This episode of the HVAC school podcast is made possible by dinner, support from testo rector seal and carrier. Thank you to testo rector sealant carrier for supporting the hvac school podcast, helping us with so many resources and really investing in technician. Training - and I do want to say all three of these companies make products that I really believe in one product is the testo 550. I've talked a lot about this set of gauges as manifold set.

That's the one we use most commonly in my business and what you get for the money that you spend. There's just no product out there that I've seen to match it. Even from just the standpoint of the fact that the clamps use the thermistor instead of a k-type thermocouple, which is significantly more accurate and when you're wanting to measure really find really fine, like temperature differences like, for example, the temperature difference across a liquid line. Dryer, where you really shouldn't have any difference whatsoever, it's really important to have very accurate test equipment and the test.

Oh five. Fifty is a great product at a great price, and it's also a nice size. The sizes you can actually handle some of the other great products that are on the market are good products, but they're very large. A lot of them use, k-type, thermocouple, Zander misters.

In the test, Oh 550, you kind of get all of it in one package. I also want to mention I've been doing a lot of conversations about a/c leak, freeze, the rector seal product and really more and more as I test this product, we're doing a lot of testing with it, we're using it in a couple cases that make sense older Pieces of equipment that has small for mercury leaks, we're testing the AC leak freeze product in that and what I'm finding the more I work with it is that I really feel comfortable that it's not going to hurt a piece of equipment both from the Bristol testing That you know Bristol did testing on the product and approved it, and so it's OEM approved by Bristol field, piece tested it and there s man gauges, and they said that it's no problem, it doesn't gum anything up. So I feel really comfortable that it's the one product that I feel comfortable that we can put into a piece of equipment if it's older and it makes sense the customers trying to get a couple more years out of it, that it's not gon na cause any Harm and above all, anything that I put into a system, I want to make sure that it doesn't cause harm at HVAC school. We also like to partner with companies that are making innovative new products, and so we have a new product sponsor, which is the Parkers Portland zoom product meets ulla.

The 10-second flame free refrigerant, fitting from Parker reduce 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. Zum lot comm for more information and now your host, the guy, who checks the air filter of every single hotel room right when he walks in, but still can't change his own filter. When he's supposed to Brian or hey cuz, they ain't. Nobody got time for a dirty air filter in a hotel room.

I mean it's one thing if it's might dirt at my house, and I can I can live in my own dirt, but it's somebody else's dirt. That's just gross! Thank you for listening to the hvac school podcast. I am brian and today on the podcast we have one of our audience. Favorites fan favorites Jim Bergman, Jim Bergman of measure, quick, the measure quick, app that he's developing that's gon na, be pretty cool and also he is the head honcho and lead product guy at redfish instruments.

But Jim came on today to talk about air flow measurement. That's one of the things that the Jim has done a lot of videos on when he was partnering with true check tools when he was one of the founders of true tech tools. He's in a lot of videos on that Jim knows a lot about airflow measurement and today on the podcast. This is part one of two.

We had a long conversation, but we started with static pressure because that's one of the questions I get very often is about static pressure, and then we go into talking about ECM motors and some other things. We don't tie up all of the loose ends because that's going to be done in part two, because it is a very long conversation, but I think you'll enjoy it here we go Jim Bergman. Did you like my joke? The other day you didn't respond to it? It was uh your chicken joke, yeah, that's pretty good, wasn't it man, I tell you, I don't know what to say. You were all like, not quite, but I was just watching your fourth of July podcast this morning.

So my fourth of July podcast. What are you talking about? Maybe your pre fourth of July podcast. I don't know what it was. Is there a live video, my video straight? Whatever you want to call it sorry everything's, a podcast I yeah cuz, I listen to them.

The podcasting yeah we've got there. Well, thank you for taking the time to this early morning. It's got to be kind of early for you, isn't it you don't usually roll out of bed around 9:00 9:30, something like that yeah, usually a lot later than that so ya know. I like this timing here, cuz I'm up at like 5:00 5:30, because I can't sleep if it's not completely dark in the room and our bedroom faces almost due east.

So this time of year, when they, you know Suns almost perfectly in the east as soon as it's hitting sunrise, I'm waking up. So I don't know my brain just starts getting act at once. I see like you're just a blue-collar guy you're, just up with the Roosters yep yep, but in wintertime man. I tell you it's not hard for me to sleep til 8:00, but I don't even know what winter is.

We don't have that in Florida. Alright, so my thought today was talk, some air flow measurement. I don't think we've really done that yet, okay cuz, I actually got a question from a listener. Actually it's Neil Neil copper reto.

So I don't really know if I count him as a listener or not he's more of a contributor. I guess, but we won't start there. I want to start with the basics. I'm gon na start with the question that everybody thinks of when they think of lilies.

Don't let me say everybody most technicians, think of them they think of measuring air flow. They immediately think of static pressure, which is interesting because that's not actually a measurement of air flow at all. So, let's, I guess start by just talking about what static pressure measurement is what it's good for and how we do it all right there. So we officially starting the podcast here, I'm according for hours and recording you're, getting your coffee and fumbling with the mic and all this kind of stuff.

