All right, so this is a short episode of the HVAC school podcast, a short episode that we're going to talk about air velocity. So this episode is all about air velocity or air velocity basics, and you will notice a little more background noise. So I've been mentioning this in a couple of podcast, but we just had our tenth child and I have not historically been the best dad when it comes to taking time off of work. And so I am taking a couple days where I'm not working as much.

But I am still doing some videos and some little things here and there as I can fit it in and in this case I'm actually driving back to our office to pick up a blower module, because the blower module on our air conditioner at our house are Downstairs air conditioner failed overnight so now we've got some driving time and with no kids no screaming, but I don't have my studio mic. So that's why you'll notice a little difference in the sound anyway before we get into the podcast. I want to thank our excellent sponsors, which you already know, which are refrigeration technologies, that refridge tech, comm makers of nylon thread, sealant and assembly lubricant. If you're, not using my log when you're putting together any sort of threads within a refrigeration circuit, then why not? It's just one of the best products out there for pretty much everything associated with making threaded connections or making players.

Even so, you traditionally used to use oil to prevent galling on flares well now by galling use. My log also want to thank Air laces for all they've done for the podcast. They make really good indoor air quality products, they're a very honest company, based on everything that I've seen I've read all their studies. I've talked a lot to the founders of air oasis.

You can find out more by going to air oasis.com /go and the reason why you're gon na go there is that there's a form you fill out and that form you fill out is so that way they can. Let you know the information of how to get the air oasis products in your marketplace. Questions like how much does it cost, for example, which is an important question to answer, and that varies obviously, because you have different distributors who carry its own and so forth. No matter where you live in the u.s.

in North America, we can get you the air Oasis products if you go to arrow Asus, comm /go, and that form is special for HVAC schools for your special treatment from the guys over at Air Oasis. I also want to thank you VI makers of the hub, smart kit, the air probes that measure temperature and humidity and enthalpy, and all that, as well as the refrigerant probes and temperature clamps. We've tested them out and I have a lot of really good things to say about the UE iHub smart kit actually had a friend of ours who's in commercial refrigeration. He heard this on the podcast went out and bought the UE iHub, and he said so far.

He really really enjoyed that he felt like it was a really good purchase. So that's good news. Also Brad Hicks from /, an HVAC in SC in South Carolina, he's been trying it out and he also likes it quite a bit. So we're getting really good feedback on the UE ihubs market and then also carrier and Mitsubishi, Mitsubishi, ductless and carrier.

Unitary products are what we've used since the beginning and Kalos and I'm very thankful to those two companies. So, let's get into velocity and air velocity measurement, because in a lot of cases, technicians are using tools to measure airflow, so they're trying to find CFM and we have to define a few things. I've talked about this a lot, but there's a difference between air velocity. The speed the air is moving air pressure.

What is the force of the air either? The directional force, which is what we call velocity pressure or the balloon force on all of the different sides of the duct and which is what we call static pressure. And then we also have CFM, which is cubic feet per minute, which is the volume of air. So, if you think of air as being boxes of stuff, that is the boxes. How many boxes of air there are, if you think of 1 foot by 1 foot by 1 foot cubes, that is a cubic foot! One foot deep! One foot wide! One foot tall! That's a cubic foot! So when we talk in CFM we're talking about how many boxes of air are we're moving, and then there is the mass of the air which we measure in pounds.

Pounds of air and mass and weight aren't exactly the same thing, but we're on earth and its gravity is pretty consistent here. As you notice, things tend to fall. What goes up must come down kind of thing so because gravity is consistent on earth, we generally sort of will approximate weight with mass, and so we talked about pounds of air and it's important to recognize that you don't always have the same pounds per volume ratio. So, if you're up in the mountains, for example, well, your air is going to be less dense, which means you're going to have less pounds of air per cubic foot.

If you're down in Death Valley, where it's very low and very dry, then you're gon na have more pounds and then also if the air is colder, it's going to have more density, so colder air is more dense. Warmer air is less dense. So there's all these different Corrections that you have to make and that's a whole nother conversation about standard air. But then we have air velocity and that's what we're getting at here.

So air velocity is simply the speed that the air is moving at an air velocity. True air velocity measurement is not a density dependent measurement. Now there are certain measurements of air velocity, so if you say a pitot tube, for example, that measures air velocity that is density dependent because it's the force exerted in pressure - and so you do have to correct for that. But the simplest way that we think about air velocity are that we measure air velocity is with a vane anemometer.

Then in the trade for any amount of time you've seen these they've got little spinning vanes in the center. I've done a lot of testing with different ones, but my primary favorite that I use for this and the simple smart probes kit from testo is the test. Oh four, oh five. I that's kind of the mainstay high quality inexpensive vane anemometer out there on the market.

