Arzel Zoning
How do you bypass? How do you make static pressure work for you, and not against you? Learn in this video how to get your zoning job running at its maximum performance!
Static pressure, but understanding that using that as a tool is going to be one of the greatest things that you’ll gain from a zoning system. The good is, because you’re going to be pushing your harder and have greater static pressure. You’re gonna have better velocity and throw from the registers. You’re going to reduce destratification in the room.
So in other words, there’s a lot of second floor bedrooms when this AC system is running, you know, you have to stoop pretty low to tell whether the AC is running or not, because air is just kind of barely coming out of the register. The increased static pressure is going to give you that velocity and throw the shower the ceilings and the walls and get that air moving in and stop that.
Everybody know what destratification is? The cold air at the bottom, hot at at the top. That’s what physics want to do. The increased static pressure is going to help mix that, decrease, BTU duct loss, so that the longer it takes to get the air from your equipment to the area that is calling, the more BTU lost you’re going to have, the faster we get there, the more BTU’s you’re going to retain and actually deliver it to the area that you want.
You’re going to satisfy the zones quicker, and then you get more BTU’s into those hard reach areas. Now the negatives could be if you have a lot of duct leakage and you increase static pressure, you’re going to have a lot more leakage. One way to know that is if it’s a middle of summer and it’s 93 degrees and humid outside and you’re in the basement and you want to go grab your hoodie out of the van because it’s so cold on air, they have leakage.
So be mindful of that. If you push the static pressure too high, you’re going to have objectionable air noise, which we talked about. And then if you really overdo it, that can be pretty hard on your customer’s equipment. If we don’t want to do that now, when it comes to bypass, we’re just going from supply to return to shut off some of that excess static pressure.
Those are the two options we offer. Here’s kind of what that ModuPASS looks like. This transmitter is looking at the internal pressure inside of the ductwork. The Arzel panel is supplying pressure to this damper and holding it closed because our static pressure is low right now. If the static pressure increases in the, supply duct, this is going to start purging pressure off of this line.
The panel is still trying to provide pressure to the line. This is a restrictor meet meter and how fast it can be replenished. This starts to bleed that off. And the spring starts to modulate the damper open. And it goes into, bypass mode. Bypass location. If your mechanical room is barely bigger in the closet and you can only put it, you know, on the back of the equipment or something to that effect, where it’s coming off to the platform directly to the return, that’s fine.
It’s not ideal. But if that’s the only place you can put it, that is, it’s acceptable. We prefer to see them maybe six, eight foot down line. That way. The supply air coming out of here goes into the return, but has more time to be diluted with other return air before going immediately back through the equipment. So while this is fine, this has less time to get diluted before going through that cycle versus a little further down the line offers more tempering to that, to the air.
That doesn’t mean putting it all the way down here is a great idea. So if the equipment’s fine but 6 or 8ft down is better, don’t assume that putting it all the way at the very end is even better. We have seen instances where people have put it in and, and then we end up forcing more supply air into the return and what it can bring back.
And we’ve turned return air grills in the hallway into supply vents, the Arzel bypass calculator. You should have one of those. So if you look at that bypass calculators, a few things I want to point out. One side is marked in the green circle at the top right says trunk damper or branch damper. There is a separate calculation for trunk tampering.
And so there’s different calculation based on whether you’re doing a trunk damper or a branch damper system at the bottom of the card, the bottom like half or whatever it says. Other bypass sizing considerations. If you’re using the calculator and you’re unsure or you’re kind of, fact some other I need an eight or a ten or I need one or I don’t need one the other.
Bypass sizing considerations making you look at different factors of your system. Is there a flex duct that the flex duct flex stuff acts almost like a sound attenuator, and it reduces airflow. And that’s how your frictional loss and it’s going to heat up potentially some of your your velocity and your air noise. If you’re, dealing with a distant zone on the opposite end of the house or the equipment on the second floor, and I have great distances to get there, but then I might not need to bypass, or I might be able to go down the side.
On the flip side, if my smallest owners are doing a calculation for as a close zone, or maybe it’s not flex and it’s hard metal pipe and it’s a closed zone. So in other words, I’m doing a calculation for my small zone being the primary bedroom. And it happens to be right above the mechanical equipment. And my supply runs are only 4 to 5ft long and or solid metal pipe.
I don’t have very much time or frictional loss to heat up velocities or air valleys. I might have to go up the size in a bypass, or if I’m on the borderline and I’m not sure if I need one or not, I might want to plan on figuring in a bypass because my follow zones right above the equipment.
Special purpose zone. That’s that’s another factor you have to take into consideration. Now, just to do a quick calculation here. Go to your trunk damper side of the bypass calculator. And then what we’re going to do is we’re going to take a 300 CFM zone with a three ton system and a what size bypass. 8 inch.
Now, what if my 300 CFM zone was either into the house or it was all flex to get there? What I suggest is figure quoted, order it, get it to the job, but don’t install it till you commission the system and see if it’s objectionably loud. And your customer should be the one to determine if it’s too loud. But there’s a thing we refer to is the sound of comfort.
And it comes from here like there’s there’s been jobs and I’ve done where it’s like a commission, the system. But I go to that primary bedroom and it’s like, wow, you can really hear the air coming out of those registers. Now. And I take the customer there and I’m like, I’m assuming this is probably too loud. All that air noise coming out of there.