Oh, that's cool all right, great, very great! Well, let's go ahead and start we'll start where you want to start at, even though it's not where I would start at, but it's alright yeah! Well, let's start where I want to start and then we'll go where you want to go okay. So if you go back and look at our industry, I think as a whole, and why do we make air flow measurements a certain way static pressure is one of those you look back. You wonder why, because you're exactly right, static pressure. Obviously, you require pressure in the duct to have flow, but just because you have pressure doesn't mean you have flow right.

We can obviously cap off the ducts, have a huge amount of static pressure, but not having well at all in the duct system. So is there a relationship between static pressure and flow yeah, absolutely there's a relationship and if we measures total static pressure across the appliance, the manufacturers measured the air flow across appliance. Then there's a relationship there. So that's all we're doing is relating a static pressure drop to a flow.

The challenge with that is static. Pressure can fluctuate all over the place. I mean guys have seen that you can make multiple static pressure measurements, depending on where you're at the plenum, how the duct system is designed. Sometimes you'll get negative static pressures where you should get positives and positives where you should get negatives.

So the question is well. Why do we even do it, and it goes back to this? Measuring air flow is easy, but measuring air flow accurately. It's very difficult and manufacturers have decided that we don't have the tools or we didn't, have the tools back in the day to measure air flow. So they're trying to come up with indirect methods using the tools that we had, that we could get air flow in the ballpark right.

So what they're trying to do is say: okay, what does a guy carry with him a typical heating and air conditioning? I carry with him that he could get a measurement of air flow cos. Obviously, manufacturers, no air flow measurement is critical, so he looked as well guys usually got some kind of manometer he's got a thermometer and he's got a wet finger and that's about what he's got to work with. So, let's see what we can do those tools and it's sort of how we got sort of external static pressure measurement. It's an indirect measurement of air flow, but it's got some issues you can but anytime you want to, but in here, because I can ramble for hours.

Yeah trust me. I know I will tell you. I had one of my employees. We were talking about the checking charge without gauges episode, which, by the way, has been extremely popular, even amongst my own staff and one of my new guys, piped up in a meeting and said man, you sure, are rude to that gym.

Guy, I'm surprised even comes on your podcast anymore, you're really rude to him. I thought you'd like to hear that. Apparently any interruption of you is considered rude by the listener. So I think you mentioning that airflow measurement is fairly difficult to take accurately meaning it's easy to stick some probes in a duct, it's difficult to get an actual, accurate result, and that is exactly what we're gon na be talking about.

Today is not only taking the measurements, but getting an accurate result that you can actually do something with the data, but I want to back up real quick because you always mentioned the appliance, and this is an important distinction. I think so. We talked about the appliance and we're talking about a system. That's moving air, that for most of us, that's either gon na, be the furnace or that's going to be a fan, coil or air handle or something like that, and so that's the appliance.

That's actually doing the moving of the air, and so the appliance manufacturer publishes some data that says you know under these conditions, it's going to produce this much air and usually those conditions are going to be under a particular static pressure conditions. So this is the pressure. Is gon na be in the ductwork or in the system? All the system is external to the appliance itself, measure that and everything else being equal. This is the output that you're gon na have, but even with that, there's some things that can affect that.

That can change especially over time that can cause appliance not to produce the airflow. That's published, let's back up just a second, because I think you should you know when we back up. You should have a backup button that way to beep as you go backwards. Yeah, you told me to do that last time and I didn't I know you're killing me here.

I asked for things you know all I did is just load my cue up with Charlie Sheen wearing like that and that doesn't work at all. I mean that's got nothing to do with. I don't think, that's helpful. So, no so, let's, let's just think for a minute cuz.

Why are we doing this in the first place? Why we up at 8 o'clock in the morning talking about air flow, this early yeah? It's a huge problem in our industry, but it isn't it isn't because here's a problem, the problem is we're trying to do things with air flow that we've never tried to do before. Until probably, I would say, I'm gon na be going back 10 or 15 years ago now. I had never measured air flow in a duct system, and I want to be clear about this because when we measure total external static pressure, we're not measuring air flow. We're measuring static pressure and we're comparing it to a rated air flow when we're measuring air flow.

We're like sticking in a pitot tube in the ductwork and we're measuring velocity pressure and then calculating an average velocity pressure and turning that into velocity and then calculating a CFM. You know there's actual things. We measure, like tools that you measure air flow with like a hot wire anemometer, is a tool that measures air floo. A vein.

Anemometer is some tool that measures air flow or we get into. You know some of the other pitot tubes things like that. They measure air flows, but when you get into static pressure, static pressure is not really a direct measurement of air flow, you're measuring a static pressure and a duct temperature rise. It's not a direct measurement of air flow.

The calculation we used in a manifold where we're calculating the mass flow across the coil is not a direct measurement of air flow, not saying that those measurements can't be very, very accurate, but there's measuring air flow and then there's estimation methods of air flow measurement. Two completely different things and there's variables that we don't take into account that we're not going to get an accurate measure air flow. Well. Why does that matter? Because at the end of the day, going back with equipment, you know say: twenty years ago we weren't measuring air flow.

