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In today's live stream, Steve Rogers (The Energy Conservatory) and Bill Spohn (TruTech Tools) join Bryan to discuss system performance checks during commissioning. This live stream has a heavy emphasis on airflow in system performance.
Some technicians cannot perform effective system performance checks because they don't know the ins and outs of their tools. These technicians fail to maximize their tools' potential by not knowing where to measure, how to measure, or what their tools can do.
Static pressure measurements are vital for system performance checks because of static pressure's relationship with airflow. Static pressure is NOT airflow; it is the force exerted in all directions in the ductwork. However, misuse of the manometer is common and leads to inaccurate airflow calculations. Technicians must understand what they must compare their static pressure measurement to. They need access to the blower chart from the manufacturer AND the specifications. Airflow should be measured BEFORE the technician checks the charge.
According to RSES, your typical A/C unit will have an airflow of 400 CFM/ton. You can expect 450 CFM/ton for a heat pump or a high sensible heat load, and you can expect 350 CFM/ton when there is lots of outdoor air coming in or when the latent heat load is high. The best way to take a measurement is to use a flow hood, vane anemometer, TrueFlow grid, or manometer and blower chart to measure the airflow and use these CFM/ton values to verify the airflow. However, these values vary with humidity, altitude, and barometric pressure.
When it comes to understanding airflow values, a good starting point is for technicians to understand how the basics of heat transfer work with airflow, especially when it comes to the intricacies of sensible and latent heat loads.
A system measurement of airflow differs from a distribution/point method of measuring airflow. Total system airflow measures the total volume going through the air handler (or furnace). You can add up the airflow of all the supply registers, but accuracy can be an issue. You also cannot account for leakage if you add up the supply registers.
External static pressure is usually measured with a diaphragm-type pressure gauge. These come in electronic or Magnehelic varieties. When it comes to the tools that measure static pressure, you must know how to use them. If the tool says that it measures a percentage of the full scale, you must account for that. If you take the measurement at face value without accounting for resolution or scale, you will get a highly inaccurate measurement. Also, due to the nature of pitot tubes, you will need to take multiple duct measurements. You can also use manometers for blower door tests to measure duct leakage, and you need a very high-quality manometer for that.
On the refrigerant side, "beer can cold" is an outdated way to measure when you have tools that can take accurate superheat and subcool readings. Superheat and subcool readings help you determine your charge and can give you some insight into the unit's efficiency.
While the refrigerant charge is important for system performance checks, technicians generally seem to have a better grasp of it than airflow.
Remember, just because an instrument gives you a value, that doesn't mean that the value is your exact measurement. Applications such as MeasureQuick also help technicians interpret their readings and collect more accurate data during performance checks.
Go to TruTech Tools ( or The Energy Conservatory ( to get your hands on a TrueFlow grid.
Read all the tech tips, take the quizzes, and find our handy calculators at

I appreciate bill spone and steve rogers for being our special guests uh on this episode of uh apprenticeship, training, class virtual session um, and actually, what made me think about this is i was there was a post in one of the facebook groups that was just talking About you know, practical measurements that uh ac technicians and installers should focus on taking, and i want to focus on the kind of the commissioning side of things side of things, because i think that's where everybody is in more of agreement. There's a lot of discussion about. What's you know an appropriate performance check to do if you're changing a capacitor or something simple like that, but i think in terms of commissioning everybody knows, we need to be doing a really good job um. So, to start with, i already introduced him by name, but bill is the uh.

Is the chief magnate, the um, the king of true tech tools? I think is the exact uh exact term and then steve rogers is the president of the energy conservatory, which often uh uh. You know as tec, so you'll see that if he could be magnate, can i be grand poobah yeah? I know i didn't give you any fancy title grand poobah would be good yeah. That would actually that would actually fit very well uh anyway. So um today's topic is going to be about performance measurements, i'm going to go ahead and give it away that we're going to be talking a lot about airflow, which is a really important, um, really important topic anyway.

Uh but both bill and steve are like airflow guys um now. Obviously we can expand this and start to talk about the house as a system or the you know, the structure and all that um today we're gon na focus primarily on the system. Uh, the actual equipment, the box uh the tests you do within the box, so um, i wan na start with you bill because you sell a lot of tools, so you see what people buy um. Where do you think uh? Well, we'll just ask it this way: what do you think are some things in terms of measurements that techs may be under under measuring or misunderstanding, even just based on the maybe some of the questions you get or really what you see people buying most often, i Think there's a misunderstanding of like where to measure how to measure the tools that they have uh and knowing the capabilities of their tools, uh, there's a person who shall go unnamed, who tried using a very low resolution manometer with a pitot tube.

Oh, i see where this is going. Okay, all right! I just caught on you invited me yeah, yeah, fair enough! Well, yeah! So talk about that a little bit because, let's, let's dig into that quickly, um and then we'll kind of back back out but sure a lot of people we'll just go straight to the manometer side of things, because this is something that you're both very passionate about. For uh, for many of the same reasons and a few different ones, um a lot of techs will take a static pressure measurement and they will first off, they will say i'm taking an airflow measurement um. So you say: did you check airflow and they're very proud and they'll say yeah? I check static pressure so address that specifically i'll turn this over to steve.

Why is that not a correct way of thinking about that yeah? Well, it's often the best you can do if you don't have the tools but um the the problem with it is that you're, comparing the static pressure to whatever the factory determined. It was in a brand new piece of equipment. So there's all sorts of things with an older piece of equipment that don't match the factory condition and the the blower chart in the manual is, you know, factory new condition and if you get uh, you know accumulation of dirt on the squirrel cage. If you get accumulation of dirt on the evaporator coil or up here in furnace land on the secondary heat exchanger, all those things are going to completely change the relationship between pressure and flow from what it was when it left the factory.

