Yes, this is a quick episode of the HVAC school podcast. We call them our short short episodes and, as always, this this podcast. This episode of this podcast is made possible because of our generous partners, carrier, Mitsubishi, comfort and rector seal, and they all three of them make great products. Retro seal is a company that you may not know by the name director seal, but you certainly know a lot of their their products.

I've talked about the safety switch aqua guard. True blue thread sealant the prophit flaring kit that I've talked about a lot they. It goes onto the end of a drill that you can use to flare and also they have a swedging kit. They have a lot of different products and you can find out more about rector seal by going to rector seal comm.

But today we're going to talk about one of the most over looked over under considered and overlooked things that every technician should be looking at when they're doing a commissioning on a system as well as a repair on a system, especially a repair. That includes the air side of the system, and that is looking up. The fan charts the factory, expanded performance data on an air handler fan coil furnace, whatever whatever you happen to have there. So let's say you: you've got a piece of equipment.

It's a gas furnace. It's got a PSC motor, so just a typical multi-speed motor there's, still some furnaces coming off the production floor of many manufacturers that have multi speed motors and you just leave it set on the factory setting or a lot of you do. I know because I've worked on a lot of these systems and they're just set up the way they came from the factory or some of you set. You know you set your fan, speed, uncool to one tap and you set your heat to another because that's what you've been told to do, but the question remains: how do you know how to set up the fan speeds? How do you know how to set up a particular air handler for a particular application, and the answer is that you don't unless you look at the fan charts, and so let's talk about this quick quickly.

The first thing is, you have to know what the design is of the equipment. Are you designing the equipment to remove maximum sensible, which means maximum capacity generally maximum capability for dropping the thermostat on the wall? So when you have a system, that's removing more sensible heat. That means that were talking about in cooling mode here. That means that it's going to drop the thermostat quickly, it's going to have high capacity you'll.

In those cases you want higher air flow levels, and so typical nominal conditions we talked about in terms of CFM per ton, will say, you know: 400 CFM per ton is the nominal setting that you want to set up, and so, if you pull out your manufacturers, Expanded performance data and you look across you - can see how much air flow you're putting out based on how many b2 BTUs you're putting out. But what you'll find very quickly is that equipment doesn't always put out what we think it should. So, just because something says 36,000 BTUs, it doesn't mean that it's gon na put out three tons of capacity and certainly not three tons of sensible capacity, because a portion of that is sensible and a portion of that is latent. Latent means the amount of heat energy that goes towards taking that vapor of water in the air and turning it into liquid water on the coil and then letting it in the drain pan that runs outside.

So when you take heat energy and you put it towards the latent side, that's for removal of moisture when you have higher air flow per BTU that equals more sensible and when you have lower airflow per BTU that equals more latent. But it also depends on the conditions, because if the conditions inside the space don't have much latent well, then there's not gon na be much Leighton removal, there's not gon na be much latent capacity, regardless of the fan, speed and so you're gon na be running a Colder coil, but that doesn't necessarily impact latent if you don't have a lot of moisture in the air. So, if you're running in what rubber meets the road, if you're running in a place like Colorado, where it's very dry and very high and altitude, the air has less density to begin with, then you generally run higher air speeds in order to get the same amount Of pounds of air over that coil and you don't care about dehumidification. In fact, you don't want to be humidify, so you run higher higher fan speeds and higher CFM per ton or a better way to say it is higher CFM per BTU.

The the the CFM per BTU ratio is is higher a more accurate way of thinking about it, rather than saying CFM per ton would be to say CFM or how many BTUs are there per CFM, and so I mean general that would be 1 CFM per 30 Btus would be 400 CFM per ton, that's another way of looking at it, and so, when you change that ratio, when you have fewer BTUs per CFM, that's an indication that you have higher airflow, because you have fewer of the heat units to every CFM of air. That's another way of thinking about it, but, however, you want to come to the conclusion in general, we're saying 400 CFM per ton is the nominal, but you can definitely go higher than that if you want to remove more sensible, less latent lower than that, if you Want more light and less sensible if you really want to know what it should be set to whenever the design was done for this particular system, they showed it on a manual J which that manual J will show you how much latent and sensible capacity you have During different seasons generally peak, but you can also look at it and during different times a day, different seasons and you can calculate how many BTUs you need both sensible and latent on the cooling side, and so that can help you set up. If you see all right, we have greater sensible further than latent. Then you have higher air flow rate or late latent and sensible.

