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If you're gon na make a good flare, as you know, any imperfections in that flare surface where it meets that meets the cone is what can result in leaking. So I'm really excited about this product and according to rector seal, it should be out on the market. Very very soon, in the next couple weeks you should start to see it hit shelves, and that is the rector seal Pro fit kit. Also, I want to thank our new product sponsor Parkers Portland and the Zoom lock tool, the exhume lock the 10 second flame free refrigerant, fitting from Parker reduced labor costs by sixty percent with no brazing no flame, and no fire spotter discover how Siouxland can help you Be more efficient and productive visit, zoom, lock, comm for more information, and now your host, the man who is actually a giant nerd but wants to be accepted by blue-collar tradesmen to fulfill some gap in his soul left there by his father or his mother.

It's definitely not just because he's a weenie Brian or yes, yes, yes, yes, this is Brian. I am the hosts of the HVAC school podcast, although whenever I have Jim Bergman on, I kind of feel like the co-host he kind of kind of runs. The show which I like Jim is Jim is a great guy and a good friend and he's kind of come out with some pretty cool products on the marketplace pretty soon. Some things you're definitely going to want to follow so keep an eye on Jim Bergman.

If you haven't listened to part 1 of this episode yet or this podcast series, I should say this - is a two-part series go back and listen to episode, one before you. Listen to this. Don't try to don't jump in the middle of this without listening to the first part, because this part is even far more nerdy than the first part I mean you are going to have a hard time. Keeping up you'll hear me, I'm not keeping up for.

Like half of it and then I kind of catch up for a little bit and then I get behind again so Jim, just rattles off tons and tons of numbers. But but what I want you to. I want you to listen this one. Slowly, maybe listen to it a couple times, because I think you're gon na pick up some really good things here and we do get into some some areas where I had confusion and then he was talking about one thing and I was talking about a different thing.

We kind of work it out, which is how a lot of these conversations happen when you're in the process of wanting to learn something. Sometimes the person who you're asking doesn't totally get what you're, saying and so part of that's part of what happened in this episode. But I think it's I think it's good. I think it's super interesting.

It's actually one of my favorite conversations that I've ever had. I learned a ton from it. So here we go. This is part two of measuring air flow with Jim Bergman.

Alright, so the next thing I wanted to get into was some more direct ways of measuring air flow and some of the techniques and pitfalls that go along with some of those. If that works, for you sure yeah, that's, I think a good place to start so the key things I guess, if we're gon na just back up, reflect a minute on what we just hit with the static pressure reading, is that at the end of the day, It comes down to this whenever you're gon na make an air flow reading. You just have to ask yourself what am I going to do with it? What am I making it for and as long as you understand, what the limitations are of the measurement method, you're using and using a measurement method is good for the purpose you want to use it for then use what. However, you want to measure it like.

I said if you're gon na just select the blower tap, then there's nothing wrong with using a total external static pressure method. If you're gon na try and measure capacity to the system. Well then, you're gon na have to use a more accurate measurement method of doing it. You know one of the things always makes me sort of laugh as guys to try and measure duct leakage.

You know so, though, take a static pressure reading at the furnace and while I'm moving a thousand CFM and then they run around with a capture, hood and they're, measuring all their outlets and they go. Oh, I'm only getting X out of mic registers here I must have duct leakage, it's like. Well, maybe you do. Maybe you don't you're, comparing two different measurements of air flow.

One is very inaccurate and one is very accurate. As far as a capture hood goes a good capture, hood and then you're, comparing the two readings, have you considered the measurement, uncertainty or just the differences in the two air flow readings? Instead of considering that everybody thinks? Oh, they got to be perfect. These two measurement methods are perfect and there can't be any discrepancy between them and that's where it makes some huge mistakes again when you go and compare these methods and it all rattled off, probably half a dozen different methods, maybe more measuring air flow. Unless you understand how to normalize those and correct them or understand their limitations, you're gon na have some challenges along the way.

So you just got to ask yourself what am I making this measurement for and that'll help in getting it down the right Road of air? For measurement so now I want to quiz you real quick before we go into this next part. I've been waiting, yes, okay, you're ready, I'm so excited all right, you, okay! So almost all measurements of air flow are not actually measurements of air volume. They're measurements of velocity that sent converted to volume is that a fair statement like even a capture hood, is not a direct measurement of CFM they're, using a pitot tube array and they're converting velocity pressure with a given volume to to the actual boyhoods air flow. That is that a fair statement, if you're gon na actually measure true CFM, I mean literally the only way of doing it - might be honestly to put a garbage bag over the register and see how fast the bag fills up.

Dang it that was gon na be my quiz yeah right, I was gon na. Ask you shoot Jim you ruined my Thunder. I had one little bit of thunder that I wanted and you didn't. Let me have it.

That's the only volume, the way that you can actually measure volume of air flow that I'm aware of is a garbage bag method, which is actually an approved method. Although a terrible, approve method and probably should not be approved, but that's another yeah, I mean that's about the only way you could actually capture the air in a bag and say: okay. This is how many CFM affair I have in this bag and that's it otherwise. Every measurement we use is a indirect measurement of air flow.

