Let's talk about finding Target Superheat. But you know what? Target superheat is okay. Where you want the super heat to be there you go. Where are you supposed to have your superheat whenever we're taking our readings? If we've been doing this for a couple months or a couple of years, we have kind of a feel for what it should look like, right? You hook up something's out of line.

You're like that doesn't look right. But honestly, taking readings, you know it. It doesn't really matter if you don't have an idea what they should be. So just this general rule of thumb like I don't think it's in the right area I'm going to investigate more works and helps us not miss big problems, but we do actually have to know what it should be before we even hook up or else we're not really doing that important of a test.

I'm just going to talk a little bit real quick about superheat. Okay somebody, the first line there. What's the first line? Okay, so Target superheat helps us understand if we're going to flood our compressor. Very basic.

Uh, not. Target super Heap or superheat in general. And super heat lets us know that we're above liquid. Point We've already finished our boiling and the compressor doesn't like liquid at all, right? So we can measure superheat right at the air handler and it'll give us a clear indication of what just happened inside that evaporator coil.

Often we're measuring superheat out at the compressor, we're hooking everything up out there and out of the compressor. You have a clear indication of how that refrigerant is making it back to the system on the note of flooding in the compressor. What will be the opposite of flooding our compressor? Starving it? Yeah, so it gets. it's overheated because it's refrigerant cooled.

So if you have low pressure or really warm refrigerant, warm refrigerant wouldn't technically be starving. But it's just not cooling it. But low pressure is often the scenario where you are, um, overheating your compressor. so it relies on the refrigerant to actually be cool.

So that's why you don't want a super high super heat. which typically means a warm suction line. One, Your system's not running efficiently, but you're also overheating your compressor. The evaporator.

It tells us. super heat lets us know if the evaporator is being fed efficiently. Why is that splitting gas, liquid, and gas? Okay, if you have a really high superheat, you're boiling off the refrigerant way too quickly. you could be feeding more cold refrigerant into the system and running that evaporator more efficiently when you switch.

when you're boiling inside the system and you're in saturation, you are still absorbing heat. You have a cold saturation temperature, but it's not changing the temperature of a refrigerant right? Because it's in saturation, so all that heat being absorbed is going to change the state. it's working at trying to change the state, but it doesn't change the temperature until it becomes superheated. Once it becomes superheated, it immediately climbs in temperature while you add heat.

So if you keep adding heat, climbs in temperature. So if you have a high superheat right after your evaporator, that means a good chunk of your coil had high superheat or became superheated. and then that coil got warm. it raised with the temperature.

So you have a section or coil that is warmer and you don't have as much heat transfer to it. So superheat lets us know that we're we're using our coil efficiently. If out of the coil we have eight degrees of superheat, it goes in the coil. Let's say 40 degrees of saturation comes out 48..

that's a very efficient coil. and you've you've only changed the temperature of the coil at the very end of that coil. did it boil off and even that was only eight degrees of difference by the time it came out the end of that coil. So it's a very efficient coil.

lets us know if it's being fed efficiently. that would be considerations of it being underfed. What about being overfed? Still liquid, still liquid? So it also lets us know the on the bottom I Put diagnosing TXV problems. So if you had like a wide open TXV your superheat would be something that really helps you diagnose that.

What would your super heat be if you had a wide open txt? Zero to nothing. So and then in that situation you are still in saturation. So in one sense you have a very efficient coil. But typically when you are have a wide open TXV it also raises the pressure.

Which means now we also have a warmer coil. So now our entire coil from start to finish is 52 degrees saturation instead of what it should be at 40 if it was metering properly. Sure, you add heat to it and it doesn't change from 50 degrees. it comes out as 50 degrees, but the entire coil is now warmer than it it could have been if we were actually properly metering so it's less efficient.

Typically a warm coil doesn't dehumidify. Well, what about if we have a really low super heat and we have a low suction pressure? What does that tell us about our load on the evaporator? we're going. we're moving to load on the evaporator. Now on the side.

Load is the term for What on our coil. That's right, it's our heat. So we are adding refrigerant. The amount of refrigerant that we are also adding heat or what I'm trying to say is that it's a balance game there.

So I usually for illustrations sake. I'll say if you have a three ton compressor, then we're trying to get rid of three tons of heat. And it's just for the sake of illustration. Makes it easy to think about if your airflow is restricted and you're only moving two tons of heat.

but your evaporator coil still has a lot more refrigerant than that moving through it, you're not going to finish boiling it off. It's not going to have nearly as much heat as it should, so the pressure is going to start coming down. It'll get colder and colder. You have a low superheat.

Low suction pressure. right? the opposite of being overfed. Still, we have a low superheat, but we have a high suction pressure. So when we are, uh, trying to find our Target superheat, we need a couple measurements: Outdoor Dry Bulb Temp and Return Wet Bulb temp.

If you guys want to open up, measure quick. I Have your probes all set up. So your outdoor dryable temp is your sensible heat. It's the heat that you can pick up with your senses most readily.

It's the heat that we all talk about when we talk about temperature. So think of sensible heat as temperature. Heat What you would read on a thermometer that's dry. Bolt Now, Return Wet Bulb is exactly that you can see in the picture illustration.

You have one of the bulbs wet and air blowing on it. so that will. What will that do to the temperature? Nope. It increases the amount of heat in the area.

