Air Flow Diagnostics w/ Joseph C Henderson
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- เผยแพร่เมื่อ 27 พ.ค. 2023
- This video is of a presentation at the 4th Annual HVACR Symposium: Air Flow Diagnostics w/ Joseph C Henderson.
Recently, the industry updated its testing standards (SEER2, EER2, etc.) to account for the static pressure of ductwork; previous testing protocols didn’t consider the effects of static pressure in the ducts.
ACCA Manual D is the industry standard of duct design, and Manual Zr deals with zoning (which depends on the integrity of the ductwork). Systems designed with Manual D tend to have better performance and airflow than systems that aren’t designed with Manual D in mind. When measuring and optimizing airflow, we can only expect better results if we use the proper test instrumentation, not just the “handometer.”
In the ductwork, we have two main sources of pressure: velocity pressure and static pressure. Air is always trying to expand, so static pressure is exerted on the surfaces of the duct and creates resistance because ducts can’t expand. When the static pressure is too high, the blower motor can perform poorly and even fail prematurely. We want just enough static pressure to ensure that we have a solid throw of supply air and smooth, quiet return air.
We can measure static pressure with manometers. Manometers measure pressure differentials, and we can use them with static pressure tips (pointed into the flow stream) to measure static pressure. A static pressure tip does not have a hole in it and is NOT the same thing as a pitot tube. Alternatively, you can insert a straight piece of tubing into the duct and point at a 45-degree angle WITH the airflow.
You want to account for all sources of resistance when measuring static pressure, so you’ll want to account for the filter and the coil. The airflow should be straight, also known as laminar airflow. You will need 3-5 feet of straight duct to ensure that you achieve that laminar flow.
You can also see how the motor is doing by taking an amp draw reading. Lower amp draws indicate that a PSC motor isn’t moving the full amount of air. Full load amps will indicate that the full amount of air is being moved, but it will not tell you if the static pressure is balanced. (Ideally, the return static should be lower than the supply static.)
Variable-speed and X13 motors tend to be more efficient, but their airflow capabilities are similar to PSC motors, and they still have their static pressure limitations. Constant-torque motors will have a slight increase in amp draw before dropping. Constant-CFM motors will pull far more amps than X13 and PSC motors.
PSC and X13 motors may only deliver air up to 0.5” of external static pressure, so you’ll want to make sure you start off with a maximum of 0.3” (0.1” on the return and 0.2” on the supply) so that the blower can handle additional resistance from coils and filters as they get dirty.
Constant-CFM motors may maintain their set airflow up to 0.8”-1” of static pressure, and you can typically start off with 0.35”-0.5” of static pressure; when the motor has to ramp up too much to maintain a constant CFM, the efficiency takes a hit. Constant-CFM motors are appealing because they tend to be quiet and efficient, but they can get louder and more inefficient under higher static pressure conditions.
To keep the static pressure down in the ductwork, you’ll want to make the trunk line as straight as possible. You’ll also want to keep flex ducts straight and tight to prevent compression, which adds resistance. Mitering the inside turns is also best practice to cut static restrictions (unless you have turning vanes). Be mindful of duct fittings, as they can significantly affect the static pressure restrictions.
Buy your virtual tickets or learn more about the HVACR Training Symposium at hvacrschool.com/symposium.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.
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I like him!....not monotoned and also funny!......thanks for sharing friend!
Even though I attended these classes and seminars, I still come back and re-watch the videos
This guy is super smart and funny as hell! It must be fun working with him.
Mr. Henderson is a great guy !!! Very Intelligent man and always keeps moving forward.
From Prosperity SC
Randy Wheeler
Randy Wheeler
This was a great teaching video. Static is so misunderstood and can confuse even the more experienced techs
As a young Technician in the trade I appreciate you sharing your knowledge about Static and Air flow, taking notes to implement it in the field... Thanks for sharing!!
Wait til the statics way off but the customer doesn't want to pay to change it by changing the duct work. The problem will always exist for everyone who is unlucky enough to be dispatched there.
Why isn’t this one of your top videos! Airflow, airflow, airflow baby!
@bryan you gotta put him on the main stage next year 🤣. I watched all classes virtually this year, no idea how I missed this class. Hope to see you in person next year 🙏🏻
Such a good teacher!! thank you
Good job, learned me some airflow!
Really great presentation, very informative - thanks!!!! As an aerospace engineer, my only question is how do ever find a service tech or installer who is qualified in duct work. I am considering buying the equipment and just doing it myself. I wanted to get static pressure checked along with a superheat measurement (piston system) and not one of the three service techs I had for an assessment even had a working manometer. So truly, any advice would be appreciated, how do you find a service tech? I did try confirming they did the static pressure measurement when making a service appointment only to find they didn't carry the manometer or it didn't work or they had no clue how to use it. I live in the Daytona Beach Fl area if you have any folks you know. Thanks!!! RZ
Sure already bought my tickets for next year's 🥳
Fantastic instruction, thank you
Outstanding presentation. Thank you for sharing
Cool video! 💯
Thanks for the education Mr. Henderson. I am grateful!
Thanks for this🎉
Well done thank you
25:34 - Rule of thumb for correct Amp draw on PCM vs ECM (X13 and Constant CFM) motors.
A Constant Torque would ramp up and have a higher current draw with restricted airflow? If they had a lower current draw with restricted airflow, they wouldn't fail like they do on undersized ductwork?
I like to measure static and use the fan. Table. If there is a better/easier? I'm told don't trust a anemometer.
Could I measure a total airflow with like a reverse blower door?
Do you have any videos that use air flow as a diagnostic for secondary heat exchanger issues?
@45:25 I actually saw that on a job 🤣
@4:45 safe to say this guy knows what he’s talking about.
I have questions why my air return sound like earthquake when it started to blow cold air
TAB work is interesting but the most stressful job in all of HVAC
How does that 3-5 foot rule work for an upflow on a furnace in a basement? Most common set up here and they just use a plenum. There’s no room to run 3-5 feet up before splitting generally
To my understanding you check static pressure somewhere after a 3 foot run of duct not a the top of the unit if it turns right away like you stated.
@@anthonybernier9952 depends on if it’s a furnace with a coil or air handler here. On Air handler the blower performance charts static includes the coil in it so 3-4 out works as they are generally horizontal in attics here for the most part. More common is a furnace with a Cased coil plopped on top. I’ll just go between the furnace and coil with one proble and hit the return no filter the other for my static there
@@LispyJesus yes, you are correct. I guess I was just talking about a air handler in that case and should’ve specified that.
That's when you use a 90 degrees tee
Hello 👋
So I am
Getting all sorts of white looking powdery stuff and like little fiber looking stuff inside the house. And I mean all over and if you clean it it just is back within a day. It looks like debris of some sort and definitely coming from the hvac air duct vents. The vents were “supposedly” cleaned by FOLKS but this stuff remains. They put an electro static filter in the furnace and took out the paper replaceable filters from both air intakes vents. Is this normal? This stuff is literally everywhere and is bothering my skin and lungs. If I take a flashlight and look it’s everywhere
he puts the flashlight on the stuff
I gotta he ablw speed things up.!?? Right? NO!?