We were just going in and we had four speeds on a PSC motor that we had to pick from right. So we just needed to get. If you really think about it in a nutshell, all we needed was an air flow measurement, accurate enough to pick the right tap on the mower. That's all we needed it's all we cared about.

So you know we had high medium high low and medium low and which one do we need to pick. So we took a static pressure. Reading we threw in a ductwork, we go. Oh this one's about 800 CFM and I got a 2-ton system.

So I'm gon na leave it on my medium load tap and there I'm good to go or my medium height tap and I'm good to go. It was pretty much that simple, because what, if we changed Brian, that we have never done, I think probably the biggest change i manifold when we design that tool brought to the industry. This is something we've been doing. In fact, if you talk to pill, spoon mean this goes clear back to that when I first started met bill and met tough, though, because honest-to-goodness when I started reading chapters 1, 2 & 3 and refrigeration air conditioning technology and ran across you know the specific heat Formula, the sensible heat formula and the total heat formula and I tried to apply those in the lab and what we were doing was temperature rise test.

You know we're trying to calculate see if I'm two temperature rise and then all of a sudden. It's like hey. You know one of my students, Matt shufflers, like hey Berkman. If you can use this formula to measure air flow, can we like rearrange it algebraically and measure capacity with it and I'm like yeah sure Matt? So let's go out there and do that, so we went outside and we make all these measurements.

You know we're using things like total external static pressure and temperature rise to get air flow. We're doing all this and the capacity is like all over the place and not only is it all over the place, but we can't even get the same answer two times in a row, so I'm still mad. I said: well, you know some things are only meant to be done in a lab. I guess, and he goes well.

We are in a lab, I'm like yeah. It gets weirder than that, but maybe a different kind of I have Matt like a scientific lab and I'm sort of thinking. After if the kids left school, I'm like dang man, I'm in a huge building, you know not only my lab and all my ceilings are connected throughout this whole building. I'm not changing conditions in this building, so I can run these furnaces or air conditioners all day.

Long, you know my units are in up shop, so I'm absorbing and rejecting heat in the same place like how come, I can't get an accurate airflow measurement. How come? I can't get kids capacities right. What the heck is going on here and really came down to this is where I had a penny in my life and figured out my goodness. It's all coming down to I'm not getting good measurements, and you know I got tests over my lab and Wells's.

We got accurate temperature, humidity measurements, all the science and all the math started to work, and then I started realizing the challenges with each one of these different types of air flow measurement methods, because we can also matter static pressure drop across the coil static pressure drop Across the filter you know total external static pressure drop across something anything can be rated for a static pressure drop and CFM. The manufacturer can do that. The problem becomes with using that as your primary measurement of airflow. Is it's accurate enough? So you can get the right blower tap, but it's not accurate enough to do things like capacity testing right.

This is where the challenge becomes. Is people are trying to use measurement to do things they never done before, and they can't get the measurement to make any sense like they're going? How am I getting two and a half tons of cooling out of my two ton, air conditioner wow? This is just impossible, then they make the measurements again now they're. Getting you know, 1.8 tons out of its like what the heck's going on here. They measure it again are getting a different measurement and they're getting frustrated with it and they say.

Oh, that can't be done. You cannot measure capacity accurately in the field. It's like well really, really, because I think a HRI measures, the capacity I mean, there's the third-party yeah. They got some pretty cool stuff.

But today, when you look at instrumentation today like what we get from just digital instruments in general, not all digital instruments want to go out there, but sensors in general have dramatically improved. You know I've used some of the stuff test I'll make some uh stuff field piece makes stuff that we did with I manifold stuff that we're seeing you cps come out with they're all reasonably accurate. Now, obviously, the more money you spend, the better sensor quality. You tend to get i've seen on the smart probes like there's 6:05.

I that thing is absolutely incredible for relative humidity and temperature. It's probably one of the better sensors are seen out there, but in typical in general, and talk about sensor quality. The more you pay for an instrument, the better the sensor is, the electronics are really a cheap part of an instrument. It's actually what we're paying for is the sensor, and when you get into things like measuring air flow, you know the pitot tube.

I don't you ever tried a pitot tube before, but it's a real pain because the measurements are so tiny and that's because the sensors we have aren't accurate enough to measure those really low pressures. Typically, you just like an inclined manometer or something like that to measure that, when we're looking at a total external static pressure and we're dealing with, you know like say, half an inch to an inch of static pressure when we're working with a pitot tube. It's like point: zero, two point: zero one inches of water column, velocity pressure right, so it's a totally different type of measurement requires a totally different type of tool. Now then, we're gon na like a blower door gauge so where you might spend 175 bucks or a hundred bucks for a little pocket.