But it doesn't. It decreases the temperature. It's just like splashing water on your arm waving it around in the air. It gets colder.

The evaporation effect: Wet bulb is basically temperature related to how fast the evaporation process happens. How much moisture do we have In the air, how much heat do we have in the air? How fast will something evaporating? If you have 99 humidity, your air can't really hold that much more water. You bring in a wet bulb and you move it around in the air. It's going to evaporate really slow.

There's not really a lot more room in the air to hold more water to. whereas if you have a drier space, you bring in that wet bulb, it'll evaporate really quick that you'll actually have a much lower wet bulb. So basically, wet bulb is taking into account your latent heat in the space. not just the sensible heat, but also the heat that's there related to moisture.

So it's taking into account your moisture so that you can accurately calculate your superheat. Target Superheat: How much heat is actually in the space? Because I'm not just changing the temperature. I'm also removing all this latent heat. The moisture in the air, right? So that's why you need your wet bulb.

All right. Tools are already turned on. The other things you would need to calculate your superheat would be a Target Superheat calculator. Does anybody know where to find that? Anywhere else you could find a Target Your Target superheat? Yep.

Google The Internet. What about Caramel? The slider? There's a there's a slider. Yep. manual manufacture chart for that specific equipment I Have one up here.

Apparently this is for R22 I Don't think it really matters. Your superheats are going to be very similar. but um, also your Measure Quick. You guys are using Measure Quick every day.

If you put in the tonnage of your system and you change it from TXV to piston and you have your probes, you have to have one actually connected to the outside air temperature Right then you're going to have your uh, your target superheat measure quick. We'll give it to you. Uh, did I mention that? Yeah, Outdoor dry bulb temperature is very important. So your two measurement outdoor dry bulb not in your indoor and then your indoor wet bolt.

All right. So the manufacturer chart. you have a outdoor indoor wet bulb, outdoor dry bulb and you just follow the lines in the intersect giving you your superheat. All right? So let's go ahead.

let's figure it out. So the we have your tools, you have what you need. Find out what the Target super heat should be on this system right here. as if it was a piston system.

HVAC School Calculator or Measure Quick if you enter in all the information now. I Have one in the return and one outside. What's the wet bulb? What's the return Wet bulb? Okay, outdoor is what 75 73 is what I have to. but it's an outdoor level.

No dry. It's dry bulbs. Outdoor Drive. all this one.

Okay, 1305. There you go. Yeah, it's really easy to uh on the calculator to just put it in the wrong slot. Okay, so that's how you, uh, actually are going to set your charge on a piston or fixed metering device, right? So if you are below the super heat that you should be and you're setting the charge, what do you need to do? Yeah, if you have a lower superheat, then what the target superheat is? You need to vent into a recovery machine? Yes, I've noticed when setting superheat on a system, it's actually a lot harder than on a TXV because the TXV is automatically adjusting and setting that superheat so you have a little bit more play.

But when setting on a piston, as soon as you get close, it's really easy to go over. You have to actually let it sit and the coil get down to temperature when you've added charge. Now, the coil has to adjust in temperature and let it sit a little bit longer and your adding process is a lot slower with the superheat. Okay, the big question of the day is, why not 10 degrees of superheat every time? Why not just say oh, we have a piston.

Let's set it for 10 degrees. It's variable. It's on temperature. What's what's variable? The the target? The target is variable.

Yep, But why is it variable? Why why not just always put it at 10. we don't have a constant temperature. Yeah, so things like outdoor temperature affect how much refrigerant, the, uh, how much pressure the refrigerant is moving at. right? So you can actually have 400 PSI on 100 degree day.

That's a lot of liquid refrigerant pushing into your piston. Or you could have, you know, 200 and 180 on a cool day. And that's a huge difference in how much refrigerant is being pushed through the exact same little hole. A little piston hole.

So if you look at this chart right here, let's say that you set it on an outdoor 65 degree day. Let's say you set it for 11. Super Heat. Um, and your indoor was 70.

you had a really warm, humid indoor indoor pool. Basically notice what happens on our superheat when we go increase the temperature outside. You notice how on this chart the numbers get lower and lower as the outdoor temperature goes up. So it's a little counterintuitive and you might think you're dealing with more heat.

But it's because as the outdoor temperature goes up and increases our liquid flow, so it's shoving a lot more into our coil and we'll actually have lower. So if you were to set it for 10 superheat on a 65 degree day outside, and then the next time it was 100 degrees, you're probably going to be down three superheat to maybe zero superheat. And of course, that's also related to the indoor heat. Tin superheat actually is a target for 65 on here as long as the indoor has an extremely low, uh, wet bulb which is fine.

That's why you actually have to know, so make sense. All right. Cool, That's it. Oh man.

wow, Thanks for watching our video If You enjoyed it and got something out of it. If you wouldn't mind hitting the thumbs up button to like the video, subscribe to the channel and click the notifications Bell to be notified when new videos come out HVAC School is far more than a YouTube channel. You can find out more by going to HVAC Ourschool.com which is our website in hub for all of our content including Tech Tips, videos, podcasts, and so much more. You can also subscribe to the podcast on any podcast app of your choosing.

You can also join our Facebook group if you want to weigh in on the conversation yourself. Thanks again for watching! Thank you Foreign.