Proper Zoning System Design

Here's what you need to know to design an HVAC zoning system that keeps your clients comfortable. Our 5 rules of zoning make it easy to get started, then we'll go into load calculations, duct design, air pressure, filters, bypass, and why duct sealant is your friend.

Transcript:

Welcome to Arzel Zoning’s zoning system design. So things to look for when we’re talking to our customers about zoning. Things to consider when it comes to the equipment design application. When we start looking at proper zoning design, one of the first things to consider is the rules of zoning. So what do we really have to consider when we’re looking at putting a zoning system into our customer’s home?

And the first rule of zoning is to get the homeowner’s input. It’s their home. They’re the ones living there. They know where their hot and cold spots are. They know where their comfort problems are. We have to get their input so we can satisfy those comfort problems. We can take care of the trouble that they’re having with their home.

And to do that, we have to know where that problem is so we get their input. That’s the very first rule of zoning. After we get the customer’s input, we have to do our load calculations. The load calculations are going to give us the information that we need to determine if we have enough equipment capacity, or if we have enough ductwork servicing that area.

Zoning can take bad ductwork and make it worse. It can take marginal ductwork and make it good. It can take good ductwork and make it fantastic. But we have to know, is there sufficient enough ductwork to handle the load conditions in this area? And one of the reasons that we say this is because if you don’t have enough ductwork, maybe they got a lofted upstairs area.

If there’s not enough ductwork servicing that area, zoning is not going to take care of the load for that area. Case in point: in Northeast Ohio, we have homes that have an attic space that got turned into living space, and maybe there was one, maybe two, six-inch runs running up to that attic space. And that attic space is generally 600 to 800ft².

The heat gain / heat loss in that area is significantly more than what you’re going to be able to take care of with two six-inch runs. So a load calculation in that area would prove to us that we have insufficient ductwork, and that zoning is not going to fix that unless we can get additional ductwork to that area first.

But place the thermostats within the zones. So the thermostat that’s in the hallway: wireless technology has come far enough, there’s no reason that those thermostats can’t be put in the zones of control. So we can take that thermostat out of the hallway and put it in the bedrooms, and then we can put a thermostat in a great room. We can put a thermostat where the people are going to spend their time.

It’s their home. Give them the control where they need it at, in the rooms that they’re going to be spending their time in. Every master bedroom deserves a thermostat. People that sleep in this room are the people who are paying for the zoning system. And with as much time as we spend sleeping in our lives, studies show that we sleep more comfortably between 65 and 68 degrees.

But in the summer months, we don’t need to keep the entire home at 65 to 68 degrees. We can just keep the bedroom at that temperature, sleep comfortably, while allowing the rest of the home to maintain at maybe something closer to 73, 74 degrees or something like that. And that’s going to save us energy, because we’re no longer trying to condition the entire home to a temperature that we can sleep at comfortably, where we’re spending eight hours out of our night.

We’re only conditioning the area that we need to at that period of time. So zoning can save energy. Every master bedroom deserves a thermostat because that’s where the people who are paying for the system are going to sleep. And then small zones can be trouble. We don’t want to go too small in our zones if we have a single stage motor, PSC motor, we don’t want to go less than 35% ductwork to equipment capacity.

If we have a two-stage variable-speed motor or a two-stage ECM motor, we don’t want to go less than 25% ductwork to equipment capacity, if we use the zone weighting feature built into the HeatPumPro.

Micro-zoning is bad. For that customer that wants to have a thermostat in every single room of their home, they’re going to be uncomfortable with their zoning system when all is said and done. They’re going to have to have a large bypass. Their equipment is going to short cycle, and it’s going to make for discomfort in those areas long term. So with a

We need to group the home similarly, and try to maintain a minimum zone size whenever possible. But to that we also don’t want to oversize our zones and we’ll talk about that later. Options that Arzel has when it comes to small zones is wild runs. A wild run is a run that blows continuously. It blows free no matter what zone is calling.

And a great location for a wild run is going to be like a mudroom or an entryway somewhere that people are moving in and out of the home. They’re constantly coming in and out, and as they come in and out of the home, they’re letting that hot, humid air in. They’re letting that cold, dry air in. It’s constantly changing the temperature conditions in that entry way.

And the homeowner is going to need constant conditioning. So that’s a great application for a wild run. Alternatively, if it’s a small zone that doesn’t need equipment control, because maybe it’s going to be an issue of over conditioning, not under conditioning, the AloneZone is a perfect solution for that application as well. The AloneZone relies on your leaving air temperature.

And if your leaving air temperature is greater than 90 degrees, on a call for heat, the thermostat and the panel will allow that damper to open, serve that heating call, thermostat satisfies, it shuts off. On the cooling side, if your leaving air temperature is less than 60 degrees, a call for cooling from the thermostat will allow the damper to open.

The thermostat satisfies and the damper shuts down. Stops over conditioning. So if you have a really small zone and you don’t want it to control the equipment, but you do want it to have its own thermostat control, the Arzel AloneZone is perfect for that application. And then the last option we should really look at, and it’s an option as long as it’s designed properly, is a bypass duct.

So we have a duct going from our supply to our return, bleeding that pressure off and allowing us to control the static in our system more effectively. But that really should be the last option that we look at. Because when we do bypass, there are some negatives to it that we need to take into consideration. So we have to be careful when we’re bypassing air.

It has to be designed appropriately. And we will talk about that later. But the Arzel HeatPumPro is designed specifically to work with two-stage blowers. It has two sets of Y contacts so we can control our condensing unit based on our leaving air temperature. But we control our furnace, our air handler, based on the size of our zones.

And if our zone weight threshold isn’t met, we keep the equipment running at the first stage capacities, W1 or Y1. So this allows us to better match the airflow to the available ductwork, which is why with a two-stage blower, we can take that safely down to about 25% ductwork to equipment capacity without having to start looking at wild runs and bypass.

So with a two stage blower utilizing the zone weight built into the Arzel HeatPumPro, we can match the airflow to the available ductwork a little more

We match the W1 call, we match the Y1 call, or with the W2 and the Y2, we match that to the available ductwork. So if my zone weight isn’t met, I disable my W2, Y2.

If my zone weight is met, I allow for W2 Y2. But the HeatPumPro also has those temperature protections built into it. So if we start to run our equipment too hot, or we start to get cold enough to where it might freeze our coil, it does stage back to condenser or it does stage back the furnace on heating calls.

Zone Weighting. The Zone Weighting allows for a true customization when it comes to controlling that W2 Y2 output. And with the HeatPumPro, I can set custom zones. So if I have a large zone, I have a medium size zone, I have two small zones, four zone panel. That large zone is capable of running W2, Y2 independently.

That medium size zone, in this case Zone 2, would disable my W2 Y2 contacts to the furnace air handler until at least two zones are calling. But then I have two small zones: Zone 3 and Zone 4. Those would disable my W2, Y2 contact until at least three zones were calling, or a combination of a small zone and a medium zone were calling.

I like to use whole numbers when I look at my Zone Weighting. I leave my air handler stage threshold at 50% and I set my large zone weight to 50%. I can use W2, Y2. I set my medium zone weight to 40%. 40 is less than 50. It needs a little more capacity and then it can run W2, Y2.

And then I set Zone 3 and Zone 4 at 20% because they’re my small zones. 20 and 20 is 40. W2, Y2 is disabled until I have additional capacity. So that allows me to have a real customization with my panel rather than just a minimum calling zone to where I have to have X amount of zones calling. Each of my zones is unique, and the panel will respond based on the uniqueness of each of those zones, or the combination of those zones.

With the HeatPumPro, we also control staging based on leaving air temperature. If we have a heat pump system that gives us four stages of heat, and if we don’t meet our heat stage threshold, we’ll step up through our equipment stages every three minutes of sample time. So we run for three minutes at a Y1 operation on a heat pump.

And then if we don’t meet our heat stage threshold, we’ll go to Y2. If we still don’t meet our heat stage threshold, we’ll go to W1. And then if we still don’t meet our heat stage threshold further, we’ll go to W2. On the cooling side of things, there’s only two stages. So if we don’t meet our cool stage threshold, we’ll step up our compressor a stage.

And what this does is it still allows us to match our W2 Y2 output to the size of our zone, but when we hit those extreme temperature conditions where we could use more capacity from the outdoor unit, but we’d still be fine to run that lower stage airflow, we can do that with the HeatPumPro with the heat stage, cool stage threshold.

And then there’s limit settings built into it as well. So if our furnace gets too hot, if our air conditioner gets too cold, those limit settings will stage us back. So the Heat Pump LAT High Limit, that’s a heating limit for the heat pump. Auxiliary LAT High Limit is a heating limit for the electric backup, or a heating limit for the gas furnace.

The Cooling LAT Low Limit is a freeze protection for our coil. If our leaving air temperature drops below the Cooling LAT Low Limit, the compressor will stage back. If we continue to stay below it for an additional three minutes of time, the compressor will stage off.

Common mistakes with zoning. People don’t do load calculations. Load calculations are important. We need to know if the equipment is sized appropriately. But they’re also going to tell us the amount of BTUs that are necessary to satisfy the zone that we’re trying to create.