Digital manometer you're gon na spend a thousand bucks for a blower door gauge right and what is its accuracy and resolution of the gauge that you're paying for that's white high quality instruments cost more money, but we can do other things with them like calculate capacity accurately. Where we can never do that with the tools we had with like standard u-tube manometer to measure static pressure and wet bulb sock, you know guys are still out there with k-type thermocouple and wet bulb socks trying to measure wet bulb and not only they're using the Wrong tool but they're doing it with the wrong process: they're using water, that's out of the tap it's that distilled water, that a cotton sock is not clean. They are sticking in an air stream where the air velocities, you know, instead of being five to six hundred feet per minute, it's 1,200 to 1,500 feet per minute, so the water's evaporating faster, it's and affecting the wet bulb temperature. All those kind of things come into play, so the instruments are critical, but also what are we trying to do with the measurement? And I think that's when we start with us and sort of dragging you along, because the static pressure is a good place to start because it got us primered there.

But the key thing is: what are you trying to do with the airflow measurement? If we're an installer, I'm sure you have install crews and you're going out there and they're. Just getting this thing set up, hey total external static pressure is perfectly fine. The guy can go out there and always got to do is get it set on the right. Blower speed and he's good to go, but if you're sending a service tech out behind him, because the customers complain - and you know it - the equipment seems to be running too long right.

The house is cooling, but it just seems like it runs forever. I just want somebody to come out and check it and see if it's working right well, if that guy's going to go out and do capacity measurements on the equipment and make sure that everything's working properly a measurement of static pressure is definitely not a suitable measurement, Because that could throw your capacity of readings off by 10 20 percent easily, because if your air flow measurements not accurate, nothing else is going to be because of straight multiplication right. If just on the standard error, formulas 4.5 times CFM times change in enthalpy, so that CFM, when you multiply it through any air or multiply straight through also - and you get a lot of uncertainty than your equations. So that's we're trying to eliminate here when we're talking about different air flow measurement methods right and so then you pointed out there are a couple different reasons why we look at air flow in a couple different use cases.

So, in a lot of cases, an installer just wants to make sure that the equipment is producing the correct CFM, so they're, just setting a charge based on the charging information that the manufacturer provides and they're wanting to make sure that the correct CFM is being produced. So the correct fans happen an old way of thinking of it, and so that's sort of the simplistic way of looking at it, because the installers not necessarily are generally not going to do delivered capacity tests. They just get everything within range and then there's the assumption that the equipment's working properly them again, that's just standard practice that maybe some people who say well more installers. Do you know that type of testing every time? Let's talk a little bit about because I think there may even be some misunderstanding about static pressure, how it works.

What we do is so, let's just break it down to the very simple step. So when you're measuring static pressure, you're taking a manometer generally and do manometer and you're putting the negative probe in the return side, you're putting the positive probe in the supply side and you're measuring that total external static first off, because this is the question I get Most often, where do you put the probes in order to measure what the manufacturer of that appliance is going to consider appropriate total external static? That's a simple question, but also like the million dollar question, because let's just make sure that we're talking the same thing here, because all this depends right. Like I'm up here in Northeast Oakland Ohio, we have primarily furnaces that we're going to measure total external static pressure on. So when you typically look at how an appliance is rated, it's rated as the appliance itself.

In other words, a furnace on the north isn't to come with a coil as an accessory item right we can heat homes where we can cool homes, but typically the furnace and the coil are two separate components. So the furnace is rated by itself. The coil is rated by itself, but if you go down where you're at in Florida, where you heat primarily with heat pumps or electric strip heat - and you have an air handler - it's typically rated with a coil in it right. So we've got two different configurations.

You got a rooftop unit, it's rated with a coil in it right we're going to be measuring a supply and return air static, but on a furnace, a gas furnace, we would not be measuring in the supply and return air plenums like we would on an air Handler on a rooftop, so it really depends. You have to look at your manufacturers guide. First of all and see: where do they want you to measure the total external static pressure? That's pretty important now in the case of a furnace which we'd have here, we'd have to be below the evaporator, coil and we'd have to be in the return. Air and we've petitioned manufacturers for years to actually put multiple static pressure ports in a piece of equipment, because, obviously you know it depends on how the equipment hooked up.

You can have a return duct in the side of a furnace. You can have in the bottom of the furnace left side right side, you know, so you need multiple points in there also, you would have multiple duct configurations which also affect the airflow and just to put this in perspective, because a lot of people don't quite understand How that happens, I just want to give you guys a visual. What happens when you have air going through a duct right? Probably the easiest way to imagine this is imagine a racetrack right if we have go out and we watch NASCAR with a driving in circles. All the time - and we take that track - and we just say you know what, instead of having circular corners, I'm gon na make square corners out of this racecar track 200 miles an hour.

People are flying around the racetrack into square corners right. Well, if you're on the inside of the track, and you try and cut that corner you're going to start to spin out and you're gon na have turbulence as you go around that corner cars are spinning out. Some of the cars are gon na make it through the sort of the center of the turn. They're drew up the upper part of the track too, when you hit that corner 200 miles now or you're gon na either smash it you're gon na probably smash into that wall.

You've got to slide in the wall you're going to have turbulence up in the two corners where you're at in the two square corners, because you got ta figure the tracks like a giant rectangle inside of another rectangle right. I mean I've got with to this duct here this track and it's cars are zipping around there. If you're in the center of the track, you have a good chance of getting through, but if you're on the outside of the inside of the track. Why and run that corner there you're gon na have some problems.

