was that I actually got the job in the first place. I hear that over and over and over again, so maybe there's something to something to being a successful, successfully tenured educator to kind of not coming out of traditional channels. It's pretty infectious, I think part of it is. You have to like to learn honestly the first year I was not very much help.

I was teaching myself. I was taking all the material that all the students had to go through and as quickly as I could reading and absorbing everything that I could so that I could be any help to them at all truthfully. I thought I knew a lot when I walked in there and once I started looking at what the students had to do. I realized, I really didn't know very much at all, and so you know it's been a constant learning process, but it was really a steep learning curve at the beginning, because we're gon na be talking about pressure, enthalpy and pressure on Toby is really nothing more than Pressures and heat, you know really that's what we're talking about making content when we say enthalpy.

How do you describe to somebody who's coming in maybe early on and air conditioning, and they want to just have a brief understanding of what a compression refrigeration system is and what it does, and you have like a simple way that you'd like to describe that. Yeah generally start by talking about trying to explain things that and make the cycle work, especially the things that people might be a little bit confused on. So the first thing you have to understand is you know, evaporation and condensation yeah. I did that boiling.

Is a cooling process, not a heating process and the idea that it reverses when you condense? So that's the first thing you have to grab a hold of, and then you understand that the point at which those processes take place is controlled by the pressure. You really understand the refrigeration cycle right there, so when somebody says saturation, what do you saturate? How do you describe that? I have to back up a bit we use, including me. We use the term evaporation and boiling interchangeably, but they're not really interchangeable. Evaporation only takes place at the surface of a liquid and it happens without having to be at the boiling point and a good example.

When you mop the floor, it never gets to 212 degrees. When you come back the next day, the waters gone because it's evaporated boiling is when the liquid is turning to a vapor inside the liquid all throughout the Lea - and I know a lot of books, including mine, talk about you know saturation as being the boiling point. If you look in some science books, what you'll see is that saturation pressure is when the pressure in the liquid, the vapor pressure in the liquid from all the bubbles that are forming in the liquid is the same as a vapor pressure. On top of the liquid, and that's why all the vapor can come out? That's also why, when you increase the pressure, then the liquid has to get hotter and you had to put more energy into it to make it boil, because the saturation pressure has to get higher so that it can be the same as the pressure on top of It now another kind of a mental picture that I'd like to use is that the liquid is saturated with heat you're, adding heat to the liquid, to the point that it can't hold the heat anymore and then, when you get to that point, just like a sponge, That's saturated with water.

If you pour more water on it, the water just drips through it with saturated liquid. Once I get a saturation point, any more heat that I add, it can't hold it anymore and it comes out in the form of charring. Some of that liquid to vapor, often when we talk about saturation from a technicians perspective, we'll simply just say it's the temperature at which something is changing state at a given pressure for a set type of matter or the set type of refrigerant. It's the temperature at which it sits in the change of state temperature.

That's a very simplistic way of looking at that and when you talk about vapor pressure, that's where things start to really get interesting and it's like a whole other level of that subject, and this is where, when you start to talk about the pressure enthalpy chart, it Kind of all surrounds this saturated state, this saturated state of refrigerant, let's just take a quick, walk through and talk about the refrigerant circuit and again I know this is all you know really early on stuff and we're talking to technicians who have been doing for years. Most of them know this, but let's just take a walk through and just describe the different points of saturation in the system so that we can kind of understand what we're dancing around here when we're working on a pressure enthalpy chart. So when we come out of the compressor where we're fully vapor, but we're not saturated, and can you go into into why that is and what has to go on in order for us to hit the saturation temperature, most systems are designed to gain a little superheat. After the refrigerant has all evaporated and the reason is compressors, don't like liquid.

Basically, you can't squeeze the liquid pressures work by squeezing and if you start squeezing liquid stuff breaks, so you have to have a little superheat to prevent that, and all superheat is is temperature. That's added, after all, the liquid is boiled off. So as long as you have a mixture of liquid and vapor, if you keep adding Heat, what you do is you just keep banking more vapor, but once you've boiled off all the liquid. Now, if I keep adding heat to it, temperature starts to go up some so that superheated vapor is what goes into the compressor and so a superheated vapor, meaning vapor, that's above its boiling temperature.