The question becomes really in my mind: more, is it density, dependent or density, independent right, because a fan moves the constant CFM independent of the air density and we've already discussed that right. So it's going to move the same CFM in a variable mass flow rate. So when you're using a vane anemometer a vane anemometer is a fan and it's going to measure the CFM independent of the air density. That's the cool thing with a vane anemometer is, you can use it really hot air really cold air really humid air dry air is always going to give you the same CFM.

It's gon na give you a very repeatable CFM, because it does not care about the air density. Now, when you measure with a hot wire, anemometer hot wire anemometers, depending on the one you buy, they may or may not correct for air temperature and they're very dependent upon air density. Because, again, what's cooling, that little hot wire off is the mass of air going across that hot wire is the mass of air goes by? It? Is the pounds of air go by it to heat from the hot wires transferred to the mass of air and, if there's less mass, to transfer to then it's gon na influence? The reading, because you're gon na have that CFM go by that cubic foot of air. Go by but it doesn't have the same density.

This goes back to the same thing like take a one cubic foot tank just of error. I've got it right here. Actually, alright. So if you put your vacuum at one cubic foot of tank - and you start evacuating it right, how much Atmos close the bail? Okay, all right, so how many cubic feet of atmosphere after we evacuate that tank down to 500 microns? How many cubic feet of atmosphere is left in that tank? Think about it.

You know you know how BIG's the tank Brian one one cubic foot so how many cubic feet of atmosphere you're left in that tank, one keep it fresh right because I don't know you're exactly right. It's always gon na be one cubic foot. Okay, because what does pressure do what's pressure doing a tank it expands got it got again what happened to the pounds of air that we're going to take of the mass of air, those in the tank? Is there less man right, negative removed, yeah? No correct? Yes, lower those zero microns right can we ever hits none zero? Now you can't, we can't hit zero microns. Just we would get into tour.

We like ten to the negative sixth or something like that when they get into really deep vacuum its. But even if you evacuated that thing for a hundred years, you'd never get all the atmosphere out of that tank. If there's one molecule of atmosphere left in that tank, it's going to occupy that one cubic foot of space, because this is gon na bounce around. In there and it's going to occupy that one cubic foot of space so you'll have one cubic foot of atmosphere in that tank, no matter how far you evacuate it, then, when we're talking about this understanding, the impacts of air density, air density is always going up And down and air density changes with temperature, barometric pressure and relative humidity so like in the case of the field piece, I want to say it's, the STA.

Is there hot wire or the test? Oh, what's the test? Oh hot wire, the 405 eyes. I have a 405 - I just haven't looked at it closely, but I do know that the field psst a2 measures, air temperature and corrects for air temperature, but it does not correct for humidity, so the bulk of air density changes with temperature. In fact, if I remember right, if you're looking at a standard psychometric chart, you know you think about the lines of specific volume there. I like a little bit of an angle.

You know going down there if you were to take from zero percent relative humidity to two hundred percent relative humidity, it's equivalent to about an 11 degree change in air temperature right on the air density, which takes you from about 13 cubic feet, 13.5 cubic feet. And let's say so or 13-point ya, thirteen, thirteen point five or thirteen point: five to thirteen point: nine! Something like that: you're gon na have this change in air density. From about, let's say: point: zero: seven, five: two point: zero: seven: three! So it's not a huge amount of change, but it is a change and if you take the in verse of the specific volume that is the specific density. So if we say a standard cubic, foot of air occupies 13.33 cubic feet of space, that's at 68 degrees.

At 0 % relative humidity at sea level, that's standard air, Oh point: zero! Seven, five pounds of air will occupy 13.33 cubic feet of space. If we take the inverse of that right, so it's thirteen point. Three three cubic feet per pound. The inverse of that is point zero, seven, five or one over thirteen point.

Three three is point: zero, seven, five pounds per cubic foot, so one cubic foot of that air would weigh point zero, seven, five pounds: that's how we can convert specific volume to specific density. That's why in the psychometric chart, that's what the lines a specific volume or force you can recalculate what your air density is at any point on the psychometric chart. Okay couple things here: couple things here: air that has higher moisture and at higher humidity both has lower density with me, their lower denson him Jim my whole trick in life. This is my claim to fame.

This is my tip that everybody out there should mimic. Is you learn things from smart people and then you repeat it back to them once sufficient time has passed, that they forgotten it they're the ones who told you it and then they think you're brilliant. That is my single greatest tip in the business so anyway, but that may be the case I don't remember. Not only does the density decrease when the humidity increases, but the thermal capacity, the actual specific heat capacity of the air increases so with a hot wire anemometer.

Even though the density is decreasing or there's not a great change in air density based on humidity, wouldn't the fact that it has greater heat capacity, wouldn't that effect a hot wire, okay, so you're getting you're getting a little confused and that specific heat is BTUs per Pound a specific heat of air does not change pretty much from like negative thirty-two. Maybe I don't know 122 degrees. Let's say right. The specific heat of the air doesn't change that much if you think about it.