And so while that might be a a good way to do it on a new system, if you're troubleshooting an older system, you could really get led uh down the wrong path and think, oh, the static pressure is looking great. I must have plenty of airflow when, in reality, the only reason the static pressure is low because everything's all clogged up and you don't have any air flow and that needs to be broken down a little further, because i've seen people just take the rating. The static pressure rating on the equipment and say that's the target number oh wow yeah and you you. You threw one phrase in there: the blower chart that is so important to what you were saying, because that sort of that sort of leads into the whole profiling deal with you know having the air flow table, the air flow chart to lower performance chart whatever that's Really what you were referring to, but some people make that critical error and just look at the equipment, static pressure rating, take a static pressure test and say: i'm fine, yeah yeah.

You have to have the blower chart for that model from the manufacturer, or you really don't know anything right and you have to have them. The original equipment blower the motor, oh yeah, and in the the squirrel cage or whatever fan is in there. The fan apparatus is in there because it's profiled with specific equipment and if you change that equipment, then it's no longer valid yeah yeah, and so it just in summary, so now that we kind of drill down. Let's back up again, if we're talking about system performance, um, i've heard it said abc, you know airflow before charge um and i think that's a really good way of looking at it, especially on commissioning um.

We know that there is a there's, a point at which we can get a little unrealistic in terms of like i said off the top of what a technician's going to do and they show up and it's a minor repair. It's a clogged drain or whatever. As far as the battery of tests are going to perform, but if we start with commissioning um, that's absolutely true. If you're not getting your airflow set in, then don't focus on the charge until or really any of the other operational tests other than just making sure it's not.

You know, like you know, going to rip itself apart or something because you know the fans hitting the shroud or something like that. Obviously, you want to do some just basic visual and audio visual uh inspections of it when it gets running, but but you really want to make sure that you have that correct, airflow airflow before charging. So let's focus on that and i'm actually going to pull open. Some of these um slides now in defense of um of rses.

Some of these are older and we've actually learned a lot since then, but this is what people will typically say and even in measure quick, it talks about this. You know 400 cfm per ton being typical, 450 cfm per ton being in cases where you have a lower humidity load, um and then 350 cfm per tonne being cases where you have higher humidity load. Does this stand up? So, let's, let's first address this because i think a lot of text. The question is well how much airflow should i have.

Is this the right answer: do we just take our tonnage and multiply it times these numbers and that's what we set our air flow to? Are you asking? Is this the right way, or is this better than what most people do? Well, i think i think answer both so um so yeah. So, let's start with. Let's start with is this better than what most people do and then let's go into what the right way is: yeah, most people, you know wave their hand in front of a couple of the supply registers and go. Oh airflow is good um, that's not a measurement and um, but so, if you can actually measure air flow, you know new system, blower chart or a true flow or a flow hood and actually measure the air flow uh and verify that what you've got and then Use these numbers that's way better than what most technicians do far better, but if you drill a little further and look at what's the the right way to do it, you should have you know your manual s report, which gives you the sensible and latent split, and You should be setting your airflow to match that sensible and latent split on that piece of equipment.

That's the the right way to do it, but that's maybe um a few more steps beyond where we need to start yeah exactly and speaking of where to start, you didn't been doing a lot of great tutorials whatever on basic physics, brian lately, heat transfer. So air is the heat transfer medium, it's it's the fluid that is actually transferring the heat off either the heat exchanger or the coiler, or back of a vice versa. So you have to know, and that's part of what gets into like the uh, the amount of uh temperature and humidity of the air, the density of the air, to become so important in the in the process. So it's really pretty intricate um, but i think not like you have to take that into every situation, but to know that you're working that the air is part of the the equation of how you you move.

Energy hvac is moving energy, yeah yeah and into your point um. When we talk in terms of cfm, that's cubic feet per minute, that is a volume flow measurement, and that means that when we're talking we're talking about air in terms of a heat moving fluid - and i also like that - you said fluid. This is since this is an apprenticeship class. This is important to know.

Fluid doesn't mean liquid. Both air and liquids, both uh vapor and liquid state are considered a fluid um. So, in the case of this fluid that we're dealing with its density changes based on based on a couple key factors, one of the biggest being the temperature but the other being humidity and then altitude also plays a big factor in there and even barometric pressure. So when we say you know when we assume that 400 cfm per ton in one location is going to move the same amount of heat as 400 cfm per tonne in another location, well, then everything is going to be incorrect and we know this most glaringly when You go up in the mountains, and the air is obviously much less dense and everybody knows that.

Well, you need more of it in order to do the same amount of heat, moving um and that's a key thing and when you start to look at you know more advanced calculators things like measure quick, you know they're, taking into account a lot of these more Complicated um density calculations and then also, of course, you know true flow same thing, you're, taking into you're, taking into account a lot of these more complicated things. So it's just important to know when you're talking about air air is actually a little more complicated than we give it credit for, and often that's because we, for whatever reason uh want to talk about it in terms of boxes of air cubic feet per minute. Rather than a mass flow rate, which is actually the weight or or total mass of the air, that's moving through um sorry, i i went a little. I went a little long-winded there.

I pushed to that direction. Yeah you did you did it's your fault. I blame you um, so so steve um. I wonder if you would be willing to talk a little bit about um, because we started going down the road of airflow measurement and some practical airflow measurements, but talking a little bit about the difference between a system, measurement of airflow versus a distribution uh or or Point method of airflow because i think a lot of people collapse those two concepts uh of well, i use.