So it's already boiled off and some heat has been added to it. Enters the compressor and again, this is, I understand, I'm being doing simple stuff here, but this is going to translate exactly into what we're going to talk about here in a couple minutes, so it enters that compressor. But inside that compressor, additional heat is added in the refrigerator different additional heat is gained. Actually, in that compressor itself and there's a couple different kinds, would you mind talking about that? A little bit most of the heat? That's added is really just mechanical energy turned into heat energy.

When you squeeze it, it heats up, it's temperature gets higher, it's really just mechanical energy that went into compressing, it turns it into heat and then there's all the more practical aspects like most compressors are cooled by the refrigerant going over the motor. So you have a little bit of heat gain there from the motor heat and then things like friction of the mechanical parts. So when that refrigerant then leaves that compressor, it has the super heat that was added after the evaporator coil and in the suction line, or in D of AD vertical and in the suction line. So there's that super heat and then there's additional super heat added.

That's equal to the additional heat. That's been added in that compressor, and so now you have refrigerant. That's superheated well above the saturation temperature for that, given head pressure, what we'll call head pressure but in this case is the discharge line discharge pressure, and so now we enter the condenser, and now we have to drop off all of that superheat before we reach the Saturation temperature inside that condenser correct, yes, yeah as you're heated up above the point where it can condense heated up above the saturation temperature. So the first amount of cooling that you do basically just drops the refrigerant temperature and then, when you hit saturation, then you start to condense most of the technicians.

Listening of this are going to be. You know residential light commercial technician, so the volca condensers out there air-cooled condensers, and so primarily that heat is being rejected to the outdoor air through the condenser air. That's traveling over so initially the first part of that condenser coil is going to be rejecting heat. That is just super heat, so it's dropping in temperature, but then it hits that saturation temperature and now it just stays at the saturation temperature until it goes from zero percent liquid one hundred percent of vapor zero percent liquid all the way to a hundred percent liquid And so once it hits the one hundred percent liquid point, then we start to drop temperature below that and that's called sub cooling.

You know it. You can actually see that to some extent, if you take like an infrared thermometer and you know, scan the end loops of a condenser cross operating, you can see a fairly quick temperature drop at first for the few loops where you're these super heating and then temperature Is more stable through you know the bulk of the condenser, although truthfully you usually do drop a little bit of temperature, because there's a little bit of pressure drop going through those tubes, then at the very end you can see the sub cooling when again that you Know you get more temperature drop because you're taking out sensible heat stead of lightning yeah, and then you make a good point, because that's an error that a lot of technicians make early on is you know they may be working on a rooftop unit or something where They don't have a liquid port and this so they're connecting to only the discharge line, which is the line between the compressor and the condenser, not after the condenser, like we're, typically used to in a liquid line, and so they'll attempt to take a sub cooling reading And they'll notice that they have you know abnormal sub cooling in most cases abnormally high sub cooling, and that's simply due to the fact that there is pressure drop across that condenser, coil and evitable II. There's always some in some cases there's more than others, and that leads to what you mentioned there that that you do have higher head pressure at the discharge line than you do at the liquid line, yep all right. So now, what's the next thing that occurs well in most systems, then we have the metering device, which would be you know, either a orifice or expansion valve or now in some systems of electronic expansion valve.

You drop the pressure and that drops the temperature and your pressure and temperature drop back into the saturated region so that you can feed the evaporator with low temperature liquid they terminate a lot of people will use, is flash gas. Is that a term that you use yeah some percentage of the refrigerant going through the metering device will flash off to a gas as it goes through the metering device? So you end up with somewhere around 25 or 30 % of the refrigerant, depending on how much subcooling you have flash is off and that helps drop the temperature of the remaining liquid so that what's going into the evaporator, I normally don't call it a saturated liquid. I call it a saturated mix and people say you know, saturated liquid, cetera to mix flash gas. It means that you have a mixture and it's no longer 100 % liquid anymore.

I've heard it said that the percentage of decrease as it as far as you know. Let's say you have a hundred percent liquid as it enters that expansion valve will say we'll say it's a TXV that the percentage of drop off. So let's say it's now: eighty percent, liquid and 20 percent vapor is proportional to the temperature differential between the liquid lines. So how much sub cooling there is in the liquid line and then the end temperature in the evaporator coil itself, so the actual boiling but you're in the evaporator coil? I haven't heard that before only thing I know for sure is that the more sub cooling you have, the less flash gas you have and at one of the places that a high efficiency units pick up.

