Hey thanks for watching in this video, my friend eric kaiser talks about measuring static pressure and using that, along with factory, fan, charts and fan curves in order to calculate airflow and to learn more about airflow in general eric's, one of the best educators in our industry And i'm really thankful that he took the time to share with everybody at the second annual hvacr symposium. It was a great time we got to meet so many different people. Eric wasn't able to be here in person, but he did zoom in to the classroom and then there was also a group of attendees virtually really a great session, and i wanted to make sure that you got a chance to see it. So thank you to eric for allowing us to use this here on the youtube channel again eric kaiser talking about static pressure measurement and airflow charts.

I hope you enjoy all right folks, well welcome to um a another class here that you're sitting in. Hopefully, you guys are learning something down there, so my name is eric kaiser coming to you from beautiful indianapolis, where it is uh, sunny and 60. Instead of i hear you guys about sunny in 85, so a little bit different. If you have questions going through we're talking about static pressure, setting up blower speeds and sizing air filters, three things that actually kind of go together.

So if you have questions while we're going through today feel free to ask those that are online, of course, can raise your hand and and uh, i think, can they type in? Can they uh come in by voice or is it just typing in on the chat? Oh, both okay, all right, so there we go if you guys online, want to ask questions, also feel free i'll pop the chat window up here in case, i see something jump up. I can see that as well, so with that who, who, in the room there uses static pressure, you ever measure static pressure. I can see you can raise your hand, see. I can see you raise your hands um right.

So it's a pretty important thing. So, let's dig into that first number, one: what is static pressure, okay, so static pressure is the force. So when they're air in inside ducts, when air is moving through ducts, we have two pressures. We have velocity pressure, which is the force of the air coming through the duct, and then we have static pressure, which is what's pushing outwards on that duct, okay and that's created by the velocity pressure pushing through here it pushes out and we use static pressure to Figure out how much resistance to air flow we have in that ductwork or in or on a component how much that component resists air flow being flowed through now.

That applies to when we measure it. That applies to that component. In that moment of time. With that specific volume of air that's moving through it all right, typically, we use a scale inches of water column or, or you might see, wg as water gauge is the scale that we use so there's somebody else with a live mic, i'm getting a little bit Of uh noise through here i'll mute them.

Okay, thanks! So that's what static pressure is right: resistance to airflow when the blower turns on it creates that resistance to airflow we push out the little guy down here is the blower right. The air is going to be the box, we're trying to move that air and the hill. Pushing back is the duct work, so static pressure, obviously changes with air volume going through ducts. So when we measure it, it's only applicable to the volume of air going through the duct at that point in time or through the component, whether it be a filter or a fitting or a grill.

Now, external static pressure, so external static pressure is anything that's outside of the blower bearing unit. So if we have a furnace right, where we've got a blower in the bottom right, we're pushing up through here that furnace is rated from the top to the bottom. Anything outside of that, or in that case you might put something in the sides of your blower compartment - that's external to the unit same thing with an air handler here where we have a negative pressure, coil right or if you have, you may have a what is It train makes air handlers now that have a positive pressure coil or a fan coil unit that has a positive pressure coil on it. I think mitsubishi does as well, so you may see it both ways, but outside of that, whatever we connect to it in the field is what we're measuring the resistance of that's, what the blower is capable of overcoming and if we put too much resistance on that.

That blower may fail prematurely things like that. So when we measure it, we measure a positive and a negative static, all right so positive negative if we hook up a dual port manometer, something like this. We put the the negative side or the low side of that dual port manometer on the inlet connect to the outlet. We get our total external static pressure or external static pressure right there.

Now we can also measure one side and then measure the other side. Okay and then we add those two numbers together. The challenge with this is that a lot of people run into if they're not familiar with it. Is you don't use these symbols because these symbols here, your plus and your minus, only mean only indicate which side of the blower you took it on they're, not part of the mathematical equation, so we get rid of those.

We just add those two numbers together and we get our external static pressure, make a sense. Okay, probably done this before i just want to go over it because i don't know who all is in here or what experience you've had. So it's a good thing to remember that, because i've seen a lot of people, try to oh i've got ta, take this and subtract this and then you end up with a really low static pressure and you're chasing your tail around going well. Why do i have a problem if i've got low static pressure, all right now, differential static or static drop? Okay? So that's the static pressure on this side.

You got a component in here like an air filter. What's the static differential or delta p, as it's sometimes called? So if we add 0.23 inches here 0.15 inches here, our air is flowing this way, we've got a .08 inch drop across that component. Okay, when we make the connection on the manometer we're going to make our positive connection over here, even if this is in the return side, we're going to make our positive connection on this side, if we're using a dual port manometer and our negative port over here, Because this is lower pressure, those two ports are in reference to each other, so the higher pressure port goes to the positive. Lower pressure is going to go to the negative.