How do you measure airflow? Well, i use a vein anemometer or i use a flow hood, but that's different than what we're talking about here when we're talking about providing the system, the right amount of airflow yeah, so total system airflow this is you know this slide is about the total volume Going through the cabinet, so whether it's a furnace or an air handler how many cfm are going through that cabinet and that number you can get there by adding up all the supply registers. But there's a couple problems with that number one accuracy can be an issue and number two. Any leakage that you have between the cabinet and all the supply registers uh is is going to be missed and so uh. You know, particularly.

We love to make really leaky. Duct systems in the midwest, because they're all indoors um, but you can measure you know, add up all the supplies and end up with 30, less airflow than what's actually going through the cabinet so um and they typically have two different purposes. You know your airflow before charge that airflow we're talking about total system airflow. How much is going through the cabinet versus individual registers now you're? Typically talking about balancing making sure that you're matching your room loads from your manual j calculation? So, balancing versus you know set up the you know the airflow and charge on a new system and your average ac technician is going to be much more responsible for system airflow than they are going to be the actual distribution system that registers you know what you're Putting into each room not to say that we're never responsible for that, but i do like to start here because i think a lot of techs like as we mentioned, um, even just knowing what generally is considered the appropriate airflow per ton for your market.

Is a nice place to start, you know, and a lot of people will poo-poo that and say: well that's worthless, it's not worthless. It's worth something uh, it's maybe not quite as detailed as it could be, but it is worth something um. I want to talk a little bit about this whole concept of static pressure, because it is the it is the um the entry drug. You know it's where we want people to start, if they're not doing anything on uh on the airflow side.

Right now - and you know here - we have a picture of a magna helix, which is the you know. The instrument made by dwyer that's been around for a really long time. It's the first thing i ever used for measuring static pressure, but what are some of the common um mistakes that can be made in choosing instrumentation and uh and then just talk about like um? I guess i guess what some of the challenges are in measuring static pressure. I'm gon na turn that over to bill well steve used to work for dwyer for a little bit.

Oh really yeah yeah on the smart hood, actually, no yeah um and the first magna helix steve was made out of stone. Is that correct? It was brought down with moses? No, that was it. It was the bronze age yeah, yeah yeah, so so mechanical gauges like this mechanical meters like this, they have mechanisms in them. Um mechanisms can like gear trains needle movement there they can be subject more subject to the position than say a digital.

One would be subject to position so laying it's on its back tipping it forward. Tipping it sideways can cause the reading to vary a little bit, and then you have to pay close attention that you're you're reading straight on down the needle and they make it pretty easy. You know, as a matter of fact, to to make good readings so you're reading straight on down down the needle into the indicator on the scale behind it, the electronic ones um. I think the sort of unfortunate part about electronic meters is just because they state a measurement range doesn't mean they make the measurement all that well, um, you have to be.

You have to know a little bit about the number that you're after the quality of measurement that you're after and if it seems like an amazingly inexpensive device. It's probably amazingly poor results that you're going to get from it right, yeah um. Anything to add to that steve yeah. I think the one thing that's probably way down in the weeds that most people don't understand it.

It's right there in the specifications for a lot of manometers, and that is if it says it's, one percent of full scale and the full scale is 60 inches of water, which sometimes it is well. That means that the whole thing is reading plus or minus 0.6 inches of water. So if you're trying to read a half an inch of water, static plus or minus 0.6, i mean you basically have a random number generator, and so you need to look carefully at. Is it a percent of full-scale kind of device and the scale is much higher than where you're trying to read, or is it a percent of reading device where it has more or less the same percentage all the way down? You know near near to the bottom yeah: that's that's endemic across all the pressure gauges yeah, but most of them are, or some of them will say, mv the testo ones, yeah.

We we tend to change on our side, but that means of measured value yeah. So it's actually the measurement at that point uh, but then um weird things happen with that, because then the the error bar kind of blips up when you trip over a certain point that kind of thing yeah and in case you haven't noticed um bill and steve - Are both uh like super nerds about instrumentation? So that's why we just went off into the weeds about uh, really uh detailed stuff like this, but it's great because the the point is. Is that just because a instrument gives you a number doesn't mean. That number is anywhere near correct and so choosing an instrument appropriately like, for example, with magna helic.

This is the exact tool that i would use and because the range is zero to one inch of water column, it tended to be fairly accurate. But you had to make sure that it was level. And so you had to have it on a stand and it had to be perfectly level otherwise, and then you had to make sure that you zeroed it out. You know, and then you have to make sure like, like bill mentioned, that you're looking straight on.

So there's a lot of challenges with some of these instruments and then i want to also talk about, and so we've been talking about, specifically about static pressure, which is the balloon pressure inside the doctor inside the unit that you're measuring. But here it lists velocity pressure. As something that um, i i think it's saying could be done by a magnet here like i'm, not necessarily here, but but this is what bill was alluding to with the measurement that i was doing um with the 605i wait. No, no.

That person was like ryan yeah. That person was me good, good, fake, surprise reaction, steve yeah yeah. Thank you steve. I appreciate that um humility is important and i'm learning that more and more every day, as i have uh older and older teenagers uh, so so bill talk through that, because this is a challenge if you are trying to measure something more complicated, like velocity pressure with A typical off-the-shelf, uh manometer, you run into some some issues there yeah so the the pedostatic tube and that's really the full name for it.