Efficiency is by adding sub cool right right. This is a lot of the easiest ways to do it. When you have more sub cooling, you're saying effectively your liquid lines cooler, I mean that's another way of saying that right and so a cooler liquid line is then closer to the temperature that you're going to achieve in the evaporator coil. And so I think this is you know: we've seen two things happen simultaneously in high efficiency equipment, in some cases, you're seeing higher sub cool, but then you're also seeing lower condensing temperature, which we run into this issue, where our sub cooling bumps up against the outdoor Temperature in the first place, which that's simply to say that you can only get your liquid as cold as the outdoor temperature is without some other form of mechanical sub cooling, which does kind of create a limitation sure we dropped down.

And now we start boiling in our evaporator coil, and I think this is where that that term boiling in the evaporator coil - and you alluded to this earlier - maybe one of the most challenging terms in our industry. And so could you speak to that? A little bit. Yeah, it is, you know when you talk about. I've got this boiling cold liquid, that's kind of counterintuitive to you know that your perception of the world and the reason is simple.

The only thing you've seen boil is water, and you know atmospheric pressure. Water boils at 212 and it's certainly not cold, but we have the relationship backwards. The boiling did not make the water hot, it's just the opposite. Actually, the boiling is actually taking heat out of the water and no easy way to prove this.

If you take a pan like an iron pan and put it on the stove and and let it get hot, then you throw water on it. Water steams off what happens to the pan it cools off. So you just have to understand that boiling is a cooling process. The boiling is not what's making the water hot, the boiling is actually cooling it off.

The second part of that, of course, is understanding that you can make you know most anything boil at different temperatures by changing the pressure. So going back to you know things we know radiator cap on your car. A whole purpose of it is to make the water boil at a higher temperature so that the water doesn't boil out of your radiator a lot of air conditioning programs like to boil water with a vacuum pump. You get a flask and put some water in it and hook up your vacuum pump to it, preferably one that you don't care for it too much, because you get a lot of water in the oil.

And you know you can see the water boil and if you do it a long time the flash will actually get cold. You get down to 50 degrees, and you know let people hold the flask and reassure them that the water is not hot at all, and it is certainly boiling just by taking the pressure down to a low pressure right. Exactly exactly - and I think that's the magic of air conditioning that certainly the general public doesn't grasp, I mean, and whenever I want to talk about, you know cuz, I'm kind of nerdy, and I know you can't believe that Carter. But I like to I like to talk about this kind of stuff that, like family reunions and not everybody, gets it, and, and so this this idea of things boiling cold at least you know, perceivably cold is one of the most challenging things, but I think this Even leaks into technicians wears a lot of like you mentioned a lot of technicians prefer to say evaporation when really evaporation.

You know we think of swamp coolers or different types of evaporative cooling. It's a very different process. It is not the same thing as what's actually going on in a vertical which truly is boiling and some boiling in the truest sense, all right. So now we go back and so now we've boiling in the evaporator coil and then a properly designed a typical evaporator, or at least the ones we work on mostly is going to add some super heat at the end of that coil.

So it's not going to boil throughout 100 % of the coil at some point towards the end of the coil. It's going to have fully boiled off and it's going to start to rise above saturation and that's what we call superheat, which means that once again we're fully vapor entering the compressor I did I'm do we miss anything here Carter. I don't think so. I think we're pretty much back to we're back to the beginning, okay, so all of that some of you may start snoring as you listen to that thinking all right.

Why did we do that? Because, essentially, when you look at a because now we're gon na move into the pressure enthalpy chart and when we talk about the pressure enthalpy chart, all we're doing is we're just taking what we just described that that process of change in and out of the saturated State, so you know, if you start at the compressor, you start at the superheated state and then you go through the superheated state. And then you go down back to the saturated state and then you go to the sub-cooled state. And then you go back from the sub-cooled state and the liquid line and you go to flash gas which is the saturated state again and then you go back around the circle. So it's just this constant cycle that we're working and when we look at a pressure.

Enthalpy chart what we're looking at is a chart, that's specific to a type of refrigerant and we're actually able to plot that, and it's simple its form. You've got what on the left-hand side, you've got pressure up and down and off the bottom. You've got pressure now on what would be your y-axis on a normal type plot you'd have your pressure and then on the bottom. You have your enthalpy and is important for people to understand that when you're looking at pressure, it's not a linear arrangement.