This way, if you were to take one pound of air and change it one degree, you would liberate 0.24 BTUs of heat. So if you took a pound of air and you changed it - four degrees you're gon na get about one BTU of heat energy. Out of it, so when we say the amount of heat required to raise one pound of water, one degree, Fahrenheit is one BTU. The amount of heat required to raise four pounds of air one degree.

Fahrenheit is one BTU, because it's specific heat of air is about 0.2 for a little bit more than four pounds of air, but you get the point. The specific heat of air does not change. Now, where you need to change your thinking. Is the pounds of air changed so because we have less pounds of air? The hot wire has less pounds to transfer its heat into alright, it's not the specific heat of the air that changed.

It's the mass of the air that changed, because the cubic foot is the same, but now it weighs unless because the air density went down, so we have that higher temperature and higher relative humidity. It's going to have lower air density, which means that one cubic foot of air now is going to occupy the same space. But it's going to have less mass. So when that air goes across that hot wire, because there's not as much heat that that air can hold, because it's gotten less pounds of it, then it's going to incorrectly give us a CFM reading.

If it doesn't take that into account. If your hot wire does not correct for air temperature and humidity and barometric pressure, it only measures. The change in the resistance of the hot wire is air goes across it. Then it's gon na have some air in there.

It might give you a correct standard CFM, but it will not give you the correct, actual CFM of air going across it and that's where things get a little wacky is you have to understand the difference again between actual CFM and standard CFM, so you may require A much higher actual CFM of airflow to keep the same mass flow rate across the coil and that's why, like I said some of your program, will ECMs you'll see instead of running twelve hundred CFM. It might be twelve hundred seventy-six CFM of air going across the coil, because the air density is low. Okay, I think I understand mostly. This is getting a little bit cool.

It's good because think about the standard air formulas. Okay, it's Q is quantity of he equals mass times specific heat times change in temperature, so it takes the amount of heat required to raise one pound of water. One degree Fahrenheit is one be to you, so you got one pound right. That's the mass! The specific heat of one and we're changing it one degree, and that's one be to you so that all fits in there one times one times one is one: that's specific heat of water is 1, so that formula works perfectly now all you're doing is you're just Subbing in air in there - and now your mass of air is, let's say for one ton: you'd have to go 30 times 60 right you're going to take it to be twos per hour.

You got to get the unit's correct, so it's 30 pounds per minute right then 3 times 6 180 pounds per hour. Is that right? So let's just do the math you real quick here, so we got 30 times. 60. That's 1,800 pounds per hour times: 0.2.

4. So let's say it's got a change of 20 right, so that'd be 8640 okay. Now what kind of heat are we talking here? Brian, just so we're both clear we're talking about change the temperature we're talking about what kind of sensible heat so divide that by let's say 0.72 and we get 0.72 12000. Okay, honest to gosh.

I just literally pulled that number out of my head and end up being 12,000 beetee's exactly so. If you took point seven two, it's a latent, sensible split. The reason I divided by 0.7 2. As I said, okay out of this 8,000 60, whatever it was BTUs.

That's 72 percent of the total heat transferred, so it divided by 0.7. That gives me the total heat transfer. 12,000 BTUs right. All that works the same, but the specific heat of air.

It's a constant for all. We care for our industry. Specific heat of air is relatively constant. The fact I can look that up real quick if you want to know exactly what it falls in between, but for all intensive purposes.

The specific heat does not change, so it's up from negative 58 104 degrees. The specific heat is 0.24 interesting, I'm still struggling with what effect humidity has on that, because we knew it decreases the density right right right, but we also know that water has higher heat content than aerials, and so, when I'm water, water, there, water, vapor water vapor. Well, it has heat energy in it, but okay, we're talking two different things here. So, let's, let's, let's back up, so we don't confuse everybody.

I think we've already done that. Okay, this is all good fun right and it's good for me, it's educational for me. That's I get a free education by Jim Burke. You know I write, I know a lot of people are gon na think we're absolutely insane, and how do we even know some of this stuff? I'm pulling this stuff out of my head.

I mean it's just you know: I've worked with it for so many years and things like that. But this is - and I know it's going to be frustrating to people listening to the podcast a little bit but honest-to-goodness. This is the nuances of air flow that make it so challenging and if you take a little bit of time to listen to the podcast to understand what we're talking about to start researching a little bit of this stuff, you're gon na find out that it's going To change your career because you're going to understand things that other people just simply do not understand and case in point, I went out to a job one time guys are out there. It's a natatorium at Kent State University.