Um people call probiviate a lot of time and call it a pedo tube, but it's. But if you remember that pedostatic name, it's measuring two things: the total pressure, as well as the static pressure, the difference between total pressure minus static pressure is the velocity pressure that velocity pressure can then be converted into a velocity reading. If you know things or can approximate like the density of the air, mainly a lot of meters will just have that programmed into it. Some of them allow you to correct for density, but but i'll tell you about a mistake.

I made a long time ago um that i thought i could average the static pressures and then get an average velocity pressure. But you can't do that because of the relationship between there's a square in there, so that that's going to square root in there. That's going to throw you off so, but today it's it's more um. I think it's a lot easier.

You a lot of the meters have built-in averaging and the calculations built into them already, so the pedostatic tube you put it into a duct, and something else to keep in mind is that the meter only knows where this what's going on, where the sample is being Taken from and if you look at any static pressure or a pedostatic tube you'll see very tiny holes, so it's only in that region around the tip of the probe that it knows what's going on. That's why you need to take multiple measurements, because the airflow - and i think everyone knows this - the airflow going across the duct is not very uniform right in effect, near equipment, transitions and ductwork um devices that are in the duct can cause even things to happen. Like uh, reverse flow, eddy currents, negative flow and you'll see a lot of that leading people down uh, false trails and wild goose chases, and i think steve knows a lot about that in the development work for like the true flow grid, um, because that's actually a Device you stick in the duct that causes its own. That causes some turbulence is to deal with turbulence yet extract these measurements.

Like we're talking about yeah yeah, that's the the biggest problem with flow and ducts. Is there's never this wonderful long straight duct that you want. I mean at least in residential pictures yeah, it's it's in pictures, um and that's you know, there's actually, the the story that you began with of apparently was brian trying to measure air flow with a pedostatic tube. There's actually, two problems that are related are sorry.

Two problems that are unrelated one is: is your manometer good enough? That's what bill talked about first and the other one is what bill just mentioned now, which is have you taken enough points, and do you have enough straight duct to even get enough points, so both of those are going to cause big big errors with pitot tubes And i think this comes down to the just to make this practical um for your we're talking residential here. So, let's focus residential your average residential service technician needs a good quality, um manometer to do static pressure, measurements, um, there's a wide range of tools that will do a decent job. The energy conservatory makes a really good one. We're going to talk about this in a minute here, um, if, if that's what you're doing, if you're doing what we're showing here, where you're measuring static pressure on the system and that's a great place to start, you just have to know what that means.

It's not a measurement of flow, it's not a measurement of volume; it is a measurement of pressure and pressure. Only so the only way it's going to mean anything is if you know how the system is set up and you're referencing, some sort of fan chart from the equipment um, so not a terrible, not a terrible measurement to take, but not super valuable all by itself And this is how you do it. You know you have your low pressure side, connection to the return. Duct, your supply pressures or your high pressure side connects into the supply duct if it's an air handler or in between the coil and the blower or in between the coil and the furnace.

If it's a furnace system - and you get a number - and that number is your total external static - so not a bad place to start. But the misconception is that it is a airflow measurement and it is not an airflow measurement by itself. So um in terms of measuring total system air flow, the problem that will become down to is it's very hard in this slide. It talks about doing the heat rise calculation method, which i have essentially just given up on uh in in real life in the field.

It talks about you know you can do you know your your pitot tube type measurements, but most of those aren't going to be practical for a technician so really for a technician in the field. You're really left with two things: one you're going to do it. This way, you're going to take static pressure and you're going to reference a chart which only works if you've got the original blower everything's pretty much clean and set up properly or if you really want to get a good system measurement, i mean i guess i also Want to just say, if you have like a a return, that's directly underneath the unit like we have sometimes in florida or a single return. Sometimes you could do that with a flow hood, but generally, something like the true flow grid is going to be.

Your best bet um, so i want you to talk through that quickly, steve about what that is, so that people can kind of understand how that works. I'll. Just preface that with saying you, you pay either pay in time and effort and knowledge or you pay for the instrument. One one way: you're going to pay to get a high quality measurement.

If you don't pay attention, you don't rtfm yeah, you don't pay for a high quality meter. You're you're not going to get a high quality measure. Don't have an expectation that you will, because you won't i'll just yeah. That's steve, actually steve.

If you want to pull up, do you happen to have a picture of um trueflow or some of your tools on your computer that you can pull up, because i made you a co-host if you want to share yeah, let me let me go ahead and find That - and i want to talk about this quickly because one of the things that bill and steve were talking about as we have this kind of duct system up, they were talking about where you can take measurements in the duct, and this is true, less so of Static pressure, but especially when you're going to take a velocity measurement or if you're going to you know, do something like a duck traverse using the students, and i did it with a hot wire anemometer. If you imagine these bends here, you're going to get a lot of turbulence around these bends, you're also going to get a lot of turbulence around the unit, especially around the top of the unit here, and so you really want to try to take measurements in the Center of straight ducts, where there's minimal turbulence - and we all know that in real life - sometimes that's really challenging as an example in florida, a lot of times we'll have these kind of short supply plenums, and then we immediately go to flex. Where do you take a good measurement there? You know, there's not a really a great place to take it, because it's super turbulent coming out of the top turbulent means that you're, spinning and bouncing and moving and then anytime, you get near a bend or anything like that and you're not going to take these Measurements within flex, a lot of people, ask that i mean you'd, have to punch holes all through the inner liner and you'd, essentially ruin it and doing that um. So, there's just a lot of challenges to taking these full system.

Airflow measurements, your point, measurements, um yeah! You do that with a with a flow hood and that's got its own set of challenges and things to watch out for which we could which bill could talk about for three hours um. But but that's you know pretty straightforward. That's going to be the standard way of doing that for most of us, but for full equipment measurements. It gets a little more challenging.