In other words, the lines aren't all equally spaced based on their value is more like a logarithmic arrangement, and the reason for that is so you can fit it all on the chart. If you had every line be the same value, the enthalpy chart would, you know, be several feet high and it would just you know, not really be possible to plot it right exactly from a practical standpoint, if you look at a common, I'm looking at an old School, you know it says freon our 22 DuPont chart here and if you start at the bottom it starts at 0.6 and then appointing and then 1 and then immediately search, jumping up so that's 4, 6, 8 and then 10 14, 20 and then 20 30, 40. So the scale changes as you go from top to bottom, all the way up to 5,000 at the top right exactly it starts jumping by hundreds at the top and so in. As far as we're concerned, I mean that's just so, it can fit on a page and cover a lot of ground, but but really it's very, very simple.

We're just the bottom is low pressures and the top has higher pressures, that's from so from top to bottom and then from left to right. We're looking at enthalpy and I'd be interested in you kind of defining that quickly. Because, again, that's one of those big scary words, the technicians, you know they kind of tend to shy away from, but really it's not that complicated well for our purposes. Enthalpy is the heat content of the refrigerant matter.

Of fact, they really tell you that when they tell you this, it actually says enthalpy and then s space BTUs per pound. So it's the BTUs per refrigerant, it's kind of funny in a way, though, because zero enthalpy is at minus 40, liquid saturated refrigerant, so there. Actually, if you look at the chart, you'll see that there's negative enthalpy, obviously there's no such thing as negative heat. It's just talking about the heat content compared to the heat content of minus 40 saturated liquid, and as far as I know, the reason is that ways they had to have some place to start right.

I tried I've tried to find out why they chose that. I found some chemistry explanations, but the chemistry explanations - don't really jive with the refrigerant. So I'm not really sure about that aspect, but I do know that all the refrigerants, if you look at the chart carefully you'll see that zero enthalpy. Is it like minus 40 liquid saturation? Well, this is another thing for those of you out there who feel overwhelmed.

Sometimes, when we talk about things that maybe you don't have a real context for just remember, Carter's been doing this 40 years and he still has questions and he's not exactly sure why things are the way they are so the deeper you get into it. The more questions you have and you inevitably find questions that are hard to answer - that's just part of the business in general and just a quick tooltip corner here I wanted to talk to you about the test. Oh smart probes, again, I've talked about them quite a bit, but there is something that technicians don't do as much as they could do, especially when they're working on split systems. It's just a good reminder out there.

If you have the test of 150 knives, which are the clamps and actually a lot of guys, will buy just the whole smart probes kit, but you don't have to. If you just want the temperature clamps, you can get just the temperature clamps by going to true tech tools and looking for a 1, 1 5 high and they're really really reasonably priced. But you can use those tests - Oh 115, Bluetooth temperature clamps to do something that I think is a good idea, which is to take a temperature differential on your suction line inside to out and your liquid line inside out. Because that gives you a really good indication.

If whether or not you're inside to outside super heat is gon na be comparable in most cases for a typical residential split system, you're, usually gon na see suction temperature differences of 5 to 8 degrees. You know sometimes even less than that depends on a decent number of variables, where the line set is run. How long it is that sort of thing, but you're gon na see, generally speaking under 10 degree differential between the inside temperature, where it comes out of your vaporators on the section line in your outside temperature. If you have a wider differential than that, then it's indication that you may want to do something about that.

Maybe further insulate the suction line, with larger armor flex, larger pipe insulation or use some sort of reflective coating around the suction line, and then, with the liquid line, you can measure to see if you have maybe a extreme pressure drop on the liquid line or whether, Maybe you have in an extreme cases, maybe a kink or a restricted filter dryer by measuring that same temperature differential inside the outside in general. Lower number is better. That's what you want to kind of keep in your mind. A lower differential liquid line inside the outside is better lower differential suction line inside the outside is better, but if you get in the habit of doing that regularly because you're making measurements inside and outside anyway, now, if you're, you're going inside and you're measuring static pressure Or you're measuring in delta T you're already there, so you might as well go ahead and grab those temperatures while you're there and then outside.

Obviously, your guys aren't gathering gathering gathering is a new word. It's like gathering and measuring all together, you're measuring your temperature and your lines outside and then also potentially your pressures, if you're doing an invasive test, and so you're already doing that and so go ahead and grab them both places. And that way you can compare those readings inside to out and that'll give you a good indication. If maybe something abnormal is going on all right.