They have a big ol pool pack unit in there and what they're trying to do is they're trying to control the evaporation rate of the pool they're having trouble with the pool losing a lot of water every single day. They can't figure out why you know the chlorine concentration is too high in their pool to get into Corrine smell inside the natatorium. So what's the solution and realized that wintertime in Ohio here gets very very cold, what's the solution get that chlorine smell out? We probably need to bring more outside air in right. Well, why is it Corrine even getting in the air, while the water is evaporating out of the pool right if the water's not evaporating right, not gon na get any smell? Well, guess what they're doing is they cranked up on the outside here and still having this huge problem? Well, what is outside air doing it when you heat it up, the humidity drops way down yeah.

So just look on a psychometric chart and you just take you know 30 degree air at 100 %. Relative humidity goes straight across you're gon na see it's like 10 percent relative humidity, so they're bringing on all this outside air and they're heating it up and drying. It out, you know, cuz it's zero degrees or 20 degrees, whatever it was outside you're heating, it up even dropping the humidity lower and then they're putting that really low humidity air inside that net for iam in the swimming pool area. So, what's gon na happen, super dry air waters evaporating out of the pool like crazy.

You know trying to to normalize the vapor pressure in the room, evaporating the water causing all kinds of problems. This is all like psychometrics 101. So what do I do? I go in there and I look at what's going on. I said you know what crank that outside air damper all the way down.

Everybody thinks I'm insane because we're saying oh well, how are you gon na get the chlorine smell out of there, because we're gon na stop the evaporation of the pool? So we crank that thing down. We get the humidity level up in the space to where it's supposed to be. You know it's all glass and speed natatorium, so we have some dewpoint stuff. We've got our monitor and things like that, but we get this thing balanced out.

Water quits, evaporating smell, goes away problem solved, it's all airflow psychometrics 101. Well, these are the types of problems that a lot of people in our industry overlook because they don't understand, fundamentals - and I know some of the stuff we're talking about seems like it's way over. Your head and way complicated, and how do we even learn some of the stuff or why do we even care? Well, I learned it because I got stuck in a classroom and I'll be darned. If I was gon na, let kids be smarter than me, and you know they would ask these questions and I, like I said, very confidently answer them, then go out in the shop and prove myself wrong.

It was exactly the same way when I went out there. They said: well, I'm telling them well. Air conditioning systems drop the relative humidity in the ductwork, and I said, let me go out and show you so I put the returned probe in the returned. It's reading.

You know 50 percent relative humidity, I throw it in supply and it's approaching 90 percent. I said well, this one must be broken, so I put in the duct, it does the same thing and I'm going man. They make really lousy, humidity probes. What the heck is wrong with this thing and again psychometrics 101, because I didn't understand what was happening is as we cooled that air down we're squeezing the water out of it.

It's now. This really cold compact air that is approaching 100 % relative humidity and when's. A humidity drop out when it mixes with a room air and he got this cold air that heats up now to the room temperature. It expands.

Now it's got much lower humidity in it than it had when it started. So yes, an air conditioner does remove humidity, but what my probe meant was relative humidity, which was the amount of humidity that there could hold versus what it's holding, not the absolute humidity, which is the changing grains of moisture, which is the amount of moisture that went In versus the amount of moisture that came out so yes, the air had much lower absolute humidity, it had higher relative humidity, and these are things like I said, as we learned so you know, even though you're not following a hundred percent of what we might be Talking about it's good to start to understand these things, because at some point in your career, you're gon na make a measurement and something's gon na click, you're gon na. Remember. You heard this and you're gon na instead of blaming the tool, which is what I did right, because I stuck my humidity probe in and it didn't read what I expected instead of blaming the tool.

Now I understand that this is what happens in a duct, so instead of blaming this airflow measurement tool, you're gon na go oh well. Maybe it's influenced by air density right or maybe it's this or maybe it's that yeah. It's gon na lead you to more questions, but at least you're gon na be able to research some of the answers. So some of these things get challenging and I don't mean to get really technical and sometimes I just spew things inadvertently.

But it's because these things have frustrated me for a huge amount of my career and I'd love to share them, because it took a long time for me to figure it route and not because any other reason, aside from it's hard to find some of this information Or current textbooks, they don't teach it. I have to go back, you know I'm sort of a history buff. I buy old books off ebay, old air-conditioning, books, old heating books. These are the engineering manuals for back in the day and they explain things sometimes much better.

Why they don't assume that we know them, you know and skip over them like the standard, your equations do in a textbook. They don't tell us. These are standard, error, equations and they'll get you in the ballpark, but they're, not exact. We all assume they're exact, because this is the equation.

It's got ta be there, but we don't take into account all the variability. You know my biggest epiphany or eye-opening to psychometrics was when i got to sit on the psychometric. Sorry right. I think it was 2009 ASHRAE rewrote psychometrics the fundamentals chapter.

I was part of the review committee for the fundamentals chapter and one of the guys I met there from trained that. I used the high molecular formulas, which are much more complicated, psychometric formulas and one of the guys says with a train. I'm, like you, guys, really need to put something about the standard air formulas in the ass-rape guide and he's like no, no, who had ever even used those with modern computers. You can get much more accurate results, unlike everybody in the field, uses those even engineers.