And if there’s not enough ductwork capacity, then we need to do something to increase that capacity. So our ductwork should be designed to be really close to the requirements based on normal conditions without zoning. And then zoning will further optimize that to provide increased performance and comfort for our customers. Now, we’re not an efficiency change in all reality, zoning actually reduces the efficiency by a couple of percentage.

However, even though the efficiency goes down, the performance goes up. And the difference in comfort that our customers will notice, that performance change, they don’t notice the change in efficiency. But on top of that, when they’re using stat setback thermostats and they’re only conditioning the parts of the home that they need to at the times that they need to condition those, that oftentimes reduces the energy consumption of the system as a whole.

So even though there is a slight decrease in efficiency for the overall performance, when customers use the stat setbacks appropriately, it results in reduced energy consumption. So lower energy bills for the customer when they use stat setbacks appropriately, but also increased performance and better comfort for our customers. So the load calculations are going to help us determine: do we have enough ductwork?

And if that ductwork is incorrect, we need to make some improvements to it. If it’s marginal, the zoning would probably be fine, but if it’s already poor ductwork…I mentioned earlier how in Northeast Ohio something I’m familiar with are these bungalow style homes where they have a lofted upstairs. It’s closed off, but it’s a lofted upstairs that was attic storage space, but it was never really part of the home as far as the condition area goes.

And they’ve got 1 or 2 six-inch runs trying to feed a 600 to 800 square foot area. Those two six inch runs are not going to be sufficient to satisfy the conditioning requirements for that area. So that would be improper ductwork. Zoning will not fix that problem.

So ductwork needs to be fixed in those applications. Micro zones. The customer wants a thermostat in every single room of their home. That is a really bad idea, with a forced-air system that’s meant to condition the entire home. While we can optimize the system by giving them control, moving those BTUs around the home as the load shifts throughout the day based on the sun moving around the home.

Or maybe there’s a really cold wind coming from the north. That’s going to change the thermal dynamics or the load conditions on the inside of the home. And when we do that, zoning helps to optimize the BTU delivery so we can handle the part of the home that’s seeing the most extreme temperature loss or the most extreme temperature gain from the sun baking it.

So micro zoning is bad. We want to group the home into similar zones of control, but we do not want to micro zone. And then when we have a small zone and we can’t get away from bypass duct, people oftentimes oversize that bypass duct. Or maybe they decide not to put it in at all when really they needed something.

So too little or too much on the bypass area is a common zoning mistake. When we look at the importance of load calculations, the load calculations tell us if the equipment too small, tells us if the equipment’s too big, and it further tells us if the equipment is just right. So when we’re doing our load calculations, we want to see: is the existing system sufficient to handle the conditions in the home?

So back in like the 1940s and and even up through probably the 1960s, furnaces were the size of small cars in basements. I’ve had to take several of those out. We like to call them Mini Coopers, because when we get down there, they’re about the size of one of those Mini Coopers, and you have to dismantle them.

Those furnaces were like 140,000 BTUs, 200,000 BTUs, and they were only about 60% efficient. But we’re ripping those out of homes, and we’re putting in high efficiency equipment. Up is up as much as 98% efficient with some of the the high-end furnaces. And when we do that, the size of the equipment changes significantly.

We’re not going to install 120,000 BTU, 98% furnace in place of a 120,000 BTU, 60% efficient furnace. No. We need to see what the actual load conditions on the home are, and from there we can match the output of the equipment to the needs of the home. So load calculations are really important to determine if our equipment is too big.

We can’t just take one of those old furnaces and throw something in that has the same input capacity. We have to do a load calculation and determine the appropriate output capacity and match our equipment to that. Then if our equipment’s too small, that causes a lot of problems too, because when we hit those extreme weather conditions, we can’t satisfy the home, we can’t satisfy the comfort needs of our customer.

So we need the load calculations to tell us if our equipment is right for the home. Issues that we run into when the equipment is too small is under conditioning. We can’t satisfy the home when it’s when we’re hitting those extreme weather conditions. Excessive run cycles. It runs 24 hours out of the day and it never satisfies the home. That causes really high energy bills, and causes discomfort for the occupants.

Now there is some benefit to your equipment being too small because on the cooling side of things, it can improve dehumidification. The longer our air conditioner runs, the more humidity we run off. The drier the air gets, the more comfortable it can be in the home. The ACCA Manual J would recommend that if you are going to undersize the cooling equipment, maybe you’re installing zoning and you want to undersize the cooling equipment slightly just for that, don’t undersize it by more than 10%.

So if the air conditioner is undersized, no more than 10% undersized. But that will improve the dehumidification and comfort in the home for the occupants. And when you install that with zoning, because we’re moving those BTUs effectively around the home, when we hit those extreme temperature conditions, the part of the home that’s comfortable is closed off.

The part of the home that’s seeing the greatest thermal gain from the sun baking the home gets those BTUs and it will satisfy comfortably. So we can do that. But we don’t want to go too far under size, no more than 10%. But if our equipment’s too small, it has a hard time maintaining that set point for heating or cooling during the extreme conditions.

So we’re under conditioning, excessive run cycles, creating discomfort for the customers. And it’s not really included here but that also has high energy bills and that’ll make our customers upset. But if the equipment’s too big, it causes short cycling. So we heat that home up too much. Maybe the equipment’s designed to run for 30 or 40 minutes out of the hour, or maybe that’s what we want it to run for.

But then we oversize the equipment and it only runs for 20 minutes out of the hour. So instead of having a ten minute cycle time, we end up with a 3 or 4 minute cycle time, and the equipment’s just constantly bouncing on and off. That’s not good for the equipment, but that’s also not good for the energy bills either, because the greatest point of energy consumption is when those large motors are starting.

They require a lot more current at the time of starting than they do to maintain for a longer run cycle. So for better energy consumption, so lower energy bills is what we’re looking for, we want the equipment to run for a longer period of time, but we only want it to run for so much out of the hour.

So when we short cycle, we can shorten the equipment life because we’re placing more stress on our motors, we’re placing more stress on our equipment. And that can also create not only a shorter equipment life, but that drafty feeling. So when we blast an area with so much heat, but it kind of lazily comes out, we don’t effectively mix the air in that room.

We can create drafty feelings because the equipment is constantly kicking on and off. That room isn’t sufficiently mixing the air. So then when the equipment kicks off, that cold air now starts to remix with the hot air, and that creates a drafty feeling that can cause discomfort for our customers as well. But when our equipment’s just right, we have optimum BTU capacity.

We have longer equipment life, so it’s more likely to reach the life expectancy that the engineers would’ve designed for it. We have reduced energy bills because we’re not starting and stopping our equipment for two to many cycles per hour, but we’re also not running it for an excessive period of time. And that’s going to make for happy occupants.

So when we’re doing our zoning design, we have to do our load calculations, and we should do that based on the rooms, based on the zones that we’re creating. We need to group similar rooms. So bedrooms get grouped with bedrooms east and west, north and south. The main floor doesn’t mix with the second floor, things like that. So we need to be mindful of how we’re grouping the home up group rooms of similar use and group it based on orientation.

When we do that, we’re able to direct those BTUs to the point of the home that’s most likely going to experience similar comfort problems or similar load conditions at the same time throughout the day. And as those load conditions change, the sun’s moving around the home during the summer months, or we have that cold north wind coming down.

The BTUs are directed to the area that it’s most needed at. Then we can satisfy that comfortably. Don’t mix floors, so don’t combine the first floor and second floor for zoning. Don’t do that. They are different in temperature zones. Hot air rises, cold air falls. When that happens and we mix the floors, we’re just going to create a hot spot on the second floor and a cold spot on the main floor of the home, or on this on the lower floor of the home.

So don’t mix the floors with your zones. Don’t mix or zone. They don’t need a thermostat in every room of the home. They just need to break the home up based on use and based on orientation. Be mindful of large glass exposure. Big, open, great rooms are popular right now with new homes. People want that two story glass window.

It’s really bad for sun exposure, but when we zone that off, we can increase the airflow, the register velocity, and we’ll talk about that later. But we wash that that glass wall better with the air. So we need to be mindful of that. And with a large glass exposure we might want to consider putting, a damper that allows continuous airflow.

So maybe we got a seven inch pipe feeding that area. We put a six inch damper in that pipe. Now that glass wall gets a continuous washing, BTUs from our system whenever it’s running. That’s going to help to reduce some of the drafty ness that we might get from that large glass exposure. Let me mindful of the east and west, because the east and west, the sun rises, the sun sets, and as it moves around the home, that’s going to change the load conditions on the interior of the home.

We’ve talked about our equipment. We’ve talked about making sure our equipment. Right. What’s the next step? What are we what are we looking for next? Once we’ve checked our equipment, once we know what size equipment’s needed for the home, once we know how many BTUs we need for our specific zones, we then have to look at the ductwork so its ductwork isn’t designed to handle the BTU needs for those homes.

We have to do some fixing, we have to do some corrections, and we have to make sure the ductwork is sufficient to handle the needs of the home to handle the needs of the zone that we’re looking to condition. Ductwork problems that we may run into: excessive length. So that builder that likes to put that furnace at the far end of the home instead of central to the home, we may end up having, duct run exceeding 100ft from end to end.