Does that make sense? Okay? Now? What tools do we need? Of course, we need a manometer. All kinds of different stuff: these are ones that i've used. I like them all. They all have pluses and minuses.

When you're talking about magna helix, sometimes they get a little iffy to read. They are sensitive to things like vibration and dropping stuff. Like that, a lot more than the digital ones are, so i don't so much like to use these in the field transport them around in my truck, unless i have a good, solid way to carry them foam filled case, something like that. The other thing is on a magna helix, if you're, using that it has to be perfectly level, you actually need to put it on a perfectly level surface in order for it to be accurate.

So i am a real big fan of digital. I used this little 510 for years. I've got the the 510i uh the new tec. Dg8 is a really nice meter because it can do static pressure and building diagnostics.

It goes you know it goes real low in the pascal scale. Even so, that's a handy thing. Plugs to be able to plug up the holes that we make in the duct work, it's a really handy thing to have you buy a little plastic plugs pretty easily. If you deal with truetech tools, they sell them.

We need some good hose. I, like a nice silicon hose that doesn't keep a memory to it. If i can find it because that way, when it comes out of my bag, i'm not trying to uncoil something and deal with pulling that out straight. You can get single port manometers, like the field piece now.

Field piece makes these single port bluetooth manometers, and then the app combines two of them together and it acts like a dual port, so they both connect up to the app and it combines them into the dual port. We need static tips of some kind, so this is a static tip, what's called a static tip, and this is another tool that i really like to use, which is just a ball inflator needle for inflating soccer balls or footballs, or anything like that and the handy Thing about that ball, inflator needle, is it's small enough that it fits through the hole of a screw. So when you're trying to measure in really tight locations like between the furnace cabinet and a coil or if you have an air handler with a built-in filter slot, you need to measure between those points that ball inflator. Needle works really well.

We'll talk about how to test that in a little bit um drill bit. I love little step bits like this to go into a a small drill or a screwdriver, with a quarter inch hex coupling on the front of it or any small drill that that's a great thing for drilling holes. And, lastly, anytime you choose a manometer. You want to choose something that has a minimum of a .01 inch water column resolution to it.

You know, find your accuracy, the one that you like, but you need that as a minimum resolution for measuring static pressure. You know the uh. The dg8 will go farther than that, but any of these other instruments and there's a lot of other ones out on the market. I didn't put them all on here.

These are just some of my favorites that i like to use all right, but that's that's a big thing, because i've seen people there used to be several digital manometers on the market. That would only go to 0.1 inch and they would try to measure static pressure and i'm, like you, can't do it because you're missing this other digit over here. That tells you where you're at it increases the accuracy of your reading. Okay now static pressure tip commonly referred to by some people as a pitot tube, but this is not actually a pitot tube.

This is a static, tip, static tips, measure on the side of the tip. This tip needs to point into the air stream and then comes back here to a single port. A pedo tube is actually going to have two gas paths inside of it and you're going to have two ports back here on the back of it and you're, going to have side measuring tips and also you're going to have a hole straight into the end of That tip that measures your velocity pressure, so this is a static tip. Now here's the way i use that ball inflator needle this is the fitting.

That's in my manometer kit. It's the eighth inch pipe thread that goes into gas valves, so that i, when i screw that into a gas valve, and then i found some silicon tubing that goes between the threaded portion of that ball, inflator needle and the threaded portion on the the eighth inch Pipe thread fitting and just slides over there real nice. I found that actually at a hardware store - and i was like - oh hey - this is perfect. I can just pop it on here pop it off when i need to again really handy little tip for measuring.

So again, static tip orientation. This needs to be pointed with the airflow. You can either point it in into that airflow or you can actually point it 90 degrees away from the airflow i prefer in. If i can get it, that's the prescribed method, but you can point it away.

If you have to you, just don't want it sideways in there right where that error is, is pushing into the side of those holes, because if you do that, then you start reading velocity pressure and i'll show you a little bit about that in a little bit. Now say you want to try out an alternate tip. Okay, so when i first decided i was going to try this ball inflator needle, because i needed something that i could go through the screw holes and a cabinet on. So i didn't have to drill holes in a cabinet, so i grabbed this ball inflator needle and i'm like how am i going to prove this right? Well, it's pretty simple! You use the differential pressure on your manometer, so you can prove out any tip that you want to try for static by connecting it to a known tip, which is your static tip hook.

The other side of your manometer up to your proposed tip that you want to use, and you should see zero differential pressure between those two. If you start seeing differential pressure, one of the tips is not reading right. It's going to be your alternate tip because that static tip should be reading correctly, provided you have it inserted correctly, all right! So that's an easy way. I've seen people use copper, tubing, um.

Some people like to use a little cap tubing, capillary tubing from refrigeration systems, because it's long and you can form it and get it around corners and things like that to take measurements and stuff in so just prove it out like this. Make sure that it's going to give you an accurate reading if you use an alternative tip style? Okay, now, let's look at test locations. Okay, so test locations is where in the duct we want to test, and one of the things we have to look out for is air turbulence in the duct, because if we get air turbulence happening inside that duct, then it will come in and it will. It will falsely affect our reading and it will be pushing in on the side of that.