I've worked with in the field, use those because these more advanced psychometric calculations well they're more accurate. They aren't conducive to use in the field and he's like well, that's why you make measurements in the field and you go back and you put them in the computer and it's like the smartphone honestly really changed a lot of our industry in the fact that you Know everybody's carrying around a computer today, and we can do things that we never did before. It's, not that the math or science has changed. It's just that again, it goes back to you know.

We have better tools at our disposal. Today we have computers and our pockets today that can correct and normalize some of these things. Some tools do that some tools, don't you just got to understand the nuances between them? If anything, I hope people are getting out of this podcast today. It's the fact that airflow measurement is not an easy thing.

It takes time to learn, there's a lot of variables. It's going to take you some time to digest it, but if you can learn air flow and learn some of the things we're talking about today, I can guarantee you'll, be one of the most valuable technicians in our industry. You'll be able to solve problems that nobody else is able to solve and understand things for yourself. You actually understand what you do for a living which, sadly, most guys in our industry.

Don't it's really funny. We think about it. The number one thing: what do we do? We're air conditioning mechanics right? What was the last time you measured? How much you conditioned the air think about that for a minute, you're, an air-conditioning mechanic. Why aren't you not measuring how much you conditioned the air? Because you can't do it accurately in the field: no, because nobody ever taught you how to do that, and nobody ever taught you how to use the tools correctly and all the things that go along with that.

So it's just interesting. It drives me a little bit insane, but I hope I didn't aggress too far, so I want to focus on what we started down, the road of which is so, let's wrap up with three different things, because these are common tools. That technicians would use a hot wire anemometer, which is what we started to talk about. I first want to just address what it is so Hotwire anemometer you can insert it into the duct and it measures air velocity, and so essentially, it's just measuring the rate at which this hot wire is cooling off.

My guess is it's measuring current correct. Is that how it's letting that change resistance versus measuring current and that's telling it all right how much air velocity is flowing over that probe and in order to measure it accurately, you have to use a traverse generally speaking like if you're using the 405, I it's Gon na be a timed Traverse, so you're gon na start and you're gon na pull it through the duct in a couple different points and depending on the duct, you know Jim's done a lot of videos on this. I'm not gon na reinvent the wheel on that, but you'd kind of averages, the velocity throughout the duct and then you enter in the volume of the doctor or whatever it is you're measuring. And then that will give you your CFM.

So the CFM is extracted from velocity. Well. Is that all correct summary of how a hot wire anemometer? Let's back up for just a minute, because I think it's important to realize that a hot wire is not an ideal air flow measurement tool for a lot of applications. I just want to shoot one by you for a second.

So let's say you get inside of a duct: let's go back to that. Little thing. That's talked about earlier with NASCAR and turbulence in a duct and cars. Spinning around just like the air is spinning around in a vortex and or like a little tornado in the duct right.

What happens when I pull that hot wire through that tornado? How many times is that air crossing that hot wire, a bunch, it's yeah and it's going to think the velocity in the duct - is very high. It's gon na give it a false impression of a high reading in the duct, even though there's no air flow there, because the air is just spinning around in a little circle, it's not flowing through the duct. It's just tribulation, the hot wire thinks it's got. This very high velocity and the bead on a hot wire is so tiny.

It's so tiny mean it's like it's smaller than the head of a pin. You hold it up to the light you like how in the heck does that even string that thing across this little open area here and there's turbulence in the probe design itself right. The very first thing you've got to ask yourself: whenever you're going to make an air flow measurement, is what method should I use because again it comes back to. We have all these different tools that are at our disposal, but utilizing a hot wire in a let's say, a flex, duct return that things got so much turbulence in there you're just completely wasting your time right, so understanding how they work is one thing but understanding Where and when you want to use two methods is, I think, almost more important yeah it may be, but I'm confused about how it works.

This is what I care about it. This very minute is because I'm thinking are anything that causes heat transfer away from that hot wire is going to result in that hot wire thinking that there's more air yeah. So if it's exposed to, let's say your coil, your cooling coil, if you're measuring close to your cooling coil and you get radiant heat transfer from the hot wire into the cold coil, it's gon na influence the reading. Okay.

So here's the final question: why wouldn't higher relative humidity air result in it cooling down faster because the air density is lower? So it's the fact that you're doing two things at once: you're decreasing the air density. At the same time, while increasing the relative humidity, that's balancing out there is that well so again, this is a great question, because it goes back to what I was talking about earlier everything in our industry. We have to go back to mass flow. Okay, it's the mass of the air that we're heating and cooling.

It's the mass of the air that we're measuring, I mean, could CFM out of your head for just a minute, get that cubic foot of air out of your head for just a second and think about go back to that formula. Just for a second Q equals mass times specific heat times change in temperature. Let's keep the specific heat at a constant and let's keep the temperature at a constant. Let's just say it's a 10 degree change, okay, just period.