So largest the largest point in the home is the furthest duct that extends out into the home. And we may end up with 120ft of ductwork equivalent length, or even more than that with the elbows and stuff like that. So excessive length, poor airflow across the air filter, air filters are oftentimes way undersized. And even when we look at the rating on those air filters, once we start to calculate that out, we see that those filters are underperforming because they’re not sized appropriately for the ductwork, for the equipment that we actually installed.

What they give us for design parameters aren’t necessarily the parameters that we need in the field. So our filters are oftentimes undersized and they have poor airflow across the filter. Maybe our Duckworth’s oversize if it’s oversize zoning, allows us to bring it back to a more appropriate size for the equipment. But the problems that we run into with that, her lack of airflow, lack of velocity.

If all zones are calling that airflow goes another nowhere just lazily comes out through each of our registers. And and it really doesn’t satisfy the needs for the home. But some, some zoning manufacturers would tell you that that that conditions not likely to happen as long as the customer is using the system appropriately, they’re they’re not trying to keep the home all at the same temperature.

The it’s okay to oversize the ductwork because when we have our zones calling, we should never have them all calling at the same time. But if you’ve gone to check in a field for any period of time, you know that that’s not the case. And for those times that the customer’s home is calling all together, you’re going to have comfort problems if you oversize that ductwork to compensate for zoning.

So understanding what we’re looking for with velocity is understanding what we’re looking for, for BTUs and all that is really necessary to making sure that our ductwork isn’t oversize. But the flip side of that coin is we don’t want our ductwork to be undersized either, because zoning takes bad ductwork, makes it worse, takes good ductwork, it makes it fantastic.

It takes marginal ductwork and makes it good. If our ductwork is undersized, we’re already running a high static pressure on that system before we even zone it down. We need to improve that work to get that static pressure down. There’s a recommended static pressure for our furnace on every single rating plate, and that recommended static is recommended for a reason.

If we’re grossly exceeding that recommended maximum static without zoning, the ductwork has to be improved before zoning is installed. If we’re doing slightly better than that. And when I look at those rating plates, the furnace is typically rated at point five total external static I would say anywhere between point four and point five is a good number to have.

If you’re exceeding point six. Zoning is not good for that system. You need to fix the static pressure before you apply zoning. So under an oversize lack of air balancing or control, that’s what zoning is designed to do for us. It gives us that control so we can move that air more effectively through the home poor, sealed, poor ceiling.

When we zone it down, we’re increasing the pressure in that ductwork. We’re increasing it enough that we’re going to push more out our drive seams, more out our clip seams. You know, if those are in areas we’re not looking to condition, we’re moving to use where we don’t need them to be at, and we’re losing them from the place that we need them to be.

So poor ceiling, leaky ductwork. That’s a problem that should be addressed. Now. Does it have to be addressed right away? Not necessarily, but it is something that we should talk to our customers about and consider doing. And then restrictive fittings are the fittings in our system designed for airflow, or are they designed for for quick fabrication? There’s a way to properly design the fittings.

There’s a wrong way to design the fittings. So how are they designed. And we’ll look at that a little bit later. But zoning improves the BTU delivery. It slows the airflow down through the furnace so that air moving through the furnace gets hotter. That hotter air has greater BTU content to deliver it into the zone itself. And a simple calculation that we can do that gives us an idea of how the system is responding without zoning is here.

BTU so how many BTUs are are in that air? BTU equals 1.08 times our CFM and that happens first. And then we multiply that by our temperature difference. So if I have a room air temperature 68 degrees I have a register outlet of 102 degrees. And I have two six inch runs. I’ve measured those there at .07 at.

So that’s 450ft per minute. And that gives me 85 cfm per six inch run. So I got two of those. That’s 170 cfm. Now I got up 1.08 times 170. And then I multiply that by 34. And I can see that those two six inch runs are delivering 6242 BTUs into my zone. So now I can take a look at my manual J calculation.

Is that sufficient for this area? Do I have the 6242 BTU s or what is my load calculation telling me I need for this area? Now? If my load calculation says I need less than that, cool. If my load calculation says I need more than that, how much more do I need? And like what the manual j it recommends?

Maybe no more than 10% under sized zoning helps to improve the BTU delivery. So once if this is a marginal number, maybe I need 7000 BTUs for that area. But I’ve got two six inch runs and they’re normally only giving me about 6240m. So I have a deficit. But that deficit is not so great that I can’t overcome that with the zoning system.

So one of the ways zoning improves is we increase our velocity through that ductwork. So now instead of 450ft per minute, we’re seeing 600ft per minute. That’s a static an external static a .12 on a six inch run. So then now I got 130 cfm per run. That’s 260 cfm total. And if all things remain equal, so my register outlet temperature stays at that 102 degrees.

My room air is still 68 degrees. I’ve measured that out and now I’ve got 9547 BTU is being delivered into that area. Well, we’ll just rounded up 9550 BTUs. So I went from 6240 BTUs to 9550 BTUs. My load calculations that I needed about 7000 BTUs for that area. So now the zoning has taken something that’s marginal and it’s made it it’s made it acceptable.

It’s made it good. But some of the things that that that zoning is going to do is just increasing. The BTU delivery is that feet per minute increase is going to increase our velocity and throw through our registers at velocity. And throw from our registers is going to forcefully mix the air floor to ceiling more effectively. And we’re going to de stratify that air.

We’re going to have less of a thermal pocket to where there’s this there’s this cold pocket at the floor. There’s this hot pocket at the ceiling. And the two are creating this, this drafty feeling has a remix with each other. When we zone it down, we more forcefully turn the air in that room. And we do a better job at reducing the temperature difference between that cold pocket and that hot pocket.

So it does stratify the air and it makes it a more uniform temperature, which is going to improve the comfort for our customers because we’ve got a more forceful turning in. While we’re not looking for the same pressures that we’re going to have in a small duct high velocity system, it follows the same principle to some to some degree, because with a small duct high velocity system, they’re looking for extreme velocities at the register face and those extreme velocities cause a forceful turning between the the temperature difference, the hot and the cold pocket, and that forceful churning of air mixes the two effectively to decrease her to do stratify the air and improve the comfort in significant ways.

So zoning does that to an extent, even though we’re not looking for those same high pressures that we would have with the small duct high velocity, we do want to see a higher delivery rate, a higher feet per minute, a greater velocity at our at a register, and that provides for greater comfort through the stratification of the air in that room.

So even though our equipment cycle may run less because we’re delivering more BTUs, that that velocity and throw the more forceful churning is more effectively mixing that hot and cold pocket, and it’s creating greater comfort. So it’s different than the short cycling we would have with oversize equipment initially, and it targets the comfort where it needs to be at.

So resources, when we’re looking at our duct design, we got manual Zr, we have manual D, manual T: Air Distribution Basics. That’s a great little manual to read through for a refresher course. There’s a lot of manuals that ACCA is offering for us that are great sources of information. Strongly recommend. If you haven’t purchased the manuals for yourself, go to ACCA’s website. Get the manuals. Great reference material when you have some questions that you need answered, and I enjoy talking about them. Sometimes when when people call me in and ask me how that works with zoning sometimes. But our air pressure is the blood pressure of our distribution. It tells us how our system’s performing. If our pressure is good, we’re golden.

If our pressure is bad, well, we’re bad. So reading our air pressure really gives us the operation of the system and tells us how it’s performing, tells us what we need to look at improving, tells us what we’ve done right, and we can take that and apply it to additional customers later on down the road. Because when we see something that’s bad and we correct it, and we retest it, and we see the difference in performance that it’s made, but we now have tangible numbers that we can bring to customers later on down the road.

And while the class I’m doing today is really a high overview of everything, it, it’s geared a little more towards the technical side of things once we really get into it. It’s not a replacement for technical classes through organizations like NCI, the National Comfort Institute. If you really want to get down to the nitty gritty about ductwork, operation, static pressure and all this, I strongly recommend the classes that they’re offering. They’re great classes. I’ve sat through a few of them, good organization to work with, and they know far more about airflow than I do, which is really good. That’s why we work with them closely and we get information from them. They like our product because it’s a very reliable product, very effective product. And we have a good relationship with them. So if you haven’t had a class from NCI for their duct design, strongly recommend it. Great organization to work with.

But your air pressure is the blood pressure of your system. And it’s really going to tell you how the system’s performing what improvements need to be made. We got a couple of different tools that we use for reading that.

Now what we’re probably not going to be using the pitot static tube a whole lot today because the digital meters have have come such a long way. We can use a hot wire nanometer if you don’t have one great tool to use for reading airflow in your ductwork, but that’s going to be, a huge benefit when it comes to performance measurements in the system.

More commonly, you get yourself a digital manometer. It’s going to come with some static tubes. It has that static source tube. So you got that little hole on the side. And that’s just measuring the pressure as it pushes outward on the ductwork. And then the simple pitot tube is right there at the very top that’s open. It’s reading the pressure air head on.

So with these different readings we’re able to calculate things like our total external static, our static pressure, our total pressure, our differential pressure. And we’ll define those here as we go along. But those are important measurements to have important numbers to understand and read, so that we can really see how this stock works performing and what we need to do to improve it.

Our total external static is a measurement in our air handling unit itself. So that gas furnace or that, that blower and or that, that air handler with the evaporator coil built into an electric furnace. It is our air as it enters the piece of equipment. It is our air is it exits the piece of equipment. And we add those two numbers together and it gives us our total external static.