So if you have a sharp corner like this, this is kind of how air looks when it tries to turn this sharp corner. Think about driving down the street in a car and you come to a sharp corner in the road. You can't make that you can't come down here with any speed and make that turn and just head the other direction. You're going to take that corner wide you're going to swing way wide.

Well, air does the same thing, because once it's going this way, it doesn't want to change and go this way unless it has to well this wall kind of forces it. So if we put a static tip in here right, we're going to get a bad measurement same thing. If we put a static tip in here, even though this might be going fairly straight - we're still going to get a bad measurement, because this right here is effectively effectively shrinking this size of this duct right. So i'm using about maybe two-thirds of that duct and i've got a third of it sucked up in turbulence, so i'm actually going to get a high static pressure reading.

If i insert my tip too close to this corner versus, if i put it in up here now, things are straightened out and i can get a real static pressure. Reading that kind of makes sense all right so be cognizant of where you're putting your tips in and taking these readings now it kind of depends on what you're doing with the reading as to how accurate you really have to get if you're looking for a year-over-year Comparison reading - okay - maybe you can put it in right here, because if something changes you're going to see a shift, the absolute doesn't matter, the absolute reading does matter when you start trying to use blower tables, and things like that, which is what we're going to talk About later on, all right now so - and this was another note - i forgot about try to take your readings two to three duck diameters downstream of that fitting okay, because that generally gets you out of that really turbulent area. If you have turning veins in there right, those turning veins air comes in and they redirect that air, so it stays a lot straighter still about one to one and a half duck diameters downstream is where you want to take that sample at just to get away From any potential turbulence that happens in here now back up one slide: this is the second most efficient fitting at turning air and making it go in the corner. The reason this is used a lot is for space because we don't often have the space to make these nice wide sweeping turns right.

We don't build buildings a lot of times or houses with room to put in these giant sweeping elbows, with a giant sweeping elbow things turn nicely in there just like they do on a long sweeping curve on an interstate when you're going really fast, you can go Around that curve, real nice and easy, you don't have sharp corners at high speeds on interstates or if you do, people tend to run off and end up in ditches or walls or whatever, and it looks like a you know a sunday afternoon in a nascar race Somewhere with a whole lot of cars in a wall, okay, so again about one to one and a half duck diameters downstream of that elbow, get you a good sample all right. Now, let's get into near equipment measurements, and - and this is something or near fitting measurements. This is actually something that i encountered so this setup right here, uh we had a return drop, coming down gas furnace, evaporator, coil plenum, and then we had this weird funky duct up here that it was elbow elbow and then duct, because there physically wasn't space to Take the plenum up high enough to make meet up with that duct, so the installer said well guess what i can put these nice elbows in here and that'll make the air turn well, not really because in order to make an elbow work in a duct, you Have to have the air going straight into the elbow and a hard radius inside doesn't work. Well it you.

It works like that square corner. We saw in the very square. Elbow works the same way, so we've got air coming up here, trying to make this corner before it can get straightened out. It gets slammed up in here and then gets slammed again to try to go down this duck.

Now. This system always had issues. I didn't install it the the company that was installed, it was long gone. The company i worked for was maintaining it and they asked me one day.

They said what can we do about this and i started doing some testing and basically, if they wanted to fix it, they opted not to it was going to require some major duct renovations, here's what we found. So you can see these two elbows here right. This is the plenum over here all right, so i'm measuring in this case right here, i'm measuring with that manometer. I got a .12 static pressure on that top hole now, you'll see, i've got a second hole drilled down here and if you look in this picture, you see that i've got two holes drilled in there and my probes are inserted.

But the thing is: look at my differential pressure between those two probes. This bottom one down here, is in a lot of turbulence because that air can't come up and make this turn fast enough. So, even halfway up that duct, where that probe was, i had a ton of turbulence back here and the airflow in this duct was terrible. This was a very clear instance of seeing being able to see that turbulence with a static pressure test, because in essence, this duct was not the same dimensional size.

If you actually drew a line from this corner somewhere up to here and from the bottom corner straight up through this corner, you know now you've got just this much duct. It was a lot smaller because the fittings were too close to each other. To make a nice smooth transition for the air, okay, so test locations near equipment, so this is going to be like an upflow gas furnace with a filter off the side of it down here with a return drop very common in my part of the country, some Parts of the country not so common, i know various places have different things. You know, if you guys are all from florida, um you're, probably you know looking a lot of garage systems.

Things like that, but air comes down here, makes that corner when you get close to this filter below the top of that filter. The air is going to start kind of trying to turn and go into that. So it's going to get real turbulent down here. You want to take that pressure right up above the filter in here in the blower compartment you kind of want to be in the bottom, the middle of that filter.

