Short 16 - Air Velocity is Useful

HVAC School - For Techs, By Techs

Bryan Orr

Training, Careers, Airconditioning, Self-improvement, Hvac, Business, Education, Refrigeration, Heating, Ac, Apprenticeship

4.8 • 985 Ratings

🗓️ 30 July 2018

⏱️ 17 minutes

🔗️ Recording | iTunes | RSS

🧾️ Download transcript

Summary

In this short podcast episode, Bryan covers how to measure air velocity directly at a return or supply and what those readings tell you.

Since many techs like to focus on CFM and static pressure readings, they can neglect air velocity in their measurements. Air velocity is the speed at which the air is moving. Conversely, static pressure is the force of the air against the sides of the ducts, and CFM is the air volume. We measure air mass in pounds (in the USA); when air is denser, you will have more pounds, but the volume will stay the same.

We primarily measure air velocity with a vane anemometer. Air moves through the vane and spins it, which informs the anemometer. That anemometer then gives you the reading. While airflow is the ultimate measurement, it is much better to take velocity measurements than none at all. Velocity can help you determine the CFM, but that requires knowledge that some techs don't have or are simply unwilling to apply. You need to know the size of the intake and have knowledge of the open/free area of the vent.

Velocity can help you determine how much throw you need to reach a certain distance. Velocity is a measure of feet per minute and can be applied to distance variables like throw. However, register sizing needs to come before measuring velocity. Velocity helps you figure out your throw and register sizing without relying on CFM measurements. Velocity can also help you identify noise issues, with higher velocities indicating noisier ductwork.

To reduce air velocity in cases where you have too much, you may need to use a balancing damper to throttle it back.

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Transcript

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0:00.0	All right, so this is a short episode of the HVAC School podcast, a short episode that we're
0:08.6	going to talk about air velocity.
0:10.6	So this episode is all about air velocity or air velocity basics and you will notice a little more background noise so I've been
0:17.3	mentioning this in a couple of podcasts, but we just had her 10th child and I have not historically been the best dad when it comes to taking time off of work.
0:25.0	And so I am taking a couple days where I'm not working as much, but I am still doing some videos and some little things here and there as I can fit it in.
0:33.0	And in this case, I'm actually driving back to our office to pick up a blower module
0:38.0	because the blower module on our air conditioner at our house, our downstairs air conditioner conditioner failed overnight so now we've got
0:43.8	some driving time and with no kids no screaming but I don't have my studio mic so that's
0:49.6	why you'll notice a little difference in the sound anyway Anyway, before we get into the podcast,
0:53.2	I want to thank our excellent sponsors,
0:55.1	which you already know,
0:56.2	which are refrigeration technologies
0:57.8	at refriggedech.com, makers of Nylog,
1:01.0	thread sealant, and assembly lubricant, if you're not using nylon when you're putting together any sort of threads within a refrigeration circuit then why not it's just one of the best products out there for pretty much everything associated with
1:13.9	making threaded connections or making flares even so you traditionally used to
1:18.7	use oil to prevent galling on flares. Well now by galling, use Nylog.
1:26.0	Also I want to thank Air Oasis for all they've done
1:28.6	for the podcast.
1:29.8	They make really good indoor air quality products.
1:31.9	They're a very honest company based on
1:33.7	everything that I've seen. I've read all their studies. I've talked a lot to the
1:36.6	founders of Air Oasis. You can find out more by going to Air Oasis.com
	...

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