That's it! Let's go back to Carter, Stanfield talking about the pressure enthalpy chart. So let's talk about how this is actually plotted, so I want you to imagine this. So if you're listening to this you've seen one of these charts almost certainly you've seen one somewhere, but it probably just made your eyes bleed and you're just like. I don't care about that.

I have no interests in it, but if you think of like a little bit of a curve, watermelon almost is cut in half and so you've got this dome, that's graphed on top of a chart and it's got all these lines going. All over the place that all mean different things, but the simplest is just top to bottom on the left is plotted. The pressure left to right on the bottom is plotted the enthalpy or the BTUs per pound, so the heat content of the refrigerant. Those are the two main areas that we focus in on and but inside this half watermelon, that's on the center of this chart inside that is the saturated State, and so that's the state in which you have a mix of both liquid and vapor.

When you look all the way on the to the left side of the watermelon, that's when you have the sub-cooled liquid region and when you look on the right side of the watermelon, that's where you have your superheated vapor region. So now we've got watermelons and and all that out of the way, any other way that you would describe this to somebody who's just maybe seen one before but trying to give them the picture in their head. Well, I used the term shark's fin. Ah, yes, that's probably better yeah! I like that.

I like this. If you imagine, the bottom of the chart is the level of the water and that's the enthalpy per pound, and you have this fin. That's sticking up out of it and then that dome. That makes up the fin inside that fin.

That's the saturated state. So that's telling you that if you plot it inside that dome, you know that you're at this edge in the saturated State. The other thing I like to point out - and this is a little bit technical, but at the very top of the curve, is your critical point and that's the point above which basically, liquid and vapor are kind of the same thing. And since it, the line shows saturated liquid on the left and saturated vapor on the right, and they join together at a critical point and that's why it kind of squishes in towards the top part of the reason, understanding that is important.

When you start looking at co2 systems and air and people talk about trans critical systems, that's where that word comes from it's. When you draw one of those systems, the high side is actually above the critical point, the low sides below it. So the system crosses the critical point in a way, and that's where that word comes from yeah. We actually talked about this recently, an episode for those of you who remember.

We were talking with Andrea Paton out from Emerson about this, and he was talking about super clip critical fluids and that's where you reach the top of that and go beyond it and in co2. That's one system where we actually see that occur or Kensie that occur within the system and our typical compression refrigeration systems were below that and so we're always kind of below at the top of that shark's fin, but in co2. If you can imagine you know we're actually plotting up above the top of that shark's fin, and that's where you hit that supercritical fluid range. I think I'm saying that right, supercritical fluid.

Does that sound right, yeah, yeah, it's a fluid and fluid is anything that can move so that can include vapor or liquid, but it's just kind of one thing once it gets to that point. It's kind of science fiction stuff. At that point, it's like all right. So when you're plotting, so let's say that we were gon na take a typical system, so we're just gon na take a typical r22 system, and we want to plot it on this, our 22 chart and for those of you who actually have Carter's book, he actually Covers this in chapter 19 and starts at page 280, so in the fundamentals of HVAC our is this is actually covered in there, and I need to stop here and just say that Carter.

When I asked him to do this, he he warned me that he doesn't even really like to consider this part of the basics, because it is a little bit more complicated than a lot of technicians really probably need for the basics. But I like to do it because I think it's a good way for you to hopefully not be so overwhelmed by it if you ever happen to bump into one of these charts or you're in the company of someone who wants to reference one at least it'll, Give you something to kind of go off of so, if you have the book, go ahead and pause, this and open it up to chapter 19 and it'll, make a little more sense or if you get it later on, you can go back and look at this, But if you were gon na plot a typical r22 system on this, where would you start on this chart? Well, basically, especially if I'm doing an operating actual system, then I want four measurements. I want to know. You know what my high side is, what my low side pressure is, but the suction line temperature is going into the compressor and what the liquid line temperature is going into my metering device.

Those are the four measurements that I need and from those you know, we can draw most systems. This is assuming we don't have big pressure drop from, say the condenser to the metering device and some other things, but that'll give us our basic plot, and so what's the shape that we're drawing on this is that a polygon? Is that the way you would describe that? What is this? What is this shape? To me? It's closer to a parallelogram right, except the left side, is the shape of a box. So, on the left side looks like a rectangle, and the right side looks like a parallelogram got it. You know, a parallelogram is basically looks like a box.