You don't want to get over here on this side, because you start getting a lot of turbulence happening in that blower compartment. You want to be as close into the face of that filter where it's coming in as possible. Then, of course, we need to measure at the top now between these two points right, the top of your furnace and the filter here. Those two are your external static pressure right.

This is duct only pressure. This is duct plus filter. This is coil plus duct, and this is duct only pressure right. So that's about the four places you take pressure tests when you're talking about static pressure on this type of a system.

Now, let's look at a different system: okay, here's an air handler or a fan coil unit. This one happens to be setting on a base and we've got an external filter rack over here we've got duct. Obviously we need to take up here. Okay, this is going to get us our duct pressure here as well, coming immediately out of the filter, you want to use these two measurements for your filter pressure.

So if you need a filter, pressure drop those two measurements right there now challenging thing is measuring this box over here, because this box is also going to have static resistance because there's no turning veins or anything in here to help turn that corner taking measurement. In here is really challenging, because it's going to be very turbulent in this box since there's nothing in here to tell it where and how to turn all right. We also probably need to take a measurement when we're doing external static pressure. We need to take our measurement right here because we don't want to use this measurement because there's extra static in that box so for external static.

We really need to measure over here and then, of course, external static on an air handler. You don't want to measure external static immediately at the top of the air handler. You need to get where the, especially. If there's a heater kit in there inside that air handler, it can be very, very turbulent all right, so we need to get up.

Typically, i, like 18 to 24 12 inches, is kind of my minimum but 18 to 24 inches. Typically above that, if possible, i understand physically, it doesn't work all the time now. This is another configuration that i've seen with an air handler and a box on the bottom of it so again to get that duct pressure. We really kind of need to test over here before we hit this elbow, because once we get into that elbow we're going to start seeing a ton of turbulence down here unless somebody put turning veins in this, which is pretty rare.

If we need external static pressure, we've got a test between that filter and the bottom of the coil again. This is where that ball needle comes in really handy for this, because there there's not a lot of space in there typically and it is, it can be really hard to get the um a hole drilled in there safely, because you don't want to hit the drain. Pan and you don't want to hit the coil, obviously so - use that ball needle to go in a screw hole or something like that. It's real handy for that and same thing with the supply static up at the top all right.

It's really hard on this one to get a perfect filter static, because if you measure right here that air is is not turning real well and it's not going to be real straight. So you would really have to play with it to figure out where the sweet spot is on the airflow and it because of the turbulence you may not ever get a good solid reading in there. Okay, filter grill test location. So if we need to test the pressure drop on that filter with a filter grill, you need to insert a probe through the filter, make a real small hole in that filter somewhere, just a little slit with a knife or something and put that probe in there To make a measurement right or if you can get to the duct right behind the filter, you know if you're, if you're within a couple feet of this fine, take a measurement unless it necks down in size.

If once it next down in size, you don't want to do that, but a lot of times we can't get to this duct real easily and we just need to come in from the front side of the filter. Grill. Okay, let's take a little bit more look at static in the duct system. This is what i like to call the static seesaw effect so because higher resistance affects airflow.

If your blower motor and it depends on what type of blower motor you have as to how this works, so if you have a piece psc or an ecm, constant torque, blower motor right, constant torque, which is your x13 style with the voltage taps on it. So that you're moving the wires around to select the motor speed, then we get a static seesaw. If something happens, where the return static goes up, our supply static is going to go down slightly. The reason is because if the return static goes up and affects the airflow, the airflow amount on the supply side goes down, which means we get that static effect.

What this means is, if you fix a problem, you find a problem say you find, you have a return problem: okay and you fix it and you lower the static on the return. Now you increase the airflow or the decrease the resistance, so you increase the potential airflow. Now your static can swing the other way and it may be high on the supply. Now it's the total of those two is the external is what we're worried about so make sure that once you fix a problem, re-measure it and make sure there's not any other problems identify the problem, fix it re-test to make sure there's nothing else.

Okay, but this is how you're going to see static work again, psc and ecm constant torque. Now on ecm constant volume motors, it's different works a little bit differently. The reason is because that constant volume motor will change rpm to try to maintain a constant volume. So if something changes on one side, like your return, static, goes up as long as it doesn't go up enough to limit the air flow volume, the supply side is going to stay the same because our air flow volume did not change our airflow volume through the Whole system didn't change even though this static went up because the blower corrected somewhat, and the blower then draws higher amperage to be able to do more work which we'll talk about a little later, all right same thing, all right.

If the supply goes up, the return static is going to stay about the same unless the supply goes up enough, that it limits the air flow on the return side. So you would have to have somebody really closing registers or a fire damper go closed or something like that. You're gon na have a major event with a constant volume motor so know what kind of motor you're testing static on if you're, using if you're doing troubleshooting with that motor all right now, if the blower bearing unit is internally dirty, say you have a fan. Coil unit and the coil or the blower wheel gets dirty in there or you have a gas furnace, a condensing gas furnace and your secondary heat exchanger gets dirty.