So if we look at the rating plate on the vast majority of residential equipment with gas furnaces, it’s going to tell you that the total external static rating is 0.5 recommended maximum on electric air handlers, because they’re a little bit different than a gas furnace, we might actually see that their their total external static is somewhere closer to 0.3.

And that’s, that’s the air as it enters the evaporator coil and as the air as it exits through the electric air handling elements. So that that pressure drop, it typically be about 0.3. Some of them are up to a 0.5. We have to look at the rating plates to see that. But before we even apply zoning we need to see is our equipment operating within those specifications.

Now we also have to be somewhat careful. There because those two numbers should be somewhat balanced. I had a job where the technicians that kept going out there said, yeah, my static pressure looks good, I’m running 0.5 with or I’m running 0.55 with that, with all my dampers open with no zoning applied. But the problem that they were running into isn’t that they were running 0.55 with all their dampers open, it’s that they were unevenly weighted.

They had high restriction on their supply side, but they had no restriction on their return side. So that 0.55 and their heat exchanger compartment, they were actually reading like 0.4 or 5. And then on the blower side they were reading 0.1 that that’s not that. That’s a restriction on the supply side that needs to be addressed. That is ductwork that’s too small on the supply side and oversize on the return side.

And while it’s not bad to be oversize on the return side, our return side. And we’ll see that a little bit later is going to be larger than on the supply side. If we have all that restriction weighted to one side of the furnace, we need to correct that air imbalance before we install zoning. So our total external static, the air that enters the piece of equipment, the air that exits the piece of equipment, add those two numbers together here, regardless of the positive or negative, we toss those symbols away when we do this calculation, add those two numbers together and that gives us our total external static.

We want to see them fairly close. No, no major difference between the two of them. But we also want to see that we’re not we’re not exceeding the maximum for that piece of equipment with all zones open. And then once we zone it down, we don’t want to exceed the maximum according to the blower performance data chart.

So while the rating plate is typically going to tell you a point five, you open up the manual blower performance data chart. You’re going to see that most manufacturers actually give you a maximum absolute maximum of 0.8. Some of them go all the way up to full into water column. So with zoning, we’re looking to push the system as close as we can to the maximum.

According to the blower performance data chart, without exceeding it, creating objectionable airflow noise for our customers. So look at the rating plate on the furnace. Make sure the ductwork before zoning is applied actually works according to that rating plate, and then apply the zoning. And we want to push that up close to the blower performance data chart maximum in the installation instructions.

And most furnaces are going to tell you that’s around 0.8. We also need to know our filter pressure drop, because this is going to tell us is our filter too restrictive. So we might have good pressure on the house side of the return. But two grade of a drop across our filter. Now, just as a good rule of thumb, there shouldn’t be greater than 20% drop across our filter from our total external static.

 

So if our equipment designed at 0.5in, that’s our recommended total static according to the rating plate on the on the blower door for most furnaces today, that would give us a pressure drop of no greater than 0.10. Now, if we open up our furnace manuals, we’ll probably see that most of them allow for maximum filter pressure, drop a 0.25.

So we need to look at that. We need to determine: is my filter going to be too restrictive? And the less restrictive we can make that filter, the better our system is going to perform. But on top of that, the less restrictive we make that filter, the better our filter is going to perform at removing allergens from the air.

We also need to check our pressure drop across our evaporator coils, see if those are too restrictive, because maybe it’s not our supply air duct itself. Maybe the system’s been in there for a while. And that evaporator coils plugged, some evaporator coils have technical data that technical data with the evaporator coil tells you the pressure drop across it.

If that pressure drop is being exceeded by greater than 15%, the coils dirty needs to be cleaned. The coils are multi-layer. It’s not just a single layer. So while you may not see the dirt on the surface, that doesn’t mean that it’s not stuck between the layers. So if you look at the engineering data for those coils and your pressure drop across it, if everything else is looking acceptable, your pressure drop across that coil exceeds 15% of the engineering data, then that coils dirty and it should be cleaned.

And then our external static. So this isn’t the total external static. This isn’t measuring the equipment. This is just measuring the ductwork that feeds the house. So our external static pressure typically if you use your your duct slide chart, if you have that your external static on that slide chart, you’re going to set it somewhere between 0.08 and 1in a water column to figure out what size duct would be appropriate.

So normal residential design is point one. When you’re designing for zoning, you may actually want to design at .08. That would probably be a better number to use on your slide chart. That way your ductwork isn’t grossly oversize, but it’s slightly better than normal design. So .08 if you’re designing a new duct system to match with zoning, use .08.

If it’s existing system, you don’t want to be exceeding 0.1 in most cases. And then once we apply zoning and our smallest zone is calling by itself, we shouldn’t be exceeding the 0.3 mark. That would be the absolute tippy top maximum. But that’s probably where your customer is going to have problems with objectionable airflow noise. In most of the testing I’ve done, and even when I was in the field installing zoning systems, my external static pressure, when I had my smallest phone calling by itself and my customer wasn’t complaining about airflow noise, I found that it was typically right around point two.

So the .17 to the .22 would actually be a great number to consider your range for maximum on your external static pressure. With a zoning system, you don’t want to exceed 0.3, and if you were exceeding 0.3, you’d probably find that your total external static. So the drop or the the static pressure through your furnace itself, you’d probably find that that is way high.

The higher that static pressure goes, the more likely we are to damage the furnace, which is why I tell you not to exceed the maximums according to the blower performance data chart. I’ve had some contractors that that never took any of that into consideration, and when they finally checked their static pressure, they saw that their furnace was running at 1.2 to 1.3 inches somewhere in their.

The problem that they were having was every few months they were having to go out and replace the squirrel cage and the and the blower motor because it was, it was just blowing apart. And the reason it was doing that is because they didn’t. Their ductwork was way too small. They didn’t do a manual J. So they oversize their equipment.

And now the two things were working against each other. And then on top of that, they put zoning in because the customer had problem getting airflow to their second floor, and they thought zoning would be the fix for that. But the ductwork going up there was insufficient to begin with. So it was a multiple, multiple problems that all just kind of came crashing down on them and they started shattering their blower wheels.

They started burning out their motors. And these were variable speed motors. So these weren’t cheap motors. And after I think their third or fourth motor, the OEM manufacturer stopped giving them warranty on them. And it all came down to they were doing something they never should have. They didn’t do their load calculation. So the furnace was oversize for the home.

They didn’t measure their ductwork. So the furnace so the ductwork was insufficient for the for the needs of the home as well. And then they installed zoning, thinking that that would take care of the poor airflow to the remote locations. And they restricted it down even further, pushed the furnace way past its rating, and they started damaging the furnace.

I don’t want you to do that. I want you to work within rating. So while the the chart on their blower door is going to tell you typically 0.5 bar forms, data charts are going to tell you the absolute maximum. Most case of 0.8 with your zoning system. You want to bump up close to that without creating objectionable airflow noise.

That way you’re not damaging your furnace and your you’re staying in a safe limit. So be mindful of airflow, noise, and usually usually your customers perception of airflow noise is going to tell you you have a problem with your static pressure before you even hook your meters up. The reason I always use my meters is because my ears don’t work the same as my customers, and because my ears don’t work the same as my customers.

My meters would tell me numbers that I could look at, and then when I would go to set somebody else’s system up, I would start the high side of the range that I found most of my customers were happy with. And then I’d let my I let the homeowner listen as they listened to it. If they had a problem, I would take it back to the middle of the range, let them listen to it again.

If they still had an issue with the noise, I would take it back to the low side of the range, let them listen to it again. And that’s usually where everybody was satisfied. And more often than not, that came down to my total external static being somewhere between, 0.68 and point seven usually. So start at the maximum.

Let your customer listen to it, back it off to mid range, let your customer listen to it. If it’s still a problem, take it back to the low side and we can do that with our XLS mojo pass control. And we’ll be able to talk about that a little bit later. Differential pressure. Differential pressure is how if we don’t have our hot wire and ometer, we can determine the velocity in our ductwork.

So we have our our pilot tube and we have our static probe. Our static probe reads the pressure as it pushes against the dock where our pilot tube reads our our face pressure. So we take those two pressures, we subtract them from one another, and then we we take 4005 multiplied by the square root of our differential pressure.

So the example to that is if I had a pressure feeding directly into my tube so that that that pilot tube feeds into the airflow. So the, the airflow, the rate at which it was flowing gave me a pressure .24. Now my static pressure gave me a 0.19. So that that gave me point this, that gave me 0.05, the square root of which was 0.2 to 3 six.

And then that multiplied by 4005, gave me 895ft per minute through that duct. And this was a 16 by ten duct. So I had 900 cfm flowing through a 16 by ten duct. And I was able to read that by getting the the flow rate. So how much pressure was feeding into the end of my, my pressure to what was my static pressure that was pushing inward through those little holes on the side and then square root of that?

And no, I cannot calculate square root. That’s what my calculator is for. So I pulled out my phone has a square root function, put my .05 into there, press the button and it gave me 0.2236. That is how in the past, before all these digital meters, people would have read their velocity. They would have calculated out their velocity to determine the air flow rate through their piece of equipment.