So i'm going to turn this over to you, steve, okay, uh we're okay share screen there we go okay, so this is the uh true flow device. This is the new digital version and the only a tiny number of people ever used. The the legacy one this one's making it easier. So what this is is this grid goes into the filter slot or the filter grill, here's a kind of end on view of it.

It's made to be just about as thick and a little thinner than a one inch filter, so it goes into the slot in place of the filter and measures the airflow and within about five minutes you can do you know two to four static pressures and then Swap the filter out and the true flow in and get an accurate system airflow, regardless of the condition of the equipment. This works just as accurately with an old fossil piece of equipment or a brand new piece of equipment. It's equally accurate either way, and it will also give you some information about the static pressures, so you can actually check the manufacturer's fan chart. Oh great bill's got the the physical device right there and he's peeking through it like a convict.

For some reason. It's making you nervous just want to show everybody lightweight this relative size of it, the modularity, it's fantastic yeah and just it bluetooth to your phone along. This is the the manometer that goes with it. You you do need a manometer for it to work properly.

Um. The the manometer and the true flow are both talking to the app on your phone, at the same time to get uh the static pressure and the true flow and and the air flow at the same time, and talk a little bit about the. So this is the dg8, and i know like some people watching it's gon na be like. Is this an ad? No, this isn't like sponsored or anything.

It just happens to be that steve and bill are two of the best people to talk about this stuff, and we have this challenge of everybody saying airflow before charge. Everybody says you got ta check your airflow, but nobody tells you how to actually do it. I mean they tell you, but then they tell you ways that don't really work in the field uh and that's a significant problem for the trade so specific to the dg8 manometer um. It has some features in it that are not make it really, unlike anything else, on the market and just talk through some of that yeah.

So what this comes from is you know our main product that we've made for decades now is the minneapolis blower door and to do a blower door test if you're not familiar with that, the one thing that relates to manometers is to do a blower test. You need a really really good manometer and they cost about well upwards of fifteen hundred dollars um. But we recognize that there's a need to make just as accurate a pressure measurement. But you don't need two channels and you don't need to calculate blower door flow and stuff like that.

So we took the same technology and put it in a smaller, simpler, cheaper, manometer, that's just as accurate, so this is capable of doing things like room pressures. You know: do you have enough return flow out of the master bedroom so that when you close the door you're, not pressurizing it um? You know it's capable of measuring tiny pressures as well, as you know, all the way up to 10 inches of water, so that, and and this is what you need um to to make the the pressure correction. A lot of people will ask the question about the the true flow grid. They're asking when i put this device in the filter slot.

Well, isn't that going to restrict the flow sum if it's more restrictive than a filter or less restrictive than a filter? And the answer is yes and that's: why we're doing a correction for the difference? So you make a measurement of the static pressure with the filter in and then make the same pressure measurement with the true flow in, and we we correct it back to what it was with the filter, yeah yeah and in the in the older version of it, Which we've used for quite some time, um didn't have some of this like connected um, you know the bluetooth connection and all that which made it a little more challenging from the math standpoint, but it works really really. Well, i mean we've measured. It we've done our own testing with it measuring against a flow hood and against some of the other reliable methods, and it's very, very accurate. So the the point that i want to make here isn't that um.

It basically is that it's very difficult to measure airflow, and if you really want to be serious about it, then that really is the tool for measuring total system airflow. I mean there really just isn't another easy way that a technician is going to be able to do it um other than you know, using your your charts and measuring static pressure and if you're not comfortable with that. Well then start there for sure. You definitely want to start there but recognize that that's only going to be valuable if everything's clean and if it's all set up properly.

If you're looking at the wrong column, then you're not going to get the right number if your pins or you're set up within your infinity control or your communicating stat, whatever aren't set up properly and you're. Looking at the wrong thing, you're easily going to get the wrong information and if you take a good hard look at those tables, they tend to jump up in values of static pressure, by like hundreds of cfm, for hundredths of an inch of water, column, change and Then going back to what steve said if your accuracy is several hundredths you're dealing with this really fuzzy number you're you're somewhere on this chart in this region here but you're, it's it's a good, it's a better than the estimate of airflow per ton. But it's not quite a measurement yeah and i i just learned a little bit more today about measuring static pressure, we're doing some some testing on the system here in the office and it's actually a residential system um. But so i measured the static pressure about four inches from the evaporator coil, and then i put another probe about 18 inches farther downstream and discovered that going farther down screen the pre downstream.

The pressure is about 20 percent higher, it's called static, pressure, regain yeah and, and you know how much static pressure regained. You get downstream of an a coil, and how far do you have to be from the a coil before it? It changes yeah levels exactly and i measured several pressures all throughout our system and found out that there's more cases of static pressure regained than there are of typical pressure going down as you move down the duct and it's just because there's there's not really a place In an entire residential duct system, where you have fully developed flow, yeah yeah, which is also why, in terms of uh, commissioning a piece of equipment, you need to hit it from a couple different angles. So, in order for us to do a better job than we are doing first, we have to get better at measuring air flow. But then we have to understand are what we are measuring and you do you make um you make compromises.

I mean that's part of it, but a good technician makes compromises, knowing they're, making compromises and then kind of doubles down on their data in order to kind of help verify that they're where they should be, and that's where a tool like measure quick using a couple Different you know, bluetooth connected devices is really going to help bring that together and say like okay, maybe maybe my airflow measurement isn't as good as it could be, but by using measure quick and it's estimated airflow and looking at you know all of my other measurements And they're all in the range that i would expect, then at least we can feel pretty good about it. So i want to talk about that quickly. This concept, that a lot of technicians have and so we're going to we're going to move to the refrigerant side. Just because we have a limited time um, but it relates directly to airflow.

