Duct Design for Great Results w/ Ed Janowiak (ACCA)
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- เผยแพร่เมื่อ 7 ส.ค. 2021
- Ed Janowiak of ACCA gives a presentation about fan and duct design, system testing, and Manual D at the second annual HVACR Training Symposium. Learn more about the 2022 HVACR Training Symposium at hvacrschool.com/symposium/.
Ed has over 35 years of HVACR experience, both in the field and through teaching. He has lived and done business in New Jersey, which has a variable climate, and he has experienced a wide range of temperatures.
When designing ductwork, we obviously want our static pressure to be close to our calculations. However, lower static pressure is usually more desirable than higher static pressure. When static pressures exceed our expectations, we have to start removing elements of our design.
The real key to good duct design is managing the occupant’s expectations. Understand what the client wants, but you must be up-front with what they can and cannot expect from their HVAC system.
Manual D requires that you pick a fan and design the ductwork around the fan. Ducts must accommodate fan pressure. (Manual Q is the opposite; you choose the fan based on the duct resistance.) Manual D’s goal is to calculate the critical path, which is the longest circulation path in the system. It’s also a good idea to comply with local codes, but it is not responsible for a design’s predictability.
To design a duct system, we also need to know how much BTUH (BTUs per hour) and CFM (cubic feet per minute) need to be delivered. We can get these figures by finding the BTU gain and loss (Manual J), and we can use Manual S to calculate our target airflow. Take the SHR (sensible heat ratio) into account, and you use all of that data to find your capacity.
We should refer to the friction rate worksheet to develop a good duct design. You initially take your external static pressure and CFM readings. Then, you discover and note the component pressure drops. You also take available static pressure and total effective length into account. In the end, you will figure out your friction rate. The purpose of that worksheet is to determine the friction rate based on the duct system’s critical path.
We use manometers to take static pressure measurements. Static pressure is NOT velocity; it is the measure of pressure against the walls of the duct. You can use static pressure as an airflow indicator.
Several components can contribute to pressure losses in the critical path, including heat exchangers, UV lights, grilles, and dampers. However, the filter is the most notorious source of pressure drops. When sizing a filter, you need to know CFM, velocity, and area. The system must have enough pressure to overcome those drops in the system.
Once you have calculated your external static pressure and losses, you can subtract those losses from your external static pressure to yield your available static pressure.
You determine your total effective length by adding the supply and return-side total effective lengths together (including trunks, runouts, and group fittings of each one’s critical path). Then, to get the friction rate, you multiply your available static pressure by 100 and divide that product by the total effective length. (You should also be able to find that value on a chart on the friction rate worksheet.)
Humans feel comfortable when they don’t notice their surroundings. So, excessive fan noise can be an unexpected source of discomfort for occupants. Watch your air velocity to avoid creating that humming sound with the fan. Don’t start off at high speed! Manual D gives us maximum air velocity guidelines to avoid comfort issues. Manual T also covers terminal velocity and grille selection, which heavily contributes to comfort. (A grille should be located in a sensible location and should have the proper throw. Grille size will determine the distribution box size.)
You must determine your heating and cooling factors to begin working on your duct design worksheet. The heating factor is the blower CFM divided by your Manual J heat loss; your cooling factor is the blower CFM divided by your Manual J heat gain.
When you use effective length charts, you must keep in mind that those effective lengths will only contribute to duct behavior predictably under a certain set of conditions. If you’re running at a slower fan velocity the friction rate will change, and you will need to do some more calculations. As friction goes up, effective length goes down.
Our external static pressures may end up higher than we anticipated due to excess length (with flex duct).
Ed also discusses:
Alternative ways to measure static pressure
Height-to-width ratio of ducts
Design software pitfalls
Return drop sizing
Sizing for flex duct systems
Round registers
Grille air velocity and sizing
Filter sizing
Standard test airflow rates for MERV ratings
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.
HVAC School and chill tonight.
sounds weird...but so very true ha
On a Friday night
For him to finally get to explaining a basic concept like static pressure at the *36 minute* mark means this video could be 75% shorter. But maybe he charges by the hour.
When I lived in NJ, I attended a class that Ed taught in Mt Laurel. It was an air flow class. The first thing he said was "guys it's all about air flow" If the air flow is not right, then your charge will not be either. Very true, especially with the crappy duct systems we see in new construction.
CFM?
Nice video. Always a quality show.
13:21 is where he says, THATS ENOUGH!
Great lesson. I needed this.
Thank you for the video and the awesome video description
Man a lot of good info very thankful!
Bryan, I appreciate the effort to provide us with duct design training but I"m certain there's a much simpler way of doing it. Some years ago I took a duct design course at the local college for two semesters, it was properly presented and easier to absorb which I appreciated. I appreciate all you do for us and hope you take this as constructive criticism. Thank you....