So if you if you don’t have the hot wire and monitors things like that, that you can use to give you that feet per minute calculation on a nice digital readout, you can do it with an old fashioned water column. You’re probably going to be using a sensitive magnet, but you can do it with those tools, and then you just have to do a little bit of math to go with that.

So fairly simple calculation, pretty old school tools. But it gives you that fee per minute. So you can determine what your CFM is going through that system. And this wasn’t stuff that I that I understood right away. But as I really started to dig into it, I wanted to look at ways that I could simplify it for contractors.

And this was the simplest way that I could come up with it. And it’s really just taking two pressures using my calculator, and that gave me my feet per minute and my duct work. Once I found the formulas and was able to understand how they worked. Very basic, simple formula that technicians can work with. They take two measurements, calculate that out, and then they can determine their feet per minute.

And once they have their feet per minute, they can turn that into CFM. If you have a duck slide chart, great. You take your feet per minute, set that to the Or. You set your duck size, find your feet per minute for that duct. And then that gives you your CFM right there. Easy on a on a duck slide chart.

So once we’ve tested our pressure, once we’ve calculated out the feet per minute, once we’ve once we’ve gotten the numbers that we need to see if the system is working appropriately, we can take that pressure and we can turn that into CFM. We can turn that into BTU. So we tested our pressure. Now we need to look at CFM and BTU to figure out is it correct.

So according to manual D our supply side has a maximum recommendation on rigid duct of 900ft per minute. On rigid duct it has a recommended of 700ft per minute. Now if you look at the return side, the return side has a recommended of 600 with a maximum of 700ft per minute. So you can already see that the return side is going to end up a larger duct size for the same amount of airflow than what you’re going to have on the supply side.

But notice how it says filter grill face velocity. We can almost take that to be our pressure drop recommendation through our filter. And that’s at 300ft per minute. But if you look at your filters themselves, those are typically rated at 500ft per minute is what those manufacturers test them at. But looking at our duct design, we’re actually seeing a recommended maximum of 300ft per minute for a filter grill for the face velocity on a filter grill.

So somewhere between 300 and 500 is where our filter should be at. And typically when we test our filter, we’re going to find out that on the vast majority of systems, it’s going to be greatly exceeding that 500ft per minute. But we need to size for for velocity, we need to know what we’re looking at. And recommendations for trunk dampers 700 to 900ft per minute.

Branch dampers or branch lines 600 to 900ft per minute. And then on our return, 607 hundred or on the branches coming off that return 400 to 700. And when we’re designing for zoning, we want to have it. If everything is open, we actually want to be designed for the lower side of these numbers. So we want to try and design our ductwork.

If we’re doing a new duct system, we want to design for the recommended numbers, which would be 706 hundred for trunk versus branch, and then on the return size six and 400 for the trunk and branch. And then once we once we have that zone down, that zoning is going to push it towards the maximum side of that spectrum or the maximum side of that range.

A typically this is more how the system is actually responding nationally. So not necessarily design, but this is usually how these things are calculated out and looking on a more national basis. And I got these out of the engineering toolbox.com. If you aren’t familiar with that site, strongly recommend it. A lot of great information there, but normally in comfort systems and we’ll consider that to be residential.

Those are typically in the main trunk line, somewhere between 700 and 89,380ft per minute, and we can already exceed that on the high side. That’s that’s greatly exceeding what we would typically be looking for with with manual D on the branch docks, 590 to 987. So again, that’s still greatly exceeding what we would typically want. But it’s more reasonable than what we’re seeing with the main trunk lines themselves.

So we want to design for the low side. And then with zoning we want to push it towards the high side, the maximum to optimize comfort and deliver those BTUs around the home. What I have here is an actual airflow test. And I did this here at our zoning. We have a test system that was provided for us by Goodman.

It’s one of their newer furnaces, which was actually really, really nice to use for this test. Gave me some great numbers to look at and consider, and this helped me to really see how how the zone weighting and the airflow respond to each other based on these different conditions. So I have four zones laid out in this test.

I have 100% of my ductwork open. I can see with my Y2 call that was running 0.49. So a 0.49 with a Y2. That’s high speed airflow. I’ve got the furnace set up for 2000 CFM for high speed airflow, which is nominal for five tons of air. I know I’m good. My blower wattage was 467W. So we have the furnace plugged into an electrical meter that’s recording the wattage for us to let us know how much energy the blower is consuming when we’re doing the test.

The 467W, a total external static, a .49 running a Y2 output. And I can see that I have a range of feet per minute on each of my registers. And these are six-inch rounds to four-by-ten registers. And that varied from the high to hundreds to just over 400ft per minute. And I can take all of those numbers and we’ll see it in the next slide.

I can take all of those numbers and turn them into a CFM rating fairly easily, just by knowing the size of my duct and and the velocity that I measured through there. And then I started to step things back. I started to close things off so that 100%, it’s actually with five zones.

I’ve got 2 16 x 10 ducts, each one under normal applications, being designed at about 1000 cfm. So I’ve got 2 16 x 10 ducts with 100% of my ductwork open. I’ve got both 16 x 10 ducts open. I’ve got four zones coming off the one side, and I’ve got a big trunk damper on the other side. I close off that big trunk damper.

So now I’ve got nine six-inch runs open on a five-ton blower and I can see how my CFM changed. I can see how my feet per minute, my velocity changed. Now my total external static, my Y1 blower is now operating at 0.22 and it’s using 122W. My Y2 blower’s operating at point six, using 520W so I can see my energy consumption go up.

But my total external statics not exceeding the maximum according to my blower performance data chart. So I still have some wiggle room with there and I can take it down further. I take that down to 35% of my ductwork. So I have zones one, two and three open. Now that’s seven six-inch runs open.

Now my Y2 blower’s running at a .69. And that’s usually about the tipping point where I found my customers, some of them would start to have airflow noise problems if I exceeded that. The vast majority of them were quite happy there around that 0.7 mark. So that’s where I come up with that recommendation of single speed systems, because this is high speed, five tons of air, single speed systems not to have more than or not to have less than 35% ductwork to equipment capacity.

So I can see what those numbers that at 35% of my ductwork open seven six inch runs on a five ton blower, I’m running a .69 and I’m using 550W of electricity. But I can continue to take that down. So when I use the zone weighting feature with my with my HeatPumPro and that two speed blower, I take it down to 25% capacity and I’m running 0.38 on my total external static.

I’m using 166 watts on my blower, and my feet per minute through my runs is starting to get closer to where I’d want it to be at on the maximum side in most cases. But I can see significant difference in how much air I’m actually delivering into that zone. I’m using less energy to do it, and I’m going to be delivering a lot more BTUs with that air, and we’ll see that in the next few slides.

As we start to actually turn these into numbers, we can work with. But at 25%, I’m really starting to stretch it when it comes to my my total external static on that high speed blower, I’m running a 0.8. And that’s that’s the maximum for my piece of equipment. Now if I’m running there, that’s if everything’s perfect. Perfect. But I know that that number is going to change as my air filter starts to get dirty.

It’s going to push my static up. And that might push my equipment to the point where it’s not healthy for my equipment. So I really don’t want to be at the maximum for my furnace at perfect, perfect conditions. But I can also see with that that I’m really starting to exceed what I want for the maximum on my feet per minute, and that’s where I’m probably going to run into an issue with velocity, airflow, noise coming from my registers.

So I need to be careful there. But for energy energy concern. Now I’m also using 605W on that variable speed blower. So it’s using quite a bit more energy than it would have otherwise. And then just to see how respond, I took it down to 15% of my duct work. So as three six inch runs open on a five ton blower.

And that’s why one operation, the furnace was running point for a five, which I would actually find to be acceptable. Now, I probably wouldn’t do that on a regular basis because my ductwork could use a little bit better when in terms of air sealing. And if you get your ductwork really tight, your numbers probably aren’t going to duplicate what I have here.

But at those numbers, I’m moving significantly more airflow when I use my low speed blower. One, and I’m doing that using a fraction of the electricity. So with 25% of my work, open 166W versus 467, so I’m using 300W less in energy on the 15%, I’m approaching 200W, but that’s still less than half of the electricity that I’m using with 100% of my ductwork open.

And here I’m pushing air to the area that needs it the most, and I’m satisfying it more effectively. And that’s going to be a performance improvement that my customer is going to be happy with. All right. So CFM, I have all my velocities from that previous chart. I can use this this formula to calculate all those out and tell me my CFM.

But just for, just for example purposes, rather than working with those numbers directly, I’m going to use some whole numbers to make it look a little bit cleaner. So my CFM is my velocity times my square inches. So how many square inches are to that duct. And then I’m going to divide that by 144. So I’m going to see that with a six inch ground duct at 500ft per minute.

That’s that’s a radius of three inches. So pi three squared gives me 28.2744in². So I can take that, multiply it by my velocity 500 feet per minute. And then divide that by 144. And that tells me at 500 feet per minute, those six inch round ducts are moving 98 cfm of air. So if you don’t have your duct slide chart, you misplaced it, this is a very simple formula you can write down and just kind of keep in the back of your mind. And if you misplace your duct slide chart, if you have if you have a meter that’ll give you your feet per minute, you can use that to quickly calculate out the actual operation of that duct. Now the 10 by 16 duct, that’s 160in².