They get this sense that well as long as my pressures are good, then my airflow's good right. So what would you say to a technician who says? Well, i look. My pressures are good. My super heat and sub cool.

You know i learned how to do that. That's good! That means my airflow's good. Doesn't it is that for me sure either one of you? If you have thought um, i i think so that i'm getting a little out of my depth and frankly i don't understand the refrigerant side as well as as the air side, but um. If you have uh, you know, depending on the state of charge and airflow, you can get errors that compensate for each other and it looks okay, but it's not yeah for sure, and you see this yeah, you see this a lot because people try to compensate for One problem with by doing something different, specifically adjusting the charge and so you'll see this where people will overcharge the system and and it will show up in sub cooling.

So there is. There is something to this um, but you'll sometimes have like these just competing problems, and people will compensate especially you know, back in the day when we had more fixed orifice metering devices um. If you had low suction pressure, they would just keep. You know just keep adding charge, your superheat would start to dive, but but this is the this is the issue when you don't have those numbers and in terms of another thing i'll say to that is another part.

Is that you don't necessarily have the precision? So you may have a system, that's within 10 percent of where it should be, and you know that, based on looking at your uh, your refrigerant side readings. But you don't know that you're completely dialed in especially with things like a dehumidification light and removal. That sort of thing that's where it really becomes important. You may have a system that looks okay in the numbers, specifically texts love to see high suction pressure.

You know because that means that we're not close to freezing um and your compression ratios tend to be lower. So, like okay, well, that's good, but you may have a significant problem with dehumidification and isn't it true that uh this all gets harder if you're doing a hot pull down and you know indoors: 95 degrees, yeah yeah. That's actually another really good point yeah yeah, because if you have a system, if you're doing a commissioning as an example, it's going to be much more difficult to estimate your airflow when you're, not at your design conditions. So the the space is still hot, and so you know techs have a harder time kind of knowing what to expect.

If you're really experienced, you can do pretty well, but that's where doing something like true flow grid, throwing it in there and just saying okay. What is my airflow? It's completely independent of my refrigerant side. Readings, make those adjustments first and then get your charge set, that it really is the ideal way of doing that yeah any thoughts bill. No, i was just looking at the uh the chat and youtube to see if we were um what was going on there.

You know, sometimes they just talk about whatever they want. It seems like it. You know we we respect that about them. They're, just having a nice time we're having a nice time we're having a conversation they're having a conversation, it's distracted, it's it's really good, but the pyro is looking forward to upcoming propane-based refrigerants.

Yes, yes, um yeah corey, says in the uh in the zoom chat and we are very, very blessed to have cory cruz, the great corey cruz of the famous txv argument, um that he healed 2022. yeah. It was of 2018, i think um, so it just to prove that sometimes even uh knock down drag out. Arguments can end up in getting employees for kayla's, so it works out um.

It makes me happy um anyway, so just focusing on specifically performance. That's the goal of this um. I get these conversations a lot or get in these conversations a lot where people will say some version of hey. I did it this way all along and i never had a problem, so i charged by beer can cold and i never had a problem or i never measured static pressure.

Yeah never had a problem that i know of exactly and that's the point so to say you never have a problem. Does that mean it? You started it up and it didn't just implode on you. Yes, i'm sure it did not. Just you know turn into a fireball right away.

That's not what we're saying what we're saying is that you may have missed out on either performance, uh capacity, efficiency, longevity or uh service of serviceability breakdown. You know issues with servicing. Those are all things that, if you're not careful on the front, that system may be operating two percent less efficient than it could be, but over the life of that unit, you're not giving the customer the value that they paid for and airflow is just undisputedly. The the area that we screw up the most yeah you you up, sold them to the 20-seer unit and uh.

They ended up with 16. You know yeah um and there's well, i think what does it say? Okay, one thing i wanted to reference quickly because i've got a couple: refrigeration guys. A couple of our grocery guys are here in the in the zoom chat. One thing that we learned um even on the grocery store refrigeration side.

Is that sometimes doing a comparative airflow measurement? Is enough, so there's a very there's, a big difference, uh in a device that needs to get the number exactly right and a device that you're using and just kind of comparing it to itself. So, for example, they'll use, vein, anemometers, relatively inexpensive ones and they'll go down a case line up and they'll compare case to case, because they should all be the same right. So now it becomes a game. More of one of these things is not like the other than it is about really caring, so much about what that velocity measurement is it doesn't matter as much you're not trying to calculate.

Can i jump in real, quick yeah? Go ahead. Chad um with uh with in refrigeration like supermarket cases, uh the airflow actually uh, is a very big important thing, because if you don't have your proper airflow, especially open cases, you will lose your air curtain and it's not going to be circulating through that case. So really, just looking at the manual it'll tell you exactly, your cfm should be out of your events and that's what we go by, what not to correct you um, but you have to be careful with the cfm measurement, because um cfm requires that you do a Traverse um velocity is really what you're measuring so when you're, when you're taking one well, you have the feet per minute: yeah! Okay! So that's what you meant to say right! Yes, talking about velocity and that's actually a really nice point to make. I think steve - and i talked about this before - is that when you start um doing comparative measurements, you could even take something like a you know, a decent vein anemometer go around a house and compare the velocities from different um supply registers.

