Hi, i'm brian with hvac school and hvac our school comm. This video today is actually about refrigerant glide, and it came from somebody who watched one of the videos, a video that I did for the Danfoss refrigerant slider app, and he said that he thought I should do. A video describing the midpoint or the average point is in addition to do and bubble points, and I thought it was a good idea, so I'm making this video today. Thank you for the requests that you had all right, so we're gon na be talking about refrigerant.

Glide we're just gon na write, glide here and Glide means that the temperature of boiling and condensing changes all right. So what occurs in a refrigerant? That's a blend, a blended refrigerant, so not a single refrigerant. We were used to dealing with our 22 back in the day and it was only a single component refrigerant, and then we moved into r410a, which is what we call an e ray azeotropic refrigerant air, as the atrophic means that there's very little change in the vapor And liquid properties between the two refrigerants that are in the mix, which means that we don't see temperature glide, which temperature glide is you know in, for all intents and purposes, for most technicians. Why we care about temperature glide is that you have to use a different temperature for your sub cooling and a different temperature for your superheat at least that's the way that we've traditionally thought about it, but it actually goes a little deeper than that and that's what We're gon na discuss today, so this is what most technicians know.

They know that for sub cooling we use bubble point and for superheat we use dew point and the way you remember. That is that this is how I remember it is that when we think of sub cool, we know, sub cooling is a sub cooled liquid and so for a liquid bubbles can appear in liquid liquid, and this is just completely just a way to remember it. But you don't see bubbles in a vapor right. You see bubbles on the liquid, so sub cooling is where we use bubble.

Point superheat is dew point: where do you see do? Do you see do in a liquid? No, you see dew in a vapor. Do in the air do comes out of the air and onto the onto the grass or whatever, and so superheat is dewpoint, but we, you know, we do more things with refrigerant and with readings than just superheat and sub cool, and this is where it gets a Little bit confusing, because if you imagine an evaporator coil and you've got an expansion valve here and that span should've, Elvis feeding refrigerant into the bottom of the evaporator coil and the refrigerant travels through. We would generally assign a temperature to this based on the saturation temperature. So we would say to at a given pressure that it has a given temperature.

So, let's use the refrigerant slider app here and we'll take a refrigerant like r22 and we're gon na go with a you know, a typical sure that we would see which BC is 75 will say. So that's a forty four point, two degree evaporator temperature. So we would say forty four point: two at 75 psi. Okay, so we'd say that's that's the temperature at which the refrigerants boiling, as it goes through that evaporator.

So we would call that the boiling temperature or the evaporator temperature - that's a common term - that we would use well with a refrigerant like the reversion that I'm going to talk about today. Just because I happen to have a tank of it. Here are 422 D, you'll notice that it's got both bubble and dew point and when I switch in between them it's 45 point five degrees Fahrenheit at du, which is what we use for superheat, which means that's the temperature it's going to be at the end of The evaporator coil, we'll say right here, because here it would generally be superheated in the suction line, but we'll say towards the end of the evaporator coil. It's gon na be 45 point five degrees, but at the beginning of the evaporator coil, when it's still in the bubble range where we have liquid refrigerant of the of the end.

Because again, you have two different types of refrigerants and they're affecting each other, and so you have this one type of refrigerant that boils at a different temperature than the other. It's gon na start boiling at 39.3 degrees. Again, this is our. This is our 422 D.

At 75 psi so, whereas at 70, Fiat 75 psi r22 would just be at forty four point two hour for 22 D is going to start at thirty nine point three and it's going to go up to want to move it over to do it's going to Go up to forty five point, five degrees, so we have a range. This range is what we call Glide, so we have a glide of six degrees you're just slightly over six degrees right. So that's our that's our differential. Now, when we're calculating superheat, we know that we use the do so.

This temperature here is what we use to calculate superheat. So if our line section line temperature is fifty five point, five degrees, we would say that we have ten degrees of superheat and that is correct right. But when we calculate things like design temperature difference so say if I was wanting to calculate all right, what exactly should this pressure be based on the indoor temperature? We talked about this on the five pillars. We talked about this and checking a church without gauges.

There's a lot of cases where we want to anticipate what the pressure will be in the system to for diagnostic purposes. Well, what temperature is in the evaporator coil is at thirty nine point three years at 45.5. Well, it's both right, and so what do we do? In order to calculate this design, temperature difference or what do we actually see our boiling temperatures? And this is where we come up with an average temperature, an average of a per to temperature or average saturation temperature or another term that uses midpoint. And so what we do is we just take these two points and I'm just going to do rough math here and so we're going to say that it's six point two degrees of Glide divided by two equals three point, one degrees.

So we take thirty nine point. Three, we had three point: one degrees where we subtract three point: one degrees from forty five point one and we come up with forty two point four, and that 42.4 is now our average evaporator temperature. Forty-Two point four degrees and the same thing is true of your condenser, so you can do the exact same mathematics and with your condensing now. If this is this technically a correct number, no, it's a rough number and it's going to be better when you're calculating your actual evaporator temperature, then using either one of these is it still exactly correct, not necessarily because you have different percentages of each refrigerant potentially, so It really depends on your refrigerant, so if you want to be more accurate, you could use different percentages for different refrigerants.

But if you want to get a rough idea, a lot of people will use this midpoint or this average. So the question is: if you have refrigerant and it's static state where it's just sitting still, what will it be? Will it be at dew point, will it be at bubble point, or will it be at this median point or middle point or average between the two and the answer is and we're going to prove this? The answer is that it will be at the bubble point. So I've got this connected to a set up to testify. 50S.

I've got a tank of Honeywell Gendron 422 D. You can see the ambient temperature of this tank is 70 point three degrees which matches up very closely with a connection to the high side, which is you know. Testo is automatically looking for the bubble point because it's looking to calculate sub cool and if I go over here and I add - and I punch in this pressure - 134 psi on the Danfoss version - slider app you'll see that it matches right up. Seventy point five.

So within you know a couple tenths of a degree now, if I change it over to do you'll see that it's significantly higher. Seventy five point eight. So it's clearly not dew point. This tank is clearly not at dew point in its static State.

It's at bubble point and it is not at the average temperature, and so it's at the higher pressure range at that at the given temperature. So at the temperature of 70.3 it's at the higher range. If I were to go into the refrigerant slider app and dictate the temperature of 70.3, you can see that's a lower pressure if we were calculating using do instead of bubble. So answer is in its static state.

The tank is going to be at the bubble point. So, just as an example on the condenser side, with 422 D, if our pressure was 200 psi, that means that it would start off with do at a hundred point four degrees Fahrenheit. So if it's coming in first, it would be superheat. So that's going to take a little bit, but once it starts condensing we're gon na say that it starts at a hundred point four degrees and then, as it goes through before it starts up cooling.

So we'll save this last pass for sub cooling. But in this range right here we're gon na change it over to bubble so 95.9, so down in here. So the range starts at 100 point four degrees at condensing and goes down to ninety five point: nine degrees at condensing. So there you have it.

That is Glide in action and then, if we're actually looking at the temperature, if we want to say what is the temperature of this condenser coil, we would have to take an average of these two, but for calculating so cool we would use the lower number, which Is the bubble - hopefully that's helpful, Brian or with HVAC school and HVAC our school comm, thanks for watching.