You could set your ductulator at .1". Or you could do it right. 🤔
This guy is too full of himself to be a teacher anyone would respect. Guys like him are a major problem in the trades. Cocky,arrogant, worse words come to mind but I'll be nice on here. And he's not rite with all he said here either. But you won't be able to convince his type. It's a shame really
i enjoy your classes and now your videos
I am Korean
I am always studying, there are many good contents, thank you always
I love the ACCA ductulator app for iPad.
I was in that class! Great job Ed
How much longer are your school vid's going to be up?
@@MJ-iy4fb most of the classroom videos will be taken down this weekend. I may blur out a couple and link the the replacement.
There is a school in town that will allow me to do some filming so I can recreate some others.
@@love2hvac is there anyway that you can leave the audio portion of the classes? Because it sounds like a prodcast.
If residential duct design is so easy, why do so many installers screw it up.
Thank goodness for ductless ac.
awesome infomation
Well that was about as clear as mud
I simply use 1 cfm per sq foot and size my room duct size based on that simple math and it works out golden. Did the static tests and right on the money. Granted it was all metal duct no flex. Reality is doing all the calculations makes more sense on complex larger systems to get everything well balanced but fact is it is your usually rounding up because calculations usually are between sizes often so there is no perfection in design no matter how complex the calculations. Willing to bet there is a common factor that could be used based on a few typical conditions that you use as a multiplier that will get you every bit as close. Most of the frictional loss factors are just that anyway.
Thank you for the review of ACCA Manual D, and for exposing the hard to find fact that TESP = ESP. If contractors actually use Manual D to design residential duct systems and retrofits, why do studies find that the majority of them are deficient? Do inspectors require acceptance tests of any kind designed to protect ignorant homeowners?
Wonderful video. Thank you for presenting this. Here's my question: Does the return air grille have to serve (get supply air from) the register that is in the critical airflow path for it to be considered in the critical air flow path? Obviously, this only applies to multiple return systems. Thank you.
how do two stage system affect your minimum velocity requirement?
Wish I had a dollar for houses and commercial sites that contractor cut corners installing undersized duct. Went round & round after installing a VFD for a 100 HP air handler. Could not run motor over 88 to 90% of full speed or motor would draw too much current. Problem went away when door on both sides of fan were tied open. Worst part the undersized duct ran up 6 floors to mechanical room. Just great on cold days when they only run 100' of duct in a 300" long room.
Some of the fittings on manual D are really hard to tell what they are based on the pictures.
Thanks. Dropbox info?
Hello I have a duct system that has a 3" round duct that I want to convert to 3.25 x 10" rectangular duct. But the top portion of the 3" is to the roof. I'd say 15-24" that I don't want to change due to the roof work. I'm running about 15' of rectangular duct. How bad is it if I convert the majority of the ductwork and leave the last 15-24"? My rangehood is a low CFM capacity. 180CFM max I believe. I know it's not ideal but how bad is this? I feel it's like fumbling at the 1yd line.... any advice good or bad would be helpful. Thx
If I got an online now can I upgrade it to a symposium before Feb.
funny thing, i reworked my hvac vents, removed the. yellow and pink hydroscopic garbage, sealed ALL connections with mastic and covered that with hytech ceramic additive mixed with rustoleum elastomeric roof paint then covered it with refectix. above my intake is a 12" pipe which leads tp hot water heater room which has a 25 inch vent with filter adjacent to fridge. both the heat from fridge and hot water heater are fed above intake on hvac. i run evergreen ecm 24/7 for filtration with merv 13, april air, and electrostatic prefilter with ecm 80cfm fresh air intake plumbed directly into furnace intake hooked up to filter box outside with 3 electrostaic prefilters. 5 uv lights. one in center of coil, one on each side and two on top with mirrors in coil housing to reflect uv light back into coil and set to timers. condensation line has cost guard pressurized drain with scupper valve. crawlspace is partially conditioned with no insulation in floor, a dehumidifier set to 50 with humidistat and temp gauge under home. temp gauge and humidistat after coil before main duct supply. not much more to do but get broans integrated system to run house exaust fan when fresh air fan is running, and a whole home dehumidifier like the santa fe which would dehumidify fresh air intake.
needs a few more uv lights
@@adb99999999999 yes in main duct line just one because of higher humidity levels whe using ac.
Yea I remember after sandy up in Rhode Island they had to bring in payloaders to shovel the beach off the road and put it back like at the water line of the ocean lol.
Notice acca fittings never assume a horizontal attic install. They also heavily penalize round tee wyes. How many rivers do you see with a bull head tee and only 90 degree takeoffs? I think ACCA's bias comes across in the TEL data.