If you have that, if the design is so that they should be fairly consistent, velocities and that's an assumption you shouldn't make, but you know when you're doing a comparative analysis, you can start to kind of pick up trends and things that are different than others and And you can start to make some distinctions there, so i'm not saying that you always have to have the the point of this. Is i'm not saying you always have to have the world's most expensive tools, but when you're trying to hit something like an airflow number for a piece of equipment, that's very different than doing something like going down a case, lineup and measuring your velocity and comparing it To a chart or comparing it to different cases, both of those are valid. You can even do sort of some um rudimentary balancing with just a vane, anemometer yeah, so in a residential situation as long as all the supply grills are the same and you're. Using your vein, anemometer in exactly the same place, you can find out at least relative to each other.

How much careful there is now you're not going to be able to say i need 123 in this room and i've got 123.. You can't get there with the band anemometer, but at least you can find out. Okay. These two bedrooms are the same.

They have the same number windows, the same number, exterior walls and this one has twice as much flow. Okay, that's uh! That's not gon na work! Yeah, exactly and and this is where um you know - the tools that are in a technician's toolbox uh run the gamut, which is why, and this i wanted to specifically focus on equipment performance during commissioning, because that's one time, you're not doing a comparative check here. You're, trying to objectively hit some numbers that are going to produce the eer seer ratings capacity ratings that you sold the customer now, because i'm assuming that most people out there, even if they're doing a like for like installation, they need to hit the numbers that that System was designed for, if that piece of equipment's going to perform the way that you know the customer's going to be happy with, and you know we're - certainly not perfect, either at this um, but really taking a good stab at commissioning uh. When you first start, the equipment is a huge part of it.

So, starting with using the best tools you can, you can get your hands on to make sure that you got your airflow right and then move into your standard measurements and those are going to be. You know sub cooling, superheat suction saturation, what we call evaporator um temperature. That's the way. I i want us to think about that.

Don't don't say suction pressure, because that pressure doesn't matter. It's the it's the evaporator temperature and then your condensing temperature. Compare those to your indoor, wet, bulb, dry, bulb and outdoor dry bulb. Take those all and put them into a into a bucket and you're going to come out with a pretty good sense of how your equipment is performing.

But if you start with your airflow not being right, and then you start trying to make tweaks and adjustments to get around that you're gon na you're, gon na have heartache and at the end, you're gon na have a lot of performance problems and you're gon na End up making other issues like in the grocery space, the example would be uh, they call them, they call them valve tweakers. You know people who go and adjust expansion valves rather than getting the air rather than checking the obvious, and the obvious in many cases is an airflow problem and it's the exact same thing. You start making other adjustments rather than getting that airflow where it's supposed to be cool, so um. I wanted to move over to you again steve um, to talk a little bit more about uh the solution that you've created we're going to do a podcast about this um a little bit further, but talking a little bit specifically about kind of the evolution of true Flow and how you see this being applied differently than these sort of instruments have been applied in the past, because it used to sort of be like all right test and balance organizations building performance organizations.

But now we really want to get better air flow instrumentation into the hands of techs yeah, so the evolution of this product came about, of course, from the original true flow, and you know the geeky people like brian and bill have known about the true flow for Many years and have uh, you know preached it as a good. You know the accurate way to really know how much airflow is going through the system, but, as we set out to come, make the next generation of the product. I realized that there was really a second problem, besides just making it easier to make the measurement, and that is that, if you're, not a super geek like bill or brian, you don't really know. Okay, so i've got 273 cubic feet or cfm per ton.

Is that okay, and so what i realized is we need an app to interpret the results for technicians to help them understand what they're getting because there's just you know, technicians have to know so much these days. Let's make it easier. Let's make it. You know like uh, you know the navigation on your phone as opposed to the map book uh, where it's gon na give you the guidance you need and not only say what is the airflow but tell you.

Okay. Is that in a good range and then, if it's too low, let's look at the static pressures and see if we can pinpoint what's making it low? Is it because you've got a filter, that's way too small for that four ton system? Is it because your uh return is way too small? Is it because you're you've got you know, somebody went up in the attic and knelt on a supply duct, and so you got a big restriction in the in the supply and we can help pinpoint that by measuring the the pressures in the system and help identify Where the problem is once we um, we go uh through the analysis and i have to give a shout out to ed jonah because we're good at measuring airflow here at the energy conservatory and pressure. But as far as coming up with all these uh, this detailed information about how much static pressure drop across a filter is too much and what should be the maximum supply static pressure? I mean that all came from ed that you know we didn't have that expertise, and so we went looking for it and found it in head. So thanks ed yeah, i was going to say that it's not measurement for measurement sake.

It's measuring for a solution yeah which, which is what everybody's you know, we're talking to that's what your job is. You got to provide solutions. You got to fix things yeah and in terms of peak performance, like that's what we're trying to achieve here, we're trying to give the customer peak performance out of this piece of equipment, and so sometimes when a system is 12 years old and it's a little dirty And it's whatever you know like okay at that point, maybe you're not so worried about um peak performance and measuring all of this most detailed stuff. Maybe at that point it's about cleaning the blower wheel.

You know like, and so that's still valuable, but but when we're especially when we're delivering a new piece of equipment to a customer, i really think we would do well to think more about um airflow and really dig into it. Um and a lot of that comes down to just as simple as you know, like steve, is saying independently. Looking at your return in your supply is one or the other the problem, rather than always saying well, i hit my you know. I hit a total external static target or my total external static is a little high.