That’s my main duct. So 800ft per minute. I took a middle of the road approach here between 700 and 900: 800ft per minute, middle of the road. That gave me, 889 cfm operating in that duct, which is close to capacity. If I pushed it up to maximum, I could fit a thousand cfm of air through that 16 x 10 duct. But almost 900 cfm of air 800ft per minute, I’m real close to my slide chart.

Those are simple calculations I can do when I lose the slide chart in the front of my van, and if I have a hot wire anemometer, I can just drill a test hole, pop that in the duct, let it read for a couple of minutes. That gives me my feet per minute, and I can easily turn that into an actual CFM calculation to see how those ducks are performing.

And that’s if I’m that’s if I have preexisting ductwork. So if I have preexisting ductwork, I’ll need the tools to measure it. If I’m designing for new ductwork though, I know what my blower needs. So I have a three ton blower, 1200 cfm, 800ft per minute. I can reverse that formula. So the square inches of my duct is now equal to 144 times my cfm, divided by divided by my velocity.

So if I want a if I want 800ft per minute through that duct, and I want and I need 1200 cfm through there, I can calculate that out to 216in². And that’s telling me I need a ten by 22 inch square duct, or I need a 16 inch round duct. So by knowing my if I’m designing for new work, I know what my blower capacity is.

I know what I want my feet per minute to be through that main trunk line. I can take those two numbers and it’ll tell me what I need as far as my square inches go, and then I can take that square inches and turn it into an actual duct size. So then I can do that same thing for my branch runs.

But I know my branch runs. I’m not designing those for the same pressure that I’m going to have in my main trunk line. So I need 150 cfm of air. I’m going to design that at middle of the road, so 400 to 600 would be my range. Typically for a branch damper I’ll design that for middle of the road 500ft per minute.

Now if I’m designing for zoning, I’ll probably take that back to 400 and 450ft per minute, but about 150 cfm. I need that into this specific area. I’m designing it at 500ft per minute. I calculate that out to 43.2in², which gives me a four by 12 duct or a seven inch round. And if we look at our standard sizes for register boots, typically a four by ten boots, a seven inch round, then the two are equivalent when it comes to airflow delivery.

So it actually makes a little bit more sense in that case. So those are simple, simple calculations that I can do. We had the calculation that gave me what my existing ductwork is operating at. I just have to be able to calculate out my feet per minute. Digital meters make that super simple. But if I don’t have digital meters, maybe I’ve got a static pressure tube and I have a static source tube.

I can take those two measurements, subtract them, use that calculation 4005 times the square root of whatever the difference between those two numbers are. And if you don’t remember them. The digital meters make life so much easier. So if you want to do the calculations, great! They are fantastic calculations to know. I tried to simplify them as much as I could, but if you don’t want to remember the calculations, I strongly recommend some of the digital meters available to you.

And I’m a big fan of the hot wire anemometers for ease of measuring. And the really nice thing when I’m, when I’m working with tools like that is I can get my all the customer involved, I can get the homeowner involved and they can start to see these numbers that I’m looking at, and then I can calculate those numbers out to show them how their system’s performing.

And when I do that, it helps to set me apart from the competition because I’m showing them something that nobody else has done before. I’m showing them how their system is actually performing, and that that really gives me a leg up on the competition when it comes to selling my customer on performance. And they’re so pretty simple calculations.

You just need the tools to measure it out. Making sure our duct fittings are designed appropriately is also very important when it comes to airflow, because our duct fittings are a source of turbulence, and that turbulence is going to affect airflow, that’s going to affect performance. So when I am looking at designing my duct fittings, if I’m making an elbow, that internal corner is important.

That internal corner is going to be a great source of turbulence if it’s not designed properly, my elbows should not be squared off. They need to have a round radius and something to think about when you’re when you’re trying to picture that in your head. Is it easier to pull a root, rope around a square corner, or is it easier to pull a rope around a radial corner?

And when you start thinking about it like that, or even a ball, is it easier to push a ball straight up around a square corner, or is it easier to push it up around a radial corner? So when we start to think about it like that, the airflow is very similar. And when we have those sharp corners, we actually create dead pockets of air as it tries to blow past there and then then realign itself in that duct and we create this dead pocket that cuts off airflow, creating turbulence and creating pressure problems.

So when we’re looking at our elbows, that internal radius needs to be 0.5 times the width. So if I have a ten inch, if I have a ten inch width on my elbow, that internal radius needs to be at least five inches. Or if I’m building a flat elbow, I’ve got, I’ve got a ten by 20 duct.

It’s a flat elbow instead of a, instead of a side elbow. That flat elbow now puts my width at 20in my radius for proper airflow needs to be ten. So my my radius on that internal elbow is 0.5 or it’s half of what my with this. And that’s that’s important for proper airflow. And that’s the same thing for my return air boots.

If my return air boot in this case it we’ll call it a 24 by ten. That’s a standard size that you’d buy at your local distributor, a 24 by ten. That internal radius should be at least five inches. If I’m designing for a five ton system, at 500ft per minute, that drop is probably going to have to be something like, a 24 by 16.

And if I’m going to bring that through a boot, that 16 inch is being my width. I’d have to have an eight inch radius on that boot. So calculating that out for proper airflow helps to overcome restriction. That’s common in most systems. And those are simple things that we can do to improve the performance of that duct system.

But past elbows we have our reducers. Our reducer should be no greater than 20 degrees or for every 12in in height, there should be no more than four inches an offset. So if I need to go from a 20 a a 20 inch duct down to, we’ll say a 12 inch duct, I would either have to make that reducer 24in in length to accommodate that 20 degrees, or four inches for every 12.

Because I need to reduce it by eight inches. That means I’d have to have a 24 inch long offset or I would have to center up that offset. So I’ve got no more than four inches tape or on either side of it. So when I’m looking to reduce the restriction through my elbows to to not have, a great amount of turbulence through there, my reducer should be no greater than 20 degrees or four inches for every 12in.

So if I’m going from, a 20 inch stock down to a 12 inch duct, I would want to center that up so I could keep it at 12in in length, or I would have to make it 24in in length to have an eight inch offset to it. So a little things to keep in mind. You don’t want to make a reducer by just blanking off four inches of the duct.

You want to give that that gradual transition, but you don’t want to be more than four inch offset for every 12in in length. So those are just some simple tips when it comes to elbows, reducers, and adapters that you’re going to be working with in the ductwork.

 

We’re going to take a look at filters. And filters are generally way undersized, so most manufacturers would recommend no greater than 0.25 of a drop across that filter or pressure differential across the filter, no greater than 0.25.

If you read the manual for your furnace, the industry as a whole recommends not to exceed 20% of my total external static. So if my furnace is rated at point five, I don’t typically want to see greater than 0.1in of drop across my filter, but the manufacturer would say a maximum of 0.25. So if my filter is brand new, 0.1in a drop across my filter is brand new, clean, and then it needs to be changed if that drop or to exceed .25.

So if you ever get those filters, I have that little whistler in them. That’s essentially what it’s doing. As your pressure drop across that filter increases the velocity through that whistler increases. And once it starts making noise, it tells you that the pressure drop across your filter is too great. It’s time to change it. And that’s that’s how it works.

So filter pressure drop. If you have a high Merv filter for energy efficiency. And these numbers are actually out of California. So they are a bit extreme. And if you if you design your filter based on those numbers, you’re going to have some massive filters. So maybe design based on ACCA manual D telling you drop or face velocity at a filter grill would be 300ft per minute.

Start there. That’s a good number. The filter manufacturers test at 500ft per minute though. So when we look at when we look at a five ton system and if we use the filter manufacturer, you’re saying 500ft per minute. And the reason I don’t like to use the filter manufacturers rating is because when I was in the field, my customer installing those, those filters with those really, really narrow pleats, those one inch filters that we all absolutely hate when the customer buys them and then tells us their furnaces is having problems, we go out there and we find out the furnace is running on limit.

And the reason it’s running on limit is because they bought a high density one inch filter. That filter is tested at 500ft per minute. So if they’re going to use those filters, they’re they’re definitely not running at that 500ft per minute. But to allow them that opportunity we need to design our filters at a much lower. We need to do by design our our filter cabinets at a much lower velocity to give the customer the option of those filters.

But even when we look at the high Merv filters, the 14 inch filters a 20 by 25 by four inch filter, Merv ten is actually only rated at 1700 CFM, and we’re slapping those to the side of five ton furnaces. Our static pressures are way too high because the manufacturers are also making their blower compartments shorter and shorter.

So when we slap that directly to the side of the furnace, we’ve now cut off a third of the filter and we’re only pulling instead of a filter that that in all reality is really only rated at 1700 feet per minute. We’re really d rating that filter to where it shouldn’t be, pulling more than 1200 feet per 1200 cfm through it.

So when we when we start to look at the filter and how we’re installing them, the vast majority of filters are installed incorrectly. They’re causing high pressure drop. And the vast majority of filters are undersized, which is also causing high pressure drop. So looking at looking at this and taking the calculations that I’ve, that I’ve given you previously, if I have a five ton furnace and I want a 500ft per minute phase velocity at that filter, I can calculate that out to tell me I need 576in² of filter.