Like, I can put the bypass in and I can I can cut that back for you. So it’s not so loud. And they’re like, are you kidding me? Like, I’ve lived in this house ten years. And he came and adjusted the blower speed. He cleaned my coil. Or he’s just the dampers and all this. And like, I’ve never heard air coming out of here.
And now I can hear, like, why would I want you to do anything to take that away from me? That sounds like comfort coming out of there. So let the customer determine whether it’s actually that loud or not. Now flip it over and go to branch damper side. Do the same calculation 300 CFM three ton system. Yeah. Branch never should be the asterisk which is borderline which tells you down here the asterisk borderline case check other bypass sizing consideration thats down here.
If it’s a distance zone, flex zone you’re probably definitely not going to need more. If it’s very short, it’s hard to metal pipe and it’s good. You know, a room right above the equipment. You might want to figure out one. Now the ModuPASS comes in three sizes, 8 to 12. I call it small, medium and large. Eight is our most common.
Ten. We sell a few, 12 of you. So very, very little for me. I kind of use it also as a barometer. If you do a bypass calculation and you need a 12, might be a more of an indication, you should go back to the drawing board, see if you can make that judgment a little bit bigger.
Why am I using the biggest margin pass or zone makes? Or is it? Actually, it’s probably because I created a really small zone on a fairly large piece of equipment. I should probably try and get more supplies on or make that zone bigger. If I need a ten, that’s probably okay. If I need 8 you know what? That’s totally fine.
A little bypass is not a bad thing. While a lot of our systems, especially if they’re multi-stage and it’s on the HeatPumPro, don’t need a bypass at all. If all you need on your system is an eight inch as fine, but that’s not very much bypass at all. When I have a branch damper system, I have the platform, I have my truck.
I want a third each way. I have hard to locate. And then I have a damper and the blower can build a static pressure up. And that can kind of settle down. When I do trunk dampers where the dampers usually at right at the plant. All right. And so now I slam the door here, slam the door here and slam the door there.
And I have this plenum in these take offs and then errors bouncing all over. I get all these weird currents. And it’s a much noisier system to try and deal with. And we found that you need more bypass when you do a trunk damper system to try and account for that to, you know, quiet the system down for instant.
For systems, a blower can build up a nice static pressure throughout the system, and it just makes it a more stable system. If you have a combination, I got like 5050 on the side of caution. Just treat it like a trunk damper system. End of the day, if you have any questions on this at all, you can just call us.
Here’s what I got. Here’s what I designed. Do you think I need a bypass or not? So typical bypass sizing. What we didn’t realize. So we work with National Comfort Institute. Is your average bypass smooth area at almost 2000ft per minute. Well, back in the 80s when we were sizing bypasses, we were treating them like a supply run. So getting pushed from the blower up through the coil and into the system and treating it like a branch run.
But if you think about a bypass, it’s usually this 3 to 4ft section of pipe connected to basically a high pressure and a low pressure. It’s getting shoved in one end and sucked out the other. So when we were sizing bypasses back in the day, we were thinking, yeah, we’re probably getting about this much airflow. We were getting far more air through bypasses of what we saw.
Our average bypass that we saw was the eight inch. You can move somewhere around 750 to 800 CFM of air mass, most or that moving that. But we were floored to find out through testing with professionals that this kind of velocity was being about. That’s the average we saw sometimes 1500. We saw as high as almost 2500ft per minute velocity.
But that would take a very small damper on still a lot of valuable airflow and static pressure if you didn’t adjust it correctly. When you’re sizing your system based off that calculator, you need the tonnage of your air conditioning. You need to know whether you’re doing trunk or branch dampers, and then you need to know the design CFM of your smallest known for how many supplies are in there.
With those three pieces of information that you guys need most any calculation. And like I said, you’re always, always welcome to call us for any questions you have or just to do the calculation for you. You don’t have to use the calculator if you don’t want.
bypass setup.
The first thing I recommend is confirm with your customer is this zone noisy. And if they say yes it is, then you install the bypass. Once you install the bypass, you’re going to start with the bypass in the closed position, and you’re going to have your customer go into that zone and you’re going to say, I’m going to go adjust the bypass incrementally and open it a little at a time.
And what I need you to do is to let me know what the noise level in this zone is acceptable, whether you got them on the phone, whether they’re going to stop on the floor or whatever your method of communication is, you’re going to use the customer. You’re going to make those small adjustments to start opening the bypass.
Once the bypass is open enough to resolve the air noise issues and your customer gets you on the phone, says, that’s it, that’s good, or stopping on the floor, that’s your adjustment. I want to I want to maintain the highest permissible static pressure in the system as I can, with as little air flow going back into the return as possible.
That air going back into your turn is taking the load off your coils, taking a load off your heat exchanger, that air going into your return. If you don’t too much of it into the return, that’s when you’re going to start tripping limits. That’s what you’re going to start a freeze in the coil. That’s going to just start slugging back to the compressor.
Who started the AC startup when it’s like 60 outside and only like 65 inside. That’s why you don’t want the bypass to know your system is with so many BTUs into your return, and you get this snowball effect where it just starts getting so cold or so hot that we start short cycling the equipment we start getting abusive.
That kind of thing. So that’s why I want you to maintain this high of a static as you can with this little bypass going into the return as possible. That’s the ideal setup.