It would definitely make NASCAR more interesting, but it would also be a lot more expensive because cars would be totally trashed out here and that's what happens when air is going through a duct when we don't have good air design. There's a lot of turbulence going around the corners and the cars are spinning out they're, spinning out well that air as it spins an adduct, can actually create negative pressures in the ductwork, because it's just like you're standing at a bus, stop you're watching a bus come By and and you don't ever feel the bus coming, but as soon as it passes by you get the suction of air, you feel you know this pull of air from the bus. That's the Bernoulli effect. It's just in training air behind it.

So air at high velocities, when a zipping by stuff creates a negative pressure behind it and we can feel that air spinning in there well that affects your static pressure measurement. So earlier I said you can get different static pressure measurements by putting your probes and different place in the duct. Well, that's a hundred percent true because, as the air is turning, what you're going to find out is it's creating different pressures in that duct system. So we don't get this like smooth, laminar pressure or like we envisioned in our head, where there's just this constant suction, because the air is also under velocity.

It's moving crashing spinning through that duct work and those philosophy of pressures gon na influence our static pressures. If we just had static pressure, static pressures bursting pressure right if we were to take a balloon and we were to blow it up and put a static pressure probe in there, that is truly static pressure. So the pressure that balloon is just sitting there in a static position, there's no flow in that balloon. It's just sitting there and it's a static pressure.

Reading, there's no static means standing pressure, just not moving. There's no change. Velocity pressure is now we let go of that balloon and that static pressure, all the sudden converts to velocity pressure and the balloon zips off and flies away. That's the velocity pressure and as the air exits that balloon and creates turbulence in there.

We no longer have this nice stable, static pressure. We have this static and velocity combined and that's what influences and screws up or reading so at the end of the day, when you ask well, where do I put my static pressure port? Well, let's say you're on the return side of a furnace. The center of the fan, like you, have obviously the inlet of the fan. You have.

The housings called a ballute where the air goes into the Fayette housing and they have the exit of the fan. You don't want to be near the inlet of the fan, so if you drill a hole in the center of the duct think about what's happening, you got a blower there. It's turning and spinning it's creating. I like this little tornado inside of the duct.

If you can visualize that blower spinning an air turning into that fan, spinning around it's creating a vortex, that's creating a little tornado inside of that doctor pulls that air in and that center that tornadoes at a higher negative pressure than it would be elsewhere in a Duct, ideally, you want to be somewhere in a corner away from wiring. That's the other thing we don't want to do when I'm drilling a hole inside of a furnace, no matter where I'm drilling at, I usually take a piece of electrical tape and wrap it around. My drill bit so I only go through about a quarter of an inch because I just need to pierce the steel right. I don't want to drill into the wiring.

If you want to put a wash draw, even as a stop you can. So you don't get the electrical take goo on your furnace, but that way when you punch through the steel you just get through there, but you know drilling a corner or something like that now. The second thing you got to realize is a lot of those cabinets. Are insulated so also we've got to get past the insulation, so you got to take a screwdriver and pokes that insulation make sure you have a good hole and then obviously you want to use a static pressure tip and a static pressure tip is different from a Pitot tube the static pressure tip just has holes around the outside of the tip and there's a lot of holes in there so tries to average the pressure again.

It's really dependent upon where you put it and if you have a piece of shop equipment, you can try this in just drill a hole. You know like right in front with a blower to go and the drill hole in the corners and look at the pressure. Differences in a return and you'll see that it could have a lot of influence on where you put it. So where do you want to put it in a place in the duct system, where there's not a lot of turbulent airflow, so you want to be away from the corners where the airs coming in, but around like.

If you go in a opposite corner like say, your Inlet is on the left side and your documents on the left then measure on the right side in a corner down there somewhere, because there's no flow of air through that the blower is creating a suction pressure. On there and that's what we don't want to measure uninterrupted from well laminar flow or Pinot in a laminar flow section of the duct, so it's not influencing your static pressure, readings same thing on the supply side. We want to be in that place in the furnace. So like in the back of the furnace is less than ideal because, where the blower is blowing up the back of a furnace, you know, if you look in a cabinet, you got one of the lower is usually all the way towards the back.

So you get higher air flow over the back of a furnace than you do over the front of the furnace right again we're trying to measure pressure and there so you know maybe go to the left to the right side of the furnace, but not directly in The back in the middle, well, the evaporator coil, because you're going to be right in the air stream coming off the blower and that's going to be probably more turbulent air than you would get on the side of the furnace. Because again we want to measure the pressure and the supply. We want to measure the pressure and return. The manufacturer has done the same and they've measured pressures at corresponding flows.