If I change my mass, if my mass goes up or down, what's gon na happen to Q, the quantity of heat straight multiplication correct, correct, it's gon na go up or down or base right. So is the mass decreases? What's Q gon na do? If I multiply three numbers together and one of them gets smaller, what's you gon na do then a decrease you's gon na go down right right. So if you're talking about a hot wire and you're talking about heat from the hot wire into the mass right, if the mass goes down, then you're going to have less heat transfer from that hot wire, because it's not transferring into the CFM of air. It's transferring into the mass of air that's going across the hot wire, so a hot wire in a vacuum.

If you put it in a vacuum, you know we could have a fan blowing in a vacuum right, it's not going to move any air at all. It's just gon na sit there and spin right, there's no mass to transfer heat into the hot wire. It's not going to see any velocity, its mass dependent, it's a density dependent device. So that's the key thing now again: why does relative humidity as it goes up because people think water has a higher specific heat, but that's water? It's liquid water, not water, vapor, we're talking two different things and be interesting.

Look up the specific heat of water vapor! I don't know that I've ever looked it up here, I'm looking it up right now. I guess you know a part of my confusion is probably the fact that, when I think of the specific heat of water vapor, I'm thinking about the latent change, you know, whenever we're doing calculations we're thinking of latent change. So I think of water as having a very high heat content, but that's probably because I'm thinking about it in terms of changing from water vapor to liquid water through the process of condensation on it right. So that's probably where my brain is messed up there when it comes to the specific heat of yes.

So I know this is all metric, but it's specific heat of water vapors about half it's less than half the specific heat of water, so specific heat. If you want to look at actually, I knew this it's chapter 1, again: refrigeration, air conditioning technology, so the amount of heat required it's about 1/2 BTU to raise one pound of ice. One degree Fahrenheit it's one BTU to raise one pound of water, one degree Fahrenheit and about 1/2 BT to raise one pound of steam. One degree Fahrenheit, the specific heat of water is one specific heat of ice is 1/2 and specific heat of water.

Vapor is 1/2. So when you're, looking at that specific heat when you're talking water vapor, it's a lot less, not it's! It's still more than air right, because air is like a quarter correct, but it's only a percentage of the air. So that relationship, especially by the time you factor in density, is going to be it's just a tiny, tiny fraction. It's just gon na be a tiny, tiny fraction, so it doesn't yeah.

Okay, that makes sense all right good, I'm glad we went through that exercise because it just makes me understand, there's a lot better about how hot wire works. So we have a hot wire at our disposal. That's not from. We can use a pitot tube, but you know: tubes are generally only practical when you get into you know: commercial applications.

You know high duct velocities, that sort of thing or, if you have really good tools, you're, not going to use a typical manometer and use a pitot tube in order to calculate see, if not accurately, because your velocities in the duct are like. You know, we're talking. Typically, in a well-designed duct system and a residential duct system, you're below 700 feet per minute - and it's not going to be high enough to really get an accurate measurement with a pitot tube hot wire would be better. For that, then, a pitot tube would because a hot wire will measure even lower velocities, another sidebar.

I know you guys don't see many furnaces up there, but one of the things I use a hot wire for is I'll, disconnect the stack or plug the stack on a 90 plus or an 80 or whatever I'm doing so. There's no draft on it and stick a hot wire inside the heat exchanger and turn the blower on and look for air leakage inside the heat exchanger. If your hot wires stays at zero, that means there's no air leaking into the heat exchanger, which means the heat exchangers tight. Now I use a hot wire for that all the time, just as a quick test, as I'm checking the heat exchanger cells at least.

Tells me where to start looking, obviously heat exchangers aren't hermetically sealed, but for the most part, if you have the detectable air movement inside of a heat, exchanger yourself, that's gon na be a problem with affecting the flame and affecting combustion, but just a cool sidebar. That's how sense of a hot wire is it's gon na be used for that too? It's sensitive, it's just very susceptible to turbulent herb. You know you know, obviously can also be damaged easily, if you're not careful with it, because it is a very, very delicate instrument, but for the most part they're built pretty well today I mean you're, not gon na. You know as long as you don't go poking around at that thermistor in there you're not gon na, really hurt it all right and then finally, we have the vane anemometer, which they do make.

You know miniature vane anemometers that can be placed inside of ductwork, which again they're, very small and so they're gon na tend to you know: they're gon na be prone to be affected by turbulence and that sort of thing, usually those are four register measurements. So you're gon na measure at or supply or it oh you mean they make yes and I'm honest honest on a road yeah, I'm thinking back to the smart probes. You know they have that little compact vein, so yeah there are veins on the end of a rod like a mini vein, anemometer Tesla for 16 tests. Oh 410 is a large vein, not sure what the number is for the medium size, maybe for 20 or something like that or for 20.

I I don't know if top my head, but yeah there's a lot of different size of veins and a vein. Anemometer measures independent of the air density. So if you use a hot wire in a vein in the same duct system, you're gon na get two different answers right, because one measures independent of density and the other depends on those a pitot tube is air density dependent. So, with a pitot tube, you gon na make air density Corrections and so is total external static pressures.