In my opinion, so I take my four oh five, I and it's got this little spinning, fan and there's very, very low resistance to flow, and so the air moving through that vein. That vane is gon na spin at approximately the same speed as the air going through it and then even within the software correct for the resistance within the anemometer. So it's going to give you a really accurate view of what the speed of the air moving through. That's what you're measuring directly with one of these vane anemometers and that's what we call air velocity air velocity in the u.s.

is measured in fpm feet per minute feet per minute of velocity feet per minute of speed. When we take one of those little vane anemometers and we hold it up to event a returner supply or a ventilation discharge, anything like that. We're going to be measuring the speed of the air coming out and now, for example, in the testo app. It has the ability for you to enter the size, so the actual square feet or square inches of volume, and then it can help.

You calculate the CFM, but this is what I want to get to here. So often we think we're interested in calculating CFM in circumstances where it really isn't necessary. So I'm not telling you not to take an accurate measurement or not to care about CFM, but what i am telling you is is that measuring velocity is better than measuring nothing and in many cases the reason why technicians don't use a rotating vane anemometer like the 405 eye is because, in order to calculate the actual CFM accurately, it requires a knowledge of not only the square inches converted to square feet of that vent or register or grill or whatever. You want to call it right.

Intake whatever not only requires that, but it also requires a knowledge of what we call the open area or a free area of that vent or another term. It's called a k, factor or area k factor. Those are two very different things, and I'm not going to talk about that right now. I need to do a video to demonstrate.

The difference is because techs get totally confused about it, but when there is mass confusion about something like there is about free area versus a K versus K factor all this text, just don't do it. So you get this vein anemometer and you hold it up to a vent. You don't know what it means right, and so what I want to do here is give you a little something to go off of to make that vein. Anemometer useful to a technician in the field: who's attempting to do good by the customer by taking some air measurements without always having to measure air flow.

So let me give you some numbers here, and these are estimates they're, not exactly firm, but they give you a really good sense. It gives you a qualitative look when you're assessing a residence, especially so this is really residential, but the bulk of you out there are residential. You can use this for commercial, but the numbers are gon na, be a little different, so you're gon na have to look that up, but in a residential supply, vent residential supply register you're generally going to measure somewhere between 700 feet per minute. This is velocity not cubic feet just velocity.

This is what your vane anemometer can measure directly with no additional calculations. You're gon na see about 700 on the high end down to on the low end about 300 and within that range the lower velocity is going to mean lower air noise, but less throw. That means that the register is going to result in less force of air. Coming out, so it's not going to throw as far the air is not going to throw as far and it's pretty easy.

So you'd look at where your vent is and you look at where you're wanting to throw to. And you look at the distance and if the dish is further than you need a little more feet per minute, a little more velocity in order to get there versus. If it's closer, then you don't need as much velocity but on the other side of the equation. When you're closer to the 300 feet per minute, you're gon na have quieter air flow, and so, if you have a room like my office, where I record podcast, sometimes I don't want to hear any noise.

So I put in this really big supply, vent and boot with a smaller duct and also it's not just a smaller duct, but it's also just where it's fed from isn't gon na feed it as much air. I generally have pretty much oversized ductwork in my house. Any way to keep my static pressure on the low side, that's going to result in lower, throw and lower air noise, so bigger, isn't always better when it comes to supply ducts and sizing. Your registers sizing your boots.

All that sort of thing, bigger, isn't always better because bigger while it does result in lower static pressure, it also results in lower throw, and so you have to kind of figure all this stuff in and Jack Rhys talked about this. You can put a really large duct in place, but just put a balancing damper in it, and so then that way you can throttle it down in order to get exactly what you want, but you need to size your register. The actual register itself needs to be sized for the throw, so you need to figure out your throw size, your register and then get that proper air velocity coming out, but you can do all of that without needing to actually measure cubic feet per minute. Now, if you want to get fancy - and you want to look up your specific register specifications - that's what you would need to do in order to know things like throw and all that.

But let's say you don't even want to do that. Let's say you go to a house: a customer has a complaint about air flow from a particular vent. What you can do is you can take your four or five. I put it on a selfie stick or a piece of PVC or whatever ever you want to fasten it and hold it up.

Look at your application on your phone and you can see the velocity coming out without measuring your CFM, based on the velocity coming out. You're gon na be able to compare that against the other registers in the house and, generally speaking, they're sized to be pretty consistent. You don't have a designer who designs a duct system. If it is designed, you don't have a designer who designs a duct system, who's like okay, now this room, I want this really high velocity in this other room like I want a really low velocity now again, if one vent hasn't much further throw then it may Have higher velocity, but you can tell that pretty easily you and look at what is this fence supposed to be doing? Is it supposed to be throwing more air across the room, because it's got a great distance to travel all right then? Maybe the designer did design it for a little higher air velocity, but you can make that assessment pretty easily in the field without having to reference manuals, so you can go through a home and you're measuring air velocities and all of a sudden you run into one.