Then you have lower air flow and generally you're setting it up. For you know, a design day is what they call it, but when you have a system that has some controls in it, where it can change the air flow based on high humidity events or low humidity events, it can adjust the air flow. Then you also can have some control over that, but in general you need to at least be able to look at that fan, chart and say all right. What what tap am I supposed to put this to in cooling in order to produce the correct amount of CFM, for the amount of capacity that I have here, and the truth is? Is that it generally even Ana nominal situation, where you you have normal conditions, often needs to be less than 400 CFM per ton, because generally just because you have a three-ton unit, doesn't mean you have 36 thousand BTUs, you could have 34,000 BTUs, and so that means You need to reduce accordingly, your CFM in order to even keep that ratio that ratio, like I mentioned - you know 30 BTUs per CFM.

So how do you set up your Howdy's in a few taps? This is we're still there. If you have a PSC motor, you have to look at how much air flow do I need in heating and that's based on your temperature rise. So you have to calculate you have to look at that, and you know in general you just you just set it up the way that the furnace come and you'd measure your temperature rise and you'd see. Am i in.

Am I in the middle of that zone, which is generally about where you want to be, you don't want to be too far high in the zone or too far low in the zone too far low in the zones gon na equal, poor comfort too far high? In the zone of your temperature rise in your furnace could equal possibly going out on overload if you got a dirty filter, so you got to set your heating air flow and then you get a turn around. You get a such a cooling airflow, and your cooling air flow is based on what I just talked about setting it up for designed a latent, sensible capacity, making sure you kind of get that balance, and all of that information is going to be available from the Manufacturer of that piece of equipment, you're gon na be able to find all of it. You're gon na be able to find, but with the laitanan sensible, is based on the outdoor conditions. You can match those after conditions to the design day, conditions that you have and your Manuel J and you can come up with a very good match and a lot of people would say well, this needs to be done in you know by the designer, but the Fact is: is that it's the service technician or the Installer, who does the commissioning on the piece of equipment and ensures that it's set up properly? The big question becomes: how do you set the airflow? So how do you know how much air flow you're producing? Well, that's where you look at those fan tables from that equipment and you measure your static pressure, your total external static across that piece of equipment, so the static pressure of the return side coming into the appliance, whatever came in the box.

So if that's the gas furnace, it's gon na, be above the filter generally and below the furnace, and then you have the supply static pressure which is going to be in between the furnace and the case coil. If it's a fan, coil, what comes in the box is a coil blower, in some cases, even an air filter. But then you have to do calculations to figure out. We know additional resistance added by heat, strips added by a filter, that's different than the factory filter or whatever the case may be and and manufactures are gon na give you all this.

If you read there, if you read their specifications, you read the total external static and then you can set the fan speed accordingly. Now some people don't like this model because for for good reasons, although I think this model is very good for commissioning and I'm doing testing on this model, it's still not a you're, still trusting what the manufacturers saying and so some people would say you need to Measure it by doing a duct Traverse or using something like a true flow grid, or some people use an airflow hood and there's other ways. There's other ways you can do it. Some people use the temperature ride, met temperature rise method, but it still comes down to you still need to at the manufacturers information.

That's the point of this episode here. This quick episode is that you've got to look at that manufacturer's information at minimum on the blower charts in order to know how you should set it up. This is all in the commissioning side. If you come to a system that has a non factory blower motor in it well now all bets are off.

I mean the non factory blower motors they're setup generally, based on the horsepower and the different ranges that they're all pretty typical, but it's not necessarily going to be exactly the same. Obviously, if you have some some gunk buildup in your blower wheel, you got to get that off. Otherwise, your measurements aren't going to be correct. At that point, you pretty much are stuck with doing a true measurement of some sort using a true flow grid.