So all you're doing when you look at a static pressure, chart you're just comparing the static pressure measured to the flow measured, usually using the tap the speed tap that you're on and I'll tell you what your approximate air flow is. But again, that's accurate enough to select the right speed for cooling, let's say, but it's not accurate enough to measure the performance of the cooling you'll get a lot of air in that if you use that for your primary air flow measurement method. Again, I always like talking about room at our estimation, so static pressure is an estimation of air flow, but it's got its place and that's for your installer to get the correct, blower speed a couple things so just to sort of summarize this first off in a Furnace you're reading below the furnace, so that would be after any additional filter racks that are installed in the return side. If you have a three inch or four inch filter that you've added in then you need to take your measurement, after that's rate, for each filter.

Yeah, usually, the furnace is rated with a filter in place, which you bring up. Another good point here is that when you're looking at like static pressure, readings they're under very specific conditions, so it's with a certain type of filter, typically they're rated with like a fiber glass, throwaway filter or a hog, hair, filter or filter. That's got very low resistance to flow. If you put in you know like a Spaceguard filter or a 3m filter, that's got a higher pressure drop.

It's definitely gon na affect your static pressure readings across your furnace. If you don't take it in the right location right. So if the furnace is rated with the filter or without the filter and the manufacturer will tell you with or without again it's gon na mess with your readings. So if they're rated with a standard filter, then you might have to include like a tenth of an inch of static pressure drop for the filter to normalize the measurement for the static pressure drop yeah.

It's not always super apparent like when you look in carriers fan coil specs, like it talks about the factory-installed filter pressure job on their filter, but it doesn't readily say: is it rated with it or is it rated without it now the amount is nominal so you're? Looking at anywhere from I'm looking at this chart right now anywhere from like point zero to up to almost 1, depending on the CFM on that particular filter. So there is some variance there, but it's not always super readily apparent. But the important thing to know is if you're, adding in a filter, you may have point one right point: zero to two point: one, not one. What did I say good one? I said one one would be very high, that'd be a very restrictive filter.

Jim, yes, Barry, so if you're, adding in an aftermarket filtration product, that's where it becomes even more important because you could have significant pressure drop across some super cherry, bomb' Betamax double pleaded: mur 14 filters. You know nothing gets through this filter, including air. So right, which comes down to what I actually did used to save the customers, probably wasn't the best thing. Customers would always ask well what's the best filter to put in, let's see, what's gon na catch the most and I would say a brick wall and then just wait and they would blink and then I would say, but no air will get through either.

So you got to kind of find something in between a fiber glass and a brick wall, mm-hmm yeah, maybe crickets, and then I would lose all my customers. I wonder why this do a podcast right right, exactly because I couldn't sell any filters. The way I've heard you say it before and I like this way, is you're measuring on both sides of what's in the box. So a furnace comes in its own box and so the furnace is rated so you're measuring directly above the furnace or in the furnace cabinet itself and then within the furnace itself.

So you're measuring, what's in the box in the case of a fan, coil air handler rtu, whatever what's in the box, already includes the evaporator coil already includes a factory filter and so on. With a caveat there, of, what it doesn't include is your electric strip heat, which is in a different box and as soon as your Installer puts, electric strip heat in an air handler he's just changed. The rating of the air handler to the design of the air handle, or so now he has to go to a different chart that says air handler with this electric strip heat and then it's going to give him a whole new set of static pressure. Readings for that configuration of the air handler right, so there's a lot of charts in there and they get relatively confusing because you got to look at model numbers.

You've got to look at heater model numbers you've got to look at maybe evaporator coils that are installed. You've got to look at filters that are installed so, like I said, sticking probes in a duct is very easy, but getting an accurate air flow measurement is not. This is why also you know when you go out there and you buy. Let's say you were to take a single-speed air handler and do a total external static pressure measure, the air flow and then take a hot wire, anemometer measure, the air flow and then take a pitot tube and measure the air flow and then take a vein.

Anemometer measure the air flow and then buy a true flow grid and measure the air flow and then do static pressure, matching method, with a duct pressure, tester to measure air flow and then do temperature rise with the electric heat to measure air flow and then put The I manifold in and two probes and spider turn a measure airflow. You would get a whole bunch of different readings now they would all agree within some semblance of something, but they would all be a little bit different and the reasons are each measurement method has its own measurement uncertainty. Each measurement method has its own Corrections that need to be applied to it. Some of them are dependent upon the air density in some of the measure independent of the air density, which is the other thing I want to harp on before we get too far into this, the challenge becomes guys say I can't get an accurate air flow measurement Because I measured using these different methods - and I get all these different results - well, the challenge becomes, is you really have to understand each method intimately and what effects it and how to correct it? What's interesting is tab, guys, guys that are actually you know test and balance guys that are formally trained in air and air flow measurement actually go to school for 3 to 5 years typically - and I like a union apprenticeship to learn how to measure air flow accurately And they have a manual, that's probably an inch and a half thick.

That goes over all the different methods you know even like we didn't talk about rpm and static pressure on a commercial rooftop unit. You know where we can measure the speed of the blower with a tachometer. Now, there's all these different methods, these guys are trained in those and then they're trained to normalize. Those measurements are correct: those measurements for the variables that impact them so that they can compare one measurement method to another and then make corrections that normalize them together.