That's higher than you would think it should be it's higher than the others. When you see that higher air velocity just look at the room, does this room need higher air velocity? Do you have a situation where it has to throw further? Well then, look at is this room one of the rooms, that's on the maybe too much airflow, maybe it's getting too hot in the winter too cold in this summer, and now we have higher air velocity, meaning that it's being fed more air than it needs. Well then, that may be one that you can go ahead and throttle back. You can throttle it back with a balancing damper.

Now, a lot of you will say: well, I'm in residential. I don't have a balancing damper as well. You have to install them. I don't know what else to say: if you want to air balance a system you have to install balancing there, but now there are some that are made that can go up inside the dock, there's pieces of sheet metal with an adjustable damper.

I don't necessarily recommend them, but in some cases it's your only option, but in order to balance you would need to balance with a balancing damper. But at that point, if you throttle down that balancing damper, you're gon na see lower velocity coming out of that register, because the register is fixed. Besides, the registers fix, if you reduce the amount of air flow you're, also going to reduce the velocity and so by. Comparing these things room to room space to space and just using some good common sense, you're gon na be able to make some slight adjustments.

Now, I'm not suggesting that a residential service technician is going out doing a test and balance using velocity. Only. I know I'm gon na get pushback on this, but here's the thing service technicians are out there to solve the problem at hand and sometimes it's just a small little adjustment that needs to be made, and sometimes a technician has the tool to do the job. But they're overwhelmed by the math side or by the I don't know what to do.

This ake a free area, all this kind of stuff side, and if they just look at air velocity, you can get some pretty good information. So, for example, if you go to event and it's got really low velocity okay, is it a baby's nursery or something where they intentionally oversized the register in order to keep low velocity it's possible, but very unlikely? In most cases, people don't think about this stuff, and so, if you're seeing event or register under normal circumstances, that's running below 300 or near 300 and the others are running near 500 600 in that range, then that tells you something that's that I'm not gon na. Go any deeper into that, but I do want to also say that there's another benefit for measuring velocity at outlets and inlets. You can also use it to look at noise issues whenever you have a filter, grill return, filter, grill returns should really be kept at the lowest possible velocity that you can kind of set it at.

So I like to see mine at below 300 feet per minute at the face. If you have one that starts to get above 350. 400. 450 in that range, you're, gon na start getting more and more noise, and when you get up into the 500 range in velocities, you're gon na definitely have noise and we've all seen this, especially when they've got the round flex duct and they didn't build out.

A box big enough and you've got all this turbulence and it's pulling right to the center of the filter. I mean we've all seen those filters where it just gets dirty in a big round spot right in the center and those tend to be really noisy, because that Center velocity is really high and the veins start to hum and all that. Well, this is just a way for you to kind of prove that there is a problem with the sizing of the doctor or the sizing of the grill. The way it's designed that sort of thing, because when you see face velocities on filter grilles that start to get up above 400 you're gon na, have issues now with a regular grill.

That's not a filter grill! You can get up to 400 450 without noise. In many cases, but you really don't want to be higher than that through trunk lines, return and supply trunk lines. You generally want to see between 700 and 1,000 feet per minute and residential is typical. You'll see some cases where it gets up to 1,200.

You don't want to see any higher than 1200 again. These are definitely rule of thumb type of numbers here and they do vary a little bit, but you're gon na find that they're actually pretty consistent. If you see a system, that's getting air velocities above a thousand you're gon na start to also have high static and you're gon na have other problems. You want your trunk lines to be higher.

Velocity than your branches. Branches are typically gon na be 500 to 700 feet per minute in that range, but then, where we were generally measuring is at the actual vents and that's where on a supply-side, typical velocities would be between 300 and 600, 300 being on the quieter side, 600. Being noisier but throwing better, there are some exceptions there, some vents that are designed some registers that are designed to throw further and they have less turbulence in the faces, and so you can run higher velocities in those when you need further throws, but with your typical Adjustable registers, they start to get really ratalie as soon as you begin to get much over that 600 feet per minute, velocity measurement. So finally, here's what I'm getting at my encouragement is: if you've, never measured airflow at outlets and returns at registers and returns.

Then just start by measuring velocity, and then you can move into the CFM side later on. Once you get really comfortable with velocity. I know that's going to be controversial. Some of your gon na be saying.

We should always be measuring that I'm just telling you that there it's a lot more difficult than you think it is, and those of you who think you've been doing a que factors and free area correctly. All these years, I'm here to tell you, there's a very good chance you haven't been and we'll talk about that in a video coming up very soon, all right there we have it. Thank you to all of our sponsors. Thank You.

Tube is pal org for helping, so many companies find great technicians if you're in the market, for that check out biz palate org and we will catch you on the flip side. I don't know why people say that kitchen looks like we'll talk to you next time. On the HVAC school podcast, you.