Air density dependent all right so quickly, though so the 417 is the large vein test. Oh 417 is a large vein anemometer that I generally use then the 410. I it's like a smaller, you know, held bluetooth device and they both allow you to use the timed Traverse method, which is the method that we're generally going to use and so a way that a lot of technicians will use it as they'll. Take a 417 or 410 I and they'll go to a central return.

You know the main return of the house and they'll paint that return so they'll, you know enter in the time. Traverse method and they'll just paint that entire return and then they'll enter in the size of it and attempt to calculate the overall CFM of the system. And so we get a question from Neil and he wanted this answered. And I think it's a good question when it comes to free area K factors, those sorts of things.

What he's experiencing is when he uses the free area calculation that the grill manufacturer gives him he's, finding that it's giving him significantly lower overall air flows than what he gets. When he's using a hood, so you use a good quality hood then he can go in and paint it with a anemometer, and he says it's just he's struggling with that and I know there's a lot. You know bill Spohn talked about this at HVAC excellence. I wonder if you have anything that you would add to that or what your approved process yeah I mean I've actually done a lot of vain air flow measurement and the interesting thing is you got a look as the year going in or going out so think About the sight of the register, you're on on a supply register right, the K factor becomes very important because the velocity coming out of there is you know.

Obviously, if you got this high velocity, but it's not a wide open area right. So if the K factors like, let's say 0.8, that means 20 % of the area is covered with register right. This is what they're telling you that's. What a K factor is just the amount of area that's covered up by the register, so if you're on a supplier register and you're measuring air flow - and you say okay, I got a velocity coming out of the fins.

I got this velocity of thousand feet per minute and then you convert it to CFM. What you're going to figure out is that, okay, you got to take it times, 0.8, because the area that you're measuring the area that you're measuring is there's only eighty percent free. Follow me around the supply now on a return, I'm with you on a central return right, we're measuring on the inlet side of that register, so the air that we're measuring going into that return. The measurement is made before the grill, so the K factor would have to be one you're not going to use K factor if you're on one side of the grill you're going to use K factor if you're on the inside of the grill you use K factor If you're on the outside of the girl, you wouldn't because a hundred percent of the air going into that vein is going in before before so think of it as a duct.

Just follow me on this exercise for a minute all right, I'm following you! So, let's imagine we got this invisible duct on the outside of our return air grill right. So we attach this a visible section of duct right: 100 % of the air is going through that duct and then it goes into the register. Now it's velocity is going to increase the little as it's going through the fins and all that kind of stuff, but all the air going into that register is not impacted by the design of the register. You follow what I'm saying once it goes through the register.

Then its velocity is going to be increased and k factor would start to be a factor if we were measuring face velocity on the inside of the register versus face flossing the outside. So the reason that he's getting these significantly lower readings or higher readings with this capture hood is because the readings are higher. You shouldn't be using the K factor on the inlet side. If that's, what he's doing that is what he's doing I've heard people say see.

I haven't used that method. Very often, I've actually used a hood more than I've used that method of painting a return with a vane anemometer I've done it on supply, vents and then see. We know that the K factor is important there, which I almost like the method. I wish somebody would invent some callers that you can snap up on into a supply event and that callers around the vents that you can actually read.

Past events, you don't have to calculate K factors because K factors are just a giant there's a lot of them out there yeah well CPS has come out with uh what they call micro hood, designed for residential applications that snaps in their small vane anemometer. I don't know how many CFM it's good up to, I want to say I think, 150 CFM, but for supply registers, there's a really cheap solution to getting a good airflow measurement. I don't know who's selling them right now. I saw him at ahr.

I thought it was very interesting and from what they're saying their initial test performance data, it did as well as some very expensive hoods. Obviously CFM limited, because it's a tiny little hood compared to a full-size captura, but for a lot of residential applications. It might be a more economical solution than a full-blown capture, hood yeah, and then you know like you, can get the cone adapter for the 417 for typical residential applications as well, which does you know it's a similar idea? It's just. It tends to increase the you're going to be really careful because it does increase the static pressure, letting it you know like the test.

Oh 420 is not that expensive. I mean it's a very reasonable price device that little cone will not work at all for supply register because that actually restricts it down to the vein size, so that creates way way too much back pressure, yeah yeah the reason that a capture mode works well, as It does not create a lot of back pressure. It uses a micro manometer to measure the pressure difference that goes back to what we were saying earlier is the reason tools are so expensive. The reason the capture hood is so expensive is it uses a very high precision, micro manometer, that's going to measure that pressure difference across that pitot tube array and that expensive manometer cost money.

It's not the capture hood itself, it's the measurement device. It's a high end! Manometer, that's costing all the bucks. So this way it is that's just the way it is alright. I think that covers it.