What's going to happen, then, well we're not going to be able to move as much air through the system because those components are dirty. So when that happens, the seesaw breaks and both sides get low because there's not enough air volume going through. That makes sense to everybody: okay, all right, okay, so this is kind of my troubleshooting um flow if you will for for static pressure. So if i see high external static pressure, i'm going to determine whether it's in the supply or the return i'm going to take separate measurements, i started the equipment i'm going to test each component down the line.

Until i find something, that's got a higher drop than what i look for higher than what i'm expecting. I have to know what the drop is on stuff. What's it supposed to be on certain components like filters, filters are a big thing and near equipment ducting, especially on the return side, is a lot of external static pressure. Look for that high differential pressure across those components.

Take your reading start. Maybe leave one probe at the furnace or at the air moving device and work your way down the duct with different holes and a second probe. So you can always have a comparison right then correct the issue. If the owner or the the money person wants to pay to, have it corrected, that's always up to them, retest the static pressure and repeat the process, if necessary, that's my troubleshooting flow chart to work with static pressure.

Now this is another big troubleshooting tool that i used in the field so anywhere. I would take a static pressure measurement. I always use the same probe type there and you cannote it next to it. If you want to, but i carry a sharpie around in my pocket.

Most of us do right. It's right there right there in the pocket. You grab a sharpie out my wife, hates it, because i chew on the lids. You know i put them in my mouth and i walk around carrying a sharpie and she's like.

Why are there teeth marks on this? Well, because that's the way i do it, i write down the heating and the cooling static pressure next to that test port. This is especially good on maintenance customers, because anytime i go back to that customer. I take that static pressure. It's similar to taking blood pressure in a human.

If i take that static pressure - and i know i'm in heating mode fan, speed or cooling mode fan speed whatever it is, and it's different than what i wrote down there when i either when i started working on the system or commissioned the system. Originally, i can go back and i can say: okay now i've got a problem, something changed, ductwork got smashed, maybe the um. You know vents closed. Somebody set a couch on top of a register.

Who knows somebody closed off? Half the house because we're not using that half the house. We don't need to put air over there well right. We know how that works out. So again, this is a really valuable troubleshooting tool and it's just a quick check once you get that set up and get those notes written in there boom boom boom you're done.

I can take four static pressures in under two minutes right and i've got a good idea of how the the air flow is performing in that system. I don't have to take complicated measurements, except maybe, when i'm setting it up. That depends on the system. All right now think outside the duct external static pressure can sometimes be increased by duct components that are not directly attached to the main duct system right.

I just read that verbatim for a reason, think about transfer grills door, undercuts louvered doors, etc. You've got to look at that whole house as part of the duct system, especially on houses that don't have returns in every room or every space, because they're, relying on these other pieces of the house to move that air and technically those are really part of the Duct system, even though they're not necessarily physically connected to the ductwork that we install right, i want to say thank you to jenny, garcia. I don't, i doubt he's sitting in here but um. I want to say thank you to him for sharing these photos with me, because this is what um happens with a um uh louvered door, so that louvered door right.

There is almost .18 static pressure, inches of water column across the louvered door. This is really common down in florida, where you have central um returns in a house he's down in south florida right on this. One he's actually he's got a dual port or actually a four port manometer. It's dual channel, two port manometer from the energy conservatory.

I think steve rogers is down there somewhere and i imagine you could see one of these in person if you haven't already so his total external static is 0.844 just this louvered door is almost .19 now a lot of times. If we're in there doing a maintenance or we're checking out a problem for somebody, we're probably going to have this door open right, we walk into the mechanical room. We leave the door open, so we can walk in and out. It's one other thing: make sure that we're checking this under normal operating conditions.

Don't change something to the airflow when you're accessing that room or something like that, because that is is going to change the reading for your system, because if he had that door open, he wouldn't have nearly this number for external static pressure right. So keep that in mind when you're doing your checks now questions about static pressure? Can you put the um the pressure tips you're talking about like the just the static pressure tips? Yes, you can put them in flex, duct um. The challenge is anytime. You put a hole in something like a piece of duct.

You need to seal it up afterwards. So how would you seal that up? Because, in order to go into flex, duct you're going to have to pierce the outer skin through the insulation and then through the inner liner and there's not going to be a good way to um seal that up. So can you yes should you that's really going to be up to you because you know, especially where you're talking? If, if that flex, duct is in an unconditioned space where it gets hot or cold, you may ultimately end up with condensation issues inside that flex duct because of that hole in there. That makes sense, yeah, okay, anybody else right now, all right, you guys doing all right, you're, not bored on me.

Okay, all right. Let's get into blower settings, blower speeds! Why do we set them all right? The factory doesn't know what components we are going to be. Connecting outside of that blower bearing unit they have no idea all they do. Is they set the blowers up to make a quick test at the factory to make sure that they run they're going to do a a quick on off test? They might run it.