That's been whacked on its side, kind of leaning, so I'd like to draw the high side line and low side line first before I even know where the corners are going to be. So I draw the lines all the way across the sharp spin and I'll find the intersections later got it okay, so that makes sense that makes sense. See you take your because you're going from the left side is your pressures I just talked about you just pick. Your pressures down take your two pressures and you just strike lines all the way across exactly exactly I'll find the corners later, and you just have to caution people that you're gon na.

Take your gauge pressure and add 15 to get to your absolute pressure because the enthalpy chart, the pressure on the enthalpy chart is absolute, usually not gauge right. So as an example, if you're looking at 80 absolute pressure, minus fourteen point, seven or like you're saying you know: 15, that's 65 in gauge pressure. So what you're seeing on the left there is always has that additional fourteen point, seven or fifteen. If you want to round up that's the atmosphere all around this as a practical matter, you know when you go to all that line.

You're gon na see that, like on the one I'm looking at, I've got a line at a hundred and I've got a line at 200. So all right, knowing exactly where you know 130, is that's kind of a guest in there anyway, right, which is, which is why, if you were wanting to do this for an engineering purpose, there's something you would either do it on a much blown-up version or you Would do it via software? This is more so for demonstration purposes if it protected exactly, and there are apps that if you know enough to play with them, you can get your exact numbers from them, but anyway I draw those two lines. First, so I have you know my condenser and evaporator at least the basic line for it. The next thing I normally draw is the compressor and that's what you need: the suction line temperature for you basically just follow that evaporator line out until you see an intersection with the temperature that you measure and the temperature lines are more or less vertical, they're a Vertical but they veer off towards the saturation line on the vapor side, so you find that intersection of the evaporator line and the suction line temperature and that's where the refrigerants going into the compressor.

Now the physics of the way compression works, the pressure increase, will follow line of constant entropy. So those fairly sharp diagonal lines that you see on the right, those are entropy and you find the nearest one and kind of go parallel to it up until you intersect. Condenser line and that's going to be where it leaves the compressor and enters the condenser. You got it got it, I'm following okay, so I'm still looking for the lines of constant entropy.

You actually lost me there a little bit when you say lines of constant. What does that even mean? What do those represent? Yeah? That is a very difficult thing to have a simple answer, for that makes sense, with refrigeration in general, entropy is everything's natural inclination to go the most disorganized state possible. So if you can imagine what your truck looks like at the end of the week on Friday after you've had three emergency calls, that's lots of interesting now in terms of the measure, I normally think of the lines of constant entropy. They are really for our purposes.

They're the lines of constant specific heat, meaning the amount of heat that I add to each pound of refrigerant to raise its temperature one degree stays the same along that line. Something a lot of people don't realize is that specific heat is not constant for all forms of vapor, in other words, as the pressure changes and even as a temperature changes the specific heat of that vapor changes. So these lines, if you follow that line up, it always takes the same amount of B to use to raise one pound of refrigerant one degree and that's why, when it is compressing it when you're, compressing, refrigerant and you're, putting that mechanical energy into it, and that's Raising its temperature, the pressure in the temperature increases at a predictable rate, and that rate is along that line of constant entropy. Okay, I think I got it.

That's that's something that I'm gon na need to actually do a little more research on, because it's a little above my paygrade, but okay. But I see what we're plotting here at least, and there are these very kind of steep lines that go. If you can kind of imagine if you're going from the bottom up there, okay they're kind of more to the left and then they go more toward the right but they're very steep. They are very steep the steepest diagonal lines on there.

I know there's a lot of lines crossing of course. Another way to do it is to also measure your discharge line temperature. The problem that you get is you got another 50 to 75 degrees of discharge line temperature inside the compressor itself that you can't measure if you're looking at a hermetic compressor the discharge gas temperature inside as it leaves the head of the compressor, is like 50 degrees, Hotter than that discharge line coming out the shell, I'm really interesting, that's one of the reasons why you know. I'm sure you've heard that you don't want the discharge line temperature to get much hotter than around 200 C different numbers 180 to 220, depending on who's, giving you the number this all usually around 200 or the reason is mineral oil - starts to break down around 300 And if we know that it's 50 to 75 hotter inside the compressor than where we're measuring that discharge line, that means you know if it's 200 outside I'm getting Paris Lee close to 300 on the inside right in the actual head of the compressor itself, exactly where, Where that oil is needed most yeah, so you could plot it by a major and discharge line temperature.