I mean we didn't get into using some of these more exotic. It's for measuring airflow, but I think the key thing to know is that it's not something that you can just listen to a podcast and go out and do you're gon na have to do some research, you're gon na have to understand exactly what you're doing and The thing with airflow that I've seen consistently is that guys who start measuring it without knowing what they're doing are far more dangerous than those who don't measure at all? I wouldn't say: they're more dangerous, they're just more confused. Well, they come to more wronger conclusions. What I've seen is there's a lot of guys who are measuring.

You know static pressure or doing some simple things and coming to incorrect conclusions about what's going on with the system that results in them telling customers things that are incorrect versus the guys who are just using beer-can cold, at least they're, not charging the customer. A lot of money, so I think my exhortation there is that if you're gon na do it do it, you know focus on it and get good at it. Don't just well! It's kind of it goes back to this, though, and be careful because you went down a slippery slope. There did I yeah you did because because it's what we're trying to do with the airflow measurement, that's the key thing, and I almost would like to take this.

A little bit more of a structured approach and let's do another podcast on air flow later on, because I'd like to structure it a little bit better, because the key thing with air flow measurement is understanding what you want to do with it. And when you say people are making mistakes, the mistake that are making is they're, trying to measure performance of the system using an air flow measurement method. That's just simply not accurate enough to do that or they're trying to dial in an exact CFM using an air flow measurement method. That's just not accurate enough to do that and there's a lot of very simple methods of measuring air flow that are accurate, but obviously they either cost money or they take a little bit more time, and you just got to understand what you want to do with That air flow measurement, so what leads people down the rabbit hole is when they assume that when they make a total external static pressure reading that their flow is gospel and it's not gon na let down this rabbit hole because it understand the challenges with the measurement.

They just made that's where we see people spending way too much time. Case-In-Point other one is a BTU output of equipment right, one ton system or a 10-ton system. I don't care whatever size you want to say, does not output one ton of cooling? It varies with the load conditions right so some days it may be outputting. You know 12,000 BTUs, some days, twelve thousand three hundred BTUs some days 11200 BTUs, depending on the load conditions right.

It's going to vary a little bit within load conditions with the relative humidity. With the return air temperature with the outdoor air temperature, with a line set length with the voltage, all those things are going to influence the output up there. So, when you're looking at air conditioner, you go, oh, it has a little bit to output. Does it does it have a low BTU output? It may have lowered the nominal, but it may just be.

They may be normal for the conditions that we have there's a lot of things to learn here. You know we're looking at air flow depending on the measurement method. We're using you go out measure air flow over the course of three different days and get three different readings, and it's simply due to changes in air density. So all those things are important.

So what we got I've realized is: do we need to make an air flow measurement accurate enough to select the right, blower, speed, high, medium or low? Are we trying to test performance if we're doing something that requires precise air flow measurement method? Then we got to use better methods of measuring here for than what we're using today, for the most part right cool that works. So today's was just a general conversation about air flow and then we'll come back at some point and do smaller segments that really address a more structured approach on all of these. I wanted to just sort of get something out there, because we've been getting a lot of requests for air flow in general. I think this does a good job, at least of having the general conversation.

If it gets across to anything it's that you probably have a lot to learn, everybody has a lot to learn. I'm still learning things even today I mean I keep learning new things every single day about what I do for a living. So that's the key thing in our industry is. This is a lifelong learning commitment.

If you're gon na be an HVAC industry for sure I saw a podcast and a website that their tagline is never stop learning. I thought that was pretty good. I, like those guys yeah. I think that was nice cool, oh yeah, well, yeah, you know I'll, send you a t-shirt and then you can.

You can wear that around just remember Jim, never, stop, learning, okay, yeah I'll, try and do that. Alright! Alright, thank you. Jim. Alright, thanks for listening all the way through to that, if you're new to this sub topic, this subject matter, this is gon na seem a little overwhelming, but trust me if you listen to part one and this again you kind of keep paying attention close attention to A human saying, you're gon na learn some things that are truly gon na set you apart, if you're in the marketplace, for some of these tools that we were rattling off, you can find almost all of them by going to true tech tools, comm using the offer Code, get schooled, no spaces, no caps and check out for a great discount.

The testo 417 is an excellent large vein anemometer. So it's gon na do a great job of getting that reading on your supply events, or you return vents to actually see this. The velocity and then convert that to a CFM output, it's gon na do a much better job than the smaller vane devices, because it's less subject to deflection, like I talked about in the last episode, the testo 420 flow hood is a good product, the testo 510 And 510 I for measuring static pressure are great products. It has makes a wide range, they have their the hot wire anemometer and the I series, and then they also have some higher-end products.

They have the small vane anemometer. They can actually go into the duct. So you can look at all those products like just typing in testo when you go to true tech tools, comm and again, if you find anything that you like use, the offer code get schooled at checkout. Thank you all for listening.

I really appreciate you. Hvac schools been growing by leaps and bounds, and it's all because of you and your interest in learning more about the job that you do every day. I appreciate all of you. If you ever want to email me, my email is brian, be rya n at hvac.

Our school comm and I'm happy to get your emails answer any questions I can. You are what make us who we are. So thank you have a good one. We'll see you next time on HVAC school.