You know of a gas furnace or something like that they may do a quick run fire on it, but they're they're not even going to get a temperature rise really on that thing, they're just it's running it's on down the line. So it's up to us in the field to set up lower speeds appropriately for our situation, whatever it's installed in right, so we set them up to match the installed components outside that blower bearing unit first thing. You really need to know what type of motor do we have ecm constant volume in today's world. We're pretty much going to see ecm constant torque.

Psc is pretty much gone now. These two set up the same though so your setup, if you were doing it on psc, should not change going to ecm constant torque. The setup steps are the same thing. We're still going to use a static pressure and a blower chart now know your equipment type.

What type of airflow are you going to set up? If you got gas or oil heat, you need to get it running with whatever factory blower speed, it was get your combustion set up right and then you need to go set that blower speed. Now you might want to check your combustion when you're done, especially if you're, using an analyzer depending on what method you're using but get the combustion or the gas pressure at least set. Then set your blower speed to the middle of that temperature rise range. That gives you a good temperature rise coming in keeps you away from condensing in the heat exchanger, and it allows you a little bit of space for your filter to get dirty and lower the airflow a little bit.

Okay. Now, when you're in an air conditioner or a heat pump, because we're dealing with the refrigerant cycle, you need to set the air flow first and then set your refrigerant charge to the airflow unless you're just charging by weight all right. But if you have to set the air flow up air flow first, then refrigerant charge so ecm constant volume. This is what we know as variable speed: okay, um design equipment.

Airflow. You need to know what that design equipment. Air flow is and we'll talk about that. In a little bit, no rules of thumb here: okay, no thumbs; no, no, no thumbs you're going to have to have the install manual it sets up by dip switches or at the uterus user interface through the the thermostat or the wall control.

That's where you do. The setup for the airflow on this when you get this set up optimally, it should be at less than 70 percent of your max external static pressure rating. Can it push up to 100 percent? Yes, can it push over 100 percent? Some motors will depends on how they're programmed. Is it good for the motor? No, it shortens the motor life all right.

Just because we can doesn't mean we should it shortens the motor life and it increases the energy use. So if you sell that as a long life piece of equipment - and you sell that as a an energy saving motor and you're running more than that 70 percent of max static, your customers not going to get what you sold them all right. So if you've got a uh say a unit, that's rated it at an inch of external static. Like some of the units are today, you don't want to run that over a 0.7 external static, that's easy, math right! You get down into some of the other.

Some of them are rated at 0.7 0.8 again that 70 percent number is kind of the sweet spot um on that motor, where it gets into lower energy ranges, still keeps the airflow moving. Gives you a little room for your filter to load up things like that? The the real the biggest enemy of these constant volume motors is high static pressure because high static pressure means they have to work harder, which means they build up heat because they are an air over motor they're, an air cooled motor. So if they start building up too much heat in them and they can't get the they don't have enough air flow for cooling, so the higher the static, the more heat they build up now, constant torque or psc, constant torque is also known as your x13 motors. All right again, we need to know what the design equipment air flow is, especially for uh.

I think for air conditioning. Okay, no rules of thumb on this. The the 400 cfm per ton does not always apply. That's a that's, a very nominal airflow.

The simplest way to do this is with external static pressure. It gets you really really close. It's the easy way to do it. If you need to dial it in more select another measurement like a a true flow grid or a duct traverse, or something like that, okay, this isn't the easiest simplest way to do it external static pressure and get the blower chart out of the installation manual.

Now this is kind of what a blower chart looks like you got to where your return, air connection is on. This manufacturer shows your wire lead color codes, so these are different sizes of units, as you can see, and they give you an approximate cooling tons like where you should start at and if you look over here that kind of correlates to your 0.5 external static pressure. But if you're not running right at five, then you got ta, make some adjustments and don't go by this right. This is a starting point.

So if you've got a two and a half ton set it on black to start with, then start measuring and making sure you've got enough air flow okay. Now the other half of that is that we've got our whoops. Let me back up one more here: okay, so the way to use this, i missed one static pressure up here on the top okay and you can interpret interpolate between these two columns. This is your external static pressure.

This is your motor speed over here. So whatever wire, color or selection, now, if it's a like the some of the constant torque motors, are just going to tell you the number of that speed tap on the side of the motor, because they only may only run two wires over the motor one for Heating one for cooling and you have to select which tap to plug into on that motor depends on the manufacturer. Okay, now we need to know what the design equipment airflow is, and this you have to get into the equipment performance data. This is part of manual s and should be done in conjunction with manual j.

So this is a, i believe, a three and a half ton unit, all right, so yeah three and a half ton unit which we're going to zoom in here. Okay, we're going to pick this part over here, all right, which is our evaporator air and we're going to go over here and look at our outdoor conditions, so we're going to zoom in a little bit so evaporator air. This is our approximate air flow going across the evaporator coil entering air wet bulb. This is very important that we get wet bulb temperature, so we need some type of a hygrometer to do that.