You just don't really get as accurate a measurement as you might need. I don't know it would make that much difference, but your line going up for the compressor. Wouldn't be quite as steep as probably it should be. You know you file your condenser across now.

What you want to do is find the intersection of the condenser line and the temperature that you measured on the liquid line now on most pH charts. Unfortunately, there are no temperature lines visible on the liquid side, but the way you can find and the temperature lines are nearly vertical on the liquid side. So you find the saturated liquid temperatures on the liquid curve and you go up and that's the way you find your liquid temperature. So your liquid line temperature.

You find that intersection of the condenser and the liquid line temperature and that's going to be the corner, leaving the condenser and entering the meter nuance then, to finish it. You just draw straight down, and so with this - we're assuming of course that leaving the condenser, and so you go outside of the shark's fin there, because you're so cool, yes yeah. This would all happen outside the shark's fin in the sub-cooled area. Now we're making the assumption that we got a system.

This you know has sub grilling and super heat right. So it's traveling - and this is where we're at this stage now, just as a reminder that this is going to be really hard to do without looking at it there's a lot of different. You can even pull up just to general. If you're, just google pressure, enthalpy charts, you can find those online and I'll I'll connect to some.

You know just a just a free version of this is you can pull up real quick, but the best way is going to be the go to the book in chapter 19 like we talked about, but if you can imagine you're, starting at the top right of This shape that we've made here and you've gone to towards the left, so you've moved left and, as you move left, you went outside of the shark's fin because it became sub-cooled and so as it became sub-cooled, it actually dropped outside of the shark's fin, because the Shark fin represents a saturated state, and so now from there you go straight down and that's where it goes in and out of the metering device and where it comes out of the metering device that becomes the bottom left-hand corner that we reference in this. In this shape, right and that's that's where the refrigerant would be entering your evaporator and on these kind of typical shapes we're really not accounting for much pressure drop in any of our aniline sets afer a split system. I mean we're really just counting on the fact that everything's direct coupled, if you had a situation where there was pressure drop, then you could certainly plot that you just wouldn't have a straight line. Then correct right, yeah, that's true! I'm sure that could be done.

I've never seen it actually done. One of the things to keep in mind is that again we're up in a region where each line represents like 100 pounds of pressure. So if you're trying to draw a line that has maybe you know 10 pounds of pressure difference from one side to the other and the space there represents 100 pounds. It's literally gon na be like maybe the thickness of the line.

It's gon na be very hard right, correct, correct, but this is like. I said it is a nice visualization tool and that's something that I think technicians would benefit from if they can kind of visualize this, because one thing that has helped me is the distance in between that bottom line and that top line it does represent the compression Ratio I mean it represents how far is al far it's traveling, so talk a little bit if you would about compression ratio and and what that means and how this can kind of help you with that. Well, a compression ratio is literally just the ratio of your absolute high side pressure to absolute suction pressure. It's just literally saying how much you have had to compress that gas and it's common sense, the more you have to compress it, the more energy it takes and the less gas you move without getting in all the technical details, as you can ratio goes up the Amount of refrigerant moved goes down, and that's really, regardless of the type of compressor you have.

Some compressors are better at high compression ratios and others, but all of them. If you asked me to do more of one kind of work, I'm gon na be able to do less of another, and that's so that's kind of what happens as your compression ratio goes up. You move less refrigerant, so we'd like to have a low compression ratio in terms of being able to move more refrigerant with less energy input and just and you can see that I'll know in the enthalpy chart, just by literally where those two lines are drawn. You don't even need the corners to see that exactly you could take just the horizontal lines draw those across and you would be able to see your compression areas really right.

You could have you know multiple scenarios or multiple designs gone on the same chart even and had just a visual comparison of you know what would happen if and then all that right, and I think it's in because it's again we get kind of bogged down in The lines and the numbers and all this kind of thing, but if you just just pick those two lines for a minute - and you say: okay, this one line, here's my discharge pressure man, this other line, here's my suction pressure and from an energy standpoint. We want these two lines to be as close together as we can. I mean that just makes sense. You're gon na move more refrigerant if those two lines are closer to each other.