But for the sake of efficiency, I actually want to be closer to say, 250ft per minute, which tells me I need 1152in² of filter. So when I’m when I’m looking at those numbers, what I’m actually seeing here. So if I have a five ton blower, I really need a filter size of 20 by 60in. That would be 220 by 25 inch filters.

And that would probably put me closer at 300ft per minute at my face velocity on those filters when I when I install those. So if I had a five ton furnace, I actually need 220 by 25 inch filters to achieve a proper phase velocity for airflow. But that’s also going to allow the air to hang out longer in that filter.

And that’s going to be better at filtering out allergens, because the the greater the velocity coming through that filter, the more allergens. I’m actually going to suck out of the filter and keep in distribution throughout my home. So if I slow that airflow down through my filter, not only do I ease up the stress on my equipment, but I also increase that filter’s capacity at catching those allergens.

And that’s going to make for healthier air for my customer. And there is a tipping point there, because if the airflow is is too low, the filter isn’t effective at actually collecting those allergens, but the airflow is too high. We’re pulling those allergens right back out of the filter and circulating back through the home. So there is a balancing point there.

But in in looking at the the size that I would need for a five ton furnace to have proper airflow through that filter and operate according to energy efficiency ranges, I would actually need 220 by 25 inch filters on a five ton furnace. So a popular one inch filter. They have varying levels. I don’t quite understand NPR. I I’ve been growing up using Merv, so I like to stick with the Merv rating.

That’s the one that I understand the best. But in this case a Merv rating, a 13. The pressure drop that they’re recommending for their filter is .19. And we can already see that that 0.19 is greater than the 20% that we would want for par for our proper airflow through that filter. So in that case, we need to go larger to reduce that pressure drop to maintain proper airflow.

But at that it’s 95% efficient at collecting the allergens in the air, which is really good. I’ve got a problem with allergies. I use a Merv 13 filter in my home, and I don’t use anything less than a Merv 13 filter, and after really studying this topic, I know now that my filter is marginal in size, but with the way I design the ductwork, I am getting full volume through there and I have a four ton blower with a 20 by 25. So so my face velocity on it is probably somewhere around 400ft per minute when it’s clean. But I have kids, I have cats, I have dogs, my wife raises birds, and every now and then there’s chickens in the basement that are sitting under a heat lamp.

So my filter sees a lot of abuse. I have to change it a lot more frequently than I like to. But some testing that was done. Homeenergy.org. They did some testing on standard filters with a pressure drop at 495ft per minute, which is the rating for these filters. But with that 495ft per minute when they were trying to maintain the airflow that a 16 by 25 is designed for.

So 1367 CFM, the pressure drop across those filters varied wildly. You can see that the only filter that even came close to the pressure drop we’re looking for was that one at the bottom, the ace 30 day. That’s the fiberglass or the hog hair filter. That’s that’s really only good for boulders and butterflies, as we like to say in the industry.

So it’s a filter good to catch boulders and butterflies. Does absolutely nothing for your allergies. But when we start to look at the higher MERV rating on the filters, the Merv 13 filter up there at the top, and that’s one of those one inch filters with the mini pleats, the ones that we absolutely hate because of the restriction that they place on the furnace, and the customer calling us up to say that their furnace isn’t working.

We get out there, find out it’s overheating or the coil’s freezing, all because they used a high Merv one inch filter, or in this case it was a high Merv two inch filter. But the pressure drop across that is 0.5. That greatly exceeds the, well, 0.5 is, is actually the pressure, the total external static rating of the furnace itself.

So if we’re running that kind of drop through the filter, what kind of pressure are we going to run inside the furnace? To get airflow through there, we’re probably going to have to be running our furnace up close to a total external static of 0.8, all the way up to that full inch mark to get a decent amount of airflow through there.

But that’s going to damage our furnace. So the things we have to do in these cases is when we see these pressure drops on these filters, we know now that our filters need to go up in size. So when we start looking at high Merv filters, we need to start increasing the size of our filters to maintain a lower face velocity on them to get the airflow through our furnace.

So if our furnace is rated at 0.25, that gives us a filter face velocity of 440ft per minute. But we know for efficiency’s sake, and the industry recommends that if our furnace has a total external static rating of 0.5, we want a pressure drop across our filter of 0.1. That actually puts us at 280ft per minute for designed velocity on those filters.

So like in the previous slide, they’re designing at 492ft per minute. A 16 by 25 inch filter should normally be able to move, and we’ll round it down. We’ll say a 16 by 25 should normally be able to move three tons of air. We shouldn’t use that on anything greater than three tons of air. But in all reality, we should be going with a 20 by 25 inch filter on a three ton drive.

Based on these numbers, the numbers that we’re really looking for when it comes to filter or pressure drop across our filter to maintain that point. One, our filter should be sized with the face velocity of 280ft per minute, so that 280ft per minute is the number that I’m going to use to determine how much filter area I need based on that first calculation that I had given you about the filters.

Based on that, designing my ductwork to handle the necessary CFM. So if I need to fit 1200 CFM through there, I have my my 1200 times 144 divided by 280, which is going to be my phase velocity. And that gives me the square inches that I’m going to need for my filter.

So when I start sizing my filters for the performance of the system, I’m going to start increasing my filter surface area to have appropriate pressure drop. But I’m also going to improve the efficiency of that filter because slowing the airflow down, I’m going to be sucking those allergens off my filter at a slower rate instead of pulling them right through the filter with that high velocity, I’m actually going to allow them to hang out in that filter and be captured more effectively.

So things to consider, things to look at, make sure when you’re designing your filter that you take a look at how you’re designing it, make sure it’s sized appropriately for the equipment and start going larger than what we’ve been doing to improve the performance of that system. So based on the parameters of the of the previous slide, that 1367 CFM, I would need a filter face area to achieve the recommended 0.1 pressure drop.

I would need a filter face area of 700in², which would actually be a 25 by 30, but that’s not a standard size filter. So if I took it back to 20 by 25 on that system and that’s going to be three and a half tons of air, so 1,367, really close to 1400, three and a half tons of air.

That would give me a filter of 20 by 25 with a face velocity somewhere, somewhere around 300 to 350, which, while exceeding what I’m looking for at that 0.1, it’s less than the maximum rating for my furnace and it gives me a happy medium. So start considering upsizing your filters. Better filtration, better airflow, easier on the equipment, better life expectancy.

Filters need to be installed for full airflow. A four ton and a five ton furnace should really have a base underneath of them for a two point return, so side and bottom, or two sides if you can. With that in mind, a 4 or 5 ton furnace with a base underneath of it. How is that filter going to install to that base?

For full airflow we need about six inches between the filter cabinet and the furnace. And then we need our elbow coming down. And that elbow is, for a five ton furnace, probably 16 by 24. For a four ton furnace, probably a 12 by 24. We need to have the proper radius on there. So once we start to have that, we’re really getting to having a large space coming off the side of the furnace.

It might actually be better to put the filter in the drop itself. And when we put the filter in the drop itself, we should come down square with the throat from our main trunk line, or even just flare it out at the top so that it’s more gradual, instead of that tight corner coming down off the main trunk line.

But we should be coming down with the full volume of that filter in the top of it. And then we build our transition to bring it down into our return drop size and into our boot. So when I was doing four and five ton furnaces, this is how I would typically install it. I like to do the two point return because that gave me a good airflow through my furnace.

I wasn’t creating a restriction through my filter. My return drop wasn’t creating a restriction, and I was getting the full volume of air coming through my filter itself, which helped to decrease the velocity and just make it much more effective in terms of operation. But as with the transition, it should still be no more than four inches for every one foot in height.

So if I’m going from a 20 inch duct down to a six inch duct, I can do that and in a space of of 12 inches, if I’m making my transition that. Just to have a more gradual, I might make that 16 inch long in my offset. But if I don’t have enough height in my basement to do that, then I would probably center it up as far as my offset goes.

So bypass duct has two forces that it’s working with that has your supply air pushing. It has your return air pulling. And those two forces working together move air through a bypass duct far faster than it does when you’re only contending with one force. So that increased air movement through there, because we’re both pushing it and we’re pulling it at the same time.

We have much lower pressure in that duct, and that moves the air at a far greater rate than you would see through a standard duct that’s only contending with one of those pressures, or one of those forces. The air through a bypass duct moves typically between 1700 and 2200 feet per minute. So when we’re designing a bypass duct, we’ll split hairs, we’ll say 2000 feet per minute, while our ductwork needs to be designed according to those Manual D charts, where .

Where it was 700 to 900 was the range. Our bypass duct is designed at about 2000 feet per minute. Because it’s got those two forces, it’s pushing and it’s pulling, and the air moves faster at a far greater rate than we have when we’re just contending with the one force. So for a bypass calculation 2000 feet per minute. And the industry hasn’t always been doing that.

The industry has used standard duct design pressures and typically using 700 to 1000 feet per minute for their duct design. And then they took their bypass and they would design that with the exact same pressures, not taking into account that they’re both pushing and pulling air through there. So those bypass ducts were able to move a lot more air than what the industry would design them for, and that would cause all kinds of problems because bypasses were oversize.

So let’s say I had a five ton furnace, 2000 cfm, I’ve got four six-inch runs, 500 feet per minute. That’s 400 cfm. So I need a bypass duct in this case of 1600 cfm. For that bypass duct, if I were designing at 700 feet per minute, that would give me a 21-inch round pipe. If I designed at 1000 feet per minute, that would give me a 17-inch round pipe.