Okay, some type of a a probe that can measure your wet bulb and dry bulb, so a psychometric probe. Okay over here we have our outdoor dry bulb, temperature, okay, total and sensible capacity. And, of course, this is our our total kilowatts out of that system, which we we're not going to worry too much about the total system, kilowatts of power usage over there now. First thing we need to know on this chart.

I picked the 95 a because it's a pretty common design temperature range somewhere around 95 and b, because this is actually ahri design conditions. So this being a two and a half ton unit, we've got 41 500 btus right there. So that's real close to that. 42.

000 of a three and a half ton unit - 95, 67. 90. The design temperatures are 95, 80, 67., so it's 95 outdoor, 80 degree dry, bulb indoor and 67 degree wet bulb. Indoor is your design conditions for hri? That's where all of your equipment capacity is rated at now it changes from there and how many people run their house at 80 degrees in the summertime.

I i know of one that used to me, but not very often anymore. My wife gets grumpy, okay, so on the chart, all right we've got 67, which is in reference to 80 degree, dry bulb, and this 62 down here, which is also reference to 80 degree dry bulb. However, there's a note: a tva rating indoor condition, 75 fahren dry, bulb 63 wet bulb. Okay, all other indoor temperatures are at 80 entering dry bulb.

So i'm going to pick and look at my ratings when i'm looking at this at that 63, because that's actually a lot closer to real life, indoor conditions and what this is. If you put this into a converter over here, you can see. What i did here is due point, so dp is dew point for human comfort. Ideally, we really want to be between 50 to 55 degrees.

Dew point now, 75 and 63 is close. It's a little high, but if i pick this 80 and 62, i'm on the bottom end of that scale and that's freezing, it's actually really cold to a human to walk into that to most humans. And if you look down here, i don't have a lot of latent anymore, especially if i get into a 400 cfm. If i look at that, 62 right here, 3882 and 3882 had zero latent removal right there.

But the reason is because i'm looking at a 50 degree dew point and that coil temperature is running right at about 50 degrees, is where our saturation temperature in that coil is so i i can't pull any more latent out. Everything at that point is going to be sensible, which is fine, because i really don't want my indoor space going colder than that. So we're going to look at this one here and that's kind of going to be our guide. We're going to use that 63 degree entering wet bulb column to figure out what we want to do and what we need to do is figure out what our sensible heat ratio is, and this number comes from the load calculation, a manual j load calculation, when you Hit that you find out what the sensible heat ratio is and its sensible heat ratio is sensible, divided by the total, so whatever the sensible number is divide by the total, and that gets your sensible heat ratio.

So you see, i've got three different ones: 0.73, 0.77 and 0.81, depending on what my airflow is so depending on what the load calculation says, this is where i decide to set my bloat my indoor air speed at what sensible heat ratio do i need this. Is your design equipment, airflow selection? So this really needs to be done before you can set up your blower speed. You need to know this information, okay, because if we go down here, we set this for that 0.73. It's not a huge change in btus, but you're going to do a lot more latent work down here than you are up here, depending on what part of the country you're in if you're, in a very dry area.

Heck go up here. For this point, eight one! But in my part of the country and um, most places, probably east of the mississippi or east of the plains, you're going to want to set somewhere between that 400 cfm per tonne or 350.. So this is at your 350. right.

So this is where we we get rid of that rule of thumb. Now. Did everybody kind of uh understand that any questions so far? Okay, now setting up with an internal filter? How are we doing on time here we're moving right along? We might actually get done early. You guys aren't asking enough questions so setting up with an uh an air handler a lot of air handlers and i don't think any furnaces anymore come with internal filters.

There used to be a couple, but there's still some air handlers out there. They come with a throwaway, essentially rock catcher plastic filter in here. The thing about that is that, most of the time that filter drop is included in the external static pressure rating. So if we take that filter out, our blower charts are no longer accurate, you start having to do some some funny math to try to get that um taken out of the external static pressure right.

So when we're doing our air flow there's a couple things i like to see on that now, if you've got an external filter that you're adding on for better filtration, i don't recommend putting anything more than that rock catcher in this filter slot, because your static pressure Is going to absolutely go through the roof? It's going to be crazy on you, because this filter slot is not large enough for that. It'll only handle a one-inch filter and it doesn't use all of that filter when it's in there, because the opening in the drain pan is not large enough and you end up using about maybe two-thirds of the filter. And you can see that when you pull the filter out and it's only dirty in the middle of it - it's not all the way even to the edges. So we put in an outside filter here, depending on the blower motor.