But we've got another challenge here, because the job of the reason why we have to separate these lines anyway is so that we can move heat in and out of the refrigerant. So we have a temperature differential and those of us who have worked on you know practical air-conditioning systems. We know our condensing temperatures have have started to drop so, whereas we used to see you know 30 degrees over ambient at condensing temperatures now, in many cases we're seeing 15 and we're even seeing some cases where are where our vaporators are getting larger and so we're Seeing lower temperature differentials on even on evaporators in some cases, and so when you consider that you're bringing those two lines closer together in order to make a more energy-efficient system. The challenge is, is the medium that you're rejecting the heat to and the medium that you're absorbing heat from you have to still stay within the ranges of what we have to work with, and we one thing that hasn't change is people still like it about the Same temperature inside their house and the temperature outside hasn't changed too terrible much either and depending on whether or not Al Gore's right.

So so we have the same kind of baseline thing that we're trying to accomplish. But in doing so, we want to keep those two lines as close together as possible in order to still perform the heat, absorption and rejection job that we have to do, which is easy to see that when you're, looking at these lines on the enthalpy chart. With respect to the evaporator side of it, we have to be careful that we still can take some water out of the air, at least here in the southeast. We have absolutely, but recently, they've made some headway on that by having better control the air flow.

You know for years, we've said the standard air flow is 400 CFM per ton. I just put a new 20 seer system with an ECM motor in my house, and your variable speed, compressor and I've kind of been watching it because it'll tell you the speed to compressors running at and it'll tell you, the air flow you're getting, and my system Tends to run closer to 300 CFM per ton, and part of that is it. You know it lets me set the humidity I want and I'm instead of setting it at 50 percent, I'm setting it at 45 percent. So system is actually slowing down the air, so it does a little bit more latent cooling, the evaporator.

I guess what I'm getting to the evaporator temperature can be a little closer to the dew point and you can still take water out of the air just by changing the amount of hair that you moved. Yep. Absolutely for sure - and that's it's the same thing I'm in Florida. So in Florida you know it's it's a very, very high latent and I have a five-speed carrier, rotary system that I put in and I love it.

I mean it's, it's fantastic and we typically run closer to the 325 to 350 CFM per ton range, but sort of the perfect storm that engineers he figured out is that if you reduce air flow, then you can still put in a larger coil, so largest possible. Coil size plus lower air flow equals lower bypass factor. This is a whole nother thing, but you get a little better efficiency out of the coil, because the goal is still you know you still are making a sacrifice when you have a higher compression ratio, meaning if you the suction pressure or if you increase the head Pressure or both and the more you separate those two lines: the less efficiency you're going to get out of that system. The fewer BTUs you're going to move per watt of input into that compressor, and it is again getting back to this enthalpy chart it's night.

It's neat to be able to see it on there because it helps you kind of visualize that thing that we talked about when we say compression ratio. Now there are quite a few things you can see the amount of refrigeration effect by looking at the points on your evaporator lawn. You can actually see the you know the BTUs that you're picking up in the evaporator for every pound of refrigerant that you move for that matter. You could even use this, of course, the engineers kind of do, but you could use it to design your system.

You draw your lines where you think your temperatures need to be and plot your points, and then you can see how many BTUs you're picking up for every pound. You move and then from that you can see how much refrigerant you have to move and that helps you select your compressor and, of course, that's. One of the ways this chart is used by engineers is to actually figure out how the parts are gon na go together right because pounds are referred to removed and that's kind of one of the phrases that I put in a recent article that I wrote is You know we move heat on the back of pounds of refrigerant and that's a that's one way to think about that. And so when we talk about an exciting expansion valve, for example, we say: well, it's a 4 ton valve or it's a 5 ton valve.

But really what we're saying is is that this valve is designed to move X, pounds of refrigerant, and this compressor is designed to move X, pounds of refrigerant and the ability at which it does. It also relies on the compression ratio. So if you have a you know: cold indoor temperature, with a hot outdoor temperature. That means you're gon na run a higher compression ratio, which means that you're gon na move you a few pounds and if it's the other direction, then you're gon na move more pounds which goes directly to the efficiency, which is why, when you look at you know Capacity on systems, you'll notice that they're rated at a particular set of conditions and when those conditions change that piece of equipment doesn't produce the same amount of capacity in varying circumstances.

So it's all yeah.