What specifically is causing this problem, you know, do you have low air flow and your static's not high at all? Okay? Well, then, that means that your unit's not set up to produce the amount of airflow and only a tool like truflow, is really going to tell you that um one of the questions that was in the chat that i wanted to ask you steve um. Let's see here, who was it who asked um gt350r asked uh? Do you have does truflow allow for different filter sizes? So talk about that, specifically with the new model, how that works yeah? So it and we've got seven of the most common adapter sizes that you can uh get so yeah build. Please uh pop that out, so the the plate fits into the adapter there's the uh the plate. That makes the measurement that's a bluetooth, uh that the bluetooth is in there and now hold up the adapter, so that adapter can you get in on the size? Okay.

So that's a 20 by 20 adapter that it snaps into and there's seven sizes uh. You can pick and choose your adapters or you can just say i want all of them and in addition to the seven common sizes there's another one which you can, which is kind of like the maximum size and you can cut it down to fit whatever oddball Size, you know, get those weird carrier, half sizes, um and so the the cut to fit adapter is intended. So the technician on site can cut it down, apply the gaskets and then use that and then you know for from then on. You have an 18 and a half by 23 or whatever the the weird size is yeah, definitely and uh and in terms of like investment.

I want to make it clear like this is an investment that you're going to have to set up, and so what? I would suggest doing you know if you're looking at this, like, i don't know how i'm going to outfit. My entire organization pick some of your best installers, who are going to be doing a lot of higher end equipment. That's where you start, and then you know then get it to where all of your install crews have it and then get to where your senior tanks happen. In addition, and then move on, i mean that's: that's the journey that i'm on right now, so yeah um.

So i don't think anybody, i don't think anybody is expecting that it's you know you're gon na go and buy um 30 sets of these, although i don't think steve or bill would mind too much if you did we'll be okay, but let me let me point Out, there's one you didn't mention, and that is something that's really come out since we started sending prototypes out to people to test this there's another application. We really hadn't even thought about and that's putting it in the hands of sales people um, because if you can get the you know a filter size and send one out with the sales person really. This is literally a five minute test and after that they do that test. They can easily figure out.

Okay, the static pressure is way high off the charts, but if we replace the three ton with a two ton, which is correctly sized not oversized, are we going to be okay with the duct system as it is, or is it still too restrictive and if you Know the static pressure and the supply static pressure and the return and the airflow you can figure that out relatively easily yeah. That's a really good point. I mean getting sales people to use tools that might require a little extra work, but but no, it actually is a really good point in terms of like preventing problems. This is where i think, a lot of sales people would be like well hey.

How does that help me sell a unit, might not help you sell a unit, but it's going to help you from having to go back 400 times to try to fix a faulty duck system or an improperly sized system. What we're hearing from people from customers that test this out i'll give joel becker a shout out. He said he wants to put one in the hands of all the sales people, because he thinks it will help help him sell more units because it will distinguish him from the other companies that had no idea if, when they put that new system in it's going To work just as bad as the old one or whether they actually actually can solve problems, yeah and so uh. You know you heard alex meany talk about um load, calc, theater uh.

This wouldn't be theater but uh. You know airflow measurements as a selling tool. Yeah and it's not just the measurements, it's sort of like any kind of measurement. You need to have an interpretation of the measurement yep uh, so the digital true flow is like reading someone's palm and then the uh.

11 thoughts on “System performance checks”
  1. Avataaar/Circle Created with python_avatars Eddie Gomez says:

    What do you guys mean by the word "cabinet"?

  2. Avataaar/Circle Created with python_avatars David Walz says:

    Can you discuss how this truflow can be used in a package system with multiple filters? Service area Nepean??

  3. Avataaar/Circle Created with python_avatars RJ_Make says:

    You guys mentioned putting the TruFlow in the hands of salesman…. What is the validity of the measurement of what is in most cases dirty equipment? Does the salesman determine the cause of low total system CFM?

  4. Avataaar/Circle Created with python_avatars Nathan Hurst says:

    I really like the things you put on here. It’s all good and enjoyable. Learn a little something every time.

  5. Avataaar/Circle Created with python_avatars Kay Zin says:

    Thank u so much fo4 your sharing. Always a mere fan of u guys.🙏

  6. Avataaar/Circle Created with python_avatars Eassyheat/ Cooling says:


  7. Avataaar/Circle Created with python_avatars Tayler Ellis says:

    I dont get the truflow grid. If you remove the filter to put the grid in the airflow does not include the filter correct? Then you make all your adjustments get the cfm where you want it then take the grid out and install the worst 1" filter with .6 static pdressure drop and say all is good. ?? From what I experience every day taking static pressure drops is a 1" filter no matter how good never cuts it. I only install a 2" or better filter on any of my installs. Though I must admit the existing ductwork out here is usually terrible. Rerurns are always 20% smaller than the supplies in my area. Ugg.

  8. Avataaar/Circle Created with python_avatars Carlos Martinez says:

    I've been out the trade for awhile, back in now and I ran across a little trouble condener starting and stopping I think it probably has to do with, oh !!! By the way it was 102 out here!!!! but unit starting and stopping I believe it has to do with high liquid pressure switch, may be dirty piston at the e-vap maybe to much refrigeration or not enough 🤔 it's a guardian 5 ton the liquid line towards the stated to freeze it's a fairly new condition I didn't have the hardware with so I was unable to repair I am going back out there (stuck) Please Advise

  9. Avataaar/Circle Created with python_avatars AD Electronic Teardowns says:


  10. Avataaar/Circle Created with python_avatars Christopher Borner says:

    The infinity control will tell you static and cfm. Will those measurements be wrong if you have dirty coi look s or blower wheel?

  11. Avataaar/Circle Created with python_avatars j smitty says:

    Gutridge in ohio in the building

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