However, knowing what I do now that a bypass duct can move air at 2000 feet per minute, that 21-inch round pipe is is going to move a lot more air than what that 2000 CFM blower can accommodate. A 17-inch round pipe is going to move a lot more air than what that blower can accommodate. So when I’m looking at designing my system, I need to take that into account in a comfort system.

While our ductwork still needs to be designed at 400 cfm per ton, if I pay attention to the blower profile on my furnace, I’m going to see that comfort profile typically has me around 350 cfm per ton. An efficiency profile may put me as high as 450 cfm per ton, and a nominal profile is going to have me right around that 400 cfm per ton.

In designing for comfort, I know that my evaporator coil won’t have a problem with freezing unless my airflow were to dip below about 230 cfm per ton, somewhere in that neighborhood. So in designing my bypass, I want to maintain maximum pressure in my system. I’m actually going to take that a little bit more than the blower profile. And I’m going to say 300 cfm per ton on that five ton system for my bypass calculation only.

This is not for duct design. This is for my bypass calculation only. Your standard duct design is still 400 cfm per ton at normal elevations. I want to say mountainous regions designed for 450 cfm per ton if you’re up there. But for normal elevations like where I’m at in Northeast Ohio in the Cleveland market, 400 CFM per ton, similar markets, 400 CFM per ton or similar elevations.

Anyway, so my bypass duct, because I want to maintain maximum velocity and I want to push it above that 0.5 mark, I want to get as close as I can to the maximum without creating objectionable airflow noise, and without creating a situation where I’m going to damage my furnace 300 cfm per ton. So that gives me a five ton 1500 cfm.

But I’m also going to increase my airflow through those six inch runs. And while we typically use 1000 feet per minute, if we design it at 900 feet per minute, that’s probably going to give us more like, like 650 or 700 CFM through those ducts. But that’s going to change my numbers a little bit. It really is all about what you’re designing for.

But historically here at our Arzel, we’ve designed those at about 1000 feet per minute, which gives us 800 cfm of air through those six inch runs. And this would be for your average customer, not every single customer out there. You do have to talk to your customers. That’s the very first rule of zoning. If you remember back to it, you do have to talk to your customers.

And if you find you have a customer that’s going to be sensitive to airflow noise, you really only want to use about 150% airflow through those six inch runs, rather than 200% airflow. So under normal conditions, normal customer, I can probably do safely 800 cfm through those six inch runs before I cause a problem for them. And that would give me a bypass requirement of 700 CFM.

Now, if I have a customer that’s more sensitive to airflow noise, I’m actually going to take that and figure at 150% airflow through those six inch runs, which will give me 600 cfm of air, and then those four six inch runs will perform at 600 CFM instead of 800 CFM. That will give me a need for 900 CFM of bypass.

 

At 700 CFM of air, I can fit that through an eight inch pipe at 2000ft per minute. If I need to take into account for that customer that might be more sensitive to airflow noise, and I need 900 cfm of bypass then, I would fit that through a ten-inch pipe and using the Arzel ModuPASS, which we’re going to see a little bit, but the Arzel ModuPASS will open and close that damper, modulating it to maintain the static pressure I’m looking for.

So I’m not going to be bypassing that full ten inch pipe worth of air. I’m only going to bypass as much as needed to maintain a specific static pressure in my supply air duct. But before we get to that, we want to take a look at where our bypass duct needs to be installed because more often than not, contractors are putting them in bad locations that cause bad things for the equipment.

There’s a proper place for the bypass duct to be installed, but let’s take a look at one of the wrong locations first. If my bypass duct is installed here, what do you guys think might be wrong with this installation?

There’s no damper?

Well, not so much thinking about a damper, just location. What’s wrong with the location?

Is that the plenum?

That is the plenum. That is the return airdrop. What’s wrong with this location?

Just too close to the furnace.

Right. It’s way too close to the furnace. My plenum is a mixing pot for my air, and it’s going to have the greatest saturation of BTU for my equipment.

So that’s the hottest point on my furnace. Now, when I look at my return air duct, that is the closest point to recirculating back through my furnace. So it has no chance to temper itself with the air coming back from my home

So now I’m dumping the hottest potential of air directly back into my furnace.

I’m going to run my limits. I’m going to tank my evaporator coil temperature, which could potentially cause liquid flood back to my compressor. But it’s also going to significantly reduce the efficiency of my evaporator coil when it comes to dehumidification, because

I’m changing that dew point to where I can no longer condense on my coil.

And that’s going to have a huge, huge performance impact on my equipment. So my bypass duct, too close to my equipment is bad. But how about this location? What might be wrong with this?

To the other extreme, too far away.

Right. So the cap on my supply air duct is designed to keep a back pressure on my system. However, the return air has its greatest draw the closer to the furnace we are. It has the least amount of draw the further away from the furnace we get. So if I’m coming off right at the end of my ductwork, I have the greatest point of pressure in my system on the supply side, pushing back into the least draw on the return side.

So now I’m forcing that pressure back into the point where it’s got the least amount of draw. The danger I run into here is that I turn my return airs in this location into supply airs. So now instead of pulling air, they’re actually pushing air. And all of my return draw being strongest at the furnace up until about the midway point,

My return air now becomes a supply air. And the the registers at this location and the return start pushing air into the room and I’m going to over condition it. So, end of your ductwork? Bad location for the bypass duct. The proper location for your bypass duct is actually going to be about eight feet away from your equipment.

That puts you at a point in your return where you still have sufficient draw, but you have a a fair amount of duct for it to actually mix itself with the air coming back from the house, and that’s going to temper it before it gets pulled back through the furnace. But on the supply side, being about eight feet away from the plenum, we’ve allowed that air more of those BTUs a chance to make it to the home itself.

So we have we have in the heating season, we’ve shed some of the BTUs to the home. We’ve got fewer BTUs to be fed through that bypass duct, but with those fewer BTUs, we’re also tempering it with the return air from the home so that we’re not just dumping this hot stream of air or this cold stream of air directly into our, our furnace.

And that’s going to help with the performance of that equipment significantly. But being that it’s about the midpoint for the return air, we also still have sufficient enough draw that we’re not running the risk of pressurizing the returns in that location. So we’re not going to over condition the customer in that area. And then duct sealing. Duct sealing is important because we want to deliver the air into the home where it needs to be at.

So when we seal our ductwork up, we’re actually not pushing the air out from our seams. We’re delivering it directly to the parts of the home that are calling. So we run less risk of over conditioning a finished basement. If we have leaky ductwork in a finished basement, we’re pushing all those BTUs out into the basement when they’re not necessarily needed.

Now in the heating season, not such a big problem, but in the cooling season, that becomes an issue because there’s very low thermal gain in a basement. So we want those BTUs to be going upstairs, not bleeding out in the basement through leaky duct work. So sealing ductwork is a good thing. So just as a recap, zoning isn’t a cure for poor design.

Look at the system, test the system, take a look and see what things we can correct to improve the performance for our customers, and then offer a fix for those inefficiencies, so that with zoning, we can maximize the comfort for our customers. And I, I missed that this slide or this this show doesn’t specifically go over our ModuPASS, but Arzel does have a modulating bypass damper.

I mentioned that earlier. It’s designed specifically to work with variable speed ECM blowers. It’s a great bypass system for PSC blowers as well. And what it does, is it the ModuPASS transmitter, or the ModuPASS transducer, we call it, samples the pressure in your supply air duct. So the external pressure in your supply duct, it takes that and it uses it to regulate the pressure going to the ModuPASS damper.

And then the ModuPASS damper wants to maintain itself open; the pressure from our pump wants to maintain it closed. And we regulate that pressure coming from the Arzel pump into that damper so it can modulate it and maintain your static pressure specifically where you want to set it at. So that system that you saw earlier that I was working with, when I want to test it with the bypass, I can set my ModuPASS transmitter using my manometer to test my external static pressure.

I can I can dial that in to maintain my pressure at between like a .19 and a .21. So it’s pretty accurate when it comes to maintaining my external static pressure. And when I’m able to get my external static pressure there and I test my furnace itself, I typically find that my furnace is going to be somewhere around that 0.7 mark, and that that allows me numbers to work with because my ears don’t work the same as the homeowners’ ears, because their perception of noise is different than mine, especially after all the duct work I’ve worked on.

Tin knocker, my ears ring. They continually ring, so my hearing doesn’t work nearly as good as the homeowners’. And when I had those numbers to work with, I can set them according to the numbers that I typically saw. I would start at the high side of the range for people. Let them listen to it.

If they were happy, I could leave it there. If they were unhappy with the noise coming from their registers, take it back to the medium size, or the mid range and then if they were still dissatisfied with mid range, I take it back to the low side of that range. And I found that the vast majority of people were were very happy with an external static in the supply air duct being around point two, and I usually found my furnace coming into the line somewhere around point seven.

So all things to look at, all things to test out, verify the system is operating and performing properly so that we don’t damage the equipment, but also to see the improvements that we can make to maximize comfort for our customers with a zoning system and with the air improvement upgrades that we can do to their ductwork.

All right. And you guys have a wonderful day.