If it's a constant volume right because they modulate to to maintain that air flow through the equipment, you can go ahead and remove that filter and seal that filter slot up. But if you have to use a blower chart and you're using a constant torque motor, you may want to leave that in there because the blower chart is not going to be usable per se. When you take that filter out, because some of those filters have got you know - maybe a 0.05 or a 1.0 static pressure on a 0.10 depending on how much air you're pulling through. So you may need to leave that in there now, depending on how you have this put in, that filter can kind of act as a little bit of an air straightener, not not a lot, not as good as turning veins, because like on this situation, one of The problems i've seen is, if we have an a shaped coil in here right.

Imagine an a shaped coil in there that airflow comes down in here and comes up and ends up all in this slab over here. This slab on this side gets shorted on airflow. We don't have laminar or even flow volume between both slabs of that coil, because again that air doesn't like to make that sharp turn and go back over into this slab so that filter in there may act a little bit like an air straightener. But not a ton, not a ton.

It's still not going to be good as something like turning veins, but this is something to keep in mind when you're doing this setup depends on what blower motor you have in here as to what you are going to do with it all right now, any questions On that so far, uh back to what you were say something there about an external filter, um, i'm kind of not lost now. Would that be? Would that be a double filter? So, if you're talking about like this system here, where, like this blue box, would represent an external filter right, so i would put, i would put like a media filter or something like that over here for better filtration, because the filter that comes in this slot is Not great at filtering it, it's not really even enough to keep the equipment clean, but the slot is not large enough for me to even put a merv 8 pleated filter in there and have a reasonable static drop across that filter. I'm going to have a lot of static pressure drop across that filter, which is going to drive my external static up, and i really don't know how to measure it. Well, because i would need to measure the original filter and then start adding on the extra drop of that new filter in there.

Does that make sense. The problem is that when i go back to use, you know like if i go back here to use this blower chart right because i'm gon na i need to measure outside of that filter. That's in the the air handler cabinet, because that filter is part of the external static pressure rating of that cabinet. So once i take that filter out, i'm changing the external static pressure rating on that cabinet.

That makes sense yeah right, because i'm i'm removing some of the resistance. That's inside the cabinet, that's already included in that static pressure rating in the blower capability. So as soon as i take that filter out, i change the parameters and this chart no longer works. Okay.

Okay, good question good question, though, thank you. So we got a question from the chat window regarding uh this, so the answer is: it depends on the motor okay. So if you're looking at the constant volume ecm, then yeah, i'm gon na, take this filter out. If i have another filter in here somewhere, if i've got a constant torque, it depends on what technique i'm going to use to measure airflow.

If i'm using that static pressure to set up my airflow, i'm going to leave this in here because that's part of the blower chart - okay, this filter was was part of the engineering in that blower chart. So if i take that out, it's really going to change the characteristics and i'm i'm not going to know exactly where i'm setting it up quite as well. The thing i want to do is i want to make sure that all this duct work from the outlet of this filter to the inlet of that air handler and all this stuff down here on my air or where that filter door is, is well sealed, so That i don't end up with a bunch of dirt being pulled in from after this filter here all right, so nathan. I hope that answered your question about uh about this factory.

Filter in here. Does all this assume a dry coil, not loaded with moisture uh. That depends on the manufacturer, and you need to look at the manufacturer's literature to tell that some of them use a wet coil. Some of them use a dry coil.

Some of them have a separate charts for both i've seen it both ways. So it's really up to the manufacturer on that, depending on how they rate it, because the challenge i have with a wet coil is how wet is wet right, because wet can vary depending on the amount of humidity that we have in the space. I really prefer a dry coil because i feel that's more of a constant uh resistance than a wet coil is going to be. Let's take a look at some air filter sizing, so air filter sizing is an easy way to reduce the external static pressure by putting in a properly sized air filter.

It's also really useful for the higher merv ratings that we're seeing requested a lot right now because of the pandemic everybody's talking about higher merv filters. Well, if we go shoving a higher merv filter into a system that was barely designed for a merv 8 guess what happens to our static pressure? It goes right on up and we'll look at some some charts here in a little bit on air filters. So for higher merv ratings, especially we've got to put in a larger filter. We need that bigger filter put in there to really make things work properly.

Otherwise, well we're going to start blowing up blower motors or running really low airflow on things which isn't very good. Okay, it's hard to explain to customers, sometimes exactly why why we need to upgrade their filter if they want a better filter just running out and throwing in that that 3m filter from the hardware store sometimes isn't the best thing, and we we need to talk to, Because we're the experts now we can't force them to change it, but we can explain it to them. Now i get asked sometimes about velocity on air filters. Velocity is used for rating purposes, so the really the only velocity that we really need to care about is.

Are we lower than the rated velocity of that filter, which is typically around 300 feet per minute, depending on what test was done, but most of the time, if we focused on pressure differential, which is what the blower cares about right, the blower doesn't care about. How fast the air is moving through that filter? It cares about the pressure differential. So if we focus on the pressure differential of filters, we're not going to have a problem with filter velocity, okay, because low pressure differential equals low velocity as well right in the residential light commercial type stuff.