Doing a duct Traverse, maybe using the temperature ride, memrise method, although that method is also subject to some quite a bit of inaccuracies, we're going to cover that on another podcast. How to actually do the sensible heat equation in order to calculate air flow based on temperature rise, but ultimately you still have to be responsible for setting it up so that way it produces the correct amount of air flow and both Heating and Cooling main point being You can't set something up for heating and assume that it's right for cooling, you can't set something up for cooling and assume that it's right for heating, especially when you have a gas appliance, because in that and that circumstance you have two totally different sources of heating And cooling, and when you have two totally different sources of heating and cooling, you've got a gas furnace that could be. Seventy thousand BTUs and you've got a an air conditioner that could be thirty, six thousand BTUs and they have different criteria for how much temperature rise is desirable. You can't assume that one is going to be correct with the other, especially in circumstances where you have a vastly oversized furnace, so where the furnace is much larger than the air conditioner.

That can cause some real challenges and, in some cases it's very difficult to get the airflow perfectly correct, but as a service technician in the field, you've got to be able to reference back to that manufacturer's. Information and you've got to know some ways of measuring air flow. If you don't have the manufacturer's information or if you have a non-standard blower device. So so, if you let's say you you're going to a system and you're replacing a x13 motor or a factory motor with a new evergreen motor or in towed line, makes one called the Flex motor.

That motor is a constant torque motor, but it isn't calibrated for air flow. So, for example, you look at the specs on that motor. It's going to tell you, you know: here's the horsepower, the different speeds, but how much airflow those speeds produce they're gon na be constant. You know relatively constant up to about point nine inches of static, they're gon na be relatively constant, but you don't.

You still don't know what it's gon na produce unless you measure that airflow, so you've got to have a way of measuring that airflow, of which there are many different ways. You can do it, but you've got to know the ways that exist in order to set it up properly. Otherwise, you really are totally guessing. If you take a flex or a Evergreen motor and you're, replacing an X 13 or a factoring motor, you really have no way of knowing what that is.

Unless it's the type of motor that you can set up to to match a factory motor in some sort of program it you know there are some options for programming, a motor module or aftermarket motor to original manufacturer specifications. But unless you know how to a read, the manufacturers charts be measure airflow you're not going to be able to set things up properly. If you're setting up commissioning a new piece of equipment, then you don't necessarily need to measure that now I know this is heresy. To some of you, but we're baby steps right, measuring the airflow isn't as important so long as the manufacturers.

Charts are correct because you've got a new piece of equipment. It's clean it's out of the box, you can measure the total external static and you can much have a much more accurate measurement, but later on once that thing gets dirty and maybe somebody is messed with it made some changes to it. Maybe it doesn't have a factory motor at that point, being able to measure that airflow in the field becomes absolutely pertinent. So you have to have some way of accomplishing that of of which there are many and Bill spoon, and I talked about that in the in the last podcast, but being able to read fan charts, looking up fan, charts regularly.

That should be a regular thing. If you go a week and you're not looking up manufacturer specs on at least you know, ten systems you're - probably not doing your job right. Frankly - and I know a lot of you aren't doing that, which is why I'm encouraging you here, it's sort of like you know, early on when people started talking about removing cores and using big hoses and evacuation people like, I don't need to do that, but what I'm telling you in testing equipment and in commissioning equipment, referencing the the the charts knowing how to use a manometer and check static pressure are the basics. I mean that's just the bare basics when it comes to measuring air flow and then from there you learn the additional skills of you know, doing a duct Traverse doing the temperature rise calculation measuring a static pressure drop across an evaporator coil, because in some cases you're Almost going to be using a couple, different measurements and averaging them in order to come up with the truth, because measuring air flow is very hard like we're going to talk about more and more as we move forward in the podcast.

Hopefully that helps - and I hope you have a great day, working out there in the in the field, and we will talk to you next time on the HVAC school podcast.