The best example I can think of this is you're really close to the ocean sea level right Brian. So if you were to go on the Weather Channel right now and look at the barometric pressure, it would be fourteen point seven, let's say because you're at sea level right your your barometric pressures 14.7. Well, if we go and look at the barometric pressure on Pikes Peak, which is at 7,000 feet above sea level, or so you would find out that the barometric pressure is also like. Fourteen point, seven fourteen point: two something like well: how is that possible right? How is it possible? I have the same parametric pressure at sea level as we Pikes Peak because they normalized at the sea level on the Weather Channel right.

They just said well we're just going to normalize it for everybody's barometric pressure for elevation. So it's all relative - and this is the kind of thing we do in the air-conditioning industry - is we've normalized things and people don't realize they've been normalized or they haven't been normalized or there's the wrong equation. Like we talked about standard air equations, the ones guys are using the calculate capacity in a 4.5 times, CFM times change in enthalpy. Let's US standard air equation, that's standard air, which means 68 degrees, Fahrenheit zero percent relative humidity at sea level.

Well, when are we ever at sea level and at 0 percent relative humidity, not very often right, so that standard air formula has some error in it that if we don't correct for it, we're going to get some inconsistent results. Our industry's rampant with those kind of things and the challenge becomes again and goes all back to this. You have guys that had extremely expensive laboratory equipment that were setting up stuff in the lab designing engineering. This stuff, I mean you, look at the work.

Willis carrier dead and completely amazed that the psychometric chart he developed, you know around 1915 or so it hasn't substantially changed. I mean they've gotten a little bit. Tighter ashtrays done a heck of a job getting a little bit better than it was and taking it really to the next level, but substantially he figured out almost everything on there. Well, how did he do that? He did it by continue eliminating variables that were influencing his temperature measurements and his humidity measurements, and when we look at the tools that were available to us, you know from 1915 are available to the technician from 1915.

All the way up. To probably you know, twelve fourteen years ago, we just didn't have field great instrumentation that could give us laboratory results and that, I guess again has completely changed. What's available to us today is much much better. Now again, you have to make a little bit of investment into air flow measurement tools and things, but you're gon na get much much better results at the end of the day.

But you have to learn how to use those tools and the limitations of each one and the manufacturer is probably not going to tell you what those limitations are, because they may not know, or they may not think you care, or they may think like in a Case of test, Oh that everybody that handles an instrument is formally trained. It's very interesting what it worked for testo and went over to germany. I found out. You can't be a technician unless you've gone through like five or six years of training, same thing in Canada.

I believe you have to have formalized training where in Ohio or Florida or things like that, I mean you may have to get a contractor's license, but that doesn't mean you've been formally trained in anything except for business and maybe how to do a heat loss calculation. It doesn't mean you have a thorough understanding. You've been to trade, school or you've been to college or you've had some kind of formal training on how to do these things, and this is where we fall down in our industry because we're again people buy a product. They think just because they get an output of X, CFM or X degrees or X, humidity that well, it's got to be correct.

Telling you right now, not necessarily because you have to understand the tool you're using the tool you're using and all of the environmental very hard, but it goes back to what I said at the beginning. You know making measurements is easy. Making them correctly is pretty darn hard. I guess, if anything, we're gon na generate in this podcast its awareness that you're not alone in your frustration, that I know you've been trying to measure airflow and you just don't seem like you can get it it's, because you need to study it more and you Need to spend some time learning about the variables and you need to spend some time like I.

I set up equipment in my house or Mike or a garage or a big area where it's not going to influence temperature, and I could continually play with it all day, long and figure out what the heck's going on here. So I can get consistent measurements and try and make those Corrections, and it's gon na take your time. There's no doubt about it, but once you start to understand that, and I honestly think this, if you understand airflow, you will be one of the best and most sought-after technicians in the industry, because seven out of ten systems today do not have correct air flow period. Seven out of ten they've done, multiple studies, California, Energy Star.

I got probably six different studies. I could cite they consistently show the same thing. Seven out of ten systems have incorrect air flow, primarily due to poor duct design. That's a big thing in California.

For Texas, a lot of the coastal states because of the way homes are constructed and materials used. You know it seems to be a big problem out there, but those airflow issues are the ones that typically go unresolved, because technicians get what I like to call as appliance fixation and what that means is they stand there at the appliance and they look at the Furnace so they look at the air handle or they look at the condenser, and they forget that that is only part of a system and they need to look at the things that are attached to it. Like the ducts and the line set and the electrical there's electrical distribution systems, there's air distribution systems, there's refrigerant distribution systems. You've got to look at everything because it's all part of a system when we're just looking at the air handle or trying to fix all the air flow problems that the air handler.

It's like trying to change somebody's heart out and put it on a bad set of arteries. You know if clogged up with plaque and gunk in there, it's not going to fix the problem. Adjusting the blower speed is probably not going to fix the problem if you're running an inch and a half of static pressure already or an inch of static pressure already, you have duct issues that need to get resolved, and these are you know, on a side bar These are some of the challenges that we get, but these are the things if you're doing your airflow measurements and you're. Looking at your points, you got to start thinking of the entire thing as a system and not just as a appliance, even though some of the measurements are gon na make her at the appliance.