GOOD
😂 I'm three minutes in and right away I'm relating - I also have a piece of yarn on a grille so I can verify air is flowing and I also set my cooling temp to 76.
All good information but the truth is unless someone is designing very complicated heavy commercial or industrial duct systems or some type of critical installation, no one that does this for a living goes through all these steps to install a 'home' duct system. The best systems for homes are home-run systems because velocity always stays the same and all you need to do is size the duct for volume, but they do need to be installed before ceilings.
Good afternoon could you tell me please where can I get (buy) flex duct calculator ruler
Hi Im just the average person who would hire a hvac guy to design my system and put it in my home. I liked watching and listening to your class but didnt understand alot of it. My question to you ED is this. As a homeowner how or what do you suggest or recommend to know if your getting the right system put into your home and if the system that they put in puts out the numbers that it should. Last question. What advice do you suggest when searching for a hvac person to hire
At minimum, a HERS inspector will have some mild input on that. I believe all HVAC replacements require a HERS report which is supposed to evaluate the ducting and determine if they are installed/sized correct and do not leak more that 15% at connections.
BBB - must be A+ and in business over 20 years.
its a bummer that he skips explaining fitting tel especially group 2. other than that so much good information
just wish you went over cfm needed for each room... im alittle confused for that part
sq feet 8foot ceiling...cfm. 10x10 room, 6 inch
Condense the knowledge. I don’t need jokes.
Yah ed is a terrible teacher just rants and brags it's so sad we only have 2 people that know how to design duct
Agree. This is an absolute waste of all of our time. I can't stand this arrogant guy. Wish bryan would stop using him. He's useless
Come on, Ed’s good and I enjoy his presentation and find him humorous. Better than delivering material too dry.
So what you’re saying is, fab a big ass sloppy plenum out of duct board, and use a run of flex duct to a register in each room. Size the system 2 tons larger than required to keep the customer happy. Oversized ductapuss for the win…quick, dirty, and off to the next job.
What happens if you oversize the duct and the unit has zone damper
As long as the supply outlet, register selection is proper, oversizing a duct and reducing velocity is not a problem. If you’re not controlling your branch run volume, who knows what’s gonna happen ( probably won’t be good).
You said ductulator
I've seen a lot of homes get built, NO WAY those contractors bothered with this math or point of view. Especially those units that have the return grill 1 to 2 feet from the blower...they do that all of the time (or at least since the 1980's through the early 2000's they did).
Judging from the comments we got quite a few that fit in the "80% don't do this".
This could have been an hour shorter if the guy would've stopped talking about irrelevant staff all the time.
If it wasn't for the staff, there wouldn’t have been an event, it’s mine boggling that you would call them irrelevant 🤷🏽♀️.
May be he’s got a part time as a comedian
Bryan thanks for the vid,but please learn how to edit these types of videos. This guy is hard to listen to,full of nothing stories that we all have in the field.
Doing ductwork systems and change outs for over 20 years. Not many companies do this. When you only have a certain amount of time given to get the job done. You can go by the .1 static pressure to design your system. Go with .5 total esp from the furnace specs. you will be just fine.
Did you mean 0.1 friction rate?
.5 is really hard to hit on a furance and ac system. Most in the field seem to run around 0.7 to 0.8 external static
@@KyleRicciardi Nope. Static pressure determines cfm of air air flow in the system. You measure static pressure with a manometer, not friction rate.
@@smacleod69 friction rate is what you select on a duct slider. 0.1 friction rate is what your referring to when sizing the duct. Unless your using velocity? There is no "static pressure" on a duct slider
@@HVAC544 I can hit point .5 if I size duct work correctly. I can even hit .5 in a change out scenario by modifying r/a ducts like upsizing and/or adding a return. Using wide louvered r/a grills instead of standard grills. Also increase the size of some supply ducts or add one. And lastly, do an air flow balance can help.
It’s difficult to listen to the screaming voice.
Agree :-)
:)
Does anyone watch this and read the silly comments? The guy is doing what he does and letting us follow him through it. Everyone commenting negatively is a whiner
Too much chitchat. Moving on.
about 15 minutes of good content and 2 hours of shooting the breeze. very frustrating
What is this? A Joke? The dude takes FOREVER to get to the point!
Well, this presenter has his comedic timing down, and I enjoyed this for that…but did I learn much…no
Why all the small talk? This guy wana be a comedian?
i feel like this class could have been about an hour if you cut out all the jokes and personal trivia.
a handful of jokes once in a while keeps peoples' attention. a constant stream of jokes just distracts attention from your class.
Borderline useless video, just be aware
Bruh I'm six minutes into this vid and I didn't come here to listen to you talk about your uncle. Do you get to the point?