You have to look at everything, that's attached to it and think about. What's happening is you're making your measurements alright, so something I want to mention. That's changed over the last, probably mostly over the last five years, but really over the last 10 to 12 years, as we've started to see ECM motor technology come into the marketplace again. This is my opinion and I'd like to hear if you have a different one, but it has become a little easier to get accurate, airflow output, accurate CFM output based on static pressure, only because there's less variability in the output when you're dealing with an old PSC Motor, an old typical you know multi-tap inductive motor that we typically work on there's large variants, depending on the external static pressure on the system.

Whereas if you look at a fan curve nowadays on, say variable speeds at carrier, F, V or F EE air handler. The airflow output is very, very consistent until you hit about 0.92 old external static. So that's a significant that's pretty high static. Now, that's not good, because the wattage is higher on the piece of equipment you're producing more heat out of the blower motor.

So it's not good to have high static, but at least makes it easier to measure and estimate the airflow. And would you agree with that statement, or would you add anything to that? No, I have a lot to add to that go ahead. Please do so. The ECM motor is probably the best invention this industry's had in the last 50 years, maybe the last hundred years as far as air movement technology goes.

But I think we need to go back and understand a couple of different things, because PSC motors and ECM motors are way way way way different. But, first of all, it's time for you to get uncomfortable in your seat, because I'm gon na start quizzing, you again yep or the audience know you or am I just a proxy for the audio. You are a proxy for the audience yeah. I think that sounds good, although you may not be reflective of the audience, but we'll give you a shot, I'm in everyman gym I'm in everyman, I'm a blue-collar guy, all right.

Mr. regular blue-collar, guys in here I'm wearing my steel toe work boots right now. All right, so, let's ask a couple questions, but first of all, thanks to this logically might be hard for you, but we'll give it a shot. What is the work that the fan does the work that the fan does? Is it moves air, okay, perfect and moves air and let's go back and just ask one more question: what kind of air doesn't move? Does it move CFM of air or does it move pounds of air or does it move both it moves both it does, but does the CFM on a PSC fan? Let me think of this.

This way. Does the CFM of a fan remain constant with the air density of a PSC fan? Okay, here's a lot about that before, don't you know never exhaust remains constant with high density. I'm trying to think of how to say what I'm wanting to say here. So it moves air independent of density right, so we're talking about boxes of air.

If we have a fan that moves a thousand boxes, a thousand CFM right, it's got to move in a thousand these cubic foot boxes. The fan doesn't care. What's in the box, it's just going to move the same thousand boxes and as the air density changes, it's going to have a constant CFM at a variable mass flow rate right all right right. This is my biggest frustration in the HVAC industry.

As far as air flow goes is what we're not teaching technicians, you know it's interesting. If you go to chapter one of the textbook, refrigeration, air conditioning technology, they take you through and they say: well, Q. You know equals quantity of heat equals your mass times. Your specific heat times your change in temperature and we're talking about mass flow formulas and not all sudden we switch over and tell technicians.

You know an area requires 400 CFM per ton. What they aren't doing right there is saying okay. This is first of all standard error. So when look at that 400 CFM per ton, that's standard air, so that means 400 times.

Point: zero, seven five pounds per foot because a standard cubic foot of air is point zero, seven, five pounds per cubic foot: that's the weight of the air, so 400 times point zero. Seven five is 30 pounds per minute per ton right 30 pounds per minute per ton. So if you've got 400 times point zero, seven five is thirty right. So we're looking at talking about 400 CFM cubic feet per minute, you're talking about thirty pounds per minute per ton; okay.

So if we're talking about a five ton system, we're talking bout 150 pounds of air per minute going across that coil, it's the mass of air that we're moving so we're talking about what that blower is doing. It is moving CFM of air, but it's actually moving. These pounds of air: that's why it takes horsepower. It takes work to move that air we're moving pounds of air through the duct and people.

Don't often consider that because we don't feel the weight of the air around us, because it's exerting the same force in all direction, you know we can feel a little bit. If you take a piece of cardboard or something you have waved through the air, you can feel the resistance of the air. That's the weight of the air pushing back on that cardboard. But overall we don't think about air resistance or air movement.

All that much and that's what we're doing we're pushing air through a duct system is removing pounds of air through the duct system. That's the physical work that we're doing so going back to our PSC motor. You know we're just talking about static pressure. Obviously, if I'm moving air through a duct, I'm gon na have some work that I'm doing and that work we normally represent that in watts of power.

So we have a constant voltage and we see our amperage go up and down as we increase or decrease their flow right. So if I clamp my amp meter on my blower, I'm gon na expect to see it a an amp drawn there right. So let me ask you a question if I block my supply duct off completely just cap it off. What's my amp drawl gon na, do your amp trial, it's gon na go down Jim okay, very good, and if I block off my return, what's my amp draw gon na, do it's gon na go down right? Why is it gon na go down? If sounds like the motors working really hard, I mean I can hear the pressure.

The pressure is going way up. I come on crazy suck it like. Yes, it's got to be doing a whole bunch more work. Now.